UBC Theses and Dissertations

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UBC Theses and Dissertations

Some ecological aspects of social behaviour in the song sparrow, Melospiza melodia Knapton, Richard Walter 1973

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C.I SOME ECOLOGICAL ASPECTS OF SOCIAL BEHAVIOUR IN THE SONG SPARROW, §§lospJLza m e l o d i a by RICHARD WALTER KNAPTON B S c . , L a k e h e a a U n i v e r s i t y , 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OP MASTER OF SCIENCE i n t h e De 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 UNIVERSITY OF BRITISH COLUMBIA September 1973 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree a t the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada i ABSTRACT The p u r p o s e o f t h i s s t u d y i s t o i n v e s t i g a t e e x p e r i m e n t a l l y some e c o l o g i c a l a s p e c t s o f s o c i a l b e h a v i o u r i n Song S p a r r o w s , H e l o s j a i z a m e l o d i a , on R e i f e l I s l a n d , B r i t i s h C o l u m b i a . Two main q u e s t i o n s a r e a s k e d : A. Does t h e t e m p o r a l p a t t e r n o f s e t t l i n g on t e r r i t o r i e s i n f l u e n c e t h e number o f o c c u p i e d t e r r i t o r i e s , and hence t e r r i t o r y s i z e , and t h e b r e e d i n g d e n s i t y i n a g i v e n a r e a ? B. A r e t h e j u v e n i l e s t h a t o b t a i n t e r r i t o r i e s , when t h e o p p o r t u n i t y a r i s e s , t h e d o m i n a n t i n d i v i d u a l s i n dominance h i e r a r c h i e s e s t a b l i s h e d d u r i n g t h e p r e - b r e e d i n g s e a s o n ? ft n e c e s s a r y p r e - r e q u i s i t e f o r b o t h q u e s t i o n s t o be a nswered i s t h a t t h e r e e x i s t s a s u r p l u s o f b i r d s which a r e n o n - t e r r i t o r i a l and p o t e n t i a l l y c a p a b l e o f b r e e d i n g , b u t w h i c h a r e p r e v e n t e d f r o m t a k i n g t e r r i t o r i e s by t h e r e s i d e n t t e r r i t o r y h o l d e r s . T h i s a l s o i s e x p e r i m e n t a l l y i n v e s t i g a t e d . Removal e x p e r i m e n t s were c a r r i e d b u t i n t h e f a l l o f 1972 and t h e s p r i n g o f 1973. S u b s e q u e n t r e p l a c e m e n t s and b r e e d i n g showed t h a t t h e r e was a s u r p l u s o f Song S p a r r o w s on t h e s t u d y a r e a t h a t were p h y s i o l o g i c a l l y c a p a b l e o f b r e e d i n g . A l l b u t one o f t h e r e p l a c e m e n t b i r d s were j u v e n i l e s , and a l l were p r o b a b l y o f l o c a l o r i g i n . Two t y p e s o f r e m o v a l e x p e r i m e n t s , s i m u l t a n e o u s and i i s u c c e s s i v e , were c a r r i e d o u t i n b o t h t h e s p r i n g and f a l l . On th e S i m u l t a n e o u s Removal a r e a s , t o t a l r e p l a c e m e n t t o o k a b o u t n i n e t o t e n d a y s . S i g n i f i c a n t l y more t e r r i t o r i e s were t a k e n , and t h e i n c r e a s e s i n b o t h s p r i n g and f a l l were a b o u t 40%. F u r t h e r , t h e mean t e r r i t o r y s i z e a f t e r t h e r e m o v a l s was 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 a t b e f o r e . F i n a l l y , t e r r i t o r y b o u n d a r i e s were c o m p l e t e l y r e a r r a n g e d f o l l o w i n g t h e r e m o v a l s . The r e p l a c e m e n t on t h e S u c c e s s i v e Removal a r e a s t o o k u p t o t h r e e t o f o u r d a y s . T h e r e was no s i g n i f i c a n t d i f f e r e n c e i n t h e number o f t e r r i t o r i e s t a k e n , n o r i n t h e mean t e r r i t o r y s i z e , a f t e r t h e r e m o v a l s . F u r t h e r , t h e t e r r i t o r i a l p a t t e r n was r e t a i n e d . B r e e d i n g d e n s i t y on a l l a r e a s , however, r e m a i n e d much t h e same b e f o r e and a f t e r t h e e x p e r i m e n t s . T h e r e f o r e , t h e r e were s e v e r a l unmated males w i t h t e r r i t o r i e s a f t e r t h e r e m o v a l s , and t h e s e unmated males p r o v e d t o have s i g n i f i c a n t l y s m a l l e r t e r r i t o r i e s t h a n mated o n e s . F a c t o r s w h i c h c o u l d have a c c o u n t e d f o r t h e d i f f e r e n t r e s u l t s o f t h e s i m u l t a n e o u s and t h e s u c c e s s i v e r e m o v a l e x p e r i m e n t s a r e d i s c u s s e d , and a p r o p o s e d e x p l a n a t i o n i s g i v e n . Dominance h i e r a r c h i e s were d e t e r m i n e d i n t h e l o o s e g r o u p s o f j u v e n i l e Song S p a r r o w s t h a t c o n g r e g a t e d o v e r t h e w i n t e r a t c e r t a i n l o c a l i t i e s a l o n g t h e hedgerows. Each g r o u p t e n d e d t o i i i be a d i s c r e t e u n i t , a l t h o u g h some i n t e r c h a n g e o f i n d i v i d u a l s ( b o t h d o m i n a n t and s u b o r d i n a t e ) o c c u r r e d . The h i e r a r c h i e s t h e m s e l v e s were s t a b l e and e s s e n t i a l l y l i n e a r , w i t h few r e v e r s a l s and t h e o c c a s i o n a l t r i a n g l e . The r e m o v a l e x p e r i m e n t s p r e s e n t e d an o p p o r t u n i t y f o r some o f t h e members o f t h e h i e r a r c h i e s t o o b t a i n t e r r i t o r i e s . I t was f o u n d t h a t , d o m i n a n t males i n t h e h i e r a r c h i e s were t h e s u c c e s s f u l o n e s i n e s t a b l i s h i n g t e r r i t o r i e s . F u r t h e r , i n t h e l a r g e s t h i e r a r c h y , o u t o f 12 j u v e n i l e m a l e s , 4 f r o m t h e t o p 5 o b t a i n e d t e r r i t o r i e s . F a c t o r s which c o u l d p o s s i b l y i n f l u e n c e t h e p o s i t i o n o f t h e b i r d i n t h e h i e r a r c h y a r e d i s c u s s e d , and t h e p o s s i b l e o utcomes o f t h e h i e r a r c h y a r e c o n s i d e r e d . i v TABLE OF CONTENTS PAGE ABSTRACT i TABLE OF CONTENTS iv LIST OF TABLES .. v i LIST OF FIGURES > v i i ACKNOWLEDGEMENTS v i i i GENERAL INTRODUCTION 1 1. . AIMS OF THE STUDY .. 1 2. THE STUDY AREA 3 3. LIFE HISTORY 5 U. METHODS 11 PART A. THE EFFECTS OF TEMPORAL SETTLING PATTERNS ON TERRITORY SIZE 16 I INTRODUCTION 16 1. Food supply and t e r r i t o r y s i z e ..... 18 2. Other environmental f a c t o r s and t e r r i t o r y s i z e ..................... 2 2 3. Temporal p a t t e r n s of s e t t l i n g on t e r r i t o r i e s 2 4 I I PROCEDURE 2? I I I RESULTS 32 1. Replacement of removed p a i r s ........ 32 2. Number of occupied t e r r i t o r i e s ...... 33 3. S i z e of t e r r i t o r i e s 35 1. Changes i n number of- t e r r i t o r i e s on the F a l l Removal Area over the winter 40 5. Breeding d e n s i t y i n the s p r i n g of 1973 42 6. D i f f e r e n c e s i n t e r r i t o r y s i z e between mated and unmated males .... 44 7. The replacement b i r d s 47 IV DISCUSSION ... 51 A. The replacement Song Sparrows and the s u r p l u s 51 B. The temporal p a t t e r n s of s e t t l i n g on t e r r i t o r i e s ..................... 55 V 1. F l u c t u a t i n g environmental resource 55 2. Pressure from i n t r u d e r s 57 3. Inexperience of the j u v e n i l e s and the temporal pa t t e r n s of s e t t l i n g 59 1. D i s r u p t i o n of t e r r i t o r i a l boundaries 63 5 . Genetic b a s i s f o r the s i z e of t e r r i t o r y .................. 67 C. Proposed e x p l a n a t i o n f o r the d i f f e r e n t r e s u l t s o f the simultaneous and the s u c c e s s i v e removal experiments ................ 68 PART B"... DOMINANCE HIERARCHIES 7 2 I INTRODUCTION , 72 I I PROCEDURE 75 I I I RESULTS 80 A. The h i e r a r c h i e s 8 0 B. Success i n g a i n i n g t e r r i t o r i e s i n r e l a t i o n to h i e r a r c h y p o s i t i o n ..... 88 IV DISCUSSION 94 a. The f u n c t i o n a l s i g n i f i c a n c e of dominance h i e r a r c h i e s .............. 94 B. F a c t o r s determining p o s i t i o n i n the dominance h i e r a r c h y 95 C. Outcomes of the h i e r a r c h i e s 102 LITERATURE CITED - 106 APPENDIX 1 .-. 118 APPENDIX 2 . , 120 APPENDIX 3 1 2 0 APPENDIX M 123 APPENDIX 5 124 APPENDIX 6 126 APPENDIX 7 . 127 APPENDIX 8 128 APPENDIX 9 129 v i LIST OP TABLES TABLE PAGE 1. Dispersal distances of juveniles from s i t e of b i r t h : f a l l 1972 - , 8 2. Results of removal experiments: numbers of occupied t e r r i t o r i e s , of both mated and unmated males 34 3. Results of removal experiments: differences i n numbers of occupied t e r r i t o r i e s of mated and unmated males 36 4. Results of removal experiments: mean t e r r i t o r y s i z e . F a l l Removal Area • 38 5. Results of removal* experiments: mean t e r r i t o r y s i z e . Spring Removal Area ................................... 39 6. Results of removal experiments: breeding density .... 43 7. Differences i n t e r r i t o r y s i z e between mated and unmated males: spring 1973. Simultaneous Removal areas ........ 46 8 . Vesting data f o r the Controls and the Experimental areas: 1973 49 9. Number of j u v e n i l e s banded, f a l l 1972 to early spring 1973 54 10. Lineage: t e r r i t o r y s i z e s from one generation to the next ^ 11. Numbers of encounters (displacements, avoidances and fights) i n f o u r dominance hierarchies ................. 12. Analysis of the avoidance interactions i n the B-C Hierarchy 84 13. Rank i n h i e r a r c h i e s and sex of Song Sparrows performing intergroup movements 87 14. Analysis of f i g h t s i n the B-C Hierarchy 89 15. Change i n s t a t u s of a juvenile female following the disappearance of an adult t e r r i t o r i a l female 92 16. Feeding order of hierarchy: appearance of f i r s t b i r d at feeding s t a t i o n s of the B-C Hierarchy 1 0 4 v i i LIST OF FIGURES , FIGURE PAGE 1. The study a r e a : R e i f e l I s l a n d and an adjacent p a r t of Mestham I s l a n d 4 2. Numbers of j u v e n i l e Song Sparrows r e s i g h t e d on the S p r i n g Removal Area from mid-December to the end of May ...... 10 3. S i n g l e n g t h s o f male and female Song Sparrows ........ 12 «». Mean weights of male and female Song Sparrows f o r a l l months 13 5. F a l l Removal Area: the movement and expansion of C o n t r o l male C6 a f t e r the removal experiment and d u r i n g the subsequent winter 41 6. S p r i n g Removal Area: Simultaneous Removal area boundaries b e f o r e and a f t e r removals 65 7. The B-C H i e r a r c h y 81 8. Number of i n t e r a c t i o n s versus d i s t a n c e w i t h i n h i e r a r c h y f o r a l l j u v e n i l e s i n the B-C H i e r a r c h y 89 9. P o s i t i o n i n h i e r a r c h y and number of i n t e r a c t i o n s : the B-C H i e r a r c h y 103 1 0 . B u l l d o z e d Area: the arrangement of t e r r i t o r y boundaries b e f o r e the dyke r e b u i l d i n g o c c u r r e d ................... 11*1 11. Cottonwood S t r e t c h H i e r a r c h y 1*9 12. Sedge Patch H i e r a r c h y 1 £ ° 13. B u l l d o z e d Path H i e r a r c h y 131 14. F i r s t B i g A l d e r and Marsh Narrows H i e r a r c h i e s 132 15. No Name C l e a r i n g H i e r a r c h y 1£3 . v i i i aCKNOWLEDGEMEHTS I am most g r a t e f u l t o my s u p e r v i s o r . Dr. J . R. K r e b s , f o r h i s a d v i c e , c r i t i c i s m and g u i d a n c e a t a l l s t a g e s o f t h i s work. Dr. C. J . K r e b s and Dr. N. R. L i l e y c r i t i c a l l y r e a d t h e m a n u s c r i p t , and a d v i c e was r e c e i v e d f r o m Dr. J . F. B e n d e l l a t t h e s t a r t o f t h e s t u d y . I s h o u l d f u r t h e r l i k e t o t h a n k P. T a i t t and W. Z a l e s , who gave v a l u a b l e a s s i s t a n c e d u r i n g t h e r e m o v a l e x p e r i m e n t s , and a l l t h e p e o p l e who a s s i s t e d i n t h e b a n d i n g o p e r a t i o n s and i n n e s t - f i n d i n g . T h e i r h e l p was t r u l y a p p r e c i a t e d . T h a n k s a r e a l s o due t o D. L a u r i e n t e , S. Bor d e n and B. Webb f o r a s s i s t a n c e w i t h t h e co m p u t e r programming. F i n a l l y , I s h o u l d l i k e t o t h a n k my w i f e , w i t h o u t whose p a t i e n c e and t o l e r a n c e t h e s t u d y would n o t have been p o s s i b l e . 1 GENERAL INTRODUCTION 1. Aims o f t h e S t u d y The p u r p o s e o f t h i s s t u d y i s t o i n v e s t i g a t e some e c o l o g i c a l a s p e c t s o f s o c i a l b e h a v i o u r i n Song S p a r r o w s , H e l o s j D i z a m e l o d i a . Song S p a r r o w s show two c l a s s i c a l e x a m ples of s o c i a l i n t e r a c t i o n : t h e t e r r i t o r y and t h e dominance h i e r a r a c h y ( N i c e 1937, 1943; Tompa 1964). T h i s s t u d y c o n s i d e r s a s p e c t s o f b o t h , and i s d i v i d e d i n t o two s e c t i o n s , t h e f i r s t d e a l i n g w i t h t e r r i t o r i a l i t y , and t h e s e c o n d d e a l i n g w i t h dominance h i e r a r c h i e s . T e r r i t o r i a l b e h a v i o u r has been shown t o d e t e r m i n e t h e b r e e d i n g d e n s i t y i n s e v e r a l p o p u l a t i o n s o f a n i m a l s (see Watson and Moss 1970; Klomp 1972). A p e r p l e x i n g p r o b l e m i n b i r d s , however, has been the v a r i a b i l i t y i n mean t e r r i t o r y s i z e , and hence p o p u l a t i o n d e n s i t y , i n a g i v e n a r e a f r o m y e a r t o y e a r . T h e r e a r e s e v e r a l e n v i r o n m e n t a l r e s o u r c e s t h a t c o u l d c o n c e i v a b l y i n f l u e n c e t e r r i t o r y s i z e a n n u a l l y , but t h e e v i d e n c e s u p p o r t i n g any o f them i s n o t u n e q u i v o c a l . T h e r e i s some e v i d e n c e (see K r e b s 1971) t h a t t h e t e m p o r a l p a t t e r n o f s e t t l i n g on t e r r i t o r i e s i s i m p o r t a n t i n d e t e r m i n i n g t h e number o f t e r r i t o r i e s o c c u p i e d i n a g i v e n a r e a . I n t h e f i r s t p a r t o f t h e s t u d y , t h e n , I e x p e r i m e n t a l l y p r o d u c e d two t y p e s o f s e t t l e m e n t p a t t e r n s , s i m u l t a n e o u s and s u c c e s s i v e , i n o r d e r t o t e s t t h i s h y p o t h e s i s . 2 In t h e s e c o n d p a r t o f t h e s t u d y , I l o o k e d a t dominance h i e r a r c h i e s i n t h e l o o s e g r o u p s o f j u v e n i l e Song S p a r r o w s t h a t c o n g r e g a t e d o v e r t h e w i n t e r a t c e r t a i n l o c a l i t i e s i n t h e s t u d y a r e a . The s t r u c t u r e and c o m p o s i t i o n o f t h e h i e r a r c h i e s were d e t e r m i n e d o v e r t h e w i n t e r , and t h e outcomes o f t h e h i e r a r c h i e s were f o l l o w e d d u r i n g t h e s p r i n g when t h e h i e r a r c h i e s began t o d i s i n t e g r a t e . I n p a r t i c u l a r , I i n v e s t i g a t e d t h e h y p o t h e s i s t h a t , g i v e n t h e o p p o r t u n i t y , t h e y e a r l i n g s t h a t o b t a i n t e r r i t o r i e s i n t h e s p r i n g a r e t h e d o m i n a n t i n d i v i d u a l s i n t h e dominance h i e r a r c h i e s e s t a b l i s h e d d u r i n g t h e p r e - b r e e d i n g s e a s o n . A n e c e s s a r y p r e - r e q u i s i t e f o r t h e i n v e s t i g a t i o n o f b o t h o f t h e s e p r o b l e m s was t h a t t h e r e e x i s t e d a s u r p l u s o f n o n - t e r r i t o r i a l b i r d s , p h y s i o l o g i c a l l y c a p a b l e o f b r e e d i n g , b u t p r e v e n t e d f r o m d o i n g s o by t h e t e r r i t o r i a l b e h a v i o u r o f t h e t e r r i t o r i a l i n d i v i d u a l s . T h e r e i s good d e s c r i p t i v e e v i d e n c e t h a t t h i s p r o c e s s was o p e r a t i n g i n a n o t h e r p o p u l a t i o n on Song S p a r r o w s i n s o u t h w e s t e r n B r i t i s h C o l u m b i a (Tompa 1962, 1 964). The p r e s e n t s t u d y was i n s t i g a t e d on, (and i n d e e d p r o v i d e d a t e s t f o r ) , t h e a s s u m p t i o n t h a t t h e r e would be s u c h a s u r p l u s o f n o n - t e r r i t o r i a l b i r d s on t h e s t u d y a r e a f r o m t h e f a l l o f 1972 t o t h e s p r i n g o f 1973. F i n a l l y , i t i s worth m e n t i o n i n g t h a t t h e dominance h i e r a r c h y and c l a s s i c a l t e r r i t o r i a l i t y a r e not c o n s i d e r e d t o be i n d e p e n d a n t f e a t u r e s o f a b i r d ' s s o c i a l b e h a v i o u r (Brown 3 1963; D a v i s 1 959). T h e r e f o r e , t h i s t h e s i s i s d i v i d e d i n t o two major p a r t s , w i t h t h e u n d e r s t a n d i n g t h a t t h e two p a r t s need not be m u t u a l l y e x c l u s i v e . 2. The S t u d y A r e a The s t u d y was c a r r i e d o u t on R e i f e l I s l a n d and an a d j a c e n t p a r t o f Westham I s l a n d ( F i g u r e 1 ) . The a r e a i s i n t h e m u n i c i p a l i t y o f D e l t a , B r i t i s h C o l u m b i a , and i s bounded t o t h e n o r t h and e a s t by t h e s o u t h arm o f F r a s e r R i v e r , t o t h e west by G e o r g i a S t r a i t and p a r t o f t h e George C. E e i f e l W a t e r f o w l R e f u g e , and t o t h e s o u t h by a g r i c u l t u r a l f a r m l a n d o f Westham I s l a n d . T o p o g r a p h y i s f l a t , t h e water t a b l e i s c l o s e t o t h e s o i l s u r f a c e f o r most o f t h e y e a r , and t h e l a n d i s o f n e c e s s i t y d y k e d . A l o n g t h e d y k e s , v a r i o u s s p e c i e s o f woody and h e r b a c e o u s p l a n t s have grown t o f o r m hedgerows. A p p e n d i x 1 g i v e s a l i s t o f t h e more common and i m p o r t a n t s p e c i e s . The s t r u c t u r e and c o m p o s i t i o n o f t h e v e g e t a t i o n i s s i m i l a r a l o n g a l l t h e hedgerows, but i s n o t i d e n t i c a l . Beyond t h e d y k e s , t h e marshes b o r d e r i n g t h e F r a s e r R i v e r and G e o r g i a S t r a i t a r e e s s e n t i a l l y f r e s h w a t e r . The water l e v e l v a r i e s w i t h t h e s e a s o n : r i v e r l e v e l s a r e h i g h d u r i n g t h e s p r i n g and e a r l y summer r u n - o f f , b u t d e c r e a s e t o f a i r l y low l e v e l s i n f a l l and w i n t e r . The water i n t h e marshes and s l o u g h s i s t i d a l , r i s i n g and f a l l i n g t w i c e d a i l y . In summer. 4 South Jetty FRASER RIVER FALL R E M O V A L A R E A N SPRING REMOVAL A R E A Figure 1 The Spudy Area: R e i f e l Island and an adjacent part of Westham Island 5 low t i d e s o c c u r i n d a y l i g h t , i n w i n t e r a t n i g h t . The l a n d e n c l o s e d by t h e d y k e s on t h e s t u d y a r e a was used p a r t l y a s p a s t u r e f o r c a t t l e , and p a r t l y as a g r i c u l t u r a l l a n d . The c r o p s grown on t h e a g r i c u l t u r a l l a n d c h anged from s e a s o n t o s e a s o n , and from y e a r t o y e a r , owing t o t h e r o t a t i o n o f c r o p s . The t e r r i t o r i a l Song S p a r r o w s were f o u n d m a i n l y i n t h e v e g e t a t i o n a l o n g t h e hedgerows, o c c a s i o n a l l y f o r a g i n g i n t h e marshes a t low t i d e . The n o n - t e r r i t o r i a l j u v e n i l e s i n t h e f a l l and w i n t e r f o r a g e d e x t e n s i v e l y i n t h e marshes when t h e water l e v e l s were low. No Song Sparrow was s e e n t o use t h e f i e l d s , e i t h e r p a s t u r e o r c r o p s , a t any t i m e . 3. L i f e H i s t o r y Song S p a r r o w s have a wide b r e e d i n g r a n g e i n N o r t h o A m e r i c a , and t h e r e c o g n i t i o n o f more t h a n 30 r a c e s (Dickerman 1963) s u g g e s t s a v e r y h i g h p l a s i c i t y o f t h e s p e c i e s t o v a r y i n g e n v i r o n m e n t a l c o n d i t i o n s . The s t u d i e s on Song S p a r r o w s by B e e r e t a l . ( 1 9 5 6 ) , P h i l l i p s and D i c k e r m a n (1957), N i c e ( 1 9 3 7 ) , J o h n s t o n (1956a,b), and M a r s h a l l (1948a #b) r e v e a l a wide v a r i e t y o f h a b i t a t t y p e s f o r b r e e d i n g , and t h e s t u d i e s o f N i c e (1943) and Tompa (1964) show a h i g h l y d e v e l o p e d a t t a c h m e n t o f t h e s e b i r d s t o t h e s i t e o f b i r t h . I n t h e l o w e r m a i n l a n d o f B r i t i s h C o l u m b i a , t h e Song 6 S p a r r o w s a r e n o n - m i g r a t o r y . The s u b s p e c i e s c o n c e r n e d , H i I i ™2££^BS# O b e r h o l s e r , i s r e s i d e n t i n t h e P u g e t Sound L o w l a n d s , G u l f I s l a n d s , and C o a s t F o r e s t b i o t i c a r e a s (Munro and Cowan, 1947). O t h e r s u b s p e c i e s o c c u r t o t h e n o r t h and e a s t , and a r e m o r p h o l o g i c a l l y d i s t i n c t . A l l b i r d s c a u g h t i n t h i s s t u d y were o f t h e s u b s p e c i e s , nu Jjorphna. The g e n e r a l b e h a v i o u r o f Song S p a r r o w s has been d i s c u s s e d i n d e t a i l by N i c e (1937, 1943). The b i r d s on H e i f e l I s l a n d showed i d e n t i c a l b e h a v i o u r p a t t e r n s i n many r e s p e c t s t o t h o s e d e s c r i b e d by N i c e , and t h e r e f o r e a d e t a i l e d d e s c r i p t i o n i s u n n e c e s s a r y . C e r t a i n a s p e c t s r e l e v a n t t o t h i s s t u d y a r e , however, d i s c u s s e d h e r e . Song S p a r r o w s have Type A t e r r i t o r i e s ( N i c e 1941). The t e r r i t o r y h o l d e r s on H e i f e l I s l a n d r e m a i n e d w i t h i n t h e i r t e r r i t o r y b o u n d a r i e s t h e y e a r r o u n d , i n c o n t r a s t t o t h e f l o c k i n g b e h a v i o u r i n w i n t e r d e s c r i b e d by Tompa (1964) f o r Song S p a r r o w s on Mandarte I s l a n d . The b i r d s on R e i f e l I s l a n d b e h a v e d t e r r i t o r i a l l y f o r a l m o s t t h e whole y e a r , t e r r i t o r i a l b e h a v i o u r c e a s i n g o n l y d u r i n g p e r i o d s o f i n c l e m e n t weather d u r i n g t h e w i n t e r months, and d u r i n g t h e p o s t - b r e e d i n g m o u l t . The i n c e p t i o n and l e n g t h o f t i m e o f m o u l t i n g v a r i e d f r o m b i r d t o b i r d ; p r o b a b l y t h e m o u l t l a s t e d 40 t o 50 d a y s , and t o o k p l a c e i n A u g u s t and September ( c f . N i c e 1937; Tompa 1964). Weather d a t a a r e g i v e n i n A p p e n d i x 2; t h e o n l y s i z e a b l e s n o w f a l l o c c u r r e d i n l a t e December, o t h e r w i s e t h e w i n t e r was v 7 r e l a t i v e l y m i l d . T e r r i t o r y b o u n d a r i e s on R e i f e l I s l a n d were w e l l - d e f i n e d , and were l i n e a r l y a r r a n g e d a l o n g t h e hedgerows. Hence, any one p a i r would have i n g e n e r a l o n l y two n e i g h b o u r i n g p a i r s . From o b s e r v a t i o n s , t h e r e was l i t t l e t r e s p a s s i n g by a d j a c e n t m a l e s i n t o e a c h o t h e r s t e r r i t o r i e s ; b o u n d a r i e s were r e c o g n i z e d and r e s p e c t e d . On b e c o m i n g i n d e p e n d e n t o f t h e i r p a r e n t s , young Song S p a r r o w s p e r f o r m e x p l o r a t o r y movements (Torapa 1964), u n t i l t h e end o f t h e p o s t - j u v e n i l e m o u l t . O b s e r v a t i o n s on young t h a t were banded s h o r t l y a f t e r l e a v i n g t h e n e s t s u g g e s t e d t h a t no l o n g d i s t a n c e s were c o v e r e d . In f a c t , most young were r e s i g h t e d w i t h i n t h e b o u n d a r i e s o f t h e i r p a r e n t ' s t e r r i t o r y a t t h i s t i m e . In t h e f a l l , a f t e r t h e p o s t - b r e e d i n g m o ult, t h e a d u l t s become t e r r i t o r i a l l y a c t i v e o n c e more, and t h i s r e s u l t s i n d i s p e r s a l o f t h e young. T a b l e 1 g i v e s t h e d i s t a n c e s c o v e r e d by i n d i v i d u a l s whose b i r t h p l a c e was known ( s e e Howard 1960, f o r a d i s c u s s i o n on l o n g - and s h o r t - d i s t a n c e d i s p e r s e r s ) . On Mandarte I s l a n d , t h e r i s e i n f a l l t e r r i t o r i a l b e h a v i o u r c o i n c i d e d w i t h t h e e m i g r a t i o n o f many young, 50% o f which were f e m a l e s , t o n e i g h b o u r i n g i s l a n d s . On R e i f e l I s l a n d , a l t h o u g h some o f t h e d i s p e r s a l d i s t a n c e s were q u i t e l a r g e , t h e r e i s some e v i d e n c e t o s u g g e s t t h a t most o f t h e j u v e n i l e s d i d not e m i g r a t e f r o m t h e s t u d y a r e a . F o r example, o u t o f 52 banded 8 TABLE 1 Dispersal distances of juveniles from site of birth; f a l l 1972 Numbers of juveniles Distance (m) 4 0-150 2 150 - 500 1 500 - 750 1 750 - 1000 2 1000 - 1500 1 1500 - 2000 9 j u v e n i l e Song S p a r r o w s t h a t were p r e s e n t on t h e F a l l Removal A r e a d u r i n g A u g u s t and September, 19% were r e s i g h t e d i n O c t o b e r and November, a f t e r t h e peak o f t e r r i t o r i a l a c t i v i t y , w i t h i n t h e s t u d y a r e a . F u r t h e r , o c c a s i o n a l v i s i t s i n t h e f a l l t o a r e a s o u t s i d e t h e s t u d y a r e a f a i l e d t o r e v e a l any banded j u v e n i l e amongst t h e many Song S p a r r o w s p r e s e n t . The young b i r d s t h a t r e m a i n e d a s n o n - t e r r i t o r i a l i n d i v i d u a l s i n t h e f a l l f o r m e d c e n t r e s o f c o n c e n t r a t i o n a t c e r t a i n f a v o u r e d l o c a l i t i e s a l o n g t h e hedgerows. T h e s e c e n t r e s o f young b i r d s p e r s i s t e d t h r o u g h o u t t h e w i n t e r as h i e r a r c h i c a l g r o u p s (see PART B ) . In t h e s p r i n g , t h e h i e r a r c h i c a l g r o u p s began t o b r e a k up, p o s s i b l y as a r e s u l t o f i n c r e a s i n g h o s t i l i t y between t h e y e a r l i n g s t h e m s e l v e s (see Tompa 1964:26). A l s o , i n t h e s p r i n g , t h e t e r r i t o r i a l b i r d s began t o e x c l u d e t h e n o n - t e r r i t o r i a l ones f r o m t h e i r t e r r i t o r i e s . From e a r l y A p r i l t o t h e end o f t h e s t u d y i n l a t e May, 1973, no n o n - t e r r i t o r i a l Song Sparrow was r e c o r d e d on t h e s t u d y a r e a . The R e i f e l W a t e r f o w l R e f u g e and t h e hedgerows a d j o i n i n g t h e s t u d y a r e a on Westham I s l a n d were a l s o s u r v e y e d , i n March and A p r i l 1973, and o n l y one banded b i r d (see A p p e n d i x 3) was l o c a t e d i n t h e two a r e a s . T h e r e seemed t o be, t h e n , a s h a r p d e c l i n e i n t h e numbers of Song S p a r r o w s on t h e s t u d y a r e a i n l a t e March and e a r l y A p r i l . F i g u r e 2 shows t h e numbers o f j u v e n i l e Song S p a r r o w s 10 Each month i s divided i n t o two two-weekly time i n t e r v a l s Figure 2 Numbers of j u v e n i l e Song Sparrows resighted on the Spring Removal Area from mid-December to the end of May 11 r e s i g h t e d i n two-weekly i n t e r v a l s f r o m mid-December t o t h e end o f Hay, s h o w i n g a s h a r p d e c l i n e i n t h e numbers s e e n i n t h e s p r i n g . Tompa (1964) f o u n d t h e same r e s u l t on Mandarte I s l a n d i n Song S p a r r o w s , and s h a r p d e c l i n e s i n numbers i n s p r i n g have been f o u n d i n s e v e r a l o t h e r s p e c i e s o f b i r d s ( e . g . C a r r i c k 1963; Dhondt 1971b; J e n k i n s e t a l , 1963; O r i a n s 1961; S m i t h 1967; Watson 1965). T h u s , a p p a r e n t l y , t h e o n l y Song S p a r r o w s l e f t on t h e s t u d y a r e a i n m i d - A p r i l were t h e t e r r i t o i a l p a i r s . 