UBC Theses and Dissertations

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UBC Theses and Dissertations

Seasonal changes in the survival of the black-capped chickadee Smith, Susan M. 1965

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S E A S O N A L CHANGES I N THE S U R V I V A L OF THE B L A C K - C A P P E D C H I C K A D E E b y S U S A N M. S M I T H B . S c . , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1 9 6 3 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T OF THE R E Q U I R E M E N T S F O R THE D EGREE OF M A S T E R OF S C I E N C E i n t h e D e p a r t m e n t o f ZOOLOGY We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H C O L U M B I A S e p t e m b e r , 1 9 6 5 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 ree l y a v a i l a b l e for reference and study. I fur ther agree that per-mission for extensive copying of t h i s thes i s for scho la r l y purposes may be granted by the Head of my Department or by h i s representat ives* It is understood that copying or p u b l i -ca t ion of th 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 Date - i -ABSTRACT A population of Black-capped Chickadees (Parus  a t r i c a p i l l u s ) l i v i n g i n a favourable environment was colour-banded, and i t s s u r v i v a l was followed, to f i n d out what prevents continual increase i n i t s numbers. A weekly census of the population was made throughout the two years of the study. A l l nests were found and the young were banded before they flew. Every two weeks throughout both winters checks were also made on an unhanded population i n a control area one and a quarter miles from the main population. Nesting success was high i n both years, with 5.0 young per pair being fledged i n 1964 and 4.5 young per pair i n 19 65. Juvenile s u r v i v a l u n t i l family break-up was almost 100% i n both years; juvenile s u r v i v a l u n t i l September seemed to be high. The sur v i v a l rate of the adults was uneven: there were two periods when i t was lower than i t was during the res t of the year. The less sharply defined period occurred during the post-breeding moult of the adults. The more sharply defined period of two weeks or less was exactly correlated i n both years with a change i n behaviour from f l o c k i n g to t e r r i t o r i a l behaviour. With the exception of one unmated female i n each year, every b i r d which survived t h i s c r i t i c a l period remained to breed or attempt to breed; hence th i s change i n behaviour i n the spring evidently removed surplus birds from the area, and thus prevented continual increase i n the population. This behaviour may be the common factor that l i m i t s the breeding populations of other species with similar ecology. - i i i -T A B L E OF CONTENTS PAGE A B S T R A C T i T A B L E OF CONTENTS i i i L I S T OF T A B L E S i v L I S T OF F I G U R E S V ACKNOWLEDGEMENTS v i I N T R O D U C T I O N 1 STUDY A R E A 3 METHODS a ) B a n d s 6 b ) R e c o r d s 7 c ) C o n t r o l O b s e r v a t i o n s 7 d) N e s t b o x e s 7 e ) S u r v i v o r s h i p 8 R E S U L T S a ) N a t u r a l H i s t o r y 10 i ) E s t a b l i s h