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Breeding behavior and feeding habits of the bald eagle (Haliaeetus leucocephalus L.) on San Juan Island,… Retfalvi, Laszlo 1965

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BREEDING BEHAVIOR AND FEEDING HABITS OF T H E BALD E A G L E (HALIAEETUS L E U C O C E P H A L U S L . ) ON SAN JUAN ISLAND, WASHINGTON by L A S Z L O I. R E T F A L V I B . S . F . (S), University of British Columbia, 1961 A thesis submitted in partial fulfilment of the requirements for the degree of MASTER OF FORESTRY in the Faculty of Forestry "We accept this thesis as conforming to the required standard T H E UNIVERSITY OF BRITISH COLUMBIA Apri l , 1965 In presenting th i s thes i s in p a r t i a l f u l f i lmen t of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make i t f r ee l y a v a i l a b l e fo r reference and study. I fur ther agree that per -mission for extensive copying of t h i s thes i s for s cho la r l y purposes may be granted by the Head of my Department or by his representatives.. It is understood that copying or p u b l i -ca t ion of t h i s thes i s for f i n a n c i a l gain sha l l not be allowed without my wr i t ten permiss ion. Department of The Un ivers i ty of B r i t i s h Columbia Vancouver 8, Canada . ABSTRACT The breeding behavior and feeding habits of the bald eagle (Haliaeetus leucocephalus L . ) were studied during 1 9 6 2 and 1 9 6 3 on San Juan Island, Washington. The primary aim of the study was to acquire information which would relate to the general decline in bald eagle numbers. Thirteen bald eagle nests were found on San Juan Island. On the basis of the spacing of these nests, the density of breeding eagles was considered to be low. The number of bald eagles varied throughout the year; the highest numbers were present in February and the lowest numbers in October. The change in eagle numbers was caused by the fluctuating numbers of juveniles. Two active nests were kept under observation, one in 1962 and another in 1963. The breeding eagles showed hostility toward intruders such as adult and juvenile bald eagles and man in the vicinity of their nesting site. The birds showed indifference toward intrusions of red-tailed hawks, crows and gulls. The chronology of breeding activities on San Juan Island was approximated with the aid of local information and with findings of former investigators. Egg-laying occurs between March 4 and 19; hatching between\ Apri l 8 and 14. The young spend 12 to 1 3 weeks in the nest during which time parental attention gradually decreases. During the first 5 weeks of the youngs' life the nest is constantly guarded by one of the parents. Parental attention markedly decreases after the young start their wing e x e r c i s e s at the age of 8 to 9 weeks. In general, the female parent spent three t i m e s as much time at the nest as did the male. F o o d was brought to the nest at i r r e g u l a r i n t e r v a l s by both the female and male par e n t s . The young were fed m a i n l y by the female during the f i r s t seven weeks of their l i f e ; l a t e r the young fed themselves. No a p p r e c i a b l e change i n the amount of food supplied to the young during their nest l i f e was observed. Young of the same nest were s i m i l a r i n size and i n d i c a t i o n s of maltreatment f r o m the others or f r o m the parents were not observed. M o s t of the food brought to the nest c o n s i s t e d of rabbit c a r r i o n . T h i s type of food i t e m was available throughout the year due to the rabbits'high m o r t a l i t y r e s u l t i n g f r o m c o l l i s i o n with automobiles on the r o a d s . F i s h was f e d to the young during the f i r s t six weeks of th e i r l i f e ; t h e r e a f t e r , m a i n l y rabbit was consumed. Rabbit c a r r i o n was the p r i m a r y source of food for young eagles i n their p o s t - n e s t l i n g p e r i o d . The d e s t r u c t i o n of breeding habitat by r e a l estate developments i s the major cause of decline i n numbers of bald eagles on San Juan Island. i v T A B L E OF CONTENTS ABSTRACT i i T A B L E OF CONTENTS iv LIST OF T A B L E S viii LIST OF FIGURES x ACKNOWLEDGMENTS xii C H A P T E R I. G E N E R A L INTRODUCTION 1 1 . INTRODUCTION 2 2. ENVIRONMENT 4 1 . Geography and Geology 4 2. Climate 6 1 . Precipitation 6 2. Temperature 6 3. Winds 7 3. Vegetation 7 4. Fauna 9 1 . Mammals 9 2. Birds 11 3. STUDY METHODS 12 1 . Observations from the ground 12 2. Aerial surveys 13 3. Time spent in the area 14 CHAPTER II. ABUNDANCE AND MOVEMENTS 16 4. INTRODUCTION 17 5. ABUNDANCE 18 1. Eyries 18 1 . Description of nests 20 2. Territories 27 2. Observations 33 3. Summary and Conclusions 44 6. MOVEMENTS 46 CHAPTER III. BREEDING 49 7. INTRODUCTION 50 8. G E N E R A L BEHAVIOR 53 1 . The adults 53 2. Vocalization 54 3. Roosts and resting places 56 4. The flight of the eagle 60 1 . Fishing flight 60 2. Soaring 61 3. Defense and attack 63 4. Nuptial flight. 64 5. Relations with birds, mammals and man 65 1 . Relations with other bald eagles 65 2. Relations with red-tailed hawks 68 3. Relations with ospreys 69 v i 4. R e l a t i o n s with crows 7 0 5. R e l a t i o n s with gulls 7 3 6. R e l a t i o n s with other b i r d s 74 7. Re l a t i o n s with m a m mals 75 8. Re l a t i o n s with man 76 6. Summary and Co n c l u s i o n s 78 9. B R E E D I N G S E A S O N 80 10. B R E E D I N G B E H A V I O R 85 1 . P r e - n e s t l i n g p e r i o d 85 1. N e s t - r e p a i r a c t i v i t i e s 85 2. Mating s 86 3. P a r e n t a l attention to eggs 88 4. Hatching 89 2. N e s t l i n g p e r i o d 90 1 . P a r e n t a l attention to the young 90 1. C a r e of the young 90 2. . F e e d i n g of the young 96 2. Development of the young 102 1. Changes i n size 102 2. Changes i n plumage 104 3. Wing e x e r c i s e s . 105 3. R e l a t i o n s h i p between young i n the same nest 108 3. P o s t - n e s t l i n g p e r i o d 109 4. Summary and C o n c l u s i o n s 114 vii 11. BREEDING SUCCESS 116 CHAPTER IV. FEEDING HABITS 123 12. INTRODUCTION 124 1. Methods of collecting food data 124 2. Former food habit studies 126 13. FEEDING HABITS OF BALD E A G L E S ON SAN JUAN ISLAND 129 1 . Sources of information 129 1. Direct observations 129 2. Debris analysis 133 2. Sources of food 139 1. Mammals 139 2. Fish 144 3. Birds 144 4. Other items 145 3. Baiting experiments 146 4. Summary and Conclusions 150 CHAPTER V . G E N E R A L CONCLUSIONS AND SUMMARY 154 14. CONCLUSIONS 155 15. SUMMARY 161 APPENDICES 163 L I T E R A T U R E CITED 176 v i i i L I S T O F T A B L E S 1 . Date and d u r a t i o n of o b s e r v a t i o n s on San J u a n I s l a n d , 1962 to 1964 . 15 2. M e a s u r e m e n t s of n e s t s and ne s t t r e e s and t h e i r p r o x i m i t y to shore and human h a b i t a t i o n s . 25 3. L i n e a r d i s t a n c e s between n e i g h b o u r i n g b a l d eagle n e s t s on San Juan I s l a n d • 29 4. B a l d eagle counts made d u r i n g 1962 to 1964 on g r o u n d and by a i r on San Ju a n I s l a n d . 34 5. O c c a s i o n a l s i g h t i n g s of b a l d e a g l e s on San J u a n I s l a n d d u r i n g 1962 and 1963 35 6. E g g - l a y i n g dates of the b a l d eagle i n v a r i o u s p a r t s of i t s b r e e d i n g r a n g e ( A f t e r B e nt, 1937). 52 7. B r e e d i n g a c t i v i t y of b a l d e a g l e s on San J u a n I s l a n d d u r i n g the s p r i n g of 1963 82 8. The a p p r o x i m a t e c h r o n o l o g y of b r e e d i n g a c t i v i t i e s of b a l d e a g l e s on San J u a n I s l a n d 84 9. O b s e r v e d c o p u l a t i o n of b a l d e a g l e s on San Ju a n I s l a n d , 1962 and 1963 87 10. The m a l e and f e m a l e b a l d eagle's p a r t i c i p a t i o n i n g u a r d i n g the young of Ne s t A d u r i n g 1962 on T u r n I s l a n d 91 11 . The m a l e and f e m a l e b a l d eagle's p a r t i c i p a t i o n i n g u a r d i n g the young of Ne s t B d u r i n g M a y 1963 at R o c k y B a y 93 12. Number and date of fo o d i t e m s brought to the ne s t by the m a l e and f e m a l e p a r e n t e a g l e s d u r i n g 1962 and 1963, on San J u a n I s l a n d 97 13. F o o d brought to the ne s t by the pa r e n t e a g l e s d u r i n g the m o r n i n g , day and evening h o u r s , d u r i n g 1962 and 1963 on San Juan I s l a n d 100 1 X 14. N u m ber of food i t e m s brought to the nest by the f e m a l e and m a l e p a r e n t b a l d eagles i n r e l a t i o n to the young's age, d u r i n g the b r e e d i n g season on San J u a n I s l a n d 101 15. F a m i l y d i s i n t e g r a t i o n and nest abandonment at N e s t A, on T u r n I s l a n d , 1962 111 16. B r e e d i n g s u c c e s s at a c t i v e b a l d eagle n e s t s on San Juan I s l a n d d u r i n g 1962 and 1963 117 17. N e s t i n g s u c c e s s of b a l d e a g l e s on San J u a n I s l a n d d u r i n g 1962 and 1963 122 1.8. D i e t of the b a l d eagle i n d i f f e r e n t l o c a l i t i e s of i t s r ange (numbers r e p r e s e n t p e r c e n t a g e s ) 127 19. D i e t of b a l d e a g l e s on San J u a n I s l a n d , b a s e d on o b s e r v a t i o n s of food i t e m s brought to the nest d u r i n g 1962 and 1963 130 20. The m o n t h l y c o n s t i t u t i o n of diet of b a l d e a g l e s on San J u a n I s l a n d , b a s e d on o b s e r v a t i o n s of food i t e m s brought to the nest d u r i n g the s u m m e r s of 1962 and 1963 132 21 . The c o n s t i t u t i o n of diet of b a l d e a g l e s on San J u a n I s l a n d , b a s e d on a n a l y s i s of d e b r i s c o l l e c t e d underneath the n e s t t r e e on T u r n I s l a n d 136 22. Rate of d i s a p p e a r a n c e of c a r - k i l l e d r a b b i t s on San J u a n I s l a n d . N u m b e r s of r a b b i t s counted on r o a d s at the b e g i n n i n g and end of 1 2 hour p e r i o d s , d u r i n g the s u m m e r of 1963 (d i s number of d i s a p p e a r e d c a r c a s s e s ) 141 23. The p a r t i c i p a t i o n of d i f f e r e n t s p e c i e s of b i r d s and m a m m a l s i n c o n s u m i n g eagle b a i t s d u r i n g the months of J u l y and August', i n 1962 and 1963 149 X L I S T O F F I G U R E S 1 . A v e r a g e m o n t h l y t e m p e r a t u r e s and t o t a l m o n t h l y p r e c i p i t a t i o n on San Ju a n I s l a n d , b a s e d on data c o l l e c t e d by F. D e a r b o r n i n 1962 and 1963 8 2. a The l o c a t i o n of b a l d eagle n e s t s on San Juan I s l a n d and the " a v a i l a b l e a r e a s " b e l o n g i n g to each nest 31 b The l o c a t i o n of b a l d eagle n e s t s on San Juan I s l a n d i n r e l a t i o n to human h a b i t a t i o n 32 3. The a r e a c o v e r e d by m e ans of a e r i a l and grou n d s u r v e y s on San J u a n I s l a n d , 1962 to 1964 37 4. Number of b a l d e a g l e s seen on San Juan I s l a n d d u r i n g 1962, 1963 and 1964 39 5. The change i n n u m b e r s of eagles throughout the y e a r on San J u a n I s l a n d 40 6. C o m p a r i s o n between the m o n t h l y changes i n p r e c i p i t a t i o n and i n eagle n u m b e r s on San Juan I s l a n d 43 7 . a P e r c h - t r e e s u s e d by the eagles of N e s t A, on T u r n I s l a n d d u r i n g 1962 and 1963 ~~ 57 b P e r c h - t r e e s u s e d by the eagles of N e s t B, at R o c k y B a y d u r i n g 1962 and 1963 ~~ 57 8. a The s p a t i a l r e l a t i o n s h i p of p e r c h - t r e e s u s e d by the eagle s on T u r n I s l a n d , 1962 and 1963 59 b The s p a t i a l r e l a t i o n s h i p of p e r c h - t r e e s u s e d by the e a g l e s at R o c k y B a y , 1962 and 1963 59 9. Steps f o l l o w e d by the f e m a l e eagle of N e s t B to c a r r y a f i s h to the nest 62 10. a C r o w s h a r a s s i n g b a l d eagle at R o c k y B a y 72 b C r o w a t t a c k s eagle a f t e r eagle has r o b b e d c r o w of i t s food 72 x i 11 . S e a s o n a l d e c r e a s e i n p a r e n t a l attendance at N e s t A on T u r n I s l a n d , 1962 94 12. The p a r e n t eagles' attendance at Nest. B d u r i n g May, 1963, at R o c k y B a y 95 13. D i a g r a m s showing the s i z e of the eaglet i n c o m p a r i s o n to the s i z e of the f e m a l e p a r e n t at N e s t B i n 1963 103 14. a P e r c h e s u s e d by the eagle t s of N e s t A, on T u r n I s l a n d , d u r i n g 1962 ~ 107 b P e r c h e s u s e d by the e a g l e t s of N e s t B, at R o c k y B a y d u r i n g 1962 and 1963 " 107 15. The p r e s e n c e of adult and j u v e n i l e e a g l e s at N e s t A on T u r n I s l a n d d u r i n g J u l y , 1962 ( e x p r e s s e d as p e r c e n t a g e of the o b s e r v a t i o n t i m e ) 113 16. The m o n t h l y change i n f i s h and r a b b i t c o n s u m p t i o n by the b a l d e a g l e s d u r i n g the s u m m e r months of 1962 and 1963 on San J u a n I s l a n d 134 17. The m o n t h l y change i n diet of b a l d e a g l e s i n A l a s k a (after I m l e r and K a l m b a c h , 1955) 135 18. F o o d h a b i t s of b a l d e a g l e s on San Juan I s l a n d . C o m p a r i s o n between data o b t a i n e d by d i r e c t o b s e r v a t i o n and by a n a l y s i s of d e b r i s c o l l e c t e d u n d e r n e a t h the nest on T u r n I s l a n d 138 19- L o c a t i o n of b a i t s u s e d to l u r e b a l d e a g l e s and other c a r r i o n f e e d e r s 147 M A P S M a p 1 . The San J u a n I s l a n d s F o l l o w i n g page 4 M a p 2. San Juan I s l a n d F o l l o w i n g page 5 x i i A C K N O W L E D G M E N T S To the m e m b e r s of the D e p a r t m e n t of Z o o l o g y and the F a c u l t y of F o r e s t r y at the U n i v e r s i t y of B r i t i s h C o l u m b i a , m y thanks a r e due. D r . M. D. F. Ud v a r d y , who s u p e r v i s e d the study, p r o v i d e d guidance, and the f a c i l i t i e s needed. F o r t h e i r a d v i c e and h e l p f u l c r i t i c i s m I am i n d e b t e d to Dean I. M c T . Cowan and to D o c t o r s J . R. A d a m s , J . F. B e n d e l l , P. G. Haddock, A. K o z a k and O. S z i k l a i . I w i s h to e x p r e s s m y s i n c e r e thanks to the people of San Juan I s l a n d f o r t h e i r f r i e n d s h i p and s e n s i t i v e u n d e r s t a n d i n g . It i s i m p o s s i b l e to thank a l l i n d i v i d u a l s by name; but I m u s t e x p r e s s m y p a r t i c u l a r i n d e b t e d n e s s to the E. S. W a l l i n g s , the H. R o g e r s , the E. J . Hudsons, the A. C. C o l l i n s , the M. M. B a v e s , C. N a s h , A. N a s h and D. M o r t e l . The study was f i n a n c e d by the N a t i o n a l R e s e a r c h C o u n c i l and the C a n a d i a n Audubon S o c i e t y ( G r a n t s to D r . M. D. F. U d v a r d y ) . Chapter I. GENERAL INTRODUCTION 2 1. I N T R O D U C T I O N In r e c e n t y e a r s m u c h atte n t i o n has been g i v e n to the b a l d eagle ( H a l i a e e t u s leucocephalus. L.) by N o r t h A m e r i c a n c o n s e r v a t i o n g r oups i n r e s p o n s e to the d e c r e a s i n g n u m b e r s of the b i r d . D r a s t i c r e d u c t i o n i n a n i m a l n u m b e r s had o c c u r r e d b e f o r e when man i n v a d e d and changed t h e i r e n v i r o n m e n t , but the case of the b a l d eagle i s s p e c i a l f o r the b i r d was cho s e n i n 1782 as the U n i t e d States' n a t i o n a l s y m b o l , thus the p r e s e n c e of the b i r d h o l d s a s e n t i m e n t a l v a l u e to the g r e a t m a j o r i t y of the N o r t h A m e r i c a n p o p u l a t i o n . The number of b a l d e a g l e s has been on the d e c l i n e ( H o w e l l , 1949). In the e a r l y p a r t of the c e n t u r y b a l d e a g l e s w e r e s y s t e m a t i c a l l y e l i m i n a t e d f r o m the A l a s k a n c o a s t by a bounty s y s t e m . The bounty law was enacted i n 1917 by the T e r r i t o r i a l L e g i s l a t u r e a f t e r the i n v e s t i g a t i o n s of the A l a s k a n f i s h c o m m i s s i o n r e s u l t e d i n c o n c l u d i n g that the b a l d eagle i s one of the s t r o n g e s t c o n t r i b u t i n g c a u s e s i n the d e s t r u c t i o n of s a l m o n d u r i n g the spawning s e a s o n (Van K a m m e n , 1916). P r o m i n e n t b i o l o g i s t s of the t i m e had no o b j e c t i o n s to t h i s s y s t e m i n the b e l i e f that e a g l e s w e r e so n u m e r o u s and i n h a b i t e d so i n a c c e s s i b l e an a r e a that a s e r i o u s r e d u c t i o n i n t h e i r n u m b e r s c o u l d not o c c u r ( B r o o k s , 1922, W i l l e t , 1927). L a t e r i t became apparent that i f the bounty l a w was con t i n u e d a s e r i o u s r e d u c t i o n i n eagle n u m b e r s was p o s s i b l e . The bounty l a w was r e p e a l e d i n 1953 a f t e r s t u d i e s r e v e a l e d that the damage done to spawning f i s h p o p u l a t i o n s , f o r m e r l y a t t r i b u t e d to e a g l e s , was not of consequence. D u r i n g the t i m e the bounty l a w was i n effect an 3 e s t i m a t e d 100,000 eagle s w e r e k i l l e d ( I m l e r and K a l m b a c h , 1955). P r e s e n t l y the b a l d eagle i s p r o t e c t e d throughout the U n i t e d S t a t e s . A b i l l e n t i t l e d " B a l d E a g l e P r o t e c t i o n A c t " was s i g n e d by the p r e s i d e n t and became l a w i n 1940. In 1.959. A l a s k a a l s o came under t h i s l a w , I m l e r and K a l m b a c h (op, c i t . ) b e l i e v e d that by the t e r m i n a t i o n of the bounty law the b a l d eagle c o u l d be e x p e c t e d to r e t u r n to n o r m a l n u m b e r s . R e c e n t l y Sprunt and C u nningham (1961) r e p o r t e d that the l a r g e s t p o p u l a t i o n of b a l d e a g l e s i s i n A l a s k a . Due to the c o n t r o v e r s i a l e c o n o m i c status of the b a l d eagle, many i n v e s t i g a t i o n s of i t s f e e d i n g h a b i t s have been u n d e r t a k e n . L i t e r a t u r e c o n c e r n i n g t h i s phase of the b i r d ' s b i o l o g y i s v o l u m i n o u s , w h i l e other a s p e c t s of i t s b i o l o g y have been n e g l e c t e d . The p r e s e n t study was s t a r t e d i n 1962 to i n v e s t i g a t e the b r e e d i n g b e h a v i o r and f e e d i n g h a b i t s of the b a l d eagle on San Juan I s l a n d , W ashington. The p r i m a r y a i m of the study was to a c q u i r e i n f o r m a t i o n w h i c h w o u l d r e l a t e to the g e n e r a l d e c l i n e of the b a l d eagle p o p u l a t i o n s . The d e c i d i n g f a c t o r i n c h o o s i n g San Juan I s l a n d as the p l a c e of study was the p r e s e n c e of s e v e r a l b r e e d i n g p a i r s of eagles i n a r e a d i l y a c c e s s i b l e a r e a , s i n c e i t was i m p o r t a n t that the study a r e a c o u l d be v i s i t e d often d u r i n g the w i n t e r and the s p r i n g when the e a r l y p h a s e s of the b a l d eagles' b r e e d i n g b i o l o g y c o u l d be o b s e r v e d , 4 2. E N V I R O N M E N T The San J u a n I s l a n d group i s l o c a t e d at the i n t e r s e c t i o n of the 1 2 3 r d m e r i d i a n of west longitude w i t h the n o r t h l a t i t u d e l i n e of 48° 30'. The group i s c o m p o s e d of s e v e r a l i s l a n d s of v a r i o u s s i z e s of w h i c h San Ju a n I s l a n d i s the seco n d l a r g e s t w i t h an a r e a of 35,448 a c r e s (143.5 sq. km) ( M a p l ) . 2.1 G e o g r a p h y and G e o l o g y T h e n u c l e u s of the i s l a n d group i s f o r m e d by O r c a s , L o p e z and San J u a n I s l a n d s . T h e s e l a r g e i s l a n d s a r e bounded on the west by H a r o S t r a i t and B o u n d a r y P a s s w h i c h s e r v e as the i n t e r n a t i o n a l b o u n d a r y between Canada and the U n i t e d S t a t e s . The S t r a i t of J u a n de F u c a f o r m s the so u t h e r n boundary, w h i l e R o s a r i o S t r a i t s e p a r a t e s the i s l a n d s f r o m the m a i n l a n d . The c o m p l e x s y s t e m of channels and h a r b o r s of Puget Sound and W a s h i n g t o n Sound a r e s u p p l i e d w i t h ocean w a t e r t h r o u g h the S t r a i t of J u a n de F u c a . A l s o the l a r g e r p a r t of the w a t e r that f l o w s i n and out of the G u l f of G e o r g i a i s d e r i v e d f r o m the south, t h e r e f o r e i t m u s t p a s s t h r o u g h the c h a n n e l s of the San J u a n I s l a n d s . C o n s e q u e n t l y , v e r y heavy t i d e s a r e p r o d u c e d i n m a ny of the c h a n n e l s . The i s l a n d s u s u a l l y have i r r e g u l a r s h o r e l i n e s , deeply i n d e n t e d by n a r r o w f j o r d - l i k e h a r b o r s . The i n t e r v e n i n g c h a nnels that a r e c o m m o n l y n a r r o w and U-shaped due to g l a c i a l e r o s i o n , often a t t a i n depths of 600 feet o r m o r e . Map 1 . The San. J u a n I s l a n d G r o u p 5 A c c o r d i n g . t o M c L e l l a n (1927), the San J u a n I s l a n d s a r e c o m p o s e d c h i e f l y of P a l e o z o i c and M e z o z o i c s e d i m e n t a r y r o c k s . The i s l a n d s w e r e c o m p l e t e l y o v e r r i d d e n w i t h g l a c i e r s and even the h i g h e s t peaks a r e s t r i a t e d and p o l i s h e d by the g l a c i a l a c t i o n . C o n s i d e r a b l e a r e a s on many of the i s l a n d s a r e c o v e r e d w i t h g l a c i a l d r i f t . San J u a n I s l a n d (Map 2), i s 14 1/2 m i l e s long and 6 1/2 m i l e s a c r o s s at i t s w i d e s t p o i n t . The long d i m e n s i o n of the i s l a n d p o i n t s i n a n o r t h w e s t e r l y d i r e c t i o n , w h i l e the so u t h e r n end p r o j e c t s out as a l o n g , n a r r o w a r m , c u l m i n a t i n g i n C a t t l e P o i n t . E x c e p t i n g the southeast p o r t i o n , the s h o r e s a r e e l e v a t e d and r o c k y . The southwest s h o r e l i n e i s b r o k e n only by one l a r g e bay, known as F a l s e B a y , w h i c h i s so s h a l l o w that the g r e a t e r p a r t of i t i s b a r e at low t i d e . A t the n o r t h w e s t p o r t i o n of the i s l a n d , f j o r d - l i k e bays known as M i t c h e l l , G a r r i s o n and W e s c o t t B a y s b r e a k up the s h o r e l i n e . The n o r t h e a s t s h o r e i s i n d e n t e d by R o c k y B a y , whose s h o r e l i n e s m ake a 90 degree angle w i t h each o t h e r . The i n n e r m o s t p a r t of the bay i s s h a l l o w but f a r t h e r out i t s depth i s g r e a t e r than 100 f e e t , except i n the i m m e d i a t e v i c i n i t y of O ' N e i l I s l a n d . N e a r the m i d d l e of the southwest side of the i s l a n d , the s h o r e s a r e f o r m e d by the r u g g e d sl o p e s of Mount D a l l a s , w h i c h w i t h an e l e v a t i o n of 1036 f e e t , i s the h i g h e s t point on the i s l a n d . To the n o r t h e a s t of the M t . D a l l a s Range t h e r e i s a l a r g e d r i f t - c o v e r e d v a l l e y , San Ju a n V a l l e y , w h i c h i s noted as good a g r i c u l t u r a l l a n d . Map 2. San J u a n I s l a n d 6 2.2. C l i m a t e 2.2.1. P r e c i p i t a t i o n The San J u a n I s l a n d s a r e l o c a t e d w i t h i n a d r y - b e l t , that i s , i n a r a i n shadow of m o u n t a i n s on the O l y m p i c P e n i n s u l a and on V a n c o u v e r I s l a n d . A l o n g the west c o a s t of V a n c o u v e r I s l a n d the annual r a i n f a l l i s about 150 i n c h e s , w h i l e i n the v i c i n i t y of V i c t o r i a i t d r o p s to only 22 i n c h e s . A c c o r d i n g to R. D. M c L e l l a n (1927), F r i d a y H a r b o r has an a p p r o x i m a t e annual r a i n f a l l of 25 i n c h e s (635 mm). R e c o r d s kept by F. D e a r b o r n at Sunset P o i n t , at the west side of San J u a n I s l a n d , show an a v e r a g e of 16.83 i n c h e s (427 mm) of r a i n f a l l i n the p e r i o d f r o m 1958 to 1963. F u r t h e r e a s t w a r d the amount of r a i n i n c r e a s e s again u n t i l the m a x i m u m i s r e a c h e d on the w e s t e r n s l o p e s of the C a s c a d e M o u n t a i n s . The annual r a i n f a l l o c c u r r i n g on Mount C o n s t i t u t i o n Range on O r c a s I s l a n d , and on other m o u n t a i n r a n g e s of the r e g i o n i s c o n s i d e r a b l y g r e a t e r than that o c c u r r i n g on the a r e a s of low r e l i e f . The r a i n f a l l on the San Juan I s l a n d s i s l a r g e l y c o n f i n e d to f a l l and w i n t e r months, although o c c a s i o n a l r a i n does o c c u r at any t i m e of the y e a r . The m o n t h l y r a i n f a l l on San J u a n I s l a n d s f o r the y e a r s 1962 and 1963 i s t a b u l a t e d i n A p p e n d i x I. 2.2.2. T e m p e r a t u r e The a v e r a g e y e a r l y t e m p e r a t u r e on San J u a n I s l a n d i s about 52° F (11 .1°C.). The c o l d e s t month of the y e a r i s J a n u a r y w i t h an a v e r a g e t e m p e r a t u r e c l o s e to f r e e z i n g point; the w a r m e s t month i s August 7 with, an a v e r a g e t e m p e r a t u r e over 60° F. T e m p e r a t u r e s s t a r t to r i s e above the y e a r l y average i n m i d - A p r i l and drop below i t i n la t e O c t o b e r . The w a r m i n g up p r o c e s s i n the s p r i n g i s g e n e r a l l y a s l o w e r p r o c e s s than the c o o l i n g off i n the f a l l . The e x t r e m e s f o r the y e a r s 1962 and 1963 w e r e r e g i s t e r e d on J a n u a r y 11, 1963, when the t e m p e r a t u r e dropped to 15° F. and on M a y 20, 1963, when t e m p e r a t u r e s r o s e to 90° F. The d i f f e r e n c e between d a y t i m e h i g h and n i g h t t i m e low s e l d o m exceeds 20° F. V a l u e s f o r the m a x i m u m , m i n i m u m and a v e r a g e m o n t h l y t e m p e r a t u r e s f o r 1962 and 1963 a r e p r e s e n t e d i n A p p e n d i x I I . F i g u r e 1 shows the r e l a t i o n s h i p between p r e c i p i t a t i o n and t e m p e r a t u r e throughout the y e a r , b a s e d on the weather data of 1962 and 1963. 2.2.3. Winds D u r i n g the w i n t e r months the r e g i o n i s swept by s t r o n g w i n d s t o r m s . S t r o n g w i n d s f r o m the south and southwest a r e u s u a l l y p r e s e n t throughout the. y e a r . The t r e e s on the w e s t side of the i s l a n d show d e f o r m a t i o n due to t h i s constant w i n d e f f e c t . The re st of the i s l a n d i s r e l a t i v e l y c a l m due to the w i n d b r e a k i n g e f f e c t of the Mount D a l l a s Range on the w e s t s i d e of the i s l a n d . 2.3. V e g e t a t i o n About 70 p e r c e n t of San J u a n I s l a n d i s c o v e r e d w i t h t r e e s , p r e d o m i n a t e l y c o n i f e r s . The p r i m a r y s p e c i e s a r e D o u g l a s f i r ( P s e u d o t s u g a m e n z i e s i i ( M i r b . ) F r a n c o ) , H e m l o c k ( T s u g a h e t e r o p h y l l a Raf. S a r g . ) , Temper atur e F ° | C° P r e c i p i t a t i o n c m I i n F i g . 1 Average monthly temperatures and total monthly p rec ip i t a t ion on San Juan Is land based on data co l lec ted by F . Dearborn i n 1962 and 1963. 9 W e s t e r n R e d C e d a r ( T h u j a p l i c a t a , Donn) and Shore P i n e ( P i n u s c o n t o r t a , D o u g l . ) . M o s t of the t r e e - c o v e r e d p a r t s a r e s i t u a t e d on the n o r t h and west side of the i s l a n d . T h i s s i t u a t i o n i s n o t i c e a b l e on a l l the i s l a n d s of the group w h e r e the s o i l i s s h a l l o w and sandy. T h i s phenomenon has been a s c r i b e d p a r t l y to the r e l a t i v e c o n s e r v a t i o n of m o i s t u r e on the n o r t h e r n or shady side and p a r t l y to the f a c t that the m o s t p r e v a l e n t w i n d s t o r m s come f r o m the south and u p r o o t the v e g e t a t i o n on the s o u t h e r n s l o p e s , e s p e c i a l l y when the s o i l i s sandy ( M c L e l l a n , 1927). M a d r o n a ( A r b u t u s m e n z i e s i i , P u r s h ) i s abundant a l l t h r o u g h the i s l a n d s , m a i n l y on the w e s t e r n s i d e . G a r r y Oak ( Q u e r c u s g a r r y a n a , Dougl.) i s found i n stands along W e s c o t t and G a r r i s o n B a y s and on the side of Mount Young. S c a t t e r e d t r e e s a r e found on the southeast side as w e l l . San J u a n V a l l e y , i n the center of the i s l a n d , i s t r e e l e s s and was p r o b a b l y c l e a r e d by the e a r l y s e t t l e r s . T o w a r d the south, t r e e s b e come s c a r c e r and l a r g e open s p a c e s a r e found w i t h r o c k y o u t c r o p s and g r a s s . M o s t of the c o n i f e r o u s stands a r e second g r o w t h as e a r l y l o g g i n g a c t i v i t i e s and f i r e have r e m o v e d the m a t u r e stands. R e m n a n t s of huge t r e e s a r e found i n the n o r t h e r n p a r t s . T u r n I s l a n d , s e p a r a t e d f r o m San J u a n I s l a n d o n l y by a n a r r o w p a s s a g e , p r e s e r v e d a s m a l l s ample of m a t u r e stands, and Douglas f i r t r e e s of 6 f e e t i n d.b.h. a r e s t i l l found. 2.4. F a u n a 2.4.1. M a m m a l s A. l i s t of m a m m a l s p r e s e n t on the i s l a n d s i s not a v a i l a b l e , 10 however i t i s thought that the m a j o r i t y of m a m m a l s found i n m a i n l a n d W ashington a r e a l s o p r e s e n t on the San J u a n I s l a n d s . The f o l l o w i n g s p e c i e s of m a m m a l s w e r e s i g h t e d d u r i n g the y e a r s of the study. One of the m o s t abundant s p e c i e s on the i s l a n d i s the i n t r o d u c e d r a b b i t ( O r y c t o l a g u s c u n i c u i u s L . ) . R a b b i t s a r e p r e s e n t on a l l the l a r g e r i s l a n d s , but t h e i r n u m b e r s on San J u a n I s l a n d a r e e x c e p t i o n a l l y h i g h . T h e s e a n i m a l s w e r e r a i s e d c o m m e r c i a l l y some 30 y e a r s ago, but g r e a t n u m b e r s w e r e r e l e a s e d when the m a r k e t f o r t h e m d e c l i n e d . The B l a c k t a i l e d d e e r , ( O d o c o i l e u s h e m i o n u s c o l u m b i a n u s , R i c h a r d s o n ) n a t i v e to the i s l a n d s , i s f a i r l y abundant on some of the l a r g e r ones. The a n i m a l s a r e v e r y t a m e i n s p i t e of the p r e s s u r e w h i c h i s e x e r t e d on t h e m d u r i n g the hunting season and i n s p i t e of the y e a r - r o u n d shooting f o r r a b b i t s . The R e d F o x ( V u l p e s f u l v a , D e s m a r e s t ) was i n t r o d u c e d to San J u a n I s l a n d to combat the s i t u a t i o n c r e a t e d by the r a b b i t s . F o x e s a r e often seen; h o w e v e r , the ex p e c t e d i n c r e a s e i n t h e i r n u m b e r s d i d not o c c u r , c o n s e q u e n t l y t h e i r i n t r o d u c t i o n as a c o n t r o l m e a s u r e was not s u c c e s s f u l . R a c o o n ( P r o c y o n l o t o r L . ) i s v e r y abundant and i s a n a t i v e to the i s l a n d . M i n k ( M u s t e l a v i s o n , S c h r e b e r ) , M u s k r a t (Ondathra z i b e t h i c a L.), S h r e w s ( S o r e x s p . ) , M i c e ( P e r o m y s c u s ) and B a t s ( M y o t i s ) w e r e a l s o s i g h t e d o f t e n . K i l l e r Whale ( G r a m p u s r e c t i p i n n a , Cope) H a r b o r P o r p o i s e ( P h o c a e n a  v o m e r i n a , G i l l ) , H a r b o r S e a l ( P h o c a v i t u l i n a , G r a y ) and Otte r ( L u t r a  c a n a d e n s i s , S c h r e b e r ) a r e a l s o abundant i n v t h e w a t e r s a r o u n d the i s l a n d s . 11 2.4.2. B i r d s A p u b l i c a t i o n by M i l l e r et a l . (1935) g i v e s an annotated l i s t of t h e . b i r d l i f e of San J u a n I s l a n d s . L a t e r p u b l i c a t i o n s by Goodge and M c M a n n a m a (195:0) and R e t f a l v i (1963) r e c o r d s p e c i e s that a r e not p r e s e n t i n M i l l e r ' s e a r l i e r p u b l i c a t i o n . A l t o g e t h e r , 191 s p e c i e s of b i r d s have been r e c o r d e d f o r the San J u a n I s l a n d group. A l i s t of the b i r d - r e c o r d s i s p r e s e n t e d i n A p p e n d i x I I . 