4. Methods The Song Sparrow p o p u l a t i o n on t h e s t u d y a r e a was o b s e r v e d c o n t i n u a l l y f r o m F e b r u a r y 1972 t o May 1973. B e c a u s e o f t h e n a t u r e o f t h e e x p e r i m e n t s , i t was n e c e s s a r y t o have a banded p o p u l a t i o n , e a c h b i r d i n d i v i d u a l l y r e c o g n i z a b l e . T h e r e f o r e , each b i r d was banded w i t h one a l u m i n i u m and one o r two c o l o u r e d b a n d s , i n v a r i o u s c o m b i n a t i o n s . D u r i n g t h e s t u d y p e r i o d , 282 Song S p a r r o w s were c a u g h t , m a i n l y i n m i s t n e t s , w i t h a few c a u g h t i n p o r t a b l e s p a r r o w t r a p s . Each b i r d was weighed, and measured f o r l e n g t h o f wing, t a r s u s , and c u l m e n . M a l e s and f e m a l e s c a n be s e x e d b o t h on b e h a v i o u r a l d i f f e r e n c e s and on w i n g l e n g t h ( N i c e 1937). F i g u r e 3 g i v e s t h e w i n g l e n g t h s f o r t h e banded b i r d s ; m ales r a n g e d from 67 t o 72 mm i n w i n g l e n g t h , f e m a l e s from 63 t o 68 mm. A l t h o u g h males on a v e r a g e weighed s l i g h t l y more t h a n f e m a l e s t h r o u g h o u t t h e y e a r ( F i g u r e 4 ) , t h e r e was t o o much o v e r l a p NUMBERS Figure 3 Winglengths of male and female Song Sparrows 13 M E A N WEIGHTS (gm) 4 Figure 4 Mean weights of male and female Song Sparrows f o r a l l months 14 between ' l i g h t * and 'heavy' f e m a l e s f o r t h i s c h a r a c t e r i s t i c t o be u s e f u l i n d e t e r m i n a t i o n o f s e x . T a r s u s and culmen measurements were t a k e n i n c a s e t h e s t u d y a r e a was u s e d a s a w i n t e r i n g ground f o r o t h e r s u b s p e c i e s o f Song S p a r r o w s . As m e n t i o n e d e a r l i e r , no s u b s p e c i e s o t h e r t h a n t h e r e s i d e n t one was i d e n t i f i e d on t h e s t u d y a r e a . J u v e n i l e s l o o s e t h e i r d u s t y , f i n e l y - s t r e a k e d plumage i n l a t e f a l l a f t e r t h e p o s t - j u v e n i l e m o u l t , and t h e n assume a plumage s i m i l a r t o t h e a d u l t s . A u s e f u l d i s t i n g u i s h i n g f e a t u r e i s t h a t a l l j u v e n i l e s have p o i n t e d r e t r i c e s , which a r e r e t a i n e d t h r o u g h t h e w i n t e r , whereas a d u l t males have r o u n d e d r e t r i c e s ( N i c e 1 9 3 7 ) . A c r i t e r i o n which I a l s o used was t h e c o l o u r o f t h e f l e s h y p a r t s a t t h e base o f t h e m a n d i b l e s . In f l e d g e l i n g s , t h e s e f l e s h y p a r t s a r e e x t e n s i v e , and a r e b r i g h t y e l l o w i n c o l o u r . In j u v e n i l e s , t h e f l e s h y p a r t s have d e c r e a s e d i n s i z e , b u t t h e y e l l o w c o l o u r a t i o n i s r e t a i n e d , and p r o v e d t o be an o b v i o u s c h a r a c t e r i s t i c when t h e b i r d was i n fe" t h e hand. C e r t a i n y e a r l i n g s ( p o s s i b l y members o f l a t e b r o o d s i n 1972) r e t a i n e d t h e y e l l o w c o l o u r a t i o n i n t o F e b r u a r y 1973. The f l e s h y p a r t s a t t h e base o f t h e m a n d i b l e s i n a d u l t s a r e dark g r e y . T e r r i t o r y b o u n d a r i e s ! were d e t e r m i n e d by n o t i n g t h e r e s p o n s e o f a t e r r i t o r i a l male t o t h e p l a y b a c k o f a s t r a n g e r Song S p a r r o w ' s s o n g on a t a p e r e c o r d e r (Sony 110A) (method d e s c r i b e d i n Dhondt 1 9 6 6 ) . T h i s method p r o v e d v e r y u s e f u l . 15 M a l e s would r e a c t q u i c k l y t o t h e new song by f l y i n g c l o s e t o t h e t a p e r e c o r d e r , and e i t h e r s i n g o r d i s p l a y . I c o u l d e l i c i t a r e s p o n s e from t e r r i t o r i a l b i r d s by p l a y i n g t h e t a p e r e c o r d e r a t v a r i o u s s p o t s a l o n g t h e hedgerow. M a l e s would n o t c r o s s t e r r i t o r y b o u n d a r i e s , b u t would f l y t o a s o n g p e r c h a l o n g t h e b o u n d a r y and s i n g . In t h i s way, t e r r i t o r y b o u n d a r i e s c o u l d be c l e a r l y d e f i n e d i n a v e r y s h o r t s p a c e o f t i m e , p a r t i c u l a r l y a s any one p a i r u s u a l l y had o n l y two n e i g h b o u r s , owing t o t h e l i n e a r i t y o f t h e hedgerow. T h u s , t h e r e l a t i v e l y c o m p l i c a t e d method o f m e a s u r i n g t e r r i t o r y s i z e i n Song S p a r r o w s a s p r o p o s e d by S u t h e r s (1960) was n o t needed. 16 PART A . T H E EFFECT OT TEMPORAL SETTLING PATTERNS ON TERRITORY S I Z E I . INTRODUCTION T e r r i t o r i a l b e h a v i o u r , and i t s i m p o r t a n c e i n d e t e r m i n i n g b r e e d i n g d e n s i t y i n p o p u l a t i o n s o f a n i m a l s , has been t h e s u b j e c t o f much d i s c u s s i o n i n r e c e n t y e a r s , e. g. Wynne-Edwards 1962; C r o o k 1965; L a c k 1966; Rowan 1966; C h i t t y 1967; Brown 1969; F r e t w e l l and L u c a s 1969; Watson and Moss 1970a; Klomp 1972). T h e r e a r e two main l i n e s o f o p i n i o n on t e r r i t o r i a l b e h a v i o u r ; (a) i t d o e s l i m i t b r e e d i n g p o p u l a t i o n s o f v e r t e b r a t e s , o r (b) i t i s s i m p l y t h e way i n which a n i m a l s , whose b r e e d i n g p o p u l a t i o n s have been l i m i t e d by some o t h e r f a c t o r , s p a c e t h e m s e l v e s o u t . Watson and Moss (1970a) l i s t f i v e c o n d i t i o n s ( Appendix 8) w h i c h t h e y 1 f e e l need t o be s a t i s f i e d i n o r d e r t o show t h a t b e h a v i o u r l i m i t s a b r e e d i n g p o p u l a t i o n . They t h e n p r o c e e d t o show t h a t no s t u d y t o d a t e has so f a r f u l l y s a t i s f i e d a l l f i v e c o n d i t i o n s . Removal e x p e r i m e n t s , i n which r e s i d e n t t e r r i t o r y h o l d e r s a r e removed and s u b s e q u e n t r e p l a c e m e n t , i f any, o c c u r s , a r e means by which c o n d i t i o n s (a) and (b) i n A p p e n d i x 8 can be d e t e r m i n e d . The r a t i o n a l e b e h i n d a r e m o v a l e x p e r i m e n t i s a s f o l l o w s . In a g i v e n a r e a , i f t e r r i t o r i a l i n d i v i d u a l s f r o m a s t a b l e p o p u l a t i o n a r e removed, and new i n d i v i d u a l s I 17 s u b s e q u e n t l y r e p l a c e them, t h e n i t c a n be deduced t h a t t h e s e r e p l a c e m e n t s had been p r e v e n t e d from s e t t l i n g on t e r r i t o r i e s i n t h a t a r e a by t h e p r e s e n c e o f t h e t e r r i t o r i a l i n d i v i d u a l s , p r i o r t o t h e r e m o v a l s . I f t h e h o l d i n g o f a t e r r i t o r y i s n e c e s s a r y f o r b r e e d i n g , t h e n i t c a n be f u r t h e r d educed t h a t t h e p r e s e n c e o f t h e t e r r i t o r y h o l d e r s l i m i t s b r e e d i n g d e n s i t y on t h a t a r e a . Such r e m o v a l e x p e r i m e n t s have been c a r r i e d o u t on a v a r i e t y o f s p e c i e s ; i n i n s e c t s ( e . g . J a c o b s 1955; Moore 1964), i n f i s h ( e . g . C l a r i c e 1 970), i n mammals (e. g. L o c k i e 1966; H e a l e y 1967; Smyth 1968), and p a r t i c u l a r l y i n b i r d s ( e . g . S t e w a r t and A l d r i c h 1951; H e n s l e y and Cope 1951; O r i a n s 1961; Watson 1965, 1967; Watson and J e n k i n s 1968; B e n d e l l and E l l i o t 1967; H a r r i s 1970; Holmes 1970; Young 1970; K r e b s 1971; Peek 1971; Young 1972). The i m p o r t a n c e o f t e r r i t o r i a l b e h a v i o u r would be e a s i e r t o d e m o n s t r a t e i f minimum t e r r i t o r y s i z e were c o n s t a n t , and e q u a l f o r a l l i n d i v i d u a l s . T h i s i s however not s o . T h e r e a r e t h r e e p r o b l e m s w h i c h a r e a s s o c i a t e d w i t h v a r i a t i o n s i n t e r r i t o r y s i z e w i t h i n a s p e c i e s : (a) t h e r e a r e d i f f e r e n c e s between i n d i v i d u a l s w i t h i n one p a r t i c u l a r p o p u l a t i o n and y e a r ; (b) t h e r e a r e d i f f e r e n c e s i n t h e mean t e r r i t o r y s i z e w i t h i n one y e a r between h a b i t a t s ; and (c) t h e r e a r e d i f f e r e n c e s i n t h e mean t e r r i t o r y s i z e w i t h i n a h a b i t a t o v e r s u c c e s s i v e y e a r s . T h i s v a r i a b i l i t y i n t e r r i t o r y s i z e has prompted L a c k 18 (1966) t o r e j e c t t h e h y p o t h e s i s t h a t t e r r i t o r i a l b e h a v i o u r r e g u l a t e s b r e e d i n g d e n s i t y . He p o i n t e d o u t t h a t i f t e r r i t o r i e s have a f i x e d minimum s i z e , t h i s has n o t o p e r a t e d i n l i m i t i n g t h e b r e e d i n g p o p u l a t i o n o f t h e G r e a t T i t s , P a r u s m a j o r , i n B a r l e y Wood, O x f o r d , s i n c e t h e b r e e d i n g d e n s i t y has v a r i e d c o n s i d e r a b l y f r o m y e a r t o y e a r . However, K r e b s (1971) a r g u e s t h a t minimum t e r r i t o r y s i z e need not be c o n s t a n t from y e a r t o y e a r f o r t e r r i t o r i a l b e h a v i o u r t o d e t e r m i n e b r e e d i n g d e n s i t y , My s t u d y was i n t e n d e d t o i n v e s t i g a t e a p o s s i b l e mechanism c a u s i n g t h e d i f f e r e n c e s i n mean t e r r i t o r y s i z e f r o m y e a r t o y e a r w i t h i n an a r e a (problem (c) a b o v e ) . I t i s worth c o n s i d e r i n g now some f a c t o r s w hich c o u l d i n f l u e n c e t h e s i z e o f t e r r i t o r y t a k e n from y e a r t o y e a r . I t s h o u l d however be s t r e s s e d t h a t t h e p o s s i b l e f a c t o r s t o be d i s c u s s e d r e f e r t o p r o x i m a t e mechanisms o n l y , n o t t o u l t i m a t e mechanisms. F u r t h e r , my a p p r o a c h t o t h e s t u d y was n o t i n t e n d e d t o e x p l a i n d i f f e r e n c e s between i n d i v i d u a l s ( p r o b l e m (a) a b o v e ) . 1. Food s u £ £ l y and t e r r i t o r y s i z e T e r r i t o r y s i z e c o u l d f l u c t u a t e a n n u a l l y w i t h f o o d s u p p l y , i f s i z e o f t e r r i t o r y was p r o x i m a t e l y a d j u s t e d t o t h e a v a i l a b i l i t y o f f o o d . The e v i d e n c e h e r e i s f a r from u n e q u i v o c a l . D i f f e r e n c e s i n mean t e r r i t o r y s i z e i n v a r i o u s h a b i t a t s 19 have been r e l a t e d t o d i f f e r e n c e s i n f o o d q u a n t i t y (and, i n some i n s t a n c e s , q u a l i t y ) i n v a r i o u s s p e c i e s , e. g. i n d i r e c t l y i n t h r e e s p e c i e s o f t i t m i c e , P a r u s spp. ( K l u y v e r and T i n b e r g e n 1953), and t h e C h a f f i n c h , F r i n g i l l a c o e l e b s , ( G l a s 1960), and d i r e c t l y (by m e a s u r i n g t h e f o o d ) i n t h e D u n l i n , C a l i d r i s a l p i n a , (Holmes 1970) , t h e Red G r o u s e , Laqppus l - _ S c o t i c u s , ( M i l l e r e t a l . 1966; Moss 1969), t h e T u r n s t o n e , M § £ § l i l lBf® I £ I®s, ( S e t t l e s h i p 1 973), and t h r e e s p e c i e s o f s q u i r r e l s o f t h e genus T a m i a s c i u r u s , (Smith 1968). In f i s h , Mason and Chapman (1965) showed a g r e a t e r b i o m a s s and h i g h e r numbers o f j u v e n i l e Coho Salmon, O n c o r h y n c h u s k i s u t c h , where t h e r e was a g r e a t e r f o o d s u p p l y . E g g l i s h a w ( 1 9 6 7 ) , on t h e o t h e r hand, f o u n d t h a t t h e b i o m a s s o f s a l m o n i d s i n two S c o t t i s h s t r e a m s , one t h r e e t i m e s r i c h e r i n f o o d t h a n t h e o t h e r , h a r d l y d i f f e r e d . E v i d e n c e t h a t d i f f e r e n c e s i n t h e mean t e r r i t o r y s i z e w i t h i n a p o p u l a t i o n o v e r a number o f y e a r s i s r e l a t e d t o f o o d s u p p l y i s f a r from c o n c l u s i v e . H a r r i s (1970) s u g g e s t e d t h a t , f o r t h e O y s t e r - C a t c h e r , Haematopus o s t r a l e g u s , t h e s i z e o f t h e t e r r i t o r y t a k e n was p r o b a b l y a compromise between the a r e a t h e b i r d s needed t o f e e d t h e i r young, and t h e a r e a t h e y c a n d e f e n d , O r i a n s ( 1 9 6 1 ) f o u n d a g e n e r a l c o r r e l a t i o n between t h e s i z e o f a Red-winged B l a c k b i r d , A ^ e l a i us Eljoe n i c e us, t e r r i t o r y , and t h e p r o p o r t i o n o f f o o d o b t a i n e d w i t h i n i t s c o n f i n e s , b u t s u g g e s t s t h a t f o o d i s p r o b a b l y n o t t h e p r o x i m a t e f a c t o r by w h i c h t e r r i t o r y s i z e i s r e g u l a t e d and t h a t 20 t e r r i t o r i a l b e h a v i o u r i n some way i s much more i m p o r t a n t . T h e r e i s some e v i d e n c e t h a t t h e q u a n t i t y o f f o o d i n a g i v e n a r e a can d e t e r m i n e t h e s i z e o f t e r r i t o r y t a k e n by t h e O v e n b i r d , S e ^ u r u s a u r o c a £ i l l u s # w i t h i n one y e a r ( S t e n g e r 1958), a l t h o u g h i n t h i s s t u d y i t i s n o t known i f age o r e x p e r i e n c e was i n f l u e n c i n g t e r r i t o r y s i z e . E v i d e n c e t h a t f o o d s u p p l y c a n i n f l u e n c e t e r r i t o r y s i z e c a n be o b t a i n e d i f m a n i p u l a t i o n o f t h e f o o d s u p p l y c a u s e s t h e t e r r i t o r i a l i n d i v i d u a l s t o change t h e s i z e s o f t h e i r t e r r i t o r i e s . I n f i s h , Symons {1968) s u g g e s t e d t h a t t h e i n c r e a s e i n a g g r e s s i o n a s s o c i a t e d w i t h f o o d d e p r i v a t i o n m ight r e s u l t i n an i n c r e a s e d s i z e i n t h e f e e d i n g t e r r i t o r y i n t h e A t l a n t i c Salmon, Salmo s a l a r . However, he c o u l d n o t d e m o n s t r a t e i n a l a b o r a t o r y e x p e r i m e n t (Symons 1971) t h a t d i f f e r i n g a v a i l a b i l i t y o f f o o d c a u s e d c h a n g e s i n t h e s i z e s o f t h e t e r r i t o r i e s o f d o m i n a n t young salmon (the s u b o r d i n a t e f r y were n o n - t e r r i t o r i a l ) . K e e n l e y s i d e and Yamamoto (1962) showed t h a t f i s h d e p r i v e d o f f o o d were more a g g r e s s i v e t h a n t h o s e r e c e i v i n g an abundance o f f o o d , whereas S m i t h (1970) f o u n d t h e r e v e r s e t o be t r u e i n Brook S t i c k l e b a c k , C u l a e a i n e o n s t a n s , w h i s t Bagnusson (1962) f o u n d t h a t a c o m p l e t e a b s e n c e o r a s u p e r a b u n d a n c e o f f o o d r e d u c e d a g g r e s s i o n i n t h e Medaka, Ory.zias l a t i o e s . I f f o o d and a g g r e s s i o n work t o g e t h e r t o d e t e r m i n e t e r r i t o r y s i z e i n f i s h , t h e n t h e y do so a p p a r e n t l y i n d i f f e r e n t ways f o r d i f f e r e n t s p e c i e s . 21 B u s t a r d (1969) showed t h a t t h e number o f f e m a l e s o f a g e k k o n i d l i z a r d , Gehyjra v a r i e g a t a , i n h a b i t i n g a stump d i d n o t v a r y w i t h d i f f e r i n g s u p p l i e s o f f o o d . He c o n c l u d e d t h a t s o c i a l b e h a v i o u r s e t an u p p e r l i m i t , b u t , as Watson and Moss (1970a) p o i n t o u t , t h e p h y s i c a l s t r u c t u r e o f t h e e n v i r o n m e n t s , and n o t b e h a v i o u r , c o u l d be l i m i t i n g , b e c a u s e a l l t h e s u i t a b l e c r a c k s were u s e d by t h e l i z a r d s . I n t h e G r e a t T i t , t h e y e a r - t o - y e a r f l u c t u a t i o n s i n t e r r i t o r y s i z e have n o t been r e l a t e d t o t h e a v a i l a b i l i t y o f f o o d f o r t h e young (Lack 1966), and K r e b s (1971) showed e x p e r i m e n t a l l y t h a t t e r r i t o r y s i z e i n t h e s p r i n g was n o t r e l a t e d t o t h e f o o d s u p p l y i n t h e p r e v i o u s w i n t e r . P i t e l k a e t a l . (1955) s u g g e s t e d an i n v e r s e r e l a t i o n s h i p between t h e mean t e r r i t o r y s i z e i n t h e P o m a r i n e J a e g e r , S t e r c p r a r i u s £ o m a r i n u s , and t h e d e n s i t y o f lemmings, b u t i t i s n o t known i f t h e b r e e d i n g b i r d s were a d j u s t i n g t h e i r t e r r i t o r y s i z e t o t h e f o o d s u p p l y , o r i f t h e r e was a d i f f e r e n c e i n t h e number o f p o t e n t i a l b r e e d e r s f r o m y e a r t o y e a r , a l l o f which s e t t l e d . I n s m a l l mammals, t h e e v i d e n c e f o r t h e i n f l u e n c e o f f o o d on p o p u l a t i o n d e n s i t y i s a l s o n o t u n e g u i v o c a l . I n P e r o m y s c u s fiSSicuAatus, B e n d e l l (1959) f o u n d t h a t e x c e s s f o o d s u p p o r t e d a p o p u l a t i o n i n a new a r e a and i m p r o v e d t h e s u r v i v a l o f t h e young, w h i l s t Fordham (1970) f o u n d t h a t p o p u l a t i o n s i z e and p r o d u c t i o n o f young i n c r e a s e d w i t h a d d i t i o n a l f o o d . E x c e s s f o o d , however, f a i l e d t o p r e v e n t t h e d e c l i n e o f a p o p u l a t i o n 22 o f M i c r o t u s c a l i f o r n i c u s ( K r e b s and B e l o n g 1965; K r e b s 1966), and o f Mus m u s c u l u s ( D e l o n g 1967; Newsome 1970). F i n a l l y , i n t h e Red G r o u s e , t h e q u a l i t y o f h e a t h e r a p p e a r s t o i n f l u e n c e t h e s i z e o f t e r r i t o r y t a k e n , n o t d i r e c t l y w i t h i n one y e a r , b u t w i t h a one y e a r l a g . T h i s has been a t t r i b u t a b l e t o d e c r e a s e d a g g r e s s i v e n e s s w o r k i n g t h r o u g h h i g h n u t r i t i o n a l l e v e l s o f t h e c h i c k s (Watson and Moss 1970b; Watson and M i l l e r 1971). 2. O t h e r e n v i r o n m e n t a l f a c t o r s and t e r r i t o r y s i z e T h e r e a r e s e v e r a l e n v i r o n m e n t a l f a c t o r s o t h e r t h a n f o o d s u p p l y which might i n f l u e n c e t e r r i t o r y s i z e f r o m y e a r t o y e a r . The n a t u r e o f t h e h a b i t a t has been s u g g e s t e d as b e i n g i m p o r t a n t i n i n f l u e n c i n g t h e numbers o f t e r r i t o r i e s i n a g i v e n a r e a i n some a n i m a l s , b o t h i n v e r t e b r a t e s e.g. D i n g l e and C a l d w e l l ( 1 9 6 8 ) , A l e x a n d e r (1961), and L i n (1963), and v e r t e b r a t e s e . g . D i x o n (1956), Snow (1958), D a v i e s and Snow (1965 ) , B u e c h n e r (1 9 6 1 ) , C a l h o u n (1963), Watson (1964), S n y d e r (1967), Zimmerman (1971), and T e s t e r and Watson (1973). Young (1970) f e l t t h a t t e r r i t o r y s i z e i n t h e S h e l d u c k , T a d o r n a t a d o r n a , was d e t e r m i n e d by t h e immediate t o p o g r a p h y o f t h e a r e a , and by t h e l i m i t s o f t o l e r a n c e o f t h e owner. C a t c h p o l e (1972) s u g g e s t e d t h a t t h e l o c a l t o p o g r a p h y o f r e e d b e d s g r e a t l y i n f l u e n c e d t h e s h a p e , b u t n o t t h e s i z e , o f t h e t e r r i t o r i e s o f Reed W a r b l e r s , A c r o c e P h a l u s s c i r p _ a c e o u s , and Sedge W a r b l e r s , 23 s c h o e n o b a g n u s . F i n a l l y , S a l e (1972) s u g g e s t e d t h a t s h e l t e r and a g o n i s t i c b e h a v i o u r were f a c t o r s r e s p o n s i b l e f o r t h e s p a c i n g p a t t e r n s o v e r c o r a l h e a d s o f a p o m a c e n t r i d f i s h , D a s c y l l u s a r u a n u s . F u r t h e r , a s h o r t a g e o f n e s t s i t e s c a n l i m i t t h e p o p u l a t i o n o f , f o r example, h o l e - n e s t i n g b i r d s , and a s u p p l y o f n e s t boxes can i n c r e a s e d e n s i t y . T h i s has been shown i n t h e G r e a t T i t (Lack 1966), and i n t h e P i e d F l y c a t c h e r , F i c e d u l a LY.£2.1§]J£I» ( V o n Haartman 1956; Enemar and S j o s t r a n d 1972). No s t u d y t o d a t e on Song S p a r r o w s ( r e f s . i n Tompa 1961) s u g g e s t s t h a t t h e n a t u r e o f t h e h a b i t a t o r a s h o r t a g e o f n e s t s i t e s has any i n f l u e n c e on t h e s i z e o f t e r r i t o r y t a k e n ( w i t h i n t h e l i m i t s , o b v i o u s l y , o f t h e t y p e o f h a b i t a t t h a t a Song Sparrow w i l l o c c u p y ) . A f u r t h e r p o s s i b l e f a c t o r which c o u l d i n f l u e n c e t h e d e n s i t y o f a t e r r i t o r i a l a n i m a l , and hence t h e t e r r i t o r y s i z e , i s i n t e r s p e c i f i c c o m p e t i t i o n . T h e r e i s some e v i d e n c e t h a t t h e d e n s i t y o f one s p e c i e s has an e f f e c t on t h e d e n s i t y o f a n o t h e r i n p o p u l a t i o n s o f b o t h i n v e r t e b r a t e s and v e r t e b r a t e s ( e . g . C o n n e l l 1961; I n g e r and G r e e n b e r g 1966; M i c h i e l s o n 1966; A y a l a 1971; Z a r e t and Band 1971; Brown 1971; S h e p p a r d 1971). F o r p a s s e r i n e b i r d s , and p a r t i c u l a r l y Song S p a r r o w s , 8. I . Y e a t o n ( p e r s . comm.) h y p o t h e s i s e d t h a t t h e more s p e c i e s c o m p e t i n g f o r some l i m i t i n g r e s o u r c e i n a g i v e n a r e a , t h e l a r g e r t h e t e r r i t o r i e s o f Song S p a r r o w s w i l l be ( ' h o r i z o n t a l ' 24 r a t h e r t h a n ' v e r t i c a l * ) . H i s h y p o t h e s i s , however, i s b u i l t on c i r c u m s t a n t i a l e v i d e n c e , and no e x p e r i m e n t s have been c o n d u c t e d t o d a t e t o t e s t i t . K r e b s (1971:17) has p r e s e n t e d some t h e o r e t i c a l l y p o s s i b l e ways i n which t e r r i t o r y c o u l d i n f l u e n c e d e n s i t y , and d i s c u s s e s e a c h method a t l e n g t h . He c o n s i d e r s some methods i n which minimum t e r r i t o r y s i z e need n o t be r e l a t e d d i r e c t l y t o t h e e n v i r o n m e n t , and one o f t h e s e methods d e a l s w i t h t h e h y p o t h e s i s t h a t t h e t e m p o r a l p a t t e r n o f s e t t l i n g on t e r r i t o r i e s c a n i n f l u e n c e d e n s i t y . 