m e n t o f P a i r s 10 i i ) T e r r i t o r y F o r m a t i o n 10 b ) N u m e r i c a l R e s u l t s 13 i ) C l u t c h S i z e 13 i i ) F e r t i l i t y a n d H a t c h i n g S u c c e s s 13 i i i ) F l e d g i n g S u c c e s s 15 i v ) J u v e n i l e S u r v i v a l 15 v ) A d u l t S u r v i v a l 17 v i ) E x c e s s B i r d s D u r i n g B r e e d i n g 2 0 D I S C U S S I O N 2 1 C O N C L U S I O N S 2 8 L I T E R A T U R E C I T E D 2 9 - i v -T A B L E 1. L I S T OP T A B L E S N u m b e r o f a g g r e s s i v e e n c o u n t e r s o b s e r v e d i n t h e s p r i n g o n t h e s t u d y a r e a . PAGE 1 1 T A B L E 2 . N u m b e r o f a g g r e s s i v e e n c o u n t e r s o b s e r v e d i n t h e s p r i n g o n t h e c o n t r o l a r e a . 12 T A B L E 3 . F e r t i l i t y r a t e a n d h a t c h i n g s u c c e s s . 1 4 T A B L E 4. S u r v i v a l o f b a n d e d y o u n g o n t h e s t u d y a r e a f r o m t h e d a y o f l e a v i n g t h e n e s t . 1 6 T A B L E 5 . S u r v i v a l o f m a r k e d b i r d s o n t h e s t u d y a r e a f r o m 1 S e p t e m b e r . 18 - v -L I S T OF F I G U R E S F I G U R E 1 . F l o c k r a n g e s a n d b r e e d i n g t e r r i t o r i e s o n t h e s t u d y a r e a : 1 9 6 3 - 6 4 . PAGE 32 F I G U R E 2 . F l o c k r a n g e s a n d b r e e d i n g t e r r i t o r i e s o n t h e s t u d y a r e a : 1 9 6 4 - 6 5 . 3 3 F I G U R E 3. S u r v i v a l o f b a n d e d y o u n g o n t h e s t u d y a r e a f r o m t h e d a y o f f l e d g i n g . 3 4 F I G U R E 4. M i n i m u m s u r v i v a l r a t e s a n d 9 5 % c o n f i d e n c e i n t e r v a l s f o r e a c h t w o w e e k p e r i o d i n 1 9 6 3 - 6 4 . 3 5 F I G U R E 5 . M i n i m u m s u r v i v a l r a t e s a n d 9 5 % c o n f i d e n c e i n t e r v a l s f o r e a c h t w o w e e k p e r i o d i n 19 6 4 - 6 5 . 3 6 F I G U R E 6. S u r v i v a l o f m a r k e d b i r d s o n t h e s t u d y a r e a f r o m S e p t . 1 s t . 37 - v i -ACKNOWLEDGEMENTS I w i s h t o e x p r e s s my s i n c e r e a p p r e c i a t i o n t o D r . D. H. C h i t t y f o r h i s v a l u a b l e a d v i c e a n d e n c o u r a g e m e n t t h r o u g h o u t t h i s s t u d y . G r a t i t u d e i s a l s o e x p r e s s e d t o D r . P. A . D e h n e l a n d t o D r . I . M c T . C o w a n f o r t h e i r c r i t i c a l r e a d i n g o f t h e m a n u s c r i p t . I am v e r y g r a t e f u l t o M a r g a r e t S k i r r o w f o r h e r h e l p i n t h e f i e l d a n d w i t h t h e m a n u s c r i p t . T h e a s s i s t a n c e o f G a i l O ' H a g a n i s a l s o g r e a t l y a p p r e c i a t e d . T h i s s t u d y w a s a i d e d b y g r a n t s t o D r . C h i t t y f r o m t h e N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a . - 1 -I N T R O D U C T I O N T h i s s t u d y a t t e m p t s t o a n s w e r t h e f o l l o w i n g g e n e r a l q u e s t i o n : w h a t p r e v e n t s c o n t i n u a l i n c r e a s e i n a p o p u l a t i o n w h o s e e n v i r o n m e n t i s a p p a r e n t l y f a v o u r a b l e ? T o b e s u i t a b l e f o r a s t u d y o f t h i s s o r t , a p o p u l a t i