12 3. S T U D Y M E T H O D S 3.1. O b s e r v a t i o n s f r o m the G r o u n d Sin c e b a l d eagle n e s t s a r e u s u a l l y b u i l t on t a l l t r e e s , often above the canopy l a y e r of the s u r r o u n d i n g stand (see s e c t i o n 5 ), i t i s d i f f i c u l t to o b t a i n a c l e a r v i e w . It i s of p r i m e i m p o r t a n c e to o b t a i n a c l e a r v i e w of the n e s t i n o r d e r to o b s e r v e the a c t i v i t i e s of the young and the adult e a g l e s . In the one p r e v i o u s m a j o r study of the b a l d e a g l e , a tower was e m p l o y e d w h i c h was c o n s t r u c t e d to the same height as the n e s t , thus a v i e w . in t o the n e s t was a c h i e v e d ( H e r r i c k , 1924). A t the s t a r t of t h i s p r o j e c t such a technique c o u l d not be e m p l o y e d as the b i r d s w e r e w e l l advanced i n t h e i r b r e e d i n g c y c l e . Any attempt to c o n s t r u c t a tower w o u l d have endangered the young's s u r v i v a l , and as a r e s u l t , w o u l d d e l a y the r e s t of the study. A n added f a c t o r was the co s t i n v o l v e d i n the c o n s t r u c t i o n of such a t o w e r . A n attempt at the b e g i n n i n g of 1963 to b u i l d an o b s e r v a t i o n p l a t f o r m on a t a l l t r e e c l o s e to the nest h a d to be abandoned when the t r e e was found to be un s a f e . The only a l t e r n a t i v e was to s e l e c t s u i t a b l e h i g h ground i n the a r e a that o f f e r e d a v i e w of the n e s t , and b r i d g e the d i s t a n c e w i t h a h i g h -p o w e r e d t e l e s c o p e . D u r i n g the s u m m e r of 1962, A N e s t on T u r n I s l a n d was kept under o b s e r v a t i o n . The vantage po i n t was set on the other s i d e of the 'chan n e l w h i c h s e p a r a t e s T u r n I s l a n d f r o m San J u a n I s l a n d . The d i s t a n c e between the vantage point and the n e s t was i n e x c e s s of 700 y a r d s . To o b s e r v e the nes t a B a u s c h & L o m b t e l e s c o p e was u s e d w i t h a 3QX power 13 e y e p i e c e . The v i e w ob t a i n e d was good, however, the nest was a p p r o x i m a t e l y 80 feet h i g h e r than the o b s e r v a t i o n p o i n t , thus a c l e a r v i e w i n t o the i n t e r i o r of the nes t c o u l d not be a c h i e v e d . T h i s d i f f i c u l t y h i n d e r e d the o b s e r v a t i o n s of the young i n t h e i r e a r l y ages and p r e v e n t e d i d e n t i f i c a t i o n of food r e m a i n s s c a t t e r e d i n the n e s t , P h o t o g r a p h s w e r e taken t h r o u g h the t e l e s c o p e e m p l o y i n g a s i n g l e l e n s r e f l e x c a m e r a . A B u s h n e l l T e l e a d a p t e r was u s e d f o r c o u p l i n g the c a m e r a to the t e l e s c o p e . The q u a l i t y of the p i c t u r e s o b t a i n e d i s o n l y m e d i o c r e due to the l o w r e s o l v i n g power of the t e l e s c o p e and the g r e a t amount of l i g h t l o s t w i t h the c o u p l i n g of the two p i e c e s of equipment. In the s u m m e r of 1963, Ne s t B at R o c k y B a y was o b s e r v e d . The d i s t a n c e between n e s t and vantage point was r e d u c e d to 600 y a r d s , however the d i f f e r e n c e between e l e v a t i o n s c o u l d not be e l i m i n a t e d . 3.2. A e r i a l S u r v e y s S e v e r a l s u r v e y s by a i r p l a n e w e r e conducted d u r i n g the study. A t the s t a r t of the p r o j e c t , the a r e a was s u r v e y e d i n o r d e r to l o c a t e n e s t i n g p a i r s of e a g l e s . A e r i a l o b s e r v a t i o n s w e r e a l s o n e c e s s a r y d u r i n g the s p r i n g when a c t i v i t i e s i n the n e s t c o u l d not be r e a d i l y o b s e r v e d f r o m the ground. L a t e r i n the s u m m e r , f l i g h t s w e r e made to a s s e s s the s i t u a t i o n s at n e s t s other than those under continuous o b s e r v a t i o n . T h e s e a i r p l a n e f l i g h t s a l s o s e r v e d as a means f o r counting the eagle s p r e s e n t i n the a r e a . O u t s i d e of the b i r d s ' b r e e d i n g season, e s p e c i a l l y d u r i n g the w i n t e r , the p r e s e n c e of the b i r d s c o u l d not be a s c e r t a i n e d by a t a l l y made at t h e i r n e s t i n g s i t e s . 14 The p l a n e s u s e d w e r e s m a l l , s i n g l e - e n g i n e d , and capable of f l y i n g at speeds down to 60 m i l e s p e r hour when p a s s i n g by the n e s t . 3.3. T i m e Spent i n the A r e a The f i r s t a e r i a l s u r v e y i n s e a r c h of eagle n e s t s was done by D r . M. D. F, U d v a r d y on M a r c h 16, 1962. A f t e r a b r i e f g round s u r v e y on A p r i l 28, 1962, continuous o b s e r v a t i o n s w e r e s t a r t e d on the 2nd day of M a y and c o n t i n u e d u n t i l September 4. S e v e r a l weekend t r i p s w e r e made d u r i n g the f o l l o w i n g w i n t e r and s p r i n g ; the o b s e r v a t i o n p e r i o d i n the s u m m e r of 1963 l a s t e d f r o m M a y 8 to August 29. Weekend t r i p s w e r e made again d u r i n g the w i n t e r of 1963 and the l a s t v i s i t was made on A p r i l 15, 1964. T a b l e 1 shows i n d e t a i l the t i m e spent i n the study a r e a d u r i n g the p e r i o d f r o m 1962 to 1964. T a b l e 1 . Date and d u r a t i o n of o b s e r v a t i o n s on San Juan I s l a n d , 1962 to 1964 Y e a r : J a n . F e b . M a r c h A p r i l M a y June J u l y A u g. Sept. O c t . Nov. Dec. 1962 16 28-29 2 --- 4 1963 19-20 23-24 13-14 13-14 8 . . . 29 21 19-20 21-27 23-24 21 1964 23-25 13-15 C h a p t e r I I . A B U N D A N C E A N D M O V E M E N T S 17 4. INTRODUCTION The bald eagle (Haliaeetus leucocephalus L . ) inhabits the North American continent; it is confined to it with the exception of birds found on the northeast coast of Siberia and on adjacent islands. The American Ornithologists' Union (1957) classifies the bald eagle into two geographic subspecies: H . l . alascanus Townsend, which ranges from northern Alaska and northern McKenzie to northern Ungava and south to British Columbia and the northern United States, and H_.l_. . leucocephalus L . , which ranges south across the United States, south to Baja California. The ranges of the two races broadly overlap across the mid section of the United States. According to this pattern, the bald eagles of San Juan Island belong to the northern race, contrary to the belief of Miller et al . (1935), who regarded them as southern bald eagles. There is a difference in size between the northern and southern subspecies, the northern bald eagle being larger than the southern race. The difference between sizes served as a basis to divide the species into two races. Peters (1931) and Friedmann (1950) prefer the name H . l . washingtoniensis Audubon for the northern subspecies since birds belonging to this race on the basis of their size are found not only in Alaska but also in northern United States. 18 5. ABUNDANCE The bald eagle is most abundant on the seacoast and by large bodies of fresh water. Concentrations of bald eagle numbers are found on the southeastern coast of Alaska, south on the coast of British Columbia, in the Great Lakes Area and also in isolated points along the Atlantic Coast, such as Chesapeake Bay and Florida (Imler and Kalmbach, 1955). Winter movements also concentrate their numbers in areas along the Mississippi River (Musselman, 1949 and Southern, 1963) and other large rivers in Missouri and Iowa (Fawks, 1961) and westward in Oklahoma (Van den Akker, 1954 and Holloran,. I960). A relatively large number of eagles is present on San Juan Island during the spring and summer, while outside the breeding season, eagles are scarce on the island. San Juan Island was used by eagles in the past; Miller et al. (1935) call them common residents and write that: "Pairs have been seen near their nests on the east side of San Juan Island". Eagles were collected from the island as early as 1858 by David Lyal l and by James Hepburn in 1862 (in Miller et al. , 1935). 5.1. Eyries The number of nests found on San Juan Island gives an indication of the number of bald eagles present as well as their probable abundance in the past. Bald eagles usually build their nests on the seashore (Broley, 1947). The nests are built of sticks as large as 3 inches in diameter and up 19 to 5 to 6 feet in. length (Oberholser, 1906 and Herrick, 1924b). Smaller sticks, twigs, grass and down are used for the lining of the nest. The size of the nest varies from 3 to 4 feet in diameter and one to two feet deep to 8 1 /2 feet in diameter and 12 feet deep (Herrick11924c). Nests are used year after year by the same pair of eagles. Large nests are the result of the bird's yearly nest building activities as new layers of sticks are added to the old nest (Herrick, 1932 and Broley, 1947). If the old nest is destroyed the birds will build a new one in the same area. Herrick (1924c) records a nest which was used for 35 consecutive years. The nests are built on tall trees and usually are located near the top. The height of nests from the ground varies from 15 feet (Broley, 1947) to 137 feet (Imler and Kalmbach, 1955) in the eagles' extensive range. Murie (1959) found bald eagles nesting on rocky cliffs and pinacles on Kodiak Island, Alaska. Eagles may have several nests which they use in alternate nesting seasons (Amadon, 1964). Howell (1937) reported a pair of eagles which built five nests in eight years. The bald eagle nests on San Juan Island were found by means of aerial surveys on March 16 and May 6, 1962, and by obtaining information from local residents. The location of nests is indicated on Map 2, following page 5 . For easier reference the nests were named with the consecutive letters of the alphabet in the chronological order of their discovery, thus the nest on Turn Island is called Nest A , as this nest was first found. 20 5.1.1. Description of Nests Nest A; is located on Turn Island, south of the Town of Friday Harbor. It is built on a Douglas fir tree, the second tallest tree on the island, approximately 130 feet from the ground. The tip of the tree, the portion from the nest to the top and approximately 15 feet, is dead. The nest is a huge structure; its estimated dimensions are 6 to 7 feet in depth and 3 1/2 to 4 feet in diameter. The nest has a history of over half a century. An old resident of Friday Harbor, M r . Jensen, recalls the shooting of eagles out of the nest for bounty around the turning of the century. The yearly nest-building activities, the adding of new layers of sticks, has resulted in a huge cylindrical structure. The nest, being located in the center of Turn Island, provides an open view toward San Juan Channel, as well as the small passage between San Juan and Turn islands. Nest B; is located on the south shore of Rocky Bay, 6 miles north of Friday Harbor. The nest tree is a Douglas fir, 100 feetin height and 4 feet in diameter at breast height. The tree is among the largest of that area and it leans out toward the water. The nest, that is built 10 feet from the dead tree top, is almost concealed within the surrounding canopies. 21 The nest, about 5 feet i n diameter and two feet deep i s a p l a t f o r m with a shallow d e p r e s s i o n i n the center. Judged by i t s size this nest appears to be a m o r e recent s t r u c t u r e than Nest A. T h e r e i s a slight elevation behind the nest t r e e , t h e r e f o r e the view toward the center of the i s l a n d i s blocked, although toward the sea there i s a 180 degree unobstructed view of open water. A c c o r d i n g to i n f o r m a t i o n f r o m l o c a l s o u r c e s , there used to be a l a r g e nest at L i m e s t o n e Point, 1.5 m i l e s north of Nest B. T h i s nest was destr o y e d s e v e r a l y e a r s ago when the nest t r e e was cut down; i t i s l i k e l y that Nest B was built a f t e r w a r d by the inhabitants of the dest r o y e d nest. Nest C; i s l o c a t e d i n the southeast p a r t of the i s l a n d , at the f o o t h i l l s of Mount D a l l a s . It i s 1600 y a r d s f r o m the seashore i n the center of a second growth stand. The surrounding a r e a was logged 15 y e a r s ago and now the dense vegetation of alder makes the a r e a h a r d to penetrate. The nest t r e e i s a 120 feet t a l l Douglas f i r , that i s f o r k e d at about 7-5 feet f r o m the ground and the nest, 4 to 5 feet i n diameter and 2 feet deep, i s lo c a t e d at this point. The nest i s w e l l c o n c e a l e d and i n v i s i b l e f r o m the roads that r u n c l o s e by. The lo c a t i o n of this nest was not known to l o c a l r e s i d e n t s u n t i l i t s d i s c o v e r y f r o m the ai r p l a n e on May 6, 1962. Nest D; i s l ocated at Point Caution, two m i l e s north of F r i d a y H a r b o r . 22 The nest tree, 250 yards from the shore, is the tallest dominant tree in the surrounding mature Douglas fir stand, approximately 120 feet tall. The nest is built 30 feet from the top, where the tree forms a fork by the rise of a thick side branch. The nest is small, 4 feet in diameter and about 1 1/2 feet in depth, and is difficult to spot from the sea as it blends into the rising hill behind. The view from the nest is unobstructed toward San Juan Channel but it is blocked toward the center of the island. Nest E ; is located only 100 yards from Nest C in the same stand. The nest tree is smaller and is also forked, housing the nest similarly to Nest C . The nest is in good condition and probably is used as an alternate nest by the Nest C pair of eagles. Nest F; is a small nest on the west side of Henry Island, west of Roche Harbor. It is seen only from airplanes and it appears to be abandoned and in bad condition. Nests G, H, I_; are located in the northern shore of Spieden Island, 3 miles north of Roche Harbor . A l l three nests appear abandoned. Spieden Island is 2.8 miles long and is narrow. The nests are evenly spaced on the northern wooded side. The nests likely were used by the same pair of eagles. 23 According to information from local sources, a former sheep herder on the island shot every eagle over a period of several years. This fact may be the cause of the present abandonment of the nests. NestJ; is half finished and is situated on the west side of San Juan Island. The nest tree is an old, irregularly grown, 80 feet tall Douglas fir and the nest is placed close to its top among branches forming a bowl. The tree is on the shore of a small bay, facing the open waters of Haro Strait. The nest is easily spotted from a road which runs only 150 yards away. The eagles, likely the Nest C pair, started to construct this nest in the summer of 1962. Nest K; is located at the tip of a small peninsula between False and Kanaka bays. The nest tree is a small Douglas fir, 80 feet in height and the nest, 4 feet in diameter and 2 feet deep, is situated 10 feet from the top, completely surrounded by dense foliage. The nest provides a view over False Bay as well as over the open waters of Haro Strait, but the view toward the south is blocked by trees. Nest L ; approximately 4 feet in diameter and 3 feet deep, is situated 20 feet from the top of a 100 feet tall Douglas f ir . (These figures are only approximations since the nest could be viewed only by means of flying.) The 24 n e s t t r e e i s l o c a t e d o n H e n r y I s l a n d , 180 y a r d s f r o m the w e s t e r n s h o r e of that i s l a n d . T h e v i e w t o w a r d the w a t e r i s b l o c k e d b y t r e e s . N e s t M ; i s l o c a t e d on the s h o r e of F a l s e Bay, 800 y a r d s f r o m N e s t K to the n o r t h . In s t r u c t u r e a n d s i z e t h i s n e s t i s s i m i l a r to N e s t K . T h e n e s t p r o v i d e s an o p e n v i e w t o w a r d F a l s e Bay, the v i e w t o w a r d the c e n t e r of the i s l a n d i s b l o c k e d b y the s u r r o u n d i n g s t a n d . O n the b a s i s of t h i s n e s t ' s p r o x i m i t y to N e s t K , i t i s a s s u m e d t h a t b o t h n e s t s a r e u s e d b y the s a m e p a i r of e a g l e s . T h e c h r o n o l o g y of the n e s t s ' d i s c o v e r y o n S a n Juan I s l a n d i s as f o l l o w s : M a r c h 16, 1962: N e s t s A a n d B_, M a y . 6 , 1962: N e s t s C , D , E , F , G , H and 'T, June 6 , 1962: N e s t J , F e b r u a r y 7, 1963: N e s t s K a n d L , A p r i l 14, 1964: N e s t M . T h e t a b u l a t i o n of the d a t a c o n c e r n i n g m e a s u r e m e n t s of n e s t s a n d n e s t t r e e s a n d t h e i r s i t u a t i o n to s h o r e a n d h u m a n h a b i t a t i o n s i s p r e s e n t e d i n T a b l e 2 . A c t i v i t i e s of e a g l e s w e r e o b s e r v e d at N e s t s A , B, C , D_and J_ d u r i n g 1962 a n d at N e s t s _ A , B, D , J_, K a n d L d u r i n g 1 9 6 3 . E a g l e s w e r e s e e n at N e s t s J B , D , a n d M i n the s p r i n g of 1 9 6 4 . N e s t s E , F_, _G, H a n d I w e r e not u s e d b y e a g l e s d u r i n g the o b s e r v a t i o n p e r i o d . T a b l e 2. Measurements of nests and nest t r e e s and their p r o x i m i t y to shore and human habitations N E S T T R E E N E S T Distance B u i l t V i ew Di stance f r o m human f r o m t r e e f r o m Success Height Dbh f r o m shore structure D i a m e t e r * Depth* top nest i n Nest (feet )* (feet)* (yards) (yards) (feet) (feet) (feet) (degrees) 1962 1963 A 145 6 100 700 4-5 6-7 15 360 + B 100 4 0 500 5 2 10 180 + + C 120 4 1600 1000 4-5 2 45 0 -D 120 - 250 500 4 1 . 5 30 270 + + E 100 - 1500 1000 3-4 2 50 0 -F • - - 50 2000 - • - - - -G - - 100 500 - - - 180 -H - - 100 500 - - - 180 -I - - 100 1000 - - - 180 -J 80 - 0 100 - - 10 270 " -K 80 - 0 650 4 2 10 180 ? + L 100 - 180 2000 4 3 20 0 ? + M 80 - 0 600 4 2 10 180 * E s t i m a t e d values Note: Nests F, G, H and I were seen only f r o m a i r p l a n e . 26 A l l b a l d eagle n e s t s found on San J u a n I s l a n d a r e found on Douglas f i r t r e e s , u s u a l l y the t a l l e s t t r e e of the s u r r o u n d i n g f o r e s t stand. In c h o o s i n g the n e s t s i t e the eagle s tend.to seek spots w h i c h p r o v i d e an open v i e w of the n e i g h b o u r i n g a r e a s . In g e n e r a l , a l t i t u d e i s sought by the b i r d s . The m e a n height of nine t r e e s h o u s i n g b a l d eagle n e s t s on San J u a n I s l a n d i s 102.7 feet (31.3 m). H o w e v e r , i n other a r e a s w h e r e t a l l v e g e t a t i o n i s l a c k i n g , the e a g l e s m a y b u i l d n e s t s c l o s e to the grou n d ( B r o l e y , 1947). E a g l e s a l s o tend to seek a r e a s u n d i s t u r b e d by human a c t i v i t i e s . The s h o r t e s t d i s t a n c e between a s u c c e s s f u l nest and human h a b i t a t i o n on San J u a n I s l a n d i s 500 y a r d s (450 m), as i n c a s e of N e s t s B and D. The s u c c e s s of b r e e d i n g a c t i v i t i e s and the n e s t s ' s i t u a t i o n to human h a b i t a t i o n s i s d i s c u s s e d l a t e r (see s e c t i o n 11). M a n y of the eagle n e s t s a r e b u i l t on dead or dying t r e e s . On San J u a n I s l a n d N e s t s A and B a r e b u i l t on t r e e s w i t h dead t o p s . On the b a s i s of s i z e , these n e s t s a r e c o n s i d e r e d to be the o l d e s t s t r u c t u r e s among the n e s t s found on the i s l a n d . Since e a g l e s seek n e s t s i t e s w h i c h p r o v i d e a wide v i e w a r o u n d , i t i s p o s s i b l e that the top of t r e e s h o u s i n g N e s t A and B w e r e dead at the t i m e when the n e s t s w e r e b u i l t . H o w e v e r , i t i s m o r e l i k e l y that the t r e e tops d i e d off as a r e s u l t of the continuous usage of the n e s t s . S i n c e b r a n c h e s above the nes t a r e u s e d by the adults as w e l l as the f l e d g i n g e a g l e s f o r p e r c h i n g , the constant g r a p p l i n g of these b r a n c h e s m a y h a v e damaged the b a r k , w h i c h r e s u l t e d i n the die off. 27 Height of t r e e being an important factor i n the eagle's s e l e c t i o n of nest s i t e s , Douglas f i r and h emlock are species l i k e l y chosen by the eagles i n the P a c i f i c Northwest. Since these two species of t r e e s are p r i m a r i l y important i n the region's f o r e s t i n d u s t r y , eagles may exert a slig h t l y h a r m f u l effect on man's c o m m e r c i a l i n t e r e s t by contributing to the m o r t a l i t y of t a l l t r e e s through t h e i r nest b u i l d i n g . However, c o n s i d e r i n g the s m a l l number of t r e e s i n v o l v e d , this damage i s n e g l i g i b l e . A l s o , t a l l t r e e s are sought by the b i r d s only i n suitable nesting a r e a s , which areas u s u a l l y l i e along the seacoast or by some l a r g e body of water where t r e e s tend to grow deformed and croo k e d as a r e s u l t of constant wind effect and growing on steep h i l l s i d e s . The eagles tend to choose t r e e s which f o r k and grow i r r e g u l a r l y . T hese types of t r e e s a r e good nesting sites yet they are c o m m e r c i a l l y l e s s valuable. 5.1.2. T e r r i t o r i e s T e r r i t o r i a l behavior was seldom o b s e r v e d among bald eagles on San Juan Island. B r e e d i n g eagles often warded off r e d - t a i l e d hawks, crows and juvenile b a l d eagles which were int r u d i n g i n the v i c i n i t y of the n e s t s . H o s t i l i t y between adult bald.eagles was o b s e r v e d only on two occa s i o n s (see section 8.5.1.). Due to the l i m i t e d number of observations, t e r r i t o r y s i z e as an a r e a defended against competing m e m b e r s of the same species cannot be d i s c u s s e d on the b a s i s of t e r r i t o r i a l behavior. T e r r i t o r y s i z e may be ca l c u l a t e d on the b a s i s of distance between neighbouring n e s t s . T h e s e t e r r i t o r i e s , however, cannot be 28 r e g a r d e d as defended a r e a s but rather as a r e a s which are a v a i l a b l e to the nesting p a i r s without i n t e r f e r e n c e f r o m the c l o s e s t neighbours. The l i n e a r distances between neighbouring nests are tabulated i n T a b l e 3. With the exception of two nests, a l l the nests on San Juan I s l a n d are l o c a t e d on or i n c l o s e p r o x i m i t y to the shore. The l i n e a r distances between 13 neighbouring nests v a r y between 2.4 m i l e s (3.86 km) and 5.7 m i l e s (9.16 km) with a me an value of 3.87 m i l e s (6.2 km). T h i s means that an a r e a of 11.7 sq. m i (30^28 sq. km) surrounding the nest site i s a v a i l a b l e to each of the existing nests on San Juan Island. These " a v a i l a b l e a r e a s " are drawn on F i g u r e 2 to i l l u s t r a t e their s p a t i a l r e l a t i o n s h i p with each other. Information available i n l i t e r a t u r e concerning t e r r i t o r i a l i t y of b a l d eagles i s s c a r c e . B r o l e y (1947) w r i t e s that: "A pair of nesting eagles appears to r e q u i r e , as a r u l e , a t e r r i t o r y extending about half a m i l e on a l l sides of the nest", but p r o v i d e s no i n f o r m a t i o n on how he a r r i v e d at this estimate. A c c o r d i n g to this estimate eagle nests are spaced o n e i m i l e apart i n suitable a r e a s . However, greater de n s i t i e s of nests were also found. B r o l e y (op. cit.) saw three active nests within 1000 feet of one another i n F l o r i d a and N i c h o l s o n (in Bent, 1937) found a concentration of 7 active b a l d eagle nests i n an a r e a of 3 1/2 by 3/4 m i l e s a l s o i n F l o r i d a . H e n s e l and T r o y e r (1964) found that 14 t e r r i t o r i e s i n K o d i a k Island, A l a s k a averaged 57 a c r e s (23.1 h e c t a r e s ) . They defined t e r r i t o r y as an a r e a defended against other b a l d eagles during the breeding season and m e a s u r e d i t by using the l i n e a r distance between the nesting site and Table 3. Linear distances between neighbouring bald eagle nests* on San Juan Island Between nests Distance (miles) A - D 3.2 D - B 4.0 B - I 3.0 B - L 4.0 L - G 3.2 C - M 2.4 minimum C - D 5.5 M - A 5.7 maximum * Groups of nests like Nests C , E , J and Nests G, H , I and Nests K, M were considered to belong to the same pair of eagles. 30 p e r c h t r e e s as a r a d i u s . The s p a c i n g of n e s t s on San J u a n I s l a n d p e r m i t s m u c h l a r g e r " a v a i l a b l e a r e a s " than the t e r r i t o r y s i z e s e s t i m a t e d or m e a s u r e d by the m e n t i o n e d i n v e s t i g a t o r s . S i n c e m o s t of the San J u a n I s l a n d n e s t s a r e l o c a t e d on the s h o r e , the " a v a i l a b l e a r e a s " of the d i f f e r e n t n e s t s i n c l u d e the g r e a t e r p a r t of the i s l a n d c o a s t l i n e w i t h i n t h e i r b o u n d a r i e s . The n e s t s a r e r e l a t i v e l y e v e n l y spaced along the c o a s t l i n e . H o w e v e r , no eagle n e s t s w e r e found on the w e s t co a s t of the i s l a n d between N e s t s IJ andJM, yet the l i n e a r d i s t a n c e between these i s over 7 m i l e s (11 km). A l s o , the C a t t l e P o i n t a r e a i s o u t s i d e the " a v a i l a b l e a r e a s " of N e s t s A and M and i s u n i n h a b i t e d by humans, yet i t was not u s e d by e a g l e s f o r b r e e d i n g p u r p o s e s d u r i n g 1962 and 1963, nor w e r e r e m n a n t s of o l d n e s t s found i n the a r e a . The " a v a i l a b l e a r e a " i s not the a r e a defended a g a i n s t c o m p e t i n g m e m b e r s of the same s p e c i e s , c o n s e q u e n t l y the t e r m " t e r r i t o r y " cannot be a p p l i e d to i t . I t s s i z e i s b a s e d on the m e a s u r e d d i s t a n c e s between n e i g h b o u r i n g n e s t s and i t i s m o r e l i k e l y that human i n t e r f e r e n c e has a g r e a t e r e f f e c t on the s p a c i n g of the n e s t s than does the i n t e r a c t i n g between the e a g l e s . In F i g u r e 2b the l o c a t i o n s of the known b a l d eagle n e s t s a r e shown i n r e l a t i o n to human h a b i t a t i o n s . T o o b t a i n a map on d i s t r i b u t i o n of human d w e l l i n g s the i s l a n d was d i v i d e d i n t o 1 k m by 1 k m s q u a r e s and the number of houses counted i n each s q u a r e . A r e a s w i t h l e s s than t h r e e houses p e r square k i l o m e t e r s a r e c o n s i d e r e d to be s u i t a b l e e a g l e - n e s t i n g F i g . 2a. T h e l o c a t i o n o f b a l d e a g l e n e s t s o n S a n J u a n I s l a n d a n d t h e " a v a i l a b l e a r e a s " b e l o n g i n g t o e a c h n e s t . F i g . 2b. The locat ion of bald eagle nests on San Juan Is land i n r e l a t ion to human habi tat ions. 33 a r e a s s i n c e the p o s i t i o n of two houses i n an a r e a of 1 sq. k m p e r m i t s a nest to be 500 y a r d s (450 m e t e r s ) away (which i s the m i n i m u m d i s t a n c e found between e x i s t i n g n e s t s and human h a b i t a t i o n s (see s e c t i o n 5.1.1.). A l l s u c c e s s f u l n e s t s on San Juan I s l a n d a r e found i n a r e a s w i t h d e n s i t i e s of 2 houses or l e s s p e r square k i l o m e t e r , w h i c h suggests that the e x i s t i n g p a t t e r n of n e s t d i s t r i b u t i o n on the i s l a n d i s a r e s u l t of human i n t e r f e r e n c e . 5.2. O b s e r v a t i o n s It was not of p r i m a r y i m p o r t a n c e i n the study to f o l l o w the changes i n b a l d eagle n u m b e r s d u r i n g the y e a r , t h e r e f o r e no s y s t e m a t i c s u r v e y s w e r e conducted. H owever, r e g u l a r counts w e r e made by means of a e r i a l and g r o u n d s u r v e y s d u r i n g the s p r i n g and f a l l months when the a r e a was v i s i t e d to obt a i n i n f o r m a t i o n on b r e e d i n g a c t i v i t i e s . A l s o , s i g h t i n g s of eagle s w e r e r e c o r d e d throughout the s u m m e r s of 1962 and 1963. The counts made by means of a e r i a l and grou n d s u r v e y s a r e p r e s e n t e d i n T a b l e 4, w h i l e T a b l e 5 p r e s e n t s the o c c a s i o n a l s i g h t i n g s of eagle s d u r i n g 1962 and 1963. The f i g u r e s p r e s e n t e d i n these t a b l e s do not i n c l u d e u n f l e d g e d e a g l e s . The counts of e a g l e s made by means of a i r c r a f t g i ve a b e t t e r a p p r o x i m a t i o n of the a c t u a l n umber of eagle s p r e s e n t on the i s l a n d than do the g r o u n d s u r v e y s . The c o a s t l i n e , w h i c h tends to a t t r a c t e a g l e s , c a n be s u r v e y e d by means of a i r p l a n e s , w h i l e the grou n d s u r v e y i s l i m i t e d to the r o a d s . A l s o , a l a r g e r a r e a along the f l i g h t path i s v i s i b l e f r o m the a i r p l a n e ; a n a r r o w e r a r e a i s v i s i b l e f r o m the r o a d s , e s p e c i a l l y i n the n o r t h e r n p a r t of T a b l e 4. B a l d eagle counts made d u r i n g 1962 - 1964 on g r o u n d and by-a i r on San Ju a n I s l a n d . Date Type of N u m b e r s seen s u r v e y Y e a r M o n t h Day A d u l t J u v e n i l e T o t a l 1962 M a r c h 16 a e r i a l 13* 2 15 1962 M a y .6 a e r i a l 9 11 20 1963 J a n . 20 grou n d 2 - 2 1963 F e b . 7 a e r i a l 21 11 32 1963 F e b . 23 grou n d 9 2 11 1963 M a r c h 13 g r o u n d 4 2 6 1963 M a r ch 14 groun d 5 3 8 1963 M a r c h 23 grou n d 4 4 8 1963 A p r i l 21 a e r i a l 8 1 9 1963 M a y 21 a e r i a l 2 3 5 1963 Sept. 21 a e r i a l 3 1 4 1963 Oct. 20 g r o u n d 2 1 3 1963 Dec. 27 grou n d 5 3 8 1964 J a n . 2 g r o u n d 4 - • 4 1964 F e b . 24 g r o u n d 7 14 21 1964 F e b . 25 g r o u n d 6 6 12 1964 A p r i l 14 a e r i a l 8 3 11 1964 A p r i l 16 a e r i a l 3 1 4 5*. U n d e r l i n e d n u m b e r s a r e the h i g h e s t n u m b e r s of b i r d s seen i n any p a r t i c u l a r month and w e r e u s e d to c o n s t r u c t F i g u r e 5. T a b l e 5. O c c a s i o n a l s i g h t i n g s of b a l d e a g l e s on San J u a n I s l a n d d u r i n g 1962 and 1963 Date N u m b e r s seen Y e a r M o n t h Day A d u l t J u v e n i l e T o t a l 1962 May- 15 7 3 10 1962 M a y 26 6 2 8 1962 June 3 6 2 8 1962 J u l y 27 2 4 6 1962 Aug. 6 2 - 2 1962 Aug. 23 2 2 4 1962 Sept. 1 - 2 2 1963 M a y 26 10* 4 14 1963 June 6 10 1 11 1963 June 27 3 - 3 1963 J u l y 1 8 3 11 1963 J u l y 7 3 2 5 1963 J u l y 11 4 7 11 1963 J u l y 16 2 - 2 1963 J u l y 31 2 2 1963 Aug. 8 1 3 4 1963 A u g . 16 3 — 3 U n d e r l i n e d n u m b e r s a r e the h i g h e s t n u m b e r s of b i r d s seen i n that p a r t i c u l a r month and w e r e u s e d to c o n s t r u c t F i g u r e 5. 36 the i s l a n d w h e r e both s i d e s of the r o a d a r e c o v e r ed w i t h t r e e s . F i g u r e 3 p r o v i d e s a c o m p a r i s o n between the a r e a s c o v e r e d i n the count by means of a e r i a l and grou n d s u r v e y s . B o t h a e r i a l and g r o u n d s u r v e y s tend to u n d e r e s t i m a t e the number of eagl e s a c t u a l l y p r e s e n t on the i s l a n d because of i n s u f f i c i e n t c o v e r a g e and because many b i r d s a r e m i s s e d due to the d i f f i c u l t i e s i n spotting them. The l a r g e s t number of b a l d e a g l e s w e r e seen d u r i n g F e b r u a r y . On F e b r u a r y 7, 1963, 21 adult and 11 j u v e n i l e b i r d s w e r e r e c o r d e d i n an a e r i a l count. On F e b r u a r y 24, 1964, 7 adults and 14 j u v e n i l e s w e r e spotted d u r i n g a gro u n d s u r v e y . The number of b i r d s i n the count m a r k e d l y d e c r e a s e d u r i n g M a r c h and A p r i l , however the f i g u r e s f o r these months a r e v e r y low i n c o m p a r i s o n to the r e p o r t s by l o c a l f a r m e r s . A f l o c k of 14 eagles (adults and j u v e n i l e s i n equal n u m b e r s ) w e r e seen by W. S u n d s t r o m on h i s f a r m (1 .5 m i l e s southeast of F r i d a y H a r b o r ) f o r s e v e r a l days d u r i n g A p r i l , 1964. T e n eagl e s and m o r e w e r e a l s o seen by E. J . Hudson d u r i n g the same p e r i o d . Twenty b i r d s w e r e counted on M a y 6, 1962, 9 adults and 11 j u v e n i l e s . T h i s was the only count i n w h i c h the number of j u v e n i l e s e x c eeded that of a d u l t s . D u r i n g the s u m m e r months eagl e s n u m b e r e d ar o u n d the y e a r l y average f i g u r e of 13 b i r d s of m o r e . N u m b e r s m a r k e d l y d e c r e a s e d a g a i n f r o m August on. The l o w e s t number of e a g l e s , 2 a d u l t s and 1 j u v e n i l e was seen on O c t o b e r 20, 1963. No s u r v e y s w e r e conducted d u r i n g N o v e m b e r 1962 and 1963, nor w e r e s i g h t i n g s by l o c a l r e s i d e n t s Fig . 3 The area covered by means of aerial and ground surveys on San Juan Island, 1 9 6 2 - 1 9 6 4 . 38 a v a i l a b l e . On D e c e m b e r 27, 1963, 5 adults and 3 j u v e n i l e s w e r e seen d u r i n g a gr o u n d s u r v e y . A count i n J a n u a r y 1962, conducted by l o c a l b i r d w a t c h e r s r e c o r d e d 48 eagle s i g h t i n g s over a two week p e r i o d . In t h i s count h o w e v e r , the same b i r d s m u s t have been r e c o r d e d s e v e r a l t i m e s d u r i n g the s u r v e y . The h i g h e s t number r e c o r d e d f o r a s i n g l e day was 15 e a g l e s (8 adults and 7 j u v e n i l e s ) . Due to the l a c k of s u f f i c i e n t data, the changes i n eagle n u m b e r s i n the c o n s e c u t i v e y e a r s of 1962, 1963 and 1964 cannot be r e l a t e d to one another; however a c o m p a r i s o n of the data obtained i n the s e y e a r s i s p r o v i d e d i n F i g u r e 4. C o m b i n i n g the data of T a b l e 4 and T a b l e 5, F i g u r e 5 was c o n s t r u c t e d to i n d i c a t e the s e a s o n a l f l u c t u a t i o n s i n b a l d eagle n u m b e r s . The n u m b e r s of adult and j u v e n i l e b a l d eagles p l o t t e d i n the f i g u r e a r e the h i g h e s t n u m b e r s seen i n each month d u r i n g the p e r i o d the data was c o l l e c t e d . The c u r v e r e p r e s e n t i n g the changes i n n u m b e r s of adult b a l d e a g l e s f o l l o w s a smoother path than does that of the j u v e n i l e b i r d s , c o n s e q u e n t l y the month to month f l u c t u a t i o n s i n t o t a l n u m b e r s i s c a u s e d by the f l u c t u a t i o n s of j u v e n i l e eagle n u m b e r s to a g r e a t e r degree than by that of the a d u l t s . The changes i n eagle n u m b e r s shown i n F i g u r e 5 a r e o n l y an a p p r o x i m a t i o n of the a c t u a l changes w h i c h take p l a c e d u r i n g the y e a r . The sudden d e c l i n e d u r i n g M a r c h and A p r i l as shown i n the f i g u r e i s p r o b a b l y an e x a g g e r a t i o n of the a c t u a l s i t u a t i o n . Since the s u r v e y s w e r e not conducted at r e g u l a r i n t e r v a l s , the r e p r e s e n t a t i v e n u m b e r s of b i r d s f o r each p a r t i c u l a r month i s b i a s e d , due to the day to day f l u c t u a t i o n s i n eagle number s. 39 CO 1—I cu u 3 2 35-3C-25-20-15 1C! 1 tzil 1 §1 M V/. 