3. T e m p o r a l p a t t e r n s o f s e t t l i n g on t e r r i t o r i e s F l u c t u a t i n g b r e e d i n g d e n s i t i e s i n d i f f e r e n t y e a r s c o u l d be t h e r e s u l t o f d i f f e r e n t d e g r e e s o f s e t t l i n g i n t h o s e y e a r s . I n t h i s way, an u p p e r l i m i t s e t t o t h e number o f s e t t l e d t e r r i t o r y owners c a n be a v a r i a b l e one. F o r t h e h y p o t h e s i s t h a t t e m p o r a l p a t t e r n s o f s e t t l i n g on t e r r i t o r i e s can i n f l u e n c e d e n s i t y , t h e r e i s some s u p p o r t i n g e v i d e n c e i n work on b i r d s and f i s h . Van den Assem (1967) f o u n d t h a t i n t h e t h r e e - s p i n e d s t i c k l e b a c k , g a s t e r o s t e u s a c u l e a t u s , t e r r i t o r y s i z e s v a r i e d c o n s i d e r a b l y w i t h t h e p a t t e r n o f s e t t l i n g . The number o f t e r r i t o r i a l m a l e s a c c o m o d a t e d i n a t a n k was n e a r l y d o u b l e when t h e males were i n t r o d u c e d s i m u l t a n e o u s l y a s when t h e y were i n t r o d u c e d s u c c e s s i v e l y . He i n t e r p r e t e d t h e r e s u l t s as 25 s u g g e s t i n g t h a t t h e r e l a t i v e d i f f e r e n c e s i n a g g r e s s i v e l e v e l s i n t h e male s t i c k l e b a c k s - a l l o f them i n t h e p r o c e s s o f s e t t l i n g and b u i l d i n g - were t e m p o r a r i l y s m a l l e r t h a n f o u n d i f males were i n t r o d u c e d s u c c e s s i v e l y . Simms (1965) r e l a t e s t h a t f o r t h e E u r o p e a n B l a c k b i r d , T u r d u s m e r u l a , t h e number o f t e r r i t o r i e s i n a s t a b l e p o p u l a t i o n was r e d u c e d by 55% a f t e r a s e v e r e snowstorm. The number o f t e r r i t o r i e s h e l d a f t e r t h e snowstorm was 93 as compared t o a b o u t 200 i n t h e p r e v i o u s y e a r , b u t r o s e t o 244 t h e f o l l o w i n g y e a r , and t h i s i s t a k e n as s u g g e s t i v e e v i d e n c e t h a t t h e p a t t e r n o f s e t t l i n g i n f l u e n c e d t e r r i t o r y s i z e . F o r t h e G r e a t T i t , K r e b s (1971) has put f o r w a r d s u g g e s t i v e e v i d e n c e t h a t i s a t l e a s t c o n s i s t e n t w i t h t h e h y p o t h e s i s . S e t t l i n g on t e r r i t o r i e s by G r e a t T i t s o c c u r s i n F e b r u a r y , and, i f s y n c h r o n y o f s e t t l i n g i n f l u e n c e s t h e c o m p r e s s i b i l i t y o f t e r r i t o r i e s , and a c o n s i s t e n t l y warm F e b r u a r y c a u s e s b o t h a d u l t s and f i r s t y e a r b i r d s t o s e t t l e more s y n c h r o n o u s l y , t h e n t h e b r e e d i n g d e n s i t y might i n c r e a s e . K r e b s showed t h a t t h e r e was a p o s i t i v e c o r r e l a t i o n between mean F e b r u a r y t e m p e r a t u r e and s u b s e q u e n t b r e e d i n g d e n s i t y . C a t c h p o l e (1972) s u g g e s t e d t h a t t e m p o r a l p a t t e r n s o f s e t t l i n g on t e r r i t o r i e s might a c c o u n t f o r t h e v a r i a t i o n s i n mean t e r r i t o r y s i z e he o b s e r v e d i n a t h r e e y e a r s t u d y o f Reed and Sedge W a r b l e r s . He a d m i t s , however, t o h a v i n g no c o n c l u s i v e e v i d e n c e t o s u b s t a n t i a t e t h e h y p o t h e s i s . 26 P o s s i b l y t h e example which b e s t s u p p o r t s t h e h y p o t h e s i s i n b i r d s i s f r o m Song S p a r r o w s on M a n d a r t e I s l a n d (Tompa 1964; 1 9 7 1). The number o f t e r r i t o r i e s f o r t h e f i r s t two y e a r s o f t h e s t u d y was c o n s t a n t , b u t i n c r e a s e d s u b s t a n t i a l l y i n t h e t h i r d y e a r o f t h e s t u d y f o l l o w i n g a c a t a s t r o p h i c m o r t a l i t y , c a u s e d by a f r e a k snowstorm i n March, o f t e r r i t o r i a l b i r d s . The s t o r m o c c u r r e d i n t h e s p r i n g a t t h e peak o f t e r r i t o r i a l b e h a v i o u r , and a p p a r e n t l y c a u s e d l i t t l e m o r t a l i t y amongst t h o s e y e a r l i n g s t h a t were no t t e r r i t o r i a l l y a c t i v e . A f t e r t h e s t o r m , t h e s e n o n - t e r r i t o r i a l b i r d s were a l l o w e d t o s e t t l e , now t h a t t h e r e s i s t a n c e f r o m t h e e s t a b l i s h e d t e r r i t o r i a l b i r d s had gone, and t h e number o f o c c u p i e d t e r r i t o r i e s i n c r e a s e d . The number o f t e r r i t o r i e s a l s o r e m a i n e d h i g h f o r t h e f o u r t h y e a r o f t h e s t u d y . I t h e r e f o r e s e t o u t t o e x p e r i m e n t a l l y i n v e s t i g a t e t h e f o l l o w i n g q u e s t i o n : i n Song S p a r r o w s , d o e s t h e t e m p o r a l p a t t e r n o f s e t t l i n g on t e r r i t o r i e s i n a g i v e n a r e a i n f l u e n c e t h e number o f t e r r i t o r i e s o c c u p i e d , and hence t e r r i t o r y s i z e , and> t h e b r e e d i n g d e n s i t y ? 27 I I . PROCEDURE In o r d e r t o t e s t e x p e r i m e n t a l l y t h e h y p o t h e s i s t h a t t e m p o r a l p a t t e r n s o f s e t t l i n g on t e r r i t o r i e s c a n i n f l u e n c e t h e number o f t e r r i t o r i e s t a k e n i n a g i v e n a r e a , i t was n e c e s s a r y t o c a r r y o u t r e m o v a l s o f t h e t e r r i t o r i a l p a i r s . The r e m o v a l e x p e r i m e n t s t h e m s e l v e s would show t h a t , i f r e p l a c e m e n t o c c u r r e d , t h e r e e x i s t e d a s u r p l u s o f Song S p a r r o w s on t h e s t u d y a r e a . I f t h e r e p l a c e m e n t b i r d s came from t h e l o o s e g r o u p s o f n o n - t e r r i t o r i a l j u v e n i l e s , t h e n i t c a n be deduced t h a t t h e r e s i d e n t t e r r i t o r y h o l d e r s were p r e v e n t i n g c e r t a i n j u v e n i l e s f r o m t a k i n g t e r r i t o r i e s on t h e s t u d y a r e a . As h o l d i n g a t e r r i t o r y f o r a Song Sparrow i s a n e c e s s a r y p r e - r e q u i s i t e f o r b r e e d i n g , t h e n i t can be f u r t h e r d e d u c e d t h a t , i f t h e r e p l a c e m e n t j u v e n i l e s were c a p a b l e o f b r e e d i n g , t h e t e r r i t o r i a l b e h a v i o u r o f t h e r e s i d e n t b i r d s l i m i t e d t h e b r e e d i n g d e n s i t y . Two t y p e s o f r e m o v a l e x p e r i m e n t s were c a r r i e d o u t : • S i m u l t a n e o u s ' and ' S u c c e s s i v e ' . A S i m u l t a n e o u s Removal i n v o l v e d t h e r e m o v a l o f t h e t e r r i t o r i a l b i r d s , b o t h males and f e m a l e s , i n as s h o r t a s p a c e o f t i m e a s p o s s i b l e , t h u s c r e a t i n g an a r e a o f s u i t a b l e h a b i t a t which was c o m p l e t e l y empty o f t e r r i t o r i a l Song S p a r r o w s . T h i s was i n t e n d e d t o a l l o w s i m u l t a n e o u s s e t t l i n g o f some o f t h e n o n - t e r r i t o r i a l Song S p a r r o w s . T h i s t y p e o f r e m o v a l was i n t e n d e d t o s i m u l a t e 28 a c a t a s t r o p h i c m o r t a l i t y o f n o n - m i g r a t o r y t e r r i t o r i a l b i r d s , b u t i t c o u l d e q u a l l y w e l l be a p p l i e d t o o t h e r i n s t a n c e s c f a v o i d o f t e r r i t o r i a l b i r d s i n an a r e a o f s u i t a b l e h a b i t a t , a s f o r example when m i g r a t o r y b i r d s r e t u r n i n t h e s p r i n g a t t h e same t i m e t o a n o n - o c c u p i e d a r e a . T h e s e t y p e s o f o c c u p a n c y a r e h e r e t r e a t e d a s e q u i v a l e n t . A S u c c e s s i v e Removal i n v o l v e d t h e r e m o v a l o f t e r r i t o r i a l p a i r s a t r e g u l a r i n t e r v a l s , s i m u l a t i n g t h e more n o r m a l s i t u a t i o n o f t h e p e r i o d i c d i s a p p e a r a n c e o v e r a l o n g e r p e r i o d of t i m e o f t e r r i t o r i a l i n d i v i d u a l s . T h i s was i n t e n d e d t o a l l o w s u c c e s s i v e s e t t l i n g o f some n o n - t e r r i t o r i a l Song S p a r r o w s . S i m u l t a n e o u s and S u c c e s s i v e r e m o v a l s were c o n d u c t e d i n the f a l l o f 1972 and i n t h e s p r i n g o f 1973. T h e s e two t i m e s c o i n c i d e d w i t h t h e two p e a k s o f t e r r i t o r i a l b e h a v i o u r o f Song S p a r r o w s ( N i c e 1943; Tompa 1964). Two d i f f e r e n t hedgerows were used f o r e a c h s e t o f r e m o v a l e x p e r i m e n t s (see F i g u r e 1 ) . Each s e t was a r r a n g e d s u c h t h a t a C o n t r o l a r e a was s a n d w i c h e d between t h e S i m u l t a n e o u s and t h e S u c c e s s i v e Removal a r e a s . B i r d s were removed e i t h e r by m i s t n e t t i n g o r by s h o o t i n g . The most s u c c e s s f u l means p r o v e d t o be t h e use o f a t a p e d song o f a s t r a n g e r Song S p a r r o w , and a m i s t n e t s t r u n g o v e r t h e t a p e r e c o r d e r . B o t h males and f e m a l e s were c a u g h t i n t h e m i s t n e t s as t h e y r e s p o n d e d t o t h e t a p e . The o n l y major p r o b l e m c o n c e r n e d t h e r e m o v a l o f f e m a l e s i n t h e f a l l (see b e l o w ) . 29 Appendix 4 g i v e s some p o s s i b l e r e a s o n s a c c o u n t i n g f o r t h e d i f f i c u l t y i n l o c a t i n g f e m a l e s a t t h i s t i m e . The F a l l Removal A r e a T h i s hedgerow c o n t a i n e d 24 t e r r i t o r i e s i n t h e f a l l o f 1972. 8 t e r r i t o r i e s were u s e d f o r t h e S u c c e s s i v e Removal, 6 f o r t h e C o n t r o l , and 10 f o r t h e t h e S i m u l t a n e o u s Removal. The 10 t e r r i t o r i e s on t h e S i m u l t a n e o u s Removal a r e a c o n t a i n e d 8 a d u l t males f r o m t h e summer, and 2 j u v e n i l e m a l e s , w i t h o u t mates, t h a t had e s t a b l i s h e d t e r r i t o r i e s f o r t h e m s e l v e s by i n t r u s i o n d u r i n g t h e e a r l y f a l l . S i m i l a r l y , t h e 8 t e r r i t o r i e s on t h e S u c c e s s i v e Removal a r e a c o n t a i n e d 1 j u v e n i l e male, m a t e l e s s , w i t h a t e r r i t o r y e s t a b l i s h e d by i n t r u s i o n e a r l y i n t h e f a l l . 9 o u t o f t h e 10 m a l e s on t h e S i m u l t a n e o u s Removal a r e a were removed i n t h e p e r i o d O c t o b e r 4 t o 7; t h e l a s t male was removed on O c t o b e r 12. T h i s l a s t male was n o t r e c o r d e d from O c t o b e r 1 t o 11, and i t i s p o s s i b l e t h a t t h e d i f f i c u l t y i n l o c a t i n g him c o u l d be due t o t h e f a c t t h a t he had n o t c o m p l e t e d t h e p o s t - b r e e d i n g m o u l t u n t i l t h e s e c o n d week o f O c t o b e r . A l s o , on t h e S i m u l t a n e o u s Removal a r e a , o u t o f a p o s s i b l e 8 f e m a l e s , o n l y 4 were removed. Some p o s s i b l e e x p l a n a t i o n s f o r t h i s d i s c r e p a n c y a r e g i v e n i n Ap p e n d i x 4. 30 The 8 males on t h e S u c c e s s i v e Removal a r e a were removed from O c t o b e r 3 t o 27, a t i n t e r v a l s o f t h r e e and f o u r days a l t e r n a t e l y . Once a g a i n , f e m a l e s p r o v e d d i f f i c u l t t o l o c a t e . Out o f a p o s s i b l e 7 f e m a l e s , o n l y one was removed (see Ap p e n d i x 4 a g a i n f o r p o s s i b l e e x p l a n a t i o n s ) . The S p r i n g Removal A r e a T h i s hedgerow c o n t a i n e d 19 t e r r i t o r i e s i n t h e s p r i n g o f 1973. 7 t e r r i t o r i e s were t a k e n f o r t h e S i m u l t a n e o u s Removal, 6 f o r t h e C o n t r o l , and 6 f o r t h e S u c c e s s i v e Removal. 7 males and 5 f e m a l e s were removed f r o m t h e S i m u l t a n e o u s Removal a r e a on March 7. Two f e m a l e s were a p p a r e n t l y m i s s i n g on t h e day o f t h e e x p e r i m e n t . One t e r r i t o r i a l male, a y e a r l i n g t h a t had t a k e n o v e r a t e r r i t o r y i n t h e f a l l o f 1972 a f t e r an a d u l t male had d i s a p p e a r e d , d i d n o t a p p e a r t o have a f e m a l e ( s i x h o u r s o f w a t c h i n g from a h i d e i n t h i s male's t e r r i t o r y f a i l e d t o r e v e a l a p a i r e d f e m a l e ) . The s e c o n d f e m a l e d i s a p p e a r e d f r o m h e r mate's t e r r i t o r y between J a n u a r y 29 and F e b r u a r y 2. The male i s t h o u g h t t o have t a k e n a j u v e n i l e f e m a l e as h i s mate; t h i s i n c i d e n t i s c o n s i d e r e d more a t l e n g t h i n PART B. 6 males and 4 f e m a l e s were removed i n p a i r s f r o m t h e S u c c e s s i v e Removal a r e a , a t i n t e r v a l s o f t h r e e and f o u r d a ys a l t e r n a t e l y , between March 3 and 23. Two f e m a l e s were a p p a r e n t l y m i s s i n g on t h e d a y s o f t h e e x p e r i m e n t a l r e m o v a l s . 31 One f e m a l e d i s a p p e a r e d s h o r t l y b e f o r e t h e r e m o v a l e x p e r i m e n t s , and was n o t s e e n a f t e r w a r d s . The s e c o n d f e m a l e d e s e r t e d h e r mate b e f o r e t h e e x p e r i m e n t s , and remated w i t h a C o n t r o l male i n e a r l y March. The C o n t r o l s C o n t r o l s i n b o t h S p r i n g and F a l l Removal A r e a s r e m a i n e d u n d i s t u r b e d d u r i n g t h e r e m o v a l e x p e r i m e n t s . 32 I I I . RESULTS 1. R e p l a c e m e n t Of Removed P a i r s The Sparing Removal A r e a On t h e S i m u l t a n e o u s Removal a r e a , 7 males and 5 f e m a l e s were removed. W i t h i n 9 d a y s , 10 males and 7 f e m a l e s had s e t t l e d . T h u s , 17 b i r d s had r e p l a c e d t h e 12 removed. On t h e S u c c e s s i v e Removal a r e a , 6 males and 4 f e m a l e s were removed. R e p l a c e m e n t p a i r s s e t t l e d on v a c a n t t e r r i t o r i e s I, d u r i n g t h e t h r e e o r f o u r day i n t e r v a l s between t h e s u c c e s s i v e :\ r e m o v a l s . By H a r c h 27, 5 p a i r s s e t t l e d . T h u s , 10 b i r d s had r e p l a c e d t h e 10 removed. The F a l l Removal A r e a On t h e S i m u l t a n e o u s Removal a r e a , 10 males and 4 f e m a l e s were removed. W i t h i n 10 d a y s a f t e r t h e r e m o v a l o f t h e n i n t h male on O c t o b e r 7, 14 males had s e t t l e d . A l t h o u g h s e v e r a l f e m a l e s were c a u g h t i n t h e f a l l o f 1972, i t was n o t known i f t h e y were p a i r e d w i t h t h e r e p l a c e m e n t b i r d s o r n o t . T h e r e f o r e , a s s e s s m e n t o f t h e number o f f e m a l e s was n o t done u n t i l t h e s p r i n g o f 1973. On t h e S u c c e s s i v e Removal a r e a , 8 males and 1 f e m a l e were removed. As i n t h e S u c c e s s i v e Removal i n t h e s p r i n g e x p e r i m e n t , r e p l a c e m e n t b i r d s s e t t l e d on v a c a n t t e r r i t o r i e s d u r i n g t h e t h r e e o r f o u r day i n t e r v a l s between t h e s u c c e s s i v e 33 r e m o v a l s . By O c t o b e r 30, 9 males had e s t a b l i s h e d t e r r i t o r i e s . Once a g a i n , s e v e r a l f e m a l e s were c a u g h t i n t h e f a l l o f 1972, bu t t h e i r r e l a t i o n t o t h e t e r r i t o r i a l males was n o t known. A s s e s s m e n t o f t e r r i t o r i a l f e m a l e s t h e r e f o r e was d e f e r r e d u n t i l t h e s p r i n g o f 1973. A f t e r r e s e t t l i n g had o c c u r r e d , t e r r i t o r i e s c o v e r e d t h e e n t i r e l e n g t h o f t h e hedgerows i n b o t h S p r i n g and F a l l Removal A r e a s (see F i g u r e 6 as an e x a m p l e ) . Some e x p a n s i o n o c c u r r e d i n i n s t a n c e s where a C o n t r o l and an E x p e r i m e n t a l a r e a met (see b e l o w ) , s u g g e s t i n g t h a t b e f o r e t h e r e m o v a l s , t h e r e was p r e s s u r e p r e v e n t i n g e x p a n s i o n (Watson 1967; K r e b s 1971). Thus, t h e r e p l a c e m e n t e x p e r i m e n t s showed t h e e x i s t e n c e o f a s u r p l u s o f p o t e n t i a l b r e e d e r s who were p r e v e n t e d f r o m s e t t l i n g on t h e s t u d y a r e a by t h e r e s i d e n t t e r r i t o r y h o l d e r s . 2. Numbers Of O c c u p i e d T e r r i t o r i e s T a b l e 2 g i v e s t h e r e s u l t s o f t h e r e m o v a l e x p e r i m e n t s f o r b o t h S p r i n g and F a l l Removal A r e a s . Numbers o f t e r r i t o r i e s o c c u p i e d by m a l e s , b o t h mated and unmated, a r e g i v e n . On b o t h S i m u l t a n e o u s Removal a r e a s , t h e r e was an i n c r e a s e i n t h e number o f o c c u p i e d t e r r i t o r i e s a f t e r t h e r e m o v a l s . I n c r e a s e s i n b o t h s p r i n g and f a l l were i n t h e r e g i o n o f 40%. On t h e S u c c e s s i v e Removal a r e a s and on t h e C o n t r o l s , t h e r e were o n l y s l i g h t c h a n g e s i n t h e numbers o f o c c u p i e d 34 TABLE 2 Results of removal experiments: numbers of occupied territories of both mated and unmated males Spring Removal Area Before After Percentage change i n number of territories Simultaneous: 7 10 +42% Successive: 6 -16.7% Control: 6 +16.7% F a l l Removal Area Simultaneous: 10 14 +40% Successive: 8 +12.5% Control: -16.7% 35 t e r r i t o r i e s (see b e l o w ) . The d i f f e r e n c e s i n t h e numbers o f t e r r i t o r i e s b e f o r e and a f t e r t h e r e m o v a l e x p e r i m e n t s a r e compared i n T a b l e 3. The d i f f e r e n c e s between t h e S i m u l t a n e o u s and t h e S u c c e s s i v e Removal a r e a s , and between t h e S i m u l t a n e o u s Removal a r e a s and t h e C o n t r o l s , i n b o t h S p r i n g and F a l l Removal A r e a s , a r e compared. The d i f f e r e n c e s i n o c c u p i e d t e r r i t o r i e s on t h e S i m u l t a n e o u s Removal a r e a s a r e s i g n i f i c a n t l y h i g h e r (P<0.05) t h a n t h o s e on t h e S u c c e s s i v e Removal a r e a s and on t h e C o n t r o l s . T h e s e d a t a s u g g e s t t h e s i m u l t a n e o u s s e t t l i n g r e s u l t s i n more t e r r i t o r i e s t a k e n t h a n i f t h e s e t t l i n g o c c u r s s u c c e s s i v e l y . 3 • S i z e Of T e r r i t o r i e s An i n c r e a s e i n numbers o f t e r r i t o r i e s i n a f i x e d a r e a n e c e s s a r i l y i m p l i e s t h a t t h e mean t e r r i t o r y s i z e d e c r e a s e s . I n t h e p r e s e n t s t u d y , t h e a r e a s were n o t e x a c t l y t h e same b e f o r e and a f t e r t h e e x p e r i m e n t s , p a r t i c u l a r l y t h e S p r i n g Removal A r e a . T h i s was due t o t h e e x p a n s i o n o f t h e t e r r i t o r i a l b o u n d a r i e s o f t h o s e C o n t r o l males t h a t had t e r r i t o r i e s a d j a c e n t t o t h e r e m o v a l a r e a s . Hence a more a c c u r a t e measure o f t h e d i f f e r e n c e s b e f o r e and a f t e r t h e r e m o v a l e x p e r i m e n t s i s t o compare mean t e r r i t o r y s i z e s . 36 TABLE 3 Results of removal experiments: differences i n numbers of occupied t e r r i t o r i e s of both mated and unmated males Simultaneous Successive Spring: +3 -1 F a l l : +4 +1 t = 3.13 P < 0.05 (one-tail) Simultaneous Control Spring: +3 +1 F a l l : +4 -1 t = 3.13 P < 0.05 (one-tail) 37 T a b l e s 4 and 5 g i v e t h e mean t e r r i t o r y s i z e s i n t h e S i m u n t a n e o u s and t h e S u c c e s s i v e Removal a r e a s , and t h e C o n t r o l s , f o r b o t h s p r i n g and f a l l r e m o v a l e x p e r i m e n t s . On t h e S i m u l t a n e o u s Removal a r e a s , t h e d i f f e r e n c e s between t h e mean t e r r i t o r y s i z e s b e f o r e and a f t e r t h e r e m o v a l s a r e s i g n i f i c a n t ; P<0.01 f o r t h e S p r i n g Removal A r e a , P<0.05 f o r t h e F a l l Removal A r e a . The mean t e r r i t o r y s i z e s on t h e S i m u l t a n e o u s Removal a r e a s a r e much s m a l l e r a f t e r t h e e x p e r i m e n t s t h a n b e f o r e . T h e r e a r e d i f f e r e n c e s i n mean t e r r i t o r y s i z e s b e f o r e and a f t e r t h e r e m o v a l s on b o t h S u c c e s s i v e Removal a r e a s , and on t h e C o n t r o l s , b u t i n no i n s t a n c e a r e t h e d i f f e r e n c e s s i g n i f i c a n t . T h e s e d a t a f u r t h e r s u p p o r t t h e h y p o t h e s i s t h a t s i m u l t a n e o u s s e t t l i n g r e s u l t s i n more t e r r i t o r i e s o c c u p i e d , w i t h s m a l l e r mean t e r r i t o r y s i z e , t h a n i f t h e s e t t l i n g i s s u c c e s s i v e . So f a r , t h e a n a l y s e s have d e a l t w i t h t h e numbers o f t e r r i t o r i e s , and t h e s i z e s o f t e r r i t o r i e s , b e f o r e and a f t e r t h e r e m o v a l e x p e r i m e n t s . I t i s n e c e s s a r y , however, t o compare t h e b r e e d i n g d e n s i t y b e f o r e and a f t e r t h e r e m o v a l s , a s some mal e s r e m a i n e d unmated d u r i n g t h e s p r i n g o f 1973. B e f o r e d o i n g s o , however, c e r t a i n c h a n g e s i n numbers o f t e r r i t o r i e s t h a t t o o k p l a c e o v e r t h e w i n t e r on t h e F a l l Removal A r e a need t o be c o n s i d e r e d . 38 TABLE 4 Results of the removal experiments: mean t e r r i t o r y s i z e . F a l l Removal Area. 2 2 N Mean T e r r i t o r y Size (m ) S(m ) Simultaneous: Before 10 2323 972 A f t e r 14 1659 652 * t = 2.01 P < 0.05 Successive: Before 8 3238 969 A f t e r 9 2878 548 t = o.96 0.2 > p y 0.1 Control: Before 6 1745 406 A f t e r 5 2094 520 t = 1.25 0.2 > P > 0.1 * S t a t i s t i c a l l y s i g n i f i c a n t 39 TABLE 5 R e s u l t s o f removal experiments: mean t e r r i t o r y s i z e . Spring Removal Area 2 2 N Mean T e r r i t o r y Size (m ) S(m ) Simultaneous: Before A f t e r 10 3638 2572 370 887 * t = 2.69 P < 0.01 ( o n e - t a i l ) Successive: Before 1890 766 A f t e r 2143 608 t = 0.60 0.45 > P > 0.3 ( o n e - t a i l ) C o n t r o l : Before 3956 611 A f t e r 3480 1229 t = 0.86 0.25 > P ^ 0.2 ( o n e - t a i l ) * S t a t i s t i c a l l y s i g n i f i c a n t \ 40 4. Changes In Numbers Of T e r r i t o r i e s On The F a l l Removal Area Over The Winter In the preceding a n a l y s e s , numbers of replacement males on the F a l l Removal Area were determined during the f a l l a f t e r the removal experiments. Changes i n the numbers of t e r r i t o r i e s on the F a l l Removal Area however occ u r r e d over the winter. By October 17, 14 j u v e n i l e males had r e p l a c e d 10 t e r r i t o r i a l males on the Simultaneous Removal area. In mid-December, the 14 replacements were s t i l l present. From mid-December to mid-March, I d i d not survey t h i s area as time was spent l o o k i n g at the dominance h i e r a r c h i e s on the S p r i n g Removal Area. (See PART B). In mid-March, i t was apparent from surveys of the breeding p o p u l a t i o n t h a t a ' n a t u r a l ' removal had taken p l a c e . Only 10 males had t e r r i t o r i e s along the hedgerow; 9 of these males were ' o r i g i n a l s ' from the f a l l , and one was a newcomer t h a t had taken over one of the ' o r i g i n a l ' s ' t e r r i t o r i e s . Of the f o u r t e r r i t o r i e s t h a t had been occupied i n the f a l l and were now n o n - e x i s t e n t , two had been expanded i n t o , and p a r t i t i o n e d , by neighbouring males, and two had been i n c o r p o r a t e d i n t o the t e r r i t o r y of a C o n t r o l male. Figure 5 g i v e s the sequence of events l e a d i n g t o the l a t t e r i n c o r p o r a t i o n . The p a r t i c u l a r male i n v o l v e d (C6), i n the s p r i n g of 1973, defended a p p a r e n t l y s u c c e s s f u l l y a t e r r i t o r y Figure 5 F a l l Removal Area: the Simultaneous Removal Area - Control. The movement and expansion of Control male (C6) a f t e r the removal experiments and during the subsequent winter 42 whose s i z e was an u n p r e c e d e n t e d 8755 s q u a r e m e t r e s , f a r l a r g e r t h a n any o t h e r Song S p a r r o w s t e r r i t o r y on R e i f e l I s l a n d . T hus, t h e 10 r e p l a c e m e n t m a l e s t h a t o c c u p i e d t e r r i t o r i e s i n t h e s p r i n g o f 1973 a c t u a l l y c o v e r e d much l e s s a r e a t h a n t h e 14 i n t h e f a l l o f 1972. I n f a c t , t h e i r combined t e r r i t o r i e s c o v e r e d an a r e a t h a t s u p p o r t e d 12 r e p l a c e m e n t males i n t h e f a l l a f t e r t h e r e m o v a l , and 8 a d u l t males i n t h e f a l l b e f o r e t h e r e m o v a l . On t h e S u c c e s s i v e Removal a r e a , 2 males o u t o f 9 r e p l a c e m e n t s d i s a p p e a r e d o v e r t h e w i n t e r . B o t h o f t h e t e r r i t o r i e s were expanded i n t o , and i n c o r p o r a t e d , by n e i g h b o u r i n g m a l e s . T h e r e f o r e , i n t h e s p r i n g o f 1973, 7 m a l e s , a l l p a i r e d , h e l d t e r r i t o r i e s . 