o n m u s t b e l i v i n g i n a n e n v i r o n m e n t w h e r e l o s s e s c a u s e d b y p r e d a t i o n , d i s e a s e , f o o d s h o r t a g e a n d o t h e r a c c i d e n t s a r e l i k e l y t o b e m i n i m a l , f o r o n l y i n s u c h a f a v o u r a b l e e n v i r o n m e n t c a n s u r p l u s b i r d s o c c u r . A l s o , i t m u s t b e p o s s i b l e t o e s t i m a t e t h e p o p u l a t i o n a t f r e q u e n t i n t e r v a l s . B e c a u s e i t s e e m e d t o f u l f i l b o t h t h e s e r e q u i r e -m e n t s , I c h o s e a p o p u l a t i o n o f B l a c k - c a p p e d C h i c k a d e e s ( P a r u s a t r i c a p i l l u s L . ) l i v i n g i n a r e s i d e n t i a l a r e a a n d s u r r o u n d i n g w o o d s o n t h e U n i v e r s i t y E n d o w m e n t L a n d s . T h e p r o b l e m t h e n r e d u c e d i t s e l f t o f i n d i n g o u t w h e n s u r p l u s b i r d s d i s a p p e a r e d e a c h y e a r a n d w h a t f a c t o r s w e r e a s s o c i a t e d w i t h t h i s d i s a p p e a r a n c e . T h e B l a c k - c a p p e d C h i c k a d e e i s a h o l e - n e s t i n g p a s s e r i n e w i t h a f a i r l y l a r g e c l u t c h s i z e ( P e t e r s o n , 1 9 6 1 , g i v e s a r a n g e o f 4-9 e g g s ) . I t r e a c h e s m a t u r i t y a n d b r e e d s t h e f i r s t y e a r a f t e r h a t c h i n g . I n N o r t h A m e r i c a i t r a n g e s o v e r m o s t o f t h e c o n t i n e n t : I n B r i t i s h C o l u m b i a i t i s " r e s i d e n t t h r o u g h o u t t h e P r o v i n c e e x c e p t i n t h e G u l f I s l a n d s , C o a s t F o r e s t , Q u e e n C h a r l o t t e I s l a n d s a n d t h e A l p l a n d s - 2 -b i o t i c a r e a s " ( M u n r o a n d C o w a n , 1 9 4 7 ) . V a n c o u v e r i s t h u s n e i t h e r t h e m o s t n o r t h e r n n o r t h e m o s t s o u t h e r n e x t r e m e o f i t s r a n g e , a n d i t i s a n o n - m i g r a t o r y r e s i d e n t i n t h i s a r e a . L i k e m a n y o t h e r m e m b e r s o f . t h e g e n u s P a r u s , t h i s s p e c i e s i s s t r o n g l y t e r r i t o r i a l d u r i n g t h e b r e e d i n g s e a s o n , b u t s p e n d s t h e r e s t o f t h e y e a r i n f l o c k s , t h u s e x h i b i t i n g t w o d i s t i n c t s e a s o n a l m o d e s o f b e h a v i o u r t o w a r d o t h e r m e m b e r s o f t h e same s p e c i e s . T h e p r o j e c t w a s s t a r t e d i n 19 63 w i t h t h e h y p o t h e s i s t h a t t h e m o r t a l i t y r a t e i n a f a v o u r a b l e h a b i t a t i s n o t c o n s t a n t , i . e . t h e r e a r e c e r t a i n p e r i o d s d u r i n g t h e a n n u a l c y c l e w h e n s u d d e n d r o p s i n n u m b e r s o c c u r . T h e o b j e c t o f t h e s t u d y w a s t o i n v e s t i g a t e t h e c a u s e s o f t h e s e s u d d e n l o s s e s . A l t h o u g h t h e r e h a s b e e n m u c h w o r k o n t h e p o p u l a t i o n e c o l o g y o f t h e f a m i l y P a r i d a e , t h e r e i s n o a g r e e m e n t t h a t a n y o n e p r o c e s s d e t e r m i n e s t h e b r e e d i n g d e n s i t y o f t