UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The significance of some insular characteristics in birds Grant, Peter R. 1964

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1964 A1 G7.pdf [ 11.54MB ]
Metadata
JSON: 831-1.0106804.json
JSON-LD: 831-1.0106804-ld.json
RDF/XML (Pretty): 831-1.0106804-rdf.xml
RDF/JSON: 831-1.0106804-rdf.json
Turtle: 831-1.0106804-turtle.txt
N-Triples: 831-1.0106804-rdf-ntriples.txt
Original Record: 831-1.0106804-source.json
Full Text
831-1.0106804-fulltext.txt
Citation
831-1.0106804.ris

Full Text

THE S I G N I F I C A N C E OF SOME INSULAR C H A R A C T E R I S T I C S I N B IRDS by P. R . GRANT A t h e s i s s u b m i t t e d i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r t h e d e g r e e o f DOCTOR OF PHILOSOPHY i n t h e D e p a r t m e n t o f Z o o l o g y We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H COLUMBIA A p r i l , 1 9 6 4 . 1 ABSTRACT The r e p o r t e d t e n d e n c y , f o r i s l a n d b i r d s t o p o s s e s s l a r g e r w i n g s and b i l l s t h a n t h e i r m a i n l a n d c o u n t e r p a r t s , was i n v e s t i g a t e d by a s t u d y o f t h e p a s s e r i n e , b i r d s o f t h e T r e s M a r i a s I s l a n d s , M e x i c o . I t was f o u n d t h a t s e v e r a l s p e c i e s s h o w e d t h i s b i l l t r e n d , b u t t h a t a t e n d e n c y f o r b i r d s t o p o s s e s s l a r g e r w i n g s was l e s s a p p a r e n t ; an u n e x p e c t e d t e n d e n c y f o r t h e t a r s u s o f i s l a n d b i r d s t o be l a r g e was a l s o d e m o n s t r a t e d . On t h e o t h e r h a n d , t h e r e i s no a p p a r e n t t e n d e n c y f o r t h e b o d y - s i z e o f i s l a n d b i r d s t o b e l a r g e r t h a n t h a t o f t h e i r m a i n l a n d c o u n t e r p a r t s . T h e b i l l and t a r s u s c h a r a c t e r i s t i c s o f t h e T r e s M a r i a s b i r d s a r e a l s o shown b y many o t h e r p a s s e r i n e b i r d s i n i s l a n d s i t u a t i o n s e l s e w h e r e i n M e x i c o a n d N o r t h A m e r i c a . The d i f f e r e n c e s i n d i m e n s i o n s b e t w e e n m a i n l a n d and T r e s M a r i a s b i r d s c a n n o t be e x p l a i n e d a s a d a p t a t i o n s t o d i f f e r e n t c l i m a t i c c o n d i t i o n s ( A l l e n ' s r u l e ) . O b s e r v a t i o n s o f f e e d i n g b e h a v i o u r , and a n a l y s i s o f g i z z a r d c o n t e n t s o f c o l l e c t e d s p e c i m e n s , r e v e a l t h a t some i s l a n d s p e c i e s h a v e a d i e t w h i c h i s d i f f e r e n t f r o m t h a t o f t h e i r m a i n l a n d c o u n t e r p a r t s , and t h s t t h e i r u s e o f p e r c h e s i s d i f f e r e n t t o o . T h i s s u g g e s t s t h a t t h e b i l l and t a r s u s a r e u s e d d i f f e r e n t l y i n t h e two r e g i o n s . I t i s p o s t u l a t e d t h a t l a r g e b i l l and t a r s u s a r e a d a p t a t i o n s t o a g r e a t e r e x p l o i t a t i o n o f t h e e n v i r o n m e n t . D i f f e r e n c e s i n h a b i t a t b e t w e e n t h e m a i n l a n d a n d i s l a n d s do n o t a c c o u n t f o r d i f f e r e n c e s i n f e e d i n g b e h a v i o u r , b u t t h e r e l a t i v e p a u c i t y o f s p e c i e s o n t h e i s l a n d s o f f e r s a n e x p l a n a t i o n . I t s u g g e s t s t h a t t h e r e i s more e n v i r o n m e n t a v a i l a b l e f o r e x p l o i t a t i o n t o e a c h o f t h o s e p r e s e n t i i on the i s l a n d s than to those on the mainland, assuming that there are approximately equal resources i n the two regions. There i s a d d i t i o n a l , i n d i r e c t evidence to suggest that the absence of several species has important e f f e c t s upon those present. I s l a n d b i r d s tend to be more drab i n plumage than mainland b i r d s , on the Tres Marias and elsewhere, and at l e a s t one species on the Tres Marias has a reduced v o c a l r e p e r t o i r e . I n view of the value of d i s t i n c t i v e plumage and song as s p e c i f i c r e c o g n i t i o n c h a r a c t e r i s t i c s , the features d i s p l a y e d by the Tres Marias b i r d s may be a t t r i b u t e d to the absence of s y s t e m a t i c a l l y c l o s e l y - r e l a t e d species. At l e a s t one species nests considerably lower in- the vegetation ©-n._th.e... Tres Marias I s l a n d s than on the mainland, which may be due to the r e l a t i v e absence of predators on the i s l a n d s . There i s evidence to suggest that the e c o l o g i c a l conditions which have permitted the e v o l u t i o n of b i l l and tarsus c h a r a c t e r i s t i c s i n i s l a n d b i r d s , have permitted the e v o l u t i o n of large body-size i n i s l a n d rodents a l s o . I f t h i s i s t r u e , then i t i s po s s i b l e that the recorded tendency f o r animals to become l a r g e r i n the course of e v o l u t i o n i s r e l a t e d t o an increase i n the amount of environment a v a i l a b l e f o r e x p l o i t a t i o n . M.D.F. Udvardy In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the U n i v e r s i t y of • B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study* I further agree that per-mission for extensive copying of t h i s t h esis f o r scholarly purposes may be granted by the Head of my Department or by his representatives. I t Is understood that copying or p u b l i -cation of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without, my written permission,, Department of The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada X ACKNOff JUDGMENTS This work was undertaken with the cooperation of the Universidad Nacional Autonoma de Mexico, and with additional assistance from the Direccion General de Gaza and Departmento de Prevencion S o c i a l , Mexico D.F. The study was financed hy the National Research Council of Canada during 1961-63 (Grant No.A-1221 to Dr. M.D.F. Udvardy), and partly by Dr. H.R. MacMillan during 1961-62; a Frank M. Chapman Award from the American Museum of Natural History met the expenses of working at that I n s t i t u t i o n . The following provided specimens on loan:- J.D. MacDonald ( B r i t i s h Museum, Nat. Hist., London); D. Amadon (American Museum of Natural History, New York); H.G. Deignan and P.S. Humphrey (Smithsonian I n s t i t u t i o n , Washington, D.C.); J.W. Hardy (Moore Laboratory, Occidental College, Los Angeles); T.R, Howell (University of C a l i f o r n i a , Los Angeles); R.T. Orr (Ca l i f o r n i a Academy of Sciences, San Francisco); A.H. M i l l e r (University of C a l i f o r n i a , Berkeley); K.E. Stager (County Museum, Los Angeles). A.R. P h i l l i p s kindly put his private c o l l e c t i o n at my disposal, C.G. Sibley (Cornell University, New York) supplied valuable l o c a l i t y information for specimens of Parula pitiayumi i n s u l a r i s and R.S. F e r r i s (Stanford University, C a l i f o r n i a ) i d e n t i f i e d plant specimens. L. Witt prepared the large number of specimens collected during t h i s study. The f i e l d work was made easier by help given by my wife and Dr. M.D.F. Udvardy, and the preparation of t h i s thesis. x i has benefited considerably from the c r i t i c i s m offered by Dr. 1. MoT. Cowan, Dr. G.G. Scudder and Dr. M.D.F. Udvardy. Additional assistance was received from sources too numerous to mention i n d i v i d u a l l y , but is nonetheless acknowledged with gratitude. I i i TABLE OF CONTENTS ABSTRACT 1 TABLE OF CONTENTS i i i LIST OF TABLES v LIST OF FIGURES ix ACENOWLEDGMENTS x GENERAL INTRODUCTION 1 MORPHOLOGY Introduction 5 Materials and methods 5 Results, I Plumage 11 Conclusions 23 II Body dimensions 24 Discussion and conclusions 32 Summary 39 THE ENVIRONMENT 40 THE CLIMATIC FACTOR 40 THE ECOLOGICAL FACTOR 43 THE BREEDING SEASONS 45 THE NICHE STUDY Introduction 49 Method and materials 49 Results 53 Conclusions and summary 68 THE HABITAT STUDY Introduction 70 Method and materials 71 i v R e s u l t s 72 C o n c l u s i o n s 75 Summary 7 6 THE COMMUNITY STUDY I n t r o d u c t i o n 77 M e t h o d a n d m a t e r i a l s 78 R e s u l t s 8 0 D i s c u s s i o n a n d c o n c l u s i o n s 88 Summary 8 9 FURTHER E V I D E N C E I n t r o d u c t i o n 90 M e t h o d and m t e r i a l s 90 R e s u l t s . I S o n g 91 I I N e s t s 94 D i s c u s s i o n a n d c o n c l u s i o n s 96 Summary 97 D I S C U S S I O N 98 a ) T h e C o m m u n i t y 98 b) H a b i t s 1 0 0 c ) C o r r e l a t i o n o f m o r p h o l o g y and h a b i t s 1 0 2 d) T h e e x c e p t i o n s t o t h e t r e n d e ) The r e l e v a n c e o f c o m p e t i t i o n f ) O t h e r g r o u p s o f a n i m a l s CONCLUSIONS AND SUMMARY 1 1 1 A P P E N D I X I T a b l e s o f m e a s u r e m e n t s a n d s t a t i s t i c s 1 1 2 A P P E N D I X I I T a x o n o m i c r e m a r k s u p o n t h e i s l a n d p o p u l a t i o n s !59 A P P E N D I X I I I T a b u l a t e d d a t a o f b r e e d i n g s e a s o n s , v e g e t a t i o n c h a r a c t e r i s t i c s , c e n s u s r e s u l t s and s o n g . 188 R E F E R E N C E S . 208 TABLES v Table 1. The species and number of specimens studied 6 2. Differences of plumage between mainland and 22 island populations 3. Differences between the means of mainland and 25 island samples of measurements 4. Table of differences: measurements of a l l the 28 island passerines contrasted with those of mainland samples 5. A comparison of plumage and dimension character- 29 i s t i c s of the mainland and island samples 6. Differences between means of island and mainland 33 samples of measurements of passerine bird s . North American and Mexican islands considered,exclusive of the R e v i l l a Gigedo and Tres Marias islands 7. Differences between means of Tres Marias island 37 and mainland samples of measurements. (Passerines only). 8 . Degree to which the island birds breed e a r l i e r or 46 later than the mainland birds 9. Feeding-niche ch a r a c t e r i s t i c s of Myiarchus 54 tuber cui i f er (i)-r(vii) 10. Feeding-niche char a c t e r i s t i c s of Melanotis 57 caerulesoens 11. Feeding-niche characteristics of Vireo hypochryseus 58 12. Feeding-niche characteristics of Icterus pustulatus 6 0 (i) Food 13. Feeding-niche ch a r a c t e r i s t i c s of Icterus pustulatus 6 l ( i i ) Method 14. Feeding-niche characteristics of Icterus pustulatus 62 ( I i i ) Perch 15. Feeding-niche characteristics of Icterus pustulatus 6 3 (iv) Food-site 16. Feeding-niche characteristics of Icterus pustulatus 64 (v) Feeding-height 17. Gizzard contents, expressed as % occurrence i n each 66 sample I w V I T a b l e s 18. H a b i t a t s o c c u p i e d by t h e b i r d s o f t h e T r e s M a r i a s 74 i s l a n d s and t h e a d j a c e n t m a i n l a n d 1 9 . C o m p a r i s o n o f s p e c i e s and i n d i v i d u a l s r e c o r d e d on 8 2 s i n g l e s u r v e y s a t M a r f a M a g d a l e n a , T e p i c and P u e r t o V a l l a r t a , i n t h e m o n t h s o f J u n e and J u l y , 1961-1962 20. C o m p a r i s o n o f n u m b e r o f s p e c i e s r e c o r d e d i n t h e 83 m o n t h s o f M a y - A u g u s t , a n d c o n s i d e r e d t o be summer - r e s i d e n t i n t h e c e n s u s a r e a s 21. T h e number o f s p e c i e s o f p a s s e r i n e s r e s i d e n t i n 85 f o r t y a c r e s a t T e p i c , c o n t r a s t e d w i t h t h e t o t a l number o f r e s i d e n t s o n M e r f a M a g d a l e n a 22. C o m p a r i s o n o f t h e number o f I n d i v i d u a l s r e c o r d e d 86 o n r e p e a t e d s u r v e y s a t T e p i c and M a r i a M a g d a l e n a 23. C o m p a r i s o n o f t h e maximum number o f t e r r i t o r i e s 87 o c c u p i e d by s p e c i e s o c c u r r i n g i n b o t h m a i n l a n d and i s l a n d t e n - a c r e a r e a s 2 4 . N e s t - h e i g h t s o f T h r y o t h o r u s f e l i x , i n m e t r e s 95 A P P E N D I X I 25. M e a s u r e m e n t s of F l a t y p s a r i s a g l a i a e 113 26. M e a s u r e m e n t s o f T y r a n n u s m e l a n c h o l i c u s 116 27. M e a s u r e m e n t s o f M y i a r c h u s t y r a n n u l u s 118 2 8 . M e a s u r e m e n t s o f M y i a r c h u s t u b e r o u l i f e r 120 29. M e a s u r e m e n t s o f M y i o p a g i a v i r i d i c a t a 122 30. M e a s u r e m e n t s o f C a m p t o s t o m a imber.be 124 31. M e a s u r e m e n t s o f T h r y o t h o r u s f e l i x 125 32. M e a s u r e m e n t s of H e l a n o t i s c a e r u l e s c e n s 127 33. M e a s u r e m e n t s of M i mus p o l y g l o t t o s 130 34. M e a s u r e m e n t s o f T u r d u s r u f o - p a l l j a t u s 131 35. M e a s u r e m e n t s o f E y a d e s t e s o b s c u r u s 133 36. M e a s u r e m e n t s o f V i r e o h y p o c h r y s e u s 135 37. M e a s u r e m e n t s o f Y i r e o f l a v o v i r i d i s 137 v i i T a b l e s 38. M e a s u r e m e n t s o f P a r u l . a . p i t i a y u m i 139 39. M e a s u r e m e n t s o f G r a n a t e l l u s yen us t us 141 4 0. M e a s u r e m e n t s o f I c t e r u s p u s t u l a t u s 143 4 1 . M e a s u r e m e n t s o f P i r a n g a b i d e n t a t a 146 4 2 . M e a s u r e m e n t s o f S p i n u s p s a l t r i a 149 43. M e a s u r e m e n t s o f R i c h m o n d e n a c a r d i n a l i s 152 44. W e i g h t s o f s p e c i m e n s c o l l e c t e d a t T e p i c , 154 N a y a r i t , i n M a r c h 1963 43. W e i g h t s o f b i r d s b e f o r e , a n d a f t e r , f r e e z i n g 155 and t h a w i n g 46. M e a s u r e m e n t s o f t h e t i b i o - t a r s u s o f I c t e r u s 156 . p u s t u l a t u s A P P E N D I X I I 47. T h e s e x and p l u m a g e o f s p e c i m e n s o f M y i a r c h u s 164 t u b e r c u l i f e r . c o l l e c t e d i n t h e months F e b r u a r y - M a y 4 8 . M e a s u r e m e n t s o f M y a d e s t e s o b s c u r u s . P r i m a r y 10. 169 49. W i n g - f o r m u l a o f t h e l o n g e s t s i x p r i m a r i e s o f 169 M y a d e s t e s o b s c u r u s 50. P l u m a g e c h a r a c t e r i s t i c s o f V i r e o f l a v o v i r i d i s 171 51. P l u m a g e c h a r a c t e r i s t i c s o f P a r u l e p i t i a y u m i 174 32. P l u m a g e c h a r a c t e r i s t i c s o f G r a n a t e l l u s v e n u s t u s 177 53. T h e " N e c k l a c e " c h a r a c t e r and w i n g - f o r m u l a o f 178 G r a n a t e l l u s v e n u s t u s 54. T h e number o f d o r s a l s t r e a k s on I c t e r u s p u s t u l a t u s 181 55. T h e s e x a n d p l u m a g e o f c o l l e c t e d s p e c i m e n s o f 182 I c t e r u s p u s t u l a t u s 56. P l u m a g e c h a r a c t e r i s t i c s o f P i r a n h a b i d e n t a t a 184 A P P E N D I X I I I 37. B r e e d i n g s e a s o n s 189 VI11 T a b l e s 38. L e n g t h o f t e s t i s i n c e n t i m e t r e s , f r o m s p e c i m e n s o f 191 I c t e r u s p u s t u l a t u s 39. Mean v a l u e s f o r t h r e e v e g e t a t i o n c h a r a c t e r i s t i c s , 192 f r o m s a m p l e s o f h a b i t a t p l o t s 60. P e r c e n t a g e c o v e r a g e o f v e g e t a t i o n i n h a b i t a t p l o t s 193 61. P u e r t o V a l l a r t a c e n s u s e s : s i n g l e s u r v e y s o f 194" t w e n t y a c r e s 62. T e p i c 19 c e n s u s e s : s i n g l e s u r v e y s o f t w e n t y a c r e s 196 63. M a r i a H a g d e l e n a c e n s u s e s : s i n g l e s u r v e y s o f 199 20 a c r e s 64. T e p i c J10 c e n s u s : s i n g l e s u r v e y o f t w e n t y a c r e s 201 63. R e s u l t s o f s i n g l e s u r v e y s made i n J u l y , 1962 202 66. R e p e a t e d s u r v e y s c e n s u s : T e p i c , J 9 : t e n a c r e s 203 67. R e p e a t e d s u r v e y s c e n s u s : M a r i a M a g d a l e n a : t e n 203 a c r e s 68. D u r a t i o n o f s o n g s o f T h r y o t h o r u s f e l i x and 20? T . s i n a l o a i F I G U R E S F i g u r e 1 . Map o f t h e s t u d y a r e a 2 . A n n u a l d i s t r i b u t i o n o f r a i n f a l l and t e m p e r a t u r e 3. T h e t e r r i t o r i e s o f M i t r e p h a n e s p h a e o o e r o u s a t T e p i c 4 . S o n g s o f T h r y o t h o r u s f e l l x and T . s i n a l o a r e c o r d e d a t T e p i c , 2 J u n e -3. S o n g s o f T h r y o t h o r u s f e l i x r e c o r d e d o n Maria M a g d a l e n e , 24 J u n e 1963 6. The e x p l o i t a t i o n o f an e n v i r o n m e n t a l r e s o u r c e by t w o s p e c i e s A P P E N D I X I v . 7 . D i a g r a m ' o f D i f f e r e n c e s , I . A c o m p a r i s o n o f t h e d i f f e r e n c e s , b e t w e e n t h e mean v a l u e s , o f t h e f o u r . p r i n c i p a l m e a s u r e m e n t s , \ 8. D i a g r a m o f D i f f e r e n c e s I I . A c o m p a r i s o n o f t h e d i f f e r e n c e s b e t w e e n t h e m a i n l a n d a n d i s l a n d b i l l -l e n g t h s a n d b i l l - w i d t h s o f f i v e s p e c i e s . GENERAL INTRO D I C T I O N S p e c i e s o f a n i m a l s l i v i n g o n i s l a n d s may h a v e m o r p h o l o g i c a l c h a r a c t e r i s t i c s n o t p o s s e s s e d by t h e i r m a i n l a n d c o u n t e r p a r t s , a f a c t w h i c h w a s r e c o g n i z e d by W a l l a c e (1881). He r e m a r k e d t h a t i n t h e C e l e b e s : " N e a r l y t h i r t y s p e c i e s o f b u t t e r f l i e s , b e l o n g i n g t o t h r e e d i f f e r e n t f a m i l i e s , h a v e a common m o d i f i c a t i o n i n t h e s h a p e o f t h e i r w i n g s b y w h i c h t h e y c a n b e d i s t i n g u i s h e d a t a g l a n c e f r o m t h e i r a l l i e s i n a n y o t h e r i s l a n d o r c o u n t r y w h a t e v e r , and a l l t h e s e a r e l a r g e r t h a n t h e r e p r e s e n t a t i v e f o r m s i n h a b i t i n g m o s t o f t h e a d j a c e n t i s l a n d s . " M u r p h y (1938 ) r e p o r t e d a s i m i l a r p h e n o m e n o n among b i r d s : " A t N i n i g o , n o r t h w e s t o f t h e A d m i r a l t y g r o u p , - - - -a c o n s i d e r a b l e number o f e n d e m i c s p e c i e s i s l a r g e r and o f d a r k e r c o l o r a t i o n t h a n t h e n e a r e s t r e l a t e d f o r m s , e l s e w h e r e . A t R e n n e l l , an o u t l i e r o f t h e S o l o m o n s , t h e e n d e m i c s u b s p e c i e s show a p r o n o u n c e d t e n d e n c y t o w a r d s r e d u c t i o n i n s i z e : i n f a c t , t h i s i s l a n d i s t h e s o l e home o f t h e s m a l l e s t known r a c e s o f many s p e c i e s o f b i r d s w h i c h a r e w i d e l y d i s t r i b u t e d t h r o u g h o u t t h e I n d o - A u s t r a l i a n r e g i o n . " T h e r e a r e r e p o r t s o f v a r i a t i o n w h i c h i s c o n s i s t e n t l y shown b y many i n s u l a r f a u n a i n d i f f e r e n t p a r t s o f t h e w o r l d . A t e n d e n c y f o r i s l a n d b i r d s t o h a v e a d r a b p l u m a g e has b e e n n o t e d b y M u r p h y and C h a p i n (1929), M u r p h y (1938), Amadon (1933) and o t h e r s . A c c o r d i n g t o L a c k (1940) a n d Ama d o n ( l o c . c i t . ) t h i s i s c o r r e l a t e d w i t h t h e a b s e n c e o f c l o s e l y - r e l a t e d s p e c i e s . The w o r k o f L a c k (1943) a n d T i n b e r g e n (1948, 1953 ) has d e m o n s t r a t e d t h e r o l e o f plujmage c h a r a c t e r i s t i c s i n s p e c i e s r e c o g n i t i o n and 2 i n t h e a b s e n c e o f s y m p a t r i c r e l a t e d s p e c i e s , i t i s l o g i c a l t o e x p e c t a r e d u c t i o n i n s e l e c t i o n f o r d i s t i n g u i s h i n g c h a r a c t e r i s t i c s . I n i s l a n d b i r d s a t e n d e n c y h a s a l s o b e e n n o t e d f o r t h e w i n g and b i l l t o be l a r g e ( M u r p h y l o c . c i t . , C h a p m a n , 1940; M a y r and V a u r i e , 1948; Amadon l o c . c i t . ) ; t h i s has r e c e i v e d t w o i n t e r p r e t a t i o n s . Amadon ( l o c . c i t . ) and A r m s t r o n g (1955) h a v e shown t h a t v a r i a t i o n i n t h e s i z e o f t h e s e two s t r u c t u r e s c a n be c o r r e l a t e d s o m e t i m e s w i t h c l i m a t i c f a c t o r s ( B e r g m a n n and A l l e n r u l e s ) , a n d L a c k and S o u t h e r n (1949 ) and Amadon ( l o c . c i t . ) a l t e r n a t i v e l y h a v e o f f e r e d an e c o l o g i c a l e x p l a n a t i o n i n t e r m s o f i n t e r - s p e c i f i c c o m p e t i t i o n . I t i s a r g u e d t h a t on t h e m a i n l a n d s e v e r a l s p e c i e s c o m p e t e f o r e n v i r o n m e n t a l r e s o u r c e s w h e r e a s on i s l a n d s s m a l l e r n u m b e r s a r e i n c o m p e t i t i o n : t h i s e n a b l e s t h o s e p r e s e n t o n t h e i s l a n d t o e x p l o i t more o f t h e r e s o u r c e s , f o r w h i c h l a r g e r s i z e i s p r e s u m e d t o b e o f a d v a n t a g e . L i t t l e a t t e m p t h a s b e e n made t o a s s e s s t h e r e l a t i v e i m p o r t a n c e o f t h e s e two g r o u p s o f f a c t o r s , c l i m a t i c and e c o l o g i c a l . F u r t h e r m o r e , t h e r e i s l i t t l e i n f o r m a t i o n o n t h e p r e v a l e n c e o f t h e s e m o r p h o l o g i c a l t r e n d s . I n t h i s c o n n e c t i o n i t i s n o t e w o r t h y t h a t H e s s e e t a l (1937) m e n t i o n a t e n d e n c y t o w a r d s s m a l l s i z e o n i s l a n d s - an o p p o s i t e t r e n d . B o u r n e (1955) a l s o r e f e r s t o t h e s m a l l d i m e n s i o n s o f some o f t h e b i r d s o n t h e Cape V e r d e I s l a n d s , " a c h a r a c t e r o f s e d e n t a r y s p e c i e s w h i c h i s o f t e n p a r t i c u l a r l y w e l l shown by i n s u l a r f o r m s . " The p u r p o s e o f t h i s r e s e a r c h .was t o I n v e s t i g a t e the r e p o r t e d t e n d e n c y f o r i s l a n d b i r d s t o p o s s e s s l a r g e w i n g s and b i l l s and i f p r e s e n t t o t r y t o e x p l a i n t h e p h e n o m e n o n . The g r o u p o f T r e s Marias i s l a n d s , i n t h e s t a t e o f N a y a r i t , M e x i c o 3 ( F i g . 1) was s e l e c t e d f o r s p e c i a l s t u d y , s i n c e i t s f a u n a i s l a r g e ( t h i r t y - f o u r b r e e d i n g , t e r r e s t r i a l s p e c i e s ) , much i s known a b o u t t h e f a u n a a l r e a d y and i t I s known t h a t t h e f a u n a l a f f i n i t i e s a r e w i t h t h e a d j a c e n t m a i n l a n d ( N e l s o n , 1 8 9 9 ; G r a n t and C o w a n , 1964). The s p e c i e s o f i n t e r e s t e x h i b i t l i t t l e i n t e r -i s l a n d v a r i a t i o n , a n d p l u m a g e - and s i z e - d i f f e r e n c e s b e t w e e n m a i n l a n d and i s l a n d b i r d s h a v e b e e n n o t e d p r e v i o u s l y ( G r a y s o n , 1871; N e l s o n , l o c . c i t . ) . H o w e v e r , t h e s e a u t h o r s had f e w s p e c i m e n s and g i v e l i t t l e o f t h e d a t a r e q u i r e d i n p r e s e n t - d a y r e s e a r c h I n t o p o p u l a t i o n d i f f e r e n c e s . Members o f t h e o r d e r P a s s e r i f ormes w e r e s e l e c t e d f o r s t u d y , b e c a u s e i n t h i s g r o u p a d e q u a t e s e r i e s o f s p e c i m e n s c o u l d be a s s e m b l e d , and b e c a u s e Amadon ( l o c . c i t . ) o b s e r v e d t h a t t h e t r e n d o f s i z e - i n c r e a s e a f f e c t s t h i s o r d e r more t h a n o t h e r s . The h a b i t a t of two o f t h e i s l a n d s , M a r i a M a g d a l e n a and M. C l e o f a s , h a s b e e n s c a r c e l y d i s t u r b e d ( Z w e i f e l , i960) , f o r b o t h a r e w i t h o u t human i n h a b i t a n t s : t h i s makes t h e s t u d y much e a s i e r t h a n s i m i l a r s t u d i e s on g r o u p s l i k e t h e H a w a i i a n i s l a n d s , w h e r e man h a s p a r t l y d e s t r o y e d t h e n a t u r a l b i o m e . MORPHOLOGY 5 INTRODUCTION In order to understand the problem i n i t s present setting, i t i s f i r s t necessary to describe the morphological differences between mainland and island populations, and to establish the morphological trends exhibited by the island birds. Although this was not designed as a taxonomic study, the material assembled was s u f f i c i e n t to enable comments to be made on the subspecific status of the island populations, and these are to be found i n Appendix I I . MATERIALS. AND METHODS A check-list of species and material studied is given i n Table 1. The nomenclature follows Friedman et a l . {1951), and Stager (1957), but has been modified i n accordance with the findings presented i n Appendix I I . A tota l of 1,918 specimens of known sex were examined, including a small number of juveniles; a few of unknown sex were also available. About half of the specimens were borrowed from Museums and other i n s t i t u t i o n s , and the rest were collected by the author and colleagues of the University of B r i t i s h Columbia. Specimens were collected at points as evenly distributed through the whole area as possible. The specimens collected by the author i n 1961, and a l l those collected by other colleagues of the University of Br i t i s h Columbia, were frozen as soon as possible, and transported to the University for preparation and Museum storage. Fat condition and length of gonad, were recorded from most of the specimens. Specimens prepared for the Museum, and bones taken from them, were allowed to dry for at least one month before study, by which time the TABLE 1 The s p e c i e s and number o f s p e c i m e n s s t u d i e d . b A d u l t A d u l t I m m a t u r e Immatu re P l a t y p s a r i s a g l a i a e L a f r e s n a y e M. B a . a l b i v e n t r i s ( L a w r e n o e ) 24 25 16 _ I, P . a . i n s u l a r i s R i d g w a y 16 14 2 T y r a n n u s m e l a n c h o l i c u s , V i e i l l o t M. T . m . o c c i d e n t a l i s H a r t e r t & 29 32 8 2 G o o d s o n I. T . m . o c c i d e n t a l i s " " " 17 15 - 1 M y i a r c h u s t y r a n n u l u s ( M i l l e r ) M . M . t . ma g i s t e r R i d g w a y 32 21 - -I. M. t . m a g i s t e r R i d g w a y 25 18 -M y i a r c h u s t u b e r c u l i f e r ( D ' O r b i g n y & L a f r e s n a y e 36 38 M. M . t . o l i v a s c e n s R i d g w a y 3 3 I. M . t . o l i v a s c e n s R i d g w a y 15 28 17 8 M y i o p a g i s v i r i d i c a t a ( V i e i l l o t ) M. m . v . j a l i s c e n s i s N e l s o n 33 19 — — I. M . v . m i n i m a N e l s o n 20 10 - -C a m p t o s t o m a i m b e r b e S c l a t e r M. C . i . i m b e r b e S c l a t e r 1 2 - — I. C . i . i m b e r b e S c l a t e r 3 2 - --T h r y o t h o r u s f e l i x S c l a t e r M. T.jf. p a l l i d u s N e l s o n 37 17 - — I. T . f . l a w r e n c i i R i d g w a y 36 27 - -M e l a n o t i s c a e r u l e s c e n s ( S w a i n s o n ) M. M . c . c a e r u l e s c e n s ( S w a i n s o n ) 29 32 — — I. M . c . c a e r u l e s c e n s ( S w a i n s o n ) 45 18 - -Mimus p o l y g l o t t o s ( L i n n a e u s ) M. M . p . l e u e o p t e r u s ( V i g o r s ) 7 9 - -I. M . p . l e u e o p t e r u s ( V i g o r s ) 4 2 - -T u r d u s r u f o - p a l l i a t u s L a f r e s n a y e M. T . r - p . r u f o - p a l l i a t u s L a f r e s n a y e 32 25 - — 1. T . r - p . g r a y s o n i R i d g w a y 20 34 - -T A B L E 1 - c o n t i n u e d 7 A d u l t A d u l t I m m a t u r e I m m a t u r e tfV 22 d*d* 22. M y a d e s t e s o b s c u r u s L a f r e s n a y e M. M . o . o c c i d e n t a l i s S t e j n e g e r I . M . o . i n s u l a r i s S t e j n e g e r V i r e o h y p o e h r y s e u s S c l a t e r M. V , h . h y p o e h r y s e u s S c l a t e r I . V . h . s o r d i d u s N e l s o n V i r e o f l a v o v i r i d i s ( C a s s i n ) M. V . f . h y p o l e u c u s V a n R o s s e m & H a c h i s u k a I . V . f . h y p o l e u c u s » » n P a r u l e ' p i t i a y u m i ( V i e i l l o t ) M. P . p . p u l c h r a ( B r e w s t e r ) M. P . p . i n s u l a r i s L a w r e n c e I . P . p . i n s u l a r i s L a w r e n c e G r a n a t e l l u s v e n u s t u s D u Bus M. G . v . v e n u s t u s D u Bus I . G . v . f r a n c e s c a e B a i r d 17 7 44 28 23 41 20 11 41 15 18 14 8 20 20 19 16 11 8 20 10 13 6 8 2 4 I c t e r u s p u s t u l a t u s ( W a g l e r ) M . ' I . p . m i c r o s t i c t u s G r i s c o m I . I . p . g r a y s o n i i C a s s i n 69 36 27 11 30 21 26 25 P i r a n g a b i d e n t a t a ( S w a i n s o n ) M. P . h . b i d e n t a t a ( S w a i n s o n ) I . P . b . f l a m m e a R i d g w a y 25 24 17 21 5 3 S p i n u s p s a l t r i a ( S a y ) M. S . p . p s a l t r i a ( S a y ) 25 14 I . S . p . p s a l t r i a ( S a y ) 27 13 R i c h m o n d e n a c a r d i n a l i s ( L i n n a e u s ) M. R . c . a f f i n i s N e l s o n 9 6 I . R . C . m a r i a e N e l s o n 35 30 4 10 8 10 NB« M. = M a i n l a n d : I . = I s l a n d . 8 majority of shrinkage due to drying i s supposed to have occurred (Anderson, i 9 6 0 ) . The four standard'dimensions, wing, t a i l , tarsus and b i l l , were chosen and measured i n the manner prescribed by Baldwin et a l ( 1 9 3 1 ) . Because the wings of some specimens were t i e d firmly to the body, the chord of the wing was measured instead of the wing flattened against the r u l e r , the usual practice now. This measurement required that the specimen be held firmly on the table, and that the folded wing l i e i n i t s correct position, following the contour of the body, and with the : feathers straight. The wing was measured from carpal joint to the t i p of the longest feather. Other measurements made were length of t a i l (from point of insertion of central r e c t r i c e s into skin, to t i p of longest r e c t r i x ) and length of integument-covered tarso-metatarsus, here referred to as the tarsus (from tibiotarsus joint, on i t s posterior aspect, to midpoint of the d i s t a l edge of one of the scutes at opposite end, usually the lowest, undivided one). A sketch of the tarsus s c u t e l l a t i o n of each species was made, so that the scute used i n the measurement could be easily recognized. The length of the b i l l was measured from a point just inside the anterior edge of the naris to the b i l l t i p , and the width was measured on the upper mandible i n the plane of the anterior edges of the nares. Other limb bones were measured as follows:-The tar some tatarsus bone (from groove i n central condyle at d i s t a l end to central point of proximal head): the tibiotarsus 9 ( b e t w e e n t h e m i d p o i n t s o f e a c h h e a d ) ; t h e f e m u r ( f r o m g r e a t e r t r o c h a n t e r t o c e n t r e o f d i s t a l h e a d ) : and t h e c o r a c o i d ( f r o m d i s t a l h e a d t o m i d p o i n t o f s h a l l o w c u r v a t u r e o f t h e p r o x i m a l e n d ) . When a p a i r e d s t r u c t u r e was t o b e m e a s u r e d , t h e l e f t member was u s e d u n l e s s d a m a g e d . A l l m e a s u r e m e n t s w e r e made t o the n e a r e s t 1/1 Oth m i l l i m e t r e . B a d l y w o r n w i n g s , t a i l s and b i l l s w e r e n o t m e a s u r e d . L i t t l e s e a s o n a l c h a n g e was o b s e r v e d i n t h e s p e c i m e n s s t u d i e d . I n 1963 f r e s h w e i g h t s w e r e o b t a i n e d f r o m s p e c i m e n s b e t w e e n f i v e m i n u t e s a n d f i v e h o u r s a f t e r t h e i r c o l l e c t i o n , and a n a d d i t i o n a l t e n w e r e t a k e n b y D r . P . A . L a r k i n . B e t w e e n one a n d f o u r months a f t e r t h e y h a d b e e n c o l l e c t e d , f r o z e n s p e c i m e n s w e r e a l l o w e d t o t h a w and w e r e t h e n w e i g h e d . A t w o - p a n b a l a n c e , m a n u f a c t u r e d by C l a y Adams C o . , was u s e d f o r t h e f o r m e r , and an Ohaus t r i f l e beam b a l a n c e f o r t h e l a t t e r . F r e s h w e i g h t s a n d f r e e z e / t h a w w e i g h t s a r e n o t s t r i c t l y c o m p a r a b l e ( T a b l e s 44 a n d 45). T h e r e f o r e a maximum a l l o w a n c e i s made o f a l o s s i n w e i g h t o f 1 gm. d u r i n g t h e f r e e z e and t h a w p r o c e s s . B e c a u s e t h e f a t d e p o s i t s o f a b i r d c a n c o n t r i b u t e 20% t o t h e t o t a l w e i g h t ( C o n n e l l e t a l . i960), w e i g h t d a t a a r e g r o u p e d a c c o r d i n g t o t h e f a t c o n d i t i o n o f t h e s p e c i m e n s , a s c l a s s i f i e d by M c C a b e (1943). T h o s e i n M c C a b e ' s c a t e g o r i e s 0 - 2 a r e r e f e r r e d t o h e r e a s " n o t - f a t " and t h o s e i n c a t e g o r i e s 3 - 5 a s " f a t " . I n t h e c o m p a r i s o n o f p l u m a g e s , u s u a l l y s p e c i m e n s c o l l e c t e d r e c e n t l y w e r e u s e d i . e . i n t h e p e r i o d 1957-19&3, and t h o s e c o l l e c t e d a t a p p r o x i m a t e l y t h e same t i m e o f y e a r . 10 M u s e u m - p r e p a r e d s p e c i m e n s w e r e p l a c e d s i d e b y s i d e u n d e r a r t i f i c i a l ( s t r i p ) l i g h t i n g c o n d i t i o n s . The C o l o u r A t l a s o f C . and J . V i l l a l o b o s ( 1 9 4 7 ) was u s e d a s a g u i d e f o r t h e i d e n t i f i c a t i o n o f c o l o u r s . P l u m a g e t e r m i n o l o g y f o l l o w s t h a t o f D w i g h t ( 1 9 0 0 ) . F o r a n a l y s i s o f t h e d o r s a l s t r e a k s i n t h e p l u m a g e o f I . p u s t u l a t u s a l i g h t w e i g h t p i e c e o f f l a t m e t a l was u s e d , w i i h a c i r c u l a r h o l e o f 12 mm. d i a m e t e r p u n c h e d t h r o u g h t h e m i d d l e . The m e t h o d o f m e a s u r i n g t h e e x t e n t o f a c o l o u r p a t t e r n i s d e s c r i b e d s e p a r a t e l y f o r e a c h s p e c i e s , w h e r e a p p l i c a b l e . D i f f e r e n t a g e g r o u p s , when i d e n t i f i e d b y p l u m a g e c h a r a c t e r i s t i c s , and t h e t w o s e x e s , a r e t r e a t e d s e p a r a t e l y . The s t a t i s t i c s a p p l i e d t o t h e d a t a h a v e b e e n o f s s i m p l e k i n d . I n a c c o r d a n c e w i t h t h e r e c o m m e n d a t i o n s o f M a y r , L i n s l e y a n d U s i n g e r (195?)»"sn a t t e m p t h a s b e e n made t o a s s e m b l e a t l e a s t f i f t e e n s p e c i m e n s i n e a c h s a m p l e . A s a c o n v e n t i o n a m i n i m u m s a m p l e s i z e o f f i v e i s c o n s i d e r e d e s s e n t i a l f o r s t a t i s t i c a l t r e a t m e n t , a n d t h e n t h e s t a n d a r d e r r o r and c o e f f i c i e n t o f v a r i a t i o n - - 1 0 0 t i m e s t h e s t a n d a r d d e v i a t i o n , d i v i d e d by t h e mean (Amadon , 1 9 5 0 ) - - h a s be e n c a l c u l a t e d . A s i g n i f i c a n t d i f f e r e n c e b e t w e e n two means i s c o n s i d e r e d t o e x i s t when two s t a n d a r d e r r o r s p l a c e d e i t h e r s i d e o f e a c h mean do n o t o v e r l a p , a p r a c t i c e r e c o m m e n d e d by D i c e and L e r a a s (19%). S i g n i f i c a n t d i f f e r e n c e s a r e s h o w n i n t h e t a b l e s ( A p p e n d i x I ) b y an a s t e r i s k p l a c e d a g a i n s t t h e i s l a n d m e a n . T h e d i f f e r e n c e s a r e e x p r e s s e d a s p e r c e n t a g e s o f t h e m a i n l a n d m e a n s , i n a s e p a r a t e a t a b l e i n t h i s c h a p t e r . A X t e s t h a s b e e n a p p l i e d a l s o t o some o f t h e d a t a . S t a n d a r d d e v i a t i o n s h a v e b e e n i n c l u d e d i n t h e T a b l e s i n A p p e n d i x I and u s e d i n t h e t a x o n o m i c a n a l y s i s i n A p p e n d i x I I . 