1 21 2 I M 1 • 1 1 962 963 964 I .21 n O N D Months F ig . 4 Number of bald eagles seen on San Juan Island in 1962, 1963 and 1964. 40 J F M A M J J A S O N D Months F ig . 5 The change in numbers of eagles throughout the year on San Juan Island. The highest number of adult and juvenile eagles seen in any month of the period 1962 -1964. 41 It a ppears that m o r e b i r d s a r e p r e s e n t on the i s l a n d d u r i n g F e b r u a r y than d u r i n g any other month of the y e a r . The s i g h t i n g s of 21 adult e a g l e s d u r i n g t h i s month i n d i c a t e that the number of p o t e n t i a l b r e e d i n g b i r d s i s g r e a t e r at the s t a r t of the b r e e d i n g season than the eventual number that attempts r a i s i n g a b r o o d l a t e r . A count of 14 j u v e n i l e e a g l e s i n t h i s month i s a l s o the h i g h e s t f i g u r e f o r the y e a r . T h i s peak i n eagle n u m b e r s appears to c o i n c i d e w i t h the l a m b i n g t i m e of m o s t of the i s l a n d ' s sheep. The s i g h t i n g s of 11 e a g l e s on F e b r u a r y 23, 1963, 21 e a g l e s on F e b r u a r y 24, and 12 e a g l e s on F e b r u a r y 25, 1964 w e r e r e c o r d e d on or near f i e l d s that c o n t a i n e d sheep w i t h n e wborn l a m b s . The r e l a t i o n s h i p between eagl e s and sheep i s d i s c u s s e d l a t e r (see s e c t i o n s 8.5.7. and 13.2.1.). T h e r e i s an apparent d e c r e a s e i n n u m b e r s d u r i n g M a r c h and A p r i l w h i c h i s p r o b a b l y due to the i n c r e a s e d h o s t i l i t y of b r e e d i n g eagles t o w a r d the non b r e e d i n g ones (see s e c t i o n 8.5.1.). D u r i n g the b r e e d i n g season the number of a d u l t s r e m a i n e d at 10 and l e s s b i r d s , w h i l e the number of j u v e n i l e b i r d s f l u c t u a t e d . On M a y 6, 1962, 11 j u v e n i l e b i r d s w e r e seen, 7 of t h e m p e r c h i n g on the same t r e e on the shore of T r o u t L a k e , w h i l e d u r i n g June the h i g h e s t number of j u v e n i l e s seen was 4 b i r d s . D u r i n g J u l y j u v e n i l e s w e r e m o r e f r e q u e n t l y s i g h t e d when the young of the y e a r s t a r t e d f l y i n g . In t h i s month adult b i r d s w h i c h r a i s e d young d u r i n g the b r e e d i n g season w e r e no l o n g e r found by t h e i r nest and w e r e s i g h t e d only o c c a s i o n a l l y . G o l d e n eagl e s ( A q u i l a c r y s a e t o s L.) and t u r k e y v u l t u r e s ( C a t h a r t e s a u r a L.) w e r e v i s i t i n g the i s l a n d d u r i n g t h i s p e r i o d , w h i c h by the f a c t that they a r e e a s i l y c o n f u s e d w i t h j u v e n i l e b a l d e a g l e s , made the r e p o r t s of l o c a l b i r d 42 w a t c h e r s l e s s r e l i a b l e . E a g l e n u m b e r s s t a r t to d i m i n i s h f r o m September on, but the b i r d s do not d i s a p p e a r f r o m the a r e a . S i g h t i n g s of 5 and 3 b i r d s w e r e r e c o r d e d f o r September and October r e s p e c t i v e l y . D u r i n g these months, eagles a r e v i r t u a l l y absent f r o m the n e i g h b o u r i n g s m a l l C a n a d i a n i s l a n d s as w e l l as f r o m the west coast of V a n c o u v e r I s l a n d (D.Hancock - p e r s . comm.). M o r e eagle s s t a r t to appear i n D e c e m b e r and the r i s e to the peak i n eagle n u m b e r s i n F e b r u a r y i s continuous throughout J a n u a r y . The h i g h e s t c o n c e n t r a t i o n s of non b r e e d i n g e a g l e s w e r e u s u a l l y l o c a t e d i n the T r o u t L a k e a r e a . U n f o r t u n a t e l y , the a r e a s e l d o m c o u l d be s u r v e y e d due to l i m i t e d a c c e s s i b i l i t y . The a r e a was m a i n l y u s e d by j u v e n i l e s , but s i n g l e a d ults w e r e a l s o found among them. F i e l d s u s e d f o r sheep g r a z i n g i n the San J u a n V a l l e y a l s o a t t r a c t e d e a g l e s . F i e l d s l y i n g to the n o r t h of F a l s e Bay, t o w a r d s the center of the i s l a n d w e r e m o s t often v i s i t e d by the b i r d s . L a r g e n u m b e r s w e r e seen d u r i n g the s p r i n g l a m b i n g season i n these v i c i n i t i e s although b i r d s up to 10 i n number w e r e seen throughout the s u m m e r . F i g u r e 5 p r o v i d e s only an a p p r o x i m a t i o n of the n u m e r i c a l changes i n the b a l d eagle p o p u l a t i o n of San J u a n I s l a n d . To obtain a better knowledge of the s e a s o n a l and y e a r l y f l u c t u a t i o n s i n n u m b e r s of e a g l e s , the c o n d u c t i o n of a s y s t e m a t i c a e r i a l s u r v e y w o u l d be n e c e s s a r y . Such a s u r v e y was beyond the means of the p r e s e n t study. A c o m p a r i s o n between the s e a s o n a l changes i n eagle n u m b e r s and the s e a s o n a l changes i n p r e c i p i t a t i o n and t e m p e r a t u r e s ( F i g u r e 6) 43 Number s 35 J 30 ^ 25 20 15 10 Temperature (F°) U 80 70 60 50 40 O N D Months Breeding r Season F ig . 6 Comparison between the monthly changes of eagle numbers and the monthly changes in precipitation and in temperature .on San Juan Island. 44 r e v e a l s that the peak i n eagle n u m b e r s o c c u r s i n the d r y and c o l d s p r i n g . N u m b e r s of ea g l e s s t a r t to d e c r e a s e as t e m p e r a t u r e s r i s e o v e r 60°F and r e a c h the l o w e s t point d u r i n g the wet f a l l . T h i s c o m p a r i s o n suggests that eagles tend to a v o i d e x c e s s i v e heat and m o i s t u r e . 5.3. C o n c l u s i o n s and S u m m a r y T h i r t e e n b a l d eagle n e s t s w e r e found on San Juan I s l a n d . B r e e d i n g a c t i v i t i e s of the b i r d s w e r e o b s e r v e d at eight n e s t s , the r e m a i n i n g s i x n e s t s w e r e not u s e d by the b i r d s . B r e e d i n g a c t i v i t i e s w e r e s u c c e s s f u l l y c o m p l e t e d at t h r e e n e s t s i n 1962 and at four n e s t s i n 1963. The n e s t s a r e b u i l t on t a l l D o u glas f i r t r e e s c l o s e to the s e a s h o r e . The m e a n d i s t a n c e f r o m the shore of f i v e s u c c e s s f u l n e s t s i s 106 y a r d s (96 m). The ne s t s a r e b u i l t i n a r e a s w h i c h a r e not f r e q u e n t e d by humans. The d i s t a n c e between s u c c e s s f u l n e s t s and human h a b i t a t i o n s r a n g e s between 500 and 2000 y a r d s , w i t h a mean value of 870 y a r d s (790 m). The n e s t s a r e spa c e d 2 to 4 m i l e s a p a r t along the coast l i n e . The p a t t e r n of ne s t s p a c i n g i s not c o n s i d e r e d as a r e s u l t of the b i r d s ' t e r r i t o r i a l b e h a v i o r s i n c e such b e h a v i o r was not o b s e r v e d , but r a t h e r as the r e s u l t of human i n t e r f e r e n c e . The s e a s o n a l changes i n b a l d eagle n u m b e r s can only be a p p r o x i m a t e d because no s y s t e m a t i c counts w e r e conducted. Counts of e a g l e s , h o w e v e r , a r e a v a i l a b l e f o r e v e r y month of the y e a r w i t h the ex c e p t i o n of N o v e m b e r . These counts w e r e obt a i n e d by means of a e r i a l and g r o u n d s u r v e y s conducted d u r i n g the s p r i n g and by means of o c c a s i o n a l 45 s i g h t i n g s of b i r d s d u r i n g the s u m m e r . The a n a l y s i s of the a v a i l a b l e data r e v e a l s that the n u m b e r s of b a l d e a g l e s on San Juan I s l a n d change throughout the y e a r . A y e a r l y average of 14 b i r d s o r l e s s a r e p r e s e n t d u r i n g the s u m m e r , w h i l e n u m b e r s m o r e than t w i c e the av e r a g e a r e p r e s e n t d u r i n g the e a r l y s p r i n g . D u r i n g the f a l l the n u m b e r s of eagle s d e c r e a s e to l e s s than a t h i r d of the y e a r l y a v e r a g e . A d u l t b i r d s a r e p r e s e n t i n n u m b e r s t w i c e as l a r g e as the number of j u v e n i l e s . The number of adult b i r d s r e m a i n s n e a r constant d u r i n g the b r e e d i n g season w h i l e the number of j u v e n i l e s f l u c t u a t e s . San J u a n I s l a n d i s a r e l a t i v e l y s m a l l a r e a i n c o m p a r i s o n to the l a r g e a r e a i n w h i c h non b r e e d i n g e a g l e s move about. T hus the f l u c t u a t i o n i n j u v e n i l e n u m b e r s may be the r e s u l t of a s a m p l i n g b i a s o c c a s i o n e d by the f a c t that the a r e a of San J u a n I s l a n d i s not an adequate s a m p l e s i z e to a s s e s s the abundance of a w i d e r a n g i n g s p e c i e s . In c o n t r a s t , b r e e d i n g adults a r e alwa y s found i n the v i c i n i t y of t h e i r n e s t i n g s i t e , thus t h e i r n u m b e r s r e m a i n r e l a t i v e l y constant i n the counts. 46 6. M O V E M E N T S A d e f i n i t e m i g r a t o r y p a t t e r n has not been o b s e r v e d , n e v e r t h e l e s s , the band r e t u r n s f r o m j u v e n i l e b a l d e a g l e s banded i n F l o r i d a p r o v e d that the young, a f t e r l e a v i n g the nest i n the f a l l , t r a v e l g r e a t d i s t a n c e s ( B r o l e y , 1947). The d i s a p p e a r a n c e of the adult b a l d e a g l e s f r o m the n e s t i n g a r e a s d u r i n g t h i s t i m e of the y e a r a l s o suggests a t r e n d to move away f r o m the b r e e d i n g g r o u n d f o r a c e r t a i n l e n g t h of t i m e . A s i m i l a r s i t u a t i o n was o b s e r v e d w i t h the b a l d e a g l e s on San J u a n I s l a n d (see F i g u r e 5) and w i t h the l a r g e p o p u l a t i o n of b a l d eagles on the w e s t co a s t of V a n c o u v e r I s l a n d (D. Hancock, p e r s . comm.). The near t o t a l d i s a p p e a r a n c e of j u v e n i l e s f r o m San J u a n I s l a n d i n the f a l l , as i n d i c a t e d by the counts, s u p p o r t s t h i s t r e n d . B u t the p r e s e n c e of adult b i r d s i n the September and O c t o b e r , 1963 counts, i n d i c a t e s that some b i r d s do not l e a v e the a r e a . The m ovements of l o c a l e a g l e s outside of the study a r e a c o u l d not be f o l l o w e d because of l a c k of m a r k i n g ; t h e i r m o v e m e n t s , t h e r e f o r e , can only be a s s u m e d . The s h a r p d e c l i n e i n eagle n u m b e r s o c c u r s b e f o r e t e m p e r a t u r e s r e a c h the y e a r l y m a x i m u m i n m i d A u g u s t , thus i n d i c a t i n g that the movement of ea g l e s i s away f r o m heat, p o s s i b l y i n a n o r t h w a r d d i r e c t i o n . The m o v e m e nts of the F l o r i d a b a l d e a g l e s i s s i m i l a r i n t r e n d ( B r o l e y , 1947). A s o u t h w a r d movement of n o r t h e r n b a l d e a g l e s i s r e p o r t e d to take p l a c e i n the c e n t r a l p a r t of the continent d u r i n g the second h a l f of D e c e m b e r (Sprunt and Cunningham, 1961), however, band r e t u r n s f r o m 47 e a g l e s banded i n A l a s k a do not i n d i c a t e such movement (Ro b b i n s , I960). P r e s u m i n g that the San J u a n I s l a n d b i r d s move n o r t h w a r d ; eag l e s seen on San Juan I s l a n d d u r i n g the f a l l m a y be b i r d s of s o u t h e r n o r i g i n . The s i g h t i n g s of adult eagles i n September w e r e of s i n g l e b i r d s not i n the v i c i n i t y of n e s t s ; h owever, the b i r d s seen p e r c h e d on N e s t B t r e e i n O c t o b e r w e r e p o s i t i v e l y i d e n t i f i e d as the r e s i d e n t adult p a i r of the p r e c e d i n g s u m m e r . A l s o , the r e s i d e n t p a i r of N e s t A was seen p e r c h e d at t h e i r n e s t s i t e i n J a n u a r y and D e c e m b e r , 1963. On the b a s i s of these s i g h t i n g s , i t i s b e l i e v e d that the adult b r e e d i n g e a g l e s of San J u a n I s l a n d do not l e a v e the a r e a . H o w e v e r , they may be absent i n N o v e m b e r , f o r w h i c h month no o b s e r v a t i o n s a r e a v a i l a b l e . B a l d e a g l e s a r e n o t e d f o r t h e i r s t r o n g s i t e t e n a c i t y . E n c o u n t e r s between b r e e d i n g adults and j u v e n i l e e a g l e s (see s e c t i o n 8.5.1.) ar e u s u a l l y between p a r e n t s and o f f s p r i n g of the p r e v i o u s y e a r who r e t u r n to t h e i r p l a c e of b i r t h (Bent, 1937 and B r o l e y , 1947). T h e s e enc o u n t e r s w e r e m o s t often o b s e r v e d d u r i n g May, when the number of j u v e n i l e s p r e s e n t on the i s l a n d i s at a h i g h l e v e l . It i s p r o b a b l e that the young r e t u r n to the nest f o r s e v e r a l y e a r s a f t e r f i r s t l e a v i n g i t . J u v e n i l e eagles i n p l u m a g e s w h i c h showed m u c h w h i t e , c h a r a c t e r i s t i c of two to t h r e e y e a r o l d b i r d s , w e r e a l s o seen i n c o n f l i c t w i t h the b r e e d i n g adults of N e s t B s e v e r a l t i m e s i n May, 1963. The number of j u v e n i l e s f l u c t u a t e s d u r i n g the s u m m e r w h i l e that of the adults i s m o r e constant. Non b r e e d i n g a d u l t s a r e s e l d o m seen on the i s l a n d (see s e c t i o n 8.5.1.). The p r e s e n c e of an abundant fo o d supply 48 seemingly acts to motivate the movements of non breeding birds during the summer . The daily movements of breeding birds are confined to the general area of the nests. The birds spend most of their time perched on a tree close to the nest (see section 8.3) as was the case with the birds of Nests A, B and D. The daily sightings of adult eagles perched on the tip of a peninsula between Mitchell and Garrison Bays during the summer of 1963 indicate that the breeding birds of Nest L on Henry Island use this spot for a vantage point. Nest L is built on the west side of Henry Island, which side of the island is facing the open waters of Haro Strait where fishing is difficult, while their vantage point, more than 2 miles away, overlooks Mosquito Pass, a narrow and shallow passage where the catching of fish is easier . The movements of breeding birds in search of rabbit carrion in the interior of the island could not be followed due to the difficulty of individual identification. Chapter III. BREEDING 50 7. INTRODUCTION Since Oberholser 1 s (1906) account of the bald eagle's economic relations, information has appeared extensively on the pages of various scientific journals. Most of the earlier papers deal with two aspects of the bird's biology: its nesting habits in the description of the "eyries", and its feeding habits. The validity of such information gathered from various sources is often questionable (e. g. Dixon, 1909, Hoxie, 1910). Many of the former observers were egg collectors, consequently measurements and descriptions of eggs recorded are accurate and abundant. On the other hand, information on breeding behavior, which requires lengthy observations, is scarce. Herrick's (1924, 1932, 1933) studies in Ohio provide abundant information on the everyday life throughout the bald eagle's breeding season, while the banding efforts of Broley (1947) supply information on the movements of the birds outside the breeding season. The majority of our present knowledge on the habits of the bald eagle is based on the works of these two investigators. A common belief is that bald eagles mate for life and use the same nest year after year. On the loss of the mate, the bird promptly acquires a new one (Herrick, 1932), The characteristic white head and tail are attained after the fourth year in the bird's life, but sexual maturity may occur sooner; consequently, it is possible to have a bird in adult plumage mated with a bird in juvenile plumage. Hoxie (1910) records a pair 51 of eagles both in juvenile plumage nesting successfully in Georgia. The clutch size of the bald eagle may vary from 1 to 3 eggs; two being the most common number. The incubation of the eggs takes 34 to 35 days (Herrick, 1932, Nicholson, 1952). Egg-laying dates vary from the north to the south in the bald eagle's extensive range. Bent (1937) provides dates for egg-laying throughout the continent (Table 6.). A well-documented phase of the bald eagle's biology,.due to the egg collectors' experiences, is the laying of a second set of eggs if the first set is removed (Bent, 1937). However, these second attempts of the birds are seldom successful in the northern part of the eagle's breeding r ange. After hatching, the young spend 10 to 13 weeks in the nest (Herrick, 1932). Family ties between parents and offsprings are still apparent two to three weeks after the young leave the nest, after which time the young are entirely independent. The movements of-the adults outside the breeding season are limited to within 100 to 200 miles of their nesting site. The young, however, cover extensive ranges, often in excess of 1000 miles. Broley (1947) has shown that young bald eagles banded in Florida travelled northward and many of them were recovered as far as Ontario and Nova Scotia. The eagles, juveniles and adults, reappear on the breeding ranges two to three months before the laying of eggs. Young of the previous year are driven from the vicinity of the nest by the parents. Territorial fights between adults of different pairs are seldom observed. Table 6. Egg-laying dates for the bald eagle in various parts of its breeding range (after Bent, 1937). Number of Mean egg-laying Breeding Area records date Alaska and Arctic America 62 Oregon and Mexico 40 Georgia, Florida and Texas 62 New Jersey and Virginia 7 5 Maine and Michigan 6 May 10 March 6 January 2 March 3 Apri l 10 8. G E N E R A L BEHAVIOR Since the majority of the observations were carried out during the breeding season, both in 1962 and 1963, observed behavior not necessarily connected with breeding activities is also included in this chapter. 8.1. The Adults Among the diurnal birds of prey, the female bird is considerably larger than the male. In the case of bald eagles this is true to the extent that after several days of observation the sexes can be identified by size alone. While watching the nest with a telescope, always from the same observation point, the eye of the observer becomes accustomed to the size differences and sexes are identified according to the relative proportions they take up in the field of vision. In addition to size, the general shape and the physique of the birds also provide distinguishing marks of the sexes. The male bird besides being smaller is always slimmer than the female. The parent birds of Nest B at Rocky Bay were identified as to their sexes with little difficulty. The female bird possessed a dark spot on her head, possibly caused by missing feathers, which enabled the observer to identify her even when she was sitting deep in the nest. Certain behavioral differences also aided in distinguishing between sexes. The male and female eagle of Nest A used separate perches, a certain branch of the nest tree, which they used consistently throughout the breeding season. 5 4 Generally the female remained longer by the nest and demonstrated a persistence which was in sharp contrast to the nervousness of the male bird. The male was always active while perched, stepping sideways, turning around or simply following the movements of the surrounding wildlife with his head and often vocalized. 8 . 2 Vocalization The repertoire of the bald eagle is limited. Bent (1937) describes it as "ridiculously weak and insignificant, more of a squeal than a scream, quite unbecoming a bird of its size and strength", while Oberholser (1906) calls it a "loud harsh scream". There are basically three different sounds uttered by the bald eagles on San Juan Island: (a) Hoarse sounds given in quick succession from the throat, sounding like; kah - kah - kah. Brewster (in Bent, 1937) describes it as "notes given quickly but haltingly and with apparent difficulty as if their author were choking or grasping for breath" . (b) A chuckling sound, similar to horse-neighing, sounding like; ye-ha-ha ye-ha-ha ha-ha-ha. In Brewster's (op. cit.) words: "it is rather a snickering laugh expressive of imbecile derision". (c) A gull-like yaap-yaap-yaap, heard mainly from the young and female. 5 5 Loud screams, mentioned by Oberholser (op. cit.), Dixon (1906) and Herrick (1932) were never heard on San Juan Island. The birds of Nest B at Rocky Bay vocalized more often than did the birds of Nest A , especially on the close approach of humans. The intensity and frequency of the calls (a), (b) and (c) varied with situations and the time of the day. Interpretive names were given to the different calls, uttered by the birds under certain circumstances. The role of these calls in the communication of the birds, however, was not studied further . (i) "threat" - often uttered on approach of humans or adult and juvenile bald eagles. Consists of the utterance of (a) repeatedly in a harsh manner, followed by (b). (ii) "mild threat" - uttered on approach of red-tailed hawks and turkey vultures. It consists of a sharp (b) without the final ha-ha-ha sounds. (iii) "annoyance" - more often uttered by the female bird, when on guard by the nest alone. Seabirds, crows and passing airplanes induced the call. It consists of (b) with the final ha-ha-ha sounds uttered slowly, often combined with (c). (iv) "greeting" - expressed on arrival of mate. A. highly pitched (b) uttered in a laughing manner . It is often heard during courtship from both sexes. Usually the vocalizing bird draws its head backward till it almost touches the back. 56 (v) "hunger call" - or gull-call (c) - most often heard from the young, in particular during the last two weeks of family disintegration. 8.3. Roosts and Resting Places During the first part of the breeding season, one of the parent birds is always in the near vicinity of the nest. The birds usually perch on the nest tree, which is the tallest dominant tree in the stand, or take positions on one of the surrounding tall trees, which frequently provide a better view of the neighbouring areas than does the nest tree itself. Later in the breeding season, the parents visit the nest only when food is to be brought in. They spend the rest of the time farther away from the nest. Figure 7a presents a view of the dominant trees of Turn Island which were used for perching by the adult birds of Nest A. The trees are lettered for easier reference,.. The nest tree is "a". Tree "b" in the center of the island provided the tallest perching position while tree "d" on the shore allowed a view of the shallow channel between Turn and San Juan Islands. Tree "c" was often used.by the fledglings before they left the area. In Rocky Bay there were fewer available perch trees (Figure 7b) and the adult birds of Nest Bwere usually perched on "n" and "p" trees. When the birds were disturbed by humans walking around the base of the nest tree, they perched farther away on trees which were normally not used, and remained on these perches for 30 to 60 minutes after the departure of the intruder . 57 Figure 7a Perch trees used by the eagles of Nest A on Turn Island in 1962 and 1963-Figure 7b Perch trees used by the eagles of Nest B at Rocky Bay during 1962 and 1963. 58 T h e m a l e p a r e n t s of N e s t s A a n d B s p e n t t h e n i g h t on t h e n e s t t r e e o r o n " b " a n d " p " t r e e s r e s p e c t i v e l y , w h i l e t h e f e m a l e s t a y e d i n t h e n e s t . L a t e r , w h e n t h e m a l e d i d n o t s p e n d t h e n i g h t at t h e n e s t s i t e , t h e f e m a l e u s e d t h e p e r c h e s f o r m e r l y u s e d b y t h e m a l e . It i s b e l i e v e d t h a t t h e b i r d s , e s p e c i a l l y t h e m a l e , u s e d p e r c h e s c l o s e t o t h e n e s t w h i c h w e r e n o t v i s i b l e f r o m t h e o b s e r v e r ' s v a n t a g e p o i n t . T h i s w a s o f t e n i n d i c a t e d i n i n s t a n c e s of d a n g e r t o t h e n e s t b y t h e s u d d e n a p p e a r a n c e of t h e m a l e b i r d . A l s o , c a l l s o f t h e a d u l t s o f t e n w e r e h e a r d w h e n no m a t u r e e a g l e s a p p e a r e d i n s i g h t at N e s t A . O u t s i d e t h e b r e e d i n g s e a s o n , t h e b i r d s r o a m a b o u t t h e i s l a n d a n d p e r c h e s a r e u s u a l l y t a k e n o n t a l l t r e e s s u r r o u n d i n g f i e l d s h e a v i l y p o p u l a t e d w i t h r a b b i t s a n d f i e l d s w h e r e s h e e p a r e r a i s e d . T h e t r e e s s u r r o u n d i n g T r o u t L a k e h a d e a g l e s p e r c h e d o n t h e m e v e r y o c c a s i o n t h e a r e a w a s v i s i t e d . T r o u t L a k e b e i n g t h e w a t e r r e s e r v o i r of F r i d a y H a r b o r i s c l o s e d t o t h e p u b l i c , t h u s i t p r o v i d e s a n u n d i s t u r b e d r o o s t i n g p l a c e f o r e a g l e s n o t p a r t i c i p a t i n g i n b r e e d i n g a c t i v i t i e s . I t w a s n o t e d t h a t d u r i n g a d v e r s e w e a t h e r c o n d i t i o n s , i n s t e a d y r a i n o r d u r i n g r a i n s t o r m s , t h e b i r d s s o u g h t s h e l t e r . A l t h o u g h t h e y u s e d t h e s a m e p e r c h t r e e s , t h e y r o o s t e d f a r t h e r d o w n f r o m t h e t o p , a l m o s t h i d d e n b y t h e f o l i a g e . I n s t r o n g w i n d t h e b i r d s m o v e d m o r e o f t e n f r o m p e r c h t r e e t o p e r c h t r e e . F i g u r e 8 i n d i c a t e s t h e s p a t i a l r e l a t i o n s h i p o f p e r c h t r e e s u s e d m o s t o f t e n b y t h e p a r e n t b i r d s of N e s t A a n d N e s t B d u r i n g a n d o u t s i d e t h e b r e e d i n g s e a s o n . 59 F ig . 8 The spatial relationship of perch trees used by the breeding adults of Nests A. and B during 1962 and 1963. 60 8.4. The Flight of the Eagle Bent (1937) describes the flight of the bald eagle as: "powerful and impressive, but not so graceful or inspiring as that of the golden eagle. Its ordinary travelling flight appears heavy and labored as it moves steadily along with slow beats of its great wings, but it is really much swifter than it seems, as is often the case with large birds". Often it attains great speeds (Herrick, 1933). Herrick (op. cit.) found that 1/400 to 1/500 of a second exposure time was needed when photographing from a distance of 38 feet in order to stop the motion of an eagle approaching its nest. When travelling on a level course the eagle often sails with motionless wings. Broley's (1947) banding records revealed that some of these birds travel long distances. A young eagle was found to cover more than 1600 miles in 32 days. During the breeding season on San Juan Island, the flights of the adults were confined to fishing trips over the water, hunting trips inland and occasional chasing flights against intruders. 8.4.1. Fishing Flight The most often practiced fishing method of eagles on San Juan Island consists of a steep dive from a tree perch by the shore, usually with a break in its speed as the water surface is approached. Often they fly low over the water and snatch the prey without any break in their flight. A fishing method, performed similar to the manner of the osprey (Oberholser, 1906) was also observed. With powerful downward thrust of the wings, the 61 cruising bird suddenly turns in the manner of a twisted sommersault and dives headlong toward the water with wings held close to the body. Plunges into the water with partial or complete submergence (Oberholser, op. cit.) were never seen, rather the dives usually ended in "wetting the legs" and the eagle's return to its former height with quick beats of the wing. If a fish is captured, it is carried in the talons to the nest with heavy and laborious wingbeats. Certain steps were often followed by the birds carrying fish in order to reach the level of the nest which is more than 150 feet from the water at Rocky Bay. On May 9, 1963 the female of Nest B captured a large fish, weighing an estimated 5 pounds. First the fish was hauled out on the rocky shore where the bird climbed higher up, then flew over to a short tree 50 yards from the nest tree. After resting for a few minutes she jumped off and flew toward the sea, then turned back toward the nest. Her first attempt to reach the nest failed and she landed again on tree p. Upon leaving tree p the bird reached the nest (Figure 9). The birds usually hold the fish in one talon, the other is used for landing on the perch. Naturally the landing is more difficult in such cases. Once the male bird of Nest A was seen falling amongst the branches some 20 feet after the initial landing effort was unsuccessful; however, he held onto the fish. 8.4.2 Soaring Soaring at great heights, characteristic of eagles, was often 62 s h o r e l i n e s h o r e l i n e F i g . 9 S t e p s f o l l o w e d b y t h e f e m a l e e a g l e of R o c k y B a y t o c a r r y a f i s h t o t h e n e s t . 63 observed during the second part of the summer. Soaring usually was performed above the nest containing the fully fledged young. On June 30, 1963 in Rocky Bay a dark object was spotted above Nest B, which after coming down to an estimated 2000 feet was identified as an adult eagle. Soaring flights always occurred on warm, clear sunny days during the afternoon hours. 8.4.3. Defense and Attack The eagle's flight is most impressive when the bird is attacked by or is attacking some avian foe. While adult eagles are seldom forced to def end themselve s, juvenile eagles often are in situations where defensive maneuvering is necessary. These situations usually are encounters with breeding adult eagles, ospreys and rarely with red-tailed hawks. The characteristic "flip", or turn on the back while presenting the claws to the attacker is performed by the eagles without effort, even without disturbing the continuity of their flight. The "flip" consists of a full turn around the anterio-posterior axis of the bird and is done in great speed. The eagle, with head turned sideways, watches the attacker above and performs the flip when the attacker reaches striking distance. Such performance was observed often,, once on April 28, 1962 on top of Mount Dallas between a red-tailed hawk and a juvenile bald eagle, only a few yards away from the observer. Similar defensive action is taken by the golden eagle, as observed on August 12, 1962 near Sportsmans Lake, on the attack of an osprey (Retfalvi, 1963). 64 An aerial maneuver previously not observed was seen on May 11 , 1963 exhibited by a juvenile bald eagle which was passing through the osprey's territory at Rocky Bay. The osprey, a good flier, does not break its dive when it nears the intruder but continues to descend beyond the former's altitude, thus blocking its way while passing in front of it. The osprey quickly ascends and similarly repeats the attack. On one such approach the young eagle suddenly thrust down its wings which made the bird turn backward in a half-completed somersault bringing the talons forward to grasp. The osprey escaped with great difficulty. When attacking, the eagle approaches its intended prey from below and seizes it with the talons, which are brought into striking position by the eagle's flip performed at the moment when the prey is in reach. Prey was captured in this way by golden eagles (Meinertzhagen, 1959) and by bald eagles (Brewster in Meinertzhagen, 1959). The male adult of Nest A attacked a juvenile red-tailed hawk which ventured close to the eyrie in this manner on June 5, 1962. 8.4.4. Nuptial Flight Probably the most spectacular among the aerial maneuvers is the so called "cartwheel-display" (Whitman in Armstrong, 1942). Such a display between two mature eagles was observed over False Bay on May 6, 1962. An adult bird was seen sitting on a rock in the center of the bay. The bird took wing on the approach of another adult eagle and the birds swooped alternately at each other, avoiding contact by side slips and mounting fast in the air . Suddenly one of the birds turned on its back and grasped the extended talons of the oncoming bird. The two birds fell together towards the water in a spinning, turning cartwheel fashion. The birds released their hold only a few yards from the water surface. The birds then departed towards Kanaka Bay but continued to swoop at each other. On June 2, 1962 two golden eagles were observed exhibiting a similar display (Retfalvi, 1963). 