i t m i c e . T h e r e a r e ' a p p a r e n t l y t h r e e m a i n s c h o o l s o f t h o u g h t a s t o w h a t f a c t o r s h a v e t h e m o s t c o n t r o l o f t h e b r e e d i n g d e n s i t y o f t i t m i c e . G i b b ( 1 9 5 4 , 1 9 5 6 , I 9 6 0 , 1 9 6 3 ) c l a i m s t h a t w i n t e r f o o d s h o r t a g e i s t h e m a i n f a c t o r d e t e r m i n i n g t h e b r e e d i n g d e n s i t y . L a c k ( 1 9 5 7 , 1 9 5 8 ) , o r i g i n a l l y s u p p o r t i n g G i b b ' s h y p o t h e s i s , now a g r e e s w i t h P e r r i n s ( 1 9 6 3 ) , w h o w r i t e s t h a t i n t h e G r e a t T i t t h e s u r v i v a l o f t h e y o u n g i n l a t e s u m m e r o r a u t u m n , d e p e n d i n g o n t h e f o o d r e c e i v e d e a r l i e r , s e e m s t o b e t h e m o s t i m p o r t a n t f a c t o r a f f e c t i n g t h e b r e e d i n g d e n s i t y o f t h i s s p e c i e s . F i n a l l y , K l u y v e r & T i n b e r g e n ( 1 9 5 3 ) - 3 -c l a i m t h a t i n f a v o u r a b l e h a b i t a t s t h e b r e e d i n g d e n s i t y s e e m s t o b e a c o n s e q u e n c e o f t e r r i t o r i a l b e h a v i o u r , w i t h s u r p l u s b i r d s g o i n g i n t o t h e l e s s f a v o u r a b l e h a b i t a t s . T h e l a t t e r a u t h o r s a r e t h e f i r s t t o s u g g e s t t h a t s u r p l u s t i t m i c e a r e e l i m i n a t e d f r o m f a v o u r a b l e h a b i t a t s b y t e r r i t o r i a l b e h a v i o u r . H o w e v e r t h e y w e r e m o r e i n t e r e s t e d i n t h e i r p r o p o s e d " b u f f e r " m e c h a n i s m t h a n i n t h e e f f e c t o f t e r r i t o r i e s a s s u c h , a n d s o d i d n o t p u r s u e t h e i d e a t h a t b r e e d i n g d e n s i t y m i g h t b e r e g u l a t e d b y t e r r i t o r i a l b e h a v i o u r . I n e a c h c a s e t h e p o p u l a t i o n s s t u d i e d w e r e a t l e a s t p a r t i a l l y m i g r a t o r y , w h i c h n e c e s s a r i l y c o m p l i c a t e s t h e i n t e r p r e t a t i o n o f d a t a , a n d n o n e o f t h e o b s e r v a t i o n s i s s u f f i c i e n t l y d e t a i l e d t o r u l e o u t a l t e r n a t i v e e x p l a n a t i o n s . S T U D Y A R E A : T h e s t u d y a r e a c o n s i s t e d o f a p p r o x i m a t e l y 1 6 0 a c r e s a d j a c e n t t o t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a c a m p u s ( F i g s . 1 a n d 2 ) . T h e b o u n d a r i e s o f t h e a r e a w e r e d r a w n s o m e w h a t a r b i t r a r i l y , t o i n c l u d e a s m a n y f l o c k s a s c o u l d b e c e n s u s e d e a c h w e e k . T h e a r e a w a s p a r t o f a r e s i d e n t i a l a r e a , a n d i n c l u d e d s t r i p s o f w o o d s a l o n g t h e e a s t a n d w e s t s i d e s . A s t h e b o u n d a r i e s w e r e c h o s e n f r o m f l o c k r a n g e s , t h e y w e r e i n e f f e c t i s o l a t i n g a s l o n g a s t h e f l o c k s t r u c t u r e r e m a i n e d i n t a c t . B e y o n d t h e e a s t s i d e w a s t h e c a m p u s , a n d b e y o n d t h e s o u t h s i d e , a l a r g e o p e n p a r k ; b o t h t h e s e w e r