11 R E S U L T S : I . PLUMAGE I f t h e a v i f a u n a o f t h e T r e s M a r f a s i s l a n d s f o l l o w s t h e u s u a l i n s u l a r t r e n d s , a r e d u c t i o n i n t h e b r i g h t n e s s , a r e a o f b r i g h t c o l o u r a n d c o n t r a s t i n g p a t t e r n I s t o b e e x p e c t e d I n t h e p l u m a g e o f t h e b i r d s . The r e s u l t s o f m a i n l a n d - i s l a n d c o m p a r i s o n s a r e d e s c r i b e d f o r e a c h s p e c i e s s e p a r a t e l y , a n d s u m m a r i z e d I n T a b l e 2 . 1 ) P l a t y p s a r i s a g l a i a e V e n t r a l l y t h e i s l a n d m a l e s a r e more u n i f o r m l y g r e y t h a n t h e m a i n l a n d m a l e s . T h e p a l e s t i n s u l a r i s s p e c i m e n s a r e a s d a r k o n t h e b e l l y a s t h e d a r k e s t a l b i v e n t r i s s p e c i m e n s ; b u t a l l o f t h e i n s u l a r i s m a l e s may be d i s t i n g u i s h e d f r o m t h e o t h e r s by a g r e y , and n o t w h i t i s h , c h i n . I n t h e f e m a l e s t h e t a i l p a t t e r n i s d u l l e r i n i s l a n d b i r d s . On m a i n l a n d s p e c i m e n s a b r i g h t c i n n a m o n c o l o u r c o v e r s a t l e a s t t h e m a j o r i t y o f t h e i n n e r v a n e o f t h e o u t e r f i v e , g r e y - b r o w n r e c t r i c e s , a n d s o m e t i m e s t h e w h o l e a r e a o f t h e f e a t h e r s , w h e r e a s on t h e t a i l s o f I s l a n d s p e c i m e n s t h e c i n n a m o n i s r e s t r i c t e d t o t h e edge o f t h e i n n e r v a n e . The r e c t r i c e s o f i m m a t u r e o r f i r s t w i n t e r ( D w i g h t , 1 9 0 0 : m f i r s t b a s i c , Humphrey and P a r k e s , 1 9 5 9 ) m a l e s r e s e m b l e t h o s e o f t h e a d u l t f e m a l e s f r o m t h e same p o p u l a t i o n . A l s o , t h e i s l a n d s p e c i m e n s e x a m i n e d w e r e s l i g h t l y more b u f f - c o l o u r e d v e n t r a l l y t h a n m a i n l a n d o n e s . A d u l t and i m m a t u r e f e m a l e s a r e i n d i s t i n g u i s h a b l e . O n l y one f l e d g e d , j u v e n i l e s p e c i m e n was a v a i l a b l e , a m a i n l a n d m a l e . T h e b o d y p l u m a g e i s c o n c o l o r o u s w i t h t h e a d u l t f e m a l e , and t h e t a i l - p a t t e r n i s o f t h e f e m a l e i n s u l a r i s c h a r a c t e r . H e n c e , t h e p l u m a g e o f i m m a t u r e m a l e a n d a d u l t f e m a l e i n s u l a r i s 12 s p e c i m e n s i s more s i m i l a r t o the Juvenal condition, t h a n a r e t h e p l u m a g e s o f e q u i v a l e n t a l b i v e n t r i s s p e c i m e n s , 2 ) T y r a n n u s m e l a n c h o l i c u s The d o r s a l s u r f a c e o f i s l a n d b i r d s i s s o m e t i m e s g r e y e r t h a n i n m a i n l a n d b i r d s ; t e n i s l a n d s p e c i m e n s , h a v i n g n o more t h a n a h i n t o f g r e e n c o l o u r i n t h e f e a t h e r s , w e r e m o r e e x t r e m e t h a n t h e g r e y e s t m a i n l a n d b i r d . S p e c i m e n s f r o m t h e m a i n l a n d , c o l l e c t e d i n t h e same m o n t h s o f t h e y e a r , w e r e u s e d i n t h i s c o m p a r i s o n . P l u m a g e a b r a s i o n d o e s n o t a c c o u n t f o r t h i s d i f f e r e n c e . P e r h a p s t h e d i f f e r e n t summer c l i m a t i c c o n d i t i o n s in the two r e g i o n s p r o d u c e a c h e m i c a l c h a n g e i n t h e p i g m e n t o f t h e d o r s a l f e a t h e r s t o d i f f e r e n t d e g r e e s ( s e e H e i n r o t h a n d H e i n r o t h , 1 9 5 8 ) . 3) M y i a r c h u s t v r a n n u l u s No p l u m a g e d i f f e r e n c e s b e t w e e n members o f m a i n l a n d and i s l a n d p o p u l a t i o n s w e r e o b s e r v e d i n t h e m a t e r i a l s t u d i e d . 4 ) M y i a r c h u s t u b e r c u l i f e r I n t h e n o r t h e r n p a r t o f t h e m a i n l a n d s t u d y a r e a ( i . e . s o u t h e r n S i n a l o a ) s p e c i m e n s a r e g r e e n e r , d o r s a l l y , t h a n i s l a n d o n e s . H o w e v e r t h e m a j o r i t y o f s p e c i m e n s c o l l e c t e d i n N a y a r i t , and a l l t h o s e e x a m i n e d f r o m J a l i s c o , a r e i d e n t i c a l i n c o l o u r t o t h e i s l a n d b i r d s , s o t h e s m a l l d i f f e r e n c e h a s n o t b e e n i n c l u d e d i n T a b l e . 2 . I n t h e m a i n l a n d s a m p l e o f e i g h t y s p e c i m e n s , s i x c o l l e c t e d i n t h e m o n t h s J u l y t o S e p t e m b e r h a v e b r o a d c i n n a m o n e d g e s t o t h e i n n e r v a n e s o f t h e o u t e r f i v e p a i r s o f r e c t r i c e s i n t h e t a i l . I n t h e c o l o u r o f t h e w i n g c o v e r t s a n d t h e n a t u r e o f t h e b o d y p l u m a g e , some show t r a c e s o f j u v e n a l p l u m a g e . The i s l a n d s a m p l e , c o l l e c t e d 13 mainly i n the months February to May, has a considerably higher proportion of specimens w i t h t a i l s patterned i n t h i s way. Because of the a s s o c i a t i o n with juvenal plumage, and t h e i r occurrence just before the beginning of the breeding season, they are r e f e r r e d to as immature ( f i r s t - y e a r ) b i r d s . The d i f f e r e n c e i n c o n t r i b u t i o n to the two samples made by those immatures recognizable by t h i s plumage i s shown i n Table 47, and i s s t a t i s t i c a l l y s i g n i f i c a n t . 5) Mviopagis v i r i d i c a t a and Oamptostoma imberbe No plumage d i f f e r e n c e s between members of mainland and i s l a n d populations were observed. 6) Thryothorus f e i i x A few i s l a n d specimens have paler rufous flanks than mainland ones do. A l l i s l a n d specimens have white underparts, i n contrast t o the buffy or rufous underparts of the mainland b i r d s . The black and white face pattern Is a conspicuous feature of both mainland and i s l a n d forms of t h i s species. In mainland specimens the areas of black and white feathers are approximately equal, whereas i n i s l a n d specimens the area of white feathers always predominates. A l s o , the black malar s t r i p e i s p a r t l y masked by white feathers i n the i s l a n d b i r d s , but never masked In mainland specimens. In mainland j u v e n i l e specimens the white of the face predominates, tkere being l i t t l e b l a c k , sometimes brown, pigment; s i m i l a r l y , the malar s t r i p e may be coloured brown or black. Thus, the mainland j u v e n i l e s resemble i s l a n d a d u l t s , i n having a face-p a t t e r n l e s s b o l d l y marked than i n mainland a d u l t s . 8) Melanoti s caerulescens A tendency towards paleness i n the throat and crown feathers e x i s t s i n the i s l a n d b i r d s . However, the majority of 14 s p e c i m e n s f r o m b o t h s a m p l e s w e r e f o u n d t o be o f s i m i l a r c o l o u r , a n d f u r t h e r m o r e one m a i n l a n d s p e c i m e n was a s p a l e a s t h e p a l e s t i s l a n d s p e c i m e n . One s p e c i m e n c o l l e c t e d o n M a r i a M a d r e by N e l s o n and G o l d m a n i n 1897 i s p u r e w h i t e o n t h e m a j o r i t y o f t h e v e n t r a l s u r f a c e . The c o l l e c t o r s o b s e r v e d o t h e r s o n t h i s i s l a n d ( N e l s o n , 1899), a s d i d G r a y s o n ( I 8 7 D , a n d t h e y w e r e o b s e r v e d on M . G l e o f a s b y H e i l f u r t h (1934). 9) M i m u s p o l y g l o t t o s No p l u m a g e d i f f e r e n c e s , b e t w e e n members o f m a i n l a n d and i s l a n d p o p u l a t i o n s , w e r e o b s e r v e d i n t h i s s t u d y . 10) T u r d u s r u f o - p a l l i a t u s A t t h e l i m i t o f t h e b l a c k - s t r e a k e d , w h i t e t h r o a t t h e r e i s a b r e a s t b a n d o f r u f o u s - b r o w n i n m a i n l a n d b i r d s , t h e same c o l o u r a s t h e s i d e s a n d f l a n k s : t h e t e r m i n a l , s t r e a k e d f e a t h e r s a r e g r e y . I n i s l a n d b i r d s t h i s g r e y c o l o u r e x t e n d s t h r o u g h o u t t h e b r e a s t - b a n d . T h e s i d e s a n d f l a n k s a r e o r a n g e - b r o w n , b u t d i s t i n c t l y d u l l e r t h a n t h e r u f o u s c o l o u r o f t h e m a i n l a n d c o u n t e r p a r t s . T h e m a i n l a n d f e m a l e s t e n d t o b e p a l e r t h a n t h e m a l e s , y e t s t i l l t h e c o l o u r i s b r i g h t e r t h a n on t h e i s l a n d b i r d s . On t h e o t h e r h a n d t h e s e x e s o f i s l a n d b i r d s a r e i d e n t i c a l l y c o l o u r e d . T h e r e a r e f o u r m a i n l a n d s p e c i m e n s h o w e v e r , a m a l e a n d t h r e e f e m a l e s , # i i e h a r e i n d i s t i n g u i s h a b l e f r o m i s l a n d s p e c i m e n s . T h e y w e r e c o l l e c t e d a t S a u t a and G h a c a l a , N a y a r i t , I n t h e y e a r s 1940-1946. T h e i r p a l e c o n d i t i o n may b e t h e r e s u l t o f f a d i n g : b u t f i f t e e n o t h e r s c o l l e c t e d by t h e same c o l l e c t o r d u r i n g t h a t s e v e n -y e a r p e r i o d , and a n o t h e r s e v e n c o l l e c t e d i n t h e p r e c e d i n g s i x y e a r s , a r e as b r i g h t l y c o l o u r e d a s f r e s h l y - c o l l e c t e d s p e c i m e n s , w h i c h a r g u e s a g a i n s t f a d i n g a s an e x p l a n a t i o n . 15 The b a c k o f m a i n l a n d m a l e s p e c i m e n s i s s l i g h t l y more r u f o u s t h a n i n t h e f e m a l e s , w h i c h a r e i n d i s t i n g u i s h a b l e f r o m a l l i s l a n d b i r d s . O n l y f i v e , r e c e n t l y c o l l e c t e d , m a i n l a n d , m a l e s p e c i m e n s w e r e a v a i l a b l e f o r c o m p a r i s o n w i t h a much g r e a t e r amount o f i s l a n d m a t e r i a l . B e t w e e n t h e s e a d i f f e r e n c e i n d o r s a l c o l o r a t i o n w a s d e t e c t e d , b u t i t w a s n o t c o m p l e t e l y s u s t a i n e d when many o l d e r , m a i n l a n d s p e c i m e n s w e r e u s e d . T h e e x c e p t i o n a l , m a i n l a n d m a l e r e f e r r e d t o a b o v e , was i n d i s t i n g u i s h a b l e f r o m a l l i s l a n d s p e c i m e n s o n t h e b a s i s o f t h i s c h a r a c t e r a s w e l l . I s l a n d b i r d s a l s o show a t e n d e n c y t o p o s s e s s p a l e r and n a r r o w e r c h i n a n d t h r o a t s t r e a k s t h a n m a i n l a n d b i r d s , e a s i l y r e c o g n i z a b l e o n l y when t h e e x t r e m e f o r m s o f t h e two s a m p l e s a r e c o m p a r e d . 1 1 ) M y a d e s t e s o b s c u r u s T h e f o r e h e a d and m a l a r s t r i p e o f some i s l a n d b i r d s a r e t i n g e d w i t h b u f f . I n a t l e a s t t w o o f t h e s p e c i m e n s t h i s a p p e a r s t o be d u e t o a g r e a s e s t a i n . G - r a y s o n ( 1 8 7 1 ) , one o f t h e c o l l e c t o r s o f t h e i s l a n d s a m p l e o f s p e c i m e n s , r e f e r s t o t h e d i f f i c u l t y o f d r y i n g h i s s k i n s i n p a p e r s b e c a u s e o f t h e f a t w h i c h t h e y a b s o r b e d f r o m t h e s k i n s . M o r e s p e c i m e n s , c o l l e c t e d f r o m t h e i s l a n d s r e c e n t l y , a r e n e e d e d t o c l a r i f y t h i s p o i n t . O t h e r w i s e , t h e r e a r e no p l u m a g e -d i f f e r e n c e s b e t w e e n t h e p o p u l a t i o n s . 1 2 ) V i r e o h v p o c h r y s e u s T h e c h i n , t h r o a t and b r e a s t o f i s l a n d b i r d s a r e d u l l e r t h a n i n m a i n l a n d b i r d s , a n e f f e c t p r o b a b l y a i d e d by t h e f a c t t h a t t h e p i g m e n t i n t h e f e a t h e r s i s l e s s e x t e n s i v e , t e r m i n a l l y , a n d the b l a c k , b a s a l h a l f o f t h e f e a t h e r s s h o w s t h r o u g h t h e o v e r l y i n g f e a t h e r s m o r e . The s i d e s o f t h e c h e s t and f l a n k s a r e d u l l g r e e n i s h , 1 I 16 wheras the same feathers on mainland birds are yellow, only | f a i n t l y green. The mid-ventral area i s yellow i n both birds, of approximately equal brightness. The dorsum i s green i n the island birds, yellowish | green i n mainland birds: plumage wear tends to obscure this ; difference, but when specimens oollected i n the same month of the year are compared, there i s s t i l l complete separation of the two samples. The colour of the pileum tends to be the same as that of the dorsum, but only extreme forms of the two populations can • be separated using t h i s character alone. 12) Vireo f l a v o v i r i d l s There are three plumage-differences between mainland and island populations, two of which are subject to seasonal v a r i a t i o n . The r e s u l t s of comparing the two samples are shown i n Table 50. They suggest that i n both regions there i s a tendency f o r the grey colour of the pileum to be converted to brown during ! the summer months. From the physical condition of the plumage i t ; is apparent that feather wear alone i s not responsible for this change, which may be produced instead by a ehemical transformation of the pigment. The black margin of the pileum, which also forms the I border of the pale superciliary s t r i p e , i s more d i s t i n c t i n mainland than i n island specimens. Perhaps associated with the ! change i n pileum colour, i t tends to become more obscure late i n ! the summer, at least i n the island sample. The most obvious difference between the two samples is 17 t h e c o l o u r o f t h e e y e - s t r i p e . Due t o t h e p r e p a r a t i o n , t h e p r e -o r b i t a l p a r t i s f r e q u e n t l y o b s c u r e i n Museum s p e c i m e n s , h e n c e t h e c o l o u r o f t h e p o s t - o r b i t a l p a r t h a s b e e n r e g i s t e r e d i n t h e T a b l e . A l l i s l a n d s p e c i m e n s h a v e a d u l l - g r e y e y e - s t r i p e , w h e r e a s i n t h e m a j o r i t y o f m a i n l a n d s p e c i m e n s t h e s t r i p e i s w h i t e . 1 4 ) P a r u l a p i t i a y u m i S p e c i m e n s o f p u l c h r a h a v e p a l e , b u f f - c o l o u r e d f l a n k f e a t h f e r s , and i n i n s u l a r i s s p e c i m e n s t h i s c o l o u r h a s a r e d d i s h o r c h e s t n u t - t i n g e . The c o l o u r a l s o e x t e n d s f u r t h e r a n t e r i o r l y (.not m e a s u r e d ) , t h e e f f e c t b e i n g g i v e n o f a l a r g e r and d a r k e r f l a n k a r e a . A l l s p e c i m e n s h a v e a p a t t e r n o f w h i t e o n t h e o u t e r r e c t r i x , o c c u r r i n g a s a s q u a r e o r r e c t a n g l e o n t h e i n n e r v a n e . On s p e c i m e n s o f i n s u l a r i s t h i s i s a l w a y s s m a l l e r t h a n o n s p e c i m e n s l a i d s i d e by s i d e . The number o f r e c t r i c e s u p o n w h i c h a w h i t e p a t t e r n i s p r e s e n t was r e c o r d e d , t h e r e s u l t s o f w h i c h a r e shown i n T a b l e 51. S o m e t i m e s t h e p a t t e r n o f w h i t e i s r e d u c e d t o an i r r e g u l a r smudge o r s p o t , i n w h i c h c a s e t h e f e a t h e r p o s s e s s i n g I t i s i n d i c a t e d b y a b a r b e n e a t h t h e r e c t r i x number . The T a b l e shows t h a t f e w e r r e c t r i c e s o f i n s u l a r i s s p e c i m e n s h a v e a w h i t e p a t t e r n t h a n p u l c h r a s p e c i m e n s . A l l t h r e e s a m p l e s o f s p e c i m e n s c o n t a i n g r e y - l o r e d and b l a c k - l o r e d i n d i v i d u a l s . I n p l u m a g e s u c c e s s i o n g r e y - c o l o u r e d l o r e s p r e c e d e b l a c k l o r e s . T h e r e a r e p r o p o r t i o n a t e l y more 2 i n s u l a r i s t h a n p u l c h r a s p e c i m e n s w i t h g r e y l o r e s , b u t a X t e s t f a i l s t o e s t a b l i s h a d i f f e r e n c e o f s i g n i f i c a n c e . 18 In those specimens with black-coloured, l o r e s , the area covered by black-pigmented feathers i s greater i n pulchra than i n i n s u l a r i s specimens. The black o r b i t a l feathers appear more prominent i n the pulchra specimens, and so do the black feathers which form a bridge of the culmen of the b i l l and l i n k the face patterns of the two sides: i n i n s u l a r i s specimens there are only a few, i n d i s t i n c t , black feathers i n these two p o s i t i o n s . Specimens of t h i s species on the more i s o l a t e d , R e v i l l a Gigedo Islands have only the grey f a c e - p a t t e r n (Ridgway 1 9 0 2 ) . T h i s , i n s u l a r i s and pulchra are w e l l i l l u s t r a t e d i n Stager ( 1 9 5 7 ) . 15) Granatellus venustus A l l mainland, immature males have a black 'necklace' between the white throat and red chest, which i s almost complete at the surface, broken only be one or two white feathers: no i s l a n d , immature males have t h i s necklace. Adult males from both regions have the necklace, but d i f f e r i n I t s completeness. Mainland specimens almost always have a complete necklace, whereas i s l a n d specimens r a r e l y do (Table 53). V a r i a t i o n occurs i n ?the extent of the red colour on the chest and b e l l y , but there i s a tendency for mainland specimens to have a l a r g e r area. Mainland, immature males have l e s s red than adult males from both regions, but d i s t i n c t l y more than i s l a n d , immature males. The p a t t e r n of white on the outer, three pairs of r e c t r i c e s i s the same In the two samples, so for a comparison of the area of white only the outer p a i r of r e c t r i c e s was used. I t was measured i n the manner described i n Appendix I I , on page 179. The r e s u l t s are shown i n Table 5 2 , and demonstrate the greater area of white 19 on the island birds. When this i s related to the overall length of the t a i l , i t i s seen that the area of white i s also r e l a t i v e l y , as well as absolutely, greater i n these specimens. 16) Icterus pustulatus Birds i n adult and immature plumage were i d e n t i f i e d i n the manner described i n Appendix II , page 180 • Mainland birds have black or brown streaks on the dorsal feathers, whereas this pattern i s reduced or completely absent i n island birds. To demonstrate this, the instrument described on page 10 was placed on the back and i n the mid-line of the Museum -prepared specimen, between the wings and with the front point of the c i r c l e against the d i s t a l t i p of the central and posterior neck feathers. Only complete and well-prepared specimens were used. The number of streaks exposed i n the central c i r c l e were counted. The results are shown i n Table 54, and demonstrate that the number of streaks are uniformly reduced in a l l the age and sex groups of island birds. In the absence of dorsal streaks, island birds resemble the mainland Juvenal plumage. There are several differences of colour, by which some of one population may be distinguished from the other. Thus, island adult males have a paler chest and belly, generally, and a less d i s t i n c t orange r u f f around the black throat. Some mainland males have orange-coloured dorsal surfaces, whereas the majority of both samples have bright yellow backs, usually paler in island birds. There are also tendencies for adult female and immature, mainland birds to have a brighter plumage than the island equivalents. 20 Table 55 shows that the proportion of immature to adult specimens is higher i n the island sample,' affecting p a r t i c u l a r l y the females. 17) Piranga bidentata In a sample of 25 mainland, adult males two specimens were coloured red on their body plumage. The remainder, and a l l Island adult males, were orange-coloured. The extent of white on the t i p s of the outer pair of r e c t r i c e s is greater i n mainland specimens. This i s shown by the measurements presented i n Table 56. Details of the method of measuring are explained i n Appendix II , on page 183. In the small sample of immature, specimens, i t was noticed that mainland birds possessed more red on the forehead and chin than island birds. 18) Spinus p s a l t r i a The sub-orbital region of mainland specimens is coloured like the ventral surface of the body, yellow, whereas i n island specimens i t i s black, the colour of the dorsal surface. This plumage-difference, involving a few, small feathers only, is the only one between the two populations. 19) Richmondena cardinalis Almost a l l adult male specimens from the island are coloured a deep red, without the purple tinge which characterizes mainland birds. In a sample of twenty-six island specimens, only two were indistinguishable from the nine mainland specimens. A l l island females have abdomens coloured cream-white: only one of the six mainland females was so coloured, the rest being pale buff, s l i g h t l y paler than the breast and sides. It is possible that the 21 exceptional b i r d was in immature plumage. A l l island females nave grey chins, whereas only two of six mainland specimens examined did. The effect of grey is produced by the black basal half of the feather showing through the overlying white feather-tips, and i n island specimens the white i n the feather t i p i s reduced. The chin patch is larger i n island birds than i n mainland birds, observed when the two samples were l a i d side by side. TABLE 2 D i f f e r e n c e s o f p l u m a g e b e t w e e n m a i n l a n d and i s l a n d p o p u l a t i o n s . B r i g h t n e s s A r e a o f b r i g h t C o n t r a s t i n g J u v e n i l e / I m m a t u r e U n c l a s s i f i a b l e c o l o u r p a t t e r n t y p e o f a d u l t p l u m a g e P l a t y p s a r i s a g l a i a e T y r a n n u s m e l a n c h o l i c u s ( x M y i a r c h u s t y r a n n u l u s M y i a r c h u s t u b e r c u l i f e r M y l o p a g i s v - i r i d i c a t a C a m p t o s t o m a i m b e r b e T h r y o t h o r u s f e l i x x M e l a n o t i s c a e r u l e s c e n s ( / M imus p o l y g l o t t o s T u r d u s r u f o - p a H i a t u s x M y a d e s t e s o b s c u r u s Y i r e o h y p o c h r y s e u s x Y i r e o f l a T o v i r l d i s x P a r u l a p i t i a y u m i G r a n a t e l l u s ' v e n u s t u s i c t e r u s p u s t u l a t u s x P i r a n g a b i d e n t a t a S p i n u s p s a l t r i a R i c h m o n d e n a c a r d i n a l i s x / C h a r a c t e r g r e a t e r i n - i s l a n d s a m p l e No d i f f e r e n c e b e t w e e n t h e s a m p l e s x C h a r a c t e r l e s s i n i s l a n d s a m p l e ( ) A t r e n d d i s p l a y e d by a s u b s t a n t i a l n u m b e r , b u t l e s s t h a n 50^ o f a s a m p l e . 23 CONCLUSIONS The summarizing of the differences i n Table 2, has i t s limitations, because of the subjective nature of their interpretation. It i s sometimes d i f f i c u l t to decide whether a difference i n colour produces an increase or decrease i n brightness or contrasting pattern. For t h i s reason no attempt has been made to c l a s s i f y differences affecting the following:- the underparts of Thryothorus f e l i x , flanks of Ferula pitiayumi, sub-orbits of Spinus p s a l t r i a and chin and abdomen of Richmondena oar di n a l i s . The results show that of the 19 species of Tres Marias islands birds studied, 10 have plumage drabber and/or more inconspicuous than mainland forms: the opposite trend, for island birds to be brighter and more conspicuous, i s seen i n only one form. Thus there i s a pronounced trend among most of these island birds towards drab and inconspicuous plumage. In three instances this has taken the form of an appraoch to juvenal or immature plumage. Considerably more striking examples of this have been described by Murphy (1938) and Amadon ( 1 9 5 3 ) . Furthermore, i n samples of Hviarchus tuberculifer, Parula pitiayumi and Icterus pustulatus a greater proportion of specimens i n immature plumage are present i n the island than the mainland samples, which may indicate a longer retention of immature plumage by the island forms. It should be noted f i n a l l y that s i x of the 19 species studied appear to be ide n t i c a l on the islands and mainland. 24 II. BODY DIMENSIONS Plumage differences having been demonstrated i n some forms, i t should be anticipated that some island birds have a longer wing and b i l l than mainland birds, according to the information presented i n the General Introduction. Measurement results are summarized i n Table 3. Camptostoma imberhe is excluded from this table because the samples are so small. The s t a t i s t i c s of each sample are given i n Tables 25 to 45 i n Appendix I. According to these tables the measurements of males and females usually do not d i f f e r from each other s i g n i f i c a n t l y , nor do immatures and adults. The results show that of the 18 species of Tres Marias island birds measured, 12 show at least one dimension longer i n the island populations, six have at least one dimension shorter, while two species are id e n t i c a l on the mainland and islands. Thus there i s a predominant trend for increase in certain dimensions, and t h i s i s especially noticeable i n the b i l l - l e n g t h and tarsus-length (Table 4, and Eig. 7 in Appendix I ) : the latter i s unexpected. The trend i s least noticeable i n wing-length and t h i s , also is unexpected. A perusal of Table 5 shows that of the 12 species established with longer dimensions on islands, four have a l l dimensions r e l a t i v e l y longer than on the mainland, four show only the tarsus longer and one shows only the b i l l longer, etc. Of the four species which have a l l external parts larger on the islands, two (the two vireo species) have a l l parts larger to approximately the same degree, while the other two (Turdus rufo-palliatus and TABLE 3 Differences between the means of mainland and island samples of measurements. Differences are expressed as percentages of the mainland means. Wing T a i l Tarsus Bill-Length Bill-Width Femur Coracoid Weight P.aglaiae ' adult cf adult $ immature o -4.5 -4 .5 (-4.1) - 2 . 7 - 2 . 7 ( - 5 . 5 ) +1.0 +1.6 (+2.6) - 5 . 2 - 5 . 7 ( - 6 . 2 ) - 8 . 8 - 7 . 8 ( - 1 2 . 2 ) - 1 . 3 - 1 . 2 ( - 1 . 5 ) - 8 . 2 - 8 . 9 ( - 9 . 2 ) T.melancholicus adult d* adult £ - 1 . 1 - 1 . 8 - 2 . 0 -2.4 - 3 . 2 - 3 . 1 - 0 . 2 - 0 . 1 - 3 . 6 - 5 . 1 - 5 . 0 -4 .7 M. tyrannulus adult d* adult £ - 3 . 5 - 2 . 9 - 2 . 9 - 2 . 0 - 3 . 2 - 3 . 3 - 3 . 9 - 5 . 0 -5.4 - 5 . 0 (-4.6) (-4.2) M. tuberculifer adult d* •> adult 9^ immature o immature $ - 2 . 7 - 0 . 9 ( - 0 . 6 ) ( - 1 . 0 ) -1.4 +0.2 (+2.1) ( - 0 . 1 ) +0.3 +2.4 (+1.6) (+1.0) - 2 . 6 +1.0 (+4.8) (+10.0) ( - 6 . 5 ) ( - 9 . 2 ) - 1 0 . 0 ( - 1 1 . 6 ) M.viridicata adult cf adult $ - 1 . 9 +0.4 - 0 . 8 +0.4 +5-9 +6.7 - 2 . 1 0 - 1 . 9 ( - 3 . 5 ) - 9 . 3 ( - 9 . 8 ) C. imberbe adult cf adult 2 T. f e l i x adult d* adult £ +4. 4 +7.5 +6.9 +12.5 +1.6 + 0.4 +13.9 +15.6 - 1 6 . 0 ' ( - 1 1 . 3 ) ' M. caeroalescens adult d* adult $ -4. 0 - 3 . 0 - 1 1 . 6 - 9 . 9 - 2 . 2 - 3 . 7 +15.3 +15.5 - 3 . 9 ( - 2 . 6 ) - 9 . 0 ( - 7 . 0 ) r o Vn TABLE 3 - eo nti nued Wing T a i l Tar sus B i l l - l e n g t h Bill-width Femur Coracoid Weight M.polyglottos adult o" - a d u l t $ (+1.2) ( + 0.4) (+1.5) (+1.3) T.rufo-palliatus adulter* adult 2 +2.9 +3.9 +2.8 +3.6 +11.2 +10.4 +14.4 +11.2 M. obscurus adulter" adult £ - 2 . 7 - 2 . 1 - 0 . 2 +0.9 +11.7 +9.6 -3.9 - 1 . 7 T. hypoehryseus adult adult <j> +6.3 +7.2 +8.3 +9.2 +6.8 +6.5 +3.5 +4.6 +0.7 +1.7 - 9 . 0 ( - 6 . 7 ) Y. f l a v o v i r i d i s adult d* adult 2 +2.9 +2. 4 +4.8 +3.3 +6.0 +6.5 +3.9 +6.3 +5.8 +4.1 (+3.2) (+2.4) P.pitiayumi adult d1 adult $ +4.7 +8.1 +14.7 +19.7 +18.5 +14.9 +0.5 - 2 . 2 G.venustus : adult (f adult $ immature <f +7.2 +6.9 +7.3 +9.2 +9.1 +11.5 +7.6 +8.7 +8.0 +2.5 - 0 . 2 +1.1 I.pustulatus adult 6* adult 0_ Immature (f immature <j> +8.4 +7.7 +8.3 +4.8 +7.7 +5.4 +8.2 +1.2 +6.1 +4.1 +5.0 +4.1 +17.2 +11.9 +17.2 +16.6 +7.6 +9.1 +6.6 +11.6 -0.42 +1.92 -5.1?, -1.4 2/! - 5.4 2 -1.42 ,1 ro ON TABLE 3 - continued Wing T a i l Ta rsus B i l l - l e n g t h Bill-width Eemur Coracoid Weight P.bidentata adult cf - 1.4 - 0 . 7 +6.0 +3.1 +10.0 ( - 3 . 5 ) ( - 1 . 3 ) adult £ -1*3 - 2 . 2 +5.5 +2.2 +7.6 +0.7 - 4 . 7 immature cf ( - 2 . 6 ) (+0.8) (+6.8) ( - 1 . 6 ) {+10.2) S. psaltria adult cf - 4 . 7 - 3 . 9 +1.7 - 9 . 6 - 9 . 8 ( - 0 . 6 ) ( - 7 . 4 ) adult $ - 3 . 8 - 4 . 3 +3.4 - 6 . 9 - 1 1 . 5 ( - 1 . 3 ) - 7 . 0 immature cf ( - 6 . 8 ) ( - 8 . 5 ) (+1.4) ( - 6 . 7 ) ( - 9 . 3 ) immature £ - 2 . 5 - 2 . 2 + 4 . 6 - 7 . 9 - 8 . 2 R.cardinalis adult cr* + 4 . 3 ( - 5 . D +12.1 +8.0 +8.8 adult £ +1.9 • - 7.4- +7.6 +3.0 +7.8 NB. A negative sign indicates that the mainland mean i s the larger, and a positive sign indicates that the island mean Is the larger. A figure i n brackets is derived from a comparison made between two samples, one of which is composed of less than f i v e individuals. 1 Weights of birds after freezing and thawing: mainland birds not f a t , island birds of unknown f a t . 2 Immatures included. ro 28 TABLE 4 . Table of Differences: Measurements of a l l the island passerine species contrasted with those of mainland samples. N U M B E R OF D I F F E R E N C E S Island specimens No Mainland specimens larger difference * larger Wing-length 7 5 5 Tail-length 7 6 4 Tarsus-length 10 4 3 B i l l - l e n g t h 6 8 3 Bill-width 3 - 2 Femur-length 1 9 2 Coracoid-length - 5 8 . .  Weight - (2) (9) NBc A difference is considered to exist when the ranges (page 10) of both male and female island measurements do not overlap those of mainland measurements, and the samples of a l l four number f i v e or more. When only-one sex i s thus represented, a difference is based upon this alone (e.g. R. cardinal is ). In view of the different 1 fat-:;condition of the:'vsamples of 'birds, . comparis pas of weight data have usually been indirect and are treated less stringently than the above data. TABLE 5 29 A comparison of plumage and dimension c h a r a c t e r i s t i c s of the mainland and i s l a n d samples Species lurna; ?e Wing T a i l Tarsus B i l l - l e n g t h P . aglaiae X / / _ / T. melancholicus _ _ - / Mo tyrannulus - / / / M, t u b e r c u l i f e r _ - - _ -M. v i r i d i c a t a _ - - X -T„ f e l i x X X X _ X M. caerulescens (/) / / / X Mo po l y g l o t t o s _ _ - - -T. r u f o - p a l l i a t u s X X X X X M. obscurus - „ - X -V . hypochryseus X X X X X V„ f l a v o v i r i d i s X X X X X P. p i t i a y u m i X X X X _ G. venustus x/ X X X — I ,. pustulatus X X X X X P. bidentata - _ - X -S, p s a l t r i a / / - / R, c a r d i n a i l s X / — X Data taken from Tables 2)5 to 43- i n Appendix I , Table 2 , and Table .'-4.. x - Plumage more drab or dimension longer i n i s l a n d sample. - = No di f f e r e n c e between mainland and i s l a n d samples. / = Plumage more bold or dimension shorter i n i s l a n d sample. 3P Icterus pustulatus) have some parts disproportionately larger than others. Thus increase In individual dimensions may or may not be connected with other parts. By combining the data on dimension - and plumage -differences (Table 5) i t becomes evident that those species which have drab plumage on the island, usually have larger external parts: while those with plumage more or less identical on mainland and islands, usually have external parts of similar size. That the shape of the b i l l is not always the same, i n mainland and island samples, is i l l u s t r a t e d by Fig.8 i n Appendix I. In contrast to the above mentioned size differences, there i s a tendency for the more centrally situated bones, the coracoid and femur, to be shorter in island birds. A relationship exists between the coracoid and wing-length measurements, and between the femur and tarsus measurements. For example, i f both femur and tarsus measurements are greater i n the island specimens, the difference i n tarsus i s the larger of the two (e.g. v>hypoohryseus, Table 3): i f both are shorter i n island specimens, i t i s the femur i n which the difference i s the larger (e.g. M. tyrannulus). These, viewed i n r e l a t i o n to the weight data, show that the- island birds have a smaller body-size than mainland birds. Using the data i n Appendix I, i t is possible to conclude that island specimens of P. aglaiae t T. melancholious. M.tyrannulus, M. tuberculifer, M. v i r i d i o a t a , T. f e l i x , M. caerulescens, V. hypoohryseus and S. psa l t r i a weigh less than mainland specimens. The data give no evidence of weight difference between mainland and i s l a n d specimens of V. f l a v o v i r i d i s , P. pitiayumi. and ! 3 1 I £• bidentata, nor any evidence of an island sample being heavier than the equivalent mainland sample. Indirect and d i r e c t comparisons of weights of T„ f e l i x and I. pustulatus yield the same r e s u l t . The results of a l l these comparisons are shown in Table 4. J It may be seen from t h i s table that a numerical correspondence exists between the weight and coracoid differences. j» In fa c t , those island samples with small coracoids have low weights, f Since a lower weight probably means a smaller volume, i t is l o g i c a l \ to expect centrally situated bones to be smaller too. The differences i n femur measurements can be interpreted as being the result of selection for longer t a r s i but smaller body. This i s supported by evidence from I. pustulatus. for which there are t i bio-tarsus measurements available also. The weight, tarsus and femur data i n Table 3 and the tibiotarsus data i n Table 46, demonstrate a graded series of differences, from a small decrease i n weight to a substantial increase In tarsus-length i n island specimens. These differences may be summarized as follows:-There is a tendency for island birds to have smaller bodies but larger exposed parts. There i s no evidence of a consistent difference between the v a r i a b i l i t y of mainland and island samples, as measured by the c o e f f i c i e n t of v a r i a b i l i t y (see Appendix I ) . 