8.5. Relations with Birds, Mammals and Man 8.5.1. Relations with Other Bald Eagles Encounters between adult bald eagles are seldom observed. Information in this regard is also scarce in the literature. Conflicts between adult bald eagles on San Juan Island were observed only on three occasions. On July 2, 1962, the female parent of Nest A warned off an adult bald eagle from the vicinity of the nest. The intruding eagle approached Turn Island from the north and was promptly attacked by the local bird. The attack was observed somewhat as follows; the female bird of Nest A left her perch and with quick wing beats approached the altitude of the intruder causing the intruding bird to increase its speed. Maneuvering for positions was not apparent and there was never less than 10 feet distance between the two birds. After chasing the intruding bird for approximately 100 yards the female returned to her mate who was uttering the "threat" call throughout the incident. The two nearly full grown young in the nest did not react in any perceivable way. A similar incident took place on March 14, 1963, at Nest A , when the female bird took the offensive again and on her return to 66 the nest engaged in a chasing flight with her mate. In both occasions the male bird stayed on his perch by the nest. A more complex encounter was observed on March 23, 1963, in San Juan Valley. Three adult birds, two side by side and one farther away, were seen perched on trees in the center of a field when the single bird left its perch, flew over to the other two birds and engaged in a chasing flight with one of them, while the other bird remained on its perch. The two birds in the air left together toward Mount Dallas. Sexes were not distinguishable because of the distance involved. The relation between breeding adults and immature birds is one of hostility, and conflicts between them were often observed. Broley (1947 ) suggests that the juveniles intruding in the territory of the breeding pairs are the previous year's young. This might be the case with the San Juan Island birds as most intruding juveniles were in the dark brown first year plumage. On May 7, 1962, at Nest C the adult bird's warning call was sufficient to turn the intruding juvenile away, but on May 10, the adult was seen pursuing the juvenile in the manner described in the case of the adult eagles' intrusion. On May 15, 1962, at Nest A, the female adult took quick action on the approach of a juvenile and chased it from the area. Later in that day the male bird of Nest A "followed" an intruding juvenile from the nest's vicinity. Generally, the breeding eagles of Nest B at Rocky Bay were more tolerant of intruding juveniles in spite of the latter's frequent visits to the area. An unusual episode occurred on May 14, 1963. Before dark 67 i n the evening a h i g h p i t c h e d " g u l l - c a l l " was h e a r d when a j u v e n i l e b a l d eagle a p p e a r e d f l y i n g s t r a i g h t t o w a r d N e s t B. The f e m a l e adult i n the nest took no apparent i n t e r e s t when the i n t r u d i n g j u v e n i l e l a n d e d among t r e e s w e l l below the nest l e v e l , however the m a l e made a sudden f a s t d i ve at t h i s young b i r d who by t h i s t i m e d i s a p p e a r e d f r o m the o b s e r v e r ' s v i e w . The adult b i r d a s c e n d e d a g a i n and r e p e a t e d the dive into the t r e e s and a l s o d i s a p p e a r e d f r o m s i g h t . No sounds w e r e h e a r d and s h o r t l y af t e r the m a l e b i r d r e t u r n e d to h i s f o r m e r p e r c h to spend the n i g h t . A v i s i t to the a r e a a r o u n d the base of the n e s t t r e e on the f o l l o w i n g m o r n i n g r e v e a l e d no signs of a f i g h t . P r e s u m a b l y the m a l e b i r d t o l e r a t e d the j u v e n i l e ' s p r e s e n c e . The i n t e r r e l a t i o n of b a l d e a g l e s not engaged i n b r e e d i n g a c t i v i t i e s i s one of m u t u a l t o l e r a n c e or i n d i f f e r e n c e . C o m m o n i n t e r e s t i n some fo o d i t e m s m a k e s t h e m gather i n g r e a t n u m b e r s at c e r t a i n l o c a t i o n s . D i x o n (1909) and W i l l e t (in I m l e r and K a l m b a c h , 1955) r e c o r d 20 to 40 eagles o c c u p y i n g one t r e e . On San J u a n I s l a n d 8 e a g l e s , a l l j u v e n i l e s except one, w e r e seen p e r c h e d on a snag by T r o u t L a k e on M a y 6, 1962. The same number of e a g l e s , 2 a d u l t s and 6 j u v e n i l e s , w e r e counted a r o u n d a four a c r e f i e l d c o n t a i n i n g sheep and n e w l y b o r n l a m b s on F e b r u a r y 24, 1964. J u v e n i l e b a l d eagles w e r e n e v e r a n t a g o n i s t i c t o w a r d t h e i r k i n d ; the o c c a s i o n a l swoops at each other w e r e made r a t h e r p l a y f u l l y r e s e m b l i n g the a e r i a l p l a y of the m a t e d a d u l t s . A d u l t b a l d e a g l e s seen i n company of j u v e n i l e s d u r i n g the b r e e d i n g season w e r e c o n s i d e r e d to be n o n - b r e e d i n g b i r d s . Such adults w e r e seen only on two o c c a s i o n s . On M a y 5, 1962, at E a g l e P o i n t two 68 juveniles were seen perched in company of an adult for two hours. On May 6, 1962, 7 juveniles and one adult were seen perching on the same tree by Trout Lake . 8.5.2. Relations with Red-Tailed Hawks The conflicts often observed between bald eagles and red-tailed hawks clearly indicate the smaller bird's hostility towards the eagle. The hostility is one sided because the eagles tend to show an indifference towards the hawks most of the time and will only turn on the offensive if overtempted or if the hawk ventures close to the eyrie. Red-tailed hawks venturing into the vicinity of eagle nests are easily warded off by the eagle's "mild-threat" call. On June 5, 1962, however, a juvenile hawk proceeded still closer to Nest A after the warning call had been uttered, upon which the male eagle on guard took the offensive, approaching the hawk with a swift flight never .observed previously. It was of interest to observe that the eagle remained beneath the hawk's altitude and when the smaller bird was overtaken, it turned on its back in preparation for the use of its talons. On the eagle's move the hawk frantically tried to gain altitude, changed the course of its flight and left the area immediately. The eagle did not pursue the intruder. The majority of the hawk's attacks are directed against juvenile bald eagles who ward off the hawk's persistent dives with a half-completed flip performed without any interruption in their flight. Red-tailed hawks are abundant on San Juan Island and nest in the wooded parts 69 of its interior. The breeding hawks fiercely attack any intruder passing through their territory. Hawks were observed to attack osprey, turkey vulture and great blue heron in a manner similar to the attacks made on the bald eagles. 8.5.3. Relations with Ospreys An osprey nest at'Rocky Bay only 750 yards from Nest B provided an excellent opportunity to observe the relations between ospreys and bald eagles. Generally the breeding adults of Nest B were indifferent towards the ospreys. The actions of the ospreys, however, showed that they regarded eagles as enemies and on the eagles' occasional close approach the smaller birds panicked and took to'the air where they stayed until the eagles left the vicinity of the osprey's nesting site. Eagles were never observed robbing ospreys of their prey, although ospreys often caught fish in the bay in view of the eagles perched at Nest B. On one occasion only was an osprey seen to abandon its prey as a result of interference by eagles. On May 16, 1963, one of the ospreys which was approaching its nest with a food item in its talons dropped the prey when both eagles of Nest B came close to the osprey nest. On two other occasions when the adult eagles flew near the osprey nest both of its occupants panicked but took no offensive action. The ospreys' attitude towards juvenile bald eagles was in sharp contrast to that towards the adult eagles. On the appearance of any 70 juvenile on the horizon both ospreys began calling loudly and took to the air rapidly gaining altitude. If the intruder approached within 200 to 300 yards of their nest it was promptly attacked. The osprey1 s attack on juvenile eagles is similar to that of the red-tailed hawk's, with the exception that the osprey dives closer to the intruder and retreats faster to its former altitude. The juvenile eagles were observed to perform the flip in response to all the osprey attacks, while among the numerous hawk-eagle encounters the flip was observed only once. Also, an osprey attack frequently resulted in the eagle changing its flight direction, which never occurred on the hawk's attack. On one occasion, on May 11, 1963, a juvenile eagle was observed to turn on the offensive during an encounter with the osprey (see section 8.4.3.). The osprey's antagonism toward juvenile eagles was also shown when the fledged young of Nest B was fiercely attacked on July 10, 1963 (see section 10.3.). 8.5.4. Relations with Crows Most annoyance and discomfort which the bald eagles of San Juan Island suffer is occasioned by crows. Rocky Bay is heavily populated with northwestern crows who were often harassing the adult eagles of Nest B. It was noted that crows generally respected the immediate vicinity of the nest tree and attacked eagles only when they were perched farther away from the eyrie, probably in the crows' own territory. However, on several occasions the crows harassed the birds even while they perched on "n" tree. On June 6, 1963, two crows persisted for 4 hours in their attack 71 on the female parent of Nest B. The two crows kept diving at the eagle alternately, sometimes coming as close as 3 to 4 feet from the eagle's head (Figure 10a) . At first the eagle was indifferent towards their actions, then she started to follow the crows' movements by turning her head and occasionally snapping at them with her bil l . An interesting feature to observe was the mobility of the eagle's neck, at times almost making full turns. The eagle changed her perch several times and finally, looking disturbed, she gave the "annoyance" call and moved around the perch nervously. The crows ceased their attacks for no apparent reason. Crows often ventured close to an eagle which had landed on rocks of the shore after a successful fishing trip. On one occasion, on May 10, 1963, a crow actually pecked at the fish held in the eagle's talons. The eagle, while panting heavily, did not react to the crow's action. On March 24, 1963, a flock of crows came close to Nest A on Turn Island, one crow even landing on top of the nest tree. This prompted the male eagle perching close by to drive into the flock and chase the crows away at high speed. Part of the flock took refuge among the trees. Bent (1937) writes: "Eagles are often attacked by crows, just as these black rascals will attack any large birds of prey; and occasionally the crow pays extreme penalty for its audacity". There are no. records of eagles killing or feeding on crows on San Juan Island (see section 13.2.3.). On July 11, 1962, the male adult of Nest A robbed a flock of crows which had been feeding on a dead rabbit. The eagle alighted in the middle of 72 F i g u r e 10b Crow mobs eagle after eagle has r obbed the crow of i t s food. 73 the flock upon which the crows scattered in all directions; picked up the rabbit and flew to the nest. One of the crows followed and harassed him for a short distance (Figure 10b). Brewster (in Bent, 1937) writes of- an incident when a crow alighted on the back of a juvenile bald eagle, forcing the eagle to "plunge headlong into the Lake" in order to escape its tormentor. Juvenile eagles were never observed to be the subject of crows' harassment on San Juan Island, on the contrary, a juvenile bald eagle was seen on one occasion to feed on a road-killed rabbit in company of crows and in mutual unconcern of the other's presence. 8.5.5. Relations with Gulls Crows as the primary source of harassment while the eagles are perched are replaced by gulls when the eagles are on wing or engaged in fishing activities. Gulls numbering in dozens followed the eagles of Rocky Bay whenever fishing sorties were made in the immediate vicinity of the nest. At low tide Rocky Bay appears as a mudflat, attracting gulls from all areas in numbers up to a hundred. When on the water or on the mudflat the gulls fear the eagle and quickly take wing with great commotion and noise. Noise provided by the gulls on O'Neil Island always indicated the eagle's presence or its passing over that island. Remnants of gulls were found in the debris collected underneath Nest A and also beneath the perch tree used by the Nest D pair at Point Caution (see section 13.1.2.). A mature bald eagle was seen to chase mew gulls on July 23, 1962, in Mosquito Pass. On May 19, 1963, the male eagle of Nest B made a dive at a glaucous-winged gull passing close to the eyrie; the gull managed to escape by means of a sharp turn in its flight. Several species of gulls are known to be part of the bald eagle's diet (Murie, 1940, Imler and Kalmbach, 1955 and Southern, 1963). Yeager (1950) records bald eagles attacking a crippled gull. Bald eagles indirectly contribute to egg losses of breeding glaucous-winged gulls on Mandarte Island, B. C. , by scaring gulls off their nests, which then are robbed by crows (Vermeer, 1964). 8.5.6. Relations with Other Birds The appearance of eagles never alarmed the numerous ducks, loons and grebes present in the neighbouring waters of Nest A and Nest B. Remnants of California murre and surf scoter were found in the debris under eagle nests on San Juan Island which indicate their presence in the eagle's diet. The capture of a male bufflehead was seen by local residents in early May, 1963. W . Huntsberry reported to M . D . F . Udvar dy (in litt. ) the sighting of an adult bald eagle feeding on a bird near Dinner Island in 1961 . The remains of the bird were identified to be of a red-breasted merpanser . Eagles are known to feed on many species of waterfowl (Imler and Kalmbach, 1955). Murie (1940) found that sea birds constitute the largest part of the bald eagles' diet on the Aleutian Islands, Alaska. Trautman (1942) reported ducks pursuing a mature bald eagle. 75 The adult eagles on San Juan Island were indifferent towards small birds passing by their nest. Tree swallows and starlings were often observed to fly around the eyrie, at times even alighting on the r im of the nest. While the adults took no notice of them, the young eagles showed their interest by moving closer to them, causing the small birds to leave. 8.5.7. Relations with Mammals Rabbit constitutes the largest portion of the eagles' diet on San Juan Island (see Chapter IV.) . Adult and juvenile eagles were often observed to perch on fence-posts in the middle of fields abundant with rabbits. The rabbits carried on with their feeding activities even when eagles perched above them but promptly headed for their holes when the birds took wing. Eagles were never observed to attack rabbits on the island. The lambing season of the island sheep extends from the middle of February to the end of Apri l . Eagles often land in fields among grazing sheep during this period. The eagles' landing does not elicit fright reactions from the sheep, only an inquiring look which these animals give any passing object or farm animals. On February 25, 1964, a juvenile eagle was seen in the middle of a field near False Bay, only a few yards away from a recently born lamb accompanied by an adult sheep. The eagle took to the air suddenly but the action did not evoke any reaction from the sheep. A small raccoon was seen on April 13, 1964, in Nest K 76 during an aerial survey. The animal was curled up in the nest as if sleeping, however, it looked up when the aircraft made a close pass. The raccoon was found in the same spot the following day when another aerial survey was made. Nest K was in use during 1963, however, it appeared abandoned in the spring of 1964; breeding activities of the resident eagles were observed at Nest M only a short distance away. Raccoons are abundant on the island yet their role in the eagles' diet is not known. The only evidence of raccoon in the bald eagles' diet was reported by Oberholser (1906). 8.5.8. Relations with Man Bent (1937) writes: "Eagles have few serious enemies except man" . It is known from the egg-collectors' extensive experiences that eagles often will abandon their nest if molested during the incubation period. The birds raise much commotion in order to scare the intruder away but no other action is taken in defence of the nest. Broley (1947) had similar findings when he climbed hundreds of trees containing nests with young at various ages. However, Bendire (in Bent, 1937) cites three instances of eagles actually swooping at nest robbers but no contact was made on these occasions. A more recent record of this nature was made by Murphy (1962) in which he claims the eagle made actual contact with the intruder, causing a superficial laceration on the forehead. The eagles on San Juan Island gave the "threat" call upon every human approach to the base of their nest tree, but further action 77 to drive the intruder away was never taken. On May 7, 1962, when a tree close to Nest C was climbed to obtain a better view of the nest, the adult eagles of that nest never attempted any attack; however, they remained in the area and raised much commotion. Their behavior was interpreted as a "threat display", exhibited to drive the intruder away. Both birds flew in short circles over the nest; their heavy wingbeats creating a swishing sound. The birds often stopped in their course and hovered in one spot with legs extended, then continued in a different direction. The entire display was a combination of swift rushing flights, short dives and quick ascends interspersed with occasional soarings. The birds vocalized strongly throughout the incident and the "threat" call uttered in their flight was incomplete, consisting only of the repeated hoarse "kah-kah-kah" sounds. It was discovered later that Nest Cwas abandoned by the birds, possibly as a consequence of the human disturbance. Eagles subjected to the presence of humans for a long period of time will become accustomed to their presence and will not panic if the base of the nest tree is visited (Nicholson, in litt. ). This proved true with the breeding eagles on Turn Island during 1962. The shore of this island is a public picnic ground which is often visited by tourists. In contrast, the breeding eagles of Nest B at Rocky Bay panicked when the nest tree was approached by humans within 100 yards and exhibited a display similar to the one observed at Nest C. The effect of the human interference on the eagles' breeding activities is discussed later (see sections 11 and 15). 78 8.6. Summary and Conclusions The male and female of a mated pair of bald eagles was easily identified due to the species' sexual size dimorphism. Special distinguishing marks as .well as behavioral differences also aided in identifying the birds as to their sexes. Three basic sounds were found to make up the limited vocal repertoire of the bald eagle. These sounds were uttered with different frequency and intensity under certain circumstances. Perch trees other than the nest tree were used by the birds in the close vicinity of the nest. The male and female eagle used their own perches consistently throughout the breeding season. Non breeding birds used the Trout Lake area and other uninhabited areas for roosting. The flight of the eagle is varied. Sudden swoops, glides and fast chasing flights are exhibited during different situations. When fishing, the eagle glides low over the water and swoops down with wings held close to the body if a prey is spotted. Swoops are often made straight from the perch. Soaring with motionless wings was observed during the second part of the breeding season on clear sunny days when rising air thermals provide the lift. A combination of swift rushing flights, short dives and quick asceni is exhibited by the birds on the approach of human intruders. This type of behavior was exhibited until the intruder left the area. It is believed that this threat display involves an extensive expenditure of the birds' energy. Such strenuous efforts in defence of the nest were exerted by both breeding 79 adults only when man intruded; intrusions by bald eagles and other birds were warded off by one of the resident eagles with a simple "threat" call or by flying towards the intruder. The female bird took the offensive in both observed instances when the intrusion involved another bald eagle, Intrusions by juvenile bald eagles were warded off alternately by the male and female birds. It may be an adaptive phenomenon to impress the intruder by size; the female, being the larger bird of the mated pair , attacks all formidable opponents, while the smaller male attacks juvenile eagles and other intruding bird species. The breeding birds were often harassed by crows and gulls but the eagles were indifferent to such harassments in the majority of the cases. Since crows are very abundant in Rocky Bay it is probable that Nest B and its immediate vicinity were included in territories of crows and the crow's antagonism toward the eagles was a manifestation of interspecific territorialism. Grows spent a considerable time harassing the eagles, however, the eagles seldom responded to the crow's attacks which suggests that the crows suffered more from this relationship through the phenomenon known as aggressive neglect (Ripley, 1961). 80 9- BREEDING SEASON At the start of the study, the chronology of breeding activities of the bald eagles on San Juan Island was approximated with the available information in literature. Bent (1937) provides information concerning the mean egg-laying dates of the bald eagle in the different parts of its range (see Table 6). According to this source of information, the mean egg-laying date of the bald eagle in Alaska is May 10 and in the Oregon-Mexico region it is March 6. The length of incubation has been established by various investigators to be 34-35 days (Herrick, 1932, Nicholson, 1952). Since the San Juan Islands are situated between the two regions mentioned above, it was presumed that egg-laying of the island's eagles occurs in early Apri l and the eggs are hatched during the first half of May. This presumption proved to be faulty. Field work on San Juan Island commenced on May 2, 1962, and at this time the active bald eagle nests contained young three to four weeks old. Nest A on Turn Island and Nest B at Rocky Bay (see Map 2) were kept under observation during the summer of 1962. Both nests contained two young which departed from the nest for the first time on July 7 and 10 and on July 1 and 2, respectively. On August 2, one of the young of Nest A was seen at the nest for the last time, the other young was found shot on August 10. In 1963, efforts were concentrated on obtaining data for the period prior to the hatching of eggs. Obtaining this information necessitated 81 several week-end trips on the island early in the spring. The limited number of these reconnaisance visits (see Table 1) along with a limited view into the nest prevented the recording of exact dates for egg-laying and hatchings. Table 7 lists the activities of adult eagles during days the island was visited. Pairs of adult eagles were observed in the vicinity of nests in January and February. Nest building activities were observed at Nest A and Nest B on February 24. The earliest observation of an adult bald eagle sitting in the nest was on March 3 at Nest A by C. Nash of Friday Harbor. On March 9 a single egg was sighted in Nest A by R. Franklin of Friday Harbor, an "Island Sky Ferries" pilot. The single egg disappeared from the nest by March 19 (sighting by R. Franklin). No egg was seen in Nest A on March 21 when an aerial survey was conducted. Adult birds were seen by Nest A during March and the first half of Apri l , but from April 21 on, the nest appeared abandoned. An adult bird was seen sitting in Nest B on March 14 and thereafter. On April 21, the birds sitting in Nests B, D, K, and L refused to move in spite of the repeated passes of the aircraft. Due to the Nest A pair's failure to breed, Nest B was kept under observation during the summer of 1963. The single young first departed from Nest B on July 9 and was not sighted at the nest site after July 24. Combining the available local information with the findings of earlier investigators, the chronology of breeding activities of the bald 82 Table 7. Breeding activities of bald eagles on San Juan Island during the spring of 1963. Date Observed from Activities Jan. 20 ground Nest A: Adult pair perched in vicinity of the ne st. Feb. 7 airplane Nests A , B , D , J , K and L : Pairs of adults in vicinity of the nests. Feb. 23 ground Nests A , J and K: Pairs of adults at the nests Feb. 24 ground Nests A and B: Nest building activities. Mar . 3 ground Nest A: One adult on nest, other nearby. Mar . 6 ground Nest A: Adult pair perched on nest tree. Mar . 8 ground Nest A: Adult sits on nest. Mar . 9 airplane Nest A: One egg in nest, unguarded Mar . 10 ground Nest A: Adult sits in nest. Mar . 13 ground Nest A: Incubation. Mar . 14 ground Nest A: Nest B: Incubation. Change-over. Nest left unguarded for 30 minutes. Incubation. Mar . 21 airplane Nest A: No egg in nest. Mar . 23 ground Nest A: Nest B: Adult pair at nest. No incubation. Incubation. Mar . 24 ground Nest A: Male chases crows from nest. Copulation. Apr . 13 ground Nest A: Nest B: Adult pair at nest. No incubation. Incubation. Change-over. Arrangin of twigs in nest. Apr . 14 ground Nest A: Adult pair at nest. Copulation. No incubation. Apr . 21 airplane Nest A: Abandoned. Nests B , D , K , L : Adult sits in nest, refuse to move. 83 eagles on San Juan Island has been approximated and is presented in Table 8. Nest repair activities start in the middle of February. Eggs are layed between March 4 and March 10; the young hatch between Apri l 8 and April 14. The young spend 12 to 13 weeks in the nest and depart for the first time between July 1 and July 10. The eagle family disintegrates in 1 5 to 32 days after the young's first flight. After August 2, only adult birds are present in the nest area. The chronology of the bald eagle's breeding activities on San Juan Island is similar to that of the "Oregon-Mexico" region (egg dates by Bent, 1937). The timing of the breeding season on San Juan Island is such that all activities associated with the raising of young occur between the beginning of March and the end of July, during which period the precipitation is at its lowest point (see Figure 6). Eggs hatch before temperatures start to rise above the yearly average and the young are fully fledged before temperatures reach the yearly maximum in August. The timing of breeding season in relation to yearly changes in precipitation and temperatures occurs similarly in Africa for the Verreaux eagle (Rowe, 1947) and in Alaska for the golden eagle (Hobbie and Cade, 1962). T a b l e 8. T h e a p p r o x i m a t e c h r o n o l o g y of b r e e d i n g a c t i v i t i e s o f b a l d e a g l e s on S a n J u a n I s l a n d A c t i v i t y D a t e L e n g t h N e s t r e p a i r F r o m F e b r u a r y 15 o n -E g g l a y i n g M a r c h 4 to M a r c h 10 -I n c u b a t i o n - 35 d a y s H a t c h i n g A p r i l 8 t o A p r i l 14 -Y o u n g i n n e s t - 12 t o 13 w e e k s Y o u n g f i r s t d e p a r t n e s t J u l y 1 t o J u l y 10 -F a m i l y d i s i n t e g r a t i o n - 1 5 t o 32 d a y s Y o u n g l a s t s e e n at n e s t s i t e J u l y 24 t o A u g u s t 2 oo 85 10. BREEDING BEHAVIOR 10.1. Pre-nestling Period This period includes all activities of the birds associated with breeding up to the hatching of the eggs. The breeding adults are found in the vicinity of their nests as early as the end of October, but do not continuously occupy it until mid December. During this, time the birds are inactive, perching side by side or hunting and fishing together. 10.1 .1. Nest Repair Activities It is an established and well substantiated belief that a pair of eagles use the same nest year after year (Herrick, 1924, Nicholson, 1952, Smith, 1936 and Howell, 1937). The birds, presumably to satisfy their nest building instinct, add new sticks to the nest every year or simply rearrange the old ones and add dried grass for the inner lining. Such activities were observed at Nest A and Nest B on February 24, 1963 with both adults participating. The birds moved about in the nest, picking up small sticks and putting them aside, often giving the faint "gull-call". These activities were performed often during the day but only for short periods as the birds would leave the nest often and return to it after a short while. No new material was observed to be brought to the nest on any of the visits. Herrick (1932) found that the building instinct of the birds remained activated for two to three weeks after the eggs are hatched, culminating in "bringing several bushels of dried grass" to the nest. Dried grass was taken to Nest A on 86 May 28 and May 2 9 in 1962 and was arranged by the parents while the young stood by attentively. Food was brought to the nest at the same time by the other parent but feeding started only after the adult finished arranging the grass. The male bird of Nest B also took grass to the nest along with a fish caught on May 10, 1963. The grass may have been picked up accidentally from the shore where the eagle landed for a rest. 10.1.2. Mating s Generally the mated birds stay close together during this period. They often engage in chase-flights, the most spectacular being the cartwheel display, observed on May 6, 1962 (see section 8.4.4.). Successful sexual union must occur before the eggs are layed, however, attempts to copulate were not observed during this period due to the short observation time. Table 9 presents the information on the observed matings. A copulation attempt by the pair of Nest A in 1963 took place after the egg, possibly layed on March 9> disappeared from the nest. The matings of the Nest A pair on May 26, 1962 and of the Nest B pair on May 10, 1963, took place while the nest contained young four to five weeks old. Herrick ( 932) also observed matings after the eggs were layed and regards this phenomenon as "an instance of redundant activity". Duration of the observed attempts at matings, 5 to 1 5 seconds is very short in light of the matings observed by Herrick (1932) in Ohio, which lasted for 1 to 2 minutes. The matings took place on top branches of trees in close vicinity to the nest tree in all observed Table 9-Observed copulations of bald eagles on San Juan Island, 1962 and 1963 Date Time Nest Place * Duration (seconds) Remarks May 26, 1962 1204 A top of b tree 15 Copulation after adults perched side by side for 30 minutes. Both leave toward sea afterward. March 24, 1963 1205 A top of n tree 10 Male chases a flock of crows away from nest area, on return alights on back of female. Male leaves afterward. Apri l 14, 1963 1000 A top of b tree 5 Copulation after adults perched side by side. Both stay on same perch after . May 10, 1963 0812 B ._ top of p tree 5 Male comes over to p tree, perches just above female. Male alights on female's back. Both birds start fishing in bay afterward. * see Figure 7. 88 instances, supporting the doubt of Herrick concerning Everett Smith's supposition (in Herrick, 1932) that it is accomplished high in the air. 10.1.3. Parental Attention to the Eggs The Turn Island nest contained one egg on March 9, 1963. No information is available concerning the exact laying date for Nest B at Rocky Bay. However, on March 14 and March 23, 1963, the adult bird was seen sitting in the nest. The single egg disappeared from Nest A before March 20, 1963 but both adults remained by the nest site and defended the nest from crows and gulls. The following notes were made at Nest A during the incubation of the egg: March 13, 1963: 1510 Male is on b tree; female is sitting in nest. Male is quiet and looks settled; female is more active, her head is always on the move and calls often in a faint "gull.-call" fashion. 1545 Male takes off toward sea; female also stands up, then resettles looks down, puts her legs apart and shakes them as she slowly settles. 1625 Female stands up, turns around and resettles in the same fashion as above, spends considerable time looking down. 1630 Male arrives back, lands on b tree, utters "annoyance-call" at a cormorant which flies by. March 14, 1963 905 A change-over:, male takes off from b tree, circles around the nest with strong, wing beats and legs extended downward, alights on edge of nest. Female takes off right away, lands on b tree. Male circles around nest once more in the same fashion, then returns and settles. 89 M a r c h 14, 1963 (cont'd.) 9 1 9 B o t h adults take off, n e s t i s l e f t alone. B i r d s engage i n chase-f l i g h t j u s t over the n e s t . 921 M a l e l e a v e s t o w a r d south; f e m a l e c o m e s back to nest and s e t t l e s . S i m i l a r b e h a v i o r was o b s e r v e d at N e s t B. A t change-over the nest was l e f t u n g uarded f o r t h r e e m i n u t e s w h i l e the m a l e b i r d was e s c o r t i n g the f e m a l e as she was l e a v i n g the n e s t . E g g s l e f t u n guarded fo r s h o r t p e r i o d s w e r e n e v e r c o v e r e d w i t h nest m a t e r i a l , as o b s e r v e d by H e r r i c k (1932). 10.1.4. H a t c h i n g The l e n g t h of the i n c u b a t i o n p e r i o d has been e s t a b l i s h e d by f o r m e r i n v e s t i g a t o r s to be 34 to 35 days ( H e r r i c k , 1932, N i c h o l s o n , 1952). The c l u t c h of N e s t A was d e s t r o y e d by unknown means, t h e r e f o r e h a t c h i n g n e v e r o c c u r r e d i n 1963. N e s t B , h o w e v e r , p r e s u m a b l y c o n t a i n e d on eaglet on A p r i l 14, 1963. The b e h a v i o r of the p a r e n t s as o b s e r v e d on above date: 1345 F e m a l e s i t s i n the n e s t i n a m anner that suggests m o r e than eggs. She i s a c t i v e , t u r n s her head often. No sight of the m a l e . 