e p h y s i c a l l y _ 4 -m o r e i s o l a t i n g t h a n t h e o t h e r t w o s i d e s . H o w e v e r , a s i n t e r - f l o c k e x c h a n g e o f i n d i v i d u a l s i n t h i s s t u d y w a s e x t r e m e l y r a r e , t h e b o u n d a r i e s w e r e c o n s i d e r e d t o b e q u i t e e f f e c t i v e . T h e r e w e r e m a n y m a t u r e s h a d e t r e e s i n t h e g a r d e n s t h r o u g h o u t t h e r e s i d e n t i a l p a r t o f t h e a r e a . N e s t s i t e s i n t h i s s e c t i o n w e r e i n D o g w o o d s ( C o r n u s n u t t a l l i ) m o s t f r e q u e n t l y , b u t a R e d A l d e r ( A l n u s r u b r a ) , a n o l d a p p l e t r e e , a n d e v e n a r o t t e n f e n c e p o s t w e r e u s e d . T h e w o o d s o n t h e e a s t a n d w e s t s i d e s o f t h e a r e a w e r e s e c o n d g r o w t h a n d h a d a c a n o p y c o m p o s e d o f r o u g h l y 8 5 % R e d A l d e r , w i t h some D o g w o o d , B i t t e r C h e r r y ( P r u n u s  e m a r c r i n a t a ) , C o t t o n w o o d ( P o p u l u s t r i c h o c a r p a ) , a n d a v e r y f e w 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 e i ) a n d R e d C e d a r ( T h u j a p l i c a t a ) . T h e u n d e r s t o r e y w a s c o m p o s e d o f S a l m o n -b e r r y a n d T h i m b l e b e r r y ( R u b u s s p e c t a b i l i s a n d R. p a r v i f l o r u s ) , R e d b e r r y E l d e r ( S a m b u c u s p u b e n s ) , S a l a a l ( G a u l t h e r i a s h a l l o n ) , T r a i l i n g B l a c k b e r r y ( R u b u s v i t i f o l i u s ) , a n d B r o o m ( C y t i s u s  s c o p a r i u s ) . R e d A l d e r w a s t h e o n l y t r e e u s e d a s a n a t u r a l n e s t s i t e b y c h i c k a d e e s i n t h e s t u d y w o o d s . To m a k e t h e a r e a a s f a v o u r a b l e a s p o s s i b l e , n e s t b o x e s w e r e p u t u p t h r o u g h o u t t h e a r e a a n d f e e d i n g s t a t i o n s w e r e m a i n t a i n e d d u r i n g t h e w i n t e r . T h u s t h e r e w a s a l w a y s a n e x c e s s o f f o o d a n d n e s t i n g s i t e s . S i n c e i t c o u l d a l w a y s b e a r g u e d t h a t t h i s p o p u l a t i o n w a s n o t l i v i n g u n d e r s u f f i c i e n t l y n a t u r a l c o n d i t i o n s , c o n t r o l o b s e r v a t i o n s w e r e made i n a n a t u r a l f o r e s t o n e a n d a q u a r t e r - 5 -m i l e s f r o m t h e m a i n s t u d y a r e a . T h e c a n o p y w a s 5 5 % d e c i d u o u s a n d 4 5 % c o n i f e r o u s , t h e m a j o r t r e e s b e i n g R e d A l d e r , B r o a d - l e a f e d M a p l e ( A c e r m a c r o p h v l l u m ) , D o u g l a s F i r , W e s t e r n H e m l o c k ( T s u g a h e t e r o p h y l l a ) , a n d R e d C e d a r . T h e u n d e r s t o r e y w a s m a i n l y R e d b e r r y E l d e r , T h i m b l e b e r r y a n d S a l m o n b e r r y . T h i s a r e a c o n t a i n e d m a n y o l d A l d e r s a n d M a p l e s , s o t h e r e w a s a g a i n a n e x c e s s o f n e s t s i t e s . T h e c o n t r o l a r e a w a s a p p r o x i m a t e l y t h e same s i z e a s t h e m a i n s t u d y