32 DISCUSSION AND CONCLUSIONS Since the tarsus and wing results do not conform to the previously described patterns, i t becomes necessary to consider whether large tarsus- and b i l l - l e n g t h are t y p i c a l of most island birds, by comparing the results of the present study with data from other islands. Usually, only the measurements of island subspecies or species are reported i n the l i t e r a t u r e , or the samples of specimens are small (less than ten). Furthermore the mainland specimens, with which they are compared, have not always been collected at the nearest point to the islands. There i s no reason to suppose that these collecting and sampling errors w i l l give a consistent bias i n any one direction. I f a l l island birds have approximately the same size as the mainland birds with which they are compared, a comparison of mean values should y i e l d the res u l t that 50f« of the island species are larger and 50% are smaller. Published measurements of island and mainland birds of North America and Mexico have been compared, and the results l i s t e d i n Table 6 . Any difference between means, however small, has been recorded. Presumably the same method was used by Murphy (1938) although i t is not e x p l i c i t . Murphy ( l o c . c i t . ) included data from the Rgvilla Gigedo Islands and Cuban avifauna, but i n both cases comparisons with the mainland avifauna are d i f f i c u l t , and these islands are therefore' excluded here. Birds from the Tres Marias are also omitted and are dealt with below. The l i s t combines data on insular subspecies and species. The proportion of island endemics with a larger b i l l (77f°) i s closely in accordance with TABLE 6 Differences between means of island and mainland samples of measurements of passerine birds. . North American and Mexican islands considered, exclusive of the R e v i l l a Gigedo and Tres Marias islands. Species Islands T a i l Tarsus B i l l Eremophila alpestris - i n s u l a r i s Santa Rosa, Santa Cruz,etc. / / X X I Cyanocitte s t e l l e r i - car lottae Queen Charlottes X / X I Aphelocoma-caerulescens insularis Santa Cruz - X X X X Troglodytes troglodytes meligerus West Aleutians X X X X T.t. kiskensis Kiska Group (Aleutians) X X X X T.t. alascensis P r i b i l o f X X X X T.t. tanagensis Andreanof Group (Aleutians) X X X X T.t. s eguamensi s Seguam Group X X X X T.t. stevensoni Amak Group X X X X T.t. petrophilus IP ox Group X X X X T.t. semidiensis Semidi Gromp X X X X T.t. h e l l e r i Kodiak Group X X / X T. beani Cozumel X X X X Thryomanes bewiekii brevicauda Guadalupe / / / X Thryomanes bewiekii catalinae Santa Gatalina / / - X T.b. leueophrys San Clemente X / / X T.b. nesophilus Santa Rosa, Santa Cruz / / / X Thryothorus-ludovicianus burleighi M i s s i s s i p p i Islands / / / X Gampylorhynchus brunneicapillus a f f i n i s Tiburon X / X X Salpinctes obsoletus guadaloupensis Guadalupe / / X X S.o. tenuirostris San Benitos / / X Melanoptila g l a b r i r o s t r i s cozumelana Cozumel X X X X Toxostoma guttatum Cozumel / / / / TABLE 6 - continued Species P o l i o p t i l a caerulea cozumelae Regulus calendula obscurus Lanius ludovicianus mearnsi Vireo griseus maynardi V. g. bermudianus Vireo button! insularis Coereba -flaveola caboti Vermivora celata sordida Dendroica petechia ruf ivertex Icterus cucullatus eozumelae I.c. duplexus. Piranga roseo-gularis cozumelae Richmondena eardinalis saturata T i a r i s olivacea intermedia Carpodacus amplus C. mcgregofi -C. mexicanus dementis Pinicola enucleator carlottae Leucosticte tephrocotis umbrine L.t. griseonucha P i p i l i o erythrophthalumus clementae P. e. consobrinus P. fuscus jamesi Passerculus princeps P. sandwichensis sanctorum Islands . l i l E , T a i l Tarsus Cozumel X X X Guadalupe / / X San Clemente / / / Florida Keys X X X Bermuda / - X Vancouver Is, / X X Quintana-Roo Ids. X X X Todos Santos, Los Coronados / X X Cozumel / / / Cozumel X / / Mujeres, Holbox / / X Cozumel, Mujeres / X X Cozumel X ~- X Cozumel X X X Guadalupe X X X San Benito X X X Los Coronados 9 / / X San Clemente, etc. I Queen Charlottes,Vancouver Is. X X X P r i b i l o f , St.Matthew X X X Aleutians X X X Santa Rosa, Santa Catalina, / / San Clemente X Guadalupe / / / Tiburon / / / Sable X X X San Benito X X X Species Aimophila' ruficeps sanctorum Amphispiza bilinea t a tortugae A.b. carmenae A. b e l l i clementae Passerella i l i a c a Insularis Junco i n s u l a r i s Melospiza melodia maxima M. m. insignia M.M. amaka M. m. graminea M.m. micronyx M.m. clementae M.M. coronados Plectrophenax n i v a l i s townsendi Rhyperboreus TABLE 6 - continued Islands Todos Santos Tortuga Carmen San Clemente Kodiak Guadalupe Attu-Atka Kodiak Group Amak Santa Barbara San Miguel Santa Rosa,San Clemente Los Coronados P r i b i l o f , Aleutians H a l l , St.Matthew Key: / Mainland mean larger - Means equal x Island mean larger Nos. Mainland mean larger Island mean larger Means equal % Island means larger Data: (samples of two or more). Obtained from the following sources:-1. Ridgway (1901, 1902, 1904 & 1907). 2. Original descriptions found by consulting A.0.U.Checklist (1957) and Mexican Checklist (1957). • -3. Queen Charlotte Island data from S .Smith, . U.B.C. (pers.comm.) Wing T a i l Tarsus B i l l x '/ X X •>, X \ X X 34 29 0 54 x / x '/ X \ X X X 32 29 2 54 / x x x x 7 [ X X X 42-15 2 71 l * / x x X X X 7 X X 4 6 2 13 1 77 X f o r 1:1 Ha, = 4 . 3 4 . P<0.05 xVor 1:1 Ha, = 8 . 5 3 . P<0.005 4« Vireo huttoni measurements made by author. VM Vn 36 Murphy's figure (78%) for subspecies alone. A similar trend i n tarsus-length, but not i n wing- or. t a i l - l e n g t h , i s • . , also -shown.i. To compare the result of this broad study with the Tres Marias avifauna i t i s necessary to consider just the island subspecies of the l a t t e r . The subspecies l i s t e d i n Table 6 are not a l l recognized by a c r i t e r i o n as stringent as the 73% rule (Amadon, 1949). Therefore, to those Tres Marias subspecies recognized i n this study (Table 1), three more species are added (Table 7), those which closely approach fulfilment of the c r i t e r i o n and Spinus p s a l t r i a . which warrants future sub s p e c i f i c recognition (see Appendix I I ) . In this group the greater size of tarsus i s best substantiated, followed by b i l l and then wing and tail.;(Table 7). It is therefore safe to conclude that the tarsus and b i l l trends displayed by the group of Tres Marias passerines, r e f l e c t a general condition on islands in North America and the rest of Mexico. It i s further concluded that i n this whole region at least, there is no obvious, overa l l tendency for island birds to have long wings. Of the non-endemics on the Tres Marias islands only Melanotis caerulescens ( i t s e l f close to subspecific status) shows disproportionate size-differences among the exposed parts between the mainland and island populations (Table 3). Of the endemic subspecies (mainly determined by plumage characteristics, and including Spinus p s a l t r i a ; see Appendix I I ) , only Vireo hypoehryseus shows the same size trend in a l l exposed parts 37 TABLE 7 Differences between means of Tres mainland samples of measurements Marias Island and (passerines only). Wing T a i l Tarsus B i l l s Island mean larger 8 8 13 9 Means equal 0 0 0 0 Mainland mean larger 6 6 1 5 % Island means larger 57 57 93 64 X for 1:1 Ha 0.14 0.14 5.14 0 . 5 7 Values of P <0.75 <0.75 <0.025 < 0 . 5 0 NB. Data taken from Table 3/ • Island subspecies, recognized i n t h i s study, and Mel a not i s caerulescens , Vireo flayoviridis, and Spinus p s a l t r i a , considered. 38 to approximately the same degree. These facts suggest that selection has acted upon individual exposed parts i n those birds which have undergone most morphological change, and that a large difference in the size of one part is not the consequence of changes i n a l l the other parts. 39 ' SUMMARY The plumage of most island birds tends to be more drab than the mainland counterparts, being duller and with reduced contrasting pattern and area of bright colour. The b i l l - l e n g t h of most island birds tends to be larger: this i s sometimes accompanied by a greater width. A trend towards a greater wing- and ta i l - l e n g t h i n island birds i s not supported by t h i s study. A stronger tendency towards greater tarsus-length i n the island birds has been revealed. This has not been noted previously as a s i g n i f i c a n t feature of an island avifauna. A review of the l i t e r a t u r e of island, passerine birds i n North America and Mexico, demonstrates that large b i l l and tarsus size are general, insular characteristics, but that large wing-length is not. I t is suggested that a large difference i n the size of one external part i s not the consequence of changes i n a l l the other external parts. 40 THE ENVIRONMENT I t i s necessary t o i d e n t i f y the s e l e c t i v e force which has produced the h i l l and tarsus trend on i s l a n d s . THE CLIMATIC FACTOR In the past, i n t r a s p e c i f i c v a r i a t i o n i n the s i z e of b i r d s has been i n t e r p r e t e d u s u a l l y i n the l i g h t of the two p r i n c i p a l ecogeographical r u l e s , the Bergmann and A l l e n r u l e s (Rensch, 1938; Snow, 1954). I t has been pointed out by Huxley (1942) that i n s e m i - t r o p i c a l regions, where winter minimum temperatures are not extreme, s e l e c t i o n should operate most s t r o n g l y i n the summer months, when temperatures are at t h e i r highest. Under the most rigorous conditions b i r d s should show adaptations to the d i s s i p a t i o n and not to the conservation of heat. Heat exchange occurs at the surface of a body, and the smaller the volume of the body the greater w i l l be the r e l a t i v e surface area, and hence e f f i c i e n c y , i n t h i s exchange. The group of Tres Marias b i r d s show a tendency towards small body-size, as i n d i c a t e d by weight, and large exposed p a r t s , which suggests that adaptation to h e a t - d i s s i p a t i o n i s greater among these than mainland b i r d s . C l i m a t i c information f o r the study area (from Contreras, 1942) i s presented i n F i g . 2. Summer maximum temperatures of Maria Madre, Mazatlan and Puerto V a l l a r t a are almost i d e n t i c a l , and give no reason to expect a s i z e -d i f f e r e n c e between mainland and i s l a n d populations. But heat exchange i s also influenced by humidity, and although no data are a v a i l a b l e f o r t h i s f a c t o r , humidity conditions may be i n f e r r e d by combining temperature and r a i n f a l l data. 4^0 Average r a i n f a l l i n mm. FIGURE 2 Annual d i s t r i b u t i o n of r a i n f a l l and temperature J J A S Months K e y Mar fa Madre Mazatlan Puerto Y a l l a r t a Tepic Average noon temperature i n °C. J I Months 42 Being dryer than any of the other regions, Maria Madre i s probably also the least humid, yet the body proportions of the island birds lead one to suppose that their environment would be the most humid. As an explanation of the size of island birds, there i s no support among t h i s evidence for the v a l i d i t y of the Bergmann and A l l e n r u l e s . Mayr and Yaurie (1948), i n studying the family Dieruridae, were able to f i n d many examples of b i l l - l e n g t h which supported Allen's rule. The exceptions to t h i s rule they interpreted as being the re s u l t of a c o n f l i c t between the operation of Allen's rule and a tendency for the b i l l to increase i n size a l l o m e t r i c a l l y , i n r e l a t i o n to body-size increase. Since the exposed parts of the Tres Marias birds are large and the body i s small, the former cannot be a product of positive allometry, and i t seems hardly l i k e l y that negative allometry w i l l be responsible for i t (Amadon, 1953). 43 THE ECOLOGICAL FACTOR To understand why i t i s that island birds tend to possess longer b i l l s and t a r s i , i t i s f i r s t neoessary to appraise the significance of small differences i n s i z e of these two structures. Bowman (1961) has presented evidence for the hypothesis that a broader b i l l i s better adapted to the crushing of seeds, and a narrow b i l l for the procurement of insects. According to the work of Kear ( 1 9 6 2 ) , birds with large b i l l s have an advantage over those with short b i l l s , at least among finches (sub-family F r i n g i l l i d a e ) , i n that t h e i r e f f i c i e n c y i s greater i n dealing with large food and a wide range of food-particle siz e s . Baldwin (1953) found that three Drepaniids on Hawaii took the same size-range of insects, but that a correlation existed between the b i l l - s i z e of each species and the mean siz e of prey " taken. Thus shape and size of b i l l are correlated with diet . Variations i n the length of tarsus in birds have received less attention. The leg serves the function of support and locomotion. Palmgren (1932) showed that i n birds which feed i n a hanging position from slender perches not only is the leg musculature different from those which feed i n a more upright position, but the tarsus i s a shorter member of the limb. Members of the families Picidae and Certhiidae, whose locomotion on tree trunks i s performed in an e s s e n t i a l l y hanging posture, are also characterized by short t a r s i . On the other hand i t is known from several studies that cursorial animals tend to have longer limbs than arboreal ones (e.g. Dilger, 1 9 5 6 ) . A long tarsus is presumably advantageous In bipedal locomotion (Davis, 1 9 5 7 ) . The 44 length of tarsus i s thus probably correlated with the nature of the perch and the way in which i t i s used. Birds which feed and move on slender, not r i g i d , perches are l i k e l y to have a shorter tarsus than those which make a greater use of firm perches. From a l l this i t follows that the large size of tarsus and b i l l of island birds i s perhaps related to a particular usage not demonstrated by the mainland birds. In other words, the part of the environment exploited, or niche (Elton, 1927), of the island birds is different from that of the mainland birds. This difference may have arisen as a consequence of the habitats being different. Or the habitats may be the same but occupied d i f f e r e n t l y i n the two regions. Again differences i n the niche may be f a c i l i t a t e d by the absence of other species i n one of the regions. In the absence of one species, another may extend the range of i t s a c t i v i t i e s , and come to occupy part of the ecological niche of the absentee. Therefore i f the morphological characteristics of island birds have an ecological significance, evidence is to be sought i n the behaviour of the birds i n the two regions, the habitats they occupy and the communities In which they are found. 45 THE BREEDING SEASONS Hartley (1953) and Gibb (1954, i 9 6 0 ) nave demonstrated seasonal v a r i a t i o n i n the feeding behaviour of birds. Enemar (1959) has s i m i l a r l y shown that the results of censusing are affected by the time of the year, i n r e l a t i o n to the breeding season, at which the census is carried out. Therefore, to make observations on the behaviour and numbers of birds i n two regions s t r i c t l y comparable, i t i s necessary to relate them to the breeding season. The most comprehensive description of the breeding season of a species comes from a study of a l l the a c t i v i t i e s performed throughout the season. But a simpler, i f less accurate one, i s obtained by the recording of the e a r l i e s t date at which each a c t i v i t y , such as nest-building, egg-laying etc., is observed to be performed. This was done i n the three years 1961 to 1963. L i t t l e v a r i a t i o n i n the r e s u l t s i n these years was detected, so they are combined, i n Table 5 7 . Comparisons between mainland and island populations can be made d i r e c t l y , for some of the species, by using a single a c t i v i t y . For others, comparisons must be indirect, using different a c t i v i t i e s and an estimated time allowance (Table 8 ) . The results of these comparisons indicate that the breeding season on the island is about four weeks behind that on the mainland. Because the data collected do not form an accurate description of events i n nature, and the estimations involved are only approximate, the figure of four weeks i s not considered to 4 6 TABLE 8 Degree to which the Island birds breed earlier (+) or later (-) than the mainland birds. Tepic Platypsaris aglaiae - 4 weeks Tyrannus melancholicus - 4 weeks Thryothorus f e l i x - 7 weeks. Melanotis caerulescens - 8 weeks Turdus rufo-palliatus - 4 weeks Vireo hypochryseus - 3 weeks Vireo f l a v o v i r i d i s Icterus pustulatus - 5 weeks Piranga bidentata - 4 weeks Puerto Vallarta - 5 weeks - 7 weeks + 2 weeks - 3 weeks The results have been calculated from the data presented i n Table %f. Indirect comparisons of breeding a c t i v i t y have been made by using the following time scale, based upon observations:-Duration of a) next-building : 1 week h) egg-laying : 1 week c) incubation : 2 weeks d) young i n the neat : 2 weeks An egg i n the oviduct of a collected specimen is considered to indicate the end of nest-building and the beginning of egg-laying. 47 be precise. But i t is significant that the majority of the comparisons y i e l d the same result. Yireo f l a v o v i r i d i s i s recorded here as being the only species breeding ea r l i e r i n the calendar year on the island than on the mainland. However, a specimen collected by C.C. Lamb at Tepic on the 22nd June, 1938, bears a label with the word "nesting", which suggests that the breeding seasons of the species in the two regions may be the same. There is supporting evidence for the lag of the .breeding season on the islands from the gonadal development of Icterus pustulatus. This species is represented by more specimens collected i n the breeding season than any other, and measurements of the gonads of males are shown i n Table 5 8 . At a time when the gonads are increasing i n size, the mean values of island specimens are lower than those of mainland specimens i n the same two-week period of the year. The island figures for the second half of June are even lower than mainland figures for the second half of May, which i s to be expected from the information given by observations (Table 5 7 ) . Lack (1946, 1954) and several others stress the b i o l o g i c a l importance of the fact that, the time at which most parent birds are feeding nestlings (maximum feeding a c t i v i t y ) , coincides approximately with the greatest available food supply during the breeding season. On the Tres Marias islands the former follows the emergence of leaves on the deciduous trees, and therefore the l a t t e r probably does too. Leaf-emergence i s dependent upon the r a i n f a l l . Perhaps a difference i n breeding-48 seasons between the mainland and islands is due to a different pattern of r a i n f a l l i n the two regions. From F i g . 2 i t may be seen that the onset of the rains occurs i n the same month, June. But by the end of July only 1;50 mm. of r a i n have f a l l e n on the islands, compared with about 185 mm. at Mazatlan, and more than twice that amount at Puerto V a l l a r t a and Tepic. Thus the rate of accumulation of moisture i n the s o i l may be an important factor i n determining the timing of the breeding season of the birds. THE NICHE STUDY 49 INTRODUCTION Since the main a c t i v i t y of birds is directed towards the finding of food, the aim of this study was to demonstrate the presence or absence of differences in the feeding characteristics of those mainland and island birds showing size differences. The pri n c i p a l objects of study were the food-sites and perches used In feeding, and the nature of the d i e t . The height at which birds feed, and the methods of feeding, have some bearing upon these characteristics (see Hartley, 1953), and were studied as well. METHODS AND MATERIALS Feeding behaviour was assessed by obtaining samples of observations. It was not possible to randomize time of day and place of observation, because of the d i f f i c u l t y of obtaining enough observations that way. The d i s t r i b u t i o n of the birds was far from even i n the mainland region, which made i t necessary to concentrate on certain areas where the birds were common and other conditions favourable. A different piece of ground was surveyed each day. On MarLa Magdalene observations were made i n and adjacent to only two arroyos, up to 4,000 metres from the shore, and i n the vegetation f r i n g i n g the beach. Because i t was d i f f i c u l t to make observations of birds feeding after mid-day, the study was r e s t r i c t e d to the period 8:00 - 12:00 A.M. The method of obtaining data was opportunistic: the following procedure was used:-50 When a b i r d was observed feeding, i t s height above ground was estimated and recorded, together with the nature of the perch and s i t e of the food, the method of feeding and the food taken. For those taking t h e i r food on the wing, characteristics of the previous and subsequent perches were recorded, including the horizontal distance of each perch from the trunk of the tree or shrub, f o r these, also, the height above ground of the prey-when taken, and the shortest distance between the two perches used, were recorded. The height and radius of the trees (canopy) were also estimated, and used i n the expression of feeding positions. Most v e r t i c a l distances were estimated to the nearest metre, and horizontal and short v e r t i c a l distances were estimated to the nearest 0 , 5 metre. When possible the accuracy of these estimations was checked, with the.author's height being used as a standard measure. The same terminology was used for the perch and food-s i t e . The trunk, the axi a l stem of a tree or shrub, and leaf are easy to recognize: limbs from the trunk were described as twigs ( < 1 cm. diameter) or branches ( >1 cm. diameter). These were not always easy to estimate, especially at a distance. When there was doubt about their i d e n t i f i c a t i o n they were recorded as twigs, so these, rather than branches, were overestimated. When possible the thickness of the limbs was checked with a 15 cm. rule. The method of feeding was described as peck, hover or flycatch, depending upon the position of the birds legs and the food. When the bird held a perch and fed, i t was described as pecking. Flycatching was considered to involve taking food i n 51 free f l i g h t , and hovering at a structure to pick off food was described as hovering. Only when a l l characteristics of the feeding a c t i v i t y were c l e a r l y observed were they recorded. The i d e n t i f i c a t i o n of the animal or vegetable food material taken was not always possible, and when i t was doubted the observation was not recorded. By this rejection of some of the observations, a bias may have been introduced. Binoculars of 8 x 30 magnification were used In this work, and observations were recorded i n a note-book. To reduce continued repetition of a single a c t i v i t y being recorded, after each observation one minute was allowed to elapse before the next recording was made. To reduce bias caused by exceptional individuals being recorded too frequently, no more than f i v e observations were recorded for each individual, when such i d e n t i f i c a t i o n could be made. At least one species of each of the foHaving morphological categories was selected for study:-1. Species with no difference i n dimensions i n the two regions: Myiarchus tuberoulifer. 2. Species with a l l exposed parts larger on the islands, and to approximately the same degree: Vireo hvpochryseus . 3. Species with b i l l and/or tarsus alone larger on the islands, or those with a l l parts larger, but b i l l and/or tarsus disproportionately so: Melanotis caerulescens and Icterus pustulatus. Both of the last two species had only larger (or disproportionately larger) b i l l s . Unfortunately no species with a larger or disproportionately larger tarsus on the islands could 52 be found i n su f f i c i e n t numbers for study in the two regions. In June, 19o2, M. tuberculifer , M. caerulescens and I. pus tula t us were studied. In July i t was not possible to obtain more than a few observations of the f i r s t two species, so attention was r e s t r i c t e d to Icterus pustulatus and an additional species, Vireo hypoehryseus. In August the study of these two species was continued on the mainland, but storms prevented a v i s i t to the islands. In A p r i l , May and June of 19D3, attention was further r e s t r i c t e d to Icterus pustulatus alone, this being the easiest species to study i n both regions. It was studied i n three mainland areas, Tepic, Sauta and Puerto V a l l a r t a , instead of the single one, Tepic, i n the previous year. In a l l the months, observations of mainland birds preceded those of island birds by about three weeks, thus making a p a r t i a l allowance for the difference i n the timing of the breeding seasons. An additional estimation of the food taken was given by the contents of the gizzards of specimens collected. When each specimen was dissected, i t s gizzard-contents were flushed into 70% alcohol, kept i n a small, labelled v i a l , and examined l a t e r . The composition of each gizzard was recorded, but the usually poor state of preservation of the contents made measurements impossible. Insects were i d e n t i f i e d to no more than ordinal l e v e l . Vegetable, not further i d e n t i f i e d , and animal matter were recorded In terms of percentage occurrence in each sample of gizzards. They were then separated in a p e t r i dish, and atmospherically dried on f i l t e r paper for no more than twelve hours. Their volume was estimated by water displacement. They 53 were placed i n graduated tubes (with 0.03 ml. divisions) and centrifuged f o r five minutes i n an International C l i n i c a l Centrifuge Chamber, at a speed of 2 , 0 0 0 - 3 , 0 0 0 revolutions per minute. Then the tubes were removed and the level of the meniscus read. Error i s introduced by the variable amount of f l u i d present i n the tissues after the drying process, and water absorption by the tissues during centrifugation. However the method was considered to be s u f f i c i e n t l y r e l i a b l e for estimating the r e l a t i v e volumes of animal and vegetable matter In each gizzard. The r e s u l t s were recorded as animal or vegetable matter predominant, or equal volumes present. They are l i s t e d In the tables In terms of percentage occurrence of each food type. The number of gizzards i n which they occurred equally was divided, and one half given to each food type. Because the majority of these results were obtained from estimations, rather than measurements, the application of s t a t i s t i c a l tests to them has been limited to a minimum. The results are expressed as percentages to make two sets of estimations comparable, and only gross differences are considered worthy of attention. RESULTS (i) Myiarchus tuberculifer (no morphological differences) No differences i n the feeding height or the food taken between mainland and island birds was apparent (Table 9). But island birds used a greater variety of methods to take the food, and a greater variety of perches. They also occupied perches nearer the perimeter of the vegetation than mainland birds, and took the food lower and on shorter f l i g h t s . A l l these differences 54 TABLE 9 Feeding-niche characteristics of Myiarchus tuberculifer. (i) Food Observations Gizzard-content s N Animal Vegetable N Animal Vegetable Island: June 51 80 20 March-June 8 100 Tepic: June 57 97 3 A p r i l - 16 94 6 August ( i i ) Method li Feck Hover Fly-catch Island: June 51 39 14 47 Tepic: June 37 3 - 97 I Island: June 51 Tepic: June 37 ( i i i ) Perch Twig Branch Trunk Ground Not Recorded 58 16 4 4 18 40 60 N Island: June 24 Tepic: June 29 (iv) Distance between perches used i n flyoatohlng. i n metres. Ay.perch distance Range 1.6 0-6 5 . 9 0-30 (v) Feeding height (flyoatching) i n metres. N Av. prey height Rang e Island: June 26 3,8 0-11 Tepic: June 24 5. 8 1-11 KB. In t h i s , and tables 10 •- 15 , a l l values l i s t e d under the headings (i) Food, ( i i ) Method ( i i i ) Perch andt (iv) Food-site are percent ages, "except' those of N (sample si z e ) . 55 TABLE 9 - continued (vi) Perch height during flycatching, in metres. N Av..height Range Ay,tree Ay. height -j.00 height Ay/tree height Island: 1st Perch 28 4 .7 0.5-10 7.0 6 7 .1 2nd Perch 28 4 .7 0.5-10 7.0 6 7 .1 Tepic: . 1st Perch 36 4 ,5 1-10 7 .3 61 .6 2nd Perch 36 4 .7 1-10.3 7.0 6 7 .1 ( v i i ) Horizontal position of feeding perch (flycatching), in metres. Av„distance Av.tree Av.distance from N from trunk Range radius* trunk - 1 0 0 Av.tree radius Island: 1st Perch 28 1 ,7 0-4 3,4 5 0 . 0 2nd Perch 28 1.4 0-4 3 .3 42.4 Tepic: 1st Perch 35 1,1 0-4 3 . 0 3 6 . 7 2nd Perch 35 1 .0 0 . 3 3. 0 3 3 . 3 * Tree radius is the horizontal distance between the t i p of the perch limb and the trunk. 5b support the impression that Island birds were feeding more within the foliage of the trees. These differences may be partly accounted for by the obvious tameness of many of the island birds, and p a r t l y by the fact that most of the mainland trees were i n f u l l leaf, whereas most of the island ones were l e a f l e s s . As explained above, page 5 2 , an attempt to study this species i n subsequent months, to substantiate these differences, f a i l e d . ( i i ) Melanotis caerulescens ( b i l l larger: tarsus s l i g h t l y smaller). The results of studying this species indicate bold differences between mainland and island birds. They show that island birds feed lower, and on a predominantly animal diet. Island birds feed frequently on the ground, whereas mainland birds rarely do (Table 10). But the r e l a t i v e tameness of Island birds, and the leaflessness of their environment, made observations of ground feeding.much easier than at Tepic. Furthermore, when a continuation of the study was attempted at Tepic i n July, much more ground-feeding was noted: but only rarely was i t possible to observe the birds c l e a r l y , and the attempt was abandoned. The evidence for a difference in diet is better founded, because i t comes from two sources (observations and gizzard analysis). While the gizzard-content data have the advantage of giving information over a period of at least four months, they are derived from small samples. The difference i s a possible one, requiring confirmation. ( i i i ) Vireo hypoehryseus ( a l l parts larger equally) According to the results obtained (Table 11), there TABLE 10 57 Feeding niche characteristics of Melanotis caerulescens. (i) Food Observations* Gizzard-content s N Animal Vegetable N Animal Vegetable Island: June 27 96 4 March-June 11 64 36 Tepic : June 78 - 100 March- 13 4 96 August ( i i ) Method I Peck Hover Island: June 51 98 2 Tepic: June 85 97 3 ( i i i ) Perch-I Twig Branch Trunk Ground Island: June 51 24 28 2 46 Tepic: June 85 77 9 - 1 4 ( i v ) Food-site (animal matter) N Leaf Twig Branch Trunk Ground Island: June 50 26 28 46 Tepic: June 7 - 100 (v) Feeding -height. i n metres**" N Av. height Ranee Av,. tree height Av.height 2 100 Av.tree height Island: June 51 2. 0 0-12 3.0 66.2 TejDic: June 85 9*7 0-14 12.4 78.1 Excluding those when food i s taken from the ground, 4. Ground-feeding included: given the value 0. 58 TABLE 11 Feeding-niche characteristics of Vireo hypoehryseus. (I) Food Observat ions Gizzard-cont ent s E Animal Vegetable N Animal Vegetable Island: July 44 100 - March-July 20 75 25 Tepic July 52 96 August 77 94 4 6 March-August 40 80 20 I Island: July 44 ( i i ) Method 1 Peck Hover Flycatch 67 31 2 >lo: July 52 71 29 August 77 84 16 ( i i i ) Perch I Leaf Island: July 44 Tepic: July 52 2 August 77 2 I l i a 77 85 88 Branch Trunk 18 5 13 10 I Leaf Island: July 44 86 Tepic: July 50 100 August 72 92 (iv) Food-site (animal matter) Twig Branch Trunk 9 5 8 (v) Feeding-height, in metres N Av. height ' Range Av.tree Av.height Island: Tepic: July 44 6 . 5 0 .5-16 height Av.tree height 5 7 6 . 5 x 100 July 52 August 77 6 . 9 5»5 1- 19 2- 12.5 9 . 2 7 ,9 7 5 . 0 6 9 . 4 5? i s no apparent difference between mainland and island populations in a l l of the feeding characteristics estimated. There is a s l i g h t tendency for the island birds to use different perches. icterus pustulatus ( b i l l disproportionately larger) The results (Tables 12-16) show that there is no difference i n the feeding method used, as defined and recorded i n this study, although i t was noticed that branch- and trunk-feeding on the island occasionally involved a Woodpecker-like probing i n the bark, a method never witnessed on the mainland. There is no obvious difference i n feeding-height either. In the months of June and July birds at Tepic feed higher than on the island: but in A p r i l this difference i s just as s t r i k i n g l y reversed. Individuals were recorded feeding lower at Sauta i n A p r i l and Hay-June, and lower i n A p r i l and higher i n May-June, and lower i n A p r i l and higher i n May-June at Puerto Y a l l a r t a , than those on the island. Differences are revealed by monthly comparisons, therefore, but are not consistent throughout the period of study. Island birds used branches and trunks more than mainland birds, as both perches and feeding-sites. Whereas the mainland birds fed at the perimeter of the trees, from leaves and twigs, island birds fed more within the tree canopy and nearer the trunk, even i n July when a l l the trees were in f u l l leaf. Observations gave no indication that this difference in location was associated with a difference in feeding posture. The data give a p a r t i a l Indication that a difference in diet exists between the populations. The observations of feeding give a measure of the r e l a t i v e number of animal and TABLE 12 Feeding-niche characteristics of Icterus pustulatus. (i) Food Observations Gizzard-cont ent s N Animal Vegetable u Animal Vegetable Island: March -.. _ _ 1 2 2 + 3 83 17 A p r i l 3 3 3 70 30 55 4 0 60 May-June 62^ 98 2 103 60 4 0 June 3 7 2 9 1 9 _ - _ July 37 2 100 _ - _ Tepic : March _ _ 10* 95 5 A p r i l 3 3 3 36 64 1 2 2 + 3 _ _ May-June 64 3 11 89 58 42 June 39 2 50 50 - -July 3 3 2 79 21 _ August 7 5 2 74 26 - - -Sauta: A p r i l 343 35 65 103 55 45 May-June 493 61 39 i o 3 75 25 Puerto A p r i l 32 53 47 _ — — Tfellarta 'May-June 513 75 25 _Q1+3 95 5 June _ - - l l 1 95 5 July - - 9 1 94 6 August - - - 5 1 88 12 KB. N = Sample size. Numerals placed against the sample size mean the following: 1 = 1 9 6 1 data: 2 = 1962 data: 3 = 1963 data. 'May-June', I 9 6 3 , covers the period May 2 7 t h - June 9 t h for mainland l o c a l i t i e s , and June 19th - 26 th for the Island: the l a t t e r , only, coincides almost exactly with 'June', 1962. The source of the observations data is the same for a l l the following tables of Icterus pustulatus in this chapter. 61 TABLE 13 Feeding-niche characteristics of Icterus pustulatus. ( i i ) Method N Peck Hover Flycateh Island: A p r i l 33 100 _ -May-June 62 100 - -June 57 96 2 2 July 37 100 - -Tepio: A p r i l 33 100 - -May-June 64 95 5 -June 39 100 - _ July 53 97 3 -August 75 99 1 -Sauta: A p r i l 34 100 - -May-June 49 100 -Puerto A p r i l 32 100 — Y a l l a r t a 'May-June 51 100 - -I 62 TABLE 14 Feeding-niche characteristics of Icterus pustulatus. ( i i i ) Perch N Leaf /Flow Fruit er/ iTwig Twig Trunk Ground Island: A p r i l 33 - 52 39 9 . May-June 62 - 46 29 23 June 57 9 46 35 10 July 37 3 54 30 9 Tepic: A p r i l 33 _ 94 6 — — May-June 64 - 95 5 June 39 8 84 8 July 53 2 77 19 2 August 75 - 96 4 Sauta: A p r i l 34 91 6 3 May-June 49 - 84 12 4 Puerto V a l l a r t a : A p r i l 32 - 88 12 -• May-June 51 - 96 4 _ 63 TABLE 13 Feeding-niche characteristics of Icterus pustulatus (iv) Food Site (Animal) N Flower/ Fruit Leaf Twig Branch Trunk Ground Island: A p r i l 23 17 4 17 22 40 May-June 61 15 18 28 28 11 June 55 7 47 36 10 July 37 66 - 24 10 Tepic: A p r i l 12 67 25 8 _ May-June 7 57 43 - _ June 19 84 - 11 5 July 42 80 9 9 2 August 55 90 8 2 - — Sauta: A p r i l 12 25 17 42 8 8 May-June 30 83 3 7 7 Puerto V a l l a r t a : A p r i l 17 53 41 6 _ May-June 38 97 3 - -64 TABLE 16 F e e d i n g - n i c h e c h a r a c t e r i s t i c s o f I c t e r u s p u s t u l a t u s . ( v ) F e e d i n g H e i g h t , i n m e t r e s . N A v .H e i g h t R a n g e A v . T r e e A v . H e i g h t H e i g h t A v . T r e e H e i g h t I s l a n d : A p r i l 33 7.3 1-15 9 . 