5- Breeding. D e n s i t y I n The S p r i n g . Of ,1973 T a b l e 6 g i v e s t h e number o f b r e e d i n g p a i r s , and t h e number o f t e r r i t o r i a l unmated m a l e s , f o r a l l a r e a s . On t h e F a l l Removal A r e a , t h e b r e e d i n g d e n s i t i e s between t h e s p r i n g o f 1972 and t h e s p r i n g o f 1973 a r e compared. D e s p i t e t h e f a c t t h a t t h e number o f t e r r i t o r i e s i n c r e a s e d a f t e r t h e e x p e r i m e n t s on t h e S i m u l t a n e o u s Removal a r e a s on b o t h S p r i n g and F a l l Removal A r e a s , t h e number o f b r e e d i n g p a i r s r e m a i n e d e s s e n t i a l l y t h e same - 14 p a i r s b e f o r e , 15 a f t e r . T h e r e were t h e r e f o r e s e v e r a l (5) unmated t e r r i t o r i a l 43 TABLE 6 Results of the removal experiments: breeding density Spring Removal Area T e r r i t o r i a l Number of Breeding p a i r s unmated males t e r r i t o r i e s Simultaneous: Before 6 1 7 A f t e r 7 3 10 Successive: Before 6 0 6 A f t e r 5 0 5 Control: Before 6 0 6 A f t e r 7 0 7 F a l l Removal Area Simultaneous: Before 8 0 8 A f t e r 8 2 10 Successive: Before 7 0 7 A f t e r 7 0 7 Control: Before 5 1 6 A f t e r 5 0 5 44 ma l e s p r e s e n t . I t i s o f i n t e r e s t t h a t Tompa (1964; 1971) f o u n d much t h e same r e s u l t on Mandarte I s l a n d . F o l l o w i n g t h e c a t a s t r o p h i c m o r t a l i t y o f t e r r i t o r i a l Song S p a r r o w s i n March 1962, t h e number o f o c c u p i e d t e r r i t o r i e s r o s e by n e a r l y 401 t o 69, w h i l s t t h e b r e e d i n g d e n s i t y r e m a i n e d r o u g h l y a t t h e same l e v e l as p r e v i o u s y e a r s - 47 p a i r s i n 1960 and 1961, 44 i n 1962. I t was not u n t i l t h e f a l l o f 1962 t h a t t h e s e t t l i n g o f j u v e n i l e f e m a l e s on t h e t e r r i t o r i e s o f unmated males r a i s e d t h e number o f t e r r i t o r i e s w i t h p a i r s t o 69. As t h e p r e s e n t s t u d y t e r m i n a t e d i n t h e summer o f 1973, t h e r e i s no e v i d e n c e t h a t t h e b r e e d i n g d e n s i t y a c h i e v e d a b a l a n c e d s e x r a t i o , e i t h e r t h r o u g h t h e d i s a p p e a r a n c e o f t h e unmated males o r t h r o u g h t h e s e t t l i n g o f f e m a l e s on t h e s e unmated m a l e s ' t e r r i t o r i e s . 1 The number o f b r e e d i n g p a i r s on t h e S u c c e s s i v e Removal a r e a s , and on t h e C o n t r o l s , r e m a i n e d e s s e n t i a l l y the same b e f o r e and a f t e r t h e r e m o v a l e x p e r i m e n t s . The s l i g h t d i f f e r e n c e s on t h e C o n t r o l s c a n be a c c o u n t e d f o r by t h e e x p a n s i o n o f t h e t e r r i t o r y b o u n d a r i e s o f c e r t a i n C o n t r o l m a l e s , a s e x p l a i n e d e a r l i e r . 6. D i f f e r e n c e s I n T e r r i t o r y S i z e Between Mated And Unmated M a l e s 45 An i n t e r e s t i n g s i d e l i g h t on t h e s i z e o f t e r r i t o r i e s i n t h e S i m u l t a n e o u s Removal a r e a s i s t h a t males t h a t d i d n o t a t t r a c t a mate had s i g n i f i c a n t l y s m a l l e r t e r r i t o r i e s t h a n t h o s e t h a t d i d ( T a b l e 7 ) . B oth N i c e (1943) and Tompa (1964) s t a t e t h a t t h e f e m a l e Song S p a r r o w s does not d i s c r i m i n a t e i n h e r c h o i c e o f male o r t e r r i t o r y , b u t s e t t l e s w h e r e v e r t h e r e i s a v a c a n t t e r r i t o r y w i t h an unmated male. F o r t h e Song S p a r r o w s on R e i f e l I s l a n d , e i t h e r t h e r e was an o v e r a l l s h o r t a g e o f f e m a l e s i n March 1973, as s e v e r a l males d i d not o b t a i n mates, o r e l s e t h e f e m a l e s d i s c r i m i n a t e d a g a i n s t males w i t h s m a l l e r t e r r i t o r i e s . T a b l e 9 g i v e s t h e number o f n o n - t e r r i t o r i a l f e m a l e s banded from f a l l 1972 t o e a r l y F e b r u a r y 1973. Of t h e 57 banded i n t h i s p e r i o d , 32 were known t o be a l i v e i n m i d - F e b r u a r y . The e v i d e n c e h e r e i s b o t h s p e c u l a t i v e and c i r c u m s t a n t i a l . A l t h o u g h i t a p p e a r s t h a t t h e r e were s e v e r a l f e m a l e s a v a i l a b l e i n t h e s p r i n g o f 1973 and t h a t t h e y d i d d i s c r i m i n a t e a g a i n s t m a l e s w i t h s m a l l e r t e r r i t o r i e s , i t i s i n t e r e s t i n g t o n o t e t h a t , on M a n d a r t e I s l a n d , t h o s e males (25) t h a t d i d n o t have f e m a l e s i n t h e s p r i n g o f 1962 o b t a i n e d mates i n t h e f a l l , a p p a r e n t l y t h r o u g h t h e p a s s i v e s e t t l i n g o f new f e m a l e s (Tompa 1964). Tompa c o n c l u d e d t h a t t h e r e was an o v e r a l l s h o r t a g e o f f e m a l e s i n t h e s p r i n g o f 1962. Y e t , even i n t h e o t h e r y e a r s o f h i s s t u d y , t h e r e were 46 TABLE 7 Differences i n territory size between mated and unmated males: spring 1973. Simultaneous Removal areas. Simultaneous Removal Areas 2 2 N Mean Territory Size (m ) S(m ) Te r r i t o r i a l males: mated 15 2828 1401 unmated 5 1736 867 * t = 1.75 P < 0.05 (one-tail) * S t a t i s t i c a l l y significant 47 unmated males w i t h t e r r i t o r i e s . He a l s o shows ( I b i d : 1 8 , T a b l e 7) t h a t unmated males had s m a l l e r t e r r i t o r i e s t h a n mated m a l e s . The s i t u a t i o n r e q u i r e s f u r t h e r i n v e s t i g a t i o n t o s u b s t a n t i a t e o r r e f u t e t h e p r e c e d i n g s p e c u l a t i o n s . 7. The R e p l a c e m e n t B i r d s F i n a l l y , i t i s w o r t h c o n s i d e r i n g some a s p e c t s o f t h e r e p l a c e m e n t b i r d s . A l l b u t one (see A p p e n d i x 3) o f t h e r e p l a c e m e n t b i r d s on b o t h r e m o v a l a r e a s were j u v e n i l e s ( o r , more a c c u r a t e l y i n t h e s p r i n g , y e a r l i n g s ) . Some o f t h e r e p l a c e m e n t b i r d s (5 m a l e s , 3 f e m a l e s ) had been banded on t h e s t u d y a r e a a s d e p e n d e n t j u v e n i l e s , and hence t h e i r p a r e n t a g e was known ( t h e q u e s t i o n o f l i n e a g e i s c o n s i d e r e d more a t l e n g t h i n t h e D i s c u s s i o n g . v . ) . A young b i r d i s d e f i n e d as d e p e n d e n t d u r i n g t h e t i m e a f t e r i t has l e f t t h e n e s t , and b e f o r e i t g a i n s i n d e p e n d e n c e from i t s p a r e n t s . I n Song S p a r r o w s , t h i s t i m e i n t e r v a l i s a b o u t 20 days ( U i c e 1943). The j u v e n i l e s t h a t r e p l a c e d t h e t e r r i t o r i a l b i r d s removed d u r i n g t h e f a l l r e m o v a l e x p e r i m e n t were p r o b a b l y a l l o f l o c a l o r i g i n . T a b l e 1 shows t h a t , d u r i n g t h e f a l l , most j u v e n i l e s do n o t d i s p e r s e more t h a n 1000 m e t r e s f r o m t h e i r b i r t h p l a c e , and t h a t t h e m a j o r i t y d i s p e r s e l e s s t h a n 500 m e t r e s . F u r t h e r , t h e y were p r o b a b l y a l l n o n - t e r r i t o r i a l , as j u v e n i l e males Song S p a r r o w s do n o t a t t e m p t t o e s t a b l i s h t e r r i t o r i e s f o r 48 t h e m s e l v e s u n t i l a f t e r t h e p o s t - j u v e n i l e moult i n t h e f a l l , and c o i n c i d e n t a l l y d u r i n g t h e r e c r u d e s c e n c e o f t e r r i t o r i a l b e h a v i o u r o f t h e r e s i d e n t b i r d s ( N i c e 1937, 1943; Tompa 1964), a t which t i m e t h e r e m o v a l e x p e r i m e n t was c a r r i e d o u t . On t h e S p r i n g Removal A r e a , o u t • o f 15 r e p l a c e m e n t y e a r l i n g m ales (10 f r o m t h e S i m u l t a n e o u s Removal, 5 from t h e S u c c e s s i v e Removal ) , 11 had been banded d u r i n g t h e p r e c e d i n g f a l l o r e a r l y w i n t e r , and 2 had been banded as d e p e n d e n t young d u r i n g t h e summer o f 1972, om t h e s t u d y a r e a . S e v e r a l o f t h e r e p l a c e m e n t y e a r l i n g s were i n v o l v e d i n dominance h i e r a r c h i e s , and hence were f o l l o w e d c l o s e l y o v e r t h e w i n t e r (see PART B ) . I t i s t e n t a t i v e l y s u g g e s t e d t h a t , c o n s i d e r i n g d i s p e r s a l d i s t a n c e s ( T a b l e 1) and t h e b e h a v i o u r o f t h e n o n - t e r r i t o r i a l j u v e n i l e s d u r i n g t h e w i n t e r (see G e n e r a l I n t r o d u c t i o n ) , t h e s e r e p l a c e m e n t m a l e s were a l l l o c a l b i r d s . I n t e r e s t i n g l y enough, o u t o f 12 f e m a l e s t h a t p a i r e d w i t h some o f t h e t e r r i t o r i a l m a l e s , o n l y 5 had been banded d u r i n g t h e p r e c e d i n g f a l l o r e a r l y w i n t e r , and one as a d e p e n d e n t young i n t h e summer o f 1972, on t h e s t u d y a r e a . The r e m a i n i n g 6 were a l l unhanded. F i n a l l y , b r e e d i n g s u c c e s s f o r t h e s p r i n g o f 1973 was compared between t h e E x p e r i m e n t a l a r e a s and t h e C o n t r o l s . R e s u l t s a r e g i v e n i n T a b l e 8. The p a i r s on t h e C o n t r o l s l a i d s l i g h t l y more eggs s l i g h t l y e a r l i e r , and had a h i g h e r r a t e o f s u c c e s s f u l n e s t s , t h a n t h e p a i r s on t h e E x p e r i m e n t a l s . The d i f f e r e n c e s however 49 TABLE 8 Nesting data f o r the Controls and the Experimental areas: 1973 N Nest success Experimental: 10 40% Control: 11 46% N Clutch s i z e Experimental: Control: 3.50 3.66 t = 0.683 P y 0.5 N Mean l a y i n g date ( s t a r t of f i r s t brood) Experimental: A p r i l 19 Control: A p r i l 17 50 a r e n o t s t a t i s t i c a l l y s i g n i f i c a n t . Tompa (1964) f o u n d t h a t , when t h e s e x r a t i o was h i g h l y u n b a l a n c e d , a s i n 1962 f o l l o w i n g t h e c a t a s t r o p h i c m o r t a l i t y o f Song S p a r r o w s on Mandarte I s l a n d , t h e r e was much i n t e r f e r e n c e i n t h e b r e e d i n g a c t i v i t i e s by t h e unmated m a l e s . Y e a r l i n g s however a r e r e p o r t e d t o have s m a l l e r c l u t c h e s , and , t o l a y t h e i r f i r s t c l u t c h l a t e r , i n some s p e c i e s o f b i r d s ( e . g . C o u l s o n 1966; Snow 1958; R i c h d a l e 1957; P e r r i n s 1965). T h e r e f o r e , t h e d i f f e r e n c e s between t h e C o n t r o l s and t h e E x p e r i m e n t a l s i n c l u t c h s i z e and i n t h e mean d a t e o f l a y i n g i n t h e Song S p a r r o w s on R e i f e l I s l a n d c o u l d be a t t r i b u t e d t o t h e i n e x p e r i e n c e o f t h e new b i r d s , r a t h e r t h a n i n t e r f e r e n c e from t h e unmated t e r r i t o r i a l m a l e s . I n summary, t h e n , i t was f o u n d t h a t t h e r e p l a c e m e n t b i r d s were a l l ( e x c e p t one) j u v e n i l e s , and were p r o b a b l y a l l n o n - t e r r i t o r i a l b e f o r e t h e r e m o v a l e x p e r i m e n t s . T h o s e r e p l a c e m e n t j u v e n i l e s t h a t were banded as d e p e n d a n t young were o b v i o u s l y o f l o c a l o r i g i n . The e v i d e n c e f o r t h e o r i g i n o f t h e r e m a i n i n g r e p l a c e m e n t b i r d s i s c i r c u m s t a n t i a l , b u t i s s t r o n g l y s u g g e s t i v e t h a t t h e y t o o were o f l o c a l s t o c k . 51 IV DISCUSSION &. The R e p l a c e m e n t Song S p a r r o w s And The S u r p l u s I t was s t a t e d i n t h e G e n e r a l I n t r o d u c t i o n t h a t a n e c e s s a r y p r e - r e q u i s i t e f o r t h e i n v e s t i g a t i o n o f s e t t l e m e n t p a t t e r n s on t e r r i t o r i e s was t h e e x i s t e n c e o f a s u r p l u s o f Song S p a r r o w s , p h y s i o l o g i c a l l y c a p a b l e o f b r e e d i n g b u t p r e v e n t e d from d o i n g s o by t h e t e r r i t o r i a l b e h a v i o u r o f t h e b r e e d i n g b i r d s . The r e m o v a l e x p e r i m e n t s and t h e s u b s e q u e n t r e p l a c e m e n t s show t h a t t h e r e i n d e e d e x i s t e d a s u r p l u s o f Song S p a r r o w s on t h e s t u d y a r e a , and t h e f a c t t h a t b r e e d i n g t o o k p l a c e on t h e r e m o v a l a r e a s a f t e r t h e e x p e r i m e n t s shows t h a t t h e r e p l a c e m e n t s were p h y s i o l o g i c a l l y c a p a b l e o f b r e e d i n g . However, a l t h o u g h t h e r e m o v a l e x p e r i m e n t s and t h e s u b s e q u e n t r e p l a c e m e n t s show t h e e x i s t e n c e o f a s u r p l u s o f Song S p a r r o w s on t h e s t u d y a r e a , t h e y do n o t r u l e o u t t h e p o s s i b i l i t y t h a t t h e r e p l a c e m e n t b i r d s would n o t have b r e d e l s e w h e r e i f t h e r e m o v a l s had n o t been c a r r i e d o u t . The d e m o n s t r a t i o n by r e m o v a l e x p e r i m e n t s t h a t a s u r p l u s o f p o t e n t i a l b r e e d e r s e x i s t s i s n o t new. Removal e x p e r i m e n t s have been c a r r i e d o u t on a v a r i e t y o f a n i m a l s ( r e f e r e n c e s i n K r e b s 1971) s i n c e t h e f i r s t l a r g e s c a l e e x p e r i m e n t s on t h e r e m o v a l o f t e r r i t o r i a l b i r d s was c o n d u c t e d i n t h e s p r i n g and summer o f 1949 and 1950 by S t e w a r t and A l d r i c h (1951) and H e n s l e y and Cope (1 9 5 1 ) . Many o f t h e r e m o v a l e x p e r i m e n t s have 52 shown c o n c l u s i v e l y t h a t a s u r p l u s o f p o t e n t i a l b r e e d e r s e x i s t s . The p r e s e n t f i n d i n g s on Song S p a r r o w s on R e i f e l I s l a n d f u r t h e r add t o t h e m a t e r i a l on t h e e x i s t e n c e o f s u c h s u r p l u s e s . The age o f t h e r e p l a c e m e n t i n d i v i d u a l s has a l s o been d e t e r m i n e d i n a few o f t h e r e m o v a l e x p e r i m e n t s . L i k e t h e Song Sparrow on R e i f e l I s l a n d , t h e r e p l a c e m e n t s have been f o u n d t o be p r i m a r i l y y e a r l i n g s i n some b i r d s , e.g. t h e B l u e G r o u s e , 2§£dracjapus o b s c u r u s , ( B e n d e l l and E l l i o t 1967) , t h e Red G r o u s e (Watson and Boss 1970b), t h e Red-winged B l a c k b i r d , A g ; e l a i u s p h g e n i c e u s , ( O r i a n s 1961), and t h e G r e a t T i t (Krebs 1971). I n s m a l l mammals, t h e s i t u a t i o n i s l e s s c l e a r ; H e a l e y (1967) c l a i m e d t h a t , f o r j?eromv.scus m a n i c u l a t u s , young p r e d o m i n a t e d i n d i s p e r s a l o n t o an empty p l o t , b u t Myers and K r e b s (1971) c o u l d n o t s u p p o r t t h i s from d a t a on d i s p e r s i n g M i c r p t u s spp. Few r e m o v a l e x p e r i m e n t s have e s t a b l i s h e d t h e o r i g i n o f t h e r e p l a c e m e n t i n d i v i d u a l s . Some r e m o v a l s have shown t h a t r e p l a c e m e n t s a r e drawn f r o m a n o n b r e e d i n g s u r p l u s p o p u l a t i o n w hich e x i s t s a t t h e p e r i p h e r y o f t h e b r e e d i n g p o p u l a t i o n ( O r i a n s 1961; Watson and J e n k i n s 1968; Young 1970; H a r r i s 1970), and a s i m i l a r s i t u a t i o n has been shown t o e x i s t i n some d e s c r i p t i v e s t u d i e s ( e . g . D e l i u s 1965; C a r r i c k 1963; and i n Song S p a r r o w s on Mandarte I s l a n d by Tompa 1964). T h i s i s n o t t h e c a s e i n t h e G r e a t T i t i n Bean Wood ( K r e b s 1971) , where 53 v a c a n t woodland t e r r i t o r i e s were o c c u p i e d m a i n l y by b i r d s t h a t a l r e a d y had t e r r i t o r i e s i n a d j a c e n t hedgerows. In t h e Song S p a r r o w s on R e i f e l I s l a n d , t h e r e i s a s u r p l u s o f a p p a r e n t l y l o c a l b i r d s , f r o m which r e p l a c e m e n t s a r e d e r i v e d , and which a p p a r e n t l y d i s a p p e a r s by t h e s e c o n d week o f A p r i l ( F i g u r e 2; a l s o Tompa 1964). A f u r t h e r n e c e s s a r y p r e - r e g u i s i t e f o r t h e i n v e s t i g a t i o n o f s e t t l e m e n t p a t t e r n s was t h a t t h e s u r p l u s o f Song S p a r r o w s on t h e s t u d y a r e a s h o u l d n u m e r i c a l l y e x c e e d t h o s e t e r r i t o r i a l b i r d s t h a t were t o be removed. T a b l e 9 shows t h e number o f n o n - t e r r i t o r i a l j u v e n i l e s banded o v e r t h e w i n t e r i n a l l a r e a s . A l t h o u g h w i n t e r m o r t a l i t y a n d / o r e m i g r a t i o n a c c o u n t e d f o r some o f t h e s e b i r d s , o u t o f 82 j u v e n i l e s banded on t h e S p r i n g Removal A r e a , 63 were known t o be a l i v e i n m i d - F e b r u a r y . T a b l e 9 r e q u i r e s some f u r t h e r e x p l a n a t i o n . T h e r e a p p e a r t o be more b i r d s p o t e n t i a l l y a v a i l a b l e t o s e t t l e on b o t h S i m u l t a n e o u s Removal a r e a s , b u t t h i s may not n e c e s s a r i l y be so f o r t h e f o l l o w i n g r e a s o n s . P r o p o r t i o n a t e l y more t i m e was s p e n t t r a p p i n g on t h e S i m u l t a n e o u s Removal a r e a s ( p a r t i c u l a r l y on t h e S p r i n g Removal Area) t h a n on e i t h e r t h e S u c c e s s i v e Removal a r e a s o r t h e C o n t r o l s . A l s o , some b i r d s moved a r o u n d t h e hedgerows, a l t h o u g h t h e m a j o r i t y t e n d e d t o r e m a i n i n c e r t a i n l o c a l i t i e s . The p r o b l e m o f i n d i v i d u a l s moving from one dominance h i e r a r c h y i n one a r e a t o a n o t h e r e l s e w h e r e i s c o n s i d e r e d i n PART B. F i n a l l y , j u v e n i l e s t e n d e d t o c o n g r e g a t e 54 TABLE 9 Number of juveniles banded, f a l l 1972 to early spring 1973 Spring Removal Area Males Females Undetermined Total Simultaneous: 29 20 1 50 Successive: 7 1 2 10 Control: 11 10 1 22 Totals: 47 31 4 82 Fall Removal Area Males Females Undetermined Total Simultaneous: 22 18 1 41 Successive: 11 7 1 19 Control: 4 1 0 5 Totals: 37 26 2 65 55 a t c e r t a i n f a v o u r e d l o c a l i t i e s a l o n g t h e hedgerows. On t h e S p r i n g Removal A r e a , t h e s i n g l e most f a v o u r e d l o c a l i t y was a t t h e j u n c t i o n o f t h e S i m u l t a n e o u s Removal a r e a and t h e C o n t r o l . Out o f 82 j u v e n i l e s banded on t h e S p r i n g Removal A r e a , no l e s s t h a n 34 were c a u g h t and banded a t t h i s l o c a l i t y . T h us, t h e r e a p p e a r e d t o be a l a r g e number o f p o t e n t i a l r e p l a c e m e n t s on b o t h r e m o v a l a r e a s . The r e s u l t s o f t h e r e m o v a l e x p e r i m e n t s show t h a t s e v e r a l o f t h e s e b i r d s were a b l e t o e s t a b l i s h t e r r i t o r i e s . The f a t e o f t h e r e s t o f t h e s u r p l u s i s n o t known. B The T e m p o r a l P a t t e r n s Of S e t t l i n g On T e r r i t o r i e s The r e m o v a l e x p e r i m e n t s and t h e s u b s e q u e n t r e p l a c e m e n t s show t h a t a g r e a t e r number o f t e r r i t o r i e s , w i t h a s m a l l e r mean t e r r i t o r y s i z e , can be a c c o m o d a t e d i n a g i v e n a r e a a f t e r a s i m u l t a n e o u s r e m o v a l . They a l s o show t h a t a s u c c e s s i v e r e m o v a l does n o t r e s u l t i n more t e r r i t o r i e s , o r a s i g n i f i c a n t l y s m a l l e r mean t e r r i t o r y s i z e , i n a g i v e n a r e a . I t i s now n e c e s s a r y t o e n g u i r e i n t o f a c t o r s which c o u l d have r e s u l t e d i n t h e s m a l l e r mean t e r r i t o r y s i z e on t h e S i m u l t a n e o u s Removal a r e a s , and i n no s i g n i f i c a n t d i f f e r e n c e s on t h e S u c c e s s i v e Removal a r e a s . 1. F l u c t u a t i n g E n v i r o n m e n t a l R e s o u r c e The s m a l l e r mean t e r r i t o r y s i z e on t h e S i m u l t a n e o u s 56 Removal area could be related to some fluctuating environmental resource, on the argument that t e r r i t o r y sizes are adjusted annually to some environmental variable. If t h i s were the case, then the t e r r i t o r y sizes on the Controls and Successive Removal areas should have fluctuated i n accordance with the Simultaneous Removal areas. This did not happen. The mean t e r r i t o r y s i z e s on the Successive Removal areas and on the Controls fluctuated i n opposite directions i n the spring and f a l l removals, although i n no case was a difference in t e r r i t o r y s i z e before and after a removal experiment s i g n i f i c a n t . It i s possible that some resource changed along only part of the hedgerow, i n both Simultaneous Removal areas. The hedgerows are not homogeneous i n vegetational structure, and there are substantial differences i n mean t e r r i t o r y s i z e between, and within, the Spring and F a l l Removal Areas (Tables 4 and 5 ) . A subjective assessment of the vegetation along the hedgerows suggested that smaller mean t e r r i t o r y size was related to a higher incidence of brambles, although no further, analysis of the vegetation was carried out. However, a reasonable assumption would be that a resource would fluctuate i n p a r a l l e l along the whole hedgerow. Thus, i t seems j u s t i f i a b l e to rej e c t the argument that a resource changed along only part of the hedgerow from 1972 to 1973. The observed r e s u l t s on mean t e r r i t o r y s i z e , therefore, 57 / c a n n o t e a s i l y be e x p l a i n e d on t h e b a s i s o f a f l u c t u a t i n g e n v i r o n m e n t a l r e s o u r c e , s u c h a s f o o d s u p p l y o r a change i n t h e n a t u r e o f t h e h a b i t a t . F u r t h e r , c a s u a l o b s e r v a t i o n s d u r i n g t h e s t u d y p e r i o d on s p e c i e s o f b i r d s c o - e x i s t i n g w i t h t h e Song S p a r r o w s a l o n g t h e hedgerows d i d n o t r e v e a l any major c h a n g e s i n numbers i n t h o s e s p e c i e s ( e . g . B e w i c k ' s Wren, Thryomanes b e w i c k i i ) t h a t m ight compete f o r some e n v i r o n m e n t a l r e s o u r c e . T h e r e f o r e , i n t e r s p e c i f i c c o m p e t i t i o n was a l s o a p p a r e n t l y u n i m p o r t a n t . 2- P r e s s u r e From I n t r u d e r s I n h i s d i s c u s s i o n on f a c t o r s t h a t might d e t e r m i n e t e r r i t o r y s i z e , K r e b s (1971) s u g g e s t s t h a t a p o s s i b l e f a c t o r m i g h t be t h e p r e s s u r e f r o m p o t e n t i a l s e t t l e r s a t t h e t i m e when t e r r i t o r i e s a r e b e i n g e s t a b l i s h e d . The r a t i o n a l e b e h i n d t h i s s u g g e s t i o n i s g i v e n i n A p p e n d i x 7. F o r t h e G r e a t T i t i n M a r l e y Wood, t h e r e a p p e a r s t o be a r e l a t i o n s h i p between w i n t e r p o p u l a t i o n o f j u v e n i l e s and s u b s e q u e n t b r e e d i n g d e n s i t y ( P e r r i n s 1965; L a c k 1966). A r e l a t i o n s h i p between number o f b i r d s i n t h e s p r i n g and b r e e d i n g d e n s i t y has a l s o been f o u n d i n t h e Wheatear, Oenanthe o e n a n t h e , (Conder 1956) and t h e T r e e S p a r r o w , S p i z e l l a a r b o r e a , (Weeden 1 9 6 5 ) . Tompa (1964) however f o u n d t h a t t h e number o f young Song S p a r r o w s t h a t s u r v i v e d t h e w i n t e r d i d n o t i n f l u e n c e t h e b r e e d i n g d e n s i t y o f t h e n e x t s p r i n g on M a n d a r t e I s l a n d . 