1415 F e m a l e stands up, p l a c e s t w i g s a r o u n d h e r s e l f , then r e s e t t l e s v e r y s l o w l y . 1450 F e m a l e stands up a f t e r t w i s t i n g her head, w a l k s a r o u n d the n e s t edge, j u m p s off and r e t u r n s a f t e r a s h o rt c i r c l e a r o u n d the n e s t . S e t t l e s v e r y s l o w l y . 1505' M a l e a r r i v e s at nest t r e e , l a n d s on top. F e m a l e c a l l s " g u l l - c a l l " , stands up and m o v e s b a c k w a r d v e r y s l o w l y , then t a k e s off and g l i d e s o v e r to p t r e e and l a n d s . M a l e j u m p s down to n e s t , m o v e s t w i g s a r o u n d h i m s e l f then s e t t l e s s l o w l y . 90 A week l a t e r w h i l e f l y i n g over N e s t B w i t h an a i r c r a f t , the s i t t i n g b i r d r e f u s e d to l e a v e the nest i n spite of the r e p e a t e d c l o s e p a s s e s of the a i r p l a n e . 10.2. N e s t l i n g P e r i o d The n e s t l i n g p e r i o d i n c l u d e s the a c t i v i t i e s of the p a r e n t s i and the young f r o m the t i m e the eggs a r e h a t c h e d up to the t i m e the young l e a v e s the n e s t . Continuous o b s e r v a t i o n s w e r e s t a r t e d on M a y 14, 1962 at N e s t A on T u r n I s l a n d and on M a y 8, 1963 at N e s t B at R o c k y Bay. In both i n s t a n c e s , at the s t a r t , the n e s t s c o n t a i n e d young t h r e e to f i v e weeks o l d . 10.2.1. P a r e n t a l A t t e n t i o n to the Young 10.2.1.1. C a r e of the Young The n e w l y h a t c h e d young a r e h e l p l e s s and r e q u i r e the c l o s e attention of the p a r e n t s . D u r i n g the e a r l y nest l i f e of the young, one or both of the p a r e n t s a r e a l w a y s on g u a r d by the n e s t , u s u a l l y p e r c h e d on top of the n e s t t r e e , or on some e q u a l l y t a l l t r e e i n the i m m e d i a t e v i c i n i t y . The p a r e n t a l attendance at N e s t A d u r i n g the 1962 b r e e d i n g season i s p r e s e n t e d i n T a b l e 10. P a r e n t a l attendance i s shown as the p a r e n t s ' r e l a t i v e p r e s e n c e by the n e s t , e x p r e s s e d as p e r c e n t a g e of the o b s e r v a t i o n t i m e . The p a r e n t s ' p r e s e n c e by the nest s t e a d i l y d e c r e a s e s as 91 T a b l e 10. The f e m a l e and m a l e p a r e n t eagle's p a r t i c i p a t i o n i n g u a r d i n g the young d u r i n g 1962 at N e s t A on T u r n I s l a n d . P e r i o d L e n g t h of o b s e r v a t i o n (minute s) P a r e n t p r e s e n t N e s t * Guar ded M o n t h Days F e m a l e M a l e M a y 14,15, 16, 466 82.2 64.5 93.4 17,18,19, 562 85.2 29. 5 94. 2 20,21,22, 797 94.9 20.5 94.9 23,24,25, 761 56.8 21.4 78.3 26,27,28, 489 95.6 15.3 95.6 29,30,31, 1047 80.0 16.7 87.8 June 1, 2, 3, 237 76.0 29.2 90.3 4, 5, 6, 1066 58.6 32. 9 92. 2 7, 8, 9, - - - -10,11,12, - - - -13, 14, 15, 2035 69.8 12.2 71 .7 16,17,18, 1950 47 .7 15.2 48.4 19,20,21, 1486 47 .7 1 . 5 47 .7 22,23,24, - - - -25,26,27, 170 100.0 0.0 100.0 28,29,30, 1712 42.8 8.0 44.6 . J u l y 1, 2, 3, 1806 39. 5 4. 3 41 . 4 4, 5, 6, 1886 41 .7 6.6 45.7 7, 8, 9, 1349 31.8 13.5 42.4 10,11,12, 1660 49. 5 9.0 51 .7 13, 14, 15, 1466 17.8 12.1 29.9 16,17,18 1321 10.0 0.9 10.9 !c P e r c e n t a g e of o b s e r v a t i o n t i m e the young grows older . The female parent spends considerably more time at the nest site than the male parent but her attendance decreases at a faster rate during the nestling period. The observation at Nest A started on May 14, 1962 and there is no data available prior to this date. However, it was assumed that during the first four weeks of the young's life one or both of the parents were constantly present by the nest. This assumption is supported by the findings of Herrick (1933) and by the data presented in Table 11 which was obtained at Nest B at Rocky Bay during May, 1963. The data of Tables 10 and 11 are plotted in Figures 11 and 12 respectively to provide a graphic representation of the seasonal decline in parental attendance. The total of percentages representing the sexes' participation in guarding the nest is usually larger than the percentage value representing the time during which the nest was attended by one of the parents, indicating that often both parents were present. However, especially during the early nestling period, the parents took turns on guard. The daily changes in parental attendance at Nest B, during May, 1963 are shown in Figure 12. The absence of one parent is compensated by the presence of the other, resulting in a high attendance During the first eight weeks of the young's life, the nest was guarded 80 percent of the time of observation but during the following two weeks parental attendance rapidly decreased below 50 percent and stayed at this level until the young flew from the nest. T a b l e 11 . The m a l e and f e m a l e p a r e n t eagle's p a r t i c i p a t i o n i n g u a r d i n g the young d u r i n g May, 1963 at N e s t B at R o c k y B a y L e n g t h of P a r e n t p r e s e n t o b s e r v a t i o n — : N e s t * D a ys (minutes) F e m a l e M a l e G u a r d e d 8 -124 100.0 70. 5 100.0 9 617 • 61.6 62.0 100. 0 10 536 88.6 67.0 100.0 11 430 59-7 47.6 100. 0 12 177 100.0 75.2 100.0 13 715 97. 5 21 .7 100.0 14 786 93.6 34.5 100.0 15 285 77. 5 26.8 77.5 16 556 88. 5 44. 6 100.0 17 175 50.0 100. 0 100. 0 18 - - - -19 283 70. 6 7 . 3 73.0 20 540 94.9 23.4 94.9 21 750 43.0 49.8 92.4 22 380 100.0 10.7 100.0 23 244 32.0 24.6 56.6 24 - - - -25 366 89.0 58.2 89. 6 26 - - - -27 433 60.2 51 . 5 100.0 28 - - -29 382 32.8 51 .1 69.2 30 - - - -31 258 69.7 12.5 69-7 * P e r c e n t a g e of o b s e r v a t i o n t i m e 100 5 6 7 8 9 10 11 12 13 14 A p p r o x i m a t e age of y o u n g ( i n w e e k s ) F i g . 11 S e a s o n a l d e c r e a s e i n p a r e n t a l a t t e n d a n c e b y N e s t A at T u r n I s l a n d , 1 9 6 2 . 4^ 100 Nest guarded Female present —. Male present Pi o • H +J > u cu CO & O O a cu CO cu u ft cu i— i DO H 6 7 F ig . 12 The parent eagles' attendance at Nest B during May, 1963, at Rocky Bay. Age of young (in weeks ) 96 In a d v e r s e weather c o n d i t i o n s the young w e r e b r o o d e d u n t i l the age of f i v e w eeks. The f e m a l e p a r e n t spent the night i n the n e s t w i t h the young w h i l e the m a l e was u s u a l l y p e r c h e d on top of the nest t r e e , d u r i n g m o s t of the nest l i f e of the young. The c u r v e i n F i g u r e 11, r e p r e s e n t i n g the attendance of the f e m a l e p a r e n t , c l o s e l y f o l l o w s the c o u r s e of the c u r v e f o r t o t a l attendance, e s p e c i a l l y d u r i n g the l a t t e r p a r t of the n e s t l i n g p e r i o d , i n d i c a t i n g that the n e s t was g u a r d e d by the f e m a l e p a r e n t f o r the m a j o r i t y of the t i m e . In g e n e r a l , the f e m a l e p a r e n t spent t h r e e t i m e s as m u c h t i m e by the nest as d i d the m a l e p a r e n t . 10.2.1.2. F e e d i n g of the Young The f e m a l e and m a l e p a r e n t brought food i t e m s to the nest i n e qual n u m b e r s d u r i n g the o b s e r v a t i o n p e r i o d , but s i n c e no data i s a v a i l a b l e f o r the f i r s t f o u r w eeks of the young's l i f e , a g e n e r a l p i c t u r e f o r the e n t i r e b r e e d i n g season cannot be o b t a i n e d i n t h i s r e s p e c t . The n u m b e r s and dates of f o o d i t e m s w h i c h w e r e brought to N e s t A i n 1962 and to N e s t B i n M a y , 1963 by the f e m a l e and m a l e p a r e n t e a g l e s a r e p r e s e n t e d i n T a b l e 12. U n t i l the age of seven w eeks, the young w e r e unable to f e e d t h e m s e l v e s and depended e n t i r e l y on t h e i r p a r e n t s . A t t e m p t s by the young to f e e d t h e m s e l v e s w e r e o b s e r v e d as e a r l y as M a y 24 i n 1962 at N e s t A and M a y 17 i n 1963 at N e s t B, w h i l e o n l y f i v e w e eks o l d , but these attempts c o n s i s t e d only of p e c k s at the food, s u c c e e d i n g only i n T a b l e 12. Number and date of f o o d i t e m s brought to the nest on San J u a n I s l a n d by the f e m a l e and m a l e p a r e n t e a g l e s d u r i n g the o b s e r v a t i o n p e r i o d i n 1962 and 1963. (1) - l e n g t h of o b s e r v a t i o n (hours) (3) - f o o d i t e m brought i n by f e m a l e (2) - t o t a l number of food i t e m s (4) - f o o d i t e m brought i n by m a l e 1962; T u r n I s l a n d N e s t 1963: R o c k y B a y N e s t Day M a y June J u l y (1) (2) (3) (4) (1) (2) (3) (4) (1) (2) (3) (4) (1) (2) (3) (4) 2 - - - - - - - - 14.3 1 1 - - - -3 - - - - - - - - 4.5 2 2 - - - -4 - - - - 1 .4 2 - 2 7.9 3 - 3 - - -5 - - - - 7.8 2 2 - - - - - - - -6 - - - - 8. 5 1 - 1 - - - - - - -7 - - - - - - - 7.4 1 - 1 - - -8 - - - - - - - - - - 2. 3 1 1 -9 - - - - - - - - - - - 10. 3 1 1 -10 - - - - - - - - - - 9- 0 3 2 1 11 - - - - - - - - 8.9 4 2 2 - - -13 - - - - - - - - - - - - 11 . 9 1 - 1 14 - - - - 13.1 1 1 - - - - - 13 . 1 2 - 2 15 5.2 2 1 1 10.6 1 1 - _ - - - -16 - - - - 10.8 4. 2 2 - - - - 9- 3 3 - 3 17 5.1 2 1 1 - - - - - - - - - - -18 4.2 1 1 - 14.2 2 1 1 _ - - - - -19 - - - - - - - _ - 4. 7 1 1 -20 - - - - 12.1 1 1 - - - - - -• - -21 6.0 1 1 - - - - - - - - 12. 5 2 1 1 23 5.4 1 - 1 - - - - - - - - 4. 6 1 - 1 24 2,. 8 1 1 - - - - - - - - - - - -25 5.3 1 1 - - - - - - - - - 5. 6 1 1 -27 - - - - - - - - - - - - 7. 2 2 - 2 28 4.2 1 1 - 8.1 2 1 1 - - - - - - -29 3.2 1 1 - 11.4 2 - 2 - - - - 6. 4 1 1 -30 7.1 1 1 - 9-1 1 - 1 - - - - - - -31 7.1 2 1 1 - - - - - - - - -T o t a l 55. '3* 14 10 4 107.1* :19 9 10 44.0*11 5 6 99- 9* 19 8 11 * T o t a l s do not i n c l u d e days when no fo o d was brought i n . 98 p i c k i n g up m o r s e l s f r o m the p r e v i o u s m e a l . W h i l e f o o d was brought to the n e s t e v e n l y by the f e m a l e and m a l e p a r e n t , the f e e d i n g of young was done a l m o s t e n t i r e l y by the f e m a l e . The m a l e p a r e n t was o b s e r v e d to f e e d the young l a t e i n the n e s t l i n g p e r i o d , on o c c a s i o n s when he was h a v i n g a m e a l and one of the young j o i n e d h i m . D u r i n g the e a r l y n e s t l i n g p e r i o d , t e a r i n g of the p r e y f o l l o w e d soon after i t was brought to the n e s t . At N e s t A i n 1962 the two young took p o s i t i o n s at the s i d e s of the p a r e n t and g r a b b e d the p i e c e o f f e r e d by the adult b i r d . It was i n t e r e s t i n g to note that the two young v e r y s e l d o m g r a b b e d at the same p i e c e o f f e r e d by the p a r e n t . The p a r e n t b i r d was steady at t e a r i n g the p r e y , and ten to f i f t e e n b i t s of fo o d w e r e o f f e r e d to the young p e r m i n u t e . The young w h i c h s e c u r e d the f i r s t b i t of f o o d o f f e r e d was u s u a l l y b usy s w a l l o w i n g w h i l e the p a r e n t o f f e r e d food to the next one, w h i c h was then taken without any i n t e r f e r e n c e . T a k i n g a l t e r n a t e t u r n s was the g e n e r a l f e e d i n g p i c t u r e d u r i n g the e a r l y n e s t l i f e . L a t e r o n l y one young attended the p a r e n t , the other was u s u a l l y s t r u g g l i n g by i t s e l f on another p i e c e of the food. L a t e r i n the n e s t l i n g p e r i o d f e e d i n g d i d not alw a y s f o l l o w the a r r i v a l of new food i t e m s and at t i m e s h o u r s p a s s e d b e f o r e the f r e s h p r e y was touched. The young u s u a l l y i n d i c a t e d t h e i r hunger by p e c k i n g at the f o o d t h e m s e l v e s , a f t e r w h i c h the p a r e n t b i r d on g u a r d p r o m p t l y d e s c e n d e d to the ne s t f r o m i t s p e r c h and s t a r t e d t e a r i n g the p r e y . F o o d was p r e s e n t i n the nest at a l l t i m e s , and no r e g u l a r i t y was o b s e r v e d i n b r i n g i n g i t i n . The number of fo o d i t e m s 99 brought to the nest during the morning, mid-day and afternoon hours are presented in Table 13. The data of this table was analyzed with an "analysis of variance" and no significant difference was found between the number of food items brought by the birds during the three different periods of the day. While there were usually two or three feeding periods per day, with an average length of 1 5 to 20 minutes during the early nest life, feeding was done more irregularly after the young were able to tear the prey themselves. However, this procedure extended hours in length, interspersed with occasional rest periods. Often when;the young were crouched down after an extensive meal and one of the parents came to the nest to feed itself, the eaglets jumped up and were attended by the parent. The feeding instinct followed the parents all through the summer and the young were observed being fed as late as July 14, 1962 at Nest A, almost a week after they were able to fly. The relationship between the young's age and the number of food items brought to the nest is shown by the data presented in Table 14. The number of food items brought to the nest per one hour of observation time varies slightly as the young grows older, however, no significant difference was found between the number of food items brought to the nest during the weekly periods of the young's age when tested with an "analysis of variance". The average number of food items per one hour observation is 0.136 for the period of observation, which gives, with an average length of daily observation of 7 . 3 hours, slightly less T a b l e 13. F o o d brought to the nest by the pa r e n t eagles d u r i n g the m o r n i n g , m i d - d a y and evening h o u r s on San Juan I s l a n d , i n 1962 and 1963. (1) - le n g t h of o b s e r v a t i o n (hours) (2) - number of o b s e r v e d food i t e m s (3) - number of o b s e r v e d food i t e m s p er one hour of o b s e r v a t i o n 1962 1963 B e t w e e n h o u r s M a y June J u l y M a y T o t a l  (1) (2) (3) (1) (2) (3) (1) (2) (3) (1) (2) (3) (1) (2) (3) P r i o r to 1115 13.8 6 0.43 38.0 5 0.13 42.5 3 0.07 39-9 5 0.12 134.2 19 0.14 1115 to 1545 42.5 3 0.07 36.0 4 0.11 63.4 - 0.00 53.9 8 0.15 195.8 15 0.08 A f t e r 1545 13.2 4 0.30 67.3 10 0.14 113.1 8 0.07 44.5 6 0.13 238.1 28 0.12 T o t a l 79-5 13 141.3 19 219.0 11 138.3 19 568.1 62 101 T a b l e 14. Number of fo o d i t e m s brought to the ne s t by the f e m a l e and m a l e p a r e n t b a l d eagle i n r e l a t i o n to the young's age d u r i n g the b r e e d i n g s e a s o n on San Juan I s l a n d in-1962 and 1963 A p p r o x i m a t e L e n g t h of age of young o b s e r v a t i o n (in weeks) (in h o u r s ) No. of I t e m s No. i t e m / H r . o b s e r v . F e m a l e M a l e T o t a l F e m a l e M a l e T o t a l 5 6 7 8 9 10 11 12 13 63. 3 67.0 51 . 5 24.1 39 -1 60.1 23.0 74. 5 61 .0 7 4 6 3 2 4 1 3 2 4 6 5 3 3 3 4 3 11 0.11 10 0.06 11 0.12 0.12 2 7 4 7 5 0.05 0.07 0.05 0.04 0.03 0.06 0.17 0.09 0.15 0.10 0.22 0.12 0.24 0.05 0.05 0.12 0.12 0.17 0.05 0.09 0.05 0.08 T o t a l 463.6 32 31 63 0.069 0.067 0.136 A v e r a g e number of h o u r s of o b s e r v a t i o n p e r day - 7 . 3 A v e r a g e number of fo o d i t e m s p er day - 0.99 102 than one (0.99) food i t e m brought to the nest per day. However, food was brought i r r e g u l a r l y to the nest. On two o c c a s i o n s , on June 16 and J u l y 11 , 1962, four food i t e m s were o b s e r v e d being brought to the nest, while frequently no new food i t e m was taken to the nest for three-days long p e r i o d s . T h e r e was no exact way to m e a s u r e the amounts of food consumed by the eaglets. Rowe (1947) estimated the d a i l y food consumption of the young V e r r e a u x eagle ( A q u i l a v e r r e a u x i ) , a b i r d s i m i l a r i n size to the b a l d eagle. He found that the eaglet's food consumption grows f r o m 3/4 ounce (21 .26 grams) per day, when newly hatched to 3 3/4 pounds (1 . 38 kg) per day when it i s about to leave the nest. T h i s amount of food i s comparable to the.food consumption of the young of bald eagles on San Juan Island as t r e a t e d above. 10.2.2. Development of the Young The average siz e of a n o r t h e r n bald eagle egg.is 74.4 mm by 57.1 mm (Bent, 1937) and the newly hatched young weighs 85 g r a m s ( H e r r i c k , 1932)^ D u r i n g the 11 to 12 weeks which the eaglets spend i n the nest, they attain the si z e of their parents (weight of juvenile b a l d eagle, captured on August 8, 1963, was 8.125 lbs-'3.675 kg), acquire the a b i l i t y to eat by themselves, and the a b i l i t y to f l y . 10.2.2.1. Changes i n Size Having no other way to, m e a s u r e the size of the young, sketches were made of i t s si z e as seen through the t e l e s c o p e . F i g u r e 13 103 a p p r o x i m a t e age: 4 w e e k s a p p r o x i m a t e age: 5 1 /2 w e e k s M a y 27 a p p r o x i m a t e age: 8 w e e k s F i g . 13 D i a g r a m s s h o w i n g t h e s i z e o f t h e e a g l e t i n c o m p a r i s o n t o t h e s i z e of t h e f e m a l e p a r e n t at N e s t B i n 1 9 6 3 . 104 shows the size of the young eaglet of Nest B at Rocky Bay in comparison to the size of the female parent on four different dates in May and June, 1963. The growth of the young is fast during this period. By the end of June the young's size approaches that of the female and exceeds the size of. the male parent. Fully fledged juvenile birds reveal average measurements with the exception of the bill which is.greater than those of the mature birds of the same sex, as found by Imler and Kalmbach (1955) in Alaska. 10.2.2.2. Changes in Plumage The newly hatched eaglet is covered with light grey down on its upper parts and white down on the head and underpafts. In about four weeks the young changes into a thicker dark grey down stage (Herrick, 1932). The two young of Nest A appeared light grey on May 6, 1962, when seen from an aircraft. Two weeks later > on May 21, 1962, black upper wing coverts were observed as the young used its wings to keep balance. The black feathers rapidly appeared and by the end of May, both young had a dark appearance, showing light grey only in the under parts of the wing.and body. In 1962, the ROcky Bay nest contained young two to three weeks older than did the Turn Island.nest, and the former already appeared black on the May 6 aerial survey. In 1963, the young of Nest B was in grey down on May 8, dark on May 21 and by the end of May showed grey only in the underparts. 105 The primaries and tail feathers appeared early but their growth was slower, being only half grown at the start of the wing exercises. 10. 2.2.3 Wing Exercises The young use their wings extensively from the moment of their hatching (Herrick, 1932) but during the first four weeks of their life they use the wings only as a support on which to lean, when they are crawling about the nest. Wing-flappings were observed as early as May 1 5 at Nest B, May 29 at Nest A in 1962 and May 16 at Nest B in 1963, but the extensive exercises so characteristic of eaglets did not start until two weeks later. At the beginning, the length of these wing-flappings was short and the exercises were performed only in the afternoons. They were more often performed from the middle of June on, when the young were nine weeks old, with an intensity that overshadowed all other i • activities of the young, including feeding. When exercising, the young usually held on to a branch imbedded in the nest and with strong wingbeats performed the motions of flying. Later the young were able to control their balance while wing flapping and no longer held on to branches but hopped about in the nest. Often the young grabbed a loose stick or remnants of previous meals and lifted them as they jumped on every wingbeat. From the middle of June the young were able to stay in the air for several seconds, performing two, and later three, wingbeats on every jump. 106 When the young w e r e i n c o n t r o l of t h e i r l a r g e w i n g s to the extent that the s t r o n g w i n d s w e r e u t i l i z e d to stay l o n g e r i n the a i r , they s t a r t e d t a k i n g e x c u r s i o n s to p e r c h e s a r o u n d and above the nest . F i g u r e 14a i n d i c a t e s the p e r c h e s the young of N e s t A c l i m b e d b e f o r e t h e i r f i r s t d e p a r t u r e f r o m the nest . The young of N e s t A i n 1962 w e r e f i r s t o b s e r v e d to j u mp out on June 29 to step No. 1; one of t h e m l a t e r that day p r o c e e d e d to step No. 2. On J u l y 4, one of the young j u m p e d to step No. 3, and on J u l y 6 to step No. .4. The young of N e s t B f o l l o w e d a s i m i l a r r o u t i n e i n 1962 and the steps i n v o l v e d a r e i n d i c a t e d i n F i g u r e 14b. Once the young v e n t u r e d out of the n e s t , the only t i m e they c l i m b e d b a c k was d u r i n g the night and when new f o o d was brought i n . Often the young s t a y e d on t h e i r p e r c h e s i n spite of the p a r e n t s ' f e e d i n g a c t i v i t i e s i n the nest . W ing e x e r c i s e s c o n t i n u e d on e x t r e m e ends of l i m b s and often the young w e r e n e a r l y b lown off by the w i n d . On J u l y 7, one of the young f l e w f r o m N e s t A ; the other f o l l o w e d i t on J u l y 10, 1962. B o t h of the young i n N e s t B w e r e f l y i n g by J u l y 2, 1962. The s i n g l e young of N e s t B i n 1963 d e p a r t e d f r o m the nest f o r the f i r s t t i m e on J u l y 9-The young's a c q u i s i t i o n of f l y i n g a b i l i t y , i s a g r a d u a l p r o c e s s w h i c h r e a c h e s a c l i m a x i n t h e i r f i r s t d e p a r t u r e f r o m the n e s t . H o w e v e r , i t i s b e l i e v e d that the young w e r e capable of f l y i n g two to t h r e e days p r i o r to t h e i r a c t u a l d e p a r t u r e . The young's f i r s t d e p a r t u r e 0 was not i n d u c e d by any p e r c e i v a b l e a c t i o n s of the p a r e n t b i r d s . H e r r i c k (1924b) b e l i e v e s that i n one i n s t a n c e the p a r e n t s s t a r v e d the young to F i g u r e 14a P e r c h e s u s e d by the eagle t s of N e s t A on T u r n I s l a n d d u r i n g 1962. F i g u r e 14b P e r c h e s u s e d by the e a g l e t s of N e s t B at R o c k y B a y d u r i n g 1962 and 1963. 108 lure them into flight. On San Juan Island, food was present in the nest and feeding of the young was observed prior and after the date of the young's departure. Consequently, starving as a means to induce the young into flight cannot be considered. 10.2.3. Relationship between Young in the Same Nest It is a well substantiated fact that among the birds of prey, and especially among eagles, the advantage of the first hatched young over its nest mate is so great that it often results in the elimination of the latter . Such was the case with a bald eagle pair in Ohio (Herrick, 1932) and similar behavior was observed with the golden eagle (Gordon, 1955) with the Verreaux eagle (Rowe, 1947) and with the African Fish eagle (Haliaetus vocifer EJaudin) (Brown, I960). Both Nest A and Nest B contained two young each in 1962. Although the early nest life of the young was not witnessed, it appeared from the similarity in their sizes and development, that neither of the young suffered maltreatment earlier. Occasional fights between the nest mates were observed at Nest A in 1962. These fights appeared more playful than serious and never amounted to more than two or three pecks at each other. When the extensive wing exercises started, the nest proved to be too small for two birds practicing at the same time. The wing of the exercising bird often hit the other young accidentally, which then, in retaliation, grabbed the wing and held it for several seconds. Rarely were pecks made at ithce other's head, but these pecks were judged 109 n o t t o be d a m a g i n g s i n c e t h e y w e r e d o n e w i t h l i t t l e f o r c e . \ 1 0 . 3 P o s t - n e s t l i n g P e r i o d T h i s p e r i o d c l o s e s t h e b r e e d i n g s e a s o n . It s t a r t s w i t h t h e a c q u i s i t i o n o f f l y i n g a b i l i t y b y t h e y o u n g a n d e n d s i n t h e d i s i n t e g r a t i o n of t h e e a g l e f a m i l y . T h e y o u n g r a p i d l y b e c o m e i n d e p e n d e n t ; and. d i s a p p e a r f r o m t h e a r e a i n t h r e e t o f o u r w e e k s a f t e r t h e y f i r s t f l e w , f r o m t h e n e s t . T h e y o u n g b i r d ' s f i r s t d e p a r t u r e f r o m t h e n e s t n e v e r r e s u l t s i n a l o n g e x c u r s i o n , r a t h e r t h e y o u n g f l i e s a r o u n d t h e n e s t a n d s h o r t l y a f t e r l a n d s o n o n e of t h e p e r c h e s u s u a l l y u s e d b y t h e p a r e n t s . W h i l e t a k i n g o f f a n d f l y i n g p r e s e n t e d n o p r o b l e m t o t h e y o u n g , l a n d i n g w a s a d i f f i c u l t t a s k w h i c h w a s n o t m a s t e r e d u n t i l d a y s a f t e r t h e y o u n g f i r s t t o o k w i n g . P e r f e c t c o f e o i l d i n a t i o n i s r e q u i r e d t o b r i n g a b o d y of c l o s e t o t e n p o u n d s , t r a v e l l i n g at h i g h s p e e d , t o a s t a l l a t t h e s a m e t i m e w h e n t h e p e r c h i s i n r e a c h o f t h e t a l o n s . T h i s c o - o r d i n a t i o n i s l e a r n e d t h r o u g h p r a c t i c e a n d c o n s e q u e n t l y t h e f i r s t l a n d i n g e f f o r t s o f t h e y o u n g a r e a w k w a r d . W h e n e n t e r i n g t h e n e s t , t h e y o u n g a p p r o a c h e s f r o m a b o v e a n d t r i e s t o b r e a k i t s s p e e d w i t h f u r i o u s w i n g b e a t s , w h i c h o n l y h e l p t o l e s s e n t h e i m p a c t t h e y o u n g m a k e s w i t h t h e n e s t . T h e y o u n g b i r d s a p p r o a c h e d l a n d i n g s p o t s , o t h e r t h a n t h e n e s t , i n a s i m i l a r , m a n n e r . B r a n c h e s d i d n o t p r o v i d e t h e l a r g e s u r f a c e o n w h i c h t o l a n d a s d i d t h e n e s t a n d w e r e o f t e n m i s s e d o n t h e f i r s t t r y w h i c h r e s u l t e d i n t h e y o u n g ' s f a l l i n g d o w n w a r d . T h e s e l a n d i n g a t t e m p t s e n d e d w i t h t h e o p e n - w i n g e d y o u n g h e l d up b y t h e d e n s e f o l i a g e s e v e r a l y a r d s b e l o w t h e i n t e n d e d 110 l a n d i n g spot. L a n d i n g on t r e e - t o p s w i t h open wings was often o b s e r v e d d u r i n g the f i r s t f i v e days of t h i s p e r i o d . The young w e r e able to l a n d on b r a n c h e s a f t e r the f i r s t f i v e days of t h i s p e r i o d ; h o w e v e r , s t i l l w i t h some d i f f i c u l t y . The young, when i n the v i c i n i t y of the n e s t , u s e d the same p e r c h e s w h i c h w e r e u s e d by the p a r e n t s d u r i n g the b r e e d i n g season. The p a r e n t s often a c c o m p a n i e d the young on these p e r c h e s . D u r i n g t h i s p e r i o d , the young a r e h e l p l e s s a g a i n s t the at t a c k s of a f o r m i d a b l e a v i a n enemy. Such h e l p l e s s n e s s was shown by the young of N e s t B when a t t a c k e d by an o s p r e y on J u l y 10, 1963. On t h i s o c c a s i o n , the young was f l y i n g t o w a r d O ' N e i l I s l a n d when the o s p r e y s t a r t e d i t s a t t a c k s . The young eagle, f l y i n g o n l y f o r the second day, p e r f o r m e d the f l i p on the c l o s e a p p r o a c h of the o s p r e y but l o s t b a l a n c e and s t a r t e d f a l l i n g t o w a r d the w a t e r . The eagle q u i c k l y r e g a i n e d i t s b a l a n c e but l o s t i t e v e r y t i m e the f l i p was p e r f o r m e d to w a r d off the c o n s i s t e n t a t t a c k s of the o s p r e y . A s a r e s u l t of the r e p e a t e d f a l l s , the young b i r d was c l o s e to the w a t e r s u r f a c e when i t e s c a p e d by heading f o r s h o re and l a n d i n g w i t h w i n g s wide open on top of a s h o r t t r e e . It was i n t e r e s t i n g . t o note that the f e m a l e p a r e n t who was p e r c h e d on the nest t r e e d i d not go to the young's a i d . S i m i l a r a w k w a r d n e s s of the young eagle was o b s e r v e d on J u l y 23, 1962 c l o s e to N e s t A when the pa r e n t eagle's swoops made the young f l i p on i t s b a c k f o r defense. Once the young l e a r n s to f l y , the nest r a p i d l y b e c o mes abandoned. T a b l e 15 p r e s e n t s data on the young's and adult's p r e s e n c e i n or a r o u n d N e s t A d u r i n g the p o s t - n e s t l i n g p e r i o d i n 1962. D u r i n g the T a b l e 15. F a m i l y d i s i n t e g r a t i o n and nest abandonment at N e s t A on T u r n I s l a n d i n J u l y , 1962. O b s e r v a t i o n B i r d s p r e s e n t at nest s i t e P e r i o d L e n g t h young p a r e n t young and p a r e n t e i t h e r young together or p a r e n t (day s) (minutes) ( p e r c e n t ^ ( p e r c e n t ) * ( p e r c e n t ) (per cen 4, 5, 6, 1886 100.0 45.7 45.7 100. 0 7, 8, 9, 1349 100.0 42.2 42.2 100.0 10, 11, 12, 1660 80. 5 51 .7 51 .7 80.5 13, 14, 15, 1466 31 .2 29.9 7.2 51 .9 16, 17, 18, 1321 6.4 10.9 5.2 12.1 19, 20, 21, 912 30.2 30. 2 12.1 48.3 22, 23, 24, 1372 16.7 17.3 3.6 30.4 25, 26, 27, 1176 0.0 10.0 0.0 10.0 28, 29, 30, 537 0.0 1.2 0.0 1.2 * P e r c e n t a g e of o b s e r v a t i o n t i m e 112 f i r s t ten days of t h i s p e r i o d , the young's p r e s e n c e i n the nest's v i c i n i t y d e c r e a s e d at a f a s t r a t e . In the f i r s t f i v e days, the young r e t u r n e d to the nest to spend the night and to eat. L a t e r they only f l e w by or a c c o m p a n i e d one of the p a r e n t s on t h e i r r a r e v i s i t s to the n e s t . The p r e s e n c e of the p a r e n t s d e c r e a s e d at a s l o w e r r a t e . F r o m the f i r st week of the p e r i o d , the adult b i r d s v i s i t e d the n e s t s i t e m o r e f r e q u e n t l y , t h a n d i d the j u v e n i l e s . T h e r e was an apparent i n c r e a s e i n the p r e s e n c e of both a d u l t s and j u v e n i l e s d u r i n g the second week of the p e r i o d but f r o m then on e a g l e s w e r e r a r e l y s i g h t e d i n the nest's v i c i n i t y . The data of T a b l e 15 i s p l o t t e d i n F i g u r e 15 to give a g r a p h i c r e p r e s e n t a t i o n of the nest-abandonment and f a m i l y d i s i n t e g r a t i o n at N e s t A i n 1962*. The f a s t r a t e of nest abandonment i n the f i r s t week of the p e r i o d i s due to the i n c r e a s i n g absence of the young f r o m the n e s t a r e a to a g r e a t e r degree than to the adult b i r d s ' a b s e n c e , whose attendance by the n e s t s i t e d e c r e a s e s at a s l o w e r r a t e . F a m i l y d i s i n t e g r a t i o n , r e p r e s e n t e d by the c u r v e w h i c h i n d i c a t e s the d e c r e a s e i n t i m e that adults and young spend t o g e t h e r , i s a s l o w e r p r o c e s s than i s the abandonment of the n e s t . F o o d was o b s e r v e d to be brought to N e s t A f o r the l a s t t i m e on J u l y 11, 1962. On J u l y 16, one of the young e x h i b i t e d a b e h a v i o r w h i c h was i n t e r p r e t e d as begging f o r food. The young was o b s e r v e d to c r a w l c l o s e to the f e m a l e p a r e n t who was p e r c h e d at the end of a l i m b on b t r e e . The young b i r d m o v e d up and down on the l i m b w i t h h e a d * - n e s t abandonment i s shown by the c u r v e f o r " e a g l e ( e i t h e r adult or young) p r e s e n t " - f a m i l y d i s i n t e g r a t i o n i s shown by the c u r v e f o r "young and adult p r e s e n t t o g e t h e r " 113 F i g . 15 T h e p r e s e n c e of a d u l t a n d j u v e n i l e e a g l e s at N e s t A o n T u r n I s l a n d d u r i n g J u l y , 1 9 6 2 . b i r d p r e s e n t b y n e s t ( e i t h e r a d u l t o r y o u n g ) a d u l t a n d y o u n g p r e s e n t at s a m e t i m e 114 h e l d l o w and w i n g s s l i g h t l y d ropped and e n d l e s s l y u t t e r e d the " g u l l - c a l l " . T h e r e was no r e s p o n s e f r o m the p a r e n t b i r d . S i m i l a r b e h a v i o r was o b s e r v e d by N e s t A on J u l y 22 and August 1, 1962. One of the young of N e s t A was shot a r o u n d J u l y 22, the other was seen i n the a r e a on August 2, and f o r the l a s t t i m e i n 1962. A d u l t b i r d s w e r e s i g h t e d by the n e s t s i t e o c c a s i o n a l l y t h e r e a f t e r ; the l a s t s i g h t i n g of an adult b a l d eagle was on A u g u s t 12, 1962. . 