9 73.8 . M a y - J u n e 62 4 . 5 0.5-10 6.7 66.2 J u n e 57 5. 1 1-12 7.6 67.1 J u l y 37 4. 2 0 . 5 -14 6.6 64.3 T e p i c : A p r i l 33 2.5 0.5-10 5.0 50.6 M a y - J u n e 64 5.5 1.5-12 1,9 69.4 J u n e 39 9.0 4-21 12.1 74.4 ^ l y 53 7„o 0-16 9.7 71.8 A u g u s t 75 4. 6 0.5-19.5 8.1 56.6 S a u t a : A p r i l 34 4 . 9 0 - 1 4 7.1 69.6 M a y - J u n e 49 2.6 0 - 9 4 . 0 63.5 P u e r t o Y a l l a r t a : A p r i l 32 3. 8 1-8 5. 9 64.9 M a y - J u n e 51 6.4 1-12 8 . 1 8 0 . 3 65 vegetable items taken, whereas the gizzard-content analysis shows the volume of each food-type present i n the alimentary tract after some digestion has taken place. Hence the results of these two methods of study need not show a close correspondence. For instance, a lack of correspondence characterizes the May-June data for Tepic and Maria Magdalena (Table 12). Approximately 6of. of the gizzard contents of both samples is animal matter. But 98?. of the observations of Island birds indicated animal matter being taken, whereas only 11% of the Tepic observations did so. Apart from the p o s s i b i l i t y of misidentification of the food objects taken, this discrepancy may be produced because island birds feed more frequently on animal matter, and the vegetable matter they do take is either bulky or d i f f i c u l t to digest, remaining i n each gizzard for a long time and thus contributing largely to each gizzard-content. An analysis of the gizzard-contents alone shows no clear difference between mainland and island birds. The smallest island sample is the only one in which vegetable matter predominates. The Tepic and Maria Magdalena samples correspond closely, while the Puerto Yallarta samples, from mainly different months, are consistently higher i n animal matter than either of them. On the other hand, an analysis of the feeding observations reveals a clear difference between the Tepic and island samples, either by monthly comparisons or by comparing the results of one time period on the island, with those of the preceding time period on the mainland. A similar difference i s seen between Sauta and island data. But, although the same difference exists between Puerto TABLE 17. Gizzard-content3, expressed as % occurrence i n each sample VEGETABLES A<VA-/A>V A M 1 M A Fruits/Seeds/ S Ga Or He An Me __. L i Co Hy_ Di Sc Ar Leaves ,&c. M 26 4 _ 22 - 4 4 11 33 7 4' - - 74 23 65 12 Platypsaris I 23 - _ _ — — 3Q.. - 4 11 3? 65 11 _ . 4 26 78 22 -M 57 - _ 7 9 7 11 - — — 5 56 44 2 - - 32 81 7 12 Tyrannus I 27 - 11 11 - - 11 11 74 33 4 - - 15 93 — 2_ H 19 - — 11 26 37 - _ _ 32 74 21 _ _ _ 32 79 21 - • M.tyrannulus I 15 - 7 7 - - 7 - - - 47 40 47 - - - 20 73 20 7 M l6 - 6 19 37 - _ 12 6 50 37 6 - 6 19 94 6 -M. tuber c u l i f er 1 8 - - - - 25 - - 12 -• 25 75 12 - - - 100 — — M 32 - _ 3 — 22 - — 6 28 56 25 3 - - 25 82 12 6 Myiopagis I 13 - - - - _ - - 54 62 8 23 - - 31 69 - 31 M 25 4 4 20 - 4 32 80 12 4 _ - 4 Thryothorus M 13 8 8 „ _ 8 23 49 15 _ _ _ 100 — 92 8 Melanotis I 11 9 — — — - 18 18 — - 45 73 36 - - - 64 36 -M 32 - 9 3 _ 9 - _ _ 47 84 _ _ _ 31 79 18 3 V.hypochryseus I 20 - — 5 — — 20 - - - 30 60 5 - - - 35 70 20 10 I 20 - 10 15 - 15 65 20 - - 10 45 60 15 25 V. flavov i r id i s I 40 - _ — — — 2 - 5 - 60 4 5 17 _ _ _ 55 53 25 22 M 85 1 5 5 — 24 - _ 50 59 13 8 - 1 50 71 20 9 Icterus I 27 - — 4 4 7 - — - 44 4 8 15 . 7 4 - 48 56 14 30 M 23 - 8 4 16 - _ 12 60 40 4 - 4 64 72 8 20 PIranga I 10 - — — — — 30 - - - 20 60 -_ _ 100 - 60 40 M 25 - _ — 4 4 _ _ _ 100 - 96 4 Spinus I 12 - 17 - 17 - - 67 33 67 -KEY: 1, l i n l a n d . I = I s l a n d . 2. Ga = Gastropoda Id = Isopoda Or = Orthoptera Is = Isoptera MB. The figures i n the l a s t three column only are d N = Sample Size Od = Odonata La He = Hemiptera LI An = Anoplura 06 Me = Megaloptera Hy1 A = Anijaai . V = Vegetable . = Lepidoptera,adult Di = Diptera = Lepidoptera, larva Sc = Scorpionidea = Coleoptera Ar = Araneida = Hymen opt era erived from volume analysis. 67 V a l l a r t a and island data, i t is smaller. Ho overt differences exist i n the nature of the animal diet of mainland and island birds (Table 1 7 ) . Goleoptera and Lepidopterous larvae are taken most frequently by birds i n a l l four areas. (v) The diet of the birds According to the results of the gizzard content analysis, l i s t e d i n Table 17 , a difference i n diet exists between mainland and island populations of P.. aglaiae, M. caerulescens. P. bidentata and S 0 p s a l t r i a . For a l l these species there are large disproportionate (page 24) size differences i n b i l l - l e n g t h too (Table 3 ) . Of the four other species characterized by large b i l l -differences, there are no data available of the diet of T. f e l i x . T, rufo-palliatus and R. c a r d i n a l i s , and for I. pustulatus the data are equivocal (see above ), Those species without a large, inter-population, difference in diet, do not have disproportionately large b i l l - s i z e differences either (Table 3 ) . P. bidentata has a more vegetable diet on the islands, and also a r e l a t i v e l y broader, b i l l . P. aglaiae and, from observations only, I. pustulatus were found to have a more animal diet, and they also have a r e l a t i v e l y narrower b i l l . These findings are i n accordance with those of Bowman (1961) on the shape of b i l l and diet of the Galapagos Finches. But differences i n diet are not always accompanied by a difference i n the shape of the b i l l (e.g. S. p s a l t r i a ). , There is thus evidence that a difference i n the size of the b i l l i s associated with a difference i n diet, but the shape or size of the b i l l cannot always be determined from a 68 knowledge of the type of d i e t . CONCLUSIONS AND SUMMARY Those species with mainland/is land differences i n b i l l -size feed on a different diet. Conversely, those species with sim i l a r b i l l s i n the two regions have similar diets. The two Yireo species, characterized by uniformly large exposed parts on the islands, have si m i l a r diets i n the two regions. Differences i n bill-shape are also correlated with dietary differences. But i t is not possible to demonstrate a correlation between a longer b i l l and qualitative characteristics of the diet. Other factors are probably involved i n the determination of large b i l l - s i z e , the most l i k e l y of which is the s i z e of the food taken (Baldwin, 1953; Kear, 1962). The t a r s i of island birds of I. pus tula t us. are larger, although not disproportionately larger when compared with the wings and the t a i l : island birds also use firm perches more frequently during feeding than do mainland birds. Island M. caerulescens, with a s l i g h t l y smaller tarsus than the mainland counterpart, may also use firm perches more frequently. . There is a possible tendency for island birds of this species to feed lower i n the vegetation, which may partly account for the greater use of firm perches. M. tuberculifer has the same tarsus-length i n the two regions, and uses similar perches i n them. V. hypoehryseus, with uniformly large exposed parts on the islands, also uses similar perches on mainland and islands. None of the species studied had disproportionately large t a r s i on the islands. However, since island birds of 69 M. caerulescens and I . pus tulatus make a greater use of firm perches, perhaps those species with disproportionately large t a r s i on the islands also do. No consistent and r e l i a b l e difference i n feeding height was demonstrated between mainland and island populations of any of the four species studied. 70 THE HABITAT STUDY INTRODUCTION Island birds may behave i n a different manner to that displayed by mainland birds, because the habitats i n the two regions are different. Lack (1942) found two B r i t i s h woodland species, Turdus merula and T. ericetoram. occurring on the almost treeless Orkney Islands: here they nested on the ground, a habit extremely rarely observed elsewhere i n the B r i t i s h I s l e s . Even i f the habitats on the mainland and islands are the same, they may be occupied d i f f e r e n t l y by each species, which may thus influence their behaviour. Lack end Southern (1949) have noted that Parus coeruleus. which occupies only broad-leafed woodlands on the continent of (North) Afr ica and Europe, feed i n a l l types of woodland on the island of Tenerife, including Pine forest. Although no mainland-is land difference i n feeding behaviour was commented upon, the b i l l of the island form is larger and of a different shape. Eor these two reasons, i t i s worth considering the p o s s i b i l i t y that the habitat of the Tres Marias has a specific influence upon the behaviour of the birds. Those birds with a different morphology and behaviour on the islands may occupy different habitats i n the two regions, while those with similar morphology might occupy similar habitats. 71 METHODS AND MATERIALS Habitat a f f i n i t i e s of each species were deduced from observations made i n the years 1961 to 1963, during the breeding season. Estimations of habitat characteristics were made at Tepic, Puerto Yallarta and Maria Magdalena i n the same period. The study areas at these three l o c a l i t i e s were approximately 8,000 x 2 ,000 metres, 6,000 x 2 ,500 metres and 4,000 x 1,000 metres respectively. The r a r i t y of some made i t possible to study eleven species only. Rather than take an impossibly time-consuming, random sample of habitats f o r each species, habitats were selected and studied as follows:- a bird (or pair) was observed for about f i f t e e n minutes and the focus of i t s feeding or t e r r i t o r i a l a c t i v i t y i d e n t i f i e d . Around this central point an imaginary 20 x 20 metre square was placed. A modified form of Ernien's (1956) scheme for habitat description was used, together with Raunkaier Ts (1934) c l a s s i f i c a t i o n of vegetation:- herb layer (2-20 cms. high), shrub layer (20 cms- 6 metres) and (tree) canopy layer ( >6 metres). The amount of ground beneath each layer was estimated, and recorded separately as the percentage area of the plot (to the nearest 10%). Tree dimensions were estimated i n the manner described in the previous chapter. From these data an average height and canopy radius were calculated for that plot. Also the number of trees occurring i n the plot was counted,* from which th e i r density was estimated. For most species between ten and twenty plots were described, on both mainland and island. Often more than one 72 species used the habitat i n one plot, p a r t i c u l a r l y on the island, which enabled a single description to suffice for a l l of them. RESULTS a) The, habitats of mainland and islands. Observations showed that the woodland on Marfa Cleofas and Marfa Magdalena resembles that which occurs on the adjacent mainland at medium elevations, 5 0 0 ' - 2 , 5 0 0 ' . Zweifel ( I 9 6 0 ) came to the same conclusion, having v i s i t e d a l l three islands. These woodlands are described as Tropical Deciduous Forest by Leopold ( 1 9 5 0 ) . However, Leopold ( l o c . c i t . ) erroneously considered the vegetation of the Tres Marfas to be of the same type as that which occurs at low elevations on the mainland coast, and called Thorn Forest. Presumably, the error arose as a result of a dearth of botanical information of the islands, which he did not v i s i t . The term Thorn Forest Is more appropriately applied to San Juanito and the vegetation on the steep, western side of M. Magdalena: i t s contribution to the total vegetation of the islands is small. Thus, in general terms, the habitats of the islands are comparable with mainland habitats. b) The occupation of the habitats Table 18 shows the habitat a f f i n i t e s of the birds. The small amount of Thorn Scrub on the islands, and a small area of Mangrove swamp on the northern side of M. Magdalena, have been ignored because they were not v i s i t e d by the author. With the exception of M. polyglottos and M. obscurus. birds appear to be 73 widely distributed on the islands. The more extensive observations of Heilfurth (1934) confirm this. Therefore, these two habitats are not considered to be important in the distribution of island birds. The table shows that a l l but five species are present in the Tropical Deciduous Forest of both regions. The single island habitat is to be contrasted with the four mainland habitats; only four species are restricted to one habitat on the mainland. Therefore, the birds live under much the same habitat conditions on the islands as on the mainland, but the range of habitats is restricted. c) Composition and other characteristics of the tropical deciduous forest habitats The vegetation of the mainland and island Tropical Deciduous Forests have several genera of trees and shrubs in common, to judge from personal observations and reports in the literature (Rose, 1899; Ferris, 1927). Among these Ceiba, Bursera, Acacia, Ficus, Ipomaea, Hamelia and several cactuses, including Pachycereus and Qpuntla , are prominent. But there are notable discrepancies. Tabebuiat Cochlospermum and Bombax species are characteristic trees of the mainland Tropical Deciduous Forest, but have not been recorded from the Islands. On the islands, Caelenodendron mexicanum is a common, locally abundant, tree but is rare on the mainland, and the same is true of Gedrela. The results of an anlysis of several characteristics of the vegetation are shown in Tables 59 and 6 0 . The height , canopy radius and density of trees a l l have a tendency to be greater on M. Magdalena than on the mainland. On the other hand TABLE 18 Habitats occupied by the birds of the Tres Marias, islands and the adjacent mainland. Island- habitat Mainland habitats Tropical Hornbeam/ deciduous deciduous Thorn .scrub oak P. aglaiae X X X T. melancholicus X X X M. Tyrannulus X X X M . tuberculifer X X X X M. v i r i d i c a t a X X X C. imberbe X X X T» f e l i x X X X X Mc caerulescens X X X M. polyglottos x l X T. rufo-pa Hiatus X X X M. obseurus ( x ) 2 X V. hypoehryseus X X X V. f l a v o v i r i d i s X X X p. pitiayumi X X v en us t us X X I. pustulatus X X X X P. bidentata X X s . p s a l t r i a X X X a . card!nails X X Pine/oak x X X X NB. 1 In coastal vegetation only, which has many Thorn Scrub elements. 2 Not observed by author. 75 the herb and shrub layers are less extensive there. In each region the species occupy habitats d i f f e r e n t l y . For example, P. aglaiae occupies part of the forest i n which the trees, are more than two metres t a l l e r than they are i n that part occupied by T. melanchollcus. A perusal of the data i n the Tables shows that these differences are reasonably consistent i n the two regions. CONCLUSIONS Since the island habitat is of a single type, Tropical Deciduous Forest, there is no opportunity for the birds to occupy a greater range of habitats than on the mainland. Only the p o s s i b i l i t y of different habitats being occupied i n the two regions exists, but a survey has shown that at least fourteen of the nineteen species occupy the same habitat on both mainland and islands. Thus there is no relationship between a difference i n morphology and a difference i n habitat occupancy. Within t h i s single habitat, there exist mainland/ island differences i n composition and structure, as indicated by a few analysed characteristics. These differences are consistent for a l l species studied, and affect the herb and shrub layers p a r t i c u l a r l y . I t is possible that the sparseness of these layers i n the Island vegetation has a bearing upon the tendency for the birds to feed lower. It has been contended by Zweifel (I960) that the presence of f e r a l goats on M. Magdalena, introduced to that island i n about 1903 (Hanna, 1926), has had an inhibitory effect upon the growth of plants contributing to these two layers: 76 observations of the vegetation on M. Cleofas lend support to this (see Plates 19, 20, i n Stager, 1957). Hence the mainland/ island differences affecting these layers, are open to question. S i m i l a r l y the significance of the other small differences i n vegetation i s d i f f i c u l t to assess. There exists the further p o s s i b i l i t y that finer, unanalyzed, structural differences of the vegetation, such as the nature of the branches, twigs and leaves (see e.g. Breckenridge, 1956) influence the behaviour of the birds. I t seems unlikely, however, that differences of this degree characterize habitats on a l l islands, which would be necessary to explain the widespread tendency for island birds to have larger b i l l s and t a r s i . It is concluded that there are no major habitat differences between the mainland and islands which have had a bearing upon the evolution of the insular fauna. SUMMARY The island habitat is of a single type, Tropical Deciduous Forest, which i s comparable with that occurring on the adjacent mainland at medium elevations. Fourteen of the nineteen species of birds occur i n this habitat i n both regions. Therefore there is no evidence of habit at-extension displayed by the island birds, and only a few occupy different habitats i n the two regions. There are small differences i n the vegetation of the Tropical Deciduous Forest i n the. two regions, but they are not considered to be of significance i n the evolution of the insular fauna. THE COMMUNITY STUDY 77 INTRODUCTION The behaviour of one animal species is influenced by the presence or absence of others. Brown and Wilson (1956), drawing upon a variety of examples, have shown that, morphologically and ecologically, two closely-related species are often most similar when i n allopatry and most dissimilar when i n sympatry. Sim i l a r l y , Lack and Southern (1949) have correlated the habitat-extension (see page 70 ) displayed by some species of birds on Tenerife with the absence of closely related species. Svardson (1949) and M i l l e r (1951) have provided other examples of t h i s correlation. I t has also been noted that island faunas are often characterized by high densities (Lack and Southern loc. c i t : Crowell, 1 9 6 2 ) . At such densities some members of a population acquire different feeding grounds (Tompa, 1963) or nest-sites (Lack, 1942;. Svardson l o c . c i t . ) . Although only short-term effects, like these, have been demonstrated, i t is possible that permanent changes in behaviour ari s e i n this way, f a c i l i t a t e d on Islands by the absence of closely-related species. Therefore these two aspects of the community, species composition and density, were examined i n an attempt to relate them i n a general way, to the morphological and behavioural p e c u l i a r i t i e s of the island birds. 78 METHODS AND MATERIALS To estimate the numbers of species and individuals i n the two regions, censuses were conducted on the mainland and on Maria Magdalena. The Msinging-male" method of censusing has been found to be the most satisfactory i n the North Temperate zone (Kendeigh, 1944; Enemar, 1959). But i n the study area the presence of several Non-Passerine species, which sing rarely i f at a l l , and some 'aberrant' Passerine species (e.g. Mel an ot i s caerulescens: both sexes sing) made a different method advisable. Therefore a l l birds seen or heard were recorded, A rectangular area was chosen, with a path running along i t s length and approximately bisecting i t . The observer started at one end, at the same time of day In each area, and walked to the other end at a speed as even and constant as possible. Birds were recorded i n a notebook during the single surveys and on a map of the census area In the repeated surveys. Single surveys of an area of twenty acres (sixty yards wide and 1,600 yards long) were carried out at Puerto Yallarta i n July and August, 196l, and In May and June, 1962. The area chosen i s i n the f o o t h i l l s of the coastal range of mountains, and close to the north-eastern outskirts of the town. At Tepic they were undertaken in June, July and August, 1962, and March, A p r i l and May, 1963. This area is referred to as J9 and is approximately 9 miles north-west of the town, and close to the highway 54 to Jalcocotan. An additional area (J10) , one mile beyond, was censused i n July, 1962. On Maria Magdalena an arroyo formed the path running 79 through the census area,which extended from a point one thousand and five hundred yards to another three thousand and one hundred yards from the sea. Surveys were made i n June and July, 1962, and i n A p r i l and June, 1963- The M. Magdalena and Puerto Va l l a r t a census areas contained Tropical Deciduous Forest, whereas at Tepic the habitat was Hornbeam/Oak Forest. Unlike the census area on the island, those on the mainland contained a l i t t l e secondary growth. Repeated surveys of an area of ten acres were made on six successive days at Tepic (J9) i n May and four weeks la t e r on M. Magdalena in June, 1963, to allow for the difference i n the timing of the breeding seasons (page 45 ): both areas lay within the origi n a l twenty acre areas. The width, either side of the central path, was fi x e d according to the l i m i t s to the observer's v i s i o n imposed by the thickness of the vegetation. At Tepic t h i s varied between 10' and 45 yards from the path. On Maria Magdalena i t was found that for a length of ground equivalent to that at Tepic the width included less than ten acres, so the length was extended by one hundred and f i f t y yards: the maximum width was t h i r t y - f i v e yards. The areas were estimated by pacing. The boundaries of the census areas repeatedly surveyed were made more conspicuous by the attachment of orange surveyors-tape to trees. The surveys were made only on days when there was l i t t l e , i f any, wind or cloud. Binoculars of 8 x 30 magnification and an Airguide pocket altimeter were used to aid the Identification of birds and for the measurement of altitudes respectively. 80 An estimation of the number of t e r r i t o r i e s i n each area was made, separately for each species, by studying on the map the positions at which birds were recorded. An example of the composite map for one species, is given i n Fi g . 3.' Additional observations, made during the return journey through the census area, assisted the recognition of t e r r i t o r i e s . RESULTS a) Number of species The details of the census results are given in Appendix I I I . The results of the preliminary work i n 1961 and 1962 indicated a difference i n number of individuals and species between the mainland and Island communities (Table 19). A difference i n the conspicuousness of birds in the two regions was considered to contribute to th i s r e s u l t , so to assess this factor birds were recorded as seen or heard during the censuses carried out i n July, 1962. A comparison of these records showed that only at Puerto Vallarta were more birds heard than seen (Table 65) . A similarity i n the Maria Magdalena and Tepic results suggested a sim i l a r i t y i n conspicuousness, therefore the repeated-survey censuses were undertaken i n these two areas. Birds were considered summer-resident i n census area i f evidence of breeding was found or i f they were observed frequently during the summer months (not only during censuses). An attempt to relate number of species to area is made in Table 20. If the Falconiform species, observed f l y i n g over the census area, are included i n the total for Tepic, there are more species in forty acres of this part of the .mainland than throughout Figure 3 81 The Territories ot Mitre phones phaeocercus af Tepic. Length of area 1300 yds., approx. Each number indicate* the position and day upon which an individual was recorded. Dotted lines show the approximate positions of'territorial'boundaries, estimated from observations of activity of the birds. 82 TABLE 19 Comparison of species and individuals recorded on single surveys at Maria Magdalena, Tepic and Puerto V a l l a r t a , i n the months of June and July, 1961-2. Maximum number of species Minimum number of individuals Maximum number of individuals Average number of individuals Marfa Magdalena Tepic Puerto Va l l a r t a 24 35 25 recorded 1?6 114 56 recorded 181 147 63 179 131 60 83 TABLE 20 Comparison of number of species recorded in the months of May - August, and considered to be summer-resident i n the census areas. Maria Magdalena Tepic Puerto Y a l l a r t a Area of 10 acres 23 25 ? Area of 20 acres 30(+2) 29(+5) 22(+3) Area of 40 acres ? 33(+6) ? Area of 22,500 acres 34 39 o 25 NB. Figures i n brackets refer to Faleoniforms seen fl y i n g over the census areas, and they are included i n the totals i n the last row:-a) Maria Magdalena: Cathartes aura, Buteo .jamaicensis . b) Tepic: Coragyps atratus. Cathartes aura, Accipiter g e n t i l i s . A. cooper i . But eo .jamaicensis and B. nitidus . c) Puerto Y a l l a r t a : Coragyps atratus, Cathartes aura and Hypomorphnus urubitinga. The numbers for 20 acres are compounded of the 10 and 20 acre census results: to the Tepic ( J 9 ) figure is added that of , J10 to give a figure for 40 acres. 84 the whole of Marfa Magdalena. Most of the families of Passerines are represented with more species at Tepic; none are better represented on the island and two are absent (Table 21). b) Number of individuals. The-results of the censuses are shown i n d e t a i l i n Appendix I I I (Tables 66 and 6 7 ) , and the derived estimations of numbers are given i n Table 2 2 . I t became apparent during and after the census at Tepic that two species, Guiraoa caerulea and Spinus p s a l t r i a , did not hold t e r r i t o r i e s but used the area solely as a feeding ground. Two weeks after the completion of the census only six S. p s a l t r i a were present, s t i l l showing l i t t l e sign of t e r r i t o r i a l a c t i v i t y . Accordingly, these two species have been treated separately in the table. The total density of birds is greater on M.Magdalena, whichever way the comparison of estimates is made. This difference i s s t a t i s t i c a l l y significant when allowance is made for those Individuals of casual occurrence or small contribution to the t o t a l , by excluding the t e r r i t o r i e s i n which individuals were recorded on one or two occasions only. This difference is mainly due to the commonest species on the island being exceedingly common. I f the two most common species on the island are excluded from the census figures, the average number of individuals recorded i n a survey becomes approximately the same i n the two areas (Tepic 81: M. Magdalena 7 7 ) . Where a d i r e c t comparison of the density of each species i s possible, the Tepic figures are more often larger than the island ones (Table 2 3 ) . TABLE 21 The number of speoies of passerines resident i n 40 acres at Tepic, contrasted with the t o t a l number of residents on Maria Magdalena Maria Magdalena Tepic Dendrocolaptidae - 1 Cotingidae 1 1 Tyrannidae 3 6 Gorvidae - 1 Troglodytidae 1 2 Mi mid a e 1 1 Turdidae 2 3 Vireonidae 2 2 Parulidae 2 4 Icteridae 1 2 Thraupidae 1 2 F r i n g i l l i d a e 2 3 Ii NB. Mimus polyglottos (Mimidae) excluded from Maria Magdalena figures. 86 TABLE 22 Comparison of the number of individuals recorded on repeated surveys at Tepic and M.Magdalena M.Magdalena Tepic % Difference Estimated minimum number of birds 26 3 2 3 4 Maximum number of feeding-ground birds - 26 Minimum number recorded on one survey 128 91 Maximum number recorded on one survey 147 122 Average number recorded on one survey 137* 1 0 3 32.7 Estimated maximum number of -,Ao -<0c in c t e r r i t o r i e s 1 1 4 8 1 2 6 1 1 Number of t e r r i t o r i e s , exclusive of single-occurrence records 128** 93 34,7 Number of t e r r i t o r i e s , exclusive of two-occurrence records 110** 80 34.1 NB. f. Difference indicates the amount by which the M.Magdalena values exceed those for Tepic. * t test: difference signif i c a n t at 0.05 l e v e l . 2. ** X t e s t : difference significant at 0.01 l e v e l . TABLE 23 Comparison of the maximum number of t e r r i t o r i e s occupied by species occurring i n both mainland and island ten-acre census areas. M. Magdalena Tepic Myiarchus tuberculifer 3 7 Myiopagis v i r i d i c a t a 1 6 Thryothorus f e l i x 7 8 Melanotis caerulescens 3 9 Vireo hypoehryseus 6 5 PIranga bidentata 6 2 Spinus p s a l t r i a 2 Number i n doubt: see text, page 8 4 . 88 DISCISSION AND CONCLUSIONS Several errors are l i k e l y to bias the results of census work, and these are c r i t i c a l l y discussed by Enemar (1959). Since the rel a t i v e conspicuousness of birds is the same at Tepic and M. Magdalena, i t i s assumed that errors i n extimation w i l l be approximately of the same kind and degree i n the two areas. Twelve summer-resident species at Puerto V a l l a r t a and twenty-one at Tepic are absent from the islands (Tables 61 and 62 i n Appendix I I I ) . I t has been demonstrated that the number of summer-resident species occurring on M. Magdalena (or the Tres Marias as a whole - see Grant and Cowan, 1964) is exceeded i n forty acres of Hornbeam-Oak Forest at Tepic . The number of species occurring i n an area of this forest equivalent to the t o t a l area of M. Magdalena is not known, but i s probably much larger. There i s less substantial evidence that the Tropical Deciduous Forest of the mainland (e.g. at Puerto Vallarta) s i m i l a r l y has a greater number of species than an equivalent area of island. Thus several species are not present on the islands, a s i t u a t i o n which favours a change i n niche of those present; but there is not enough ecological information to indicate why some species have undergone this change while others have not. It was pointed out i n the Introduction to this Chapter that a high population density of an island species might aid the process of niche-change. The community of birds on M. Magdalena was found to have a density greater than the mainland community, by almost 35%. But a ma inland/is land comparison of individual species f a i l e d to show a uniformly high density among the island 89 species, and two of the species which exhibit the morphological characteristics being investigated, M. v i r i d i c a t a and G.venustus. are among the four rarest species (Table 6 7 ) . As was pointed out by H e i l f u r t h (1934), there is l i t t l e regional variation i n the abundance and d i s t r i b u t i o n of the island birds, and t h i s i s supported by the author's observations. Therefore the r a r i t y of these two species i n the census area is probably indicative of their-true, r e l a t i v e frequency on the island. \ I t i s possible that when the species f i r s t colonized the island they existed at a high density, their behaviour underwent modification and later the level of density of several species f e l l . But on present evidence alone, no universal cor r e l a t i o n of morphological change with high density can be demonstrat ed. SUMMARY The community structure on M. Magdalena d i f f e r s from that at Tepic, on the mainland, i n two ways. There are fewer species i n an area of forty acres or more, and the to t a l density of birds i s greater. The difference i n densities is the result of the most common species on the island being exceedingly common. Otherwise, there is no obvious tendency for the island population of a species to be at a greater density than the mainland one. Therefore only the f i r s t aspect, the species composition, is considered to have had an influence upon the ecological niches of the island birds. FURTHER EVIDENCE 90 INTRODUCTION The ecological work gives evidence that a difference i n the dimensions of the h i l l and tarsus between mainland and island populations of some species, is related to a difference i n behaviour, which in turn i s related to the absence on the islands of several species, presumed to be ecologically similar to those present. Also, on page 1 , i t was suggested that the drabness of plumage of some of the island birds is associated with the absence of systematically related species. The purpose of this Chapter i s to present additional, indirect evidence to show that the absence of other species affects the behaviour of those present. The song and nest-position of Thryothorus f e l i x are described. METHODS AND MATERIALS The recordings of the song of T, f e l i x and the sympatric (mainland only) T. sinaloa were made with a "National" Transistor Tape recorder, but without the usual accessories, such as a parabolic r e f l e c t o r . Ferrodynamics magnetic recording tapes were run at a speed of 3t"/seoond, with the microphone placed up to t h i r t y metres from the singing bird. Recordings were made on the mainland, at Tepic, in the f i r s t week of June, 19&3, and on Marfa Magdalena i n the t h i r d week of that month. Only birds i d e n t i f i e d certainly, by plumage characteristics, were recorded on the mainland. Tape recordings were obtained of two individuals of T. sinaloa. four mainland T. f e l i x . and members of f i v e pairs of island T, f e l i x . They were later analyzed with a Missilyzer 91 Sound Spectrograph, and recorded on kymograph paper. 1 The heights of nests, and the trees in which they were found, were1 estimated to the nearest metre when above three metres, and to the nearest 0.3 or 0.3 metre below this height. RESULTS I. Song Both mainland species of Thryothorus have two song patterns which have been described here as Types A and B. One of each type, f o r each species, is represented in fig,.. 4, A" difference between the two species i s seen to exist In the shape of the repeated four notes in Type A song. Although the pattern exhibited by T. sinaloa was also recorded for T. f e l i x , the f e l i x pattern shown i n the Figure appears to be species s p e c i f i c . But larger samples of song recordings of both species are required to establish a difference s a t i s f a c t o r i l y . In contrast to these two the island birds have only one type of song, without these repeated notes. The song of the male may be either of the character shown i n Fig, 3., or have an additional terminal note. The female pattern (Fig. %) Is unvarying. The shortness of the island songs i s shown by the data i n Table 68 . The mainland songs of T. f e l i x are two to three times as long as the island songs of that species. A possible difference exists i n length of song between mainland _• f e l i x and T. sinaloa. The island song was heard, but not recorded, frequently on the mainland in March and A p r i l , and occasionally throughout the breeding season, whereas i n the months April-August the mainland song was never heard on the island. It 94 was observed that the island song was produced by foraging birds. When both members of a pair foraged together they sang together. F i g . 