58 F o r t h e Song S p a r r o w s on R e i f e l I s l a n d , t h e w i n t e r p o p u l a t i o n o f banded n o n - t e r r i t o r i a l j u v e n i l e s was l a r g e , and i t was l a r g e s t on t h e S i m u l t a n e o u s Removal a r e a s (see T a b l e 9 ) . F o r example, 82 j u v e n i l e s were banded on t h e S p r i n g Removal A r e a , and, o f t h e s e , 50 were banded on t h e S i m u l t a n e o u s Removal a r e a . T h u s , i t a p p e a r s t h a t t h e r e were more b i r d s p o t e n t i a l l y a v a i l a b l e t o s e t t l e on b o t h S i m u l t a n e o u s Removal a r e a s , b u t a s e x p l a i n e d e a r l i e r , t h i s may n o t n e c e s s a r i l y be s o , f o r t h e r e a s o n s g i v e n . I f an i n c r e a s e i n t e r r i t o r i e s on t h e S i m u l t a n e o u s Removal a r e a s was c a u s e d by t h e p r e s s u r e o f a l a r g e number o f p o t e n t i a l s e t t l e r s , t h e n one might s u p p o s e t h a t a s i m i l a r s o r t o f p r e s s u r e would have been e x e r t e d on b o t h t h e S u c c e s s i v e Removal a r e a s and t h e C o n t r o l s . No s i g n i f i c a n t d i f f e r e n c e s o c c u r r e d i n any o f t h e s e l a t t e r a r e a s , t h e r e f o r e one c a n c o n c l u d e t h a t , f o r t h e s e a r e a s , p r e s s u r e from i n t r u d e r s was not i m p o r t a n t . I t may be w o r t h m e n t i o n i n g t h a t t h e n o n - t e r r i t o r i a l b i r d s f o r m e d dominance h i e r a r c h i e s (see PART B) i n t h e l a t e f a l l , and r e t a i n e d them t h r o u g h t h e w i n t e r . I t i s c o n c l u d e d t h a t a c o n s e q u e n c e o f t h e dominance h i e r a r c h y i s t h a t t h e d o m i n a n t i n d i v i d u a l has p r e c e d e n c e t o a v a c a n t t e r r i t o r y o v e r s u b o r d i n a t e s i n t h e s p r i n g . The y e a r l i n g m a l e s do n o t a p p a r e n t l y c o l l e c t i n a g r o u p and t r y t o f o r c e an e x i s t i n g t e r r i t o r y h o l d e r t o s h r i n k t h e b o u n d a r i e s o f h i s t e r r i t o r y , t o 59 accomodate one o r more o f t h e g r o u p . ( I t s h o u l d be s t r e s s e d , however, t h a t ' p r e s s u r e f r o m i n t r u d e r s ' does n o t i m p l y t h a t t h e b i r d s gang up i n g r o u p s - s e e A p p e n d i x 7 ) . A l t h o u g h most d o m i n a n t Song S p a r r o w s i n t h e h i e r a r c h i e s o b t a i n e d t e r r i t o r i e s (PAST B ) , i t i s n o t known i f a l l males competed f o r t e r r i t o r i e s , o r j u s t t h e dominant i n d i v i d u a l s competed. A l t h o u g h t h e h y p o t h e s i s t h a t t h e p r e s s u r e r e s u l t i n g from a l a r g e number o f p o t e n t i a l s e t t l e r s c a u s e d a r e d u c t i o n i n t h e mean t e r r i t o r y s i z e t a k e n on t h e S i m u l t a n e o u s Removal a r e a s (but n o t t h e S u c c e s s i v e Removal a r e a s , o r t h e C o n t r o l s ) , c a n n o t be e l i m i n a t e d , i t a l o n e i s n o t c o n s i d e r e d n e a r l y s u f f i c i e n t t o e x p l a i n t h e r e s u l t s . 3- Inexperience Of The J u v e n i l e s And The T e m p o r a l P a t t e r n s Of S e t t l i n g I f c h a n g e s i n an e n v i r o n m e n t a l r e s o u r c e , o r p r e s s u r e from p o t e n t i a l s e t t l e r s , c a n n o t f u l l y e x p l a i n t h e o b s e r v e d r e s u l t s , t h e n t h e i n e x p e r i e n c e o f t h e r e p l a c e m e n t b i r d s and t h e p a t t e r n o f s e t t l i n g ( s i m u l t a n e o u s and s u c c e s s i v e ) on t e r r i t o r i e s c o u l d be a f a c t o r . Y e a r l i n g s have been shown t o t a k e s m a l l e r t e r r i t o r i e s t h a n a d u l t s i n t h e Marsh T i t , P a r u s p a l u s t r i s , ( S o u t h e r n and M o r l e y 1950), t h e G r e a t T i t (Dhondt and H u b l e 1968; Dhondt 1 9 7 1 a ) , t h e White-crowned S p a r r o w , Z o n o t r i c h i a l§M£2£llH2* ( R a l p h and P e a r s o n 1971) , and t h e B l a c k - c a p p e d ' C h i c k a d e e , P a r u s a t r i c a p i l l u s , ( S t e f a n s k i 1967). N i c e (1937) 60 and Tompa (1964) , however, c o u l d n o t show f o r Song S p a r r o w s t h a t t h e r e was a s i g n i f i c a n t d i f f e r e n c e between t h e mean t e r r i t o r y s i z e s o f f i r s t y e a r b i r d s , and t h o s e o f o l d e r b i r d s , and weeden (1965) f o u n d s i m i l a r r e s u l t s i n t h e T r e e Sparrow i n A l a s k a . I t i s p o s s i b l e t h a t i n e x p e r i e n c e o f t h e s e t t l i n g b i r d s was p l a y i n g a p a r t i n t h e s m a l l e r t e r r i t o r i e s t a k e n on t h e S i m u l t a n e o u s Removal a r e a s , a s a l l t h e r e p l a c e m e n t b i r d s were y e a r l i n g s . on t h e S u c c e s s i v e Removal a r e a s , however, i n e x p e r i e n c e was a p p a r e n t l y u n i m p o r t a n t , a s mean t e r r i t o r y s i z e s were much t h e same b o t h b e f o r e and a f t e r t h e r e m o v a l s , a l t h o u g h o n c e a g a i n t h e r e p l a c e m e n t b i r d s were a l l y e a r l i n g s ( e x c e p t one; s e e A p p e n d i x 3 ) . The r e t e n t i o n o f t h e t e r r i t o r i a l s y s t e m on t h e S u c c e s s i v e Removal a r e a s i s p r o b a b l y v e r y i m p o r t a n t i n t h i s r e s p e c t , and i s c o n s i d e r e d a t l e n g t h i n t h e s e c t i o n on d i s r u p t i o n o f t e r r i t o r i a l b o u n d a r i e s . However, one e x p l a n a t i o n c o u l d be t h a t , i n g e n e r a l , j u v e n i l e s do have a t e n d e n c y t o t a k e up a s m a l l e r t e r r i t o r y t h a n an a d u l t , b u t t h a t t h i s i s n o t a p p a r e n t when o n l y a s i n g l e v a c a n c y a p p e a r s i n t h e t e r r i t o r i a l p a t t e r n . The v a c a n c y may i n i t i a l l y be l a r g e r t h a n t h e r e p l a c e m e n t j u v e n i l e i s r e a d y t o d e f e n d , b u t i t i s n o t l a r g e enough t o be d i v i d e d i n two between two r e p l a c e m e n t b i r d s . T h i s i n i t i a l t e n d e n c y would be masked i f t h e d i s a p p e a r a n c e o f t e r r i t o r y h o l d e r s , w i t h s u b s e q u e n t r e p l a c e m e n t s , o c c u r r e d p e r i o d i c a l l y , a s 61 happened i n t h e s t u d i e s on Song S p a r r o w s o f N i c e and Tompa ( c a t a s t r o p h i c m o r t a l i t y a p a r t ) , and i n t h e s u c c e s s i v e r e m o v a l e x p e r i m e n t s i n t h e p r e s e n t s t u d y . The t e n d e n c y might not be masked i f a l a r g e s t r e t c h o f s u i t a b l e hedgerow c o m p l e t e l y empty o f t e r r i t o r i a l Song S p a r r o w s was p r e s e n t , a s i n t h e s i m u l t a n e o u s r e m o v a l e x p e r i m e n t s . From r e s u l t s on t h e S u c c e s s i v e Removal a r e a s , however, a f t e r a p e r i o d o f t h r e e o r f o u r d a y s ( t h e t i m e i n t e r v a l ( s ) between e a c h s u c c e s s i v e r e m o v a l ) , t h e r e p l a c e m e n t j u v e n i l e male a p p a r e n t l y had e s t a b l i s h e d t h e o r i g i n a l b o u n d a r i e s w i t h h i s n e i g h b o u r s , i n d i c a t i n g t h a t p e r h a p s t h e i n i t i a l t e n d e n c y ( i f p r e s e n t ) t o t a k e a s m a l l e r t e r r i t o r y had d i s a p p e a r e d . The t e n d e n c y t h e n t o t a k e a s m a l l e r t e r r i t o r y m i ght be c o n n e c t e d w i t h l e v e l s o f a g g r e s s i o n . The r e p l a c e m e n t j u v e n i l e s might be l e s s a g g r e s s i v e i n i t i a l l y , p o s s i b l y b e c a u s e t h e y a r e on u n f a m i l i a r g r o u n d , and t h e r e f o r e i n c l i n e d t o t a k e a s m a l l e r t e r r i t o r y . I f a l l t h e r e p l a c e m e n t s have t h i s i n i t i a l low l e v e l o f a g g r e s s i o n , a s i n a s i m u l t a n e o u s r e m o v a l e x p e r i m e n t , t h e n a s e t o f s m a l l e r t e r r i t o r i e s c o u l d r e s u l t . I f j u s t one r e p l a c e m e n t j u v e n i l e i s i n v o l v e d , as i n a s u c c e s s i v e r e m o v a l , t h e n a f t e r t h r e e o r f o u r d a y s h i s l e v e l o f a g g r e s s i o n might have r i s e n t o t h e p o i n t where he c a n c l a i m t h e whole o f t h e 62 t e r r i t o r y he has a c q u i r e d 1 . Van den Assent (1967) f o r t h e t h r e e - s p i n e d s t i c k l e b a c k e x p l a i n e d h i s o b s e r v a t i o n s , t h a t s i m u l t a n e o u s i n t r o d u c t i o n s i n t o a t a n k r e s u l t e d i n a l a r g e r number o f t e r r i t o r i e s t h a n d i d s u c c e s s i v e i n t r o d u c t i o n , i n a s i m i l a r manner; p r o b a b l y , t h e r e l a t i v e d i f f e r e n c e s i n a g g r e s s i v e l e v e l s o f t h e male s t i c k l e b a c k s - a l l o f them s i m u l t a n e o u s l y i n t h e p r o c e s s o f s e t t l i n g and b u i l d i n g - were t e m p o r a r i l y s m a l l e r t h a n f o u n d i f m ales were i n t r o d u c e d s u c c e s s i v e l y . I n Song S p a r r o w s on Mandarte I s l a n d , Tompa (1964) showed t h a t t h e s e t t l i n g i n l a r g e numbers o f s u b o r d i n a t e , p r e v i o u s l y n o n - t e r r i t o r i a l j u v e n i l e s r e s u l t e d i n a l a r g e r number o f t e r r i t o r i e s t a k e n a f t e r t h e c a t a s t r o p h i c m o r t a l i t y . F u r t h e r , t h e r e i s some e v i d e n c e ( e . g . B r i a n 1949; Brown 1963; D i x o n 1965; P h i l l i p s 1971) t h a t t h e l e s s f a m i l i a r an a n i m a l i s w i t h an a r e a , t h e more l i k e l y t h a t a n i m a l w i l l be s u b o r d i n a t e ( t h i s i s c o n s i d e r e d i n g r e a t e r d e t a i l i n PART B under p r i o r o c c u p a n c y and e x p e r i e n c e and p o s i t i o n i n t h e h i e r a r c h y ) . T h e r e i s no c o n c l u s i v e e v i d e n c e from t h e s t u d y t o 1. An i n d e p e n d a n t measure o f ' l e v e l o f a g g r e s s i o n ' s h o u l d be t a k e n i n o r d e r t o v e r i f y t h i s h y p o t h e s i s . One p o s s i b l e method would be t o m o n i t o r a b i r d ' s r e s p o n s e t o a t a p e p l a y b a c k - a method which might be p a r t i c u l a r l y u s e f u l i n t h e c a s e o f Song S p a r r o w s , w h i c h p r o v e d t o be v e r y r e s p o n s i v e t o a s t r a n g e r Song S p a r r o w ' s s o n g . 63 s u b s t a n t i a t e t h e h y p o t h e s i s t h a t t h e s e t t l i n g b i r d s a r e i n i t i a l l y l e s s a g g r e s s i v e , and hence more i n c l i n e d t o t a k e a s m a l l e r t e r r i t o r y . S u g g e s t i v e e v i d e n c e s u p p o r t i n g t h e h y p o t h e s i s i s ; (a) a l l t h e r e p l a c e m e n t s were young, n o n - t e r r i t o r i a l b i r d s , and (b) most were s u b o r d i n a t e t o a d u l t s i n t h e dominance h i e r a r c h i e s (PART B ) . A f u r t h e r f a c t o r i s t h e r e t e n t i o n , o r d i s r u p t i o n , o f t h e t r a d i t i o n a l t e r r i t o r y b o u n d a r i e s , t o be d i s c u s s e d n e x t . B e f o r e l e a v i n g t h i s s e c t i o n , however, i t may be w o r t h c o n s i d e r i n g t h e p r o b l e m o f t i m e o f r e p l a c e m e n t . On t h e S u c c e s s i v e Removal a r e a s , a t i m e i n t e r v a l o f t h r e e t o f o u r d a y s i s s u g g e s t e d a s b e i n g t h e l e n g t h o f t i m e needed f o r t h e r e p l a c e m e n t b i r d s t o r e - e s t a b l i s h t h e t e r r i t o r y b o u n d a r i e s w i t h n e i g h b o u r s . The v e r y f a c t t h a t t h e r e were n e i g h b o u r s w i t h f i x e d t e r r i t o r y b o u n d a r i e s p r e s e n t m i g h t have a i d e d t h e s e t t l i n g b i r d i n q u i c k l y e s t a b l i s h i n g h i s b o u n d a r i e s . On t h e S i m u l t a n e o u s Removal a r e a s , t h e r e were no s u c h g u i d e l i n e s t o f o l l o w , and t h u s b o u n d a r i e s may have t a k e n much l o n g e r t o f i x . T h i s may p a r t l y e x p l a i n t h e n i n e o r t e n d a y s needed f o r t o t a l r e p l a c e m e n t . 4. D i s r u p t i o n Of T e r r i t o r i a l B o u n d a r i e s i Both Simms (1965) and Tompa (1964) n o t e d t h a t t h e i n c r e a s e i n number o f o c c u p i e d t e r r i t o r i e s f o l l o w i n g a c a t a s t r o p h i c m o r t a l i t y was a c c o m p a n i e d by t h e t o t a l 64 r e a r r a n g e m e n t o f t e r r i t o r y b o u n d a r i e s . The t r a d i t i o n a l t e r r i t o r i a l s y s t e m o f t h e Song S p a r r o w s on t h e s t u d y a r e a b r o k e down c o m p l e t e l y on t h e S i m u l t a n e o u s Removal a r e a s , and t h e hedgerows were d i v i d e d up i n t o t e r r i t o r i e s e n t i r e l y anew. The S i m u l t a n e o u s Removal a r e a on t h e S p r i n g Removal a r e a i s g i v e n i n F i g u r e 6, w i t h t h e o l d and new t e r r i t o r y b o u n d a r i e s shown. I t i s a p p a r e n t f r o m F i g u r e 6 t h a t t h e r e p l a c e m e n t b i r d s were n o t i n f l u e n c e d by t h e t e r r i t o r i a l s y s t e m b e f o r e t h e r e m o v a l s . T h e 1 o n l y s i m i l a r i t i e s i n t h e t e r r i t o r y b o u n d a r i e s o c c u r a l o n g t h e n a r r o w e s t s e c t i o n o f t h e hedgerow. The g e n e r a l l i n e a r i t y o f t h e t e r r i t o r y a r r a n g e m e n t i s p r e s e r v e d . The t e r r i t o r y b o u n d a r i e s a l o n g t h e S u c c e s s i v e Removal a r e a s r e m a i n e d much t h e same b e f o r e and a f t e r t h e e x p e r i m e n t s . A l t h o u g h new b i r d s s e t t l e d a f t e r t h e r e m o v a l s , t h e t r a d i t i o n a l t e r r i t o r y p a t t e r n was r e t a i n e d , i n c o n t r a s t t o t h e S i m u l t a n e o u s Removal a r e a s . I t i s worth c o n s i d e r i n g some o f t h e e x p l a n a t i o n s t h a t might a c c o u n t f o r t h e r e t e n t i o n o f t h e t e r r i t o r i a l p a t t e r n i n t h e S u c c e s s i v e Removal a r e a s . I t i s p o s s i b l e t h a t t h e s t a b i l i t y o f t h e t e r r i t o r y p a t t e r n i s due t o t o p o g r a p h i c f e a t u r e s ; t h e h a b i t a t i s s t r u c t u r e d s u c h t h a t t h e t e r r i t o r i a l b i r d s f i x t h e i r b o u n d a r i e s a c c o r d i n g t o c e r t a i n l a n d m a r k s . The s t a b i l i t y i n t e r r i t o r i e s f r o m y e a r t o y e a r i n t h e Song T h r u s h , T u r d u s p h i l g m e l g s , ( D a v i e s and Snow 1965) and t h e E u r o p e a n B l a c k b i r d , Figure 6 Spring Removal Area: boundaries before and a f t e r the removal . experiments on the Simultaneous Removal area 66 T_«. m e r u l a , (Snow 1958) have been a t t r i b u t e d t o f e a t u r e s o f t h e h a b i t a t . Song Sparrow t e r r i t o r i e s a r e c l e a r l y d e f i n e d , and p r e s u m a b l y t h e b i r d s r e c o g n i z e t h e b o u n d a r i e s between t h e m s e l v e s and t h e i r n e i g h b o u r s . The r e c o g n i t i o n o f b o u n d a r i e s , however, i s most l i k e l y a p r o d u c t o f t h e i n t e r a c t i o n s between t h e b i r d s t h e m s e l v e s , and i s n o t r e l a t e d d i r e c t l y t o f e a t u r e s o f t h e h a b i t a t . A s e c o n d e x p l a n a t i o n i s t h a t t h e t r a d i t i o n a l t e r r i t o r y p a t t e r n i s r e s p e c t e d by t h e t e r r i t o r i a l i n d i v i d u a l s . When a v a c a n c y o c c u r s , a new r e p l a c e m e n t b i r d c a n s e t t l e b e f o r e n e i g h b o u r i n g b i r d s b e g i n t o e n c r o a c h i n t o t h e v a c a t e d a r e a . I n t h e p r e s e n t s t u d y , a r e p l a c e m e n t male Song Sparrow would have t o c o n t e n d w i t h o n l y two n e i g h b o u r i n g males a l o n g t h e S u c c e s s i v e Removal a r e a s , owing t o t h e l i n e a r i t y o f t h e hedgerow. I t i s n o t known how l o n g i t t a k e s f o r t h e r e p l a c e m e n t b i r d t o ,become f a m i l i a r w i t h t h e e x i s t i n g t e r r i t o r y b o u n d a r i e s , o r how l o n g t h e a d j a c e n t males w a i t b e f o r e a t t e m p t i n g t o expand t h e i r b o u n d a r i e s i n t o t h e v a c a t e d a r e a . From t h e f a c t t h a t t h e t e r r i t o r y b o u n d a r i e s d i d n o t change a f t e r t h e e x p e r i m e n t s on t h e S u c c e s s i v e Removal a r e a s , and t h a t t h e r e m o v a l s were c o n d u c t e d on a t h r e e and f o u r day s c h e d u l e , t h e n one c a n deduce t h a t t e r r i t o r y b o u n d a r i e s had been d e t e r m i n e d i n an i n t e r v a l o f a maximum o f f o u r d a y s . In some s e d e n t a r y p a s s e r i n e s t h a t , l i k e t h e Song S p a r r o w , r e t a i n t h e i r t e r r i t o r i e s t h r o u g h o u t t h e y e a r , as i n t h e 67 E u r o p e a n R o b i n , E r i t h a c u s r u b e c u l a , (Lack 194 3) and t h e W r e n - t i t , Chamaea f a s c i a t a , ( E r i c k s o n 1938), one o f t h e f i r s t a c t i v i t i e s o f t h e newly s e t t l e d b i r d s i s t o e x p l o r e t h e t e r r i t o r y b o u n d a r i e s , l e a d i n g t o t h e r e - e s t a b l i s h m e n t o f t h e f o r m e r b o u n d a r i e s w i t h n e i g h b o u r s . S i m i l a r e x p l o r a t o r y b e h a v i o u r has been d e s c r i b e d i n M c c o r m i c k ' s Skua, C a t h a r a c t a M££2£ f i i £ K i # (Young 1972). I t seems r e a s o n a b l e t o a r g u e t h a t t h e newly s e t t l e d Song S p a r r o w s on R e i f e l I s l a n d would a l s o show s u c h b e h a v i o u r a l p a t t e r n s . On t h e S i m u l t a n e o u s Removal a r e a s , however, any one r e p l a c e m e n t male, on e x p l o r i n g t h e t e r r i t o r y b o u n d a r i e s , would f i n d o t h e r r e p l a c e m e n t males d o i n g t h e same t h i n g a t t h e same t i m e , w i t h no g u i d e l i n e s t o f o l l o w . T h i s c o u l d f u r t h e r e x p l a i n t h e l e n g t h o f t i m e t a k e n t o f i x t h e b o u n d a r i e s . 5. G e n e t i c B a s i s F o r The S i z e Of T e r r i t o r y I t i s n o t known how f a r t e r r i t o r i e s c a n be c o m p r e s s e d . Klomp (1972) d i s c u s s e s t h e p r o b l e m o f an optimum s i z e o f t e r r i t o r y t h a t i s g e n e t i c a l l y f i x e d , and g i v e s c i r c u m s t a n t i a l e v i d e n c e t h a t l e n d s s u p p o r t t o t h e e x i s t e n c e o f an optimum s i z e t h a t i s g e n e t i c a l l y f i x e d f r o m S c h o e n e r (1968) and G i b b ( 1 9 6 2 ) . However, Klomp s t a t e s t h a t , a l t h o u g h i t i s h i g h l y p r o b a b l e t h a t t e r r i t o r y s i z e has a g e n e t i c b a s i s , t h e r e a r e no i n d i c a t i o n s t h a t t h e v a r i a t i o n s o f t h i s a t t r i b u t e among i n d i v i d u a l s o f t h e same s p e c i e s a r e b a s e d on d i f f e r e n c e s i n t h e i r g e n e t i c make-up. Most o f t h e d i f f e r e n c e s seem t o be o f 68 a m o d i f i c a t o r y n a t u r e . a t e r r i t o r y o f a p a r t i c u l a r s i z e may be p a s s e d on f r o m one g e n e r a t i o n t o t h e n e x t . T a b l e 10 g i v e s t h e o n l y e x a m p l e s o f l i n e a g e f r o m t h e s t u d y a r e a , i n which t h e p a r e n t s o f a p a r t i c u l a r male a r e known, and t h a t p a r t i c u l a r male o b t a i n e d a t e r r i t o r y t h e f o l l o w i n g y e a r . The d a t a a r e t o o few t o be t e s t e d s t a t i s t i c a l l y , b u t t h e g e n e r a l i m p r e s s i o n i s t h a t t h e t a k i n g o f a l a r g e o r s m a l l t e r r i t o r y i s p a s s e d on f r o m one g e n e r a t i o n t o t h e n e x t . However, s m a l l t e r r i t o r i e s a p p e a r t o be t a k e n where t h e r e i s a h i g h i n c i d e n c e o f b r a m b l e s , and t h e r e f o r e a v e g e t a t i o n a l f a c t o r c o u l d a l s o be i n v o l v e d . The d a t a a r e n o t s u f f i c i e n t f o r any f i r m c o n c l u s i o n s t o be drawn, and t h e m a t t e r i s n o t p u r s u e d f u r t h e r h e r e . C. P r o p o s e d E x p l a n a t i o n F o r The D i f f e r e n t R e s u l t s Of The S i m u l t a n e o u s And The S u c c e s s i v e Removal E x p e r i m e n t s The S u c c e s s i v e Removal a r e a s d i d n o t show a s i g n i f i c a n t c hange i n t h e number o f t e r r i t o r i e s , o r i n mean t e r r i t o r y s i z e , a f t e r t h e r e m o v a l s b e c a u s e r e p l a c e m e n t o c c u r r e d s u c c e s s i v e l y on a o n e - t o - o n e b a s i s , and t h e t r a d i t i o n a l t e r r i t o r i a l p a t t e r n was r e t a i n e d . Each r e p l a c e m e n t j u v e n i l e may i n i t i a l l y have been p r e p a r e d t o d e f e n d o n l y a p a r t o f t h e v a c a n t t e r r i t o r y , b u t , p e r h a p s b e c a u s e o f t h e r e l u c t a n c e o f n e i g h b o u r i n g t e r r i t o r y h o l d e r s t o expand t h e i r b o u n d a r i e s i m m e d i a t e l y i n t o t h e v a c a n t a r e a , and p o s s i b l y b e c a u s e o f t h e 6 9 TABLE 10 Lineage: t e r r i t o r y s i z e s from one generation to the next 2 2 Generation 1 T e r r i t o r y s i z e (m ) Generation 2 T e r r i t o r y s i z e (m ) W/0 2708 R/BL 1824 W/0 2708 LP/BL 1444 W/DP 1625 Y/LP 2166 DP/M 1264 M/W 722 G/R 5054 B/B 3249 70 p r o p o s e d e x p l o r a t o r y b e h a v i o u r o f t h e new b i r d , t h e s i z e and b o u n d a r i e s o f t h e t e r r i t o r y o f t h e removed b i r d were t a k e n by t h e r e p l a c e m e n t b i r d , p r o b a b l y i n a m a t t e r o f t h r e e t o f o u r d a y s . The S i m u l t a n e o u s Removal a r e a s , on t h e o t h e r hand, showed s i g n i f i c a n t c h a n g e s i n number o f t e r r i t o r i e s , and i n mean t e r r i t o r y s i z e s . The t r a d i t i o n a l t e r r i t o r i a l s y s t e m was c o m p l e t e l y b r o k e n down, and t e r r i t o r y b o u n d a r i e s were fo r m e d e n t i r e l y anew, w i t h o u t a p p a r e n t g u i d e l i n e s . I n c o m p a r i s o n w i t h t h e S u c c e s s i v e Removal a r e a s , t h e t i m e t a k e n t o f i x t h e t e r r i t o r y b o u n d a r i e s t o o k much l o n g e r ( n i n e t o t e n d a y s ) . A l l t h e r e p l a c e m e n t s were young b i r d s , and i t seems r e a s o n a b l e t o a r g u e t h a t i n e x p e r i e n c e a n d / o r u n f a m i l i a r i t y w i t h t h e a r e a were p o s s i b l e f a c t o r s a f f e c t i n g t h e s i z e o f t e r r i t o r y t a k e n . I t i s p o s t u l a t e d t h a t t h e r e p l a c e m e n t b i r d s i n i t i a l l y had l o w e r l e v e l s o f a g g r e s s i o n , and hence were l e s s l i k e l y t o i m m e d i a t e l y c l a i m a s i z e o f t e r r i t o r y e q u i v a l e n t t o t h a t o f t h e removed a d u l t s . T h u s , t h e t e m p o r a r y low l e v e l o f a g g r e s s i o n o f t h e r e p l a c e m e n t b i r d s , a l l s i m u l t a n e o u s l y a t t e m p t i n g t o s e t t l e , c o u l d have r e s u l t e d i n a l a r g e r number o f t e r r i t o r i e s t a k e n , w i t h a s m a l l e r mean t e r r i t o r y s i z e . I n summary, t h e n , t h e r e m o v a l e x p e r i m e n t s showed t h a t , on t h e s t u d y a r e a , t h e r e was a s u r p l u s o f b i r d s t h a t were p h y s i o l o g i c a l l y c a p a b l e o f b r e e d i n g . The r e p l a c e m e n t b i r d s 71 were a l m o s t a l l j u v e n i l e s , and were p r o b a b l y a l l o f l o c a l o r i g i n . The s u c c e s s i v e p a t t e r n o f s e t t l i n g on t e r r i t o r i e s d i d n o t show s i g n i f i c a n t c h a n g e s i n numbers o f t e r r i t o r i e s , o r i n mean t e r r i t o r y s i z e s . The s i m u l t a n e o u s p a t t e r n o f s e t t l i n g on t e r r i t o r i e s r e s u l t e d i n h i g h e r numbers o f t e r r i t o r i e s , and s m a l l e r mean t e r r i t o r y s i z e s . P o s s i b l e f a c t o r s which might a c c o u n t f o r t h e s e r e s u l t s a r e d i s c u s s e d , and a p r o p o s e d e x p l a n a t i o n i s g i v e n . 