10.4. S u m m a r y and C o n c l u s i o n s N e s t - r e p a i r a c t i v i t i e s of the e a g l e s w e r e o b s e r v e d at the end of F e b r u a r y , m o r e than two weeks b e f o r e the l a y i n g of the eggs. No new m a t e r i a l was o b s e r v e d b e i n g brought to the n e s t , the r e p a i r a c t i v i t i e s c o n s i s t e d of the r e a r r a n g i n g of s m a l l t w i g s w i t h i n the n e s t by the f e m a l e and m a l e b i r d s . D r i e d g r a s s was seen brought to the n e s t by the b i r d s d u r i n g May, at w h i c h t i m e the nest c o n t a i n e d young 4 to 7 w eeks o l d . C o p u l a t i o n of the b i r d s has been o b s e r v e d up t i l l the end of May, long a f t e r the eggs w e r e hatched. D u r i n g the i n c u b a t i o n of the eggs, the n e s t was c o n s t a n t l y g u a r d e d by one of the a d u l t s . B o t h sexes took t u r n s i n i n c u b a t i n g the eggs. The b i r d i n t e n d i n g to r e l i e v e i t s mate e x h i b i t e d a f l i g h t w h i c h r e s e m b l e d the n u p t i a l d i s p l a y b e f o r e i t e n t e r e d the n e s t . The eggs w e r e l e f t u n c o v e r e d f o r short p e r i o d s ; however, one of the adults a l w a y s r e m a i n e d i n the p r o x i m i t y of the n e s t . The i n c u b a t i n g b i r d a p p e a r e d a c t i v e at a l l t i m e s and was often o b s e r v e d to r e a r r a n g e t w i g s around.itself. 115 A f t e r h a t c h i n g the attention of the a d u l t s s l o w l y d e c r e a s e d . The d e c r e a s e i n p a r e n t a l attention i s g r a d u a l throughout the b r e e d i n g season. F r o m the t i m e the eggs a r e l a y e d u n t i l the young.are four to f i v e w e eks o l d , the nest i s c o n s t a n t l y g u a r d e d by one of the p a r e n t s , w h i c h u s u a l l y i s the f e m a l e , whose s h a r e i n g u a r d i n g the n e s t i s t h r e e t i m e s as l a r g e as that of the m a l e . D u r i n g t h i s p e r i o d , the young are i n the downy stage and a r e unable to f e e d t h e m s e l v e s . The p a r e n t s ' c l o s e attendance p r o v i d e s a s e c u r i t y a gainst p o s s i b l e p r e d a t o r s as w e l l as a d v e r s e weather c o n d i t i o n s . P a r e n t a l at t e n t i o n s h a r p l y d e c r e a s e s when the young's w i n g e x e r c i s e s s t a r t at the age of eight to nine w e eks. D u r i n g t h i s t i m e the p a r e n t b i r d s spend m o r e t i m e away f r o m the n e s t than they spend by i t and u s u a l l y v i s i t the nest o n l y when fo o d i s brought. The young have a t t a i n e d the s i z e of the p a r e n t s and l e a r n e d to f e e d t h e m s e l v e s d u r i n g t h i s p e r i o d . The m a j o r p a r t of the young's t i m e was spent f l a p p i n g t h e i r w i n g s . T h e r e was no a p p r e c i a b l e change i n the amount of f o o d s u p p l i e d to the young d u r i n g the e n t i r e season. P a r e n t a l at t e n t i o n s l i g h t l y i n c r e a s e d d u r i n g the p e r i o d the young s t a r t e d f l y i n g . The f a s t r a t e of nest abandonment d u r i n g the p o s t - n e s t l i n g p e r i o d was c a u s e d by the young's i n c r e a s e d absence f r o m the nest s i t e . The p a r e n t e a g l e s s t i l l v i s i t e d the neat after the young had l e f t the a r e a . 116 11 . B R E E D I N G S U C C E S S B r e e d i n g a c t i v i t i e s w e r e o b s e r v e d at 8 n e s t s out of the 13 b a l d eagle n e s t s on San Ju a n I s l a n d . E a g l e s u s e d N e s t s A, B, C_, D and N e s t s J , K, L f o r v a r i o u s lengths of t i m e d u r i n g 1962 and 1963. N e s t M was i n use d u r i n g the s p r i n g of 1964 when o b s e r v a t i o n s stopped. N e s t s E , F , G, H and I a p p e a r e d abandoned. T a b l e 16 p r e s e n t s a s u m m a r y of the eagle's b r e e d i n g a c t i v i t i e s at n e s t s i n u se d u r i n g 1962 and 1963. The b r e e d i n g a c t i v i t i e s at N e s t A and B a r e d i s c u s s e d i n d e t a i l on the p r e c e d i n g pages. I n f o r m a t i o n r e g a r d i n g b r e e d i n g a c t i v i t i e s at the other n e s t s was obt a i n e d by means of a e r i a l s u r v e y s and by o c c a s i o n a l g r o u n d c h e c k s at t h e i r s i t e s . N e s t A was u s e d d u r i n g both y e a r s of o b s e r v a t i o n , h o w e v e r , the eagle s m anaged to r a i s e a b r o o d only i n 1962. N e s t A i s l o c a t e d on T u r n I s l a n d . The n e a r e s t h o use* i s on San Juan I s l a n d m o r e than 700 y a r d s away. T u r n I s l a n d i t s e l f i s a W i l d l i f e Refuge but i t s s h o re i s a p u b l i c p i c n i c ground. G r e a t n u m b e r s of t o u r i s t s v i s i t the San Ju a n I s l a n d f o r c a m p i n g , s e t t i n g up t h e i r tents l e s s . t h a n 200 y a r d s f r o m the nest t r e e . The nest i s not v i s i b l e f r o m the s h o r e s of T u r n I s l a n d , h o w e v e r , i t i s e a s i l y spotted e i t h e r f r o m the water or f r o m the opposing s h o r e s of San J u a n I s l a n d . The p r e s e n c e of humans did; not seem to d i s t u r b the eagle's b r e e d i n g a c t i v i t i e s i n 1962 when two young w e r e r e a r e d i n the n e s t . In 1963, however, the eagle s f a i l e d to continue t h e i r i n i t i a l * by house, an i n h a b i t e d human d w e l l i n g i s meant. 117 T a b l e 16. B r e e d i n g s u c c e s s at active bald eagle nests on San Juan Island i n 1962 and 1 9 6 3 . N e s t S u c c e s s of b r e e d i n g a c t i v i t i e s i n : i n u s e 1962 1963 2 y o u n g f l e d g e d 1 egg l a i d , l a t e r d i s a p p e a r e d . N o f u r t h e r a t t e m p t s to b r e e d . B D J K L M 2 y o u n g f l e d g e d I n i t i a l b reeding a c t i v i t i e s . Nest abandoned due to human i n t e r f e r e n c e . 1 young fledged N e s t - b u i l d i n g a c t i v i t i e s i n June. Nest lat e r abandoned. Not known Not known Not known 1 y o u n g f l e d g e d . O r i g i n a l c l u t c h s i z e not k n o w n . N o b r e e d i n g a c t i v i t i e s 1 young fledged I n i t i a l b r e e d i n g a c t i v i t i e s i n e a r l y s p r i n g . Nest later abandoned. 1 young p r o d u c e d 1 young p r o d u c e d Not i n use T o t a l number of 5 4 young produced: 118 b r e e d i n g a c t i v i t i e s p r e s u m a b l y due t o h u m a n i n t e r f e r e n c e . T w o n e w h o u s e s w e r e b e i n g b u i l t i n t h e s p r i n g of 1963 o n l y 800 y a r d s a w a y f r o m t h e n e s t . T h e n o i s e a n d c o m m o t i o n w h i c h a c c o m p a n i e d t h e c o n s t r u c t i o n c o u l d h a v e b e e n t h e p r i m a r y c a u s e f o r t h e f a i l u r e o f t h e e a g l e ' s b r e e d i n g a c t i v i t i e s . P o s s i b l y a n a d d i t i o n a l c a u s e of t h i s f a i l u r e i s t h e m o r e f r e q u e n t h u m a n v i s i t s t o t h e b a s e of t h e n e s t t r e e , r e s u l t i n g f r o m g r e a t e r p u b l i c a w a r e n e s s of t h e T u r n I s l a n d n e s t due t o t h e p u b l i c i t y g i v e n t o t h e p r e s e n t s t u d y . N e s t B w a s t h e m o s t p r o d u c t i v e n e s t o n S a n J u a n I s l a n d p r o d u c i n g t w o e a g l e t s i n 1962 a n d o n e e a g l e t i n 1 9 6 3 . T h e n e s t i s l o c a t e d o n t h e s o u t h e r n s h o r e of R o c k y B a y i n a n a r e a of l i t t l e r e a l e s t a t e d e v e l o p m e n t . T h e b i r d s w e r e e a s i l y d i s t u r b e d b y h u m a n s a n d s h o w e d h o s t i l i t y t o w a r d i n t r u d e r s a p p r o a c h i n g t h e v i c i n i t y o f t h e i r n e s t i n g s i t e . S u m m e r c o t t a g e s a r e l o c a t e d 500 - 700 y a r d s a w a y f r o m t h e n e s t t r e e b u t a r e s e p a r a t e d f r o m t h e n e s t b y d e n s e v e g e t a t i o n , t h u s t h e n e s t i s r e l a t i v e l y i s o l a t e d f r o m h u m a n h a b i t a t i o n s . I n i t i a l n e s t i n g a c t i v i t i e s w e r e o b s e r v e d at N e s t C i n M a y , 1 9 6 2 . T h e n e s t w a s d i s c o v e r e d o n M a y 6, 1 9 6 2 , a n d o n t h a t d a y o n e a d u l t b i r d w a s s i t t i n g i n t h e n e s t a n d a n o t h e r w a s p e r c h e d n e a r b y o n a t a l l t r e e . O n M a y 7, 1 9 6 2 , t h e b i r d s a b a n d o n e d t h e n e s t a f t e r t h e y w e r e d i s t u r b e d b y t h e a u t h o r w h i l e a t t e m p t i n g t o l o o k i n s i d e t h e n e s t b y c l i m b i n g a t r e e o n l y 30 y a r d s a w a y . T h e b i r d s s t a y e d b y , t h e n e s t f o r t h e n e x t t h r e e d a y s d u r i n g w h i c h t i m e t h e y c h a s e d i n t r u d i n g j u v e n i l e s f r o m t h e v i c i n i t y o f t h e n e s t o n t w o o c c a s i o n s . N o a d u l t b i r d s w e r e o b s e r v e d at t h i s n e s t d u r i n g t h e r e m a i n i n g p a r t of t h e f o l l o w i n g s u m m e r a n d d u r i n g t h e e n t i r e s u m m e r o f 1 9 6 3 . T h e n e s t t r e e i s l o c a t e d at t h e s o u t h e r n f o o t h i l l s o f M o u n t D a l l a s , at an e l e v a t i o n of 3000 f e e t , 1600 y a r d s a w a y f r o m t h e s e a s h o r e . A n a r e a d e n s e l y v e g e t a t e d w i t h a l d e r l i e s b e t w e e n t h e n e s t t r e e a n d t h e n e a r e s t f a r m b u i l d i n g l o c a t e d o v e r 1000 y a r d s a w a y . T h e n e s t i s n o t r e a d i l y a p p a r e n t ; i t i s s i t u a t e d on a t a l l t r e e i n a b o w l of t h i c k b r a n c h e s 75 f e e t f r o m t h e g r o u n d . I t s e x i s t e n c e w a s n o t k n o w n t o l o c a l r e s i d e n t s p r i o r t o i t s d i s c o v e r y o n M a y 6, 1 9 6 2 . O p e n f i e l d s , 600 t o 700 y a r d s f r o m t h e n e s t , a r e u s e d f o r r a b b i t h u n t i n g . I t i s l i k e l y t h a t e a g l e s c a n n o t e n d u r e t h i s d i s t u r b a n c e . H o w e v e r , i t i s b e l i e v e d t h a t t h e d i s t u r b a n c e c a u s e d b y t h e a u t h o r o n M a y 7, 1962 m a d e t h e b i r d s a b a n d o n t h e n e s t i n 1962 a n d c e a s e t o u s e i t i n 1 9 6 3 . O n e e a g l e t w a s r e a r e d i n N e s t D d u r i n g b o t h t h e 1962 a n d 1 9 6 3 b r e e d i n g s e a s o n s . T h i s w a s t h e m o s t p r o d u c t i v e n e s t a f t e r N e s t B s i n c e i t p r o d u c e d y o u n g i n b o t h y e a r s . T h e o r i g i n a l c l u t c h s i z e , h o w e v e r , w a s n o t k n o w n . T h e n e s t i s w e l l i s o l a t e d f r o m h u m a n h a b i t a t i o n s , t h e n e a r e s t h o u s e b e i n g o v e r 500 y a r d s a w a y . T h e n e s t t r e e i s 250 y a r d s f r o m t h e s h o r e a n d i t s t a n d s o n a h i l l s i d e at a n e l e v a t i o n o f 1 20 f e e t . T h e a r e a s u r r o u n d i n g t h e n e s t s i t e b e l o n g s t o t h e U n i v e r s i t y of W a s h i n g t o n . N e s t b u i l d i n g a c t i v i t i e s of a n e a g l e p a i r w e r e o b s e r v e d at N e s t J i n e a r l y J u n e , 1 9 6 2 . L a t e r t h a t m o n t h a n e a g l e w a s s e e n s i t t i n g i n t h e n e s t b u t n o e g g w a s p r o d u c e d . T h e a d u l t b i r d s w e r e n o t s e e n b y t h i s n e s t f r o m J u l y o n . T h e p r o x i m i t y of N e s t J t o N e s t C ( 1 5 0 0 y a r d s ) s u g g e s t s t h a t b o t h n e s t s b e l o n g t o t h e s a m e p a i r of e a g l e s . I t i s a l s o l i k e l y t h a t t h e e a g l e s o b s e r v e d at N e s t J w e r e t h e s a m e b i r d s w h o s e n e s t i n g a c t i v i t i e s h a d b e e n d i s t u r b e d at N e s t C d u r i n g e a r l y May,> 1 9 6 2 . A n a d u l t p a i r of 120 e a g l e s w e r e s e e n p e r c h e d o n t h e n e s t t r e e a g a i n o n F e b r u a r y 7 a n d 2 3 , 1963 b u t n o b r e e d i n g a c t i v i t i e s w e r e o b s e r v e d f r o m t h e r e o n . T h e n e s t t r e e i s l o c a t e d o n t h e s h o r e i n a n a r e a f r e q u e n t e d b y h u m a n s . T h e n e a r e s t h o u s e i s o n l y 100 y a r d s a w a y . A r o a d p a s s e s 150 y a r d s f r o m t h e n e s t a n d p r o v i d e s a c l e a r v i e w i n t o t h e n e s t . I t w a s i n t e r e s t i n g t o f i n d t h a t i n s p i t e o f so m u c h h u m a n a c t i v i t y i n t h e n e i g h b o u r h o o d of t h e n e s t , t h e b i r d s m a d e a t t e m p t s t o b r e e d . T h e e x i s t e n c e of N e s t K w a s n o t k n o w n i n 1 9 6 2 . I t w a s f o u n d on A p r i l 21,. 1 9 6 3 d u r i n g a n a e r i a l s u r v e y , at w h i c h t i m e a b i r d w a s s e e n o n t h e n e s t . D u r i n g t h a t y e a r one e a g l e t w a s r e a r e d i n t h e n e s t . T h e o r i g i n a l c l u t c h s i z e w a s n o t k n o w n . T h e n e s t t r e e i s l o c a t e d o n t h e t i p o f a p e n i n s u l a b e t w e e n F a l s e a n d K a n a k a b a y s , 650 y a r d s a w a y f r o m t h e n e a r e s t h o u s e a n d i s w e l l i s o l a t e d f r o m h u m a n a c t i v i t i e s . N e s t L w a s d i s c o v e r e d o n A p r i l 2 1 , 1 9 6 3 . I t i s l o c a t e d o n t h e n o r t h - w e s t p a r t o f H e n r y I s l a n d , 180 y a r d s a w a y f r o m t h e s h o r e . T h e r e a r e o n l y t w o h o u s e s b u i l t o n t h i s i s l a n d a n d b o t h a r e m o r e , t h a n o n e . m i l e a w a y f r o m t h e n e s t . I t i s b e l i e v e d t h a t t h e b i r d s a r e s u b j e c t e d t o l i t t l e d i s t u r b a n c e b y h u m a n s . T h e n e s t w a s i n s p e c t e d o c c a s i o n a l l y b y m e a n s of a i r s u r v e y s . I t i s n o t k n o w n w h e t h e r i t w a s u s e d i n 1962; h o w e v e r , one e a g l e t w a s r e a r e d i n t h e n e s t d u r i n g t h e 1 9 6 3 s e a s o n . N e s t M w a s d i s c o v e r e d o n A p r i l 14, 1 9 6 4 , d u r i n g t h e l a s t v i s i t t o S a n J u a n I s l a n d . T w o a d u l t b i r d s w e r e s e e n b y t h e n e s t at t h i s d a t e ; o n e b i r d w a s s i t t i n g i n t h e n e s t . T h e n e s t i s l o c a t e d o n t h e n o r t h e r n s h o r e o f F a l s e B a y , 800 y a r d s a w a y f r o m N e s t K. T h e d i s t a n c e f r o m t h e n e s t t o t h e 121 n e a r e s t h o u s e i s 8 5 0 y a r d s , h o w e v e r , a r o a d r u n s o n l y 600 y a r d s f r o m t h e n e s t . It i s a s s u m e d t h a t N e s t s K a n d M b e l o n g t o t h e s a m e p a i r o f e a g l e s a n d a r e u s e d b y t h e m i n a l t e r n a t e y e a r s . N e s t K w a s u s e d i n 1 9 6 3 a n d i n i t i a l b r e e d i n g a c t i v i t i e s w e r e o b s e r v e d at N e s t M i n A p r i l , 1 9 6 4 . E i t h e r of t h e t w o n e s t s c o u l d h a v e b e e n u s e d d u r i n g 1962 a s a n a d u l t p a i r of e a g l e s w e r e f r e q u e n t l y s i g h t e d o v e r F a l s e B a y d u r i n g t h e s u m m e r o f t h a t y e a r . F i v e p a i r s o f e a g l e s a t t e m p t e d b r e e d i n g i n 1962 a n d o n l y 3 p a i r s s u c c e e d e d i n r a i s i n g . a b r o o d . N e s t s A a n d B p r o d u c e d t w o y o u n g e a c h w h i l e o n l y o n e y o u n g f l e d g e d i n N e s t D w h i c h g a v e a n a v e r a g e o f 1.66 y o u n g p e r s u c c e s s f u l n e s t . N e s t i n g s u c c e s s , a n i n d i c a t i o n of t h e s u c c e s s of a c t i v e n e s t s , w a s 6 0 % . I n 1 9 6 3 t h e n e s t i n g s u c c e s s w a s h i g h e r ( 6 6 . 6 % ) ; h o w e v e r , t h e p r o d u c t i v i t y w a s l o w e r , o n l y o n e y o u n g p e r s u c c e s s f u l a c t i v e n e s t . T h e c o m p a r i s o n o f n e s t i n g s u c c e s s b e t w e e n 1 9 6 2 a n d 1 9 6 3 i s p r o v i d e d i n T a b l e - 1 7 . T a b l e 17. N e s t i n g s u c c e s s of b a l d eagles on San Juan I s l a n d i n 1962 and 1963 No. young P e r c e n t a g e No. No. n e s t s No. young p e r s u c c e s s f u l of p a i r s Y e a r a c t i v e n e s t s s u c c e s s f u l f l e d g e d n e s t s u c c e s s f u l 1962 1963 5 6 3 4 5 4 1.66 1.00 60.0 66.6 Chapter IV FEEDING HABITS 124 12. INTRODUCTION The feeding habits of the bald eagle are well documented in literature and perhaps belong to the best illustrated phases of its biology. Recent studies have centered on the variety of its diet to reveal its economic status and to provide scientific proof for the justification of the protection by American and Canadian legi slations. The bald eagle is primarily a carrion feeder. Direct observations carried out by various investigator s indicate that the food item obtained is more often a dead or dying animal, or one disabled by injury, sickness or food deficiency (Munro, 1938, Murie, 1940, Oberholser, 1906, Smith, 1936). The bird will feed readily on carrion even when the carrion is well advanced in decomposition. On the other hand, the eagle is quite capable of killing live animals and will do so during the winter when there is no easier way of securing food (Bent, 1937). Fish constitute the largest portion of the bald eagles' diet; mammals, birds and reptiles are eaten in proportion to their availability. The various methods of collecting the feeding habit data also yield different results. 12.1 Methods of Collecting Food Data The most accurate method of collecting data is by direct observation of the food items consumed in the nest; the difficulty, however, of keeping a close watch on the nest from dawn to dusk makes this method hard to employ. Also, correct identification of food items requires that 125 t h e o b s e r v e r i s i n c l o s e v i c i n i t y of t h e n e s t . T h i s i s h i n d e r e d ; b y t h e h e i g h t f a c t o r o n t h e P a c i f i c N o r t h w e s t w h e r e n e s t s g e n e r a l l y a r e b u i l t i n t r e e s 100 f e e t a n d t a l l e r . I n o r d e r t o p r o v i d e a n e y e - l e v e l v i e w of t h e n e s t , t h e o b s e r v e r h a s t o r e m a i n a g r e a t e r d i s t a n c e f r o m t h e n e s t , w h i c h d i s t a n c e i n t u r n h a s t o be o v e r c o m e b y t h e u s e of a p o w e r f u l t e l e s c o p e . B y o b s e r v i n g t h e n e s t f o r s e v e r a l h o u r s e a c h d a y t h r o u g h o u t t h e b r e e d i n g s e a s o n , a n a c c u r a t e p i c t u r e of t h e b i r d ' s d i e t c a n b e o b t a i n e d . A r e l a t i v e l y e a s y , a n d o f t e n p r a c t i s e d , m e t h o d i s t h e a n a l y s i s of d e b r i s c o l l e c t e d u n d e r n e a t h t h e e a g l e ' s n e s t s . P r o p o r t i o n s o f i t e m s c a n be c a l c u l a t e d b u t n o t t h e i r w e i g h t s b e c a u s e of t h e b i r d ' s t e n d e n c y t o t e a r t h e i r l a r g e r p r e y a n d t a k e o n l y s m a l l p o r t i o n s t o t h e n e s t . A h u g e f i s h s k u l l u n d e r n e a t h t h e n e s t w o u l d o n l y i n d i c a t e t h a t a f i s h h e a d w a s c o n s u m e d , w h i c h t h e b i r d s c o u l d h a v e p i c k e d up f r o m a n e a r b y c a n n e r y . T h e m e t h o d , h o w e v e r , i s a d v a n t a g e o u s i n p r o v i d i n g a q u a l i t a t i v e p i c t u r e o f t h e e a g l e ' s d i e t t h r o u g h o u t t h e y e a r s o f t h e n e s t ' s u s e . A t h i r d a n d a c c u r a t e m e t h o d i s t h e a n a l y s i s o f t h e s t o m a c h c o n t e n t s . H o w e v e r , t h e l a r g e q u a n t i t y o f s t o m a c h c o n t e n t s r e q u i r e d t o y i e l d a n a c c u r a t e r e s u l t m a k e s t h i s m e t h o d n o t a p p l i c a b l e i n l i g h t o f t h e g r e a t e f f o r t s m a d e t o p r e s e r v e t h e b i r d ' s e x i s t e n c e . T h e o n l y s t u d y u s i n g s t o m a c h c o n t e n t s of b a l d e a g l e s w a s m a d e i n A l a s k a . T h e s p e c i m e n s w e r e c o l l e c t e d f r o m 1940 t o 195 3 d u r i n g w h i c h p e r i o d t h e b o u n t y l a w i n A l a s k a w a s s t i l l i n e f f e c t ( I m l e r a n d K a l m b a c h , 1 9 5 5 ) . T h e p r o b l e m of k i l l i n g t h e b i r d s t o c o l l e c t s t o m a c h c o n t e n t s c a n b e e l i m i n a t e d b y a n a l y z i n g e a g l e " p e l l e t s " . P e l l e t s a r e t h e u n d i g e s t i b l e 126 a n d r e g u r g i t a t e d p a r t s of c o n s u m e d f o o d i t e m s . T h i s m e t h o d t e n d s t o m i n i m i z e t h e r e p r e s e n t a t i o n o f i t e m s w h i c h a r e m a i n l y c o m p o s e d o f d i g e s t i b l e m a t e r i a l s a n d o v e r e s t i m a t e i t e m s t h a t a r e h a r d t o d i g e s t . 1 2 . 2 . F o r m e r F o o d H a b i t S t u d i e s F o o d h a b i t s t u d i e s of t h e b a l d e a g l e e m p l o y i n g t h e s e t e c h n i q u e s a r e p r e s e n t e d i n T a b l e 18. I n c o l u m n 1 of T a b l e 18, t h e a n a l y s i s o f 435 b a l d e a g l e s t o m a c h c o n t e n t s i s p r e s e n t e d ( a f t e r I m l e r a n d K a l m b a c h , 1 9 5 5 ) . T h e l a r g e r p a r t o f t h i s s a m p l e w a s c o l l e c t e d f r o m t h e c o a s t a l a r e a s o u t h a n d s o u t h e a s t o f J u n e a u , A l a s k a , b e t w e e n 1940 a n d 1 9 5 2 , t h u s t h e f i g u r e s p r o v i d e a p i c t u r e of t h e b a l d e a g l e ' s d i e t i n t h e a r e a o f i t s g r e a t e s t a b u n d a n c e . I t e m s of t h e s t o m a c h c o n t e n t s d e f i n i t e l y i d e n t i f i e d a s c a r r i o n , a r e d e a l t w i t h s e p a r a t e l y . T h e a u t h o r s (op. c i t . ) b e l i e v e t h a t m o r e t h a n h a l f of t h e f o o d i t e m s f o u n d b y t h e b i r d s w a s c a r r i o n . C o l u m n s 2 a n d 3 p r e s e n t d a t a c o l l e c t e d b y M u r i e (1940) o n t h e A l e u t i a n I s l a n d s , A l a s k a , i n 1936 a n d 1937 r e s p e c t i v e l y . T h e f i g u r e s f o r 1936 w e r e o b t a i n e d t o a g r e a t e r d e g r e e f r o m p e l l e t a n a l y s i s . T h e r e p r e s e n t a t i o n o f i n v e r t e b r a t e s i n t h i s a n a l y s i s i s e x a g g e r a t e d due t o t h e i r u n d i g e s t i b l e e x o s k e l e t o n s . T h e 1937 d a t a , o b t a i n e d f r o m a l a r g e r s a m p l e , i s b a s e d on f o o d r e m a i n s f o u n d w i t h i n t h e n e s t , c o n s e q u e n t l y i t . g i v e s a m o r e e x a c t f i g u r e o f t h e b i r d ' s d i e t o n t h e A l e u t i a n I s l a n d s . F o o d r e m a i n s c o l l e c t e d b y W. B . T y l e r ( i n I m l e r a n d K a l m b a c h , 1955) a r e f r o m u n d e r n e a t h n e s t t r e e s i n M a r y l a n d a n d V i r g i n i a b e t w e e n 1936 a n d 127 T a b l e 18. D i e t of t h e b a l d e a g l e i n d i f f e r e n t l o c a l i t i e s o f i t s r a n g e . ( N u m b e r s r e p r e s e n t p e r c e n t a g e s . ) (1) s t o m a c h a n a l y s i s of 435 s t o m a c h s ( I m l e r a n d K a l m b a c h , 1955) (2) a n a l y s i s of r e m a i n s c o l l e c t e d f r o m 19 n e s t s ( M u r i e , 1940) (3) a n a l y s i s of r e m a i n s c o l l e c t e d f r o m 18 n e s t s ( M u r i e , . 1940) (4) a n a l y s i s of r e m a i n s c o l l e c t e d f r o m u n d e r n e a t h n e s t s i n M a r y l a n d a n d V i r g i n i a b y W. B . T y l e r ( i n I m l e r a n d K a l m b a c h , 1955) (5) a n a l y s i s of 59 p e l l e t s c o l l e c t e d b y R. D. S m i t h a t t h e B l a c k w a t e r W i l d l i f e R e f u g e ( i n I m l e r a n d K a l m b a c h , 1955) (6) a n a l y s i s of 630 p e l l e t s c o l l e c t e d b y R. H. I m l e r i n K a n s a s ( i n I m l e r a n d K a l m b a c h , 1955) I t e m s (1) (2) (3) (4) (5) (6) F i s h 65.7 18.8 6.1 52.4 4.2 -B i r d s 18.8 58.9 8 6 . 0 33. 3 50.4 1.1 M a m m a l s 1.2 5.3 7.6 4.7 29.8 9 8 . 9 R e p t i l e s - - -• 2.6 2.1 -I n v e r t e b r a t e s 2.0 16.1 - 0.7 -V e g e t a b l e m a t t e r - - -• 3 3 12.1 -C a r r i o n 1 2.3 _ 128 1937 a r e t h e b a s i s f o r t h e d a t a p r e s e n t e d i n c o l u m n 4, T a b l e 18. F i f t y - n i n e p e l l e t s c o l l e c t e d b y R. D. S m i t h ( i n I m l e r a n d K a l m b a c h , 1955) i n t h e B l a c k w a t e r W i l d l i f e R e f u g e b e t w e e n 1 9 3 3 a n d 1 9 3 4 w e r e a n a l y z e d a n d t h e f i g u r e s a r r i v e d at a r e p r e s e n t e d i n c o l u m n 5, T a b l e 18. A c c o r d i n g t o I m l e r a n d K a l m b a c h (1955) t h e p e l l e t m a t e r i a l t e n d s t o m i n i m i z e t h e p r o p o r t i o n o f f i s h e a t e n b e c a u s e m a n y of t h e s m a l l f i s h b o n e s a r e e i t h e r d i g e s t e d o r s c a t t e r e d a f t e r r e g u r g i t a t i o n . N o e v i d e n c e o f f i s h r e m a i n s w e r e f o u n d i n t h e 630 p e l l e t s c o l l e c t e d b y R. H. I m l e r ( i n I m l e r a n d K a l m b a c h , 1955) b e t w e e n 1935 a n d 1941 n e a r S t o c k t o n , K a n s a s . T h e d a t a p r e s e n t e d i n c o l u m n 6, T a b l e 18 s h o w s t h a t t h e e a g l e s w e r e s u b s i s t i n g a l m o s t e n t i r e l y o n m a m m a l i a n f o o d : j a c k r a b b i t s ( L e p u s c a l i f o r n i c u s G r e y ) a n d c o t t o n t a i l r a b b i t s ( S y l v i l a g u s f l o r i d a n u s A l l e n ) w e r e e a t e n a l m o s t e x c l u s i v e l y . 129 13. F E E D I N G H A B I T S O F B A L D E A G L E S O N S A N J U A N I S L A N D 1 3 . 1 . S o u r c e s of I n f o r m a t i o n T h e m e t h o d s u s e d t o s t u d y t h e f e e d i n g h a b i t s of t h e b a l d e a g l e s o n S a n J u a n I s l a n d w e r e d i r e c t o b s e r v a t i o n s of f o o d i t e m s b r o u g h t t o t h e n e s t a n d a n a l y s i s of d e b r i s c o l l e c t e d u n d e r n e a t h t h e n e s t t r e e s . 1 3 . 1 . 1 . D i r e c t O b s e r v a t i o n s O b s e r v a t i o n s of f o o d i t e m s b r o u g h t t o t h e n e s t d u r i n g t h e n e s t i n g s e a s o n s of 1962 a n d 1 9 6 3 , c o m b i n e d w i t h i n f o r m a t i o n o n f e e d i n g a c t i v i t i e s g a t h e r e d a f t e r t h e y o u n g l e f t t h e n e s t b u t s t i l l a s s o c i a t e d w i t h t h e p a r e n t s , a r e p r e s e n t e d i n T a b l e ^ 19. T h e o b s e r v a t i o n s w e r e c a r r i e d out at t w o s e p a r a t e l o c a t i o n s . D u r i n g , t h e s u m m e r o f 1 9 6 2 , N e s t A o n T u r n I s l a n d w a s o b s e r v e d a n d f o o d c o n s u m p t i o n r e c o r d e d , w h e r e a s i n 1 9 6 3 t h e i n f o r m a t i o n o n f o o d w a s g a t h e r e d at N e s t B at R o c k y B a y , due t o t h e f a i l u r e of t h e A N e s t ' s p a i r t o r a i s e a b r o o d t h a t y e a r . T h e p e r c e n t a g e s p r e s e n t e d i n T a b l e 19 a r e c a l c u l a t e d o n t h e b a s i s of v o l u m e t r i c a m o u n t s c o n s u m e d . S i n c e e x a c t m e a s u r e m e n t s c o u l d n o t be t a k e n , t h e s i z e o f t h e f o o d i t e m w a s e s t i m a t e d i n t o c a t e g o r i e s of s m a l l , m e d i u m a n d l a r g e . V o l u m e t r i c f a c t o r s of 1, 2 a n d 3 w e r e a p p l i e d t o t h e m r e s p e c t i v e l y a n d t h e p e r c e n t a g e s w e r e c a l c u l a t e d o n t h i s b a s i s . R a b b i t ( O r y c t o l a g u s c u n i c u l u s L . ) i s c o n s u m e d t o t h e l a r g e s t e x t e n t , t h e n f i s h ( m a i n l y O p h i o d o n a n d S e b a s t o d e s s p e c i e s ) t o a l e s s e r d e g r e e . P o r t i o n s o f a h a r b o u r s e a l ( P h o c a v i t u l i n a L . ) w e r e b r o u g h t t o t h e n e s t i n J u l y , 1 9 6 2 , o b t a i n e d f r o m a c a r r i o n t h a t w a s w a s h e d a s h o r e 130 T a b l e 19-D i e t of b a l d e a g l e s o n S a n J u a n I s l a n d , b a s e d o n o b s e r v a t i o n s of f o o d i t e m s b r o u g h t t o t h e n e s t d u r i n g 1962 a n d 1 9 6 3 . I t e m s : N o . of O b s e r v a t i o n s E s t i m a t e d V o l u m e C o n s u m p t i o n * 1962 1 9 6 3 1962 1 9 6 3 1962 1 9 6 3 F i s h 19 20 34 27 43.0 36. 5 R a b b i t 20 22 38 4 3 4 8 . 3 58.1 S e a l 3 - 4 - •5.1 -B i r d s 1 2 1 4 I - 2 5.4 F r o g 1 - 1 1.2 -C r a b 1 1 - 1.2 -T o t a l 45 44 79 7 4 100.0 100. 0 * ( i n p e r c e n t a g e s ) 131 n e a r T u r n I s l a n d . A b u f f l e h e a d ( B u c e p h a l a a l b e o l a ) w a s s e e n t o be c a p t u r e d i n M a y 1963 a n d o n t w o o t h e r o c c a s i o n s u n i d e n t i f i e d b i r d s w e r e s e e n b e i n g b r o u g h t t o t h e n e s t . O n a n o t h e r o c c a s i o n , a l a r g e c r a b f r o m t h e b e a c h w a s t a k e n up t o t h e n e s t . A f o o d i t e m p i c k e d u p b y t h e f e m a l e a d u l t of N e s t A f r o m a n e a r b y p o n d i n 1962 w a s i d e n t i f i e d as. a f r o g . S i n c e t h e d a t a p r e s e n t e d i n T a b l e 19 w a s c o l l e c t e d d u r i n g t h e b r e e d i n g s e a s o n s , t h e f i g u r e s o n l y s h o w t h e b i r d ' s d i e t d u r i n g , t h e s p r i n g a n d t h e s u m m e r a n d i n p a r t i c u l a r t h e k i n d o f f o o d t h a t w a s f e d t o t h e y o u n g . T h e b i r d s ' y e a r a r o u n d f e e d i n g h a b i t s a r e n o t p r o v i d e d b y t h e s e f i g u r e s . T h e c o n s t i t u t i o n of t h e e a g l e s ' d i e t c h a n g e s a s t h e y o u n g g r o w o l d e r . T h e n u m b e r a n d k i n d o f f o o d i t e m s b r o u g h t t o t h e n e s t d u r i n g t h e s u m m e r m o n t h s of 1962 a n d 1 9 6 3 a r e t a b u l a t e d i n T a b l e 2 0 . T h e m o n t h l y c h a n g e i n f i s h a n d m a m m a l i a n f o o d c o n s u m p t i o n d u r i n g t h e m o n t h of M a y , J u n e , J u l y a n d A u g u s t , 1962 a n d 1963 h a s b e e n a n a l y z e d w i t h a n " a n a l y s i s of v a r i a n c e " . " F " w a s f o u n d t o be s i g n i f i c a n t at t h e 0.05 p r o b a b i l i t y l e v e l ; S o u r c e D f SS M S F 1.64 N.S. 1.00 N.S. 4.28* at 0.05 M o n t h 3 2 1 4 . 7 1 . 3 -T y p e 1 20 20.0 M x T 3 558 186.0 E r r o r 8 347 4 3 . 4 T o t a l 15 1139 T a b l e 20. T h e m o n t h l y c o n s t i t u t i o n o f d i e t of b a l d e a g l e s o n S a n J u a n I s l a n d , b a s e d o n o b s e r v a t i o n s of f o o d i t e m s b r o u g h t t o t h e n e s t d u r i n g t h e s u m m e r s of 1962 a n d 1 9 6 3 . (1) N u m b e r of o b s e r v a t i o n s (2) A m o u n t of f o o d (no u n i t ) (3) P e r c e n t a g e v a l u e of i t e m s i n d i e t I t e m s M a y J u n e J u l y A u g . S e p t . (1) (2) (3) (1) (2) (3) (1) (2) (3) (1) (2) (3) (1) (2) (3) F i s h 2 4 38 7 4 . 5 7 15 36.6 3 3 6.4 5 5 4 5 . 5 39 61 40.6 R a b b i t 5 9 17.5 14 25 61.0 20 40 8 5 . 0 2 5 4 5 . 5 41 79 52.7 S e a l - - - - - 3 4 8.6 - 3 4 2.7 B i r d 1 3 6.0 1 1 2.4 - - - " ~ - 2 4 2.7 F r o g - - - - - - - 1 1 9-0 1 1 0.6 C r a b ' 1 1 2.0 - - - - - - - - - 1 1 0.6 T o t a l 31 51 22 41 26 47 8 11 87 150 133 T h e c o n s u m p t i o n o f f i s h p r e d o m i n a t e s d u r i n g t h e e a r l i e r p a r t o f t h e s e a s o n ; i n t h e l a t e r p h a s e m a i n l y r a b b i t i s c o n s u m e d . F i g u r e 16 i s t h e g r a p h i c a l r e p r e s e n t a t i o n of t h e a b o v e t r e n d a n d i s b a s e d o n t h e d a t a of T a b l e 19. W h i l e t h e b i r d s of N e s t A f e d o n m a m m a l i a n f o o d d u r i n g t h e e a r l y n e s t l i n g s t a g e t o a l a r g e r e x t e n t t h a n d i d t h e b i r d s o f N e s t B , t h e t r e n d i n c h a n g i n g . f r o m a p r e d o m i n a n t l y f i s h d i e t t o a p r e d o m i n a n t l y m a m m a l i a n d i e t w a s o b s e r v e d i n b o t h i n s t a n c e s . A s i m i l a r t e n d e n c y , a l t h o u g h l e s s p r o n o u n c e d , c a n be s e e n i n t h e d a t a of I m l e r a n d K a l m b a c h (1955) w h e n t r a n s f o r m e d i n t o a g r a p h ( F i g u r e 17); t h e d e c r e a s e i n f i s h c o n s u m p t i o n i s p r o n o u n c e d a s t h e y o u n g n e a r s t h e e n d of i t s n e s t l i f e w h i l e t h e c o n s u m p t i o n of o t h e r f o o d i t e m s s u d d e n l y i n c r e a s e s . 13.1.2. D e b r i s A n a l y s i s F o o d r e m a i n s c o l l e c t e d u n d e r n e a t h N e s t A o n T u r n I s l a n d i n 1962 a r e a n a l y z e d i n T a b l e 21 . T h e m e t h o d of c o l l e c t i n g t h e d e b r i s w a s s u c h t h a t b o n e s l y i n g i n c l o s e v i c i n i t y o f e a c h o t h e r w e r e c o l l e c t e d i n s e p a r a t e b a g s t o a v o i d d u p l i c a t i o n o f t h e s a m e i t e m i n t h e c a l c u l a t i o n of t h e d i e t . T h e p e r c e n t a g e s e x p r e s s e d t h e r e f o r e i n d i c a t e n u m b e r s r a t h e r t h a n v o l u m e s . T h e m o s t a b u n d a n t i t e m s i n t h e d e b r i s w e r e t h e r e m a i n s of r o c k f i s h ( S e b a s t o d e s s p e c i e s ) a n d l i n g c o d ( O p h i o d o n e l p n g a t u s G i r a r d ) . S k u l l s of g i a n t s c u l p i n ( S c o r p a e n i c h t h y s m a r m o r a t u s A y e e s ) , a r r o w t o o t h f l o u n d e r ( A t h e r e s t e s s t o m i a s J o r d a n a n d G i l b e r t ) a n d I r i s h l o r d ( H e m i l e p i d o t u s h e m i l e p i d o t u s T i l e s i u s ) w e r e a l s o f o u n d . 134 F ig . 16 The monthly change in fish and rabbit consumption during the years of 1962 and 1963 on San Juan Island. 100 90 F i g . 