5 i l l u s t r a t e s the combined song of a pair. This behaviour was observed on the mainland too, where the sexes of the birds were confirmed by the c o l l e c t i n g of a pair, after they had been observed singing. On the other hand the mainland song was invariably produced by a bird engaged i n no other a c t i v i t y , and two birds of different pairs frequently sang alternately, suggesting that the song was functioning as t e r r i t o r i a l advertisement. The island song was never heard i n t h i s context. I I . Nests A l i t t l e evidence suggests that T. f e l i x nests lower i n the vegetation on the island than on the mainland. The data are shown i n Table 24. On the mainland only one of eighteen nests was found lower than 12/3 metres above the ground, while both island nests were found at a height of less than a | metre. The f i r s t island nest was occupied by a Parula Warbler, F« pitiayumi, and three of i t s eggs. But because a l l other Z* f e l i x nests found were of this "bent-bottle" shape, unlike a l l the P. pit iayumi nests found on the island, i t is considered to have been constructed by T. f e l i x . The second nest was used by a pair of T. f e l i x . That this difference i n nest-height i s a generality i s suggested by the fact that old nests are frequently seen i n mainland forests, conspicuously supported by the lower limbs of trees, but have never been seen, or recorded by other ornithologis on the islands. 95 TABLE 24 Nest-heights of Thryothorus f e l i x . i n metres. M A I N L A N D I S L A N D Height of nest Height of nest Height of nest tree Height of nest tree 2.5/3 2/4 2^/4 2/4 ^/A 5/6 1.7 / 2 4/8 2.7/3 5/9 5/6 2/3.5 3/15 Ml* Mainland: Tepic, Puerto T a l l e r t a , Sauta. 9/i4 Island: Maria Magdalena. 96 DISCUSSION AND CONCLUSIONS Neither of these island characteristics of T. f e l i x Is r e s t r i c t e d to this species alone, or even to the birds of the Tres Marias islands. Nelson (1899) noted the less "musical" song of the Tres Marias populations of M. caerulescens and P. bidentata. There may also be a difference between mainland and island populations of I, pus tula tus. A c a l l of four to seven notes., uttered by a b i r d disturbed while feeding, was heard frequently on the mainland but never on the island. Voice p e c u l i a r i t i e s have been reported for the birds of the Canary Islands (Lack and Southern, 1949), Azores (Marler and Boatman, 1951) and Bermuda (Bourne, 1957). On the Tres Marias, Grayson (1871) observed that Leptotila verrauxl l a i d i t s eggs upon the ground "with but l i t t l e pretension to forming a nest", whereas on the mainland i t has -been observed by the author to nest i n shrubs and low trees at a height of one to three metres above the ground. Aberrant ground-nesting on islands has also been reported for three species by Hatt et a l . (1938). It may be postulated that the reduction i n repertoire of song i s the result of diminished selection for species s p e c i f i c recognition. It i s the absence of T. sinaloa from the islands which permits this reduction i n T. f e l i x : perhaps P. bidentata and P. erythrocephala (mainland only; Table 66) provide another example (see above). Thus a common explanation i s offered for the reduction i n plumage and song characters of island birds. Similarly, the phenomenon of ground-nesting on 97 the Tres Marias may also be a response to the absence of other species, but in this case i t is predators which are absent. A nest placed on the ground i s exposed to greater danger than one suspended from a t h i n branch above ground. Bourne (1955) commenting upon the tendency for birds to nest high i n the vegetation on the Cape Verde Islands, considers this habit to be a response to egg predation from the abundant rats and f e r a l cats. - On the Tres Mar fas there are no cats, rats are rare, and generally there i s a dearth of mammal and r e p t i l e species (Neslon, loc. c i t j Zweifel, i 9 6 0 ) , which suggests that the pressure of egg-predation i s lower here than on the mainland. SUMMARY The island population of T. f e l i x is characterized by two behavioural p e c u l i a r i t i e s . The song of birds on M.Magdalena is simple, and the repertoire does not include the ' t e r r i t o r i a l ' song of mainland birds. There is evidence that nests are placed lower i n the vegetation (or on the ground) than on the mainland. These two habits are interpreted as being responses to the absence of other species, the closely-related T. sinaloa i n the f i r s t case and predators i n the second. 98 DISCUSSION On the Tres Marias islands more than half of the passerine species are characterized by long t a r s i and/or b i l l s . This has also been demonstrated for passerine birds on other Mexican and North American islands. On the Tres Marias there is evidence that a) the feeding ecology of island birds is different from that of t h e i r closest r e l a t i v e s on the adjacent mainland; b) that there are fewer species i n the island community and c) that there are no major differences i n habitat between the mainland and Islands. Before these findings are interpreted f u l l y , an assessment should be made of whether these are ecological characteristics of islands i n general or the Tres Marias alone. This i s made d i f f i c u l t by the lack of quantitative information, the paucity of ecological work on islands and the prominence given i n the past to the study of the fauna of oceanic (well isolated) rather than continental islands of the Tres Marias type, a) The Community Although the fact, that islands contain fewer species than the mainland, has rarely been demonstrated hitherto by census work, i t has been suggested several times (Hatt et a l . 1 9 3 8 ; Lack and Southern, 1 9 4 9 ; Amadon, 1 9 3 3 ; Watson, 1962).. Keast ( 1 9 6 1 ) described an area of sclerophyl forest i n S.W. Australia which was encircled by a different habitat and, li k e islands surrounded by water, this contained r e l a t i v e l y few species. It is noteworthy that no author to date has suggested that islands contain more species than the adjacent mainland. Many reasons 99 for the so-ealled impoverishment of island faunas have been proposed. These include their physical i n a c c e s s i b i l i t y (Lack and Southern loc. c i t ; Slud, i 9 6 0 ) , the accidental nature of the dispersal of potential colonizers (Hatt et a l . l o c . c i t . ) and the lack of suitable and varied habitat (Hatt et a l . , l o c . c i t ; Mayr and Vaurie, 1948; Amadon, loc. c i t ; Braestrup, 1956; Bourne,1957)• Recently Preston (1962) has demonstrated In mathematical terms,, that a relationship exists between area and the number of species of birds present , which i s well supported by empirical evidence. He shows that a discrete area, such as an island, w i l l always contain fewer species than an equal sample of a larger area, such as a continent. This is because the relationship between area and number of species present Is not a straight-line one, but conforms to a logarithmic equation. Thus, i f the part of the mainland being compared with the island is half the to t a l area of the continent, i t w i l l contain many more than half of the to t a l number of species. In b i o l o g i c a l terms, the existence of species i n the sample is dependent upon their existence beyond i t as well. Islands, without this 'reserve' area, support fewer species. I t may be deduced from this that the b i o l o g i c a l reason for the paucity of species on islands i s related to the minimum population size necessary for a species to maintain i t s e l f . The determinants of this minimum include the area of each habitat (Lack and Southern, l o c . c i t ; Bourne, 1955), the area of the island i t s e l f , and perhaps the nature of the associations or interactions of the species within the community. Thus, from theoretical estimations and empirical 100 evidence, i t seems l i k e l y that a l l Islands have fewer species than comparable areas and habitats on the adjacent mainland, b) Habit s Very few observations on the behaviour of island birds have been reported. Bourne {1955) observed novel feeding habits displayed by some of the birds of the Gape Verde islands, which suggested a convergence towards the habits of absent, closely-related species. Voous (1957) noted that the range of feeding habits of Mimus gilvus on some of the Caribbean islands was greater than on the N. American continent; and si m i l a r l y the Bermuda endemic, Vireo griseus, was found to use a greater variety of feeding methods than i t s mainland r e l a t i v e (Crowell, 1 9 6 2 ) . More frequently, differences in the behaviour of mainland and island birds have been inferred from differences in habitat occupancy (Hatt et a l . l o c c i t ; Mayr, 1942; Moreau, 1940; Lack and Southern, l o c . c i t ; Svardson, 1949; M i l l e r , 1951; P i t elks, 1951; Gibb, 1951; Marler and Boatman, 1951; Cullen et a l . 1952; Amadon, loc. c i t ; Bourne, 1955, 1957; Voous, 1957; Slud, l o c . c i t ; Keast, l o c . c i t ; Rand and Rabor, 1 9 6 3 ) . When the difference i s as radical as that between grassland and forest, (Huxley, i 9 6 0 ) , this i s a reasonable inference. The example given by Huxley (loc. c i t . ) concerns the species Anthus pratensis in Iceland, which occupies not only grasslands and heath there, as i t does elsewhere in i t s range, but also Birch Forest; a difference in, song, produced by the forest inhabitants, leads one to suspect other behavioural differences. 101 Most authors have been able to correlate the habitat differences witii the absence, from the island, of species systematically closely-related to those present. For example Svardson (194-9, l o c . c i t . ) noted that on the mainland of Sweden six species of the genus Par us occur, while on the island of Gotland only three are found. Two of these occupy a broader spectrum of habitats than they do on the mainland. The habitat-increment of each species i s occupied, on the mainland, by two of those which have f a i l e d to colonize ihe island. This phenomenon of habitat-extension is not r e s t r i c t e d to islands and the example given above i s paralleled by another, Involving two of the same species i n the northern part of the mainland (Durango, 1944; also Snow, 1954). For habitat extension to occur i t is not necessary for the absent species to be closely related, systematically, to the one present. In the isolated sclerophyl forest i n Australia, Keast ( l o c . c i t . ) found a species of one genus ecologically replacing an absentee of another, both systematically and ecologically quite diff e r e n t . Therefore, on islands, where the habitat is similar to that which occurs on the mainland, i t may be supposed that i t is the absence of an ecologically different species (systematically related or not) which permits another to extend or modify i t s behaviour and thus occupy a different niche. It is pertinent to this suggestion that several authors have remarked upon the rarity with which congeneric species occur on islands together (e.g. Mayr, 1931; Rand and Rabor, 1 9 6 3 ) ; moreover, when a species-102 ' pair does occur on an island the ecological differences between i t s members are considerable (Mayr and Vaurie, l o c . c i t ; Bourne, 1955; Rand and Rabor l o c . c i t . ) . The only known example of a species occupying a smaller range of habitat on islands has been described by Lack and Southern ( l o c . c i t . ) . F r i n g i l l a coelebs occupies broad-leaved and coniferous woods throughout it's continental range and on the two Canary Islands, Raima and Hierro. But on Tenerife and Gran Canaria, i t s absence from coniferous woodlands is explained by the presence of the endemic F,. teydea, which occupies nothing but coniferous woods. In view of the foregoing remarks i t is not surprising to find that some species, occurring only on mountain tops elsewhere, are present at low altitudes on islands. This has been reported by Mayr ( l o c . c i t . ) , Amadon ( l o c . c i t . ) Braestrup ( l o c . c i t . ) and Rand and Rabor ( l o c . c i t . ) . Species r e s t r i c t e d to mountain tops (which do not have a r i c h fauna) are, i n effect, isolated on islands. In summary, the majority of evidence available suggests that changes i n the niche within a single habitat, and changes i n habitat-occupancy, which occur on islands, are associated with the absence of other species, c) Correlation of morphology and habits An attempt to find supporting evidence for a correlation between tarsus-length and behavioural p e c u l i a r i t i e s of island birds f a i l s , because such l i t t l e work has been done on the behaviour of island birds. However, the b i l l has been studied frequently. Voous ( l o c . c i t . ) reported that specimens of Mimus 103 gilvus on the Garribean Islands have a larger h i l l than those i n North America, and considered t h i s to he related to the observed greater range of food taken. On Tenerife Parus operuleus has a b i l l of the same shape and size as P . ater, and i s thus larger than the b i l l of the mainland birds of P. coeruleus (Lack end Southern l o c . c i t ; . no measurements g i v e n j j . In the absence of P . ater on Tenerife, it's habitat i n general, and food in particular, are exploited by P. coeruleus. Marler and Boatman ( l o c . c i t . ) and Amadon ( l o c . c i t . ) were able to correlate the larger b i l l of some of the birds on the Azores and G-ulf of Guinea islands respectively with a difference i n habitats occupied and hence, by implication, with a difference i n habits. But this c o r r e l a t i o n could not be extended to include a l l species with large b i l l s on these islands. Birds of the genus Ale c t o r i s tend to have large b i l l s when their a l t i t u d i n a l range is large, and small b i l l s Waen the range i s small (Watson l o c . c i t . ) . As was suggested by the author, the size of b i l l may be p s r t l y determined by the variety of food taken, which i s presumably greater i n the larger a l t i t u d i n a l d i s t r i b u t i o n . Thus the evidence available gives support to the contention that the morphological characteristics of island birds are related to a usage made possible by the absence of other species. d) The exceptions to the trend The morphological and behavioural p e c u l i a r i t i e s of the Tres Marias birds are paralleled by birds i n other island 104 s i t u a t i o n s . T h e p r o c e s s by w h i c h a d a p t a t i o n s , s u c h a s t h e s e , become m a n i f e s t e d i n i s l a n d p o p u l a t i o n s h a s b e e n c o m p r e h e n s i v e l y d i s c u s s e d by H a y r ( 1 9 6 3 : c h . 1 7 ) . I t i s n e c e s s a r y t o c o n s i d e r why i t i s t h a t n o t a l l b i r d s on i s l a n d s d i s p l a y t h e m o r p h o l o g i c a l t r e n d s . Among t h e T r e s M a r i a s p a s s e r i n e s , some h a v e a p p r o x i m a t e l y t h e same s i z e o f b i l l a n d t a r s u s o n m a i n l a n d and i s l a n d s , o t h e r s h a v e s m a l l e r s t r u c t u r e s o n t h e i s l a n d s . M a i n l a n d and i s l a n d p o p u l a t i o n s o f t h e s e a r e i s o m o r p h i c , w h i c h i n d i c a t e s t h a t s e l e c t i o n h a s n o t f a v o u r e d a c h a n g e o f f o r m . T h i s may b e b e c a u s e e c o l o g i c a l l y s i m i l a r s p e c i e s h i n d e r a c h a n g e o f n i c h e , and i t may be s i g n i f i c a n t t h a t f o u r o f t h e i s o m o r p h i c g r o u p a r e r e l a t e d s y s t e m a t i c a l l y ( t h e two M y i a r c h u s and t h e two Y i r e o s p e c i e s ) , a n d p e r h a p s e c o l o g i c a l l y t o o . A l t e r n a t i v e l y , o r a d d i t i o n a l l y , t h e r e may n o t h a v e b e e n s u f f i c i e n t i s o l a t i o n , i n t i m e o r s p a c e , f o r s e l e c t i o n t o be e f f e c t i v e . T h r e e o f t h e i s o m o r p h i c g r o u p a r e p a r t i a l o r c o m p l e t e m i g r a n t s (T . m e l a n c h o l i c u s , M . t y r a n n u l u s and V. f l a v o v i r i d i s ) : i t i s p o s s i b l e t h a t a f e w m a i n l a n d i n d i v i d u a l s a c c o m p a n y t h e m i g r a n t s on t h e i r r e t u r n t o t h e i s l a n d s , and d i s r u p t t h e e f f e c t s o f s e l e c t i o n ( M a y r , 1 9 6 3 ) . The two s p e c i e s w h i c h , o n t h e i s l a n d s , show t h e g r e a t e s t r e d u c t i o n i n e x p o s e d p a r t s ( P . a g l a i a e and S . p s a l t r i a ) . a r e a l l o m o r p h i c , t h e i r t a r s i , f o r i n s t a n c e , b e i n g a p p r o x i m a t e l y t h e same s i z e i n t h e two r e g i o n s . The s m a l l n e s s o f t h e i r b i l l s may b e a c o n s e q u e n c e o f t h e i r b o d i e s b e i n g s m a l l e r , o r i t may be a t t r i b u t a b l e to a n e c o l o g i c a l f a c t o r , s u c h a s t h e p r e s e n c e o f a n e c o l o g i c a l l y s i m i l a r s p e c i e s . The l a t t e r seems p l a u s i b l e i n 105 v i e w o f t h e w e l l - e s t a b l i s h e d t e n d e n c y f o r two c l o s e l y - r e l a t e d s p e c i e s ( s y s t e m a t i c a l l y a n d , p r e s u m a b l y , e c o l o g i c a l l y ) t o be m a r k e d l y d i f f e r e n t i n s i z e o f b i l l when i n s y m p a t r y ( C h a p i n , 1 9 4 9 ; Y a u r i e , 1951; Amadon l o c . c i t ; B rown and W i l s o n , 1956; S e l a n d e r a n d O i l i e r , 1 9 6 3 ) . I n t h e a b s e n c e o f t h e r e l e v a n t i n f o r m a t i o n , i t i s i m p o s s i b l e t o o f f e r a s i n g l e e x p l a n a t i o n f o r t h e e x c e p t i o n s t o t h e m o r p h o l o g i c a l t r e n d s o n o t h e r i s l a n d s ( H e s s e e t a l . 1937; B o u r n e , 1 9 5 5 ) . A d d e d t o t h e e c o l o g i c a l f a c t o r s and t h e c o n s e q u e n t i a l e f f e c t s o f b o d y - s i z e d i f f e r e n c e s , c l i m a t i c f a c t o r s ( A l l e n ' s r u l e ) may b e i m p o r t a n t . A l l t h e s e f a c t o r s may i n t e r a c t t o p r o d u c e b i r d s w i t h s m a l l b i l l s and t a r s i o n i s l a n d s . F o r e x a m p l e , t h e e c o l o g i c a l i n t e r p r e t a t i o n g i v e n t o t h e l a r g e b i l l o r" P a r u s c o e r u l e u s o n T e n e r i f e , b y L a c k a n d S o u t h e r n ( l o c . c i t . ) , was c o n t e s t e d b y Snow ( 1 9 5 4 a ) , who p o i n t e d o u t t h a t a e l i n e o f i n c r e a s i n g s i z e w i t h d e c r e a s i n g l a t i t u d e w o u l d a c c o u n t f o r i t . H o w e v e r , t h i s d o e s n o t e x p l a i n the c h a r a c t e r i s t i c s h a p e o f t h e b i l l o f t h e T e n e r i f e b i r d s , a n d i t w o u l d seem t h a t a c o m p l e m e n t a r y a c t i o n o f c l i m a t i c and e c o l o g i c a l f a c t o r s has b e e n i n v o l v e d i n t h e s e l e c t i o n o f t h i s b i l l ( s e e a l s o S n o w, 1 9 5 4 b ) . The e x c e p t i o n s t o t h e m o r p h o l o g i c a l t r e n d t h e r e f o r e do n o t i n v a l i d a t e t h e i n t e r p r e t a t i o n g i v e n t o t h e t r e n d , e ) The r e l e v a n c e o f c o m p e t i t i o n The t e r m c o m p e t i t i o n h a s b e e n e m p l o y e d i n e c o l o g y t o mean t h e demand a t t h e same t i m e by more t h a n one o r g a n i s m f o r t h e same r e s o u r c e s o f t h e e n v i r o n m e n t , e i t h e r i n e x c e s s o f i m m e d i a t e s u p p l y ( D a r w i n , 1859) o r n o t n e c e s s a r i l y so r e s t r i c t e d 106 (Udvardy, 1951; Brown and Wilson, 1 9 5 6 ) . Amadon ( l o c . c i t . ) , Growell ( l o c . c i t . ) and others refer to the reduced i n t e r s p e c i f i c competition on islands as a factor determining the morphology and ecology of the birds: i t appears that the Darwinian concept of competition is implied. This may be correct, but i t is i n s u f f i c i e n t to explain the insular characteristics of birds, as the following argument w i l l show. F i g . 6 i l l u s t r a t e s a hypothetical situation, in which two species exploit an environmental resource on the mainland, and only one does so on an island. The two mainland species can compete only i n the zone of overlapping requirements, E-G; but the single island species exploits part of the environment, G - K, which is not competed for on the mainland. I t can be argued that species 1 does not exploit this f r a c t i o n on the mainland because, i n the past, those individuals which did so suffered strong competition from individuals of species 2 , and were eliminated by selection. But this need not have been the r e s t r i c t i o n imposed upon species 1, since other factors, such as sus c e p t i b i l i t y to predation or a c c e s s i b i l i t y of food, may have been involved. It is better, therefore, to place emphasis upon the absence of other species on islands, rather than upon the possible competitive relations of the species. This judgment is reinforced by the evidence of reduced plumage and aberrant song and nesting characteristics of island birds, which t e s t i f y to non-competitive aspects of species-relationships, f) Other groups of animals It is worth considering whether the ecological and morphological characteristics of the birds are shared by other 107 FIGURE 6 The exploitation of an environmental resource by two species I S L A N D MAINLAND Species 1. Species 2 Species 1. A E G K A graded, environmental resource 108 groups of animals on islands. The l i t t l e information available i n the l i t e r a t u r e indicates that the ecological conditions enumerated above are experienced by other groups. Preston (1962) suggests that faunal Impoverishment i s not r e s t r i c t e d to birds, and indeed a reduced number of species on islands has been reported for mammals (Hatt et a l . 1 9 3 8 ; Lowe, 1 9 5 5 ; Delany, 1 9 6 1 ; Main, 1 9 6 1 ) , for reptiles (Dunn, 1 9 3 4 ; Hatt et a l , l o c . c i t ; C l i f f , 1 9 5 4 ; Lowe, l o c . c i t ; Zweifel, i 9 6 0 ) for amphibia (Hstt et a l . , l o c . c i t . ) and for arthropods (Ants) (Wilson, 1 9 6 1 ) , Wilson ( l o c . c i t . ) noticed a tendency for the smallest Islands to be populated by the most dissimilar species, under which conditions the few species present extended their normal use of habitats. Hatt et a l . ( l o c . c i t . ) and Main (loc. c i t . ) commented upon the same phenomenon applying to insular mammals. From t h i s i t might be supposed that the feeding and locomotor apparatus of non-avian animals w i l l have undergone adaptive modification. Foster ( 1 9 6 3),in comparing the Q,ueen Charlotte Island and mainland populations of Marten (Martes amerioana) i n B r i t i s h Columbia, found a dietary difference, which he was able to relate to the "heavier dentition and associated areas i n the s k u l l " of the island form. But such examples have been reported rarely, which suggests that a trend, p a r a l l e l i n g that i n birds, does not exist. On the other hand there are numerous reports of "gigantism" and "dwarfism" on islands, applying to gastropod molluscs (Bole, Bre l i h and Zei, 1961) r e p t i l e s (Kramer and Mertens, 1 9 3 8 ; Schuster, 1950 ) and 109 mammals (Krumbiegel, 1943) p a r t i c u l a r l y . Since the tendencies towards size-change are in opposite directions i t i s d i f f i c u l t to arrive at a clear idea of a general trend from these reports, i f one exists at a l l . A trend can only be established from a large number of examples. McOabe and Cowan (1945) attempted to find a general pattern of variation in the morphological features of mice l i v i n g on the offshore islands of B r i t i s h Columbia,, yet f a i l e d to find one. Foster ( l o c . c i t . ) , using the published measurements of a large number of mammal species, established that a trend towards large size exists among insular rodents, and an opposite trend exists among larger mammals. Of sixty-eight species i n the former group, sixty insular forms were found to be larger than their mainland counterparts. The environmental factors believed to a f f e c t body-size have been discussed by Rensch ( 1 9 5 9 ) , and are considerably more numerous than those which affect exposed parts, such as appendages. Hence body-size differences are the more d i f f i c u l t to interpret. Nevertheless there is evidence that those same ecological conditions which have permitted the evolution of b i l l and tarsus characteristics of birds on islands, have also permitted the evolution of large rodents on islands. Chapman (1940) and Watson (1962) have drawn attention to the fact that large b i l l s are characteristic of birds l i v i n g on both mountain-tops and islands; and on page 102 the ecological a f f i n i t i e s of these two environments were pointed out. It i s of interest, therefore, that large body-size is characteristic of f i v e species of rodents l i v i n g on mountains and islands i n Europe(Zimmermann,195 110 The r e l i c t hypothesis, proposed by Barret-Hamilton and Hinton (1914) and Zimmermann ( l o c . c i t . ) , to e x p l a i n t h i s f e a t u r e , has been contested r e c e n t l y by Mayr ( 1 9 5 2 ) , Steven (1965) and Cook ( 1 9 6 I ) , who consider the large s i z e to be an adaptation to the p r e v a i l i n g conditions. I t may be suggested that the adaptation i s p r i m a r i l y t o metabolic e f f i c i e n c y (Rensch l o c . c i t . ) : the absence of e c o l o g i c a l l y s i m i l a r species w i l l perhaps lead, s e c o n d a r i l y , to the greater e x p l o i t a t i o n of environmental resources. Whereas lar g e s i z e may be a disadvantage on the mainland i n the face of heavy predator pressure (Falconer, 1953), i t i s not so on i s l a n d s because t h i s pressure i s presumed to be l e s s (Foster, l o c . c i t , ) . I f i t i s indeed true that the adaptations of a species are influenced by the presence or absence of others to t h i s extent, i t may help to e x p l a i n why, i n the course of e v o l u t i o n , there has been a tendency for i n d i v i d u a l species of mammals to become larger (Cope, 1896 ) , which has p a r a l l e l s i n several other groups of animals as w e l l (Huxley and Haldane„ 1927; Newell, 1949). I l l CONCLUSIONS AND SUMMARY 1. C e r t a i n m o r p h o l o g i c a l a n d b e h a v i o u r a l c h a r a c t e r i s t i c s o f t h e T r e s M a r i a s b i r d s a r e p a r a l l e l e d b y b i r d s i n o t h e r i s l a n d s i t u a t i o n s . 2 . S e v e r a l i s l a n d b i r d s h a v e l a r g e r b i l l s and t a r s i t h a n do t h e i r m a i n l a n d c o u n t e r p a r t s , and i t I s s u g g e s t e d t h a t t h i s i s b e c a u s e t h e y e x p l o i t a g r e a t e r r a n g e o f e n v i r o n m e n t a l r e s o u r c e s . 3. T h e b i l l i s l o n g e r b e c a u s e i t d e a l s - w i t h a g r e a t e r r a n g e o f f o o d - s i z e s , a n d t h e t a r s u s i s l o n g e r b e c a u s e t h e v a r i e t y o f p e r c h e s u s e d i s g r e a t e r . 4 . T h e d i f f e r e n c e s i n u s a g e a r e n o t r e l a t e d t o a d i f f e r e n c e i n h a b i t a t s o c c u p i e d , b u t a r e r e l a t e d t o a d i f f e r e n c e i n t h e number o f s p e c i e s i n t h e m a i n l a n d and i s l a n d c o m m u n i t i e s , t h e r e b e i n g f e w e r o n t h e i s l a n d , 5 . The a b s e n c e o f s e v e r a l s p e c i e s o n a n i s l a n d l e a v e s some o f t h e e n v i r o n m e n t a v a i l a b l e f o r t h o s e p r e s e n t t o e x p l o i t , a s s u m i n g t h a t t h e r e a r e e q u a l r e s o u r c e s i n t h e two e n v i r o n m e n t s , 6. T h e r e i s e v i d e n c e t o s u g g e s t t h a t t h e e c o l o g i c a l c o n d i t i o n s w h i c h h a v e p e r m i t t e d t h e e v o l u t i o n o f b i l l and t a r s u s c h a r a c t e r i s t i c s i n i s l a n d b i r d s , a l s o h a v e p e r m i t t e d t h e e v o l u t i o n o f l a r g e b o d y - s i z e i n i s l a n d r o d e n t s . 7. I f t h i s i s t r u e , t h e n i t i s p o s s i b l e . t h a t t h e r e c o r d e d t e n d e n c y f o r a n i m a l s t o g e t l a r g e r i n t h e c o u r s e o f e v o l u t i o n i s r e l a t e d t o a n i n c r e a s e i n t h e a m o u n t o f e n v i r o n m e n t a v a i l a b l e f o r e x p l o i t a t i o n . 112 APPENDIX I. Tables of measurements and s t a t i s t i c s of body dimensions and weights. The following abbreviations have been used:-No. - Number x - Mean SD. -Standard deviation Sx - Standard error of the mean CV. - Coefficient of variation Wing No. -Range X . SD. Sx C V . T a i l No.-Range X • SD. SX C V . Tarsus TABLE "25 Measurements of Platypsaris aglaiae A I N L A N D .. ... Adult cf* 24 8 7 . 6 - 9 4 . 9 91.04 1 - 3 1 4 0.268 1 . 4 4 5 Adult ? • • 19 85.1-92.6 89.79 1<590 O.565 1.771 Immature d* 14 . 81 . 2 - 9 3 . 8 88 .47 2 , 0 1 0 0.537 2.272 23 6 2 . 1 -68 .8 6 6 . 4 2 ' , 1 .288 0 .268 1.939 21 63.8-69.1 66.05 1.467 0.320 2.221 10 63.3-71.1 66.18 2.125 0.672 3.211 Adult d* 16 8 2 . 5 - 8 8 . 9 8 7 . 1 8 * 1.329 0.332 1 . 5 2 4 I S L A N D Adult £ 14 8 2 . 3 - 8 9 . 5 85 . 7 6 * 1.752-0 . 4 6 8 2 . 0 4 3 16 61.2-66.7 64.61* 1.265-0.316 1.959 13 5 9 . 2 - 6 7 . 0 6 4 . 2 8 * 1 . 784 0 . 4 9 5 2 . 7 7 5 Immature cf 2 84.3-85.3 84.85 6 2 . 3 - 6 2 . 8 62.55 No-.- 23 25 16 16 14 Range 19.5-21.8 19.6-22.6 19.3-21.8 20.4-22.0 2 0 . 8 - 2 2 . 2 X 21.06 21.26 20.71 21.27 21.60 SD. 0.438 0,593 0,551 0 .426 0.369 Sx 0.091 0.119 0.138 0.106 0.099 GY. 2.080 2.789 2 .661 2 .003 1,708 21.2-21.3 21.25 TABLE 25 - c o n t i n u e d H A I N L A I D B i l l L e n g t h A d u l t c f N o . 24 R a n g e 1 0 . 7 - 1 3 . ! X 1 2 . 2 0 S D . 0 . 4 6 1 S x 0 . 0 9 4 GV. 3 . 7 7 9 A d u l t ? 23 1 1 . 1 - 1 3 . 2 1 2 . 4 9 0 . 3 4 5 0 . 1 1 4 4 . 3 6 3 B i l l W i d t h N o . Range S S D . S x CY. 8 7 . 3 - 8 . 1 7 . 6 1 0 .260 O .098 3 . 4 1 7 I m m a t u r e d* 14 1 1 . 2 - 1 2 . 9 1 2 . 2 6 0 . 3 4 0 0 . 0 9 1 2 . 7 7 3 16 7 . 7 - 8 . 3 7 . 8 5 0 . 1 4 0 0 . 0 3 5 1 . 7 8 3 7 . 7 - 8 . 0 7 . 8 6 G o r a o o i d N o . R a n g e X S D . S x GY. 1 6 . 8 - 1 8 . 1 17.37 0.538 0 .203 3 .097 8 1 6 . 1 - 1 8 . 4 17 .62 0 . 6 6 0 0 . 2 3 3 3.746 1 7 . 2 - 1 7 . 6 1 7 . 4 0 I S L A N D A d u l t 0* 15 1 1 . 0 - 1 2 . 2 11.57* 0.312 0 . 0 8 1 2.697 15 6 . 8 - 7 . 2 6 . 9 4 * 0 . 1 1 4 -0 . 0 2 9 1 . 6 4 3 1 5 . 9 - 1 6 . I 1 5 . 9 5 * 0.080-0 . 0 3 3 0.502 14 7 . 0 - 7 . 4 7 . 2 5 * 0.100 0.026 1.379 12 1 5 . 8 - 1 6 . 3 1 6 . 0 6 * 0.125 0.036 0.778 I m m a t u r e d" 2 1 1 . 2 - 1 1 .8 11 .50 6 . 8 - 7 . 0 6 , 9 0 15 .8 I-1 4^ TABLE 25 - continued A I N. L A N D Femur No. Range i SD. Sx GY. Adult cf 7 17.6-19.5 18.71 0.552 0 .209 2 .950 A d u l t ? 7 18.6-19.4 19.05 0.338 0.128 1.77.6 Fresh Weight No. Range 1 SD. Sx C T . _ _ -h) Fat Weight after Freeze/Thawing No-. Range X Immature d* 3 1 8 . 3 - 1 8 . 6 18 .47 Fresh Weight a) Not Fat No. 6 3 Range 2 7 . 2 - 3 1 . 2 2 9 . 9 - 3 0 . 1 i 29 .13 3 0 . 0 0 SD. 1 .720 Sx O.7O2 GY. 5 .906 2 7 . 5 - 2 9 . 9 28.70 I S L A Adult d* Adult $ 5 9 1 8 . 2 - 1 8 . 7 1 8 . 5 - 1 9 . 0 18.46 18.80 0 . 2 8 0 0 .150 0.125 0 . 0 5 0 1.517 0.798 Immature o7* 1 18.5 2 3 . 0 2 7 . 1 2 3 . 9 0 24.4-27.2 2 5 . 6 7 1 .009 0.336 ?-?5i a) Fat unknown 23.5-25.4 24 .37 1 24.00 116 TABLE 26 Measurements of Tyrannus melanoholious M A I N L A N D I S L A N D Wing cf ? c? ? No. 27 32 17 15 Range. 106.7-115-9 104.8-113.4 1 0 7 . 0 - 1 1 3 . 9 1 0 2 . 9 - 1 1 1 . 4 1 112.47 108.76 111.28 1 0 6 , 8 1 * SD. 1.859 1.766 1 .301 1.916 Sx 0.554 0.312 0.315 0 .495 CV. 1.635 1.624 1.169 1.794 T a l l No. 26 29 16 14 Range 8 5 . 4 - 9 7 . 0 83 .0-92.8 8 7 . 1 - 9 1 . 8 80.3-89 .5 X 9 2 . 2 3 87.41 90.42 8 5 . 3 3 * SD. 3.312 2 . 2 l 6 1.385 2.211 Sx O.630 0.412 0.346 0 .591 CV. 3.484 2.535 1.532 2 . 5 9 1 Tarsus No. 30 32 17 14 Range 1 7 . 6 - 2 0 . 0 1 7 . 9 - 2 0 . 0 1 7 . 3 - 1 9 . 1 1 7 . 1 - 1 9 . 3 X 19.14 19.11 18 .52* 18 .51* SD, 0.473 0.541 0.436 0.417 Sx 0,086 0.096 0.106 0.111 CV. 2.475 2.831 2 .354 2.253 B i l l Length No. 30 32 17 15 Range 1 7 , 1 - 1 9 . 7 1 6 . 9 - 1 9 . 4 1 7 . 3 - 1 9 . 1 1 6 . 1 - 1 9 . 1 2 18,49 18 .10 18 .45 18 .08 SD. 0.554 0.458 0,466 0 . 6 4 0 SX 0.101 0 . 0 8 1 0.113 0.16.5 CV. 2,996 2 .530 2.528 3.540 117 TABLE 26 - continued Coracoid cf £ % No. 8 10 15 10 Range 19 . 2 - 2 0 . 7 19 . 1 - 2 0 . 4 17 .8-19 .6 18.5-19 .4 X 2 0 . 1 2 19.84 19.11* 1 8 . 9 1 * SD. 0 .394 0.249 0.319 0.367 S i 0.139 0 . 0 7 9 0 . 0 8 2 0.116 CV. 1 .958 1 .235 1.669 1.941 Femur No. 14 18 15 13 Range 1 7 . 9 - 1 9 . 4 1 8 . 7 - 2 2 . 2 1 7 . 2 - 1 9 . 4 1 7 . 9 - 1 8 . 9 X 1 8 . 9 1 19.36 1 8 . 2 3 * 1 8 . 3 8 * SD. 0 .397 0.486 O.362 0.307 SX 0 .106 0,115 0 . 0 9 3 0 . 0 8 5 CV. 2.099 2 .510 1.986 1 .670 Fresh Weight a) Not Fat No. 2 2 1 Range 39 .0-41 . 7 3 7 . 0 X 40. 55 5 7 . 0 0 3 2 . 0 Fresh Weight b) Fat No, 6 5 Range 3 0 . 9 - 3 4 , 5 3 2 . 7 - 3 9 . 1 2 3 3 . 4 3 3 5 . 2 2 SD. 1 .016 1 .944 Sx 0.415 O .869 CV. Iz^l 5 .520 Weight after Freeze/Thawing a) Not Fat No. 12 9 Range 35.5-40 .6 36.5-40 .5 X 3 7 . 9 9 3 9 . 0 0 SD. 1 .500 1 .300 Sx 0 . 4 3 3 0.433 CV. 3-948 3 . 3 3 3 Weight after Freeze/Thawing b) Fat No. 2 2 Range 38 ,5-40 .9 36 . 7 - 4 3 . 0 x 3 9 . 7 0 3 9 . 8 5 118 T A B L E 27 M e a s u r e m e n t s o f M y i a r c h u s . t y r a n n u l u s M A I N L A N D I S L A N D W i n g c? i ? N o . 31 21 25 18 R a n g e 102.9-113.9 1 0 0 . 4 - 1 1 0 . 4 1 0 1 . 0 - 1 1 0 . 4 96 .4 - 1 0 6 . 1 1 109.17 1 0 4 . 8 6 105.30* 1 0 1 . 8 4 * S D , 2 . 4 2 5 1 . 9 6 4 1 . 6 2 5 2,125 S x 0 . 4 3 6 0 . 4 2 9 0.325 0,501 GY. 2 . 2 2 1 1 . 8 7 3 1 . 5 4 3 2 . 0 8 7 T a i l N o . 32 20 23 18 R a n g e 9 1 . 7 - 1 0 5 . 4 8 8 . 4 - 1 0 0 . 8 9 1 . 1 - 1 0 4 . 2 8 7 . 3 - 9 7 . 2 X 9 8 . 6 6 94.87 9 5 . 7 7 * 92 .93 S D . 2 . 8 9 3 2.799 1 . 6 7 8 2.267 S x 0 . 5 1 1 0.626 0.350 0 . 5 3 4 GY. 2.932 2.950 1.752 2.439 T a r s u s N o . 31 21 25 18 R a n g e 2 2 . 1 - 2 6 . 1 23.0-26.2 2 2 . 5 - 2 5 . 6 2 2 . 6 - 2 5 . 2 X 2 4 . 7 8 24.56 2 3 . 9 8 * 23.76* S D , 0.790 0 . 8 6 8 0 . 5 3 6 0 . 6 6 6 S x 0 . 1 4 2 0 . 1 8 9 0.107 0.157 GY. 3 . 1 8 8 3 . 5 3 4 2.235 2.803 B i l l L e n g t h N o . 31 19 24 18 R a n g e 1 7 . 4 - 2 2 . 9 1 7 . 8 - 1 9 . 5 1 7 . 1 - 1 9 . 5 1 6 . 2 - 1 9 . 7 X 1 9 . 2 8 1 8 . 6 2 18 . 5 2 * 17.68* S D . 0 . 6 7 3 0 . 4 0 2 0 . 5 3 3 O.689 S x 0 . 1 1 9 0.092 0.109 0.162 GY. 3 . 1 2 8 2.159 2 . 8 7 8 3 . 8 9 7 119 TABLE 2? - c o n t i n u e d M A I N L A N D I S L A N D C o r a c o i d c? ? C? f N o . 4 3 6 6 R a n g e 1 9 . 4 - 2 1 . 7 2 0 . 2 - 2 0 . 9 1 9 . 4 - 2 0 . 2 1 9 . 3 - 2 0 . 0 X 2 0 . 7 7 2 0 . 4 7 1 9 . 8 2 1 9 . 6 0 S D . 0 . 3 0 0 0 . 3 2 0 S i 0 . 1 3 1 0 , 1 3 1 C V . 1 . 5 1 4 1 . 6 3 3 Femur N o . 5 6 8 7 R a n g e 2 2 . 1 - 2 3 . 0 2 1 . 7 - 2 2 . 9 2 0 . 0 - 2 1 . 8 2 0 . 2 - 2 1 . 8 X 2 2 . 3 6 2 2 . 3 0 21.16* 2 1 . 1 9 * S D . 0 . 3 4 0 0 . 4 0 0 0.626 0 . 5 5 5 S x 0 . 1 5 2 0 . 1 6 3 0 . 2 2 1 0 . 2 1 0 C V . 1 . 5 2 1 1 . 7 9 4 2 . 9 5 8 2 . 6 1 9 F r e s h W e i g h t a ) Not F a t b) F a t N o . 2 3 1 R a n g e 39 . 0 - 46 . 7 4 3 . 0 - 5 0 . 7 X 4 2 . 8 5 4 5 . 6 4 0 . 4 W e i g h t a f t e r F r e e z e / T h a w i n g a ) N o t F a t F a t U n k n o w n N o . 4 4 2 4 R a n g e 4 2 . 9 - 4 8 . 3 3 8 . 2 - 4 4 . 4 3 6 . 6 - 4 1 . 0 3 4 . 9 - 4 0 . 8 X 4 6 . 1 0 4 2 . 3 0 3 8 . 8 0 3 7 . 4 5 W e i g h t a f t e r F r e e z e / T h a w i n g b) F a t N o . 2 R a n g e 4 5 . 4 - 4 5 . 5 X 4 5 . 4 5 TABLE 28 Measurements of Myiarchus tuherculifer A I N L A N D I S L A N D Wing Adult c? No. 36 Range 7 8 . 2 - 8 7 . 0 X 8 2 . 6 3 SD. 1.978 Sx 0 . 3 3 0 CV. 2 .394 Adult? 36 7 1 . 8 - 8 6 . 7 77 .47 2 .002 0.334 2 .584 Immatured" Immature? 7 3 . 5 - 7 9 . 2 7 3 . 2 - 7 6 . 2 76 .97 7 4 . 6 7 Adult J 1 15 7 5 . 7 - 8 3 . 0 8 0 . 4 1 * 1 .662-0.429 2 .067 Adult? 28 7 4 . 2 - 8 3 . 2 7 6 . 7 6 1 . 480 0. 280 1 .928 Immature 6* Immature ? 