72 PART B DOMINANCE HIERARCHIES I INTRODUCTION Schelder'up-Ebbe (1922) i s c r e d i t e d as b e i n g t h e f i r s t b i o l o g i s t t o r e c o g n i z e t h e i m p o r t a n c e o f dominance h i e r a r c h i e s i n g r o u p s o f a n i m a l s . He d i s c o v e r e d t h e e x i s t e n c e o f a l i n e a r p e c k - o r d e r i n d o m e s t i c f o w l , s u c h t h a t e a c h b i r d was e i t h e r d o m i n a n t o r s u b o r d i n a t e t o any o t h e r , and t h a t t h e d y a d i c s i t u a t i o n was e s s e n t i a l l y i r r e v e r s a b l e . S i n c e t h e n , dominance h i e r a r c h i e s have been o b s e r v e d i n numerous s p e c i e s o f a n i m a l s , b o t h d o m e s t i c ( e . g . G u h l 1953; Wood-Gush 1965) and w i l d . F o r w i l d a n i m a l s , h i e r a r c h i e s have been documented i n i n v e r t e b r a t e s , e.g. t h e C o c k r o a c h , Nauphoeta c i n e r e a , (Ewing 1970), and t h e M a n t i s S h r i m p , G o n g d a c t y l u s b r e d i n i , ( D i n g l e and C a l d w e l l 1969); i n l o w e r v e r t e b r a t e s , e . g . t h e L e o p a r d F r o g , Rang p i p i e n s , ( B o i c e and W i t t e r 1969); i n h i g h e r v e r t e b r a t e s , e.g. t h e P r a i r i e Dog, Cynomys l u d o y i c i a n u s , (Anthony 1955), t h e B o t t l e - n o s e d D o l p h i n , T u r s i o p s t r u n c a t u s , ( M c B r i d e and Hebb 1948), and l a b o r a t o r y m i c e , Mus m u s c u l u s , ( L e v i c k and B e i l h a r z 1973); i n p r i m a t e s , e.g. l e m u r s . Lemur s p p . , ( J o l l y 1966), and baboons, P a p i o s p p . , ( H a l l and D e v o r e 1965); and i n man, (Sommer 1967; K r e b s 1973). I n d e e d , t h e h i e r a r c h y i s c o n s i d e r e d by some ( e . g . I t o 1970) t o be one o f t h e most i m p o r t a n t c o n c e p t s i n 73 a n i m a l s o c i a l b e h a v i o u r . ^ v T h e r e i s a w e a l t h o f o b s e r v a t i o n a l m a t e r i a l on h i e r a r c h i c a l r e l a t i o n s h i p s i n b i r d s . T h e s e r e l a t i o n s h i p s have been f o u n d i n s u c h d i v e r s e g r o u p s a s c o l o n i a l t r e e - n e s t i n g h e r o n s ( N o b l e , Worm and S c h m i d t 1938), l e k s p e c i e s (Watts and S t o k e s 1971; B r u l l , c i t e d by K r u i j t and Hogan 1967), p i g e o n s (Bennet 1 9 3 9 ) , p a r r o t s (Masure and A l l e e 1934b), and v a r i o u s p a s s e r i n e s ; i n c o r v i d s (Brown 1963; L o r e n z 1952; L o c k i e 1956), i n p a r i d s ( B r i a n 1949; D i x o n 1966; Odum 1942), and i n f r i n g i l l i d s ( T o r d o f f 1954; Tompkins 1933; Tompa 1964; S a b i n e 1959; W e s s e l l and L e i g h 1941; Shoemaker 1939). A l m o s t h a l f o f t h e s e b i r d s t u d i e s , however, were done u n d e r u n n a t u r a l c o n d i t i o n s , i n l a b o r a t o r i e s , a f a c t o r which c o u l d p o s s i b l y have i n f l u e n c e d t h e a n i m a l ' s b e h a v i o u r (see Brown 1963:460). G a r t l a n (1968) a l s o e x p r e s s e s s i m i l a r s e n t i m e n t s when he s t r e s s e s t h a t c a r e s h o u l d be t a k e n i n i m p o s i n g s o c i a l models on what a r e n o t s o c i a l u n i t s . S e v e r a l o f t h e s t u d i e s c o n d u c t e d i n t h e w i l d were o f w i n t e r f l o c k s o f b i r d s t h a t . b r e e d i n a d i f f e r e n t g e o g r a p h i c a r e a f r o m t h a t i n which t h e y w i n t e r . Hence, t h e r e i s no i n f o r m a t i o n on t h e f i n a l outcome o f t h e h i e r a r c h y . I n d e e d , a l t h o u g h t h e f u n c t i o n o f t h e dominance h i e r a r c h y has been t h e s u b j e c t o f much d i s c u s s i o n (e.g. L a c k 1954, 1966; Wynne-Edwards 1962), t h e c o n s e q u e n c e s a r e n o t w e l l u n d e r s t o o d . ( 74 A few s t u d i e s i n b i r d s have f o l l o w e d t h e dominance h i e r a r c h y t h r o u g h t h e w i n t e r u n t i l i t s breakdown i n t h e s p r i n g . Odum (1942) r e p o r t e d t h a t t h e t o p t h r e e males i n a f l o c k o f B l a c k - c a p p e d C h i c k a d e e s e s t a b l i s h e d t e r r i t o r i e s i n t h e s p r i n g , and D i x o n (1965) f o u n d s i m i l a r r e s u l t s i n C a r o l i n a C h i c k a d e e s , P a r u s c a r o l i n e n s i s . Tompa (1964) d e t e r m i n e d t h e s t a t u s o f e i g h t j u v e n i l e m ales i n a group o f Song S p a r r o w s on Man d a r t e I s l a n d , and f o u n d t h a t t h e grou p was composed o f two a l p h a , f o u r b e t a , and two gamma b i r d s , a l t h o u g h no d a t a on how t h e r e l a t i o n s h i p s were d e t e r m i n e d a r e g i v e n . In t h e s p r i n g , t h e two a l p h a b i r d s a p p a r e n t l y had no d i f f i c u l t y i n e s t a b l i s h i n g t e r r i t o r i e s , b u t o n l y two o f t h e b e t a and n e i t h e r o f t h e gamma b i r d s s u c c e e d e d i n o b t a i n i n g t e r r i t o r i e s . I t h e r e f o r e i n v e s t i g a t e d t h e f o l l o w i n g q u e s t i o n ; when t h e o p p o r t u n i t y a r i s e s , a r e t h e j u v e n i l e s t h a t o b t a i n t e r r i t o r i e s t h e dominant i n d i v i d u a l s i n dominance h i e r a r c h i e s e s t a b l i s h e d d u r i n g t h e p r e - b r e e d i n g s e a s o n ? The p o p u l a t i o n o f Song S p a r r o w s on R e i f e l I s l a n d p r e s e n t e d an e x c e l l e n t o p p o r t u n i t y t o l o o k a t t h e n a t u r e o f t h e h i e r a r c h i e s , and t h e i r c o n s e q u e n c e s . The j u v e n i l e s f o r m e d l o o s e a s s o c i a t i o n s i n t h e f a l l , and c o n g r e g a t e d a t s p e c i a l f a v o u r e d l o c a l i t i e s a l o n g t h e hedgerows. A l a r g e p r o p o r t i o n o f t h e Song S p a r r o w s i n t h e a r e a had been c o l o u r - b a n d e d by l a t e f a l l , e n a b l i n g i n d i v i d u a l r e c o g n i t i o n . F i n a l l y , t h e r e m o v a l e x p e r i m e n t i n t h e s p r i n g would p r e s e n t a c h a n c e f o r s e v e r a l y e a r l i n g s t o o b t a i n t e r r i t o r i e s . 75 I I PROCEDURE The S p r i n g Removal A r e a was t h e o n l y hedgerow a l o n g which t h e h i e r a r c h i e s were d e t e r m i n e d . F e e d i n g s t a t i o n s ( t a b l e s ) were s e t up i n each a d u l t m a l e ' s t e r r i t o r y i n t h e f a l l o f 1972. N i n e t e e n t a b l e s were s e t up; t h e y were made o u t o f f l a t p i e c e s o f plywood, m e a s u r i n g 60cm by 40cm. B a i t (a m i x t u r e o f y e l l o w and w h i t e m i l l e t , b a r l e y and o a t s ) was put o u t a t i r r e g u l a r i n t e r v a l s a t e a c h s t a t i o n t h r o u g h o u t t h e w i n t e r , m a i n l y a f t e r December, and a f t e r t h e p e r i o d o f t h e w i n t e r ' s w o r s t weather (see monthly weather summary. A p p e n d i x 2 ) . O n l y a s m a l l amount o f b a i t (about t h r e e h a n d f u l s ) was put o u t a t a s t a t i o n on any one day. Song S p a r r o w s were r e a d i l y a t t r a c t e d t o t h e f e e d i n g s t a t i o n s , a s were a number o f o t h e r s e e d - e a t i n g p a s s e r i n e s , p r i n c i p a l l y J u n c o s , J u n c g s p p., Towhees, P i p i l o e r y t h r o p h t h a l m u s , and Fox S p a r r o w s , P a s s e r e l l a i l i a c a . Any f o o d l e f t a t t h e s t a t i o n a t t h e end o f t h e day had gone by e a r l y m o r n i n g , p r e s u m a b l y e a t e n by r o d e n t s . i A h i d e was e r e c t e d c l o s e t o a f e e d i n g s t a t i o n when t h a t s t a t i o n was u n d e r o b s e r v a t i o n . The b i r d s d i d n o t a p p e a r t o be e f f e c t e d by t h e p r e s e n c e o f t h e h i d e . A c a s s e t t e t a p e r e c o r d e r (Sony 110a) and a m i c r o p h o n e were u s e d t o r e c o r d t h e a c t i v i t i e s a t t h e s t a t i o n ; i n t h i s way, f u l l a t t e n t i o n was g i v e n t o t h e i n t e r a c t i o n s between t h e b i r d s . 76 A l l i n t e r a c t i o n s between Song S p a r r o w s were r e c o r d e d . I n t e r a c t i o n s between Song S p a r r o w s and o t h e r b i r d s a t t h e f e e d i n g s t a t i o n s were a l s o n o t e d (see A p p e n d i x 5 ) . A l l e n c o u n t e r s i n v o l v i n g Song S p a r r o w s i n v a r i a b l y t o o k p l a c e between o n l y two b i r d s a t a t i m e , and i n a l l e n c o u n t e r s a wi n n e r and a l o s e r c o u l d be c l e a r l y d e t e r m i n e d . The i n d i v i d u a l c a u s i n g t h e o t h e r t o r e t r e a t was n o t e d as dominant; t h e r e t r e a t i n g i n d i v i d u a l was n o t e d as s u b o r d i n a t e . E n c o u n t e r s were d i v i d e d i n t o t h r e e c a t e g o r i e s : d i s p l a c e m e n t s , a v o i d a n c e s , and f i g h t s . (a) D i s p l a c e m e n t s B i r d A i s f e e d i n g a t t h e b i r d t a b l e o r on t h e gr o u n d below. B i r d B a p p e a r s , and e i t h e r makes a r a p i d d e t e r m i n e d f l i g h t a t B i r d A, o r q u i c k l y hops i n t h r e a t p o s t u r e ( N i c e 1943:156) d i r e c t l y a t B i r d ft. B i r d B has wings • o u t - o f - p o c k e t * , body f e a t h e r s f l u f f e d o u t , head l o w e r e d , and beak p o i n t i n g a t B i r d A, who i n v a r i a b l y f l i e s o f f b e f o r e c o n t a c t i s made. On b e i n g d r i v e n o f f , and p r o v i d i n g a n o t h e r d o m i n a n t b i r d i s n o t a l r e a d y p r e s e n t . B i r d A would u s u a l l y f l y e i t h e r t o t h e t a b l e o r t o t h e g r o u n d below, d e p e n d i n g on where i t had j u s t been d i s p l a c e d . S h o u l d a s u b o r d i n a t e be p r e s e n t , t h e n i t would be d r i v e n o f f by B i r d A. D i s t a n c e s between t h e b i r d s v a r i e d f r o m o n e - h a l f t o one 77 m etre, and a p p e a r e d t o i n c r e a s e a s s p r i n g a p p r o a c h e d . (b) A v o i d a n c e s B i r d A i s f e e d i n g a t t h e t a b l e o r , more o f t e n , on t h e g r o u n d below. B i r d B a p p e a r s and hops t o w a r d s t h e f e e d i n g a r e a , w h i l s t a d o p t i n g a m i l d t h r e a t e n i n g p o s t u r e , w i t h wings • o u t - o f - p o c k e t * . B i r d A assumes an a l a r m p o s t u r e ( N i c e 1943:225), w i t h r a i s e d c r e s t f e a t h e r s , body f e a t h e r s s l e e k e d down, and neck s t r e t c h e d o u t and up. As B i r d B a p p r o a c h e s , B i r d A hops away from t h e f e e d i n g a r e a . D i s t a n c e s o nce a g a i n between b i r d s v a r i e d , but were r o u g h l y one m e t r e . (c) F i g h t s Two b i r d s ' s q u a r e o f f * , d i r e c t l y f a c i n g e a c h o t h e r . B o t h have t a i l s f a n n e d and g e n e r a l l y d e p r e s s e d , wings • o u t - o f - p o c k e t ' , body c l o s e t o t h e g r o u n d , f e a t h e r s p u f f e d o u t , and f r e q u e n t l y b i l l open. The two b i r d s g e n e r a l l y a r e q u i t e c l o s e t o e ach o t h e r , a b o u t 20 t o 30 c e n t i m e t r e s a p a r t , and o f t e n r e m a i n m o t i o n l e s s i n t h e s e p o s t u r e s f o r s e v e r a l s e c o n d s . Two p o s s i b l e outcomes a r e d i s t i n g u i s h a b l e : (1) one b i r d c l o s e s i t s b i l l , t u r n s i t s head, and t h e n f l i e s o f f w i t h t h e o t h e r i n c l o s e p u r s u i t . T h e r e t h e n f o l l o w s a p r o l o n g e d c h a s e t h r o u g h t h e s h r u b b e r y , and (2) t h e b i r d s p h y s i c a l l y f i g h t . They s p r i n g i n t o t h e a i r t o g e t h e r , p e c k i n g , and 78 a t t e m p t i n g t o c l e n c h c l a w s , e a c h t r y i n g t o surmount the o t h e r . The two b i r d s c a n r i s e a s much as t w e l v e f e e t above t h e g r o u n d , b e f o r e one g i v e s way and f l i e s o f f , w i t h t h e a c c o m p a n y i n g c l o s e p u r s u i t by t h e v i c t o r and a p r o l o n g e d c h a s e t h r o u g h t h e u n d e r b r u s h . Each t y p e o f e n c o u n t e r ( d i s p l a c e m e n t , a v o i d a n c e , and f i g h t ) was g i v e n e q u a l w e i g h t i n t h e a n a l y s i s , and a l l t h r e e t y p e s o f e n c o u n t e r s were combined. T h i s seemed j u s t i f i a b l e on t h e g r o u n d s t h a t i n t e r a c t i o n s d i d n o t i n v o l v e more t h a n two Song S p a r r o w s a t a t i m e , and t h a t t h e d e c i s i o n a s t o who was t h e v i c t o r i n an e n c o u n t e r was n o t i n d o u b t . T h i s i s i n c o n t r a s t t o t h e i n t e r a c t i o n s i n some o t h e r f r i n g i l l i d s ( e . g . S a b i n e 1959). As m e n t i o n e d e a r l i e r , t h e j u v e n i l e Song S p a r r o w s c o n g r e g a t e d a t s p e c i a l f a v o u r e d l o c a l i t i e s a l o n g t h e hedgerow. T h e s e l o c a l i t i e s f r e q u e n t l y encompassed more t h a n one a d u l t m ale's t e r r i t o r y , and t h e r e f o r e o b s e r v a t i o n s a t d i f f e r e n t f e e d i n g s t a t i o n s i n v o l v e d t h e same g r o u p o f j u v e n i l e s . T h e s e o b s e r v a t i o n s were combined i n t h e a n a l y s i s . F u r t h e r , t h e same g r o u p o f i n d i v i d u a l s r a n g i n g o v e r more t h a n one t e r r i t o r y would i n e v i t a b l y i n t e r a c t w i t h more t h a n one a d u l t t e r r i t o r i a l male and f e m a l e . I n t e r a c t i o n s i n v o l v i n g d i f f e r e n t a d u l t males and t h e g r o u p o f j u v e n i l e s were combined, a s were i n t e r a c t i o n s i n v o l v i n g d i f f e r e n t a d u l t f e m a l e s and t h e j u v e n i l e s . A l s o , c e r t a i n f e e d i n g s t a t i o n s a t t r a c t e d o n l y t h e a d u l t male and h i s 1 79 f e m a l e d u r i n g t h e o b s e r v a t i o n p e r i o d , and hence no h i e r a r c h y was r e s o l v e d . M a t r i c e s were c o n s t r u c t e d f o r e a c h h i e r a r c h i c a l g r o u p (see R e s u l t s ) . The outcomes o f t h e h i e r a r c h i e s were f o l l o w e d d u r i n g t h e s p r i n g a s t h e h i e r a r c h i e s began t o b r e a k - u p , and p a r t i c u l a r l y t h e y were f o l l o w e d i n t h e r e m o v a l a r e a s where t h e r e m o v a l e x p e r i m e n t s p r e s e n t e d an o p p o r t u n i t y f o r some o f t h e members o f t h e h i e r a r c h i e s t o o b t a i n t e r r i t o r i e s . 80 I I I RESULTS (A) The H i e r a r c h i e s Seven h i e r a r c h i e s were d e t e r m i n e d a l o n g t h e hedgerows, and m a t r i c e s were c o n s t r u c t e d f o r each one. The B-C H i e r a r c h y i s r e p r e s e n t e d i n t h e t e x t ( F i g u r e 7 ) , and t h e r e m a i n i n g s i x a r e i n c l u d e d i n t h e A p p e n d i c e s . The number o f Song S p a r r o w s i n v o l v e d i n t h e h i e r a r c h i e s r a n g e d from t w e n t y - s e v e n down t o f i v e i n d i v i d u a l s . The amount o f t i m e s p e n t w i t h e a c h g r o u p o f b i r d s i s g i v e n . The heavy b i a s i n amount o f t i m e s p e n t on t h e B-C H i e r a r c h y i s p a r t l y due t o t h e f a c t t h a t t h e g r o u p o f b i r d s c o n c e r n e d wandered o v e r an a r e a i n c o r p o r a t i n g t h r e e t e r r i t o r i e s , and hence t h r e e f e e d i n g s t a t i o n s . As n o t e d e a r l i e r , o b s e r v a t i o n s a t d i f f e r e n t s t a t i o n s i n v o l v i n g t h e same g r o u p o f b i r d s were combined i n t h e a n a l y s i s . In a l l h i e r a r c h i e s , t h e m a j o r i t y o f i n t e r a c t i o n s i n v o l v e d d i s p l a c e m e n t s . T a b l e 11 shows t h e numbers o f e n c o u n t e r s ( d i s p l a c e m e n t s , a v o i d a n c e s , and f i g h t s ) i n f o u r h i e r a r c h i e s . As an example, t h e B-C H i e r a r c h y was b a s e d on a g r a n d t o t a l o f 1153 i n t e r a c t i o n s , o f w h i c h o n l y 9% were a v o i d a n c e s , l e s s t h a n ^% f i g h t s , and t h e r e s t d i s p l a c e m e n t s . On t h e whole, males t e n d e d t o be i n v o l v e d i n more e n c o u n t e r s t h a n f e a a l e s . I n t h e B-C H i e r a r c h y , b i r d s a t t h e t o p o f t h e h i e r a r c h y ( m o s t l y males) were i n v o l v e d i n more i n t e r a c t i o n s t h a n b i r d s l o w e r 81 Figure 7 B - C HIERARCHY LOSER 5 \ G B Bl \ R Y R 9 W R R DB <f B 8 tf Y LP tt G Y tf w ® tf 0 • G tf R Y tf w BG tf B BG 11 tf BY BY tf w © 9 R ® tf B RW 1 9 LP 80 tf y<B 9 B BY 9 B ® 9 G © 9 B © 9 G DB 9 JL. DB 9 LO R 9 B © G B8I R Y R 4 5 7 22 13 7 6 3 6 11 4 11 1 6 13 2 13 4 2 W R ROB 3 6 2 7 7 4 4 1 2 5 5 16 4 6 5 3 4 8 B 3 6 5 4 c 13 11 5 ' 6 8 2 8 1 10 6 2 8 1 3 Y LP 6 8 3 4 5 2 2 1 5 1 3 7 3 4 6 2 9 2. Y 1 1 1 2 5 5 3 1 1 W ® 1 34 3 14 10 11 2 22 2 3 24 1 6 18 1 12 2 1 5 £ OG 1 9 17 1 5 17 3 1 15 3 18 4 20 1 3 1 R T \ 5 6 5 5 9 3 10 2 6 6 2 6 w BG 2 1 \ 11 9 9 16 6 6 3 10 12 1 14 2 8 BS 4 1 2 \ 10 2 16 6 7 5 1 2 20 1 3 BY BY 2 \ 5 2 6 1 3 1 1 1 W © \ 1 2 1 3 2 3 1 R ® 1 1 \ 1 7 10 4 3 8 9 1 B RW 1 \ 2 1 4 LP BO 6 5 1 1 \ 2 1 1 2 Y ® 3 1 \ 2 4 16 7 B BY 1 \ 2 1 4 B ® \ 7 2 6 3 Q © 2 \| 1 7 1 8 © 1 1 1 G OB 1 2 1 B 08 1 \ IS. R \ 8 © \ 1153 INTERACTIONS , 0 1 AVOIDANCES 80 MAN HOURS 7 F I G H T S 82 TABLE 11 Numbers of encounters (displacements, avoidances and f i g h t s ) i n four dominance h i e r a r c h i e s Hierarchies Displacements Avoidances Fights T o t a l B-C 1043 101 7 1153 Sedge Patch 142 41 3 186 Bulldozed Path 160 11 3 174 Cottonwood Stretch 153 17 0 170 83 down ( m o s t l y f e m a l e s ) (see F i g u r e 9 b e l o w ) . Of t h e s e v e n f i g h t s i n t h e B-C H i e r a r c h y , s i x were male-male e n c o u n t e r s , and t h e s e v e n t h m a l e - f e m a l e . However, males were o n l y s l i g h t l y more i n v o l v e d i n a v o i d a n c e i n t e r a c t i o n s t h a n f e m a l e s ( T a b l e 12). A l l s e v e n h i e r a r c h i e s a r e s t r i k i n g l y l i n e a r . T h e r e a r e v e r y few r e v e r s a l s 1 ; O n l y 4% o f a l l i n t e r a c t i o n s i n t h e B-C H i e r a r c h y i n v o l v e d r e v e r s a l s . T h i s t y p e o f a r r a n g e m e n t c o r r e s p o n d s w i t h t h e c l a s s i c a l * p e c k - r i g h t * o f S c h e l d e r u p - E b b e ( 1 9 2 2 ) , and n o t t h e •peck-dominance* o f Masure and a l l e e ( 1 9 3 4 a ) . N i c e ( 1 9 4 3 ) , f r o m o b s e r v a t i o n s on young Song S p a r r o w s she was r a i s i n g , c o n c l u d e d t h a t j u v e n i l e Song S p a r r o w s p a s s from s u p e r c e d e n c e t h r o u g h p e c k - d o m i n a n c e t o a c l e a r - c u t p e c k - o r d e r by t h e t i m e t h e y a r e t h r e e months o l d . E x t r a p o l a t i n g t h i s t i m e p e r i o d t o t h e j u v e n i l e Song S p a r r o w s on R e i f e l I s l a n d , t h e n , s t a b l e l i n e a r ' p e c k - r i g h t * r e l a t i o n s h i p s s h o u l d have been e s t a b l i s h e d amongst the g r o u p s o f j u v e n i l e s by e a r l y w i n t e r . As o b s e r v a t i o n s on t h e h i e r a r c h i e s s t a r t e d a f t e r December, t h e n one might n o t e x p e c t many r e v e r s a l s . I t seems l i k e l y t h a t more r e v e r s a l s would 1. In e n c o u n t e r s between any two b i r d s (a and B ) , a would p r e d o m i n a n t l y be t h e w i n n e r o v e r B. O c c a s i o n a l l y , B would win s u c h an e n c o u n t e r , and t h i s would be c l a s s e d as a r e v e r s a l . I n t h e m a t r i c e s , numbers o f r e v e r s a l s a p p e a r below th e d i a g o n a l l i n e s . 84 TABLE 12 Analysis of the avoidance interactions i n the B-C Hierarchy Won Lost Total Males: 83 26 109 Females: 18 75 93 Total: 101 101 - % 2 = 64.74 P < 0.001 85 have been recorded e a r l i e r i n the winter, as the rank of each bird was being decided. Reversals did not involve i n d i v i d u a l s that were seen less often. In the B-C Hierarchy, those individuals (9) that were involved i n more than one reversal were a l l prominent, d a i l y members of the hierarchy, when under observation. Also, reversals did not tend to occur l a t e r than e a r l i e r during the observation period. Out of 43 reversals on the B-C Hierarchy, 40 man hours before February 12 showed 24 reversals, 40 man hours after February 12 showed 19 reversals. •Triangles', where A dominates B, B dominates C, and C dominates A, the rela t i o n s h i p remaining stable, are a frequently observed phenomena of dominance hierarchies, e. g. in domestic fowl (Masure and Allee 1934b); in Oregon Juncos (Sabine 1956); in Black-capped Chickadees (Odum 1942); and i n White-eyes, Zosterops l a t e r a l i s , (Kikkawa 1961). Brown (1963) found that t r i a n g l e s i n the S t e l l e r ' s Jay, Cyanositta s t e l l e r i , were transient, the l i n e a r s i t u a t i o n soon asserting i t s e l f . In Song Sparrows, tr i a n g l e s occurred only in the B-C Hierarchy, and remained stable during the observation period. It was found that t r i a n g l e s involved birds i n the middle of the hierarchy only, with both sexes involved. In a l l hierarchies, the adult male and his female were the dominant birds at the feeding station located in t h e i r t e r r i t o r y . The only time that pairs from adjoining 86 t e r r i t o r i e s f e d a t t h e same s t a t i o n was when t h e t a b l e was p l a c e d o n , o r v e r y c l o s e t o , t h e b o u n d a r y s e p a r a t i n g t h e two p a i r s , a s h a p p e n e d i n t h e C o t t o n w o o d S t r e t c h H i e r a r c h y . O t h e r w i s e , a d u l t s r e s p e c t e d t e r r i t o r y b o u n d a r i e s , and t r e s p a s s i n g d i d n o t o c c u r . The r e m a i n d e r o f e a c h h i e r a r c h y was composed o f j u v e n i l e s , r a n g i n g i n numbers f r o m two t o t w e n t y - t w o . F a c t o r s w h i c h m i g h t d e t e r m i n e t h e d o m i n a n t o r s u b o r d i n a t e s t a t u s i n t h e h i e r a r c h y a r e i n c l u d e d i n t h e d i s c u s s i o n . A l t h o u g h t h e g r o u p s o f j u v e n i l e s r e m a i n e d r e l a t i v e l y i n t a c t , some i n t e r c h a n g e o f i n d i v i d u a l s b e t w e e n h i e r a r c h i e s d i d o c c u r . Some 14% o f a l l j u v e n i l e s i n v o l v e d i n t h e h i e r a r c h i e s p e r f o r m e d i n t e r g r o u p movements. I n O r e g o n J u n c o s ( S a b i n e 1 9 5 9 ) , C a r o l i n a C h i c k a d e e s ( D i x o n 1 9 6 5 ) , and Wood P i g e o n s , C o l u m b a p a l u m b u s , ( f i u r t o n e t a l . 1 9 6 6 ) , g r o u p i n t e r c h a n g e s i n v o l v e d b i r d s o f l o w r a n k o n l y , and t h e s e b i r d s m a i n t a i n e d t h e i r l o w p o s i t i o n i n t h e new g r o u p t h e y j o i n e d . Tompa (1964) m e n t i o n e d t h a t o n l y s u b o r d i n a t e Song S p a r r o w s were i n v o l v e d i n i n t e r c h a n g e s b e t w e e n g r o u p s on M a n d a r t e I s l a n d . T h i s was n o t t h e c a s e f o r Song S p a r r o w s on R e i f e l I s l a n d . Not o n l y d i d i n d i v i d u a l s o f l o w r a n k p e r f o r m i n t e r g r o u p movements, b u t a l s o i n d i v i d u a l s o f m i d d l e and e v e n u p p e r r a n k s ( T a b l e 1 3 ) . T h e s e w a n d e r i n g b i r d s assumed t h e same s t a t u s i n t h e new g r o u p a s t h a t w h i c h t h e y had h e l d i n t h e o l d one. M o s t e x a m p l e s a r e o f l o w r a n k e d b i r d s , and o f 87 TABLE 13 Rank i n hierarchy and sex of Song Sparrows performing intergroup movements Sex Hierarchy p o s i t i o n Male Female T o t a l Top t h i r d 2 0 2 Middle t h i r d 2 1 3 Bottom t h i r d 0 5 5 T o t a l 4 6 10 Each hierarchy was divided i n t o three sections i n order to eliminate the differences i n numbers of j u v e n i l e s i n each hierarchy. The adult males and females were not used i n the a n a l y s i s ; hence only the j u v e n i l e s were numerically divided i n t o the three categories, top, middle, and bottom. 