17 T h e m o n t h l y c h a n g e i n d i e t of b a l d e a g l e s i n A l a s k a . ( A f t e r I m l e r a n d K a l m b a c h , 1955) U l 136 T a b l e 21 . The c o n s t i t u t i o n of diet of b a l d e a g l e s on San Juan I s l a n d , b a s e d on a n a l y s i s of d e b r i s c o l l e c t e d u n d e r n e a t h the nest t r e e on T u r n I s l a n d . O c c u r r e n c e F o o d I t e m s N u m b e r P e r c e n t F i s h r o c k f i s h (Sebastodes s p e c i e s ) 17 l i n g c o d (Ophiodon elongatus G i r a r d ) 8 giant s c u l p i n ( S c o r p a e n i c h t h y s m a r m o r a t u s A y r e s ) 3 a r r o w t o o t h f l o u n d e r ( A t h e r e s t h e s s t o m i a s J o r d a n and G i l b e r t ) 2 r e d I r i s h l o r d ( H e m i l e p i d o t u s h e m i l e p i d o t u s T i l e s i u s ) 1 T o t a l 31 50.8 B i r d s G u l l ( L a r u s s p e c i e s ) 2 s u r f s c o t e r ( M e l a n i t t a p e r s p i c i l l a t a ) 2 C a l i f o r n i a m u r r e ( U r i a aalgae) .2 U n i d e n t i f i e d 11 T o t a l 17 27.9 M a m m a l s R a b b i t ( O r y c t o l a g u s c u n i c u l u s L.) 13 21 . 3 137 The b i r d r e m a i n s i n c l u d e d w i n g s , l e g s and s k u l l s of g u l l s ( L a r u s s p e c i e s ) , s u r f s c o t e r s ( M e l a n i t t a per s p i c i l l a t a ) and C a l i f o r n i a m u r r e ( U r i a a a l g a e ) . S k e l e t o n r e m a i n s of s e v e r a l other b i r d s w e r e a l s o found; h o w e v e r , t h e s e b i r d s c o u l d not be i d e n t i f i e d . R a b b i t ( O r y c t o l a g u s c u n i c u l u s ) r e m a i n s w e r e abundant. S e v e r a l s k u l l s , p a r t s of the s k e l e t o n and t o r n p i e c e s of hide w e r e p r e s e n t . The s k i n s , however , were, excluded, f r o m the counts a s . t h e i r c o n d i t i o n i n d i c a t e d that they w e r e p i c k e d up as r e m a i n s of r a b b i t s skinned-by h u n t e r s . The base of N e s t A t r e e on T u r n I s l a n d was v i s i t e d again i n 1963; h o w e v e r , no new food r e m a i n s w e r e found. No fo o d r e m a i n s w e r e found i n the i m m e d i a t e a r e a s u r r o u n d i n g the base of N e s t B t r e e i n 1962 and 1963. The d e b r i s c o l l e c t e d u n d e r n e a t h the T u r n I s l a n d n e s t i s l i k e l y an a c c u m u l a t i o n of s e v e r a l y e a r s ' food r e m a i n s . The p e r c e n t a g e s f i g u r e s of T a b l e 19 and 20 a r e p l o t t e d i n F i g u r e 18, i n d i c a t i n g the p o s s i b l e r e s u l t s i n c a l c u l a t i o n of the d i e t , w h i c h v a r i e s a c c o r d i n g to the method by w h i c h the data i s obtained. W h e r e a s the data of the two t a b l e s cannot be c o m p a r e d s i n c e T a b l e 19 te r e p r e s e n t a t i v e only f o r the food c o n s u m e d d u r i n g the b r e e d i n g season and T a b l e 21 i s an i n d i c a t i o n of the y e a r a r o u n d diet; h o w e v e r , they s e r v e as a means to -demonstrate the v a r i e t y of r e s u l t s p o s s i b l e when c a l c u l a t i n g the diet by / e m p l o y i n g d i f f e r e n t methods of c o l l e c t i n g data. The d e t a i l e d a n a l y s i s of d e b r i s c o l l e c t e d underneath N e s t A i s p r e s e n t e d i n A p p e n d i x I V . 138 100 r D i r e c t o b s e r v a t i o n D e b r i s a n a l y s i s 80 -.2 60 -3.1 I t e m s F i s h B i r d M a m m a l O t h e r Fig. ' ; 18 F o o d h a b i t s of b a l d e a g l e s o n S a n J u a n I s l a n d . C o m p a r i s o n b e t w e e n d a t a o b t a i n e d b y d i r e c t o b s e r v a t i o n a n d b y a n a l y s i s of d e b r i s c o l l e c t e d u n d e r n e a t h t h e T u r n I s l a n d N e s t . 139 13.2 S o u r c e s of F o o d 13.2.1. M a m m a l s The r e a s o n f o r the eagles' e x t e n s i v e c o n s u m p t i o n of food of m a m m a l i a n o r i g i n on San Juan I s l a n d i s the abundance of r a b b i t s . R a b b i t s a r e p i c k e d up as c a r r i o n f r o m r o a d s i d e s a n d . f i e l d s . No r a b b i t k i l l s by the eagles w e r e ever o b s e r v e d . R a b b i t s showed no f e a r t o w a r d s the e a g l e s even when the b i r d s p e r c h e d on fence p o s t s 10 to 15 y a r d s away. It a p p e a r s that the a v a i l a b i l i t y of r a b b i t c a r r i o n accounts f o r the eagle's l a c k of i n t e r e s t i n the l i v e r a b b i t s . The abundance of c a r c a s s e s i s due to the r a b b i t s ' h i g h m o r a l i t y t h r o u g h c o l l i s i o n w i t h a u t o m o b i l e s and to the s t r o n g hunting p r e s s u r e that i s e x e r t e d on the r a b b i t p o p u l a t i o n throughout the y e a r . A l a r g e r number of r a b b i t s a r e k i l l e d d u r i n g the s u m m e r months due to the i n c r e a s e d t o u r i s t t r a f f i c and a p o p u l a t i o n c o n t a i n i n g many young a n i m a l s . A n e s t i m a t e d 450 r a b b i t s a r e k i l l e d d a i l y on the San J u a n Island, r o a d s d u r i n g the s u m m e r . (Appendix V ) . S i m i l a r l y , r a b b i t .carcas.ae.s-.are a l so abundant i n the ' f i e l d s , w h i c h a r e u n r e t r i e v e d a n i m a l s k i l l e d or wounded by h u n t e r s . M a n y r a b b i t s a r e a l s o k i l l e d by the h a y - c u t t i n g m a c h i n e s i n l a t e M a y and e a r l y June when the h a y - f i e l d s a r e h a r v e s t e d . T h e s e f r e s h l y m owed f i e l d s a t t r a c t e a g l e s as w e l l as c r o w s and r e d - t a i l e d hawks. Up to f o u r m a t u r e eagle s c o u l d be seen at t i m e s on a f i e l d 5 a c r e s i n a r e a . W i t h i n one h a l f hour on one o c c a s i o n , the f e m a l e p a r e n t of N e s t A brought two r a b b i t s to 140 to the n e s t f r o m a f i e l d mowed the day b e f o r e some 900 y a r d s away. In both i n s t a n c e s the b i r d h ad to f i g h t a f l o c k of c r o w s w h i c h p r e v i o u s l y had been f e e d i n g on the c a r r i o n ( F i g u r e 6b). M o s t of the r a b b i t s a r e k i l l e d d u r i n g the night when b l i n d e d by the g l a r e of the h e a d l i g h t s ; they a r e h i t by a u t o m o b i l e s . C o n s e q u e n t l y , r a b b i t c a r c a s s e s a r e m o s t abundant, on r o a d s i n the m o r n i n g . The c a r c a s s e s r a p i d l y d i s a p p e a r from.the r o a d s d u r i n g the day. O n l y a few f l a t t e n e d r e m a i n s w h i c h p r o b a b l y a r e no l o n g e r p a l a t a b l e to the b i r d s a r e found on the pavement by the a f t e r n o o n . The e a g l e s a r e not the o n l y b i r d s f e e d i n g on c a r - k i l l e d r a b b i t s . C r o w s , r a v e n s , r e d ^ t a i l e d hawks and t u r k e y v u l t u r e s along w i t h f e r a l h o u s e c a t s take p a r t i n c o n s u m i n g the c a r c a s s e s . T a b l e 22 shows the d i s a p p e a r a n c e of c a r - k i l l e d r a b b i t s b a s e d on counts of c a r c a s s e s on the r o a d made at the s t a r t and end of 12 hour p e r i o d s d u r i n g the s u m m e r months of 1963. Two r o u t e s of equal l e n g t h w e r e used: between F r i d a y H a r b o r and R o c h e H a r b o r , and between F r i d a y H a r b o r and L i m e k i l n L i g h t h o u s e . The two r o u t e s w e r e u s e d to i n d i c a t e d i f f e r e n c e s between the n o r t h e r n f o r e s t e d r e g i o n w i t h low r a b b i t p o p u l a t i o n and the souther open f i e l d s v i th h i g h r a b b i t o c c u r r e n c e . The r a t e of d i s a p p e a r a n c e b a s e d on the counts was found to be 20 p e r c e n t h i g h e r f o r the southern r o u t e : 10.8 c a b b i t s d i s a p p e a r e d i n the south a g a i n s t 8.4 r a b b i t s i n the n o r t h d u r i n g the 12 hour p e r i o d . These two means w e r e te s t e d ' w i t h " t t e s t " and " t " was s i g n i f i c a n t o n l y at 0.25 p r o b a b i l i t y l e v e l . W h i l e the s t a t i s t i c a l t e s t shows no s i g n i f i c a n t d i f f e r e n c e between the two v a l u e s at h i g h e r p r o b a b i l i t y l e v e l , i t i s b e l i e v e d on the 141 T a b l e 22. R a t e of d i s a p p e a r a n c e of c a r - k i l l e d r a b b i t s o n S a n J u a n I s l a n d . N u m b e r s of r a b b i t s c o u n t e d o n r o a d s at t h e b e g i n n i n g a n d e n d of t w e l v e h o u r p e r i o d s , d u r i n g t h e s u m m e r of 1963. ("d" i s n u m b e r of d i s a p p e a r e d c a r c a s s e s . ) N o r t h R o u t e S o u t h R o u t e 6 A M 6 P M d 6:30 A M 6:30 P M d M a y 25 15 3 12 11 1 10 M a y 29 8 7 1 7 1 6 J u n e 4 7 7 0 9 2 7 J u n e 18 23 3 20 18 3 15 J u n e 22 18 5 13 17 2 15 J u n e 26 12 2 10 : 5 0 5 J u n e 28 5 1 4 n 1 10 J u l y 1 1 5 1 4 13 2 11 J u l y 29 14 6 8 16 1 15 A u g . 7 20 8 12 14 0 14 A v e r a g e 12.7 4. 3 8.4 12.1 1. 3 10.8 142 basis of general observations that a difference between the disappearance rate of the two routes exists. A larger sample size possibly would have shown the difference more conclusively. These figures can provide only a rough comparison since there were feeding activities prior to the morning count which altered the count, also there were additional rabbits killed during the day before the afternoon count. The higher numbers of birds of prey, along with crows and ravens in the southern part of the island are responsible for the difference. A congregation of eagles around the fields occurs during lambing season in late February and early March. Some of the sheep-raising farmers of San Juan Island believe that eagles kill new-born lambs; however, the majority of them do not subscribe to such a belief. Nevertheless, early accounts of the habits of the bald eagle give an ample supply of eyewitnesses observing feats of the eagle such as carrying a lamb of its own weight for several miles (Bent, 1937, Oberholser, 1906). Later investigator s, however, did not give credit to such accounts. An eagle is capable of killing a lamb; however, to carry it is beyond its power. An eagle's weight-lifting capability varies with circumstances. Altitude, wind conditions and the birds' individual characteristics contribute to the weight-lifting capabilities. Sperry (in Arnold, 1954) found that an 11 pound golden eagle is unable to lift 5 1/4 pounds, while Walker and Walker (in Huey, 1962) claim that 8 pounds is beyond eagles' weight-lifting capacity. Huey (1962) considers that birds can carry a weight up to 21 percent of their body weight. 143 According to local information, eagles on San Juan Island fed readily on carcasses of lambs. Feeding on placentas was also reported. The cause of early mortality of lambs is most often exposure; however, at times birds, most often ravens, may be responsible for injuries that could result in the death of the young animal. In the early summer of 1962, a lamb was reported to be blinded by birds. Both eyes were pecked out at a very early age yet the lamb managed to feed normally and follow its mother by sound alone. Usually this kind of injury would have resulted in death. It was presumed that ravens were responsible for the injury since, in the case of an eagle attack, the lamb would not have survived. There was no instance of finding remains of sheep of any age underneath the nest trees, nor were sheep remains observed being brought into the nest at any time during the two summers the eagles were kept under observation. The skeleton of a full grown deer was found on the shore of Rocky Bay in 1963, immediately below Nest B. Any association between the death of the deer and the eagles of Nest B is unlikely. The carcass was probably washed ashore close to Nest B by chance. The carcass of a harbor seal was washed aihore not far from Turn Island in July, 1962. The parents and the already flying young of Nest A, along with two turkey vultures, attempted to feed on it. A considerable amount was consumed from the head region around the bullet hole, but the tough hide of the seal prevented the birds from tearing the rest of the body apart. After five days the carcass was washed away by the sea. 144 1 3 . 2 . 2 . F i s h F i s h c o n s t i t u t e a l a r g e p o r t i o n of t h e e a g l e ' s d i e t o n S a n J u a n I s l a n d . F i s h a r e p i c k e d up e i t h e r a l i v e ,or d e a d a n d f l o a t i n g f r o m t h e w a t e r s a r o u n d t h e n e s t . F i s h i n g a c t i v i t i e s w e r e o f t e n o b s e r v e d d u r i n g 1963 at R o c k y B a y . M o s t of t h e l i v e f i s h c a u g h t w e r e s m a l l , v a r y i n g b e t w e e n e s t i m a t e d w e i g h t s of one t o f i v e p o u n d s . F l o a t i n g d e a d f i s h w e r e u n d o u b t e d l y p i c k e d u p b y t h e e a g l e s i f s e e n . W h e n o b s e r v a t i o n i s m a d e f r o m a c o n s i d e r a b l e d i s t a n c e , t h e r e i s d i f f i c u l t y i n knovaaag w h e t h e r t h e f i s h i s d e a d o r a l i v e w h e n p i c k e d f r o m t h e w a t e r . T h e y o u n g e a g l e s a r e a l r e a d y f l y i n g w h e n s a l m o n f i s h i n g a n d c a n n i n g o p e r a t i o n s c o m m e n c e . A g r e a t a m o u n t of w a s t e i s d u m p e d i n t o t h e w a t e r s b y t h e c a n n e r y i n G r i f f i n B a y a n d t h e e a g l e s a l o n g w i t h t h e e v e r p r e s e n t g u l l s t a k e t h e i r s h a r e i n t h e f e a s t . E a g l e s a r e o f t e n s p o t t e d o n D i n n e r I s l a n d , s o u t h of t h e c a n n e r y ; h o w e v e r , no s i g h t i n g s w e r e r e c o r d e d i n t h e i m m e d i a t e v i c i n i t y of t h e c a n n e r y . T i d e s w a s h t h e f i s h w a s t e s f u r t h e r o f f s h o r e w h i c h m a k e s i t l i k e l y t h a t t h e e a g l e s u t i l i z e t h e m i n t h e m o r e o p e n w a t e r s . 1 3 . 2 . 3 . B i r d s B i r d s m a k e up a v e r y s m a l l p o r t i o n i n t h e e a g l e s ' d i e t o n S a n J u a n I s l a n d . R e m a i n s of o n l y t h r e e b i r d s w e r e o b s e r v e d b e i n g b r o u g h t i n t o t h e n e s t d u r i n g 1962 a n d 1963 a n d of t h e s e o n l y one c a p t u r e w a s s e e n . i I n t h e d e b r i s u n d e r t h e n e s t s , b i r d r e m a i n s w e r e r e p r e s e n t e d t o a l a r g e r e x t e n t . I t w a s p r e s u m e d t h a t m o r e b i r d s w e r e c a u g h t d u r i n g t h e w i n t e r s w h e n d i r e c t o b s e r v a t i o n s w e r e n o t c a r r i e d o u t . D u r i n g t h e e a r l y s p r i n g t h e 145 waters around the i s l a n d abound i n numbers of s c o t e r s , buffleheads and scaups along with c o r m o r a n t s , yet none of these b i r d s showed fear towards the eagles f l y i n g overhead. D u r i n g the winter months, some of these b i r d s would no doubt f a l l p r e y to the eagles. C rows a r e the greatest antagonists of eagles, although their r e m a i n s were not found i n the d e b r i s . C r ows caught i n t r a p s , intended for eagles, (see section 13.3) were left there as bait but were never m o l e s t e d by the eagles. R e m ains of crows and rave n s were found i n d e b r i s c o l l e c t e d by M u r i e (1940) and Imler and Kalmbach (1955) which i n d i c a t e s their v u l n e r a b i l i t y , but the s c a r c e r e c o r d of the i r r e m a i n s suggests that these species are most often able to elude the eagles' attack. 13.2.4. Other Items F o o d i t e m s other than mammalian, f i s h and avian i n o r i g i n seldom o c c u r r e d in the bald eagles' diet on San Juan Island. A n i t e m i d e n t i f i e d as a f r o g was p i c k e d up by the female parent of Nest A. f r o m the shore of a s m a l l pon^twhich was often v i s i t e d by the b i r d s during 1962. The eagle's manner of catching the f r o g was spectacular; a sudden dive sideways f r o m a low gliding flight after which the b i r d flew straight back to the nest with the p r e y . D u r i n g 1962, a c r a b was p i c k e d up f r o m thejf'shore of T u r n Island and taken to the nest. The eagle was f i r s t n o t i c e d while i t was on the ground making s e v e r a l attempts to secure a hold on the c r a b with one foot. The b i r d had di f f i c u l t y i n taking off as only one foot was us e d i n the ki c k - o f f p r o c e s s ; the other holding the c r a b was h e l d off the ground. 146 D r i e d g r a s s w a s s e e n b r o u g h t t o t h e n e s t i n 1962 a n d 1 9 6 3 . V e g e t a b l e m a t e r i a l w a s f o u n d b y I m l e r a n d K a l m b a c h (1955) i n t h e s t o m a c h s of A l a s k a n b a l d e a g l e s a n d i n p e l l e t s c o l l e c t e d o n t h e A t l a n t i c C o a s t b y W. B . T y l e r a n d F . R. S m i t h ( i n I m l e r a n d K a l m b a c h , 1 9 5 5 ) . I t i s b e l i e v e d , h o w e v e r , t h a t t h e v e g e t a b l e m a t t e r w a s i n g e s t e d b y c h a n c e w h i l e t h e e a g l e s c o n s u m e d s t o m a c h s of s o m e v e g e t a r i a n p r e y . F e e d i n g o n v e g e t a b l e m a t t e r w a s n o t o b s e r v e d i n c a s e s of t h e S a n J u a n I s l a n d b i r d s . 1 3 . 3 . B a i t i n g E x p e r i m e n t s E x p e r i m e n t s t o t r a p a n d m a r k e a g l e s w e r e c a r r i e d o u t d u r i n g t h e l a t t e r h a l f o f t h e s u m m e r i n 1962 a n d 1 9 6 3 . S i n g l e s p r i n g , V i c t o r N o . 1 t r a p s w e r e u s e d t o c a p t u r e b i r d s b y t h e i r t o e s . R a b b i t c a r r i o n w a s u s e d f o r b a i t . T h r e e a n d f o u r t r a p s w e r e p l a c e d a r o u n d a r a b b i t c a r c a s s . B o t h t h e b a i t a n d t r a p s w e r e a n c h o r e d b y s t a k e s d r i v e n i n t o t h e g r o u n d . T r a p - l i n e s w e r e s e t up at f o u r d i f f e r e n t l o c a t i o n s ( N o . 1 t o N o . 4 i n F i g u r e 19). T h i s m e t h o d p r o v e d u n s a t i s f a c t o r y i n c a p t u r i n g e a g l e s due t o t h e e x t r e m e w a r i n e s s o f t h e b i r d s . A t t h e b e g i n n i n g . o f t h e t r i a l s t h e r e w e r e d e f i n i t e s i g n s of e a g l e s f e e d i n g o n t h e b a i t s . T h e j a w s of t h e t r a p s f o u n d s n a p p e d w e r e p r o b a b l y r e l e a s e d b y t h e e a g l e s b u t t h e t a p e -p a d d e d j a w s w e r e u n a b l e t o h o l d t h e m . W i t h t h e r e m o v a l of p a d d i n g s a n d b y c a m o u f l a g i n g t h e t r a p s , o t h e r s p e c i e s of b i r d s a s w e l l a s m a m m a l s w e r e 147 Point F ig . 19 The location of baits used to lure eagles and other carrion feeders. 148 easily captured; eagles no longer were using the baits. The participation of eagles in consuming the baits started again when heaps of dead rabbits were placed put as free baits. The participation of several other carrion-feeders was also recorded. After it was realized that these records could indicate the relative share of these other species in the consumption of the rabbit carcasses, more free baits were placed out in 1 963 on further locations (No. 5 to N o . 7 in Figure 19). Set number of rabbit carcasses were placed outand the participants' relative consumption was observed and recorded, the results of which are presented in Table 23. In 1962 the baiting experiments were started in July and were carried through August. In 1963 baits were regularly placed out during June, July and August. Five and ten carcasses were placed in one spot which numbers were kept constant by replacing disappeared carcasses and strongly decomposed ones. Two to three checks were made daily at the location of baits and the species present were recorded. Local residents also aided in obtaining information on the "participation of different species. Each sighting of a species counted as a unit, thus the percentages presented in Table 23 are based on numbers rather than volumes. Consequently, the result is biased since-large birds consumed a larger part of the bait than did the smaller birds. 1. During 1962, four birds (1 recte-tailed hawk and 3 crows) and six mammals (2 minks and 4 feral housecats) were captured by the traps. One bald eagle, seven crows and one raccoon were caught in 1963, The eagle, a juvenile, was captured at Trout Lake with traps set under water, using salmon heads as baits. The young eagle died shortly after it was released. The raccoon was captured under similar conditions at Sportsmans Lake. 149 Table 23. ( -The participation of different species of birds and mammals in consuming the rabbit carcasses, used to bait eagles during the summer of 1962 and 1963. P a r t i c i p a t i o n Species N u m b e r 1962 1963 P e r c e n t a g e 1962 1963 Bald eagle (Haliaeetus leucocephalus) 17 11.5 28.8 Red-tailed hawk (Buteo jamaicensis) 13.1 8.5 Turkey vulture (Cathartes aura) 11.5 11.8 Harrier (Circus cyaneus) 1.6 Northwestern crow (Corvus caurinus) 25 19 .41 . 0 32. 2 Raven (Corvus corax) 9.9 8.5 Mink (Mustela vison) Feral .housecat 2 5 3.3 8.2 10.2 Total 61 59 150 I t w a s f o u n d t h a t c r o w s c o n s u m e d m o s t of t h e r a b b i t c a r c a s s e s . E a g l e s p a r t i c i p a t e d m o r e i n 1 9 6 3 t h a n i n 1962 due t o t h e p l a c i n g of b a i t i n v i e w of N e s t B ( N o . 5 i n F i g u r e 19)- R a b b i t s w e r e a l w a y s p r o m p t l y c o n s u m e d at t h i s l o c a t i o n . P o s s i b l y r a c c o o n s , r e d f o x e s a n d d o g s p a r t i c i p a t e d i n c o n s u m i n g t h e b a i t m a i n l y at n i g h t ; h o w e v e r , n o r e c o r d s w e r e m a d e of t h e m . I n 1962 a t r a p l i n e w a s s e t up a t L o c a t i o n N o . 3 ( F i g u r e 19) w h i c h w a s i n t e n d e d f o r t h e e a g l e s of N e s t A o n T u r n I s l a n d . B y c o i n c i d e n c e , t h e t r a p w a s p l a c e d i n f r o n t o f a m i n k d e n w h e r e t w o y o u n g m i n k s w e r e c a u g h t . A f t e r w a r d s t h i s t r a p l i n e w a s r e m o v e d . F e r a l h o u s e c a t s a r e a b u n d a n t o n t h e i s l a n d a n d i t i s b e l i e v e d t h a t t h e i r p e r c e n t a g e p a r t i c i p a t i o n i s s o m e w h a t h i g h e r t h a n t h a t s h o w n i n T a b l e 2 3 . 1 3 . 4 . S u m m a r y a n d C o n c l u s i o n s I n f o r m a t i o n o n t h e f e e d i n g h a b i t s of b a l d e a g l e s o n S a n J u a n I s l a n d w a s o b t a i n e d b y m e a n s of d i r e c t o b s e r v a t i o n s of f o o d i t e m s t a k e n t o t h e n e s t b y t h e b i r d s a n d b y m e a n s of a n a l y z i n g t h e d e b r i s c o l l e c t e d u n d e r n e a t h t h e n e s t s . T h e d i e t o f t h e y o u n g c h a n g e d f r o m a p r e d o m i n a n t l y f i s h d i e t d u r i n g t h e e a r l y s t a g e of t h e i r n e s t l i f e t o a p r e d o m i n a n t l y m a m m a l i a n d i e t d u r i n g t h e l a t e r s t a g e . T h e d i e t o f t h e b a l d e a g l e s b a s e d o n d i r e c t o b s e r v a t i o n w a s f o u n d t o b e d i f f e r e n t t h a n t h e d i e t c a l c u l a t e d b y m e a n s of d e b r i s a n a l y s i s . R a b b i t s w e r e m a i n l y c o n s u m e d b y t h e e a g l e s . T h i s f o o d i t e m w a s o b t a i n e d a s c a r r i o n f r o m t h e r o a d s a n d f i e l d s w h e r e m a n y r a b b i t s 151 w e r e k i l l e d b y c a r s a n d b y f a r m i n g e q u i p m e n t . L o c a l r e s i d e n t s r e p o r t e d e a g l e s f e e d i n g o n c a r c a s s e s of l a m b s ; h o w e v e r , no e v i d e n c e of s h e e p r e m a i n s w e r e f o u n d i n t h e d e b r i s u n d e r n e a t h t h e n e s t s . E a g l e s w e r e o b s e r v e d t o c a t c h s m a l l f i s h . R e m a i n s of l a r g e f i s h f o u n d i n t h e d e b r i s w e r e p o s s i b l y p i c k e d u p a s c a r r i o n . N o e v i d e n c e of s a l m o n w a s f o u n d i n t h e d i e t of t h e e a g l e s o n S a n J u a n I s l a n d . B i r d s c o n s t i t u t e d a s m a l l p e r c e n t a g e of t h e e a g l e s ' d i e t . T h e l a r g e a m o u n t of r a b b i t c a r r i o n a v a i l a b l e o n t h e i s l a n d w a s c o n s u m e d b y s e v e r a l s p e c i e s of b i r d s . E a g l e s u t i l i z e d t h i s s o u r c e of f o o d t o a l a r g e e x t e n t a s i n d i c a t e d b y t h e i r p a r t i c i p a t i o n i n c o n s u m i n g r a b b i t c a r r i o n s p l a c e d out a s f r e e b a i t s . W h i l e T a b l e 21 i s f a r f r o m a t r u e r e p r e s e n t a t i o n of t h e y e a r a r o u n d d i e t of S a n J u a n I s l a n d e a g l e s , n e v e r t h e l e s s , i t p r o v i d e s i n f o r m a t i o n b y p r e s e n t i n g a s a m p l e o f f o o d i t e m s w h i c h w e r e c o n s u m e d t h r o u g h o u t t h e y e a r s t h e n e s t w a s i n u s e . T h e t e n d e n c y of t h e e a g l e s t o t e a r t h e i r l a r g e r p r e y a n d t a k e o n l y p a r t s i n t o t h e n e s t i s p a r t l y r e s p o n s i b l e f o r t h e d i f f e r e n c e s i n t h e d a t a of T a b l e 19 a n d T a b l e 21 . F u r t h e r m o r e , f i s h c a u g h t i n t h e w a t e r a r e a l w a y s t a k e n w h o l e a n d t o r n up i n t h e n e s t , l e a v i n g a l l r e m a i n s i n t h e v i c i n i t y , t h u s l a r g e l y e x a g g e r a t i n g t h e p r o p o r t i o n of f i s h i n t h e d i e t . T a b l e 19 p r e s e n t s d a t a o n f e e d i n g h a b i t s d u r i n g t h e b r e e d i n g s e a s o n , c o n s e q u e n t l y i t p r e s e n t s t h e d i e t of t h e g r o w i n g y o u n g . R a b b i t c a r r i o n i s f e d t o t h e y o u n g d u r i n g t h e s e c o n d h a l f of t h e i r n e s t l i f e ; a k i n d of food" item t h a t t h e y o u n g a r e m o s t l i k e l y t o 152 e n c o u n t e r o n c e t h e p a r e n t - o f f s p r i n g r e l a t i o n s h i p c e a s e s . T h e a l t e r a t i o n i n f e e d i n g h a b i t s s h o w m i n F i g u r e 16 c a n n o t b e e x p l a i n e d b y t h e s e a s o n a l c h a n g e i n f o o d a v a i l a b i l i t y . W h i l e t h e r e i s a n a p p a r e n t i n c r e a s e i n t h e a b u n d a n c e of r o a d - k i l l e d r a b b i t s d u r i n g t h e s u m m e r , s u c h c a r r i o n i s a l s o a v a i l a b l e t h r o u g h o u t t h e y e a r . F i s h i s a v a i l a b l e t o t h e s a m e e x t e n t t h e y e a r a r o u n d ; w i t h a p o s s i b l e i n c r e a s e w h e n s a l m o n f i s h i n g s t a r t s i n t h e s e c o n d h a l f of t h e s u m m e r . N o r e m a i n s of s a l m o n , h o w e v e r , w e r e f o u n d i n t h e a n a l y s i s o f t h e d e b r i s c o l l e c t e d f r o m t h e b a s e of t h e T u r n I s l a n d n e s t t r e e . A d e f i n i t e p r e f e r e n c e f o r f i s h i s t h o u g h t t o e x i s t . O n s e v e r a l o c c a s i o n s d u r i n g t h e s u m m e r of 1 9 6 2 , f i s h a n d r a b b i t w e r e b r o u g h t t o t h e n e s t w i t h i n o n e h a l f h o u r . I n e v e r y i n s t a n c e t h e y o u n g a b a n d o n e d t h e r a b b i t f o r t h e f i s h . D u r i n g t h e e a r l y p a r t o f t h e n e s t l i n g p e r i o d w h e n t h e y o u n g w e r e f e d b y t h e p a r e n t s , t h e f e e d i n g a d u l t b e h a v e d s i m i l a r l y : w h e n f i s h w a s b r o u g h t t o t h e n e s t b y t h e m a t e , t h e r a b b i t w a s a b a n d o n e d a n d t h e t e a r i n g of t h e f i s h p r o c e e d e d . O u t s i d e t h e b r e e d i n g s e a s o n , t h e a d u l t b i r d s a r e l i k e l y t o h a v e f e e d i n g h a b i t s w h i c h r e s e m b l e t h e d a t a o f T a b l e 21 , w h i l e t h e y o u n g of t h e y e a r f e e d s t o a l a r g e r e x t e n t o n r a b b i t c a r r i o n . T h e s t o m a c h c o n t e n t s of one c a p t u r e d j u v e n i l e b a l d e a g l e c o n t a i n e d a g r e a t a m o u n t of r a b b i t h a i r , a f e w r a b b i t c l a w s a n d s o m e g r a s s . T h e c o n t e n t s of t h i s s t o m a c h a n d t h e n u m e r o u s o b s e r v a t i o n s of t h e i s l a n d ' s i n h a b i t a n t s of y o u n g e a g l e s f e e d i n g on d e a d r a b b i t s i n t h e f a l l , s u g g e s t t h a t t h e y o u n g e a g l e s a f t e r b r e a k i n g r e l a t i o n s h i p w i t h t h e p a r e n t s , f e e d a l m o s t e n t i r e l y o n r a b b i t c a r r i o n . T h e 153 f l y i n g a b i l i t y of t h e s e y o u n g b i r d s i s s t i l l l i m i t e d , t h e r e f o r e t h e t a s k of s e c u r i n g a f i s h out of t h e w a t e r m a y p r e s e n t t o o d i f f i c u l t a p r o b l e m f o r t h e m . F e e d i n g o n r a b b i t c a r c a s s e s r e q u i r e s n o g r e a t f l y i n g a b i l i t y . T h e b a l d e a g l e i s p r i m a r i l y a f i s h e a t e r i n t h e g r e a t e s t p a r t of i t s r a n g e . W h e r e a s t h e b i r d s s h o w a c e r t a i n p r e f e r e n c e f o r f i s h , t h e y w i l l n e v e r t h e l e s s f e e d on t h e m o s t a v a i l a b l e f o o d i t e m s . M u r i e (1940) f o u n d t h a t e a g l e s o n t h e A l e u t i a n I s l a n d s , A l a s k a , f e d m a i n l y o n s e a b i r d s , t h e m o s t a b u n d a n t m e m b e r s of t h e f a u n a . S i m i l a r l y o n S a n J u a n I s l a n d , t h e l o c a l e a g l e s f e d p r e d o m i n a n t l y o n r a b b i t c a r r i o n , t h e m o s t a b u n d a n t f o o d s o u r c e of t h a t a r e a . C h a p t e r V G E N E R A L C O N C L U S I O N S A N D S U M M A R Y 155 14. C O N C L U S I O N S It i s b e l i e v e d that b a l d e a g l e s w e r e m o r e abundant on San J u a n I s l a n d d u r i n g past y e a r s . B r e e d i n g a c t i v i t i e s w e r e o b s e r v e d d u r i n g 1962 and 1963 at 8 n e s t s out of the 13 b a l d eagle n e s t s on the i s l a n d ; the other 5 n e s t s w e r e not used. The number of unused n e s t s i n d i c a t e s that m o r e eagles w e r e u s i n g San Ju a n I s l a n d as a b r e e d i n g g r o u n d d u r i n g the pas t . The d e n s i t y of b r e e d i n g e a g l e s on San J u a n I s l a n d i s c o n s i d e r e d low i n l i g h t of eagle d e n s i t i e s r e p o r t e d i n A l a s k a and F l o r i d a . A c c o r d i n g to L o c k i e and R a t c l i f f e (1964), e a g l e s tend to e x h i b i t a t e r r i t o r i a l b e h a v i o r when d e n s i t i e s i n c r e a s e to a c e r t a i n p o i n t . T e r r i t o r i a l i t y p r e v e n t s a f u r t h e r i n c r e a s e i n n u m b e r s and thus a c t s as a s a f e g u a r d to e n s u r e food s u p p l i e s (Amadon, 1 964). " The low d e n s i t i e s on San Ju a n I s l a n d qannot be a t t r i b u t e d to c o m p e t i t i o n f o r n e s t i n g s i t e s npr to food s h o r t a g e . B r e e d i n g e a g l e s showed h o s t i l i t y t o w a r d s other b i r d s , i n c l u d i n g t h e i r own k i n d i n the v i c i n i t y of t h e i r nest; however , n e i g h b o u r i n g a c t i v e n e s t s a r e spa c e d so f a r apart that the b i r d s of these n e s t s do not come i n contact w i t h each other . In g e n e r a l , the a r e a s a v a i l a b l e f o r the occupants of a c t i v e n e s t s without i n t e r f e r e n c e f r o m the c l o s e s t n e i g h b o u r s i s over lTJjtirnes as l a r g e as the t e r r i t o r y s i z e r e q u i r e m e n t o f ±>ald e a g l e s , e s t i m a t e d by B r o l e y (1947). The low d e n s i t i e s cannot be a t t r i b u t e d to food shortage e i t h e r , i n l i g h t of the e v e r - p r e s e n t food s u p p l y i n the f o r m of r a b b i t c a r r i o n . The h i g h r a b b i t m o r t a l i t y on the i s l a n d p r o v i d e s a v i r t u a l l y i n e x h a u s t i b l e food supply f o r 156 t h e e a g l e s a s w e l l a s f o r o t h e r s p e c i e s of b i r d s . R a b b i t c a r r i o n i s f e d t o t h e e a g l e t s d u r i n g t h e l a t t e r p a r t of t h e i r n e s t r l i f e ; l i k e w i s e , t h e a d u l t s a l s o f e e d o n i t e x t e n s i v e l y . R a b b i t c a r r i o n i s a l s o t h e p r i m a r y s o u r c e o f f o o d f o r y o u n g e a g l e s i n t h e i r p o s t - f l e d g l i n g p e r i o d , w h e n t h e i r f l y i n g a b i l i t y i s s t i l l l i m i t e d . It a p p e a r s t h a t t h e o n l y m a j o r f a c t o r r e s p o n s i b l e f o r t h e l o w d e n s i t i e s o f e a g l e s o n S a n J u a n I s l a n d i s h u m a n i n t e r f e r e n c e . T h e f a i l u r e of t h e e a g l e s ' b r e e d i n g a c t i v i t i e s at N e s t A i n 1 9 6 3 , N e s t C i n 1962 a n d N e s t J i n 1 9 6 3 c a n be e x p l a i n e d o n l y b y t h e d i s t u r b a n c e c a u s e d b y h u m a n a c t i v i t i e s . I n a d d i t i o n t o h u m a n i n t e r f e r e n c e w h i c h d i s t u r b s t h e e a g l e ' s b r e e d i n g a c t i v i t i e s a n d t h e r e f o r e r e d u c e s t h e n u m b e r of y o u n g p r o d u c e d d u r i n g t h e b r e e d i n g s e a s o n , t h e i n d i s c r i m i n a t e k i l l i n g o f b a l d e a g l e s b y h u m a n s a l s o c o n t r i b u t e s t o t h e r e d u c t i o n of e a g l e n u m b e r s o n S a n J u a n I s l a n d . R a b b i t h u n t e r s f r e q u e n t t h e i s l a n d t h r o u g h o u t t h e y e a r a n d e a g l e s o f t e n f a l l v i c t i m to t h e i r s h o o t i n g . T h e i r a c t i o n i s d i f f i c u l t t o e x p l a i n s i n c e t h e s h o o t i n g o f a b i r d o f f e r s n o m a t e r i a l g a i n s , n o r d o e s i t