14 7 1 . 3 - 8 0 . 3 76 .54 2 .138 0 .571 2 .793 8 7 2 . 1 - 7 7 . 4 7 3 . 8 9 2 .040 0 . 7 2 1 2 . 7 6 1 T a i l No. 35 Range 7 3 . 4 - 8 2 . 3 1 7 8 . 7 5 SD. 2 . 084 Sx 0 .352 CV. 2 .646 33 6 9 . 3 - 8 2 . 2 74.28 1.901 0.331 2 .559 6 9 . 2 - 7 7 . 1 7 3 . 9 0 7 1 . 2 - 7 3 . 1 72.15 15 7 2 . 8 - 7 9 . 9 77 .62 1.543 0,398 1.988 28 7 1 . 6 - 8 1 . 8 7 4 . 4 4 1 .704 0 .322 2 . 2 8 9 7 1 . 2 - 7 9 . 1 75 . 44 2 . 2 8 0 0 .760 3 . 0 2 2 8 6 7 . 9 - 7 7 . 1 7 2 . 0 5 2.357 0 . 8 3 3 3 . 2 7 1 Tarsus No. 36 38 3 3 15 28 17 8 Range 1 7 . 6 - 2 0 . 2 1 6 . 0 - 1 9 . 6 1 8 . 1 - 1 9 . 5 1 7 . 7 - 1 8 . 8 1 8 . 0 - 1 9 . 8 1 7 . 7 - 1 9 . 5 1 6 . 8 - 1 9 . 8 1 7 . 4 - 1 9 . 4 X 18 .99 1 8 . 2 2 18 .73 1 8 . 3 0 1 9 . 0 5 1 8 . 6 6 * 1 9 . 0 3 1 8 . 4 9 SD. 0.474 O.665 O.368 0 . 4 0 3 O.663 0.537 Sx 0.079 0.108 0 .095 0 .076 0.161 0 . 1 9 0 c v . 2.496 3 . 6 5 0 1.932 2 .160 3 . 4 8 4 2 .904 B i l l Length No. 35 38 3 3 13 27 15 8 Range 1 2 . 5 - 1 5 . 1 1 2 . 1 - 1 4 . 7 1 1 . 6 - 1 3 . 3 1 1 . 8 - 1 2 . 3 1 2 . 9 - 1 4 . 3 1 2 . 2 - 1 4 . 8 1 2 . 2 - 1 3 . 8 1 2 . 6 - 1 3 . 9 x 13.98 13.17 1 2 . 7 0 1 2 . 0 3 1 3 . 6 2 1 3 . 3 0 1 3 . 3 1 13 . 24 SD. 0 .444 0 .514 0.429 0 . 4 0 0 0 . 414 0 . 414 Sx 0 .075 0.083 0.119 0 .077 0.107 0 . 146 c v . 3.176 3 . 9 0 3 3 . 1 5 0 3 . 008 3 . 1 1 0 3.127 ro o 121 TABLE 28 - continued M A I N L A N D I S L A N D Coracoid d* ? cf I No. 5 3 5 1 Range 15.6-16.3 14.6-16.5 14.0-14.5 X 15.84 15.73 14 .26* 13 .9 SD. 0.335 0.210 Sx 0.150 0.094 CV. 2.115 1.473 Femur No. 2 3 4 1 Range 15.8-16.1 15.3-18.0 14.7-15.2 X 15.95 1 6 . 3 0 14.92 14.8 Fresh Weight a) Not Fat No. 3 2 3 Range 18.6-19.7 17.0-17.8 11.4-12.9 x 19.00 17.40 12.00 Fresh Weight b) Fat No. 1 2 Range 13.4-14.4 X 16.0 13.90 Weight after Freeze/Thawing Not Fat Fat Unknown No. 2 18 18 Range 15.1-23.4 11.0-14.3 10.3-14.3 X 19 .25 12 .63 12 .50 SD. 0.984 O.988 Sx 0 .232 0 .233 CV. 7.791 7.904 122 TABLE 2? M e a s u r e m e n t s o f M y i o p a g i s v i r i d i c a t a . M A I N L A N D I S L A N D W i n g c f s c f ? N o . 32 19 20 10 R a n g e 65.9-71.4 61.7-72.4 61.1-70.7 61.8-67.0 X 68.71 64.45 67.40 64.73 S D . 1 . 4 9 2 1.575 1.963 1.189 S i 0.264 0.361 0.439 0.376 C V . 2 . 1 7 1 2.444 2.912 1.837 T a i l N o . 31 18 20 10 R a n g e 61.5-73.1 57.8-68.7 59.2-70.0 56.8-63.6 X 66.99 61.29 66.43 61.56 S D . 2.050 1.787 2.704 1.800 S x O.368 0 . 421 0.605 0.569 C V . 3.060 2.916 4.070 2.924 T a r s u s N o . 31 19 20 9 R a n g e 16 .2 -18 .6 15.8-17.7 17.2-19.0 17.2-19.1 1 17.33 16.65 18 . 3 6 * 17.76* S D . 0.550 0.508 0.488 O.560 S x 0 . 099 0.117 0.109 0.187 CV. 3 . 1 7 4 3.051 2.658 3.153 B i l l L e n g t h N o . 26 14 14 8 R a n g e 6.5-7.6 6.3-7.4 6.8-7.4 6.6-7.1 2 7 .18 6 .87 7.03 6.87 S D . 0 . 164 0.220 0.185 0 . 143 S x 0.032 0.059 0 .049 0.051 C V . 2 . 284 3.202 2.632 2.082 123 TABLE 29 - continued M A I N L A N D I S L A N D Coracoid ? <? No. 18 9 7 4 Range 1 2 . 8-14 . 0 12.3-13.4 12.1-12.4 1 1 . 3 - 1 1 . 7 X 1 3 . 3 0 1 2 . 8 1 12.24* 11 .55 SD. 0.318 0.314 0.123 S x 0.075 0.105 0.046 GY, 2.356 2.451 1.005 Femur No. 14 8 5 4 Range 13.7-14 .9 13.5-14 .5 13.9-14 .3 1 3 . 2 - 1 3 . 7 1 14.44 1 3 . 9 9 14.16 1 3 . 5 0 S D . 0 . 3 4 3 0.357 0 . 1 6 0 S x 0.092 0.126 0 .072 CV. 2.375 2 .552 1.130 Fresh Weight a) Not Fat No. 14 7 2 Range 1 1 . 3 - 1 3 . 6 1 0 . 1 - 1 2 . 1 9 . 9 - 1 0 . 2 X 12 .36 11.27 1 0 . 0 5 S D . 0 . 5 9 5 0.515 S x 0.159 0.195 GV. 4.814 4 . 5 7 0 Fresh Weight h) Fat No. 6 2 Range 9 . 6 - 1 0 . 8 9.3-10.1 X 1 0 . 2 3 9 . 7 0 S D . 0.440 S x 0.180 GV. 4 .301 124 TABLE 30 Measurements of Camptostoma imberbe M A I N L A N D I S L A N D Wine d* ? C? i No. 1 2 3 2 Range 50.2 -50.7 5 3 . 8 - 5 5 . 5 5 1 . 6 - 5 1 . 8 X 5 3 . 0 5 0 . 4 5 5 4 . 6 0 51 .7 T a i l No. 1 2 3 2 Range 3 6 . 7 - 3 9 . 2 42 .3-46.9 40.9-41.2 X 3 9 . 8 37 .95 44 .60 41.05 Tarsus No. 1 2 3 2 Range 14.1-14.6 13.6-14.9 13 .8-14 .0 X 14.9 14 .35 14.37 1 3 . 9 0 B i l l Length No. 1 1 3 2 Range 4 . 7 - 5 . 9 4 . 4 - 5 . 9 1 6 .4 5 . 8 5 . 5 0 5 .15 125 TABLE 31 Measurements of Thryothorus f e l i x M A I N L A N D I S L A N D Wine ? <? Wo. 37 17 35 25 Range 53.2-59.2 50.2-57.8 54.1-63.4 54.3-62.9 X 56.89 53.71 59.41* 57.76* SD. 1.095 1.517 1.976 2.112 Sx 0.180 0.368 0.334 0.422 CV.' 1.925 2.824 3.326 3.657 T a i l No. 31 16 31 24 Range 48.3-56.3 43.6-53.8 51.7-60.0 50.7-60.0 X 52.49 49.31 56.10* 55.45* SD. 1.278 2.285 1.927 2.796 Sx 0.230 0.571 0.346 0.571 CV. 2.435 4.634 3.435 5.042 Tarsus No. 35 16 36 26 Range 19.6-22.6 20.4-22.3 20.1-22.8 19.8-22.4 X 21.56 21.35 21.90 21.43 SD. O.563 0.587 0.606 0.578 Sx 0.095 0.147 0.101 0.113 CV. 2.611 2.749 2.767 2.697 B i l l Length No. 36 17 34 25 Range 9.4-12.0 9.6-11.5 11.1-14.3 11.3-13.8 X •10.91 10.59 12.43* 12.24* SD. 0.417 0.376 0.604 0.471 Sx 0.069 0.091 0.104 0.094 CV. 3.822 3.551 4.859 3.848 126 TABLE 31 - continued M A I N I A N D I S L A N r ) Coracoid c? ? I No. 9 4 Range 12.9-14 .2 1 2 . 9 - 1 3 . 8 X 1 3 . 9 0 13 .25 SD. 0.312 Sx 0.104 CV, 2.245 Femur No. 13 3 Range 1 6 . 0 - 1 7 . 2 1 5 . 6 - 1 6 . 3 X 16 .73 1 6 . 0 3 SD. 0.404 Sx 0.112 CV. 2.415 Fresh Weight Not Fat Fat Unknown No. 6 4 1 Range 1 3 . 2 - 1 6 . 1 1 1 . 5 - 1 3 . 5 1 14 .90 12.57 14.6 SD. 0 . 8 8 0 Sx 0.359 CV. 5 . 9 0 6 Weight after Freeze/Thawing Not Fat Fat Unknown No. 5 1 22 8 Range 13.0-16.4 9.0-14 .6 1 0 . 5 - 1 3 . 1 1 14 .54 13 .3 12 .21* 1 1 . 8 0 SD. 1.365 1.233 0.829 Sx 0 . 6 1 0 0 . 2 6 3 0.293 CV. 9-. 388 10.098 7 .025 127 TABLE 32 Measurements of Melanotis eaerulesoens M A I N L A N D I S L A N D Wing <? ? <? I No. 25 25 44 18 Range 1 0 6 . 4 - 1 2 1 . 3 1 0 5 . 1 - 1 1 8 . 0 1 0 2 . 5 - 1 1 7 . 3 9 9 . 4 - 1 1 0 . 9 X 114.17 110.26 1 0 9 . 5 8 * 1 0 6 . 9 0 * SD. 3.126 2.822 3.154 2 . 0 7 1 SX 0.625 0.564 0.475 0 .488 GV.. 2.738 2 .559 2.878 1.937 T a i l No. 28 25 39 16 Range 1 1 2 . 9 - 1 3 1 . 6 1 0 6 . 3 - 1 2 6 . 3 9 9 . 6 - 1 1 7 . 3 9 2 . 6 - 1 1 1 . 9 X 123.47 116.38 1 0 9 . 2 0 * 104 .90* SD. 3.740 4 . 4 6 4 4 . 5 8 9 3 . 8 0 0 S i 0.707 0 . 8 9 3 0.735 0 . 9 5 0 CV. 3 . 0 2 9 3.836 4 .202 3 . 6 2 2 Tarsus No. 29 31 45 18 Range 2 7 . 3 - 3 0 . 9 2 7 . 4 - 3 1 . 1 2 6 . 4 - 3 0 . 8 26 . 2 - 3 0 . 1 X 29.18 2 9 . 3 0 28 .54* 28 .23* SD. 0.709 0 . 8 7 0 0.769 0 .684 Sx 0.132 O.156 0.115 0.161 CV. 2 . 4 3 0 2.970 2.694 2.423 B i l l Length No. 28 28 39 17 Range 1 5 . 5 - 1 9 . 6 14 . 2 - 1 9 . 1 1 8 . 4 - 2 2 . 4 1 8 . 3 - 2 1 . 8 1 17.42 17.13 2 0 . 0 9 * 1 9 . 7 9 * SD. 0.879 0.941 0.784 0.563 Sx 0.167 0.178 0.126 0.137 CV. 5.046 5 . 4 9 3 3 . 9 0 2 2 .845 128 TABLE 32 - continued No. 6 2 3 5 Range 2 1 . 5 - 2 3 . 1 22.1-24 . 1 2 0 . 4 - 2 0 . 7 19.7-21.1 X 2 2 . 4 3 23 .15 2 0 . 3 7 2 0 . 5 2 3D. 0.480 0 .430 S x • 0.196 0.192 CV. 2.140 , 2.096 Femur No. 5 2 4 5 Range 25.O-26.7 2 7 . 1 - 2 7 . 5 24 . 3 - 2 5 . 3 24 . 8 - 2 6 . 7 1 2 5 . 8 4 2 7 . 3 0 24 .82 2 5 . 6 0 SD. 0.940 0 . 7 0 0 Sx 0,420 0.313 CV. 5.638 2 .734 Fresh Weight a) Not Fat No. 12 4 Range 5 7 . 1 - 6 6 . 2 6 2 . 5 - 6 9 . 7 x 6 3 . 4 7 6 6 . 3 SD. 2 .518 Sx 0.727 c v . 3 . 9 6 7 Fresh Weight b) Fat No. 1 3 Range 50.2-57.6 % 55.3 5 5 . 0 5 1 2 9 TABLE 32 - continued M A I N L A N D I S L A N D Weight afte r Freeze/Thawing Fat Unknown No. 14 3 Range 45.2-66.6 57.6-59 I 5 7 . 5 2 58 .50 SD. 5.186 Sx 1.386 •cv. 9 .016 Weight after Freeze/Thawing Fat No. 1 2 Range 56.3-68.0 X 6 2 . 3 62.15 130 T A B L E 33-M e a s u r e m e n t s o f Mimus p o l y g l o t t o s M A I N L A N D I S L A N D W i n g d* £ % N o . 7 9 4 2 R a n g e 102.8-119.2 104 .0-118 .5 107.4-119.9 102.2-112.1 I 112.30 109.23 113.67 107.15 S D . 4 .700 5.366 S x 1.776 1.789 GV. 4.185 4 .913 T a i l N o . 6 8 3 2 R a n g e 1 0 7 . 4 - 1 2 8 . 2 104 .3 - 1 2 7 . 8 113 .0 - 1 2 7 . 7 9 9 . 1 - 1 0 8 . 9 X 117.52 1 1 4 . 6 5 117.93 1 0 4 . 0 S D . 5 . 1 6 4 7 . 3 5 7 S x 2 . 1 0 9 2 .601 C V . 4 . 3 9 4 6 . 4 1 7 T a r s u s N o . 7 9 4 2 R a n g e 32.1-34.9 30.9-33.6 32.2-35.8 30.6-34.0 x 32.96 32.20 33.45 32.30 S D . 0.810 1.025 S x 0.306 0 . 342 C V . 2.458 3.183 B i l l L e n g t h N o . 5 8 3 2 R a n g e 12.2-13.5 11 .3 -14 .5 1 2 . 2 -14 . 2 13.0-13.1 X 12.86 13.01 13.03 13.05 S D . 0.590 0.959 S x 0.264 0.137 C V . 4.588 3.391 F r e s h W e i g h t a ) F a t N o . 2 R a n g e 47.8-48.7 £ 48.25 W e i g h t a f t e r F r e e z e / T h a w i n g F a t Unknown N o . 3 R a n g e 42 . 1 -57 .8 X 48.37 131 TABLE 34 Measurements of Turdus ruf o-palliatus M A I N L A N D I S L A N D Wing cf ? cf ? No. 33 23 19 32 Range 1 1 7 . 3 - 1 2 8 . 2 1 1 5 . 7 - 1 2 3 . 4 1 2 1 . 9 - 1 3 1 . 2 1 1 8 . 5 - 1 3 1 . 2 1 2 3 . 2 2 12 0 .43 126.75* 125.17* S D . 2.899 2 . 0 1 0 2.475 2.528 S x 0 , 5 0 5 0.419 0.568 0.447 0 7 . . 2.353 1.669 1.953 2 .020 Ta i l No. 33 24 19 34 Range 9 1 . 8 - 1 0 5 . 4 9 0 . 4 - 1 0 1 . 9 9 5 . 4 - 1 0 7 . 9 8 4 . 4 - 1 0 5 . 7 I 9 9 . 3 0 9 6 . 0 5 1 0 2 . 0 8 * 9 9 . 5 1 * S D . 3.287 2 .570 3 .110 2 .486 S x 0.572 0.525 0.713 0.426 C V . 3 . 3 1 0 2.676 3.047 2.491 Tarsus No. 33 25 20 33 Range 2 9 . 4 - 3 3 . 8 2 9 . 3 - 3 4 . 5 3 3 . 0 - 3 6 . 3 3 1 . 9 - 3 8 . 1 X 3 1 . 3 0 31.42 3 4 . 8 0 * 3 4 . 7 0 * S D . 0.987 0.975 0.732 0.858 S x 0.172 0.195 0.164 0.152 CV. 3.153 3 .103 2.103 2.473 B i l l Length No. 31 23 20 31 Range 12.2-14 .6 1 2 . 3 - 1 5 . 2 1 3 . 3 - 1 6 . 2 14 . 2 - 1 7 . 4 X 1 3 . 2 8 13 .87 15.19* 15 .43* S D . 0.495 0.417 0 . 6 8 1 0 . 5 5 0 S x 0 . 0 8 9 0.087 O .152 0.099 CV. 3.727 3 . 0 0 6 4 . 4 8 3 3.564 132 TABLE 34 - continued M A I N L A N D I S L A N D Coracoid d* ? No. 4 3 1 Range 2 3 . 3 - 2 5 . 2 2 3 . 6 - 2 5 . 0 X. 24 .40 2 4 . 2 3 23.4 femur No. 4 2 1 3 Range 2 4 . 7 - 2 7 . 3 2 6 . 2 - 2 6 . 3 26.9 -27 .6 x 26 .15 26 .25 2 7 . 5 2 7 . 3 3 Fresh Weight a) Not Fat No. 3 Range 65.O-68.O X 6 6 . 5 0 Weight after Freeze/Thawing Fat Unknown No. ? 13 Range 6 6 . 5 - 7 9 . 1 6 3 . 5 - 8 3 . 7 X 71 .82 74 .34 SD. 4 .640 5 .138 Sx 1 .547 1 .425 CV. 6 . 461 6 . 911 133 TABLE 33 Measurements of Myadestes obscurus M A I N L A N D I S L A N D Wing <f ? cf i No. 16 12 7 8 Range 9 7 . 8 - 1 0 9 . 5 9 6 . 1 - 1 0 6 . 3 9 8 . 6 - 1 0 3 . 5 9 6 . 1 - 1 0 0 . 1 X 103.76 1 0 0 . 2 4 1 0 0 . 9 9 9 8 . 0 9 S D . 2 . 7 2 1 2 . 3 8 9 2.115 1 . 4 7 1 S x 0 . 6 8 0 0 . 6 9 0 0 . 7 9 9 O .520 CV." 2 . 6 2 2 2 . 3 8 3 2 . 0 9 4 1 . 5 0 0 T a i l No. 17 12 6 8 Range 9 4 . 6 - 1 0 5 . 4 8 8 . 1 - 1 0 1 . 0 0 9 5 . 3 - 1 0 4 . 2 9 3 . 1 - 9 9 . 2 X 1 0 0 . 5 9 9 4 . 7 6 1 0 0 . 4 0 9 5 . 5 7 S D . 2 . 3 5 6 2.665 4 . 0 4 0 1 . 8 2 9 S x 0 . 5 7 1 0.769 1 .650 0 . 6 4 7 C Y . 2 . 3 4 2 2 . 8 1 2 4 . 0 2 4 1 . 9 1 4 Tarsus No. 17 14 7 8 Range 1 8 . 9 - 2 2 . 9 1 8 . 2 - 2 1 . 1 2 2 . 2 - 2 3 . 3 2 1 . 8 — 2 2 . 8 X 2 0 . 3 8 2 0 . 2 1 2 2 . 7 6 * 2 2 . 1 5 * S D . 0 . 7 3 4 0 , 6 7 5 0 . 4 5 7 0 . 2 2 9 S x 0 . 1 7 8 0 . 1 8 0 0 . 1 7 3 0 . 0 8 1 C Y . 3 . 6 0 2 2 . 3 5 0 2 . 0 0 8 1 . 0 3 4 B i l l Length No. 16 13 7 8 Range 6 . 8 - 8 . 9 6 . 8 - 8 . 1 7 . 1 - 7 . 7 7 . 1 - 7 . 6 1- 7 . 7 2 7 . 4 8 7 . 4 2 7 . 3 5 S D . 0 . 4 3 9 O .388 0 . 2 3 0 0 . 1 7 1 S x 0 . 1 1 0 0.108 0 . 0 8 7 0 . 0 6 0 C Y . 5 . 6 8 7 5 - 1 8 7 3 . 1 0 0 2 . 3 2 7 134 TABLE 33 - continued M A I N L A N D I S L A N D Coracoid e No. 1 7 Range 1 9 . 9 - 2 1 . 1 X 2 0 . 8 2 0 . 5 3 SD. O.385 Sx 0,145 GV. 1.875 Femur No. 1 6 Range 2 0 . 1 - 2 0 . 7 I 2 0 . 3 2 0 . 3 5 SD. 0.250 Sx 0.102 CV. 1.233 Fresh Weight a) Not Fat No. 1 1 3 8 . 2 135 TABLE 34 M e a s u r e m e n t s o f V i r e o h y p o e h r y s e u s M A I N L A N D I S L A N D Wing. O* ? H o . 40 20 28 20 R a n g e 6 0 . 4 - 6 9 . 1 5 8 . 5 - 6 4 . 3 6 3 . 6 - 7 0 . 3 6 4 . 5 - 6 9 . 8 X 6 3 . 5 8 6 1 . 58 6 7 . 7 4 * 6 6 . 0 4 * S D . 1 . 5 2 2 1 . 2 4 9 1 . 4 1 0 1 . 0 7 7 S x • 0 . 2 4 1 0 . 2 7 9 0 . 2 6 6 0 . 2 4 1 GV . 2 . 3 9 4 2 . 0 2 8 2 . 0 8 1 1 . 6 3 1 T a i l N o . 42 19 24 19 R a n g e 5 0 . 5 - 5 8 . 9 5 0 . 2 - 5 6 . 8 5 8 . 3 - 6 2 . 3 5 7 . 2 - 6 1 . 9 X 5 5 . 7 4 5 3 . 7 4 6 0 . 4 5 * 5 8 . 6 9 * S D . 1 . 4 3 7 1 . 5 2 6 0 . 9 7 0 0 . 8 5 4 S x 0 . 2 2 4 0 . 3 5 0 0 . 1 9 8 O . I 9 6 C V . 2 . 5 7 8 2 . 8 4 5 1 . 6 0 5 1 . 4 5 5 T a r s u s N o . 43 20 27 20 R a n g e 1 7 . 8 - 1 9 . 9 1 7 . 9 - 1 9 . 4 1 9 . 0 - 2 1 . 2 1 8 . 9 - 2 0 . 9 X 1 8 . 7 1 1 8 . 8 4 1 9 . 9 7 * 2 0 . 0 6 * S D . 0 . 4 7 7 0 . 3 7 7 0 . 4 5 7 0 . 4 6 7 S x 0 . 0 7 3 0 . 0 8 4 0 . 0 8 8 0 . 1 0 4 C V . 2 . 5 4 9 2 . 0 0 1 2 . 2 8 8 2 . 3 2 8 B i l l L e n g t h N o . 42 20 27 17 R a n g e 7 . 9 - 9 . 6 8 . 0 - 9 . 3 8 . 6 - 9 . 8 8 . 7 - 9 . 6 X 8 . 8 0 8 . 7 0 9 . 1 1 * 9 . 1 0 * S D . 0 . 3 4 1 0.358 O .270 0.225 S x 0 . 0 5 3 0 . 0 8 0 0 . 0 5 2 0 . 0 5 5 C V . 3 . 8 7 5 4.115 2 . 9 6 4 2 . 4 7 3 13 6 TABLE 36 - continued M A I N L A N D I S L A N D Coracoid cf I No. 12 9 6 4 Range 13.3-14.1 13.2 -13.7 1 2 . 3 - 1 2 . 7 1 2 . 2 - 1 2 . 9 X 13.74 13.47 1 2 . 5 0 * 12.57 SD. 0 . 1 9 1 0.141 0.160 ss 0.053 0.047 • O.065 cv. • 1 .390 1.047 1 .280 Femur No. 14 10 7 5 Range 14.1-15.2 14 .3-15 .1 14 .4-15 .1 14 .8-15.2 X 14.75 14.71 14.76 14.96 SD. 0.269 0.224 0.237 0.140 Sx 0 . 0 7 2 0 .071 0 . 0 9 0 0 . 0 6 3 CV. 1.824 1.523 1.606 0 .936 Fresh. Weight a) Not Fat No. 5 1 Range 12 .9-14 .1 X 13 .52 13 .5 SD. 0 . 5 8 0 Sx 0.259 CV. 4 . 2 9 0 Weight after Freeze/Thawing Fat Unknown No. 14 3 Range H.I - I3.O 10.6-13.4 X 11.91 12.03 SD. 0.494 Sx 0.132 CV. 4.148 137 TABLE 37 Measurements of Vireo f l a v o v i r i d i a M A I N L A N D I S L A N D Wing cf ? cf % No. 23 19 41 16 Range 7 6 . 4 - 8 3 . 8 7 5 . 0 - 7 9 . 8 7 8 . 8 - 8 7 . 6 76.8-82 .8 x 81.13 77 .45 8 3 . 4 7 * 79.31*" SD. 1.637 0.976 1.152 1 . 3 8 0 SX . 0.341 0.224 0.180 0.345 C V . 2.018 1 .260 1 .380 1.740 T a i l No. 22 19 41 15 Range 5 0 . 7 - 5 8 . 9 4 9 . 0 - 5 4 . 9 5 3 . 2 - 6 2 . 2 5 0 . 4 - 5 7 . 9 X 55.85 5 2 . 2 8 5 8 . 5 2 * 5 3 . 9 9 * SD. 1.695 1 .394 1.325 I . 6 0 9 Sx O.361 0 . 3 2 0 0.207 0.415 C V . 3 . 0 3 5 2.666 2.264 2 . 9 8 0 Tarsus No. 23 19 41 16 Range 1 7 . 2 - 2 0 . 0 1 8 . 1 - 1 9 . 8 1 9 . 1 - 2 0 . 9 1 9 . 0 - 2 1 . 2 X 18 .89 18 .78 2 0 . 0 3 * 2 0 . 0 0 * SD. 0.554 0 .426 0.345 0 .653 Sx 0.116 0 . 0 9 8 0.054 0.163 C V . 2.933 2.26 8 1.722 3 .265 B i l l Length No. 23 19 40 16 Range 9 . 6 - 1 1 . 8 9 . 3 - 1 0 . 8 1 0 . 1 - 1 2 . 8 9 . 7 - 1 2 . 8 X 10 .59 9 . 9 0 11 .00* 1 0 . 5 2 * SD. 0.456 0.322 0.423' 0.488 Sx 0.095 0.074 0.067 0.122 C V . 4 . 3 0 6 3 .253 3 . 8 4 5 4 .639 138 TABLE 37 - continued M A I N L A N D I S L A N D Coracoid <? ? c? ? No. A 4 25 12 Range 1 5 . 7 - 1 6 . 3 15.4-15.9 14 . 5 - 1 7 . 3 1 5 . 3 - 1 6 . 6 I 15 .97 15.67 1 6 . 4 8 16.04 S D . 0.397 0.325 S x 0.079 0.094 CV. 2.409 2 . 0 2 6 Femur No. 5 8 27 13 Range 1 5 . 7 - 1 6 . 5 1 5 . 6 - 1 6 . 7 1 6 . 5 - 1 7 . 8 1 5 . 9 - 1 7 . 8 X 16.18 16.12 17 .12* 1 6 . 7 8 * S D . 0 . 3 2 0 0 . 3 0 0 0.292 0.635 S X 0.143 0.106 0.056 0.176 CV. 1.978 1 .861 1.706 3 .784 Fresh Weight Fat Unknown Not Fat No. 7 2 1 Range 1 7 . 3 - 1 9 . 1 20.3 -20.5 X 17 .96 20.40 1 8 . 0 S D . 0.626 S x 0.237 CV. 3 . 4 8 6 Fresh Weight Fat No. 16 4 Range 1 7 . 4 - 2 2 . 2 1 9 . 2 - 1 9 . 8 t 20.18 19 .52 S D . 1.287 S x 0.322 CV. 6.378 Weight after Freeze/Thawing Fat No. 2 1 Range 1 9 . 0 - 2 1 . 1 X 2 0 . 0 5 19-7 TABLE "38 Measurements of Parula pit iayumi II MAINLAND (pulchra) Wing c? ? No. ' 18 ' 11 Range 52.9-59.2 51 .2-54 .3 X 55.36 52.14 SD. 1.348 O.696 Sx" 0.318 0.210 CT. 2.435 1.335 MAINLAND C? • 10 5 1 . 7 - 6 2 . 5 59.14 2.289 0.724 3.870 (insularis) 8 ' 5 2,9 - 5 8 . 0 5 5 . 0 6 1.529 0.541 2.777 T a i l No. Range X SD. Sx 0Y. 18 " 3 9 . 6 - 4 7 . 5 42.86 1.771 0.417 4 .132 ' 10 ' 38.8-42.2 40.20 1.067 0.337 2.654 4 3 . 8 - 5 3 . 7 5 0 . 4 8 1 .902 0.634 3 . 7 6 8 8 4 3 . 3 - 4 9 . 3 4 6 . 3 2 1 .434 O.507 3 .096 Tarsus No. " Range X SD. Sx 19 10 ••' 11 8 1 5 . 4 - 1 7 . 0 15.8-16.9 18.0-20.0 17.2-19.5 16.14 16.39 19.24 18.29 0 .270 0.344 0.404 0.597 0.062 0.109 0.122 0.211 1.673 2.099 2.100 3.264 B i l l Length No. 19 9 10 Range 7 . 2 - 8 . 1 7 .1-8 .3 7 . 0 - 8 . 2 X 7.68 7.79 7 .63 SD. 0.247 O.269 0;338 Sx 0.055 0 . 0 9 0 0.107 CY. 3.216 3 .453 4 . 4 3 0 " 8 ' 7 . 4 - 8 . 0 7 .69 0.215 0.076 2.796 III XSLANJ. . • 41 5 3 , 0 - 6 2 . 0 5 7 . 9 9 * 1.717 0 . 2 6 8 2 . 9 6 1 ( i n s u l a r i s ) ? 20 5 4 . 9 - 5 9 . 2 5 6 . 3 8 * 1.017 0 . 2 2 7 1 .804 36 44 . 9 - 5 3 . 1 4 9 . 1 5 * 1.537 0.256 3 . 2 2 9 39 1 8 . 1 - 2 0 . 1 19 .12* 0 . 4 0 9 O.O65 2.139 39 7 . 2 - 8 . 3 7.72 0.217 0 .035 2 . 8 1 1 19 4 5 . 9 - 5 0 . 2 4 8 . 1 1 * * 0.912 0 . 2 0 9 - I . 8 9 6 20 1 7 . 8 - 1 9 . 8 18.84* 0 . 3 9 9 O.089 2.118 20 7 . 1 - 8 . 2 7 .62 0.229 0 . 0 5 1 3 . 0 0 5 H -v>i TABLE 38 - continued I I I M A I N L A N D I S L A N D Goracoid d* ? cf ? No. • 3 1 1 Range 11 .4-11 .5 X 11 .43 1 0 . 5 1 0 . 4 Femur No. 2 - 1 1 Range 11 .1-11 .9 X. 11 .50 12.0 12 .1 MAINLAND I MAINLAND I I I S L A N D cf 9. Fresh Weight , Not Eat - Fat Unknown I*at Unknown No. • 6 1 • 2 .3 1 Range 7 . 0 - 8 . 0 6 . 9 - 7 . 7 6 . 9 - 7 . 3 x • ' 7 . 4 3 6 .4 7 . 3 0 7 .07 7.2 SD. 0.440 Sx 0.180 CV. 5.922 _ Weight after Freeze/Thawing No. •20 3 Range 5 . 0-8 . 1 5.2-6.7 X SD. Sx CV. 6.79 0.486 0.109 7.158 5 . 9 0 NB. A second placed against difference between Island an Island - Sample" "mean * indi cates and Mainland I I means. a 2-standard error Wing Adult cf No. 15 Range 5? .-7-63.1 t 61.59 SD. O.966 S x 0.249 CV. I . 5 6 8 TABLE M Measurements of Granatellus venustus, A- I N L A N D Adult £ Immature cf Immature 2 5 7 . 9 - 6 0 . 3 59 .18 0 . 8 0 2 0.267 1.355 5 8 . 3 - 6 2 . 5 5 9 . 8 3 1.572 0.642 2.627 5 4 . 8 - 5 9 . 8 5 7 . 3 0 T a i l No. 14 Range 6 5 . 6 - 7 4 . 5 X 7 0 . 0 9 SD. 2 .031 s x 0 . 5 4 3 CV. 2 . 8 9 8 6 4 . 8 - 7 1 . 6 67 .97 2.344 0 . 7 8 1 3.449 66.3-71.6 67.88 2.840 1.270 4.184 6 2 . 2-71 . 5 6 6 . 8 5 Tarsus No. 15 Range 1 8 . 7 - 2 0 . 8 X 19.73 SD. 0 .455 Sx 0.117 c v . 2.306 10 18.5-20.1 19.53 0.414 0.131 2.120 18.9-21.0 19.55 0.640 0.261 3.274 2 19.6 1 9 . 6 0 B i l l Length No. - 14 10 6 Range 8.0-9.5 8.1-^ 9.9 8.4-9.3 X 8.76 8.84 8 . 8 0 SD. 0.298 0.458 0 . 3 6 0 Sx 0.080 0.145 0.147 CV. 3.402 5.181 4.091 8.2-8.4 8 . 3 0 I S L A N D Adult cf Adult $ Imngturecf Immature % 18 12 6 3 63.4-67.9 6 1 . 7 - 6 4 . 5 6 3 . 2 - 6 5 . 1 62 .0-62 .7 6 6 . 0 3 * 6 3 . 2 8 * 6 4 . 1 7 * 6 2 . 3 0 0.906- O.745 0 .602 0.214 0 . 2 1 5 0.246 1 .372 1 .180 0 . 9 3 8 17 71.4-79.9 76.53* 1.871-0.454 2.445 12 7 0 . 7 - 7 6 . 7 7 4 . 1 7 * 1.229-0.355 1.657 74.3-78.8 75.66* 1.430 0.540 1.890 7 2 . 2 - 7 6 . 8 7 4 . 2 0 18 2 0 . 0 - 2 2 . 3 21 .22* 0.375-0 . 0 8 8 i;%9 13 2 0 . 8 - 2 1 . ! 2 1 . 2 3 * 0.226-O.O63 1 .063 8 2 0 . 4 - 2 1 . 8 21 .11* 0 . 3 4 3 0.121 1.625 4 20.8-21.9 21 .35 17 8 . 5 - 9 . 5 8 .98 0.232 O.056 2.584 12 8 . 5 - 9 . 3 -8.82 0.180 0 .052 2.041 8 . 6 - 9 . 3 8 . 9 0 0.200 0 .076 2.247 4 8.7 - 9 . 2 8 . 9 0 TABLE 39 - continued M A I N L A N D Coracoid No. Range X SD. Sx CV. Femur No. 9 7 Range 14.1-14.8 14.2-14.7 X 14.41 14.41 SD. 0.264 0.218 Sx 0.088 0.082 CV. 1.832 1.513 Adult cT Adult $ Immature d* Immature $ Fresh Weight " a) Not Fat No. 4 1 Range 1 0 . 2 - 1 1 . 3 X . 10.75 11.4 Fresh Weight h) Fat No. 2 3 Range 11.4 10.5-11.2 X 11.40 .. 10.93 Weight after Freeze/Thawing Fat Unknown No. 2 Range 9.6-10.2 X 9 .90 I S L A N D A l l d V 8 1 1 . 9 - 1 2 . 5 1 12 .15 0.214 0.076 1 .761 A H 5 1 . 8 - 1 2 . 1 11 .98 0 . 0 9 0 0.040 0 . 7 5 1 M r o TABLE 40 Measurements of Icterus pustulatus A I N L A N D Wing No. Adult o" 66 Range 91.9-105.5 86.1-97.0 X SD. S i GY. 96.22 1.662 0.205 1,727 90.71 2.216 0.455 2.445 Immature d" Immature $ 15 13 85.7-97.8 82.9-95.3 91.69 90.35 3.042 2.042 0.785 O.566 3.318 2.260 I S L A N D Adult d* Adult 9- Immatured* Immature $ 36 11 17 9 7 . 8 - 1 0 8 . 3 9 5 . 0 - 1 0 0 . 4 92 .2-104, 1 0 4 . 2 8 * 9 7 . 6 5 * 99.29* 1.489- 1.645- 2.352 0.248 0.496 0.570 1.428 1 .685 2.369 23 90.5-99.4 94.73* 2.093 0.436 2.209 T a i l No. 61 '17 ' 11 6 Range 76 .9-96 .0 7 4 . 2 - 8 9 . 8 7 5 . 9 - 8 7 . 4 7 9 . 2 - 8 6 . 7 X 84,61 81.23 79.46 82 .77 SD. 2.279 1.954 2 .518 3 .120 Sx 0.29 2 0 .474 0 .759 1.274 CY. 2.694 2.406 3 .169 3 .769 33 86.9-94.7 91.11* 1.770-0.308 1.943 11 79.5-89.7 85.65* 2.935-0.885 3 .427 13 8 1 . 1 - 8 9 . 8 8 6 . 0 0 * 2.700-0.749 3 .140 15 78.4-86.9 83.77 1.592 0.411 1.900 Tarsus No. 66 25 28 22 35 10 20 25 Range 23,3-26.,9 23.4-25.9 23.8-26.1 23.3-26.4 24.7-28.3 25.1-26.4 25.1-27.8 24 .4-27.0 X 24.96 24.76 25.12 24.89 26.48* 25.77* 26.36* 25.90* SD. 0.575 0.535 O.656 0.437 0.645, 0.307- 0 . 4 4 9 - 0.462 Sx 0.071 0.107 0.124 0.093 0.109 0.097 0.100 0.092 CV. 2.304 2.161 2.611 1.756 2.436 1.191 1.703 1.784 B i l l Length No. 66 24 27 23 32 10 19 24 Range 13.8-16.8 13.5-16 .9 1 2 . 8 - 1 5 . 9 13 .5 -16 . 3 1 5 . 5 - 1 9 . 2 15 .6-17 .5 16.7-I8.5 1 5 . 5 - 1 8 . 8 X 14 .78 14 .89 14.67 14.58 17 .32* 1 6 . 6 6 * 1 7 . 2 0 * 1 7 . 0 0 * SD. 0 .474 0 .625 0.530 0.465 0 .735- 0 .644- 0 .378- O.670 Sx 0 ,058 0 .128 0 .102 0.097 0.130 0 .204 0.087 0.137 c v . 3.207 4 .197 3 .613 3 .189 4 . 2 4 4 3 .866 2.198 3 . 9 4 1 TABLE 4 0 - continued M A I N L A N D-Adult cf f d u l t ? Immature cf Immature ? Adult cf Adult ? Immature cf Immature B i l l Width No. 5 4 Range 4 . 7 - 5 . 6 X 5.03 SD. 0 . 1 7 6 Sx 0.024 CV. 3.499 2 2 4.6-5.4 4 . 9 6 0.175 0 . 0 3 7 3 . 5 2 8 25 4.6-5.6 5.03 0 . 2 0 3 0.041 4 . 0 3 6 19 4.5-5.2 4.91 0.141 0 . 0 3 2 2 . 8 7 2 2 3 8 4 . 8 - 5 . 9 5.3-5.7 5.41* 5.41* 0.255- 0 . 1 0 6 0 . 0 5 3 O .037 4 . 7 1 3 1.959 1 6 5 . 1-5 .8 5 . 3 6 * O . 163 0.041 3.041 1 9 5 . 2 - 6 . 0 5 . 4 8 * 0 . 2 0 8 0 . 0 4 8 3 . 7 9 6 Coracoid A 1 1 6 V A l l ? ? Allcfcf A l l ? ? No. Range X SD. Sx CV. 42 18.2-21.2 19.88 0 . 5 4 8 0 . 0 8 5 2.757 2 5 1 8 . 4 - 2 0 . 4 19.28 0.442 0.088 2 . 2 9 3 9 I 8 . 2 - 1 9 . 3 18 .87* 0 . 3 8 6 -0 . 1 2 9 2 . 0 4 6 7 1 7 . 9 - 1 8 . 6 1 8 . 2 3 * 0 . 2 9 5 0 . 1 1 1 1.618 Femur No. Range X SD. Sx CV. 4 3 20.5-23.3 2 1 . 9 2 0 . 5 3 6 0 . 0 8 2 2 . 4 4 5 25 19 .4-22.6 2 1 . 4 9 0 . 4 8 7 0.099 2.266 9 1 9 . 3 - 2 2.7 2 1 . 8 3 0 . 8 0 1 0 . 2 6 7 3 . 6 6 9 1 0 2 1 . 3 - 2 2 . 9 2 1 . 9 0 0 . 4 8 9 0 . 1 5 5 2 . 2 3 3 Fresh Weight a) Not Fat No. Range 2 SD. Sx CV. 25 36.1-41.6 38 .48 1 . 1 0 7 0 . 2 2 1 2.877 13 31.8-40.6 3 6 . 3 5 2 . 3 5 4 0 . 6 5 3 6.476 3 33.9-38.9 3 6 . 8 7 t—1 145 TABLE 40 - c o n t i n u e d M A I N L A N D I S L A N D F r e s h W e i g h t b) F a t ? N o . 1 2 7 3 R a n g e 33.9-35.7 3 8 . 1 -40 . 3 37.2-40.5 X 32.3 34.80 38.64 38.93 S D . 1.610 S x 0.608 G V . 4.167 W e i g h t a f t e r F r e e z e / T h a w i n g N o t F a t F a t Unknown N o . 15 6 14 12 R a n g e 3 1 . 0 -41 . 0 32.0-37.8 33.2-39.4 29.0-38.5 X 37.29 35.13 36.78 34.64 S D . 2.085 2.120 1.857 1.918 S x 0.538 0.866 0.496 0.554 GV. 5.591 6.035 5 . 0 4 9 5.537 W e i g h t a f t e r F r e e z e / T h a w i n g F a t N o . 1 3 R a n g e 34.0-37.0 X 4 1 . 0 35.57 TABLE 41 Measurements of Piranga bidentata M A I N L-A N D I S L A N D Wins; Adult d* Adult ? Immature d* Adult d" Adult £ Immature cT No. 24 17 4 23 21 2 Range 94.3-103 .7 90 .3-104 .2 94 . 3 -97 . 8 9 4 . 4 - 1 0 1 . 1 : 8 9 . 4 - 9 6 . 3 92 .8 -93 .4 X 99.01 94.65 95.62 97.66* 93.46 93.10 SD. 1.713 2.367 1.376 1.627 Sx 0.350 0.592 0.287 0.355 CV. 1.732 2.501 1.409 1.741 T a i l No. •23 17 4 22 1-8 ' 2 Range 77.6-^84.8 7 5 . 2 - 9 6 . 6 7 2 . 7 - 7 8.I 78.7-83.9 . 75.0-82.3 77.1-77.3 X 8 I . 9 4 80.42 76.55 81.33 78.68 77.20 St). 1.587 3.695 1.454 1.649 SX 0.331 0;924 0.310 O.389 cv.. 1.937 4.595 1.788 2.096 Tarsus No. •25 18 ' 5 "24 21 3 Range 19.7-?23.0 19.1-22 .8 1 9 . 6 - 2 1 . 5 21.4-22 .8 20.0^23 .8 21 .9-22 .7 2. ' 20.89 20.88 20.82 22.17* 22.02* 22.23 SD. 0.392 0.715' 0.622 O.363 0.610 Sx' 0.078 o;i73 0.278 0.074 0.133 CV. 1.876 3.424 2.987 1.637 2.770 B i l l Length No. '24 18 4 23 - • 2 1 3 Range 12.1-14.3 12.0-14.3 13.2 -13.6 13. 0-"-14.1 12.7^14.3 12.7-13.9 X " 13.24 1 3 . 3 1 13.45 1 3 . 6 5 * 13 .60 13.23 SD. 0.530 0.498 0.270 0.460 SX 0.108 0:121 O.O56 0.131 CV. 4 . 0 0 3 3.742 1.978 3.382 TABLE 41 - continued . _ M A I N.L-A N D I S L A N D B i l l Width Adult cf Adult £ Immature cf Adult cf Adult $ Immature cf No. 18 •• '13 ' 5 15 16 1 Range 7.2-8.5 7.5-8.1 7.3-7.8 8 . 2-9 . 0 8 . 2-9 . 0 X ' 7.79 7 .92 7.62 8.57* 8 . 5 2 * 8.4 sb. 0,265 0.107 0 . 2 2 0 0.154 • 0 . 2 0 5 SX' 0 , 0 6 2 0 . 0 3 0 0.098 0.040 0 . 0 5 1 CY, - 5.402 1 .351 2.887 1.797 2.406 Coracoid No. 6 ' ' 11 " 1 2 6 Range 19.0-19.8 1 8 .6 - 2 0 . 1 19 . 2-19 . 4 18 . 1-19 . 0 t 19.55 19.37 19.6 19 . 3 0 1 8 . 4 5 * sb. 0 . 3 2 0 0.453 •0.280 SX 0.131 0.137 ,0.114 CY. l.b37 2.339 1.518 lemur No. 5 9 1 3 6 Range 20 . ,3-20.6 1 9 . 8 - 2 0 . 9 20.7-21.6 19.8-20.9 X ' 20.42 2 0 . 2 9 19.8 21.13 2 0 . 4 3 sb. 0:130 0 . 2 9 1 O.36O Sx' 0.058 0 .097 0.147 CY. O.636 1.434 I . 7 6 2 Eresh Weight Not Eat Eat Unknown No. 8 ' 7 3 Range 33.O-36.6 33.1-39.4 32.0-38.4 X ' 3 4 . 5 4 3 4 . 4 7 35 . 2 0 sb. 1.357 1.785 sx 0.480 0.675 CY. 3.929 5 .178 148 F r e s h W e i g h t No. Range X TABLE 41 - continued M A I N L A N D I S L A N D Adult c? Ad u l t ? Fat 1 3 3 3 . 0 - 3 8 . 5 3 9 . 2 36.47 Weight after Freeze/Thawing No. Range X SD. Sx C V . Fat Unknown 8 8 32.0-48.4 32.6-37.8 38.84 35.17 4.751 1.457 1.680 O.515 12 .23 4.143 Wing No. Range X SD Sx CV. A d u l t cf A d u l t % 25 6 5 . 7 - 6 8 . 0 6 6 . 0 7 1.116 0 . 2 2 3 1.689 14 6 I . 8 - 6 5 . 6 6 3 . 8 3 0 .838 0.224 1.313 N D Immature cf Immature 2 4 6 1 b Adult cf Adult $ Immature cf Immature? 6 3 . 1 - 6 6 . 4 6 5 . 4 7 6 1 . 3 - 6 3 . 8 6 2 . 6 8 0.984 0 .402 1 . 570 26 6 0 . 3 - 6 5 . 0 6 2 . 9 8 * 1 .006 0.197 1.597 13 5 8 . 5 - 6 4 . 0 6 1 . 4 2 * 1.130 0 .313 1 . 840 5 8 . 4 - 6 2 . 0 6 1 . 0 1 0 .836 0 . 2 7 9 1 .370 10 5 9 . 2 - 6 4 . 0 61 . 12 1.382 0 . 4 3 7 2 . 2 6 1 T a i l No. 20 13 4 5 24 13 10 8 Range 40 . 2 - 4 6 . 9 39.3-44 .2 4 1 . 6 - 4 3 . 9 39.4-41.7 3 8 . 3 - 4 3 . 6 38.4-41 . 7 37.2-40 .7 3 8 . 5-40 . 3 X 42 .87 4 1 . 9 0 4 3 . 0 0 40.46 41.21* 40 .10* 3 9 . 3 3 3 9 . 5 7 SD. 1.358 1.525 1 .010 0.869- 0.850- 1 . 0 0 9 0.543 Sx 0 . 3 0 4 " 0 . 4 2 3 0.452 0.177 0 .236 0.319 O.192 CV. 3.168 3 . 6 4 0 2.496 2.1Q9 2 .120 2 .565 1 .372 Tarsus No. 25 . 14 3 8 26 15 10 9 Range 1 1 . 3 - 1 3 . 1 1 1 . 4 - 1 2 . 6 1 1 . 9 - 1 2 . 0 1 1 . 4 - 1 2 . 2 1 1 . 3 - 1 3 . 2 1 1 . 3 - 1 3 . 0 1 1 . 1 - 1 2 . 8 1 1 . 8 - 1 2 . 9 x 12 .03 11 .98 11 .93 11.86 1 2 . 2 3 1 2 . 3 9 1 2 . 1 0 1 2 . 4 0 * SD. 0 . 3 H 0 . 3 0 3 0 . 243 0 . 3 3 4 0.474 0 . 5 8 2 0.275 Sx 0 . 0 6 2 0 . 0 8 1 0 . 0 8 6 0 . 0 6 6 0 . 1 3 1 0 .184 0 . 0 9 2 CV. 2 .585 2.529 2 .049 2.731 3 . 8 2 6 4 . 8 1 0 2 .218 B i l l length No. - 23 4 7 26 13 10 6 Range 7 . 3 - 8 . 6 7 . 0 - 8 . 6 7 . 2 - 8 . 3 7 . 1 - 8 . 6 7 . 1 - 7 . 5 6 . 8 - 7 . 8 6 . 9 - 7 . 6 7 . 0 - 7 . 3 X 8 . 10 7 .71 7 . 8 0 7 . 8 0 7 . 5 2 * 7.18* 7 . 28 7 .18* SD. O.309 0 . 3 0 1 0 . 400 0.125- O.163- 0.222 0.108 Sx 0 .064 0.083 0.151 0 .025 0 . 045 0 . 0 7 0 0 . 044 c v . 3 .815 3 . 9 0 4 5 .128 1 .708 2 . 2 7 0 3 . 049 1 .504 TABLE 42 - continued A I N L A N D Adult d1 Adult $ Immatur ecf I m m a j b u r e ? B i l l Width No. Range X SD. Sx 23 4 .2-4 .8 4 . 3 0 0.159 0 . 0 3 3 14 4.2-4.9 4 .51 0 .163 0.044 4.2-4.5 4.42 8 4.1-4.7 4.40 0.171 0 . 0 6 0 3 .886 I S L A N D Adult Adult? iKuasturecTjjmmature? 22 3 . 9 - 4 . 3 4 . 0 6 * 0 . 0 7 5 0.016 1 .847 11 3.7-4.3 3.99* 0.143 0.043 3.584 3 . 9 - 4 . 1 4 . 0 1 0 . 0 6 6 0 . 0 2 2 1 .651 8 3 . 9-4 . 1 4.04* 0.071 0 . 0 2 5 1.757 Coracoid Mldtf A l l ? ? A l l d V All?£ No. 11 5 4 6 Range 13.9-13.9 12.8-13.3 12.2-13.0 11.7-12.5 X 13.44 13.10 12 .45 12.18* SD. 0 .176 0.200 0.328 Sx 0 .053 0.089 0.134 OV. 1 .310 1 .527 2.693 Femur No. 12 6 3 4 Range 11.3-12.3 1 1 . 3 - 1 2 . 0 11.1-12.2 11.3-11.9 X 11.74 11 .70 11 .67 11.55 SD. 0.224 0.200 Sx 0*065 0*082 GY. 1.908 1 .709 V n N o . Range X 4 9 . 5 - 1 0 . 8 1 0 . 0 2 8 . 1 Fresh Weight b) Fat No. 2 1 Range 1 0 . 3 - 1 0 . 7 X 1 0 . 5 0 9.6 Weight a f t e r Freeze/Thawing No. Range X . SD. S i . CV. 8 . 5 - 9 . 9 9 . 0 3 3 8 . 6 - 9 . 6 9 . 0 7 16 6 . 0 - 9 . 0 8.16 0.589 0.147 7.218 13 6 . 4 - 8 . 6 7 . 9 1 0.556 0 .219 7 . 0 2 9 T i 152 TABLE 43 Measurements of Richmondena oardinalis M A I N L A N D I S L A N D Has <r ? d* I No. 9 6 32 29 Rang- : . o - 9 3 . 8 8 7 . 8 - 9 2 . 1 9 0 . 9 - 9 9 . 0 8 7 . 9 - 9 4 . 9 X 91 .04 89.93 94 .98* 91 .66 SD. 2.095 I . 3 6 0 1 .546 1.779 Sx O.698 0.555 0 .273 0 .330 CV. 2.301 1.519 1 .628 1.941 T a i l No. 4 6 24 18 Rang- : . 1 - 1 0 6 . 7 9 7 . 7 - 1 0 4 . 4 8 9 . 5 - 1 0 1 . 6 8 8 . 0 - 9 7 . 3 X 101.90 1 0 0 . 5 0 96.68 9 3 . 0 8 * SD. 2 . 2 8 0 2 . 6 8 1 1.929 s s 0 .931 0.547 0.455 c v . 2 . 2 7 0 2.773 2 . 0 7 2 Tarsi; No. 8 6 35 29 Range .'• ' . . 3 - 2 5 . 6 2 5 . 1 - 2 6 . 3 2 5 . 7 - 2 9 . 7 2 5 . 2 - 2 8 . 9 X 2 5 . 1 0 2 5 . 4 3 28 .14* 2 7 . 3 9 * SD. 0.371 0.412 0.686 0 .819 Sx 0.131 0 .168 0 .116 0 .155 CV. 1 .478 1 . 6 2 0 2 .438 2 .990 B i l l . Length No. 8 6 35 30 Range 1 2 . 2 -15 . 2 1 2 . 8 - 1 4 . 1 1 2 . 7 - 1 5 . 8 1 2 . 7 - 1 5 . 4 X 13.21 13.47 14 .27* 13.87 SD. 0 . 649 0 .540 0.424 0 .534 Sx 0.229 0 .220 0 .072 0.099 CV. 4 . 9 1 3 4 . 0 0 9 2.971 3 . 8 5 0 153 TABLE 43 - continued B m J V l d t h <? J cf ? Ho.. 8 6 23 23 Range. 8 . 3 - 8 . 7 8 . 2 - 8 . 6 8 . 6 - 1 0 . 0 8 . 5 - 9 . 8 X 8 .52 8 . 3 5 9 . 2 7 * 9 . 0 0 * SD. 0.126 0.140 0.277 0.245 SX 0.045 0 .057 0 . 0 5 8 0.051 CV. 1 .479 1.677 2 .988 2.722 Coragold No. 1 Range X 18.8 femur No. 6 Range 21.0-22.6 X 2 1 . 9 0 SD. O.56O SX 0 .229 GV. 2 .557 fresh Weight a) f a t No. 1 Range X 59.1 Weight after Freeze/Thawing fat Unknown No. 9 12 Range 33-8-41 .5 29.1-41 .2 1 • 38 .29 35-25 SD. 2 .191 3 . 1 0 0 Sx 0.730 0.895 CV. 5-722 8.794 154 T A B L E 44 W e i g h t s o f s p e c i m e n s c o l l e c t e d a t T e p i c . N a y e r i t . i n M a r c h 1 9 6 3 . SPECIMENS Myiopagis v i r i d i c a t a i.le la n o t i s o a e r u l e s c e n s V e r m i v o r a c e l a t a P l a t y p s a r i s a g l a i a e L ' i t r e p h a n e s p h a e o c e r c u s Thryothorus s i n a l o a Thryothorus f e l i x Thryothorus f e l i x 113lanot is o a e r u l e s c e n s Melanotis o a e r u l e s c e n s Myadestes o b s c u r u s Basileuterus r u f i f r o n s Melospiza l i n c o l n i i C h a n g e i n w e i g h t , b e t w e e n f i r s t and l a s t w e i g h i n g , i n gms . A f t e r 3 - 4 h o u r s A f t e r 4 - 5 hours •0.2 •0.1 •0.1 0 -0.1 - 0 . 4 - 0 . 4 - 0 . 4 - 0 . 2 - 0 . 2 0 -0.1 -0.1 Specimens f i r s t w e i g h e d w i t h i n h a l f - a n - h o u r o f c o l l e c t i o n . • TABLE 4 5 Weights of birds before, and after, freezing and thawing. Date Time Time Fresh Weight after Change i n Weight Collected Collected Weighed Weight Freezing & Thawing . Specimen Piranga bidentata ? 18 March 1 7 1 5 hrs. 1 9 0 5 hrs. 3 5 . 2 gms 3 4 , 3 - 0 . 9 gms Empidonax d i f f i c i l i s 2 n 1 7 2 0 1 9 0 5 1 1 , 1 1 0 , 8 - 0 . 3 Parula pit iayumi 2 it 1 7 3 0 1900 7 , 2 6 , 7 - 0 . 5 Myiarchus tuberculifer cf n 1800 1 8 5 3 12 . 9 12 . 5 - 0 . 4 Myiarchus tuberculifer cf n 1 8 0 0 1900 1 1 . 4 1 1 , 0 - 0 . 4 Myiarchus tuberculifer cf r» 1 8 0 0 1 9 0 0 1 1 , 7 1 1 , 4 - 0 . 3 Thryothorus f e l i x cf 1 9 March 1 5 3 0 1 8 1 0 1 4 . 6 - 1 4 , 6 0 Seirus noveboracensis cf n 1 1 4 0 1 8 1 0 1 5 . 5 1 5 . 6 + 0 . 1 Piranga bidentata °_ tr 1 3 4 0 1 8 1 0 3 2 . 0 3 2 . 6 + 0 . 6 Piranga bidentata? t» 1310 1 8 2 5 3 8 . 4 3 7 . 8 - 0 . 6 Specimens were collected on Maria 1 agdalena , 18 - 19 March 1 9 6 3 , and weighed before being frozen (data supplied by P.A. Lsrkin): later they were weighed immediately.after thawing s 25 A p r i l - 2 May, 1963 (L. Witt), Vn Vn TABLE 46 Measurements of the tibio-tarsus of Icterus pustulatus MAINLAND ISLAND No, 10 10 Range 32 . 9- 37 . 7 35 . 0- 37 .2 X 35.63 36.15 SX 0.418 0.218 % Difference between means 1,5 % Difference calculated as in Table 3 . 157 FIGURE 7 D i a g r a m , o f D i f f e r e n c e s I . A c o m p a r i s o n o f t h e d i f f e r e n c e s , b e t w e e n t h e mean v a l u e s , o f t h e f o u r p r i n c i p a l m e a s u r e m e n t s , negative Positive W i n g Mean p o s i t i o n + 1 .091 20 15 1 0 - 5 5 + 1 0 15 20 T a i l Mean p o s i t i o n + 1 , 4 7 4 20 15 1 0 - 5 5 + 1 0 15 20 T a r s u s Mean p o s i t i o n + 5.118 15 10 - 5 5 + 1 0 15 20 B i l l - l e n g t h 20 15 Mean p o s i t i o n + 3.458 1 0 - 5 5 + 1 0 15 20 Data taken f r o m T a b l e 3. Each d i f f e r e n c e , b e t w e e n a m a i n l a n d and i s l a n d mean v a l u e o f a m e a s u r e m e n t , i s e x p r e s s e d J a s a p e r c e n t a g e o f t h e m a i n l a n d mean . F I G U R E 8 158 D i a g r a m of Differences I I , A comparison of the differences between island and mainland bill-lengths and bill-widths of five species. B i l l -w i d t h r -20 + .20 + [10 -10 P I • I 10 120 B i l l - l e n g t h Data t a k e n f r o m T a b l e 3 I - I c t e r u s pus t u l a t u s R, - R i c h m o n d e n a c a r d i n a l i s P P i r a n g a b i d e n t a t a P I = P l a t y p s a r l s a g l a i a e S = S p i n u s p s a l t r i a P • % + 1 0 • 20 159 A P P E N D I X I I T a x o n o m i c r e m a r k s u p o n t h e i s l a n d p o p u l a t i o n s . I n t h i s A p p e n d i x i t i s shown w h e r e t h e r e s u l t s o f t h e p r e s e n t s t u d y d i f f e r f r o m t h o s e o f p r e v i o u s w o r k e r s . M u c h o f t h e d e s c r i p t i v e d e t a i l o f t h e s p e c i m e n s i s t o "be f o u n d i n C h a p t e r 1 , a n d i s o n l y s u m m a r i z e d h e r e . T h e - u n e v e n t r e a t m e n t g i v e n t o t h e s p e c i e s i s i n p r o p o r t i o n t o t h e i r t a x o n o m i c c o n f u s i o n and t h e c o m p l e x i t y o f d e s c r i p t i o n . M o r p h o l o g i c a l c h a r a c t e r s h a v e b e e n u s e d i n d i v i d u a l l y , and t h e c r i t e r i a s u g g e s t e d b y Amadon ( 1 9 4 9 ) h a v e b e e n e m p l o y e d f o r t h e r e c o g n i t i o n o f s u b s p e c i e s . U s u a l l y a 15% s e p a r a t i o n o f one p o p u l a t i o n f r o m 100% o f t h e o t h e r h a s b e e n s o u g h t . I n s e v e r a l i n s t a n o e s , a d i f f e r e n c e i n t h e s t a n d a r d d e v i a t i o n s o f t h e t w o s a m p l e s h a s l e d t o p a r t i a l s e p a r a t i o n o n l y ; t o t h e s e , t h e f o r m u l a f o r s e p a r a t i n g 91% o f one f r o m 91% o f t h e o t h e r h a s "been a p p l i e d . The t e r m " t a x o n o m i c c r i t e r i o n " h a s b e e n u s e d t o r e f e r t o one o r t h e o t h e r m e t h o d o f s e p a r a t i n g t w o s a m p l e s . 