88 f e m a l e s i n p a r t i c u l a r , but t h e d o m i n a n t male {Red/Yellow) i n t h e B u l l d o z e d P a t h H i e r a r c h y i n l a t e J a n u a r y , was f o u n d i n e a r l y F e b r u a r y h i g h i n t h e s c a l e i n t h e B-C H i e r a r c h y , and i n m i d - F e b r u a r y was f o u n d as t h e d o m i n a n t male i n t h e Cottonwood S t r e t c h H i e r a r c h y , a d i s t a n c e o f a b o u t 1000 m e t r e s . T h i s male, i n t e r e s t i n g l y enough, was t h e o n l y d o m i n a n t j u v e n i l e male i n t h e h i e r a r c h i e s n o t t o o b t a i n a t e r r i t o r y (see (B) The C o n s e q u e n c e s o f t h e H i e r a r c h i e s ) . An a n a l y s i s o f t h e f i g h t s i n t h e B-C H i e r a r c h y ( T a b l e 14) shows t h a t i n d i v i d u a l s t h a t a r e c l o s e r t o g e t h e r i n t h e h i e r a r c h y a r e s i g n i f i c a n t l y more l i k e l y t o be i n v o l v e d i n f i g h t s t h a n t h o s e t h a t a r e f a r t h e r a p a r t . T h e r e f o r e , a c o m p l e t e a n a l y s i s was r u n on a l l i n t e r a c t i o n s ( d i s p l a c e m e n t s , a v o i d a n c e s , and v f i g h t s ) i n t h e B-C H i e r a r c h y t o i n v e s t i g a t e f u r t h e r t h e p o s s i b i l i t y t h a t b i r d s c l o s e r t o g e t h e r i n t h e h i e r a r c h y i n t e r a c t more t h a n t h o s e f a r t h e r a p a r t . F i g u r e 8 g i v e s t h e r e s u l t s o f t h e a n a l y s i s . T h e r e i s no c o r r e l a t i o n between d i s t a n c e i n h i e r a r c h y and "numbers o f i n t e r a c t i o n s . T h u s , b i r d s which a r e c l o s e r t o g e t h e r i n t h e h i e r a r c h y a r e n o t n e c e s s a r i l y more l i k e l y t o i n t e r a c t t h a n a r e b i r d s which a r e f a r t h e r a p a r t . (B) S u c c e s s i n G a i n i n g T e r r i t o r i e s i n r e l a t i o n t o H i e r a r c h y P o s i t i o n Of t h e s e v e n h i e r a r c h i e s ( F i g u r e 7 and A p p e n d i x 8) NUMBER OF INTERACTIONS 10 o _1_ CO o —I— J>0 Oo o o • >• • MOOo DO D X 4^ J>t> >&•• • ipt> O D D C J O o • J>o oo o • > " • • a a o • oo-Jpaa • > ( t O O O oa o J>a oo o o <J> Oa o o o o • o d> • o o o JI o o o <po o o o o o $ 0 0 o o o a * N)JP O D O "D a p ro co -< 11 1 p b 00 x + CD CO > X o • mm> > 2 s r r > > m rn mm .< .< < 5: "n 2 • m > 5 > > m ? r r " > m m r~ m Figure 8 Number of i n t e r a c t i o n s versus distance w i t h i n hierarchy fo I a l l j u v e n i l e s i n the B-C Hierarchy 89 TABLE 14 Analysis of fights i n the B-C Hierarchy Number of juveniles i n the B-C Hierarchy = 22 Number of fights observed = 7 Random sample size ('pairs' from Random Digits Tables) = 70 Distance i n hierarchy* 1 2 3 4 5 6 7-22 Numbers of 'pairs' of birds: Observed 1 0 1 2 2 1 0 Expected .3 .5 .2 .3 .7 .4 4.6 D = 0.76 P 0.01 Kolmogorov-Smirnov one-sample test * Distance i n the hierarchy refers to how far apart i n numbers one member was from the other member of a 'pair'. Thus, i f the distance in the hierarchy i s 1, then the two birds involved i n a fight were next to each other i n the hierarchy. If the distance was 5, then there were 4 other birds i n the hierarchy between the 'pair'. 90 d e t e r m i n e d , f o u r ( B i g A l d e r , B u l l d o z e d P a t h , No-Name, and Sedge Path) were i n t h e S i m u l t a n e o u s Removal a r e a , one (Marsh Narrows) was i n t h e S u c c e s s i v e Removal a r e a , and one (Cottonwood S t r e t c h ) was on t h e C o n t r o l . The s e v e n t h (B-C) was where t h e S i m u l t a n e o u s Removal a r e a and t h e C o n t r o l met, and i n c o r p o r a t e d two t e r r i t o r i e s i n t h e S i m u l t a n e o u s Removal a r e a and one on t h e C o n t r o l . (1) S i m u l t a n e o u s Removal A r e a As e x p l a i n e d i n PART A, t e n males e s t a b l i s h e d t e r r i t o r i e s i n the S i m u l t a n e o u s Removal a r e a a f t e r t h e r e s i d e n t t e r r i t o r y h o l d e r s had been removed. Of t h e s e t e n , s e v e n had f i g u r e d i n t h e h i e r a r c h i e s . The d o m i n a n t males i n t h e f o l l o w i n g h i e r a r c h i e s o b t a i n e d t e r r i t o r i e s : No-Name, Sedge P a t c h , B i g A l d e r , and B-C. The s e c o n d males i n t h e B u l l d o z e d P a t h and B-C H i e r a r c h i e s a l s o o b t a i n e d t e r r i t o r i e s , and f i n a l l y t h e f i f t h male i n t h e B-C H i e r a r c h y o b t a i n e d a t e r r i t o r y . The d o m i n a n t male (Red/Yellow) i n t h e B u l l d o z e d P a t h H i e r a r c h y was t h e o n l y t o p b i r d i n t h e h i e r a r c h i e s on t h e S i m u l t a n e o u s Removal a r e a n ot t o o b t a i n a t e r r i t o r y a l o n g t h i s s t r e t c h o f hedgerow. As e x p l a i n e d e a r l i e r , t h i s p a r t i c u l a r male was c o n s p i c u o u s by i t s w a n d e r i n g b e h a v i o u r , h a v i n g been a p r o m i n e n t member o f t h r e e h i e r a r c h i e s . I t i s c o n c e i v a b l e t h a t t h i s male was n o t p r e s e n t a l o n g t h e S i m u l t a n e o u s Removal a r e a when t h e r e m o v a l t o o k p l a c e . 91 T h r e e males t h a t e s t a b l i s h e d t e r r i t o r i e s d i d n o t t a k e p a r t i n t h e h i e r a r c h i e s . One o f t h e s was banded i n x D e c e m b e r on t h e C o n t r o l , and was n o t r e s i g h t e d u n t i l t h e week o f t h e s i m u l t a n e o u s r e m o v a l e x p e r i m e n t . The s e c o n d was s e e n o c c a s i o n a l l y t h r o u g h o u t t h e w i n t e r a l o n g t h e S i m u l t a n e o u s Removal a r e a , b u t was n o t r e c o r d e d a t any f e e d i n g s t a t i o n d u r i n g t h e t i m e t h a t o b s e r v a t i o n s were made. The l a s t was an unbanded male t h a t e s t a b l i s h e d a t e r r i t o r y i n t h e r e g i o n where hedgerows from flestham I s l a n d j o i n t h e s t u d y a r e a , and i t i s q u i t e p o s s i b l e t h a t t h i s i n d i v i d u a l s p e n t t h e w i n t e r o u t s i d e t h e s t u d y a r e a . Of t h e s e v e n f e m a l e s t h a t p a i r e d w i t h t h e new t e r r i t o r i a l m a l e s a f t e r t h e r e m o v a l s , o n l y one had ^ e e n a p r o m i n e n t member i n t h e h i e r a r c h i e s . T h i s f e m a l e ( B l a c k / B l u e ) had a low p o s i t i o n i n t h e Sedge P a t c h and B u l l d o z e d P a t h H i e r a r c h i e s b e f o r e F e b r u a r y 3. A f t e r t h i s d a t e , she r a p i d l y moved up t h e s c a l e . T a b l e 15 shows a s i g n i f i c a n t d i f f e r e n c e i n t h e number of i n t e r a c t i o n s won and l o s t a f t e r F e b r u a r y 3. The a d u l t f e m a l e i n t h e a r e a o f t h e B u l l d o z e d P a t h H i e r a r c h y was l a s t s e e n on J a n u a r y 29, and i t i s t h o u g h t t h a t B l a c k / B l u e assumed t h e a d u l t f e m a l e ' s p o s i t i o n i n e a r l y F e b r u a r y . On t h e d e a t h o f t h e a d u l t male d u r i n g t h e r e m o v a l s , s h e p a i r e d w i t h one o f t h e r e p l a c e m e n t m a l e s . (2) S u c c e s s i v e Removal A r e a s O n l y one h i e r a r c h y was d e t e r m i n e d a l o n g t h e S u c c e s s i v e 92 TABLE 15 Change i n status of a j u v e n i l e female following the disappearance of an adult t e r r i t o r i a l female Before Feb.3 A f t e r Feb.3 T o t a l I n t e r a c t i o n s : Win 2 23 25 Lo*se 11 5 16 Totals 13 28 41 X 2 = 17.09 P < 0.005 The adult female was l a s t seen on January 29. Juvenile female (Black/Blue) presumably assumes the adult female's r o l e i n e a r l y February. The j u v e n i l e female wins s i g n i f i c a n t l y more i n t e r a c t i o n s , not only with b i r d s below her, but p r i m a r i l y with b i r d s above her; hence her change i n status. 93 Removal a r e a . I t c o n s i s t e d o f f i v e b i r d s , o f which o n l y two were j u v e n i l e s , and b o t h f e m a l e s . One o f t h e s e f e m a l e s s u c c e e d e d i n p a i r i n g w i t h a new male a f t e r t h e r e m o v a l , t h e o t h e r f e m a l e d i s a p p e a r e d . I t i s p o s s i b l e t h a t t h e r e p l a c e m e n t b i r d s , most o f which were unbanded, c o u l d have s p e n t t h e w i n t e r a c r o s s Ewen S l o u g h i n t h e F a l l Removal Area ( F i g u r e 1 ) . (3) C o n t r o l Of 11 j u v e n i l e s t h a t t o o k p a r t i n t h e Cottonwood S t r e t c h H i e r a r c h y , none were s e e n a f t e r t h e r e m o v a l e x p e r i m e n t s . I n e a r l y May, however, one o f t h e a d u l t males d i e d ( t h e c o r p s e was f o u n d on May 4). On May 5, a male had t a k e n e v e r t h i s t e r r i t o r y , and a p p a r e n t l y a l s o t h e a d u l t f e m a l e . T h i s r e p l a c e m e n t male had been t h i r d b i r d i n t h e B-C H i e r a r c h y . The B-C H i e r a r c h y was t h e l a r g e s t o f t h e h i e r a r c h i e s , and was t h e o n l y one s u p p l y i n g more t h a n one t e r r i t o r i a l male amongst t h e r e p l a c e m e n t s . A n a l y s i n g t h i s h i e r a r c h y , o u t o f 12 j u v e n i l e m a l e s t h a t t o o k p a r t i n t h e h i e r a r c h y , f o u r f r o m t h e t o p f i v e o b t a i n e d t e r r i t o r i e s . T h i s i s h i g h l y u n l i k e l y t o have o c c u r r e d by c h a n c e (P = 0.01). The e v i d e n c e , t h e n , s t r o n g l y s u p p o r t s t h e h y p o t h e s i s t h a t , g i v e n t h e o p p o r t u n i t y , t h e j u v e n i l e s t h a t o b t a i n t e r r i t o r i e s a r e t h e d o m i n a n t i n d i v i d u a l s i n dominance h i e r a r c h i e s e s t a b l i s h e d d u r i n g t h e p r e - b r e e d i n g s e a s o n . 94 IV DISCUSSION (a) The Functional Significance of Dominance Hierarchies Gartlan (1968) suggests that the primary function of the s o c i a l dominance hierarchy i s to relate population size to available resources. Wynne-Edwards (1962) suggests that hierarchies can function as a s o c i a l g u i l l o t i n e for subordinate i n d i v i d u a l s during times of food shortage, although Lack (1966), whilst concurring that the few in d i v i d u a l s near the bottom of the peck-order starve or emigrate when the numbers of the species are up against the food l i m i t , regarded t h i s as a consequence, not a function. Lack argues that the hierarchy arises as a response to scarce food resources, and not as an a n t i c i p a t i o n of them. Wynne-Edwards, however, maintains that the hierarchy i s pre-adaptive for conditions of privation. There i s evidence that can be put forward supporting both arguments; however, i t i s frequently d i f f i c u l t to d i f f e r e n t i a t e between cause and e f f e c t of the dominance hierarchies i n most instances. I t i s even more d i f f i c u l t to relate the food shortage hypothesis with the hierarchies in Song Sparrows, where a l l the bottom, hence subordinate birds, are females! The g u i l l o t i n i n g of subordinates i n times of food shortage, then, would presumably ef f e c t females far more than males. 95 A f u r t h e r argument i s t h a t h i e r a r c h i e s f u n c t i o n i n r e d u c i n g a g g r e s s i v e e n c o u n t e r s between i n d i v i d u a l s , t h u s c o n s e r v i n g e n e r g y , b u t a g a i n i t c a n be a r g u e d t h a t t h i s i s a c o n s e q u e n c e , and n o t a f u n c t i o n , o f t h e h i e r a r c h y . T h e r e i s good e v i d e n c e t h a t h i e r a r c h i e s a r e i m p o r t a n t i n r e d u c i n g a g g r e s s i v e e n c o u n t e r s i n work on mammals (e.g. Anthony 1955; C a l h o u n 1971; K i n s e y 1971), and on d o m e s t i c b i r d s (e. g. G u h l 1956). Lack (1954) a l s o a r g u e d a l o n g s i m i l a r l i n e s when he s t a t e s t h a t t h e p e c k - o r d e r has s u r v i v a l v a l u e f o r b o t h s t r o n g e r and weaker i n d i v i d u a l s , f o r t h o s e h i g h e r b e c a u s e t h e y o b t a i n f o o d w i t h v e r y l i t t l e f i g h t i n g , and f o r t h o s e l o w e r b e c a u s e i t s a v e s them w a s t i n g t i m e on f i g h t s w hich t h e y would l o s e anyway, and t h e i r e n e r g i e s c a n be c o n s e r v e d f o r s e a r c h i n g e l s e w h e r e . I t seems r e a s o n a b l e t o a r g u e t h a t a g g r e s s i o n between i n d i v i d u a l Song S p a r r o w s has been r e d u c e d b e c a u s e o f t h e h i e r a r c h i e s , p a r t i c u l a r l y a s f i g h t s a r e r a r e , r e v e r s a l s a r e few, and t h e h i e r a r c h y i s s t a b l e . Dominance h i e r a r c h i c a l b e h a v i o u r , l i k e t e r r i t o r i a l b e h a v i o u r , c o u l d f u n c t i o n i n v a r i o u s ways f o r d i f f e r e n t a n i m a l s . F o r Song S p a r r o w s , t h e f u n c t i o n a l s i g n i f i c a n c e o f t h e h i e r a r c h y c o u l d be t o r e d u c e a g g r e s s i v e i n t e r a c t i o n s , t o i d e n t i f y a s u r p l u s , o r t o d e t e r m i n e t h e dominant i n d i v i d u a l s t h a t m i g h t o b t a i n a t e r r i t o r y g i v e n t h e o p p o r t u n i t y . D a t a f o r any one o f them a r e n o t u n e q u i v o c a l . (b) F a c t o r s d e t e r m i n i n g p o s i t i o n i n t h e Dominance H i e r a r c h y 96 I t has a l r e a d y been shown t h a t t h e h i e r a r c h y i n Song S p a r r o w s i s e s s e n t i a l l y l i n e a r and s t a b l e . I t i s worth now c o n s i d e r i n g some o f t h e f a c t o r s which might d e t e r m i n e t h e dominance o r s u b o r d i n a n c e o f t h e i n d i v i d u a l s c o m p r i s i n g t h e h i e r a r c h y . Sex and p o s i t i o n i n h i e r a r c h y I n Song S p a r r o w s , j u v e n i l e m ales were dom i n a n t o v e r j u v e n i l e f e m a l e s . In t h e B-C H i e r a r c h y , f o r example, o u t o f 22 j u v e n i l e s , 12 f r o m t h e t o p 14 were m a l e s . A l t h o u g h t h i s a r r a n g e m e n t c a n be f o u n d i n some o t h e r p a s s e r i n e s p e c i e s (e. g. Red C r o s s b i l l , L o x i a c u r y i . r o s t r a , ( T o r d o f f 1 9 5 5 ) ) , i t i s n o t t h e c a s e i n P a r u s s p e c i e s ( D i x o n 1966; Odum 1942; B r i a n 1949), o r i n S t e l l e r » s J a y (Brown 1964), where t h e f e m a l e t a k e s t h e r a n k o f t h e male she p a i r s w i t h . In c e r t a i n i n s t a n c e s , a s i n B l a c k - c r o w n e d N i g h t - H e r o n s , N y c t i c o r a x M£ii£2ia2[» ( N o b l e , Worm and S c h m i d t 1939) , males and f e m a l e s a r e g r a d e d w i t h o u t r e g a r d t o s e x , s u g g e s t i n g an a s e x u a l s i t u a t i o n . , G u h l (1956) f o u n d f o r d o m e s t i c f o w l t h a t c o c k s do n o t n o r m a l l y peck hens, and t h e r e f o r e a b r e e d i n g f l o c k u s u a l l y has two h i e r a r c h i e s , one f o r ea c h s e x . The h i e r a r c h i e s i n Song S p a r r o w s c a n n o t be d i v i d e d i n t h i s manner, as b o t h s e x e s were i n v o l v e d i n t h e i n t e r a c t i o n s . An i n d i v i d u a l c a n c l i m b t h e s o c i a l l a d d e r by p a i r i n g w i t h 97 a d o m i n a n t b i r d o f t h e o p p o s i t e s e x . Brown (1963) r e l a t e s an i n s t a n c e o f a male moving up t h e s c a l e o f dominance a f t e r p a i r i n g w i t h a d o m i n a n t a d u l t f e m a l e . I n t h e Song S p a r r o w s , a j u v e n i l e f e m a l e ( B l a c k / B l u e ) moved up t h e h i e r a r c h y a f t e r t h e a d u l t f e m a l e had d i s a p p e a r e d i n t h e p e r i o d J a n u a r y 29 t o F e b r u a r y 3. Her s u c c e s s i n i n t e r a c t i o n s i n c r e a s e d s i g n i f i c a n t l y a f t e r t h i s p e r i o d (see T a b l e 1 4 ) . She a p p a r e n t l y p a i r e d w i t h t h e a d u l t male on t h e d i s a p p e a r a n c e o f h i s mate, and, a f t e r t h e s p r i n g r e m o v a l e x p e r i m e n t , she p a i r e d w i t h t h e r e p l a c e m e n t young male. S i z e and p o s i t i o n i n h i e r a r c h y f S i z e has been f o u n d t o be a f a c t o r i n d e t e r m i n i n g h i e r a r c h i c a l p o s i t i o n i n B o t t l e - n o s e d D o l p h i n s ( M c B r i d e and Hebb 1948), and i n New F o r e s t P o n i e s ( T y l e r 1972). F r e t w e l l (1969) f o u n d t h a t , i n t h e Oregon J u n c o , d o m i n a n t s had l o n g e r wings t h a n s u b o r d i n a t e s . Song S p a r r o w s v a r y c o n s i d e r a b l y i n w e i g h t ( F i g u r e 4) and i n w i n g l e n g t h ( F i g u r e 3) , but no r e l a t i o n s h i p between w e i g h t o r w i n g l e n g t h and p o s i t i o n i n h i e r a r c h y was f o u n d . Thus, i t c a n n o t be a r g u e d t h a t t h e l a r g e s t o r h e a v i e s t b i r d s were t h e ones t h a t o b t a i n e d t e r r i t o r i e s . Age and p o s i t i o n i n h i e r a r c h y Age and dominance have been f o u n d t o c o r r e l a t e i n d o m e s t i c f o w l (Shoemaker 1939), b u t n o t i n s h o r t - l i v e d p a s s e r i n e s (R. I. S t e w a r t p e r s coram). A more s u b t l e 98 r e l a t i o n s h i p between age and dominance o c c u r s i n t h e Sage G r o u s e , C e n t r o c e r c u s u r o p h a s i a n u s , ( W i l e y 1970), where t h e r e i s a c e n t r i p e t a l movement o f t e r r i t o r i a l males t o w a r d s a m a t i n g c e n t r e o f t h e ^ Lek^)as v a c a n c i e s a r i s e o v e r t h e y e a r s . In Song S p a r r o w s , any one h i e r a r c h i c a l g r o u p i s c o m p r i s e d o f a t most two a d u l t b i r d s i n any one t e r r i t o r y , and t h e r e s t j u v e n i l e s . Age t h e n c o u l d o n l y be i m p o r t a n t w i t h r e s p e c t t o t h e j u v e n i l e s t h e m s e l v e s , f o r example i f t h e i n d i v i d u a l s f r o m t h e f i r s t b r o o d s were dominant o v e r t h o s e from s e c o n d o r t h i r d b r o o d s . R e s u l t s , however, c o u l d be c o n f u s e d w i t h t h e i d e a s o f p r i o r o c c u p a n c y and e x p e r i e n c e , t o be d i s c u s s e d n e x t . T h e r e i s some e v i d e n c e , a l b e i t meagre, t o s u g g e s t t h a t , f o r j u v e n i l e s , age i s n o t i m p o r t a n t i n d e t e r m i n i n g p o s i t i o n i n t h e h i e r a r c h y . The age o f t h e two t o p j u v e n i l e m ales i n t h e B-C H i e r a r c h y a r e known, as t h e y were banded i n t h e summer o f 1972, a t a s t a g e o f d e v e l o p m e n t when t h e i r age c o u l d be d e t e r m i n e d (see A p p e n d i x 6 f o r c a l c u l a t i o n s o f a g e ) . The s e c o n d b i r d was a p r o d u c t o f a f i r s t b r o o d , b u t t h e t o p b i r d was t h e p r o d u c t o f e i t h e r a s e c o n d o r t h i r d b r o o d , and was c a l c u l a t e d t o be a b o u t 60 d a y s younger t h a n t h e s e c o n d b i r d . N e v e r t h e l e s s , he was t h e d o m i n a n t j u v e n i l e i n t h e l a r g e s t h i e r a r c h y . P r i o r o c c u p a n c y and e x p e r i e n c e and p o s i t i o n i n t h e h i e r a r c h y E x p e r i e n c e a n d / o r p r i o r o c c u p a n c y ( p r i o r r e s i d e n c y , f a m i l i a r i t y w i t h t e r r i t o r y ) and t h e r e l a t i o n s h i p w i t h 99 h i e r a r c h y r a n k h a s r e c e i v e d much a t t e n t i o n i n r e c e n t y e a r s . T h e s e r e l a t i o n s h i p s have been f o u n d i n f i s h , e. g. P h i l l i p s ( 1 9 7 1 ) ; i n b i r d s , e. g. Brown (1964); and even i n man, e. g. K r e b s (1973). I n t h e G r e a t T i t ( B r i a n 1949), C a r o l i n a C h i c k a d e e (Dixon 1965), B l u e T i t , P a r u s c a e r u l e u s , ( C o l g u h o u n 1942), and S t e l l e r ' s J a y (Brown 1963), t h e p o s i t i o n o f t h e b i r d i n t h e dominance o r d e r c o r r e s p o n d s w i t h t h e d i s t a n c e o f i t s t e r r i t o r y f r o m th e f e e d i n g p l a c e ; t h e r a n k o f t h e i n d i v i d u a l v a r i e d i n v e r s e l y w i t h i t s d i s t a n c e f r o m i t s t e r r i t o r y . I n Song S p a r r o w s , t h i s phenomenon p r o b a b l y does n o t a p p l y . T e r r i t o r i a l a d u l t s c o u l d n o t be e n t i c e d f r o m t h e i r t e r r i t o r i e s even when f o o d was s u p p l i e d i n t h e i r n e i g h b o u r ' s t e r r i t o r y . I t seems u n l i k e l y t h a t t h e y were n o t aware o f t h e p r e s e n c e o f t h e f o o d , p a r t i c u l a r l y by t h e n o i s y f e e d i n g b e h a v i o u r of j u n c o s a t t h e f e e d i n g s t a t i o n s . The i n c e n t i v e t h e n t o l e a v e t h e i r t e r r i t o r i e s was a p p a r e n t l y n o t s t r o n g enough t o overcome t h e r e c o g n i t i o n o f , and r e s p e c t f o r , t e r r i t o r i a l b o u n d a r i e s . The j u v e n i l e s c o m p r i s i n g t h e r e s t o f t h e h i e r a r c h y were n o n - t e r r i t o r i a l , and t h e r e f o r e would n o t be i n v o l v e d i n t h i s i d e a . S a b i n e (1959) s u g g e s t e d t h a t t h o s e j u n c o s t h a t a r r i v e d f i r s t on t h e w i n t e r i n g g r o u n d s were i n , g e n e r a l d ominant t o g r o u p s t h a t a r r i v e d l a t e r . P r i o r r e s i d e n c y , however, was n o t t h o u g h t by Kikkawa (1961) t o be a f a c t o r i n d e t e r m i n i n g 100 h i e r a r c h y p o s i t i o n i n W h i t e - e y e s ; he s u g g e s t e d t h a t any a d v a n t a g e c o n f e r r e d on b i r d s w i t h p r e v i o u s f a m i l i a r i t y w i t h an a r e a was masked by t h e l a r g e number o f b i r d s p r e s e n t , The s i t u a t i o n r e g a r d i n g p r i o r o c c u p a n c y and h i e r a r c h i c a l p o s i t i o n i n Song S p a r r o w s i s c o m p l i c a t e d by t h e f a c t t h a t o n l y ' j u v e n i l e s can be c o n s i d e r e d . a l l a d u l t s were t o p b i r d s i n t h e i r own t e r r i t o r i e s . The j u v e n i l e g r o u p s a r e most l i k e l y f o rmed a b o u t t h e same t i m e i n c e r t a i n a r e a s a l o n g t h e hedgerow, d u r i n g t h e r e c r u d e s c e n c e o f f a l l t e r r i t o r i a l b e h a v i o u r o f t h e t e r r i t o r i a l a d u l t s . I f t h i s s u g g e s t i o n i s t h e c a s e , t h e n t h e j u v e n i l e s a p p e a r t o a r r a n g e t h e h i e r a r c h i c a l p o s i t i o n s w i t h o u t r e g a r d f o r p r e v i o u s f a m i l i a r i t y w i t h an a r e a , b e c a u s e no i n d i v i d u a l would have t h a t f a m i l i a r i t y . One c o u l d p o s s i b l y a r g u e t h a t t h o s e j u v e n i l e s t h a t happened t o a r r i v e f i r s t , d u r i n g t h e d i s p e r s a l phase (see G e n e r a l I n t r o d u c t i o n ) , a t one o f t h e c e n t r e s o f c o n c e n t r a t i o n would have an a d v a n t a g e o v e r l a t e r a r r i v a l s . No d a t a s u p p o r t i n g o r r e f u t i n g t h i s i d e a a r e a v a i l a b l e . I t seems, t h e r e f o r e , t h a t l o n g - t e r m p r i o r o c c u p a n c y i s n o t a f a c t o r i n d e t e r m i n i n g t h e p o s i t i o n o f a j u v e n i l e Song Sparrow i n t h e h i e r a r c h y . S h o r t - t e r m p r i o r o c c u p a n c y , however, c a n n o t be r u l e d o u t as a p o s s i b l e f a c t o r . O t h e r f a c t o r s and t h e p o s i t i o n i n h i e r a r c h y The t o p b i r d s may be g e n e t i c a l l y d i f f e r e n t from b i r d s o f l o w e r r a n k . F u r t h e r , s o c i a l r a n k c o u l d be g e n e t i c a l l y 101 i n h e r i t e d . Sade (1967) however has a r g u e d t h a t dominance i s n o t an i n t r i n s i c f e a t u r e o f an i n d i v i d u a l , b u t a ' r o l e * a c q u i r e d by him. I have no e v i d e n c e s u p p o r t i n g o r r e f u t i n g a h y p o t h e s i s b a s e d on g e n e t i c f e a t u r e s t h a t might d e t e r m i n e a j u v e n i l e Song S p a r r o w ' s p o s i t i o n i n t h e dominance h i e r a r c h i e s on R e i f e l I s l a n d . A l t h o u g h t h e dominance h i e r a r c h i e s a r e