a p p e a l t o t h e t r o p h y - c o n s c i o u s n e s s of s o m e of t h e h u n t e r s . T h e b a l d e a g l e , b e i n g a n a t i o n a l b i r d o f t h e U.S.A. , a p p r o a c h e s t h e s t a t u s of a s a c r e d . o b j e c t a n d k i l l i n g a b i r d i s c o n s i d e r e d a n u n p a t r i o t i c a c t . N e v e r t h e l e s s , e a g l e s a r e s t i l l s h o t at a n d f r e q u e n t l y k i l l e d b y h u n t e r s . T o u r i s t s w h o v i s i t t h e i s l a n d b y b o a t o f t e n c a r r y g u n s w h i c h t h e y u s e f o r t a r g e t s h o o t i n g . D u r i n g t h e s u m m e r of 1 9 6 2 , t o u r i s t s u s i n g t h e s h o r e s of T u r n I s l a n d f o r c a m p i n g w e r e o f t e n o b s e r v e d t o do s u c h s h o o t i n g . O n one o c c a s i o n t h e l o c a l p o l i c e f o r c e h a d t o b e c a l l e d t o s t o p t h e i r a c t i o n s w h e n t a r g e t p r a c t i c e e v o l v e d i n t o a c a r e l e s s s h o o t i n g at f l o a t i n g o b j e c t s i n 157 the w a t e r w i t h the s t r a y b u l l e t s approaching, r e s i d e n c e s on the opposing s h o r e . Such t o u r i s t s , no doubt, w i l l shoot at eagles w h i c h come to t h e i r s i g h t . In a d d i t i o n to the eagle m o r t a l i t y o c c a s i o n e d by the i n d i s c r i m i n a t e shooting of c e r t a i n r a b b i t hunter s and t o u r i s t s , a number of e a g l e s a r e k i l l e d y e a r l y by l o c a l r e s i d e n t s , m a i n l y s h e e p - r a i s i n g f a r m e r s who s t i l l h o l d the b e l i e f that e a g l e s k i l l n e w-born l a m b s . The m a j o r i t y of t h e m do not s u b s c r i b e to such a b e l i e f , but some w i l l not p a r t f r o m t h e i r c o n v i c t i o n and i n t e n d to p r o t e c t t h e i r s t o c k by the shooting of eagles w h i c h come c l o s e to t h e i r f a r m s . The 1940 B a l d E a g l e A c t , f o r b i d d i n g the k i l l i n g of e a g l e s , l e a v e s p r o v i s i o n s f o r such a c t i o n i n s i t u a t i o n s when one's m a t e r i a l c o n c e r n s ar e i n danger. Due to t h i s f a c t , the l o c a l c o n s e r v a t i o n o f f i c e r i s unable to e n f o r c e the-law s i n c e a f a r m e r who shoots an eagle a l w a y s can c l a i m that he has done so i n p r o t e c t i o n of h i s l i v e s t o c k . D u r i n g the p e r i o d of the study, one j u v e n i l e eagle was found dead of a shot-gun wound and four other dead eagle s (2,adults and 2 j u v e n i l e s ) w e r e r e p o r t e d by v a r i o u s l o c a l r e s i d e n t s . S e v e r a l other b i r d s may have been k i l l e d d u r i n g t h i s t i m e w h i c h m a k e s i t safe to a s s u m e that at l e a s t 3 e a g l e s a r e k i l l e d y e a r l y by v i s i t i n g h u n t e r s , t o u r i s t s a n d . l o c a l r e s i d e n t s . T h i s number c o n s t i t u t e s m o r e than 5 0 % of. the number of young p r o d u c e d y e a r l y and i s m o r e than 2 0 % of the a v e r a g e number of b a l d e a g l e s w h i c h a r e p r e s e n t throughout the y e a r on San J u a n I s l a n d . P o s s i b l y the g r e a t e s t f a c t o r i n the r e d u c t i o n of b a l d eagle n u m b e r s on San Juan I s l a n d i s the f a s t r a t e of r e a l estate d evelopments 158 on the s e a s h o r e . The San Juan I s l a n d group i s an a t t r a c t i v e a r e a f o r r e t i r e d p e r s o n s and due to sudden i n c r e a s e s i n r e a l estate p r i c e s f a r t h e r south on the c o a s t , t h i s , r e g i o n i s b e c o m i n g m o r e p o p u l a r . If the p r e s e n t t r e n d i n h o u s i n g developments c o n t i n u e s , the n e s t i n g s i t e s of b a l d e a g l e s on San J u a n . I s l a n d w i l l be d e s t r o y e d at a f a s t r a t e . The n e s t i n g f a i l u r e of the T u r n I s l a n d e a g l e s i n 1963 and the absence of the b i r d s f r o m the n e s t s i t e i n the s p r i n g of 1964 a r e b e l i e v e d to be due to the u p s u r g e i n h o u s i n g d e v elopments on the o p p o s i n g shore of San Juan I s l a n d . M o r e new houses w i l l l i k e l y be b u i l t i n t h i s l o c a t i o n s i n c e the a r e a i s not o v e r l y developed. S i n c e T u r n I s l a n d i s f e d e r a l l y owned, the i s l a n d i t s e l f i s safe f r o m r e a l estate developments; h o w e v e r , the i n c r e a s e d human a c t i v i t i e s and consequent n o i s e on the opposing shore 600 to 700 y a r d s away m a y cause the e a g l e s to a v o i d the i s l a n d . .The b i r d s w e r e found to be t o l e r a n t t o w a r d s human d i s t u r b a n c e d u r i n g 1962, t h e r e f o r e i t i s p o s s i b l e that the e a g l e s w i l l r e s u m e u s i n g the nest when the e x c e s s i v e n o i s e w h i c h a c c o m p a n i e s the c o n s t r u c t i o n s c e a s e s a f t e r a l l the i n t e n d e d houses a r e b u i l t . The f u t u r e of N e s t B at R o c k y Bay, the m o s t p r o d u c t i v e n e s t d u r i n g 1962 and 1963, i s l e s s p r o m i s i n g . The g e n e r a l a r e a a r o u n d the nest s i t e , p r e s e n t l y u n d e r d e v e l o p e d , i s c o n s i d e r e d to have a h i g h r e a l estate v a l u e . The b i r d s of t h i s nest w e r e i n t o l e r a n t t o w a r d s the p r e s e n c e of humans i n the v i c i n i t y of the n e s t i n 1962 and 1963. A n y f u t u r e a c t i v i t y i n the a r e a i n the f o r m of r o a d and house c o n s t r u c t i o n w i l l undoubtedly r e s u l t i n the eagles' abandonment of the n e s t . To save the n e s t , the 159 s u r r o u n d i n g a r e a , m e a s u r i n g a m i n i m u m of 300 y a r d s i n a l l d i r e c t i o n s f r o m the nest t r e e , s h o u l d be l e f t u n d i s t u r b e d . The p o s s i b i l i t y of such an endeavour, c o n s i d e r i n g the c o s t s i n v o l v e d , a p p e a r s r e m o t e . W i t h the e x c e p t i o n of N e s t _J, the s i t e s of other a c t i v e n e s t s a r e l i k e l y to r e m a i n u n d i s t u r b e d i n the n e a r f u t u r e . N e s t C i s l o c a t e d i n an a r e a w here l i t t l e human d i s t u r b a n c e i s l i k e l y to o c c u r . S i n c e the nest s i t e i s f a r t h e r away f r o m the s h o r e , i t i s o u t s i d e the sphere of r e a l estate i n t e r e s t s . The s u r r o u n d i n g a r e a . i s not u s a b l e f o r f a r m i n g because of the abundance of r o c k y o u t c r o p s . The f u t u r e of N e s t D a p p e a r s to be the m o s t p r o m i s i n g among a l l the a c t i v e n e s t s on the i s l a n d . The n e s t i s l o c a t e d i n a s t a t e -owned a r e a w h i c h belongs to the F r i d a y H a r b o r O c e a n o g r a p h i c L a b o r a t o r i e s and i s i n t e n d e d to be kept i n i t s n a t u r a l state. N e s t s K and M a r e s i t u a t e d on the s h o r e of F a l s e B a y i n an a r e a w h i c h i s made u n a t t r a c t i v e f o r r e a l estate development by the unpleasant odor of the bay when i t i s t o t a l l y e x p o s e d at low t i d e s . H owever, a f u r t h e r a g r i c u l t u r a l development of the a r e a i s p o s s i b l e . N e s t L , l o c a t e d on the n o r t h w e s t s i d e of H e n r y I s l a n d i s l i k e l y to r e m a i n f r e e f r o m human d i s t u r b a n c e . The w e s t side of the i s l a n d i s steep and i t f a c e s the open w a t e r s of H a r o S t r a i t , w h i c h m a k e s the i s l a n d a l m o s t i n a c c e s s i b l e to boats. Due to these f a c t o r s and to the l a c k of r o a d s , t h e r e i s no r e a l estate development on the w e s t e r n s h o r e of the i s l a n d . The g e n e r a l c o n c l u s i o n i s that due to the r e c e n t u p s u r g e i n r e a l estate developments and to the e x p e c t e d c o n t i n u a t i o n of such 160 d e v e l o p m e n t s , t h e b a l d e a g l e p o p u l a t i o n of S a n J u a n I s l a n d w i l l p r o b a b l y b e r e d u c e d i n f u t u r e y e a r s . S i n c e m o s t of t h e w a t e r f r o n t a r e a s a r e p r i v a t e l y o w n e d , t h e p r e s e r v a t i o n o f n e s t s i t e s a s w i l d l i f e r e f u g e s i s u n l i k e l y . T h i s i s a n i l l u s t r a t i o n of t h e e c o n o m i c s of l a n d u s e w h e r e r e a l e s t a t e i n t e r e s t i s c o m p e t i n g a g a i n s t w i l d l i f e c o n s e r v a t i o n a n d i n t h e f u t u r e t h e l a t t e r l i k e l y w i l l l o s e . 161 15. S U M M A R Y 1 . The b r e e d i n g b i o l o g y and the f e e d i n g h a b i t s of the b a l d eagle ( H a l i a e e t u s l e u c o c e p h a l u s L.) w e r e s t u d i e d on San J u a n I s l a n d , W a s h i n g t o n d u r i n g 1962 and 1963. 2. The p u r p o s e of the study was to f i n d f a c t s w h i c h w o u l d r e l a t e to the g e n e r a l d e c l i n e of b a l d eagles throughout N o r t h A m e r i c a . 3. The m e thod of study i n v o l v e d d i r e c t o b s e r v a t i o n s c a r r i e d out f r o m a ground l o c a t i o n near the n e s t s and o b s e r v a t i o n s by means of a e r i a l s u r v e y s . 4. On the b a s i s of the s p a c i n g of n e s t s , i t was c o n c l u d e d that the d e n s i t y of b r e e d i n g e a g l e s on San Juan I s l a n d i s low. 5. The number of ea g l e s on San Juan I s l a n d changed throughout the y e a r . The h i g h e s t n u m b e r s w e r e p r e s e n t d u r i n g F e b r u a r y and the l o w e s t n u m b e r s d u r i n g O c t o b e r . . The change i n n u m b e r s of ea g l e s was c a u s e d by the f l u c t u a t i n g n u m b e r s of j u v e n i l e s . 6. B r e e d i n g b a l d e a g l e s showed h o s t i l i t y t o w a r d i n t r u d i n g adult and j u v e n i l e b a l d e a g l e s and t o w a r d man. The e a g l e s w e r e i n d i f f e r e n t t o w a r d h a r a s s m e n t by c r o w s and g u l l s . 7 . B r e e d i n g eagles a p p e a r e d by t h e i r nest i n J a n u a r y and n e s t - r e p a i r a c t i v i t i e s w e r e o b s e r v e d i n F e b r u a r y . The c h r o n o l o g y of b r e e d i n g a c t i v i t i e s was as f o l l o w s : e g g - l a y i n g between M a r c h 4 and 10, h a t c h i n g between A p r i l 8 and 14, the young's f i r s t d e p a r t u r e f r o m the nest between J u l y 1 and 10. 162 8. The young w e r e c l o s e l y g u a r d e d by the p a r e n t s d u r i n g the f i r s t f i v e w eeks of t h e i r l i f e . P a r e n t a l at t e n t i o n m a r k e d l y d e c r e a s e d after the s t a r t of the young's w i n g e x e r c i s e s at the age of eight to nine w e eks. The f e m a l e p a r e n t guarded-the n e s t to a l a r g e r extent than d i d the m a l e p a r e n t . 9. No a p p r e c i a b l e change was o b s e r v e d i n the amount of f o o d s u p p l i e d to the young throughout t h e i r n e s t l i f e . B o t h m a l e and f e m a l e p a r e n t s took an e q u a l s h a r e i n b r i n g i n g food to the n e s t . The young of the same nest d i d not appear to s u f f e r m a l t r e a t m e n t f r o m each other or f r o m the p a r e n t s . 10. F e e d i n g h a b i t s w e r e s t u d i e d by means of d i r e c t o b s e r v a t i o n of food i t e m s brought to the n e s t and by a n a l y s i s of d e b r i s found underneath the n e s t . 11 . R a b b i t was c o n s u m e d to the l a r g e s t extent. R a b b i t was p i c k e d up by the b i r d s as c a r r i o n . R a b b i t c a r r i o n was. the m o s t abundant f o o d i t e m on San Juan I s l a n d . 12. F e e d i n g h a b i t s a l t e r e d d u r i n g the b r e e d i n g season f r o m a p r e d o m i n a n t l y f i s h diet d u r i n g the f i r s t f i v e w e eks of the young's l i f e , to p r e d o m i n a n t l y m a m m a l i a n di e t t h e r e a f t e r . R a b b i t c a r r i o n was the p r i m a r y s o u r c e of f o o d f o r young eagl e s i n t h e i r p o s t - n e s t l i n g p e r i o d . 13. The number of b a l d e a g l e s on San J u a n I s l a n d c a n be e x p e c t e d to d e c r e a s e i n f u t u r e y e a r s due to the d e s t r u c t i o n of s u i t a b l e b r e e d i n g a r e a s by r e a l estate, d e v e l o p m e n t s . A P P E N D I C E S The m o n t h l y m a x i m u m , m i n i m u m and a v e r a g e t e m p e r a t u r e s on San J u a n I s l a n d f o r the y e a r s of 1962 and 1963 (in F°). (Obtained f r o m F. D e a r b o r n , F r i d a y H a r b o r , Washington.) Y e a r J a n . F e b . M a r c h A p r i l M a y June J u l y Aug. Sept. Oct. Nov. Dec. Max. 56 58 66 71 68 80 85 80 83 64 58 54 1962 M i n . 38 22 2 9 37 36 42 45 48 42 42 36 37 A v g . 47.4 43.4 44.7 50.0 53.5 57.3 60.2 60.4 59-0 52.9 48.1 42.2 Max. 52 62 60 70 90 84 83 85 81 66 55 48 1963 M i n . 15 31 32 38 38 44 48 49 45 38 2 9 30 A v g . 36.6 47.7 45.5 51.1 56.9 59-2 60.9 61.8 60.6 52.8 46.2 41.1 T h e m o n t h l y v a r i a t i o n s i n r a i n f a l l o n S a n J u a n I s l a n d f o r t h e y e a r s of 1962 a n d 1 9 6 3 ( i n i n c h e s ) . O b t a i n e d f r o m F . D e a r b o r n , F r i d a y H a r b o r , W a s h i n g t o n . Y e a r J a n . F e b . M a r c h A p r i l M a y J u n e J u l y A u g . S e p t . O c t . N o v . D e c . T o t a l 1962 1.07 0.88 1.51 0.85 0.86 0.45 0.17 1.64 0.44 1.34 4.33 2.78 1 6 . 4 4 1 9 6 3 0.79 1.83 0.44 0.93 0.30 0.66 1.07 0.30 1.51 4.06 3.58 0.71 16.18 166 A p p e n d i x III L i s t of B i r d s of t h e S a n J u a n I s l a n d s S p e c i e s of b i r d s o b s e r v e d b y M i l l e r e t . a l . , (1935) * S p e c i e s o f b i r d s o b s e r v e d b y G o o d g e (1950) **• S p e c i e s of b i r d s o b s e r v e d b y M c M a n n a m a (1950) *** S p e c i e s of b i r d s o b s e r v e d b y R e t f a l v i (1963) 1. C o m m o n L o o n G a v i a i m m e r ( B r u n n i c h ) 2. A r c t i c L o o n G a v i a a r c t i c a L . 3. R e d - t h r o a t e d L o o n G a v i a s t e l l a t a P o n t o p p i d a n 4. R e d - n e c k e d G r e b e P o d i c e p s g r i s e g e n a B o d d a e r t 5. H o r n e d G r e b e P o d i c e p s a u r i t u s L . 6. W e s t e r n G r e b e A e c h m o p h o r u s o c c i d e n t a l i s L a w r e n c e 7. P i e d - b i l l e d G r e b e P o d i l y m b u s p o d i c e p s L . 8. S h o r t - t a i l e d A l b a t r o s s D i o m e d e a a l b a t r u s P a l l a s 9. S o o t y S h e a r w a t e r P u f f i n u s g r i s e u s G m e l i n 10. F o r k - t a i l e d P e t r e l * O c e a n o d r o m a f u r c a t a G m e l i n 11 . D o u b l e - c r e s t e d C o r m o r a n t P h a l a c r o c o r a x a u r i t u s L e s s o n 12. B r a n d t ' s C o r m o r a n t P h a l a c r o c o r a x p e n i c i l l a t u s B r a n d t 13. P e l a g i c C o r m o r a n t P h a l a c r o c o r e x p e l a g i c u s P a l l a s 14. G r e a t B l u e H e r o n A r d e a h e r o d i a s L . 15 , A m e r i c a n B i t t e r n ** B o t a u r u s l e n t i g i n o s u s R a c k e t t 16. C a n a d a G o o s e B r a n t a c a n a d e n s i s L . 17 . B r a n t B r a n t a b e r n i c l a L . 18 . B l a c k B r a n t B r a n t a n i g r i c a n s L a w r e n c e 19. S n o w G o o s e C h e n h y p e r b o r e a P a l l a s 2 0. M a l l a r d A n a s p l a t y r h y n c h o s L . 21 . G a d w a l l A n a s s t r e p e r a L . 22. B l u e - w i n g e d T e a l * A n a s d i s c o r s L . 2 3 . P i n t a i l A n a s a c u t a L . 24. G r e e n - w i n g e d T e a l A n a s c a r o l i n e n s i s G m e l i n 25. E u r o p e a n W i d g e o n M a r e c a p e n e l o p e L . 26. A m e r i c a n W i d g e o n M a r e c a a m e r i c a n a G m e l i n 27. C a n v a s b a c k A y t h y a v a l i s i n e r i a W i l s o n 28 . G r e a t e r S c o u p A y t h y a m a r i l a L . 29- C o m m o n G o l d e n e y e B u c e p h a l a c l a n g u l a L . 30. B a r r o w ' s G o l d e n e y e » B u c e p h a l a i s l a n d i c a G m e l i n 31 . B u f f l e h e . a d B u c e p h a l a a l b e o l a L . 32. O l d s q u a w C l a n g u l a h y e m a l i s L . 33. H a r l e q u i n D u c k H i s t r i o n i c u s h i s t r i o n i c u s L . 34. W h i t e - w i n g e d S c o t e r M e l a n i t t a d e g l a n d i B o n a p a r t e 167 35. Su r f S c o t e r M e l a n i t t a per s p i c i l l a t a L . 36. C o m m o n Sc o t e r O i d e m i a n i g r a L . 37 . Hooded M e r g a n s e r L o p h o d y t e s c u c u l l a t u s L . 38. C o m m o n M e r g a n s e r M e r g u s m e r g a n s e r L. 39. R e d - b r e a s t e d M e r g a n s e r M e r g u s s e r v a t o r L . 40. T u r k e y V u l t u r e C a t h a r t e s a u r a L . 41 . Goshawk A c c i p i t e r g e n f i l i s L. 42. Sharp shinned Hawk A c c i p i t e r s t r i a t u s V i e i l l o t 43. C o o p e r 1 s Hawk A c c i p i t e r c o o p e r i B o n a p a r t e 44. R e d - t a i l e d Hawk Buteo j a m a i c e n s i s G m e l i n 45. Rough-legged Hawk Buteo lagopus P o n t o p p i d a n 46. G o l d e n E a g l e A q u i l a c h r y s a e t o s L . 47. B a l d E a g l e H a l i a e e t u s l e u c o c e p h a l u s L. 48. M a r s h Hawk C i r c u s cyaneus L . 49- O s p r e y P a n d i o n h a l i g e t u s L . 50. P e r e g r i n e F a l c o n F a l c o p e r e g r i n u s T u n s t a l l 51V P i g e o n Hawk F a l c o c o l u m b a r i u s L . 52. S p a r r o w Hawk F a l c o s p a r v e r i u s L . 53. B l u e G r o u s e Dendragapus o b s c u r u s Say 54. R u f f e d G r o u s e B o n a s a u m b e l l u s L . 55. Bobwhite C o l i n u s v i r g i n i a n u s L. 56. C a l i f o r n i a Q u a i l L o p h o r t y x c a l i f o r n i c u s Shaw 57 . M o u n t a i n Q u a i l O r e o r t y x p i c t u s D ouglas 58. R i n g - n e c k e d P h e a s a n t P h a s i a n u s c o l c h i c u s L . 59- C h u k a r P a r t r i d g e * * * A l e c t o r i s g r a e c a M e i s n e r 60. G r e y P a r t r i d g e P e r d i x p e r d i x L . 61 . S a n d h i l l C r a n e G r u s c a n a d e n s i s L . 62. V i r g i n i a R a i l R a l l u s l i m i c o l a V i e i l l o t 63. A m e r i c a n Coot * F u l i c a a m e r i c a n a G m e l i n 64. B l a c k O y s t e r c a t c h e r Haematopus b a c h m a n i Audubon 65. S e m i p a l m a t e d P l o v e r C h a r a d r i u s s e m i p a l m a t u s B o n a p a r t e 66. K i l l d e e r C h a r a d r i u s v o c i f e r u s L . 67. A m e r i c a n G o l d e n P l o v e r P l u v i a l i s d o m i n i e a M u l l e r 68. B l a c k - b e l l i e d P l o v e r ** S q u a t a r o l a s q u a t a r o l a L . 69- S u r f b i r d A p h r i z a v i r g a t a G m e l i n 70. B l a c k T u r n s t o n e . A r e n a r i a m e l a n o c e p h a l a V i g o r s 71 . Ruddy T u r n s t o n e ** A r e n a r i a i n t e r p r e s L . 72. W h i m b r e l N u m a n i u s phaeopus L . 73. Spotted Sandpiper A c t i t i s m a c u l a r i a L . 74. W a n d e r i n g T a t t l e r ** H e t e r o s c e l u s i n c a n u m G m e l i n 75. G r e a t e r Y e l l o w - l e g s * Totanus m e l a n o l e u c u s G m e l i n 76. L e a s t Sandpiper E r o l i a m i n u t i l l a V i e i l l o t 77 . D u n l i n E r o l i a a l p i n a L. 78 . L o n g - b i l l e d D o w i t c h e r L i m n o d r o m u s s c o l o p a c e u s Say 79. S e m i p a l m a t e d Sandpiper E r e u n e t e s p u s i l l u s L . 168 8 0 . W e s t e r n S a n d p i p e r E r e u n e t e s m a u r i C a b a n i s 8 1 . S a n d e r l i n g C r o c e t h i a a l b a P a l l a s 8 2 . N o r t h e r n P h a l a r o p e L o b i p e s l o b a t u s L . 8 3 . P a r a s i t i c J a e g e r ** S t e r c o r a r i u s p a r a s i t i c u s L . 84. G l a u c o u s - w i n g e d G u l l L a r u s g l a u c e s c e n s TNTaumann 8 5 . W e s t e r n G u l l L a r u s o c c i d e n t a l i s A u d u b o n 8 6 . H e r r i n g G u l l L a r u s a r g e n t a t u s P o n t o p p i d a n 8 7 . C a l i f o r n i a G u l l L a r u s c a l i f o r n i c u s L a w r e n c e 8 8 . R i n g - b i l l e d G u l l ** L a r u s d e l a w a r e n s i s O r d 8 9 . M e w G u l l L a r u s . c a n u s L . 90. B o n a p a r t e ' s G u l l L a r u s P h i l a d e l p h i a ( O r d ) 91 • H e e r m a n n ' s G u l l L a r u s h e e r m a n n i C a s s i n 92. S a b i n e ' s G u l l * X e m a s a b i n i S a b i n e 93. C o m m o n T e r n S t e r n a h i r u n d o L . 94. C a s p i a n T e r n ** H y d r o p r o g n e c a s p i a P a l l a s 9 5 . C o m m o n M u r r e U r i a a a l g e P o n t o p p i d a n 96. P i g e o n G u i l l e m o t C e p p h u s c o l u m b a P a l l a s 97. M a r b l e d M u r r e l e t B r a c h y r a m p h u s m a r m o r a t u m G m e l i n 98. R h i n o c e r o s A u k l e t C e r o r h i n c a m o n o c e r a t a P a l l a s 9 9 . T u f t e d P u f f i n L u n d a c i r r h a t a P a l l a s 1 00. B a n d - t a i l e d P i g e o n C o l u m b a f a s c i a t a S a y 10 1 . B a r n O w l *** T y t o a l b a ( S c a p o l i ) 1 0 2 . S c r e e c h O w l O t u s a s i o L . 103 . G r e a t H o r n e d O w l B u b o v i r g i n i a n u s G m e l i n 104. S n o w y O w l N y c t e a s c a n d i a c a L . 105. P i g m y O w l G l a u c i d i u m g n o m a W a g l e r 106. S p e o t y t o c u n i c u l a r i a M o l i n a 107 . S a w - w h e t O w l A e g o l i u s a c a d i c u s G m e l i n 108 . C o m m o n N i g h t h a w k C h o r d e i l e s m i n o r F o r s t e r 109- R u f o u s H u m m i n g b i r d S e l a s p h o r u s r u f u s G m e l i n 110. B e l t e d K i n g f i s h e r M e g a c e r y l e a l c y o n L . I l l . Y e l l o w - s h a f t e d F l i c k e r C o l a p t e s a u r a t u s L . 112. R e d - s h a f t e d F l i c k e r C o l a p t e s c a f e r G m e l i n 1 1 3 . P i l e a t e d W o o d p e c k e r D r y o c o p u s p i l e a t u s L . 114. L e w i s ' W o o d p e c k e r A s y n d e s m u s l e w i s G r e y 1 1 5 . R e d - b r e a s t e d S a p s u c k e r S p h y r a p i c u s v a r i u s L . 116. 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N o r t h w e s t e r n C r o w 132. C h e s t n u t - b a c k e d C h i c k a d e e 1 3 3 . R e d - b r e a s t e d N u t h a t c h 134. B r o w n C r e e p e r 135. H o u s e W r e n 136. W i n t e r W r e n 137. B e w i c k ' s W r e n 138. L o n g - b i l l e d M a r s h W r e n 139. R o c k W r e n 140. R o b i n 141 . V a r i e d T h r u s h 142. H e r m i t T h r u s h 1 4 3 . S w a i n s o n ' s T h r u s h 144. W e s t e r n B l u e b i r d 1 4 5 . G o l d e n - c r o w n e d K i n g l e t 146. R u b y - c r o w n e d K i n g l e t 1 4 7 . W a t e r P i p i t 1 4 8 . C e d a r W a x w i n g 149- E u r o p e a n S t a r l i n g *** 1 5 0 . H u t t o n ' s V i r e o * 1 5 1 . S o l i t a r y V i r e o 1 5 2 . W a r b l i n g V i r e o 1 5 3 . O r a n g e - c r o w n e d W a r b l e r 154. Y e l l o w W a r b l e r 155. A u d u b o n ' s W a r b l e r 156. T o w n s e n d ' s W a r b l e r 1 5 7 . M a c G i l l i v r a y ' s W a r b l e r 1 5 8 . Y e l l o w t h r o a t 159- W i l s o n ' s W a r b l e r 1 6 0 . H o u s e S p a r r o w * 1 6 1 . W e s t e r n M e a d o w l a r k * 1 6 2 . R e d - w i n g e d B l a c k b i r d 1 6 3 . B r e w e r ' s B l a c k b i r d 164. B r o w n - h e a d e d C o w b i r d *** 1 6 5 . W e s t e r n T a n a g e r 166. B l a c k - h e a d e d G r o s b e a k *#* 167. P u r p l e F i n c h 1 68 . P i n e S i s k i n 169- A m e r i c a n G o l d f i n c h S t e l g i d o p t e r y x r u f i c o l l i s A u d u b o n H i r u n d o r u s t i c a L . P e t r o c h e l i d o n p y r r h o n a t a V i e i l l o t P r o g n e s u b i s L . C y a n o c i t t a s t e l l e r i G m e l i n C o r v u s c o r a x L . C o r v u s c a u r i n u s B a i r d P a r u s r u f e s c e n s T o w n s e n d S i t t a c a n a d e n s i s L . C e r t h i a f a m i l i a r i s L . T r o g l o d y t e s a e d o n V i e i l l o t T r o g l o d y t e s t r o g l o d y t e s L . T h r y o m a n e s b e w i c k i A u d u b o n T e l m a t o d y t e s p a l u s t r i s W i l s o n S a l p i n c t e s o b s o l e t u s S a y T u r d u s m i g r a t o r i u s L . I x o r e u s h a e v i u s G m e l i n H y l o c i c h l a g u t t a t a P a l l a s H y l o c i c h l a u s t u l a t a N u t t a l l S i a l i a m e x i c a n a S w a i n s o n R e g u l u s s a t r a p a L i c h t e n s t e i n R e g u l u s c a l e n d u l a L . A n t h u s s p i n o l e t t a L . B o m b y c i l l a c e d r o r u m V i e i l l o t S t u r n u s v u l g a r i s L . V i r e o h u t t o n i C a s s i n V i r e o s o l i t a r i u s W i l s o n V i r e o g i l v u s V i e i l l o t V e r m i v o r a c e l a t a S a y D e n d r o i c a p e t e c h i a L . D e n d r o i c a a u d u b o n i T o w n s e n d D e n d r o i c a t o w n s e n d i T o w n s e n d O p o r o r n i s t o l m i e i T o w n s e n d G e o t h l y p i c t r i c h a s L . W i l s o n i a p u s i l l a W i l s o n P a s s e r d o m e s t i c u s L . S t u r n e l l a n e g l e c t a A u d u b o n A g e l a i u s p h o e n i c e u s L . E u p h a g u s c y a n o c e p h a l u s N a g l e r M o l o t h r u s a t e r B o d d a e r t P i r a n g a L u d o v i c i a n a W i l s o n P h e u t i c u s m e l a n o c e p h a l u s S w a i n s o n C a r p o d a c u s p u r p u r e u s G m e l i n S p i n u s p i n u s W i l s o n S p i n u s t r i s t i s L . 170 1 7 0 . R e d C r o s s b i l l 1 7 1 . R u f o u s - s i d e d T o w h e e 172. S a v a n n a h S p a r r o w 173. V e s p e r S p a r r o w 174. O r e g o n J u n c o 175. C h i p p i n g S p a r r o w 176. W h i t e - c r o w n e d S p a r r o w 177. G o l d e n - c r o w n e d S p a r r o w 178. W h i t e - t h r o a t e d S p a r r o w 179. F o x S p a r r o w 1 8 0 . S o n g S p a r r o w L o x i a c u r v i r o s t r a L . P i p i l o e r y t h r o p h t h a l m u s L . P a s s e r c u l u s s a n d w i c h e n s i s G m e l i n P o o r c e t e s g r a m i n e u s G m e l i n J u n c o o r e g a n u s T o w n s e n d S p i z e l l a p a s s e r i n a B e c h s t e i n Z o n o t h r i c h i a l e u c o p h r y s F o r s t e r Z o n o t h r i c h i a a t r i c a p i l l a G m e l i n Z o n o t h r i c h i a a l b i c o l l i s G m e l i n P a s s e r e l l a i l i a c a M e r r e m M e l o s p i z o m e l o d i a W i l s o n 171 A p p e n d i x I V T h e d e t a i l e d a n a l y s i s of d e b r i s c o l l e c t e d f r o m t h e b a s e of N e s t A t r e e on T u r n I s l a n d i n 1 9 6 2 G r o u p s of f o o d r e m a i n s s c a t t e r e d u n d e r n e a t h t h e n e s t w e r e c o l l e c t e d i n t o s e p a r a t e p a p e r b a g s . T h e c o n t e n t s of e a c h b a g w e r e a n a l y z e d a s t o t h e n u m b e r a n d k i n d of f o o d i t e m s . T h e p a r t i a l r e m a i n s of a f o o d i t e m i n e a c h b a g w e r e c o u n t e d a s o n e u n i t . B a g 1 . F i s h B a g 2. F i s h B i r d R a b b i t 1 H e m i l e p i d o t u s h e m i l e p i d o t u s - s k u l l r o o f 1 O p h i o d o n e l o n g a t u s - s k u l l , j a w s , v e r t e b r a , p a r t s of s h o u l d e r g i r d l e 2 S e b a s t o d e s s p e c i e s - j a w s , p r e o p e r c u l a , H y o i d b o n e s , s h o u l d e r g i r d l e s 1 O p h i o d o n e l o n g a t u s - j a w s 1 L a r u s s p e c i e s - s y n s a c r u m , f e m u r , h u m e r u s , w i n g a s s e m b l y a n d f e a t h e r s 1 O r y c t o l a g u s c u n i c u l u s - h i n d f o o t Bag. 3. F i s h . 1 S e b a s t o d e s s p e c i e s - a r t i c u l a r b o n e B i r d 1 L a r u s s p e c i e s - s y n s a c r u m , w i n g a s s e m b l y - f e a t h e r s b r o w n w i t h l i g h t t i p s B a g 4 . F i s h 2 S e b a s t o d e s s p e c i e s - j a w s a n d o p e r c u l a r s e r i e s of one; l o w e r j a w of o t h e r 1 O p h i o d o n e l o n g a t u s - p r e m a x i l l a r y a n d m a x i l l a r y B i r d s 2 U n i d e n t i f i e d - one v e r y l a r g e s y n s a c r u m - o n e s k u l l a n d p a r t of k e e l , 2 l e g b o n e s R a b b i t 1 O r y c t o l a g u s c u n i c u l u s - h a l f of l o w e r j a w , f i v e v e r t e b r a e 172 B a g 5. B i r d 1 U n i d e n t i f i e d - w i n g a s s e m b l y w i t h l o n g b l a c k f e a t h e r s a n d p a r t of k e e l ; v e r y l a r g e B a g 6. B i r d s 2 U n i d e n t i f i e d - s y n s a c r u m , v e r t e b r a e , l e g b o n e s , p a r t of k e e l of s m a l l b i r d - k e e l , h u m e r i of l a r g e b i r d B a g 7. F i s h 3 S e b a s t o d e s s p e c i e s - 2 c o m p l e t e s e t s of j a w s , 1 d e n t a r y ; 2 p a i r o p e r c u l a r s , 2 p a i r a r t i c u l a r s , a n d 1 e x t r a ; 1 p a i r m a x i l l a r y , 2 i n d i v i d u a l p r e o p e r c u l a r s B i r d s 1 M e l a n i t t a p e r s p i c i l l a t a 1 U n i d e n t i f i e d - s k u l l , h u m e r u s , w i n g a s s e m b l y of s m a l l e r b i r d , b l a c k f e a t h e r s R a b b i t 1 O r y c t o l a g u s c u n i c u l u s - s k u l l B a g 8. F i s h 2 S e b a s t o d e s s p e c i e s - r i b s , d o r s a l s p i n e s a n d i n t e r n e u r a l s - r e a r h a l f s k u l l , j a w a n d p a l a t i n e s e r i e s , o p e r c u l a r s , p r e o p e r c u l a r s B a g 9.- B i r d 1 L a r u s s p e c i e s - l a r g e k e e l w i t h w h i t e f e a t h e r s ; h u m e r u s b l a c k w i t h w h i t e t i p s B a g . 1 0 . F i s h 1 O p h i o d o n e l o n g a t u s - l a r g e j a w s R a b b i t s 2 O r y c t o l a g u s c u n i c u l u s - s k u l l , v e r t e b r a e , p e l v i c g i r d l e of one - l o w e r j a w of a n o t h e r B a g 1 1 . F i s h 1 S e b a s t o d e s s p e c i e s B i r d 1 U n i d e n t i f i e d - s y n s a c r u m , h u m e r u s , l e g b o n e , a n d l a r g e b l a c k f e a t h e r s R a b b i t 1 O r y c t o l a g u s c u n i c u l u s - l o w e r j a w , v e r t e b r a e , p e l v i s , s a c r a l v e r t e b r a e B a g 12. F i s h 4 A t h e r e s t e s s t o m i a s (1) O p h i o d o n e l o n g a t u s (1) S e b a s t o d e s s p e c i e s (2) B a g 12. B i r d s ( C o n t ' d . ) R a b b i t 1 B a g 13. F i s h B a g .14. B i r d B a g .15. F i s h U n i d e n t i f i e d - 1 l a r g e s y n s a c r u m , k e e l - s m a l l e r k e e l , s y n s a c r u m , s k u l l , h u m e r u s O r y c t o l a g u s c u n i c u l u s - s k u l l , l e g b o n e s S e b a s t o d e s s p e c i e s - s k u l l , m a x i l l a r i e s , d e n t a r i e s a n d a r t i c u l a r s - d e n t a r y , o p e r c u l a r s , a n d a r t i c u l a r of a n o t h e r U n i d e n t i f i e d O p h i o d o n e l o n g a t u s - 2 s e t s of j a w s S e b a s t o d e s s p e c i e s - 1 s e t of j a w s ; 2 u n l i k e p r e o p e r c u l a r s , o p e r c u l a r s 1 s e t m a x i l l a r i e s B a g 16. F i s h B i r d 1 S e b a s t o d e s s p e c i e s R a b b i t 1 - 1 d e n t a r y , a r t i c u l a r , m a x i l l a r y , p r e o p e r c u l a r U r i a a a l g e - s k u l l w i t h b e a k , s y n s a c r u m , .wing O r y c t o l a g u s c u n i c u l u s - s k u l l " B a g . 17. B i r d B a g .18. F i s h B i r d R a b b i t 1 U r i a a a l g e - s k u l l w i t h b e a k , s y n s a c r u m , w i n g 1 O p h i o d o n e l o n g a t u s 1 A t h e r e s t e s s t o m i a s 1 S c o r p a e n i c h t h y s m a r m o r a t u s 1 S e b a s t o d e s s p e c i e s 1 C l a m s h e l l 1 M e l a n i t t a p e r s p i c i l l a t a 5 O r y c t o l a g u s c u n i c u l u s 174 A p p e n d i x V R a b b i t m o r t a l i t y t h r o u g h c o l l i s i o n w i t h a u t o m o b i l e s A p p r o x i m a t e l y 450 r a b b i t s a r e k i l l e d d a i l y o n t h e r o a d s of S a n J u a n I s l a n d b y m e a n s of c o l l i s i o n w i t h a u t o m o b i l e s . T o a r r i v e at t h i s f i g u r e , t h e f o l l o w i n g c a l c u l a t i o n w a s m a d e : N u m b e r of r a b b i t s k i l l e d p e r d a y = ( N u m b e r of r a b b i t s k i l l e d p e r r o a d m i l e p e r a u t o m o b i l e = X) t i m e s ( T o t a l l e n g t h of r o a d s = Y) t i m e s ( T o t a l n u m b e r of a u t o m o b i l e s = Z ) . A c o u n t w a s m a d e to d e t e r m i n e X. R o u t e s o n t h e n o r t h e r n a n d s o u t h e r n p a r t s of t h e i s l a n d w e r e u s e d t o c o u n t t h e n u m b e r of r a b b i t s • • . ! k i l l e d w h e n d r i v i n g w i t h a n a u t o m o b i l e (See F i g u r e 19 f o r r o u t e s ) . B o t h r o u t e s a r e p a v e d a n d a r e 10 m i l e s l o n g . S i n c e r a b b i t s a r e k i l l e d m o r e f r e q u e n t l y d u r i n g t h e n i g h t c o u n t s a l s o w e r e m a d e a f t e r d a r k . T h e n u m b e r of r a b b i t s k i l l e d d u r i n g t h e t r i a l s i s a s f o l l o w s : I n D a y l i g h t I n D a r k D a t e N o r t h S o u t h N o r t h S o u t h May- 25 1 _ 3 3 M a y 29 - 3 2 2 J u n e 4 2 1 1 3 J u n e 18 - 1 2 1 J u n e 22 - - 2 -J u n e 26 2 2 - 2 J u n e 28 1 2 1 2 J u l y 11 2 1 1 3 J u l y 29 1 2 3 1 A u g . 7 - 1 3 2 A v e r a g e 0.9 1 . 3 1.8 1.9 175 T h e n o r t h a n d s o u t h a v e r a g e f o r t h e d a y l i g h t h o u r s i s 1 . 1 r a b b i t s a n d 1 .85 r a b b i t s f o r d a r k . A t o t a l o f 2.95 r a b b i t s a r e k i l l e d b y a s i n g l e c a r o v e r a 24 h o u r p e r i o d o n a 10 m i l e l o n g r o u t e . 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