16 0 Platypsaris aglaiae i n s u l a r i s (Mainland ssp. alblventrls) In Ridgway's diagnosis of the island subspecies (1887), i t was stated that the male wing and b i l l (length) were smaller than those of mainland males, and that females were "smaller" too, the b i l l being d i s t i n c t l y so. However these differences are below the level at which separate subspecies are now recognized. Island adult males are characterized by a grey chin, this being whitish i n mainland counterparts. Immature males and adult females have the same t a i l pattern. On mainland specimens a bright cinnamon colour covers at least the majority of the inner vane of the outer, f i v e , grey-brown r e c t r i c e s , and sometimes the whole area of the feathers, whereas on the t a i l s of island specimens the cinnamon is r e s t r i c t e d to the edge of the inner vane. The b i l l of island birds is smaller, but only b i l l -width of female specimens meets the required taxonomic c r i t e r i o n . The heaviest, fat insularis specimens, of both sexes, are lighter than the li g h t e s t , not-fat albiventris specimens: the sample sizes are small, but this strongly suggests that island birds are li g h t e r than mainland ones, and this may prove to be useful taxonomically. Webster (1963) has referred to the presence of some rose on the throat of the female as being a f a i r l y common variation, and also noted some examples of sex-reversal of plumage. No evidence, of either characteristic, i s provided by the specimens collected by the author and members of the l 6 l U n i v e r s i t y o f B r i t i s h C o l u m b i a ( M a i n l a n d 30 s p e c i m e n s : i s l a n d 28 s p e c i m e n s ) . T y r a n n u s m e l a n e h o l i o u s o c c i d e n t a l i s a n d M y i a r c h u s t y r a n n u l us m a g i s t e r No i n s u l a r s u b s p e c i e s h a v e b e e n , o r a r e , r e c o g n i z e d f o r t h e s e t w o s p e c i e s . M y i a r c h u s t u b e r c u l i f e r o l i v a s c e n s ( f o r m e r l y , i s l a n d s s p . t r e s m a r i a e ) On t h e P a c i f i c , c o a s t a l m a i n l a n d two s u b s p e c i e s o c c u r , o l i v a s c e n s i n t h e n o r t h and q u e r u l u s i n t h e s o u t h . N e l s o n ( 1 9 0 4 ) d e s c r i b e d t h e i s l a n d p o p u l a t i o n a s a n o t h e r s u b s p e c i e s , u s i n g two m a l e a n d s e v e n f e m a l e s p e c i m e n s . The sub s p e c i f i c c h a r a c t e r s w e r e c o n s i d e r e d t o be t h e f o l l o w i n g : -a ) S l i g h t b u f f y b o r d e r s o n i n n e r w e b s o f i n n e r t a i l f e a t h e r s ( r e c t r i o e s 2 - 6 ) . b ) B i l l p r o p o r t i o n a t e l y l o n g e r and b r o a d e r t h a n i n o l i v a s c e n s . He a d d e d t h a t t h i s was t h e g r e y e s t f o r m o f t h e s u b s p e c i e s , t h a t t h e c h i n , t h r o a t and b r e a s t w e r e o f a d u l l e r , more a s h - g r e y c o l o u r t h a n i n o l i v a s c e n s . and c o n c l u d e d t h a t "The p r e s e n t f o r m o n l y n e e d s c o m p a r i s o n w i t h o l i v a s c e n s f r o m w h i c h i t i s e a s i l y d i s t i n g u i s h e d by t h e c h a r a c t e r s m e n t i o n e d . " B u t R i d g w a y (1907) p u b l i s h e d t h e d i s t r i b u t i o n o f t h e two c o a s t a l s u b s p e c i e s , b a s e d u p o n c o l l e c t e d s p e c i m e n s , w h i c h i n d i c a t e d t h e b r e e d i n g r a n g e o f p l i v a s o e n s t o be f r o m S i n a l o a n o r t h w a r d s , and o f q u e r u l u s t o be f r o m s o u t h e r n S i n a l o a s o u t h w a r d s . A c c o r d i n g t o t h i s t h e s o u t h e r n l i m i t o f t h e d i s t r i b u t i o n o f o l i v a s c e n s i s a p p r o x i m a t e l y one and a h a l f degrees of latitude north of the Tres Marias islands (see Fig . l ) , hence birds from the latter should have been compared more properly with specimens of querulus. A further complication is that specimens collected subsequently from Nayarit, have usually defied the efforts of their collectors to classify them, and have been given both subspecific names on each label. The population of Myiarchus tuberculifer in the mainland study area is apparently a continuous one, there being no obvious topographical or vegetational barriers hindering the movement of individuals. Furthermore, morphological variation within the sample of specimens is of a graded nature. For these two reasons island specimens were compared with a l l mainland specimens collected in the study area, regardless of the name on the label. The latter w i l l be referred to as the mainland population or sample. Cri t i c a l plumage comparisons were made with specimens collected in the past three years, but the conclusions reached were supported by the evidence from older specimens, Kelson's comments (above), upon a difference in colour of chin, throat and breast between mainland and island . populations, were not verified. An examination of the t a i l pattern revealed a difference in the number and proportion in each sample of individuals with a broadly cinnamon (buff)-edged t a i l . In the mainland sample of eighty specimens only six were so patterned, a l l collected in the months of July, August and September. In 16? the colour of the wing coverts and the nature of the body plumage some of them show traces of juvenal plumage, because of which they are described here as being in immature plumage. The island sample, mainly collected between February and May, contains a high proportion of these immatures; specimens in adult and immature plumage, collected in these months in both regions, are listed in Table 4? , The difference between the groups of the contribution made by Immature birds is obvious at a glance. But, whatever the reason for this difference may be, the t a i l pattern cannot be used as diagnostic of the island population. According to Nelson (loc.cit.), island specimens are greyer dorsally, than a l l mainland specimens, and are particularly distinct from specimens of olivascens. In this study six Sinaloa specimens were more olivaceous, or greener, dorsally than island specimens. The dorsal colouring of the specimens from the islands and Jalisco is either brown or intermediate between brown and olivaceous, never olivaoeous i t s e l f . The whole brown to olivaoeous range of colouring was exhibited by the group of birds collected in Nayarit. Considering a l l the mainland specimens together, or just the Nayarit ones alone, not even half of them were distinguishable from the Island specimens, so this plumage characteristic cannot be used diagnostically either. There is no difference between the measurements of mainland and island birds. The width of the b i l l was not measured, but no difference was apparent: certainly there is 164 TABLE 47 The sex and plumage of specimens of Myiarchus tuberoullfer. oolleoted in the months February to May. M A I N L A N D I S L A N D cf ? cf S Adult 14 11 13 26 Immature 0 0 15 8 Xtest applied to Island Immature $2 = 161.33 dfr P<0,001 NB. The test derived an expected value from the known values for Island Adult and Immature and Adult 165 no d i f f e r e n c e i n i t s l e n g t h ( T a b l e 3 ) . The c l i n a l n a t u r e o f p l u m a g e - c o l o u r v a r i a t i o n i n t h e s t a t e o f N a y a r i t h a s l e d t o t a x o n o m i c c o n f u s i o n , w h i c h o n l y a more c o m p r e h e n s i v e s t u d y o f t h e m a i n l a n d p o p u l a t i o n , t h r o u g h o u t i t s o l i v e s o e n s - q u e r u l u s r a n g e , c a n r e m o v e . I t i s t h e r e f o r e r e c o m m e n d e d t h a t t h e o r i g i n a l s u b s p e c i f i c name, o l i v a s c e n s ( R I d g w a y 1 8 8 4 ) be a p p l i e d t o a l l m a i n l a n d a n d i s l a n d s p e c i m e n s u n t i l s u c h s t u d y i s u n d e r t a k e n . M y i o p a g i s v i r i d i c a t a m i n i m a ( M a i n l a n d s s p . j a l i s o e n s i s ) The i s l a n d s u b s p e c i e s was o r i g i n a l l y d e s c r i b e d ( N e l s o n , 1898) a s b e i n g g r e y e r t h a n m a i n l a n d b i r d s , e s p e c i a l l y o n t h e t o p o f t h e h e a d a n d n e c k . H o w e v e r , no p l u m a g e d i f f e r e n c e s , b e t w e e n m a i n l a n d a n d i s l a n d b i r d s , w e r e f o u n d i n t h i s s t u d y . The i s l a n d s u b s p e c i e s was g i v e n t h e name m i n i m a . b e c a u s e o f t h e s u p p o s e d l y s h o r t e r w i n g and t a i l , b u t m a i n l a n d -i s l a n d d i f f e r e n c e s a r e s m a l l ( T a b l e 29). L a r g e - w i n g e d s p e c i m e n s h a v e b e e n c o l l e c t e d on t h e i s l a n d s and r e f e r r e d t o a s m a i n l a n d b i r d s ( N e l s o n l o c . c i t ; Bond and de S c h a u e n s e e 1 9 4 4 ) ; b u t t h e i r m e a s u r e m e n t s f a l l w i t h i n t h e r a n g e o f m e a s u r e m e n t s o f o t h e r i s l a n d b i r d s . C o n f u s i o n h a s o b v i o u s l y a r i s e n b e c a u s e i n s u f f i c i e n t i n a t e r i a l w a s a v a i l a b l e f o r a p r o p e r s t u d y . The o n l y s i g n i f i c a n t d i f f e r e n c e I s i n t a r s u s - l e n g t h , b u t i t i s n o t S u f f i c i e n t t o meet t h e t a x o n o m i c c r i t e r i o n . A c l e a r d i f f e r e n c e e x i s t s b e t w e e n t h e p o p u l a t i o n s i n b o d y w e i g h t . A s a m p l e o f s i x w e i g h t s o f f a t , i s l a n d b i r d s a p p r o a c h e s t o no more t h a n 0 .5 g m . , a s a m p l e o f f o u r t e e n w e i g h t s 166 o f n o t - f a t , m a i n l a n d b i r d s ( T a b l e 2,9') , The d i f f e r e n c e w o u l d p r o b a b l y be g r e a t e r i f f a t - f r e e b i r d s f r o m b o t h r e g i o n s w e r e c o m p a r e d . The c o r a c o i d s o f i s l a n d b i r d s a r e a l s o , s i g n i f i c a n t l y , s m a l l e r t h a n t h o s e o f m a i n l a n d b i r d s . The s u b s p e c i f i c d i s t i n c t i o n o f t h e i s l a n d p o p u l a t i o n i s u p h e l d o n t h e b a s i s o f t h i s e v i d e n c e . C a m p t o s t o m a i m b e r b e i m b e r b e . T h i s s p e c i e s h a s r a r e l y b e e n c o l l e c t e d o n t h e i s l a n d s , a n d was o n l y f o u n d t o b e r e s i d e n t i n 1963 ( G r a n t and Gowan 1 9 6 4 ) . The s m a l l amount o f m a t e r i a l g i v e s no i n d i c a t i o n o f a n i m p o r t a n t d i f f e r e n c e e x i s t i n g b e t w e e n m a i n l a n d and i s l a n d p o p u l a t i o n s . T h r y o t h o r u s f e l i x l a u r e n o i i ( M a i n l a n d s s p . p a l l i d u s ) The i s l a n d s u b s p e c i e s i s d i s t i n g u i s h e d f r o m m a i n l a n d b i r d s by t h e p o s s e s s i o n o f w h i t e , and n o t r u f o u s , u n d e r p a r t s , a n d s m a l l e r b l a c k s t r e a k s o n t h e f a c e . R i d g w a y (1878) a l s o m e n t i o n s t h a t i s l a n d b i r d s h a v e p a l e r r u f o u s f l a n k s , t h e u n d e r -t a i l c o v e r t s a r e l e s s b a r r e d a n d t h e b a c k i s g r e y e r . The f i r s t two o f R i d g w a y ' s c h a r a c t e r s a p p l y t o a f e w s p e c i m e n s o n l y , and t h e t h i r d i s i n c o r r e c t . The b i l l i s c o n s i d e r a b l y l o n g e r i n t h e i s l a n d b i r d , b u t o n l y t h e f e m a l e s a m p l e s meet t h e t a x o n o m i c c r i t e r i o n . T h e . i n a d e q u a t e w e i g h t d a t a s u g g e s t t h a t m a i n l a n d b i r d s a r e m a r k e d l y h e a v i e r t h a n i s l a n d b i r d s . T h i s may p r o v e t o be a u s e f u l t a x o n o m i c c h a r a c t e r when more d a t a a r e a v a i l a b l e . M e l a n o t i s c a e r u l e s c e n s c a e r u l e s c e n s . ( F o r m e r l y , i s l a n d s s p . l o n g i r o s t r i s ) . N e l s o n (I898) d e s c r i b e d an i n s u l a r s u b s p e c i e s on t h e b a s i s o f p a l e r c o l o u r , s m a l l e r s i z e and l a r g e r b i l l . A tendency 16? towards paleness does exist, but this character was found to separate less than half of the island birds from mainland ones. The main size-differences of exposed parts affect t a i l - and b i l l - l e n g t h (Table 3 2 0 • The taxonomic c r i t e r i o n is most closely approached by the b i l l s of female specimens, but is not met by any. The weight and coracoid data show that body-size may be d i s t i n c t l y smaller i n the island birds. But at present there i s no satisfactory evidence that a large enough difference exists between the two populations to merit subspecifie d i s t i n c t i o n , and i t i s therefore recommended that they should be considered consubspecific. Mimus polyglottos leueopterus No obvious differences were found to separate the few Island and mainland specimens available for comparison. It's status as a breeding species on the islands has not yet been established (Grant and Cowan 1964). Turdus ruf o-pa H i a t u s graysoni (Mainland ssp. r u f o - p a l l i a tus) The island subspecies may be recognized by duller and greyer chest-band and flanks. One male and three female specimens with this colour i n the plumage have been collected on the mainland i n the last twenty-five years. I t is possible that birds i n this plumage occur i n the mainland population at such a frequency that the use of chest-band colour as a diagnostic character i s questionable. But the paleness of the plumage may be the result of fading, for which reason they are not considered to invalidate the island subspecies. Nelson 168 (1899) also collected a specimen on the mainland i n this plumage, but i t s feathers were worn. The colour of the back of recently-collected male specimens i s redder i n mainland birds, but more specimens are needed to confirm t h i s . By this character, females of the two populations are indistinguishable. The island birds have paler and narrower brown chin and throat streaks, but this also needs further attention. The larger tarsus-length of the island male is a diagnostic character, and female tarsus-length, and b i l l - l e n g t h of both sexes, come close to meeting the taxonomic c r i t e r i o n . Eyadestes obscurus insularis (Mainland ssp. occidentalis) Stejneger (1882) described the insular subspecies upon finding several small differences between mainland and island specimens. The present study f a i l e d to ver i f y four of these differences - flanks tinged with olive i n island specimens; l i g h t , buff edges to the tips of the innermost secondaries; small white spot on the t i p of a l l the t a i l feathers; wing less pointed and f i r s t primary longer (see Tables 4-0 and 49). The f i r s t three plumage characters were found i n both mainland and island specimens. A f i f t h difference has been substantiated. The forehead and malar stripe are tinged with buff, to varying degrees, i n only island specimens. However, i n at least two specimens, including one examined by Stejneger, t h i s appears to be due to a grease stain. Therefore, u n t i l better-prepared specimens from the islands are available, this difference is to be ignored. 169 T A B L E 48. M e a s u r e m e n t s o f M y a d e s t e s o b s c u r u s . P r i m a r y 10. MAINLAND I S L A N D N o . , 17 9 R a n g e 21.1-26.8 22.2-26.1 1 23.76 2 4 . 4 9 S D . 1 . 1 8 9 0 .861 0.289 0.287 C V . 3 . 0 0 4 3.516 T A B L E 49. W i n g F o r m u l a of t h e L o n g e s t S i x P r i m a r i e s o f M y a d e s t e s o b s c u r u s 768594 768954 768549 765849 678594 675894 MAINLAND: 12(75.Of.) 1 3 I S L A N D : 5(55.6f.) - 1 2 - 1 I n e a c h c a t e g o r y t h e l o n g e s t p r i m a r y i s t h e f i r s t number i n d i c a t e d a n d t h e s h o r t e s t i s t h e l a s t . 170 The tarsus i s larger i n Island birds by an amount which s a t i s f i e s the taxonomic c r i t e r i o n . The sample of specimens is small however, and more material Is required to confirm this difference. U n t i l an adequately equipped study is undertaken i t i s recommended that the name i n s u l a r i s be retained, Vireo hypoehryseus sordidus (Mainland ssp. hypoehryseus) The chin, throat, breast and flanks are duller than in mainland birds, as was correctly diagnosed by Nelson ( 1 8 9 8 ) . The dorsum and pileum of island birds is greener, less yellow, than i n mainland birds. However, Nelson ( l o c . c i t . ) was incorrect i n stating that a difference existed i n the colour of the b i l l . A l l exposed parts are larger in island birds, but only the larger t a i l - l e n g t h of Island birds (both sexes) meets the taxonomic requirement. A l i t t l e evidence suggests that Island birds are markedly l i g h t e r , and that body-weight may be a taxonomically useful character when examined more thoroughly. Vireo. f l a v o v i r i d i s hypoleucus (Formerly, island ssp. f o r r e r i , yon Madarasz) There are three plumage differences between mainland and island birds, but none is s u f f i c i e n t to j u s t i f y the island birds being recognized as subspecifically d i s t i n c t . Island birds tend to have a grey-brown pileum more frequently than mainland birds do, and to have a less d i s t i n c t , pale superciliary stripe and black border to i t (Table5 0 ) . Von Madarasz (1885) found that the chin, throat and chest of his single, island specimen was grey, and not pure white as i n mainland specimens, but no difference i n ventral colouring was revealed i n the present study. TABLE 50 Plumage characteristics of Vireo f l a v o v i r i d l s Pileum colour Grey-Brown M A I N L A N D _™2_JL_ H§Z June July August Sept, 9 19 3 - 2 3 3 I S L A N D A p r i l May June July August Sept 5 24 3 10 Eye-stripe colour White Grey Not determined 7 2 19 3 5 1 Black border to - eye-stripe 25 7 3 D i s t i n c t 6 14 5 _. 2 1 2 _ „ Indistinct 3 6 1 2 1 2 9 1 Absent _ 2 _ 2 2 13 7 1 Not determined - - - • - - 3 3 _ 372 From, the measurements of specimens, there is no reason to believe that there i s any character diagnostic of the island birds. Therefore the mainland and island populations are considered to be consubspecific, Parula pitiayumi insularis (Mainland ssp. pulchra) In the following ways Ridgway (1902) considered insularis d i s t i n c t from the mainland subspecies, pulchra;-1 . Flanks darker, grey or chestnut. 2. Less white on wing coverts. 3. Area of white on l a t e r a l r e c t r i c e s smaller, and on only outer two pairs of rectrices (not three). 4. Lores and orbits not darker than pileum. 5 . Lores and orbits not black. Recently Stager ( 1 9 5 7 ) has referred to specimens with the characteristics of i n s u l a r i s being collected on the mainland at San Bias, Nayarit (see F i g . 1 ) . Therefore, plumage comparisons have been made between island specimens and mainland ones collected at l o c a l i t i e s away from the coast. Differences having been established, specimens from coastal Nayarit and Isla Isabel were then compared with both samples. The flank character was confirmed i n this study. No measurements were made of the extent of white on the wing coverts and l a t e r a l r e c t r i c e s , but there was no apparent difference between mainland and island specimens In the nature of the former character„ However, when f i f t e e n mainland specimens were compared with twenty-four island specimens, It was seen that no island specimen had as much white on the outer 173 r e c t r i x a s t h e m a i n l a n d s p e c i m e n w i t h t h e s m a l l e s t a m o u n t . The p a t t e r n o f w h i t e on t h e r e c t r i c e s c o n s i s t s o f a t r u n c a t e d w h i t e t i p t o t h e i n n e r vane, o f t h e f e a t h e r . The number o f f e a t h e r s u p o n w h i c h a w h i t e p a t t e r n was p r e s e n t , was r e c o r d e d f o r e a c h s p e c i m e n , t h e t o t a l s o f w h i c h a r e s h o w n i n T a b l e 5 X S o m e t i m e s t h e p a t t e r n i s r e d u c e d t o a n i r r e g u l a r s p o t , i n w h i c h c a s e t h e f e a t h e r p o s s e s s i n g i t i s i n d i c a t e d by a b a r b e n e a t h t h e r e c t r i x n u m b e r . The r e s u l t s show t h a t t h e m a j o r i t y o f e a c h p o p u l a t i o n a r e s e p a r a b l e , b u t t h a t o v e r l a p o c c u r s . The f o u r t h c h a r a c t e r m e n t i o n e d by R i d g w a y ( l o c . c i t . ) i s i n c o r r e c t , f o r t h e l o r e s and o r b i t s o f b o t h m a i n l a n d and i s l a n d s p e c i m e n s a r e d a r k e r t h a n t h e p i l e u m , and i n s e v e r a l s p e c i m e n s a r e b l a c k ( T a b l e 51). M a i n l a n d s p e c i m e n s h a v e a l a r g e r a r e a o f b l a c k . N o t o n l y a r e t h e o r b i t a l f e a t h e r s more p r o m i n e n t l y b l a c k , b u t t h o s e w h i c h b r i d g e t h e c u l m e n a r e c o n s p i c u o u s l y b l a c k , w h e r e a s i n i s l a n d s p e c i m e n s a f e w , b l a c k f e a t h e r s o n l y a r e p r e s e n t , f o r m i n g an i n d i s t i n c t b r i d g e . A l t h o u g h t h i s d i f f e r e n c e i s one of s m a l l d e g r e e , i t was p o s s i b l e t o d i s t i n g u i s h b e t w e e n m a i n l a n d and i s l a n d s p e c i m e n s by u s i n g t h i s c h a r a c t e r . The m o s t d i s t i n c t i v e p l u m a g e c h a r a c t e r o f i n s u l a r i s i s t h u s t h e f l a n k - c o l o u r . T h i s s u b s p e c i e s i s a l s o r e c o g n i z e d b y a l o n g e r t a r s u s . F e m a l e s may be r e c o g n i z e d by a l o n g e r w i n g and t a i l a s w e l l , b u t s i n c e t h e m a i n l a n d s a m p l e o f s p e c i m e n s i s s o s m a l l (11), t h e s e c h a r a c t e r s s h o u l d be h e l d i n a b e y a n c e . On I s l a I s a b e l , and a t S a n B i a s and L a P e n i t a , a l l i n t h e s t a t e o f N a y a r i t , t w e n t y - o n e s p e c i m e n s h a v e b e e n t a k e n TABLE 31 Plumage -characteristics of Parula pit iayumi Colour of lores 1. MAINLAND (pulchra) I I . MAINLAND (insularis ) I I I . • ISLAND (insula r i s ) Black 15 3 10 1 18 3 Grey 4 7 1 7 9 11 Outer r e c t r i c e s patterned with white 654 4 -- - - • -654 11 3 - - - -65 4 6 2 4 3 -61 - •- 7 1 18 8 6 - 1 1 2 3 3 6 - - 1 1 3 3 X test applied to Island cf "Grey-Lores". %*= 1 .91 df^. P < 0 . 2 The expected value i s derived from the known values for Mainland I "Grey-Lores"do , total Mainland I dV and tota l Is land der. 175 between the years of 1897 and 1963. Some have insular i s written on the lab e l , others insularis x pulchra. Seventeen of these are of undoubted, i n s u l a r i s plumage, a l l possessing the chestnut-coloured flanks. They exhibit the same t a i l - p a t t e r n as specimens of insularis collected on the Tres Marias islands (Table 51), although the feature i s not diagnostic. Those with black lores have an i n d i s t i n c t 'culmen-bridge', also l i k e the Tres Marias birds, and their measurements are clear l y closer to those of the Tres Marias sample of i n s u l a r i s than to pulchra. They should be considered as members of i n s u l a r i s . The reason for the i d e n t i f i c a t i o n of four of them as 'hybrids' is unknown. One male and one female were collected at San Bias i n 1963 by the author, and found to have the pulchra feature of pale-coloured flanks. The female was subsequently l o s t , but the i d e n t i f i c a t i o n was confirmed at the University of B r i t i s h Columbia, when the male was compared with specimens of pulchra and i n s u l a r i s . I t had the other pulchra features of a white area on the outer three pairs of re c t r i c e s , a d i s t i n c t black 'culmen-bridge' and a short tarsus. The specimen i s now i n the University Museum. Two female specimens, collected by A. R. P h i l l i p s at La Penita de Jaltemba i n 1955 and now i n his col l e c t i o n , were examined i n May, 1963, and compared with seven specimens of pulchra. The colour of the flanks suggested that they were members of the insularis subspecies, but no specimens of this subspecies were available for comparison. Only two pairs of re c t r i c e s were white-patterned i n both specimens, and neither specimen had black lores. The wing measurements are 176 within the observed range of pulchra. but beyond that of . i n s u l a r i s : the t a i l measurements are within the ranges of neither, but between the two: and one tarsus measurement is s i m i l a r l y between the two observed ranges and the other i s within the insular is range. The tarsus measurement and flank colour suggest closer a f f i n i t y with the island population and the specimens are thus tentatively l i s t e d as insularis specimens i n Table 51. Granatellus venustus francescae (Mainland ssp. venustus) The mainland sample of specimens examined was biased towards the north of the mainland region, being drawn from Sinaloa and Nayarit only (individuals were observed i n the state of J a l i s c o ) . Nevertheless the material was s u f f i c i e n t to cast a doubt upon the v a l i d i t y of a l l the taxonomic characters referred to by Baird ( l 8 6;4 - l 8 7 2 ) i n his original description of the island subspecies. There is no difference i n the graduation of the wing (Table 53) and the extent of the wing coverts, i n contrast to Baird's remarks ( l o c . c i t . ) . Nor are the sides of the breast of island specimens pure white, but they are plumbeous, as i n mainland specimens. Differences do exist however i n the nature of the black, pectoral necklace and t a i l pattern (Baird l o c . c i t . ) and the extent of the ventral red coloration. Island adult males usually do not possess the black pectoral necklace which characterizes mainland birds, but the d i s t i n c t i o n i s not as clear as Baird ( l o c . c i t . ) indicated (Table 53) . On the other hand no island, immature male examined TABLE 52 Plumage characteristics of Granatellus venustus M e a s u r e m e n t s M A I N L A N D I S 1 .Width of Rectrix 6 No. Range X SD. Sx CV. 2.Length of white pattern on r e c t r i x 6 . Adult 6 . 0 - 7 . 5 6 . 6 0 O . 6 5 0 0 . 2 9 1 9 . 8 4 8 Adult Immature 3 5 . 5 - 6 . 0 5 .67 No. Range X S D . Sx CY. 24.5-34.0 2 8 . 8 6 3.143 1.188 10.890 24 . 5 - 2 5 . 5 2 5 . 0 0 Adult 8 6 . 5 - 8 . 0 7.37 0 .466 O . 1 6 5 6 . 3 2 5 _ L A N D Adult 6 6.0-7.0 6.42 0 .500 0.204 7.788 Immature 1 7 . 0 13 34 .0-43 .0 38.38* 2.198-0 . 6 1 0 5.727 3 1 . 0 - 3 9 . 5 3 4 . 2 1 2.118 0 . 8 0 0 6 . 1 9 1 34.5-41.0 37.75 3.Length of longest r e c t r i x of specimens recorded in(2). No. 6 Range 6 7 . 5 - 7 3 . 0 % -69.75 S D . 1 . 9 0 0 s f 0.776 CV. . . . 2.724 6 2 . 0 - 7 1 . 5 6 6 . 2 5 4. Individual ratios.(2);(3) No. 6 Range 0.37-0.46 2 0.402 SD. 0.0340 St 0.0139 CV. -8.45-77 NB. See text, page 179 , 0.36-0.40 0 .377 13 7 1 . 5 - 8 0 . 0 7 6 . 3 5 * 1.904-0.528 2 .494 7 0 . 5 - 7 5 . 5 7 3 . 8 6 1.537 0.426 2 . 0 8 1 2 7 4 . 5 7 4 . 5 0 13 7 2 0 . 4 6 - 0 . 5 6 0 . 4 3 - 0 . 5 3 0 . 4 6 - 0 . 5 5 0 . 5 0 4 * 0.463 0.505 0 . 0 2 3 5 0.0248 D . O O 6 5 0 . 0 0 9 4 4 . 6627 5.5564 T for explanation of measurements. TABLE 55 The 'Necklace' character of Granatellus venustus Adult cfcf only MAINLAND ISLAND Necklace broken 1 13 Necklace complete at surface 12 2 Necklace complete beneath surface 1 1 The wing-formula of Granatellus venustus E x c e p t i o n s M A I N L A N D I S L A N D Adult cf Adultj. Immature cf Immature 2 Adult cf Adult? Immature cf Immatur Longest pair = 6 , 5 2 2 0 0 2 2 0 0 2nd pair - 7,4 4 2 0 0 2 2 0 0 3 r d pair = 8 , 3 2 1 0 0 0 1 0 0 4th pair = 1,2 0 0 0 0 0 0 0 0 Shortest = 9 0 0 0 0 0 0 0 0 Sample size 13 7 5 2 15 8 5 1 179 showed a trace of ihecnecklace, whereas a l l mainland counterparts had the complete neoklace, although sometimes incomplete at the surface ( i . e . partly masked b y white feathers). Baird ( l o c . c i t . ) mentions that the t a i l is longer, broader, rounder and with more white, i n island specimens. Ho attempt was made to measure the 'roundness' of the d i s t a l t i p of the t a i l , since no difference between mainland and island specimens was apparent. The pattern (but not size) of white on rect r i c e s 3 - 6 i s the same in both groups, so only r e c t r i x 6 was used i n the measurement of the white. I t was measured from the d i s t a l t i p of the feather to a point on the rachis, level with the meeting of black and white at the outer edge of the inner vane. At this same l e v e l , the width of the feather was measured from the rachis to the same edge. The measurements displayed i n Tables 39 and 52 indicate that the mean ta i l - l e n g t h and tail-width is greater In island specimens, and that there i s an absolutely and r e l a t i v e l y larger area of white on the tail. The majority of both mainland and island samples of adult males had approximately the same amount of red vent r a l l y . A few island specimens were observed to have less, and a few mainland specimens more, than th i s . However, a l l mainland immature males had more red than a l l the island immature males, yet less than adults of both samples. The ventral colour and pattern of immatures, and the white t a i l - p a t t e r n of adults and immatures, separate the two populations, but the samples used i n these comparisons were a l l un s a t i s f a c t o r i l y small. However, this study has revealed that 180 the large, Island sample of adult males has a -wing-length greater than the mainland sample, by an amount which s a t i s f i e s the taxonomic c r i t e r i o n . Island females have a longer wing and tarsus by the required amount as well, but the samples are u n s a t i s f a c t o r i l y small (Table 5 9 ) . Icterus ~ pustulatus graysonil (Mainland ssp. miorostictus) From a study of specimens moulting their t a i l feathers i t was seen that olive or grey-olive r e c t r i c e s were replaced by blackish or completely black ones. Most specimens had either olive or black t a i l s ; some possessed rectrices b a s i c a l l y black but suffused with brown, with an olive patch invading the black on the inner vane, and this i s described as blackish. No female had a black t a i l , so those with blackish t a i l s are described as adults and those with olive t a i l s as immatures. Three males i n each sample had blackish t a i l s . Because of the s i m i l a r i t y of their body plumage to that of specimens with olive t a i l s , they are a l l considered immatures. Males with black t a i l s are described as adults. From single specimens of an island male and female (in immature plumage), Cassin (1867) was able to describe the essential differences between mainland and island birds of this species, namely a reduced number of dorsal streaks i n the plumage and generally larger size (of external parts) in the l a t t e r . The method of analyzing the f i r s t character is described on page 19 . Table 54 shows the complete separation of these populations effected by means of this analysis. Other plumage differences do exist but are of lesser importance. TABLE 54 The number of dorsal streaks on Icterus pustulatus M A I N L A N D I S L A N D Adult cf Adult $ Immature cf Immature $. Adult cf Adult? Immature cf Immature Ho." 51 • 17 14 9 25 8 14 16 Range 22-43 21-39 0-34 25-33 1-18 0-10 0-9 0-10 x 30.4 27.O 2 2 . 9 28.7 5 . 7 * 3 . 5 * 3 . 8 * 3 . 2 * SD. 3 . 7 0 0 4 . 0 0 0 8 . 3 8 5 2.662 3 . 6 4 6 ' 4 . 0 0 0 ' 2 . 6 9 2 ' 3 . 5 6 0 Sx 0.518 0 . 9 7 0 2.241 0 . 8 9 0 0.729 1.414 0.719 0 . 8 9 0 TABLE 55 The sex and plumage of collected specimens of Icterus pustulatus M A I N L A N D I S L A N D , 6 * - 2 ? £ Adult 69 27 36 11 Immature 30 26 21 25 % 2 t e s t applied to Island adult 2 : = 8 6 . 5 3 d f 1 . P < 0 . 0 0 1 X t e s t applied to Island immatured: = 1.79 df-^ P <0.20 NB. The f i r s t test derived an expected value from the known values for Mainland $$ and for the immature group of Island . S i m i l a r l y , . the second test used the values for Mainland oa and for Island adultdo. y-1 CO 182 Island birds tend to be paler and with less orange colour in the body plumage. There, are proportionately more immature specimens i n the island sample (Table 5 5 ) , which may be the result of a retardation of plumage succession. The larger wing-length of island adult males is a diagnostic character of the subspecies. The larger b i l l - l e n g t h of island, adult and immature males and immature females also meets the taxonomic c r i t e r i o n , which the adult female samples just f a i l to do. A l i t t l e evidence suggests that mainland birds are heavier than island birds, but more data are required to c l a r i f y t h i s . Piranga bidentata flammea (Mainland ssp. bidentat a) Ridgway (1887) considered male, Island birds to be paler and more orange than mainland males, with the rump and the "ground-colour" of the back olive-greyish, and with pure white wing-bands. The yellow of the underparts and the olive of the upper parts of island females were described as much paler than i n mainland birds. Bone of these differences were substantiated In this study. The body plumage of mainland and island females is the same, and only two mainland males examined could be distinguished from island males. These were coloured red, whereas a l l other specimens were orange. The colour of the back and wing-bands is also the same in both populations of males (cf. LeFebvre and Warner., 195% Later, Ridgway (1902) commented upon the greater extent of white on the rectrices of island birds. In the present study t h i s was measured on r e c t r i x 6. In most, male 183 specimens i t is a patch on the inner vane only, truncated proximally, and i t was measured from the proximal edge to the d i s t a l t i p . In most, female specimens however, i t is not truncated, hut follows the outline of the feather p a r a l l e l to the outer edge of this vane. Unless the white, at i t s proximal end, extended towards the rachis quite d i s t i n c t l y for more than half of the width of the vane, i t was not measured, and recorded as " l i t t l e or no white present". Worn rectrices were not me'asured, and two specimens were so heavily worn that presence or absence of white could not be determined. The results of this analysis are shown i n Table 5 6 , and confirm Ridgway»s ( l o c . c i t . ) diagnosis. The samples of male measurements, as they stand, do not overlap. Measurements of two mainland specimens were not included, because the l e f t and right rectrices were patterned to a different degree. Thus, In one specimen a measurement of only 1 6 . 0 mm was obtained from one unworn outer r e c t r i x , while the other r e c t r i x , heavily worn, had an obviously longer, white t i p . In the second specimen a measurement of only 13.0 mm was taken from one feather, while the other had no white at i t s t i p . Both specimens have been c l a s s i f i e d according to the r e c t r i x which was not measured, and recorded as such In the Table. Immature males collected on the mainland possessed more red on the forehead and chin than those collected on the island, but the difference is small and probably not r e l i a b l e enough for i d e n t i f i c a t i o n purposes. Ridgway (1887) also referred to island birds as being 184 TABLE 56 Plumage characteristics of Piranga bidentata White pattern on outer r e c t r i x . Number of individuals MAINLAND White present: L i t t l e or no feather wear White present: heavy feather wear L i t t l e or no white present 3 2 2 7 ISLAND 11 1 4 0 0 15 Measurements of white No. Range X 3 4 2 2 . 0 - 2 7 . 3 12 . 0 - 1 8 . 0 2 3 . 8 1 5 . 1 11 1 15.5-21.0 18.2 16.5 For explanation of measurements see text, page 183. 