based on a g g r e s s i v e e n c o u n t e r s , i t i s f r e q u e n t l y d i f f i c u l t t o d e t e r m i n e i f t h e most a g g r e s s i v e b i r d i s t h e dominant b i r d . F i g u r e 9 shows t h a t t h e r e i s a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n between p o s i t i o n i n h i e r a r c h y and t h e number o f i n t e r a c t i o n s i n which e a c h b i r d was i n v o l v e d . However, as K r e b s (1973) p o i n t s o u t , an a l p h a i n d i v i d u a l need n o t show t h e h i g h e s t f r e g u e n c y o f a g g r e s s i v e b e h a v i o u r , b e c a u s e h i s p o s i t i o n i s s t a b l e . The f a c t t h a t t h e h i e r a r c h i e s i n Song S p a r r o w s a r e s t a b l e , and y e t t h e r e i s a h i g h e r i n c i d e n c e o f i n t e r a c t i o n s c o n c e r n i n g b i r d s a t t h e t o p end o f t h e h i e r a r c h y , r e q u i r e s f u r t h e r i n v e s t i g a t i o n . In summary, t h e n , t h e r e a p p e a r s t o be l i t t l e c o n c l u s i v e e v i d e n c e i n t h i s s t u d y s u p p o r t i n g any f a c t o r (s) t h a t might d e t e r m i n e t h e r a n k t h a t an i n d i v i d u a l Song Sparrow h e l d i n t h e h i e r a r c h y . M a l e s d o m i n a t e d f e m a l e s . S i z e , age, and l o n g - t e r m p r i o r o c c u p a n c y were n o t t h o u g h t t o be i m p o r t a n t , b u t s h o r t - t e r m p r i o r o c c u p a n c y and p o s s i b l y g e n e t i c o r a g g r e s s i o n 102 f e a t u r e s were n o t r u l e d o u t . F i n a l l y , i t i s worth l o o k i n g a t t h e outcomes o f t h e h i e r a r c h i e s , and i n p a r t i c u l a r t h e i d e a t h a t t h e dominant i n d i v i d u a l s i n t h e h i e r a r c h i e s were t h e s u c c e s s f u l ones i n o b t a i n i n g t e r r i t o r i e s when t h e o p p o r t u n i t y a r o s e . (c) Outcomes o f t h e H i e r a r c h i e s In c e r t a i n h i e r a r c h i c a l g r o u p s o f a n i m a l s , t h e r e i s a p r o n o u n c e d f e e d i n g o r d e r (e. g. Anthony 1955; G u h l 1956; Dix o n 1965). The dominant i n d i v i d u a l f e e d s f i r s t , f o l l o w e d by s u b o r d i n a t e s i n d e s c e n d i n g o r d e r . The a p p e a r a n c e o f t h e f i r s t Song Sparrow a t t h e f e e d i n g s t a t i o n was n o t r e l a t e d t o i t s p o s i t i o n i n t h e dominance h i e r a r c h y . T a b l e 16 g i v e s t h e p o s i t i o n o f t h e f i r s t b i r d t h a t a p p e a r e d on t h e t e n days t h a t were s p e n t i n o b s e r v i n g t h e B-C H i e r a r c h y . I n f a c t , s u b o r d i n a t e s a r r i v e d f i r s t j u s t a s o f t e n a s d o m i n a t e s , and f e m a l e s a s o f t e n a s m a l e s . Shoemaker (1939) f o u n d t h a t , i n a l a b o r a t o r y p o p u l a t i o n o f c a n a r i e s , S e r i n u s s e r i n u s , t h e d o m i n a n t males had a much h i g h e r b r e e d i n g s u c c e s s t h a n s u b o r d i n a t e s . T h e r e i s no e v i d e n c e f r o m t h e p r e s e n t s t u d y t o s u p p o r t o r r e f u t e t h i s s u g g e s t i o n . In c e r t a i n l e k s p e c i e s , (e. g. Sage G r o u s e , W i l e y 1970), not o n l y i s i t i m p o r t a n t f o r males t o o b t a i n a t e r r i t o r y t o 103 P O S I T I O N IN H I E R A R C H Y Figure 9 P o s i t i o n i n h i e r a r c h y and number of i n t e r a c t i o n s : the B-C Hierarchy The l i m i t a t i o n s o f t h i s a n a l y s i s are acknowledged. Each b i r d d i d not spend an equivalent amount o f time at the feeding s t a t i o n . Some b i r d s fed without an i n t e r a c t i o n o c c u r i n g . The manifestations of aggressive behaviour are discussed i n the t e x t . 104 mate, b u t i t i s a l s o i m p o r t a n t t o o b t a i n c e r t a i n f a v o u r e d t e r r i t o r i e s t o e n s u r e s u c c e s s f u l m a t i n g s . T h e r e a r e s e v e r a l s p e c i e s o f b i r d s i n which t h e a c q u i s i t i o n o f a t e r r i t o r y i s a p r e - r e q u i s i t e f o r o b t a i n i n g a mate, and hence b r e e d i n g . I n many o f t h e s e s p e c i e s , t h e p r e s e n c e o f a dominance h i e r a r c h y i n t h e p r e - b r e e d i n g s e a s o n has been d e t e r m i n e d . The c o r r e l a t i o n between dominance i n t h e h i e r a r c h y and s u c c e s s v i n o b t a i n i n g a t e r r i t o r y has been shown i n o n l y a few p o p u l a t i o n s . Odum (1942) r e p o r t e d t h a t t h e t o p t h r e e males i n a w i n t e r f l o c k o f B l a c k - c a p p e d C h i c k a d e e s e s t a b l i s h e d t e r r i t o r i e s i n t h e s p r i n g . D i x o n (1965) f o u n d s i m i l a r r e s u l t s i n C a r o l i n a C h i c k a d e e s , as d i d Tompa (1964) i n Song S p a r r o w s . The r e s u l t s i n t h e p r e s e n t s t u d y f u r t h e r s t r e n g t h e n t h i s c o r r e l a t i o n , t h a t t h e i n d i v i d u a l s t h a t o b t a i n t e r r i t o r i e s a r e t h e d o m i n a n t o n e s i n dominance h i e r a r c h i e s e s t a b l i s h e d d u r i n g t h e p r e - b r e e d i n g s e a s o n . I n summary, t h e n , g r o u p s o f j u v e n i l e Song S p a r r o w s c o n g r e g a t e d i n t h e f a l l a t c e r t a i n f a v o u r e d l o c a l i t i e s a l o n g t h e hedgerow. H i e r a r c h i e s were f o r m e d , which by m i d - w i n t e r were l i n e a r s t a b l e , w i t h few r e v e r s a l s . In t h e h i e r a r c h i e s , males d o m i n a t e d f e m a l e s . S i z e , age, and l o n g - t e r m p r i o r o c c u p a n c y were n o t t h o u g h t t o be i m p o r t a n t i n d e t e r m i n i n g th e r a n k t h a t an i n d i v i d u a l h e l d i n t h e 1 0 4 TABLE 16 Feeding order of hierarchy: appearance of f i r s t b i r d at feeding s t a t i o n s of the B-C Hierarchy Sex P o s i t i o n of b i r d i n hierarchy Number of days Male Female F i r s t seven 3 3 0 Middle eight 4 2 2 Last seven 3 0 3 T o t a l s : 22 b i r d s 10 105 h i e r a r c h y . S h o r t - t e r m p r i o r o c c u p a n c y and p o s s i b l y g e n e t i c o r a g g r e s s i o n f e a t u r e s were n o t r u l e d o u t . The r e m o v a l e x p e r i m e n t s and s u b s e q u e n t r e p l a c e m e n t s showed t h a t t h o s e y e a r l i n g s t h a t o b t a i n e d t e r r i t o r i e s i n t h e s p r i n g on t h e S p r i n g Removal A r e a were t h e d o m i n a n t i n d i v i d u a l s i n t h e h i e r a r c h i e s e s t a b l i s h e d d u r i n g t h e p r e - b r e e d i n g s e a s o n . 106 LITERATURE CITED A l e x a n d e r , R. D. 1961. A g g r e s s i v e n e s s , t e r r i t o r i a l i t y , and s e x u a l b e h a v i o u r i n f i e l d c r i c k e t s ( O r t h o p t e r a r G r y l l i d a e ) . B e h a v i o u r 17: 130-223. A n t h o n y , A. 1955. B e h a v i o u r p a t t e r n s i n a l a b o r a t o r y c o l o n y o f P r a i r i e Dogs, Cynomis l u d o y i c i a n u s . J . Mammal. 36: 69-78. Van den Assem, J . 1967. T e r r i t o r y i n t h e t h r e e - s p i n e d s t i c k l e b a c k G a s t e r o s t e u s a c u l e a t u s . 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The b e h a v i o u r and s o c i a l o r g a n i z a t i o n o f t h e New F o r e s t P o n i e s . Anim. Behav. Monogr. 5: 187-94. Watson, A. 1964. A g g r e s s i o n and p o p u l a t i o n r e g u l a t i o n i n Red G r o u s e . N a t u r e 202: 506-7. Watson, A. 1965. A p o p u l a t i o n s t u d y o f P t a r m i g a n , Laggpus mutus , i n S c o t l a n d . J . Anim. E c o l . 34: 135-72. Watson, A. 1967. T e r r i t o r y and p o p u l a t i o n r e g u l a t i o n i n t h e Red G r o u s e . N a t u r e 215: 1274-75. Watson, A. and D. J e n k i n s . 1968. E x p e r i m e n t s on p o p u l a t i o n c o n t r o l by t e r r i t o r i a l b e h a v i o u r i n t h e Red G r o u s e . J . Anim. E c o l . 3: 595-614. Watson, A. and G. R. M i l l e r . 1971. T e r r i t o r y s i z e and a g g r e s s i o n i n a f l u c t u a t i n g Red G r o u s e p o p u l a t i o n . J . Anim. E c o l . 40: 367-83. Watson, A. and R. Moss. 1970a. Dominance, s p a c i n g b e h a v i o u r and a g g r e s s i o n i n r e l a t i o n t o p o p u l a t i o n l i m i t a t i o n s i n v e r t e b r a t e s . IN: A n i m a l p o p u l a t i o n s i n r e l a t i o n t o t h e i r f o o d r e s o u r c e s . A. Watson (ed) B l a c k w e l l , O x f o r d : 167-218. Watson, A. and R. Moss. 1970b. S p a c i n g a s a f f e c t e d by t e r r i t o r i a l b e h a v i o u r , h a b i t a t , and n u t r i t i o n i n Red G r o u s e . IN: B e h a v i o u r and e n v i r o n m e n t : t h e use o f s p a c e by a n i m a l s and men. A. H. E s s e r (ed) Plenum P r e s s , New Y o r k - London. Watts, C. R. and A. W. S t o k e s . 1971, The s o c i a l o r d e r o f T u r k e y s . S c i e n t . Amer. 224 ( 6 ) : 112-8. Weeden, J . S. 1965. T e r r i t o r i a l b e h a v i o u r o f t h e T r e e S p a r row. Condor 67: 193-209. W e s s e l l , J . P. and H. L e i g h . 1941. S t u d i e s o f t h e f l o c k o r g a n i z a t i o n o f t h e W h i t e - t h r o a t e d S p a rrow. W i l s o n B u l l . 53: 222-30. Wood-Gush, D. G. M. 1965. The s o c i a l o r g a n i z a t i o n o f d o m e s t i c b i r d c o m m u n i t i e s . Symp. Z o o l . S o c. Lond. 14: 219-31. 1 17 W i l e y , R. H. J r . 1970. T e r r i t o r i a l i t y and non-random m a t i n g i n t h e Sage G r o n s e , C e n t r o c e r c u s u r o p h a s i a n u s . O n p u b l . Ph. D. T h e s i s , The R o c k e f e l l e r U n i v e r s i t y , New Y o r k . Wynne-Edwards, V. C. 1962. A n i m a l d i s p e r s i o n i n r e l a t i o n t o s o c i a l b e h a v i o u r . O l i v e r and Boyd. E d i n b u r g h . Young, C. W. 1970. T e r r i t o r i a l i t y i n t h e Common S h e l d u c k T a d o r n a t a d o r n a . I b i s 112: 330-5. Young, E. C. 1972. T e r r i t o r y e s t a b l i s h m e n t and s t a b i l i t y i n M c c o r m i c k ' s Skua. I b i s 114: 234-44. Z a r e t , T. M. and A. , S. Rand. 1971. C o m p e t i t i o n i n t r o p i c a l s t r e a m f i s h e s : s u p p o r t f o r t h e c o m p e t i t i v e e x c l u s i o n t h e o r y . E c o l o g y 52: 336-42. Zimmerman, J . L. 1971. The t e r r i t o r y and i t s d e n s i t y d e p e n d a n t e f f e c t i n S p i z a a m e r i c a n a . Auk 88: 590-612. 118 APPENDIX 1. L i s t o f s p e c i e s o f most common and most i m p o r t a n t p l a n t s a l o n g t h e hedgerows and a d j o i n i n g marsh. The hedgerow was c o m p r i s e d o f a t h i c k , f r e q u e n t l y i m p e n e t r a b l e t a n g l e o f s m a l l t r e e s and s h r u b s , w i t h t h e o c c a s i o n a l s t a n d o f mature t r e e s . The main s p e c i e s o f s m a l l t r e e s were AInus r u b r a , S a l i x h o o k e r i a n a , Sambucus r a c e m g s a , C r a t a e g u s d o u g l a s i i , and P r u n u s s p p . S h r u b s c o n s i s t e d m a i n l y o f C o r n u s s t o l o n i f e r a , Rubus s p e c t a b i l i s , R.. l a c i n i a t u s , J * i m a c r o p h y l l u s , Rosa s p p . , S y m p h o r i c a r p o s a l b u s , and L o n i c e r a s p p . F i n a l l y , t h e s t a n d s o f mature t r e e s were p r i n c i p a l l y P o p u l u s t r e m u l o i d e s , P.. t r i c h o c a r p a , A I n us r u b r a , and P s e u d o t s u g a m e n z i e s i i . A c o m p l e t e and d e t a i l e d v e g e t a t i o n a l s u r v e y o f t h e h e r b a c e o u s p l a n t s was n o t a t t e m p t e d . The most common and i m p o r t a n t o n e s , however; a r e l i s t e d h e r e : H e r a c l g u m l a n a t u m , V i c i a s p p . , C i r s i u m l a n c e o l a t u m , U r t i c a l y a l i i , P e t a s i t g s s p e c i o s a , A n a p h o l i s m a r g a r i t a c e a , E g u i s e t u m a r y e n s e , P t e r i d i u r a a g u i l i n u m , and s e v e r a l s p e c i e s o f g r a s s i n c l e a r e d a r e a s . The marsh a d j a c e n t t o t h e hedgerow was c o m p r i s e d m a i n l y o f : S a l i x s p p . , H y r i c a g a l e , T y p h a 1 a t i f o l i a , S c i r p u s S E ® r i c a n u s , C a r e x l y n g b y e i , I ^ y s i c h i t o n ka rots h a t c e n s e . 119 APPENDIX 2 Weather data from the Meteorological Office, Vancouver International Airport Mean monthly temperatures Jan. Feb. Mar. Apr. May June July Aug.- Sep. Oct. Nov. Dec. 1972: — 39.0 44.6 44.6 54.7 58.3 62.3 64.0 54.3 46.1 43.0 35.2 1973: 36.0 40.5 43.2 47.4 53.7 Normal (37 y r ) : 36.3 40.0 42.5 48.1 54.3 59.5 63.4 62.7 57.6 50.1 42.9 38.9 Monthly temperature : ranges Jan. Feb. Mar. Apr. May June July ft Aug. Sep.- Oct. Nov. Dec. 1972 Max. — 56.0 62.0 60.9 75.0 73.4 81.4 80.7 77.9 62.1 56.6 51.8 Min. ~ 17.4 30.0 30.8 41.1 45.9 47.9 48.0 35.0 30.2 25.4 12.0 1973 Max. 52.9 58.1 53.2 60.6 76.6 Min. 13.1 24.3 28.1 33.9 36.8 Precipitation - Jan. Feb. Mar. Apr. May_ June July Aug. Sep. Oct. Nov. Dec. R a i n f a l l : 1972: — 5.25 6.98 45.1 1.17 1.84 3.20 0.92 3.14 2.09 4.61 11.34 1973: 5.43 2.69 2.69 0.51 1.91 Normal: A.95 4.29 3.51 2.39 1.87 1.78 1.17 1.46 2.41 4.81 5.47 5.96 Snowfall: 1972: — 0.3 0.4 1.9 TR 6.4 1973: 4.7 TR 0.1 TR Normal: 8.8 3.1 2.1 TR 0.9 5.7 Totals: 1972: — 5.28 7.05 4.70 1.27 1.84 3.20 0.92 3.14 2.09 4.61 11.82 1973: 5.92 2.69 2.70 0.51 1.91 Normal: 5.80 4.57 3.69 2.40 1.87 1.78 1.17 1.46 2.41 4.81 5.56 6.51 120 APPENDIX 3 D e s t r u c t i o n o f a s t r e t c h o f dyke ( , B u l l d o z e d A r e a ' ) . I n J u n e , 1972, 800 f e e t o f dyked hedgerow on t h e F a l l R emoval A r e a was r e b u i l t . T h i s e n t a i l e d t h e t o t a l d e t r u c t i o n o f t h e v e g e t a t i o n , and r e p l a c i n g i t w i t h g r a v e l and r o c k . T h i s s t r e t c h o f hedgerow s u p p o r t e d a number o f Song S p a r r o w s ; F i g u r e 10 g i v e s t h e t e r r i t o r y b o u n d a r i e s t h a t e x i s t e d b e f o r e t h e b u l l d o z i n g s t a r t e d . 3 m a l e s and 1 f e m a l e were known a l o n g t h i s s t r e t c h . A l l 4 b i r d s d i s a p p e a r e d i n l a t e J u n e . However, no l e s s t h a n 3 o f t h e s e 4 were r e l o c a t e d . One male ( B l a c k / O r a n g e ) must have s p e n t t h e summer a s a c r y p t i c n o n - t e r r i t o r i a l b i r d a l o n g t h e hedgerow c l o s e t o t h e B u l l d o z e d A r e a , as he t o o k o v e r a t e r r i t o r y a d j a c e n t t o t h e B u l l d o z e d A r e a when t h e r e s i d e n t male was removed on O c t o b e r 3/1972 d u r i n g t h e f a l l r e m o v a l e x p e r i m e n t s . A s e c o n d male (Green/Green) was l o c a t e d i n e a r l y March 1973 a s a s t r o n g l y t e r r i t o r i a l b i r d i n a s t r e t c h o f s h r u b b e r y a b o u t 2000 m e t r e s t o t h e s o u t h on Westham I s l a n d . The t h i r d b i r d , t h e f e m a l e (LP/White) , p a i r e d w i t h a C o n t r o l male a b o u t 300 m e t r e s from h e r d e s t r o y e d t e r r i t o r y , a p p a r e n t l y a f t e r t h i s m ale's f e m a l e d i s a p p e a r e d i n e a r l y s p r i n g . Figure 10 Bulldozed Area: before the dyke the arrangement of t e r r i t o r y boundaries r e b u i l d i n g occurred 122 T h e s e d a t a s u g g e s t t h a t a d u l t s c an s u r v i v e as n o n - b r e e d i n g , n o n - t e r r i t o r i a l b i r d s t h r o u g h t h e summer, i n s p i t e o f t h e f a c t t h a t t h e s u r p l u s o f b i r d s on t h e s t u d y a r e a seemed t o be composed o n l y o f j u v e n i l e s . \ 7 123~ APPENDIX 4 P o s s i b l e r e a s o n s why f e m a l e s were d i f f i c u l t t o l o c a t e i n t h e f a l l o f 1972. Some p o s s i b l e r e a s o n s why f e m a l e s were d i f f i c u l t t o l o c a t e i n t h e f a l l o f 1972 a r e g i v e n h e r e . 1. I t i s p o s s i b l e t h a t n o t a l l f e m a l e s were o u t o f moult by e a r l y O c t o b e r , when t h e r e m o v a l s t o o k p l a c e . M o u l t i n g i n d i v i d u a l s a r e e x t r e m e l y d i f f i c u l t t o f i n d . N i c e (1937) f o u n d t h a t t h e Song S p a r r o w s i n O h i o m o u l t e d i n A u g u s t and S e p t e m b e r , w i t h t h e o c c a s i o n a l b i r d n o t f i n i s h i n g u n t i l m i d - O c t o b e r . C a s u a l o b s e r v a t i o n s o f m o u l t i n g b i r d s on B e i f e l I s l a n d were made i n 1972, and September seemed t o be t h e month i n w h i c h m o u l t i n g most o c c u r r e d . However, one male removed on O c t o b e r 4 f r o m t h e S i m u l t a n e o u s Removal a r e a was s t i l l i n p a r t i a l m o u l t . 2. F e m a l e s a r e g e n e r a l l y more d i f f i c u l t t o l o c a t e t h a n m a l e s , and a p p a r e n t l y a r e l e s s r e s p o n s i v e i n t h e f a l l t h a n i n t h e s p r i n g ( N i c e 1943; Tompa 1964). 3. F e m a l e s d e s e r t t h e i r mates most o f t e n i n t h e l a t e summer and e a r l y f a l l . N i c e (1943) showed t h a t i n o n l y 31% o u t o f 55 p o s s i b l e i n s t a n c e s d i d f e m a l e s r e t u r n t o t h e i r f o r m e r t e r r i t o r i e s . 3056 went t o a d j a c e n t t e r r i t o r i e s , and 33^ t o t e r r i t o r i e s 100-700 m e t r e s d i s t a n t . T h u s , i t seems q u i t e l i k e l y t h a t s e v e r a l o f t h e t e r r i t o r i a l m a l e s d i d n o t have f e m a l e s i n t h e f a l l o f 1972. 124 APPENDIX 5 I n t e r s p e c i f i c i n t e r a c t i o n s between t s o n g S p a r r o w s and o t h e r s e e d - e a t i n g p a s s e r i n e s a t t h e f e e d i n g s t a t i o n s . Song S p a r r o w s i n t e r a c t e d w i t h most o f t h e o t h e r s p e c i e s o f b i r d s t h a t f e d a t t h e f e e d i n g s t a t i o n s . T h e r e were t h r e e common s p e c i e s , Oregon J u n c o , Fox S p a r r o w , and Towhee, t h a t f r e q u e n t e d t h e s t a t i o n s , o f which t h e j u n c o was by f a r t h e most abundant.. O c c a s i o n a l l y , o t h e r s e e d - e a t e r s s u c h as House F i n c h , Carjgodacus m e x i c a n u s , and L i n c o l n ' s S p a r r o w , H e l g s p i z a l i n c o l n i i , o c c u r r e d a t t h e s t a t i o n s . From o b s e r v a t i o n s , a v e r y g e n e r a l l i s t i n o r d e r o f i n e t r s p e c i f i c d o minance c o u l d be c o m p i l e d t h u s : Towhee Fox Sparrow Song Sparrow L i n c o l n ' s Sparrow House F i n c h O regon J u n c o however, c e r t a i n Song S p a r r o w s would t h r e a t e n b o t h Towhees and Fox S p a r r o w s . On o c c a s i o n , a Song Sparrow would d r i v e o f f a Fox S p a r r o w , b u t t h i s was r a r e , and u s u a l l y Fox S p a r r o w s t o o k p r e c e d e n c e o v e r Song S p a r r o w s . Towhees t e n d e d t o r e m a i n i n d i f f e r e n t t o t h e t h r e a t e n i n g b e h a v i o u r o f t h e Song S p a r r o w , and would f e e d and l e a v e i n d e p e n d e n t l y o f s u c h b e h a v i o u r . J u n c o s were r e a d i l y d r i v e n o f f by a l l t h e o t h e r 125 / s e e d - e a t e r s , b u t o f t e n s h e e r numbers a l l o w e d them t o f e e d r e l a t i v e l y c l o s e t o p o t e n t i a l a n t a g o n i s t s w i t h o u t i n d u c i n g r e t a l i a t i o n . 126. APPENDIX 6 Age and p o s i t i o n i n h i e r a r c h y : t h e t o p two b i r d s i n t h e B-C H i e r a r c h y The age o f t h e t o p two j u v e n i l e m ales i n t h e B-C H i e r a r c h y a r e known. The f i r s t d o m i n a n t j u v e n i l e ( B l u e / B l u e ) was banded on J u l y 25, w i t h no s i g n s o f p o s t - j u v e n i l e m o u l t , and i t had p r o b a b l y j u s t g a i n e d i n d e p e n d e n c e f r o m i t s p a r e n t s (s e e N i c e 1 9 ^ 3 ) . I t s . a g e on J u l y 25 was p u t t e n t a t i v e l y a t 35-40 d a y s . The s e c o n d male on t h e dominance s c a l e ( Y e l l o w / L P ) was banded on May 25, a t t h e f l u t t e r i n g s t a g e o f d e v e l o p m e n t ( S t a g e 4 o f N i c e 1943).. T h e r e f o r e i t was between 10 and 16 d a y s o l d . T h u s , i n J a n u a r y , when t h e p o s i t i o n s o f t h e s e two b i r d s were d e t e r m i n e d , B l u e / B l u e would be a b o u t 200 d a y s o l d , and Y e l l o w / L P would be a b o u t 260 d a y s o l d . B l u e / B l u e would be a p r o d u c t o f most l i k e l y a s e c o n d b r o o d , and Y e l l o w / LP a p r o d u c t o f a f i r s t b r o o d . Y e t , B l u e / B l u e was t h e t o p j u v e n i l e o f t h e l a r g e s t h i e r a r c h y . 127 APPENDIX 7. P r e s s u r e f r o m i n t r u d e r s : E x p l a n a t i o n . I f e a c h p o t e n t i a l s e t t l e r makes x i n t r u s i a n s p e r day on t o a r e s i d e n t ' s t e r r i t o r y , t h e t o t a l number o f i n t r u s i o n s = Nx (N = n o s . o f p o t e n t i a l s e t t l e r s ) . The v a l u e o f Nx i s p r o p o r t i o n a l t o t h e t i m e t h e r e s i d e n t s p e n d s i n d e f e n c e ( T ) . T i s a l s o p r o p o r t i o n a l t o t e r r i t o r y a r e a , s o i n o r d e r t o keep T c o n s t a n t , ,when Nx goe s up, t e r r i t o r y s i z e g o e s down - t h e a s s u m p t i o n b e i n g t h a t t h e b i r d d o e s n o t have much s p a r e t i m e t o i n c r e a s e T. 128 APPENDIX 8 The f i v e c o n d i t i o n s o f Watson and Moss. Watson and Moss (1970a) put f o r w a r d t h e f o l l o w i n g f i v e c o n d i t i o n s w h i c h need t o be met t o show t h a t b e h a v i o u r l i m i t s a b r e e d i n g p o p u l a t i o n . A. A s u b s t a n t i a l p a r t o f t h e p o p u l a t i o n d o e s n o t b r e e d , e i t h e r b e c a u s e a n i m a l s d i e ; o r b e c a u s e t h e y a r e i n h i b i t e d f r o m b r e e d i n g e v e n t h o u g h t h e y s u r v i v e , and may b r e e d i n l a t e r y e a r s . B. Such n o n - b r e e d e r s a r e p h y s i o l o g i c a l l y c a p a b l e o f b r e e d i n g i f t h e more d o m i n a n t o r t e r r i t o r i a l ( i . e. b r e e d i n g ) a n i m a l s a r e removed. C The b r e e d i n g a n i m a l s a r e n o t c o m p l e t e l y u s i n g up some r e s o u r c e , s u c h a s f o o d , s p a c e , o r n e s t s i t e s . I f t h e y a r e , t h e r e s o u r c e i t s e l f i s l i m i t i n g . D. The m o r t a l i t y o r d e p r e s s e d r e c r u i t m e n t due t o t h e l i m i t i n g f a c t o r ( s ) c h a n g e s i n an o p p o s i t e s e n s e t o , and a t t h e same r a t e a s , o t h e r c a u s e s o f m o r t a l i t y o r d e p r e s s e d r e c r u i t m e n t . E. I f (A) , (B) , (C) , and (D) a r e f u l f i l l e d , and t h e numbers c h a n g e f o l l o w i n g c h a n g e s i n f o o d , t h e n f o o d and b e h a v i o u r a r e b o t h l i m i t i n g t h e b r e e d i n g p o p u l a t i o n . 129 C O T T O N W O O D S T R E T C H L O S E R \ 6 LP \ L P LP 2 jjBUnt) 6" R Y Y © o" G G d* LP RW d1 w © 2 Black © - 11 9 G ® ? LP L -D ? B 0 0 B 2 BO B G LP LP LP \ 14 « 1 9 3 2 5 3 5 1 M LpUnb \ 5 2 5 7 10 1 3 4 5 R Y \ 2 2 1 4 3 2 1 4 Y © 1 2 3 1 1 1 G G 1 2 11 1 1 2 2 LP RW 11 7 1 1 w © 5 2 1 2 Black <D \ 2 1 RW RW 1 G ® 1 LP L-D 1 BO OB 1 BO B 170 I N T E R A C T I O N S 13 M A N H O U R S Figure 12 S E D G E PATH (W) DC LU it \ cf GB GB cf G BY cf R Y ? Black B cf 0 Y LO cf R G SEF ? R B ? Y B ? Y DG '? W Y ? BO RW cf W DG ? B © ? B BY cf LD BY GB GB \ 2 15 1 1 3 6 9 4 9 8 G BY \ 1 4 2 1. 1 4 R Y 1 2 3 7 6 Black B 2 1 3 3 1 4 2 O Y 11 2 2 7 5 2 R G 1 \ 2 1 2 8 R B 1 1 3 1 Y B 2 2 2 Y DG 1 2 1 2 W Y 1 1 \ 3 2 BO RW \ 4 W DG 1 4 B © 2 B BY 1 LD BY \ 186 INTERACTIONS 15 MAN HOURS 121 Figure 13 B U L L D O Z E D P A T H S L O S E R oc LU 5 . cf \ M s _o_ R cf R Y cf L P ® cf Black 2 Black 2 Y DG 2 w 2 B ® 2 RW D P DG B Y BY M DP 10 « 5 2 10 1 0 R \ 11 1 5 1 2 0 6 R Y 9 2 6 34 1 6 5 L P ® 1 2 1 3 Black D G 1 10 3 Black B \ 4 2 2 1 Y DG 2 3 W Y 3 B ® \ 1 RW BY \ 174 INTERACTIONS 22 MAN H O U R S 1g2 Figure 14 FIRST BIG A L D E R L O S E R cr LU z \ 1 © LD LD R © B W 0_ Y Y DG Bl BO 1 9 5 2 1 1 L D LD 6 2 6 1 R © 9 5 3 1 B W 4 1 0 Y 2 1 Y DG \ 1 Bl BO \ 61 INTERACTIONS; 6 MAN HOURS M A R S H N A R R O W S L O S E R 4 ? ? ? \ Y i f © UNB BO O B B l © M B ^ 2 4 UNB 1 BO O B 1 B l © 8 INTERACTIONS; 5 MAN HOURS 1 ^ Figure 15 N O - N A M E C L E A R I N G L O S E R 42 INTERACTIONS 11 MAN HOURS 

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