185 "Rather larger, and with r e l a t i v e l y much larger b i l l " than mainland birds. The width of the b i l l , more than any other size character, closely approaches the taxonomic c r i t e r i o n . It i s only just met by the female samples, and the males samples only just f a i l to meet i t . Thus, there i s evidence that island birds are distinguished by a smaller white t i p to the outer rectrices and a wider b i l l . U n t i l more data.are available to confirm these characters, i t i s recommended that the subspecific d i s t i n c t i o n of the island population be retained. Spinus p s a l t r i a p s a l t r i a The adult breeding plumage is composed of a completely black dorsum and a white pattern i n the d i s t a l half of rectrices 3 - 6 . These two features are not always present together. Some specimens with this t a i l pattern have a substantial amount of green In the dorsal plumage, and some black-backed birds have white on rectrices 4 - 6 only. But with white on the outer two rectrices, or fewer, no male has a completely black, dorsal plumage, for which reason these are designated immature specimens. Most females have white on r e c t r i c e s 4 - 6 or none at a l l . There is only one dorsal colour, olive-green. The two t a i l patterns were used as the basis of c l a s s i f i c a t i o n , the few individuals with white on only one or two pairs of rectrices being included i n the adult group. Hitherto no differences have been reported to exist between mainland and island specimens, but i n this study a difference was found which affected males with black plumage 186 i . e . a l l adults and some immatures. The black of the dorsal plumage, meeting the yellow of the ventral plumage, forms a line on the side of the face, which runs posteriorly from the base of the b i l l , beneath the eye. In mainland specimens the yellow-coloured feathers extend dorsally up to the lower l i d of the eye, whereas In island specimens the yellow/black line runs uninterruptedly and d i s t i n c t l y beneath the eye. The length and width of the b i l l are smaller i n island specimens; the difference i n b i l l - w i d t h of males i s s u f f i c i e n t for taxonomic d i s t i n c t i o n . The island population i s thus characterized by the black sub-orbital region and smaller bill-width of adult males, and w i l l be described as a new subspecies i n a later publication. Richmondena cardinal is mariae (Mainland ssp. af f i n i s ) . In his o r i g i n a l description of the island subspecies, Nelson (1898) refers to i t as resembling the subspecies igneus (of Ba.ja California) more than any other. However, i t is more lo g i c a l to compare i t with a f f i n i s , whose range is on the adjacent mainland i n the state of Sinaloa, and perhaps further south. Five specimens of igneus were available too, and i t was noted that island birds differed from both subspecies i n the same way. The nine adult males of affinus examined were distinguishable from twenty-four island specimens, i n having a purple tinge to the red plumage of the body: two island birds were identical to the mainland birds. Nelson ( l o c . c i t . ) thought that dorsal feathers of island birds were edged with grey to a 18? lesser extent than mainland birds, but a comparison of specimens i n unworn plumage showed that this was not so. Island females have cream-white abdomens: only one of the six mainland females was so coloured, the rest being pale buff. A l l island females prepared i n such a way that an examination of the throat and chin was possible, possessed a larger area of white or grey i n this region than any of the mainland specimens, i n which paleness appears to be r e s t r i c t e d to the chin. This character was not measured. Two of the six mainland females had grey chins, but a l l the island birds did. Island males have a longer tarsus than mainland males. This character i s diagnostic. The plumage characters mentioned may be diagnostic too; but a larger number of specimens of the poorly-known mainland subspecies i s required to assess them properly. 188 APPENDIX I I I . Tabula-ted data1 of./feeding- seasons, veg etat io n char a c t er is t i c s, o ensus results.and song. T A B L E 57 B r e e d i n g S e a s o n s . R e c o r d s o f t h e f i r s t o b s e r v a t i o n s o f b r e e d i n g a c t i v i t i e s , l i s t e d i n p e r i o d s o f one w e e k . P l a c e S p e c i e s N e s t N e s t w i t h o u t b u i l d i n g e g g s Egg i n o v i d u c t N e s t w i t h o f a d u l t e g g s N e s t w i t h y o u n g E l e d g e d j u v e n i l e s - , P . a g l a i a e M I Mar 22-28 J u n e 19-25 J u n e 12-18 J u l y 10-16 J u l y 17-23 m e l a n c h o l i c u s H I • M a y 15-21 J u n e 19-25 * J u n e 5-11 J u l y 24 - 5 0 * J u n e • J u l y 2 6 -July 2 3-9 M . t y r a n n u l u s M I * J u n e 2 6 - Ju l y 2 M . t u b e r c u l i f e r M I J u l y 3-9 M. v i r i d i c a t a M I May 15-21 J u l y 3-9 £• i m b e r b e M I * J u n e 5-11 1- f e l i x M I J u n e 19-25 M a y 15-21 * M a y 29 -June 24 J u l y 3 1 -Aug.5 M. o a e r u l e s c e n s M I J u n e 19-25 May 2 9 -June 4 T . r u f o - p a H i a t u s M I J u n e 19-25 J u n e 5-11 J u l y 10-16 TABLE 57 - continuea Species Place Nest Nest building without eggs Egg of i n oviduct adult Nest with _egf&§. Nest with Fledged young juveniles Y. hypoehryseus M I May 29-June 4 June 2 9 -July 25 I- f l a v o v i r i d i s M I *July 3-9 June 19-25 * July 31-Aug ! • pitiayumi M I June 19-25 <£• venustus M I June 19-25 July 31-Aug .5 I. pustulatus M I (*April 15-21) -May 15-21 June 19-25 •May 22-28 June 19 - 2 5 (May 22-28 ) *June 26-July - July 24-30 2 p. hidentata H I May 22-28 June 26 -July 2 July 10-16 s. p s a l t r i a M I July 10-16 R. cardinalis M I June 19-25 July 24-30 NB.An asterisk indicates a Puerto Yallarta record: other mainland records refer to Tepic. Bracketed records were not duplicated i n the following three weeks, and are considered highly exceptional. They have been excluded from the calculations used i n Table 8. M = Mainland. I = Island. i - 1 1?1 TABLE 5:8 Length of t e s t i s i n centimetres from specimens of Icterus pus tula tus: l i s t e d i n periods of two weeks. Time Period M A I N L A N D I S L A N D N Range X N Range X March (2) 6 0.2-0.4 0.32 1 0 .10 A p r i l (1) 6 0 . 1 - 0 . 5 0.35 A p r i l (2) 1 0 . 6 0 5 0.1-0.4 0.26 May- (2) 9 0.9-1.4 1.20 June (1) 9 0.8-1.4 1 .08 June • (2) 6 0 . 6 - 1 . 3 0.97 N - Sample Size X = Mean TABLE 59 Mean values f o r three vegetation c h a r a c t e r i s t i c s , from samples of habitat p l o t s . MEAN VALUE ± 2 S.E. Tree canopy Species N Tree height radius Tree density P.aglaiae (T) » f• ( I ) 14 10 8.79*1.44 8.35*1.20 3.79*0.78 3.30±0.54 6 .07*2.02 •10.70*1.40 T.melancholicus(PV) rt a n ( j ) 20 9 5, 65*0 .52 6.17*1.72 2.40*0.34 2. 94*0.38 4.95*1.66 4.33*1.42 M. tyrannulus (PV+T) » ft n ( j ) 10 13 5 . 6 V 1 . 2 0 *8.73*0.86 2. 40*0.54 *3.27*0 .32 *^16.20±1 .18 10.23*1.62 M . t u b e r c u l i f e r (T) H tt H ( J ) 12 12 7.58*1.14 8.87*1.12 3.12*0.48 3.37*0.44 6.12±1.62 *9.75*1.04 M . v i r i d i c a t a (T) 11 n it ( j ) 9 10 5.94*0.86 *8.95*1.78 2.61+0.74 3.15*0.48 6.44*2.38 *12 .40*1.40 T. f e l i x (T) TT II (pyj rt H ( ! ) 17 9 13 6.29+1.00 5.89*1.08 ^.54* 1.04 2.74*0 .50 2.17*0.38 *3.38*0.38 7.06*1.44 9.67*4.56 • 1 0 . 5 4 * 1 . 2 8 M.oaerulescens (T) n n n (!) 17 11 7.26*0 .86 *10.18*1 .20 3. 09*0.40 3 . 5 0 * 0 . 4 8 7 . 7 1 * 1 . 2 6 =•10.82*1.82 V.hypochryseus (T) M tt it (!) 12 10 6 . 1 2 ± 1 . 0 4 *9.00*1.52 2.71*0.34 3 . 4 5 * 0 . 5 2 7.50*1.62 *11 .30±2.00 I . pustulatus (T) t i n ti (PV) n n it ( ! ) 12 20 20 8.08*1.52 5.37*0.48 *9.10*0.86 4 . 0 0 * 0 . 9 0 2. 05*0 .20 *3.41*0.28 . 7.33*3.00 1 1 3 . 2 5 * 4 . 4 2 8 . 2 0 * 1 . 5 2 P. bidentata (T) " » " ( I ) 10 12 8.30*1.94 9 . 0 8 * 1 . 0 0 3-10*0.44 3-57*0.52 7 . 6 0 * 1 . 6 8 • 1 1.58* 1 .54 S. p s a l t r i a (PV+T) Tt n n ( ! ) 9 10 5.22+1.44 5.85±1.18 2.28*0.76 2.80+0.36 3.44*1.86 6.40*2.72 * Ranges of i s l a n d and ma inland values do not overlap. A second a s t e r i s k i n d i c a t e s non-overlap of ranges when two comparisons are, made. Each of these values i s unduly i n f l u e n c e d by the exceptionally .high density of trees i n one habitat p l o t . KB.In t h i s and the f o l l o w i n g t a b l e , (T) r e f e r s t o Tepic, (PV) to — Puerto V a l l a r t a and (I) to Island (Maria Magdalena). TABLE 60 Percentage coverage of vegetation i n habitat plots, expressed as mean 10% class. Herb Shrub Ganopj?; P. aglaiae ( T ) 40-49 30-39 80-89 tt (I) 0-9 20-29 80-89 T. me lan cholicus(PV) 30-39 40-49 30-39 n (I) 10-19 40-49 30-39 M. tyrannulus (FV+T) 30-39 50-59 50-59 « ft ft (I) 0-9 20-29 80-89 M . tuberculifer (T) 50-39 60-69 70-79 n M i t (I) 0-9 20-29 80-89 M. v i r i d i c a t a (T)' 7 0 - 7 9 70-79 50-59 H » t i (I) 10-19 30 90 f e l i x (T) 50-59 70 50-59 n n ( P V ) 20-29 60-69 60-69 t t rt (I) 0-9 20 80-89 M . caerulescens (T) 40-49 50-59 80-89 « ft H (I) 0-9 10-19 80-89 hypoehryseus (T) 50-59 60-69 70-79 n w w (I) 0-9 20-29 80-89 I' pustulatus (T) 20-29 30-39 80-89 n t t t t (PT) 50-59 40-49 50-59 t t 11 t i (I) 0-9 20-29 8O-89 £• bidentata (T) 40-49 40-49 80-89 89 (I) 10 30 80-89 3 . p s a l t r i a (PV+T) 40-49 70-79 60-69 TI w (I) 10-19 30-39 60-69 NB.The samples, upon which the data are based, are the same as i n Table 5 9 . The mean class is calculated by considering 49.5% to be 0 , 40-49% to be - 1 , 50-59% t p be +1, 60-69% to be +2,etc each individual recording i s given a number, a l l the numbers a summed and the resulting number is divided by the sample size. This gives a number with a sign, which can be translated into a 10% class. TABLE 6 l - • ' PUERTO VALLARTA CENSUSES: Single Survey of 20 acres: A l t i t u d e 300? - 800'. 29 May 19o2 19 June 1962 12 July 196l 13 August 1961 ... Species 9.00-10.17 A.M. 9.00-10.08 A.M. 9.00-10.20 A.M. 9.00-10.33 A.M. Hypomorphnus urubitinga - 1 *Columba f l a v i r o s t r i s 3 1 - -Zenaida a s i a t i c a 3 -*Columbigallina passerina 1 5 2 1 *Leptotila verrauxi - 2 3 -Ara m i l i t a r i s 6 2 - -*Aratinga canicularis 3 8 - -'Amazona f i n s c h i - - 10 3 Crotophaga ani 1 *Morococcyx erythropygus 3 - - 2 *Nyctidromus a l b i c o l l i s - - 1 1 Phaethornis superciliosus 1 -*Chlorostilbon c a n i v e t i i - - 1 1 *Cynanthus l a t i r o s t r i s 4 1 2 1 *Amazilia r u t i l a 1 - 2 2 *Trogon citreolus - 1 2 -*Trogon elegans - - 1 -*Centurus chrysogenys 2 3 1 3 • Xiphorhynchus flavigaster - - - 1 Tyrannus melaneholicus 5 -Tyrannus cr a s s i r o s t r i s 2 -MegarLynchus pitangua - - - 1 NO Species Myiarchus nuttingi *Myiarchus tyrannulus '"Empidonax" Calocitta formosa *Cissilopha san-blasiana *"Thryothorus" -Vireo f l a v o v i r i d i s I c t e r i a virens Granatellus venustus *Euthlypis lachrymosa *Cassiculus melanicterus * I c t er us pus tu la t us *Rhodinocichla rosea *Saltator cperulescens *Oyanocompsa parellina -Passerina versicolor •Melozone kieneri - UNIDENTIFIED TABLE 6 l - continued 29 May 1962 9.00-10.17 A.M. 19 June 1962 9 . 0 0 - 1 0 . 0 8 A.M. 12 July 1961 9 . 0 0 - 1 0 . 2 0 A.l 13 August 1961 9 . 0 0 - 1 0 . 5 3 A.M. TOTAL INDIVIDUALS TOTAL. SPECIES . 5 8 2 1 1 5 2 JL 66 24 5 15 1 1 6 1 2 56 18 9 20 1 1 1 63 18 1 5 25 1 4 2 2 1 JL 64 20 "Thryothorus" always includes two species:- Thryothorus sinaloa and T . f e l i x . *' Refers to those species, considered to.be summer-resident i n the census area: 22 species. UNIDENTIFIED usually includes Hummingbirds and Trogoxts. March TEPIC J9 CENSUSES: Species *Leptotila verrauxi Aratinga canicularis *Hylocharis leucotis *Amazilia beryllina 8 *Trogon elegans 2 •Piculus a u r i c u l a r i s 3 Dendrocopos scalaris *Xiphorhynchus fl a v i g a s t e r • Platypsar-is aglaiae 1 Tityra semifasciata 2 *Tyrannus erass i r o s t r i s Myiodynastes luteiventris *Myiareh;us tuberculifer 4 *Contopus pertinax 3 "Empidonax1' - - 2 •Mitrephanes phaeocercus 9 *Myiopagis v i r i d i c a t a 'Calocitta formosa Xanthoura yncas Campylorynchus brunneicapillus -•Thryothorus sinaloa •Thryothorus f e l i x 2 *"Thryothorus" 8 TABLE 62 Single Surveys'of 20 acres: A l t i t u d e 3 5 5 0 ' - 3 5 9 0 ' A p r i l 1 4 4 1 2 2 1 7 3 2 3 9 May June July August 11 1 1 15 2 1 3 1 1 1 9 4 8 1 1 2 2 8 3 1 1 4(2) 1 12 1 1 1 1 2 6 3 6 1 11 t-1 NO ON TABLE Species March *Melanotis caerulescens 9 *Turdus assimilis 9 *Myadestes obscurus 7 *Gatharus au r a n t i i r o s t r i s 7 ;Popioptila a l b i l o r i s 1 *Vireo hypoehryseus 2 Vireo s o l i t a r i u s *Tireo gilvus 7 -ffiniotilta varia 1 Vermivora r u f i c a p i l l a 15 Parula pitiayumi Dendroica nigrescens 1 Oporornis tolmiei 4 Wilsonia pu s i l l a 10 *Myioborus miniatus 4 *Euthlypis lachrymosa 2 ' Basileuterus culicivorus 4 *Basileuterus rufifrons 3 *Tangavius aeneus *Icterus pustulatus 1 Tanagra musica *Piranga bidentata 1 *Piranga erythrocephala *Saltator coerulescens 'Pheucticiis melanocephalus 4 62 - continued A p r i l May June July August 11 10 20 11 5 9 17 18 9 -2 5 10 4 8 7 10 - 5 4 _ — - - 1 4 7 10 11 5 2 _ - - 1 - 1 — 3(1) — - 1 2 1 — - - -2 — - - -4 - - - -6 3 5 3 5 - 2 •j 1 1 10(3) 1 2 1 1 1 1 2 - - 1 - -1 — 4(2) 3 1 1 2 2 4 Species Guiraca caerulea Passerina versicolor Garpodacus mexioanus Spinus atriceps *Spinus p s a l t r i a *Melozone kieneri Aimophila ruficeps Helospiza l i n c o l n i i UNIDENTIFIED TOTAL INDIVIDUALS 158 136 124 147 114(8) 94 TOTAL SPECIES - 3_4 28 24 28 23 23 March = 26 March 1963; 9 . 0 5 - 1 0 . 5 0 A.M. A p r i l = 14 A p r i l 1963; 9 . 0 0 - 1 0 . 3 5 A.M. May = 26 May 1965; 9 . 0 0 - 1 0 . 1 5 A.M. June =» 14 June 1962; 9 . 0 0 - 1 0 . 3 2 A.M. July = 20 July 1962; 9 . 0 0 - 1 0 . 3 2 A.M. August = 14 August 1962; 9 . 0 0 - 1 0 . 3 5 A.M. "Thryothorus" includes both T.sinaloa and T . f e l i x : i n the species totals both of these are included, even though not always i d e n t i f i e d , since they were later found to be i n approximately equal numbers. * Refers to those species considered to be summer-resident i n the census area: 29 species. UNIDENTIFIED includes mainly Hummingbirds. Bracketed numbers refer to juveniles. TABLE .62 - continued larch A p r i l May - - 4 3 16 -10 2 3 4 2 19 5 16 7 June July August 3 -2 15 4 13 4 3 11 4 TABLE 63 MARIA MAGDALENA CENSUSES: Single Surveys of 20 acres: A l t i t u d e 10*-25». 28 June 1962 28 July 1962 25 A p r i l 1963 26 June I963 Species 9 , 0 0 - 1 0 , 1 5 A.M. 9 .00-10 .35 A.M. 9.00-1.0.24 A.M. 8.55-10.17 A.I Chondrohierax uncinatus 1 - - -•Columba f l a v i r o s t r i s 1 1 - -•Zenaida a s i a t i c a 7 1 - 4 *Columbigallina passerina _ 3 2 6 *Leptotila verrauxi 5 11 15 13 *Forpus cyanopygius - - 2 2 *Amazona ochrocephala 1 3 2 2 *Coccyzus minor - - - 2 *Cynanthus l a t i r o s t r i s 6 - 2 3 *Amazilia r u t i l a 1 2 6 2 •Trogon-elegans - 1 - 2 *Dendrocopos scalaris 2 3 5 2 •platypsaris aglaiae 4 2 7 2 *Tyrannus melancholicus 3 1 - 1 *Myiarchus tyrannulus 17 18 - 8 *Myiarchus tuberculifer 1 2 10 4 *Myiopagis v i r i d i c a t a 1 - - -Empidonax d i f f i o i l i s 2 *Camptostoma imberbe 1 •Thryothorus f e l i x , 4 3 8 9 *Melanotis oaerulescens 5 1 13 2 1—' NO S O TABLE 63 - continued Species 28 June 1962 9.00-10.13 A.M. 28 July 1962 9 . 0 0 - 1 0 . 3 5 A.M. 25 A p r i l 1963 26 June 1963 9.00-10.24 A.M. 8 . 5 5 - 1 0 . 1 7 A.M •Turdus rufo-paHiatus 20 29 17 23 Hylocichla ustulata - - 2 — *Vireo hypoehryseus 4 8 11 6 *Vireo f l a v o v i r i d i s 34 25 3 30 'Mniotilta varia - - 1 — *Parula pitiayumi 49 45 37 65 *Granatellus venustus - - 2 2 * Icterus pustulatus 7 1 9 9 *Pira-nga bidentata 2 4 1 8 ^Richmondena cardinalis 6 10 12 7 *Sp.inus ps a l t r i a - - - 2 UNIDENTIFIED - 2 1 1 TOTAL INDIVIDUALS TOTAL SPECIES 181 22 175 20 170 22 218 26 * Refers to those species considered to be summer-resident i n the census area: 28 species. o o TEPIC J10 CENSUS: Species TABLE Single Survey of 64 20 acres: A l t i t u d e 3.40O ' - 3 . 6 0 Q t . 21 July 1962 9.00-10.40 A J Buteo nitidus 1 *Leptotila verrauxi 1 *Amazilia beryllina 2 *Trogon elegans 1 *Xiphorhynchus flavigaster 1 *Platypsaris aglaiae 1 *Myiodynastes luteiventris 1 *Myiarchus tuberculifer 4 *C ont opus pertinax 1 *Mitrephanes phaeoGercus 3 *Xanthoura yncas 2 * f ,Thryothorus w 12 *Melanotis caerulescens 9 *Turdus assimilis 35 *Myadesies obscurus 1 *Catharus a u r a n t i i r o s t r i s 5 *Tireo hypoehryseus 9 *Basileuterus culicivorus 1 *Myioborus miniatus 5 *Euthlypis lachrymose 4 *Tangavius aeneus 2 *Tcterus pustulatus 1 *Piranga bidentata 1 *Spinus ps a l t r i a 2 *Melozone kieneri 3 • UNIDENTIFIED 1 TOTAL INDIVIDUALS TOTAL SPECIES 109 26 NB. "Thryothorus" includes both species T.sinaloa and T. f e l i x . Refers to those species considered to be summer-resident i n the census area: 25 species. Not a l l the summer-resident species were recorded. ro o r - 1 202 TABLE 65 Results of single surveys made i n July, 1962. No. of b i r d s Seen/heard Heard/seen Seen Heard % of tot a l heard only Tepic, J 9 . 13 21 30 42 3 9 . 6 Tepic, J10. 26 24 19 40 3 6 . 7 Puerto V a l l a r t a 6 7 6 27 5 8 . 7 Maria 1 Magdalena 23 29 36 68 3 2 . 3 NB. Seen/heard refers to birds seen f i r s t and heard l a t e r , and those heard f i r s t are l i s t e d under Heard/seen. Pa rent-dependent juveniles (8) are excluded from the J 9 figures. Repeated Surveys Census: TEPIC, Species May 20 *Leptotila verrauxi -Chlorostilbon eanivetti 2 •Hylocharis leucotis 3 •Trogon elegans - - 3 ' Phloeoeeastes guatemalensis •Xiphorhynchus flavigaster 'Tyrannus c r a s s i r o s t r i s Myiodynastes - l u t e i v e n t r i s •Myiarchus tuberculifer 1 'Contopus richardsonii •Gontopus pertinax 2 Empidonax d i f f i c i l i s •Mitrephanes phaeocercus 7 *Myiopagis v i r i d i c a t a 1 •Thryothorus sinaloa 1 •Thryothorus f e l i x 1 •"Thryothorus" 10 •Melanotis oaerulescens 12 *Turdus assimi1is 14 •Myadestes obscurus 6 •Catharus a u r a n t i i r o s t r i s 5 TABLE 66 £ 2 : 10 acres: Altitude 3 . 6 0 0 * - 5,900'. ay 21 May 22 May 23 May 24 May 25 Maximum No, , of T e r r i t o r i e s , _ 1 1 1 _ - - - - 1 1 1 4 4 2 3 — 3 - - - 3 _ — 1 - - 1 — 1 1 2 - 2 — - - - 1 1 3 .- - - 1 3 3 4 5 7 1 7 — - - • 1 1 1 2 1 1 1 1" 2 1 — - - 2 2 8 9 10 8 6 7 - 5 7 3 4 6 — - l 3 - 5 3 5 3 1 1 8 3 7 9 6 8 -10 6 10 6 7 9 12 10 13 14 12 12 6 7 8 2 5 6 7 7 9 6 10 9 Species P o l i o p t i l a a l b i l o r i s Ptilogonys cinereus *Vireo hypoehryseus *Vireo gilvus Wilsonia p u s i l l a *Myioborus miniatus *Euthlypis lachrymosa *Basileuterus rufifrons *Tangavius aeneus *Piranga bidentata *P±ranga erythrocephala *~Saltator coerulescens 'Guiraca caerulea Passerina versicolor Spinus atriceps *Spinus p s a l t r i a *Melozone kieneri -UNIDENTIFIED TOTAL INDIVIDUALS TOTAL SPECIES TABLE 66 - continued May 20 May 21 May 22 May 23 May 24-Maximum No. May 25 of T e r r i t o r i e s . 1 - - - - - 1 — — 1 3 1 - 2 4 6 6 6 10 3 5 — 2 1 4 1 - 4 _ — •- - 2 2 8 4 3 6 4 4 5 — — _ 1 1 1 1 1 2 2 - - 2 2 1 2 1 1 1 - 2 1 1 1 1 2 l ' 2 1 4 2 1 1 3 3 _ 2 — - 1 2 1 — •- - 2 5 2 2? 1 — - - - - 1 .- — - 2 - - 1 LO 6 8 6 15 11 5? 2 3 4 6 8 3 5 1 - 1 - - 1 99 22 91 21 99 23 122 25 113 24 97 24 126(+7?) "Thryothorus f r always includes both species, T.. sinaloa and T. f e l i x . * Refers to those species considered to be summer-resident i n the census area: 27 species. TABLE 67 Repeated Surveys Census: MARIA MAGDALENA: 10, acres: Altitud_e 15' - 3 5 ' . Maximum No Species June 21 June 22 June 23 June 24 June 23 June 26 - r ° * O T l e s Buteo jamaicensis •Caraeara cheriway 1 1 1 1 - 1 *Zenaida-asiatica 3 2 4 3 - 1 3 •Columbigallina passerina 1 7 - - - ~ 4 •Leptotila verrauxi 3 2 2 2 4 3 4 • Eorpus cyanopygius - - - - - 2 1 Amazona ochroeephala 2 Coccyzus minor 2 •Nyctidromus a l b i c o l l i s _ _ 1 - - 1 1 •Cynanthus l a t i r o s t r i s 3 3 3 1 7 6 4 •Amazilia r u t i l a 1 - 4 2 3 3 3 Trogon-elegans - - - - - 1 1 *Dendrocopos scalaris 4 4 2 3 1 - 4 •Platypsaris aglaiae 4 2 1 1 1 - 2 •Tyrannus melancholicus 2 - 1 - 1 2 1 •Myiarchus tyrannulus 11 10 7 10 9 6 9 •Myiarchus tuberculifer 2 2 - 2 2 4 3 Myiopagis v i r i d i c a t a - 1 - - - - -•Camptostoma imberhe - 1 - - - 1 1 ro o Species •Thryothorus f e l i x *Melanotis oaerulescens •Turdus rufo-palliatus •Vireo hypochryseus * Vireo f l a v o v i r i d i s •Parula pitiayumi •Granatellus venustus •icterus pustulatus •Piranga bidentata •Richmondena cardinalis Spinus p s a l t r i a UNIDENTIFIED TOTAL INDIVIDUALS TOTAL SPECIES TABLE 67 - continued Maximum No June 21 June 22 June 2} June 24 June 25 June 26 of _ T e r r i t o r i e s 9 4 11 7 5 12 7 3 5 - 1 - 1 3 13 • 13 11 9 12 11 9 7 6 3 4 4 4 6 19 2.3 17 22 27 20 19 40 37 37 39 34 47 32 mm _ — - 2 1 2 4 6 9 7 4 4 5 4 4 7 7 6 5 6 13 9 6 6 8 6 11 _ 1 - - - 1 2 - 2 1 3 - 1 147 145 128 129 132 143 148 20 21 18 18 18 22 UNIDENTIFIED . refers, entirely to Hummingbirds. * Refers to those species considered to be summer-resident i n the census area: 23 species ro o ON 207 T A B L E 68 D u r a t i o n o f s o n g s o f T . f e l i x a n d T . s i n a l o a . , i n s e e s , , m e a s u r e d f r o m s o n o g r a p h s . T . f e l i x : T E P I C T . s i n a l o a : T E P I C T . f e l i x : M.MAGDALENA A B A B a * £ 2.35 4) 2 .40 4) 1.85 1) 1 .90 1) 1.20 1) 0.85 4) 2 .40 4) 3.10 4) 2.35 1) 1.25 2) 0.85 5) 2.55 5) 2.65 3) 0.70 2) 0.85 6) 2.25 5) 2.65 3) 1.10 2) 0.85 6) 2.30 3) 1.25 5) 0.80 6) 2.45 4) 0.80 5) 0.85 4) 0.90 5) 0.85 4) 0.85 5) 0.85 4) 1.15 5) 1.05 5) 1.05 5) 1.20 5) 1.20 N B . B r a c k e t e d numbers r e f e r t o i n d i v i d u a l s . 208 REFERENCES Amadou D. 1949. The seventy-five percent rule for subspecies. Condor jjl, 250-258. 1950. The Hawaiian Honeycreepers (Aves, Drepaniidae). B u l l . Amer. Hus. Nat. Hist. 25_(4), 155-262. ; 1953. Avian systematios and evolution i n the Gulf of Guinea. B u l l . Amer. Mus. Nat. Hist.100(3),397-431. Anderson, R.M. i 9 6 0 . Methods of collecting and preserving vertebrate animals. Nat. Mus. Canada. B u l l . N 0 . 6 9 . Armstrong, E.A. 1955. The Wren. Collins, London. Baird, S.F, 1864-72. Description of Granatellus francescae. n.s. Review Amer. Birds. I, 2 3 2 . Baldwin, P.H, 1953. Annual cycle, environment and evolution in the Hawaiian Honeycreepers. Univ. Cel. Publ. Zool. J52, 285-398. Baldwin, S.P. H.C. Oberholser and L.G. Worley, 1951. Measurements of Birds. Science publications, Cleveland Museum of Natural History. Barrett-Hamilton, G.E.H. and M.A.C. Hinton, 1910-1921. A history of B r i t i s h Mammals. Bole <T., S. B r e l i h and M. Zei, 196l. Les Pulmones et les Lezards insula ires et le probleme de leur speciation dans l'archipel de Roving (Rovigno). In Le peuplement des l i e s Mediterraneenes et le probleme de . l ' i n s u l a r i t e : Colloques internat ionaux du Centre National de la Recherche Scienti fique. Editions du Centre National de la Recherch Scienti fique, Paris. Bond, J. and R.M. de Schauensee, 1944. The results of the 5th George Vanderhilt expedition. Monog. Acad. Nat. S c i . Philadelphia 6, 7-56. Bourne, W.R.P. 1955. The birds of the Cape Verde Islands.Ibis 21> 5 0 8 - 5 5 6 . 1957. The breeding birds of Bermuda. Ibis 21, 94-105. Bowman, R.I. 196l. Morphological d i f f e r e n t i a t i o n and adaptation i n the Galapagos Finches. Univ.Cal.Publ.Zool .58 , 1-302 . Braestrup, F.W, 1956, The significance of "oceanic" a f f i n i t i e s of the vertebrate fauna on Rennel1 Island. The Natural History of Rennell Island, 1 ( 9 ) , 135-148. Danish Science Press, Copenhagen, 2 0 9 Breckenridge, W.J. 1956. Measurements of the habitat-niche of the Least Flycatcher. Wilson B u l l . , 6 8 , 47-51, Brown, W.L,, Jnr., and E . 0 , Wilson, 1956. Character displacement. Syst.Zool,., j> ( 2 ) , 4 9 - 6 4 . Cassin, J. 1867. A t h i r d study of the Icteridae. ProcAcad, Nat, S c i , Philadelphia XIX, 4 8 , Chapin, J, 1949. Relationship and voice i n the genus Calamocichla Ornithologie als biologische Wissenschaft (Heidelberg), 7 - l 6 . Chapman, F.M, 1940, The post-glacial history of Zonotriohia capensis. B u l l . Amer. Mus .Nat .Hist. 77» 381-438 . C l i f f , F.S. 1954. Snakes of the islands i n the Gulf of California Mexico. Trans. San Diego Soc.Net.Hist. 12( 5 ) , 67-Connell, C.P. E.P. Odum and H. Kale, i 9 6 0 . Fat-free weights of birds. Auk 2 1 , 1-9. Contreras, A.A. 1942, Mapa de las provincias climatologicas de la Republics Mexicans, Mexico. Secretaria de Agricultura y Foment o, Institute Geografico, pp.1-54. Cook, L.M. 1 9 6 l . The edge effect i n population genetics. Amer, Nat. I£J ( 8 8 4 ) , 2 9 5 - 3 0 7 . Cope, E.D. I 8 9 6 . Primary Factors of Organic Evolution, Chicago, Crowell, K.L. 1962. Reduced i n t e r s p e c i f i c competition among the birds of Bermuda, Ecology 4J5 ( 1 ) , 75-88, Cullen, J.M. P.E. Guiton, G.A, Horridge, and J. Peirson. 1952. Birds on Palma and Goner a (Canary Islands). Ibis 2±, 6 8 - 8 4 . Darwin, C. 1859. The Origin of Species. Murray, London. Davis, J. 1957. Comparative foraging behaviour of Spotted and Brown Towhees. Auk 21 (2)» 129-166. Delany, M. 1961. The ecological d i s t r i b u t i o n of small mammals i n North West Scotland. Proc.Zool.Soc.Lond. 137.. ( 1 ) , 107-126. Dice, L.R. and H.J, Leraas, 1936 . A graphic method for comparing several sets of measurements. Contr.Lab.Vert. Genet. Univ.Mich, No.3, l-3« Dilger, W.C. 1956. Ecological isolating mechanisms i n thrushes, Wilson B u l l , 6 8 , 171-199. 210 Dunn, E.R. 1934, Physiography and herpetology i n the Lesser A n t i l l e s , Gopeia 1954. 105-111, Durango, S, 1944. N&gra jamforelser r6*rande t a l l t i t a n s , Par us a t r i c a p i l l u s boreal is S e l ys, och karmesens, Par us p a l u s t r i s palus t r i s L., b i o l o g i , Ornis Fennica 21, 33-42, Dwight, J , , J r . 1900, The sequence of plumages and moults of the passerine b i r d s of New York. Ann. N,Y. Acad. Sc i . 1 3 ( 1 ) , 7 3 - 3 6 0 . E l t o n , C. 1927. Animal Ecology. SIdgwick and Jackson, London, Emlen, J.T., J r . 1956. A method f o r describing and comparing avian habitats,, I b i s _9_8 (4), 5 6 5 - 5 7 6 . Enemar, A. 1959 . On the determination of the s i z e and composition of a passerine b i r d population during the breeding season. Var F a g e l v S r l d , Suppl. 2 , 1-114. Falconer, D.S. 1953. S e l e c t i o n for large and small s i z e i n mice, J.Genet, 5_1, 47 0 - 5 0 1 . F e r r i s , R.S. 1927. P r e l i m i n a r y report on the f l o r a of the Tres Marias I s l a n d s . Contr. Dudley Herbarium, Stanford U n i v e r s i t y , 1 ( 2 ) , 6 3 - 8 1 , F o s t e r , J.B. 1963„ The e v o l u t i o n of the native land mammals of the Q,ueen Charl o t t e Islands and the problem of i n s u l a r i t y . Ph.D, t h e s i s , Univ, B r i t , C o l . , Vancouver^ B.C. Friedman, H., L, Griscom and R. T. Moore, 1957. D i s t r i b u t i o n a l c h e c k - l i s t of the b i r d s of Mexico, p t . I I . P a c i f i c Coast Avifauna 2£, 1 -202. Gibb, J.A. 1951 . Birds of the Maltese I s l a n d s . I b i s 21, 109-127. — 1954. Feeding ecology of t i t s , with notes on Treecreeper and Goldcrest. I b i s _9_6, 515-543. . .__ i 9 6 0 . Populations of T i t s and Goldcrests and the food supply In pine p l a n t a t i o n s . I b i s 102, 163-208. Grant, P.R. and I.MoT. Cowan, 1964. A review of the^avifauna of the Tres Marias Islands, Nayarit, Mexico, Condor (In P r e s s ) . Grayson, A.J. 1871. The physical geography and the natural h i s t o r y of the islands of the Tres Marias, Proc.Bost, Nat. H i s t , Soc. 14, 261-302. 211 Hanna, G. 1926 . Expedition to the Revillagigedo Islands, Mexico, i n 1925. General Report. Proc. Cal. Acad.Sci. Ser.4 , vol.15, 1-93. Hartley, P.H.T. 1953. An ecological study of the feeding habits of the English Titmice. J . Anim.Ecol,22, 261-288. Hatt, R.T., J. Van Tyne, L„C. Stuart,.C.H. Pope and A.B.Grobman. 1938. Island l i f e : a study of the land vertebrates of the islands of eastern Lake Michigan, Cranbrook Inst. S c i . 22, 1-179. H e i l f u r t h , F. 1934. Beitrag zur Faunistik, Okologie and Beseidelungsgeschichte der Vogelwelt der Tres-Marias Inseln (Mexico). Proc.VIIIth Int. Ornith. Congr., 4 5 0 - 4 7 5 . Heinroth, 0 . and K. Heinro-th, 1958. The Birds. University of Michigan Press. Hesse, R. , W.C. Allee and K.P. Schmidt, 1937. Ecological Animal Geography, Wiley, New York. Humphrey, P.S. and K.C. Parkes, 1959 . An approach to the study of molts and plumages. Auk 7_6: 1-31. Huxley, J".S. 1942. Evolution: the Modern Synthesis. George Allen and Unwin Ltd., London, . . — i 9 6 0 . Natural history i n Iceland, Essay i n • Knowledge,,Morality and Destiny. New York. —. . , and J.B.S. Haldane, 192 9. Animal Biology. Clarendon Press, Oxford. Kear, J. 1962. Food selection i n finches, with special reference to i n t e r s p e c i f i c differences. Proc.Zool.Soc. Lond. 158, 163-204. Keast, A, I 9 6 I . Bird speciation on the Australian continent. B u l l , Mus. Comp. Zool, Harvard, 12J. ( 8 ) , 307-495. Kendeigh, S.C. 1944. Measurements of bird populations. Ecol. Monog, 14, 6 7 - 1 0 6 . Kramer, G., and R, Mertens, 1938. Rassenbildung bei westistrianischen Inseleidechsea i n Abhangegheit von Isolierungsalter une Arealgrosse. Arch.f. Naturgesch, X-,189-234. Krumbiegel, I. 1943. Zur kenntnis der saugetierfauna von Fernando Po. Arch, Naturgesch,, new ser . 1 1 , 305-349. Lack, D. 1940. Evolution of the Galapagos Finches. Nature 146, 324-327. 212 Lack, D. 1 9 4 2 . The birds of the Orkney Islands. Ibis 1 4 t h Ser.6, 4 6 1 - 4 8 4 . 1 9 4 3 . The l i f e of the Robin. H.F. and G.Y/itherby, London. 1 9 4 6 . Clutch and brood size i n the Robin. Brit.Birds 12, 9 8 - 1 0 9 , 1 3 0 - 1 3 5 . 1 9 5 4 . The Natural Regulation of Animal numbers. Clarendon Press, Oxford. and H.N. Southern, 1 9 4 9 . Birds on Tenerife. Ibis 9 1 , 6 0 7 - 6 2 6 . Lefebvre, A. and D.W. Warner, 1 9 5 9 . Molts, plumages and age groups i n Piranga bidentata i n Mexico. Auk j 6 , 2 0 8 - 2 1 7 . Leopold, A.S. 1950. Vegetation zones of Mexico. Ecology 3 1 , 507-518. Lowe, C.H.,Jr. 1 9 5 5 . Island faunas i n the Gulf of C a l i f o r n i a . Evolution 2, 3 3 9 - 3 4 4 . Main, A.R., 1961. The occurrence of the Macropodidae on islands and i t s climatic and ecological implications. J. Roy. Soc. W.Aust. 44, 8 4 - 8 9 . Marler, P.J. and D.J, Boatman, 1 9 5 1 . Observations on the birds of Pico, Azores. Ibis 9J>, 9 0 - 9 9 . Mayr, E. 1 9 3 1 . Birds collected during the Whitney South Sea Expedition XVI. Amer.Mus. Nov. J 0 2 , 1 - 2 1 . 1952. Notes on evolutionary l i t e r a t u r e . Evolution j>, 1 3 8 - 1 4 4 . 1963. Animal Species and Evolution. Bellknap Press, Cambridge, Mass. . E.G. Linsley and R.L. Usinger, 1 9 5 3 . Methods and Principles of Systematic Zoology. McGraw H i l l , New York. — and C. Vaurie, 1 9 4 8 . Evolution i n the Dicruridae (Birds). Evolution 2 , 2 3 8 - 2 6 5 . McCabe, T.T. 1943. An aspect of the collector's technique. Auk 6 0 , 5 5 0 - 5 5 8 . — and I. MoT. Cowan, 1 9 4 5 . Peromysous maniculatus macrorhinus and the problem of i n s u l a r i t y . Trans. Roy. Can. Inst., 1 1 7 - 215 . M i l l e r , A.H. 1 9 5 1 . A comparison of the avifaunas of Santa Cruz and Santa Rosa Islands, Californi8.Condor 5 3 . 1 1 7 - 1 2 3 . 213 Moreau, R.E. 1940. Contribution to the ornithology of the East African Islands. Ibis Ser. 14 (4), 48-91. Murphy, R.C. 1938. The need of insular exploration as illustrated by birds. Science J38, 533-539. _ ™ . — a n d j # Chapin, 1929. A collection of birds from the Azores. Amer. Mus. Nov. 384. 1-23. Nelson, E.W. 1898. Descriptions of new birds from the Tres Harass Islands, Western Mexico. Proc. Biol. Soc. Wash. 12, 5-11. 1899. Birds of the Tres Marfas Islands. N . A m e r , Fauna 14, 7-62. -•- — 1904. A revision of the North American species of Myiarchus. Proc. Biol. Soc. Wash. XVII. 49. Newell s N.D. 1949. Phyletic size increase, an important trend, illustrated by f o s s i l vertebrates. Evolution J3, 103-124. Palmgren, P. 1932. Zur Biologie von Regulus r. regulus (L.) und Parus atrioapillus borealis Selys. Acta Zoologica Fennica 14, 1-113. Pitelka, F.A. 1931. Speciation in the genus Aphelocoma. Univ. Cal. Publ. Zool. j>0, 195-464, P r e s t o n , F.W. 1962, The canonical distribution of commonness and rarity, I and II. Ecology 4J5, 185-215 and 410-431. Rand, A.L. and D.S, Rabor, i960. Birds of the Phillipine Islands: Siquijor, Mount Malindang, Bohol and Samar, Fieldlana: Zoology J5£ (7), 225-441. Raunkeier, C. 1934. The Life Form of Plants and Statistical Plant Geography. Clarendon Press, Oxford. Rensoh, B. 1938. Bestehen die Regeln klimatischer Parallelitflt-zu Recht? Arch. Naturgesch. (N.F.) J, 364-389. 1959, Evolution above the species level. London. Ridgway, R, 1878, Description of a new wren from the Tres Marias Islands, Mexico. Bull. Nutt. Ornith, Club J5, 10, . 1884. Description of some new North American b i r d s . Proc. Biol. Soc. Wash, II, 91. 1887. Manual of North American birds I, 324-5, 456-7, J.B. Lippencott Co., Philadelphia, 214 R i d g w a y , R . 1901-190?. B i r d s o f N o r t h and M i d d l e A m e r i c a , B u l l U . S . N a t . M u s . J>0: I - I V . R o s e , J . N . 1899. P l a n t s o f t h e T r e s M a r i a s I s l a n d s . N . A m e r . F a u n a 14, 77-91. S c h u s t e r , 0 . 1950* D i e k l i m a p a r a l l e l e A u s b i l d u n g d e r K 3 r p e r p r o p o r t i o n e d b e i P o i k i l o t h e r m e n . A b h . S e n c k e n b . N a t u r f . G e s . 482, 89 p p . S e l a n d e r , R . K . and D . R . G i l l e r , 1963. S p e c i e s l i m i t s i n t h e W o o d p e c k e r genus C e n t u r u s ( A v e s ) , B u l l , A m e r , M u s . N a t . H i s t . 124 (6). 217-27 3. S l u d , P . I960, The b i r d s o f F i n c a " L a S e l v a " , O o s t a R i c a : a ' t r o p i c a l wet f o r e s t l o c a l i t y . B u l l , A m e r . M u s , N a t . H i s t . 121 (2), 1-148, S n o w , D.W. 1954(a). T r e n d s i n g e o g r a p h i c a l v a r i a t i o n i n P a l a e a r c t i c members o f t h e genus P a r u s . E v o l u t i o n 8 , 19-28. 1954(b). The h a b i t a t s o f E u r a s i a n t i t s ( P a r u s s p p , ) . I b i s .26, 565-585. S t a g e r , K . B . 1957.. The a v i f a u n a o f t h e T r e s M a r f a s I s l a n d s , M e x i c o . A u k 24, 413-432, S t e j n e g e r , L , 1882. D e s c r i p t i o n s o f two new r a c e s o f M y a d e s t e s o b s c u r u s L a f r , P r o c , U . S . N a t , M u s . I V , 371-373. S t e v e n D . M , 1953. R e c e n t e v o l u t i o n i n t h e g e n u s C l e t h r i o n o m y s . S y m p . S o c . E x p . B i o l . 2» 310-319. S v a r d s o n , G . 1949. C o m p e t i t i o n and h a b i t a t s e l e c t i o n i n b i r d s . O i k o s I , 156-174. T i n b e r g e n , N . 1948. S o c i a l r e l e a s e r s a n d t h e e x p e r i m e n t a l m e t h o d r e q u i r e d f o r t h e i r s t u d y , W i l s o n B u l l , 60.6-52. 1953. The H e r r i n g G u l l ' s w o r l d , C o l l i n s , L o n d o n . Tompa , F . S . I 9 6 3 . F a c t o r s d e t e r m i n i n g t h e n u m b e r s o f S o n g S p a r r o w s on M a n d a r t e I s l a n d , B . C . P h . D . t h e s i s , U n i v . B r i t . C o l . , V a n c o u v e r , B . C . U d v a r d y , M . D . F . 1951. The s i g n i f i c a n c e o f i n t e r s p e c i f i c c o m p e t i t i o n i n b i r d e c o l o g y . O i k o s £ (1),98-123, V a u r i e , 0 . 1951. A d a p t i v e d i f f e r e n c e s b e t w e e n two s y m p a t r i c s p e c i e s o f N u t h a t c h e s ( S l t t a ) . P r o c , X t h I n t . O r n i t h . C o n g r . , I63-I66. V i l l a l o b o s , C . a n d J . V i l l a l o b o s , 1947. C o l o u r A t l a s . E l A t e n e o , B u e n o s A i r e s , 215 von Madarasz, J. I885. Ornithologlai KSzlemenyek A Magyar Nemzeti Muzeum Gyujtemenye,b8l. Termeszetrajzi Fuzetek 2, 85-86, Voous, K,H, 1957. Studies on the Fauna of Guraoao and other Garrlbean islands, ed. P.W. Hummelink, VII, The birds of Aruba, Curacao and Bonaire, Wallace, A.R, 1881, Island Life. MacMillan, London, Watson, G.E. 19&2. Three sibling speoies of Aleotoris partridge. Ibis 104, 353-367. Webster, J.D. 1963. A revision of the Rose-throated Beoard. Condor £ | ( 6 ) , 383-399. Wetmore, A, 1957. The birds of Isle Coiba, Panama, Smiths, Miso. Coll, 3J4 (9), 1-105. Wilson, B,0, 196l, The nature of the taxon oyele in the Melanesian Ant fauna, Axaer. Nat, XCV (882), 169-193. Zimmermann, K. 1950, Die Randformen der Mitteleuropaisohen tmhlmause, In A. Jordans and F. Peus (ed,) Syllegomena Biologica Festschrift Kleinsohmidt, Leipzig. 454-471. Zweifel, R.G, i 960 . Results of the Puritan-Amerloan Museum of Natural History expedition to Western Mexioo, 9. Herpetology of the Tres Marfes Islands. Bull. Amer. Mus. Nat. Hist. 112 (2), 81-128, 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0106804/manifest

Comment

Related Items