a r e a , a n d e a c h w i n t e r s u p p o r t e d a t l e a s t t h r e e f l o c k s . E a c h f l o c k c o n t a i n e d 6-12 c h i c k a d e e s ; t h u s w h e n t h e f l o c k b r e a k - u p o c c u r r e d i n t h e s p r i n g , t h e d i f f e r e n c e w a s e a s i l y o b s e r v e d e v e n t h o u g h t h e b i r d s w e r e u n h a n d e d . - 6 -METHODS a ) B a n d s E a c h m a r k e d b i r d w a s g i v e n a n u m b e r e d a l u m i n u m b a n d s u p p l i e d b y t h e C a n a d i a n W i l d l i f e S e r v i c e , a n d f r o m o n e t o t h r e e c o l o u r e d s p l i t p l a s t i c b a n d s b o u g h t f r o m A . C. H u g h e s , M i d d l e s e x , E n g l a n d . S i x c o l o u r s w e r e u s e d : r e d , y e l l o w , g r e e n , b l u e , o r a n g e , a n d b l a c k . T h e s e w e r e d i s t i n g u i s h a b l e i n t h e f i e l d ; a n y m o r e c o l o u r s h a v e b e e n f o u n d i n o t h e r s t u d i e s t o b e c o n f u s i n g . E a c h i n d i v i d u a l m a r k e d i n t h e s t u d y h a d a d i f f e r e n t c o l o u r c o m b i n a t i o n . D u r i n g b o t h w i n t e r s c h i c k a d e e s w e r e c a p t u r e d w i t h m i s t n e s t s p l a c e d n e a r f e e d i n g s t a t i o n s . T h i s m e t h o d o f c a p t u r e w a s s u c c e s s f u l o n l y f r o m e a r l y N o v e m b e r t o t h e e n d o f F e b r u a r y , a s t h i s i s t h e o n l y p e r i o d w h e n c h i c k a d e e s c o m e r e g u l a r l y t o t h e f e e d i n g s t a t i o n s . A t f i r s t t h e y o u n g w e r e m a r k e d a t t h e n e s t a t 10 t o 1 4 d a y s o f a g e . L a t e r b r o o d s w e r e m a r k e d w h e n t h e y w e r e n e a r e r t o t e n d a y s o l d , b e c a u s e i t s e e m e d t h a t a t a n e a r l i e r a g e d i s t u r b a n c e w a s l e s s l i k e l y t o m a k e t h e n e s t l i n g s l e a v e t h e n e s t p r e m a t u r e l y . I n e a c h c a s e o n l y p a r t o f t h e b r o o d w a s r e m o v e d a t a n y o n e t i m e t o r e d u c e t h e p o s s i b i l i t y o f t h e a d u l t s ' d e s e r t i n g t h e n e s t . No d e s e r t i o n s o c c u r r e d d u r i n g t h e s t u d y a f t e r t h e y o u n g h a d b e e n b a n d e d . b ) R e c o r d s R e g u l a r c h e c k s o n t h e p o p u l a t i o n w e r e p o s s i b l e b e c a u s e t h e s t u d y a r e a w a s a d j a c e n t t o t h e c a m p u s . S i g h t r e c o r d s o f t h e p o p u l a t i o n w e r e made a t l e a s t o n c e w e e k l y t h r o u g h o u t t h e p r o j e c t . T h e p r e s e n c e a n d b e h a v i o u r o f e a c h m a r k e d i n d i v i d u a l w e r e r e c o r d e d , a s w e r e t h e l o c a l i t y a n d c o m p o s i t i o n o f t h e f l o c k . c ) C o n t r o l O b s e r v a t i o n s One w h o l e m o r n i n g ' s o b s e r v a t i o n s w e r e made e v e r y t w o w e e k s t h r o u g h t h e w i n t e r o n t h e c o n t r o l a r e a . E s t i m a t e s o f t h e n u m b e r s a n d c h e c k s o n t h e b e h a v i o u r o f i n d i v i d u a l s w e r e m a d e . H o w e v e r , a s t h e r e w e r e n o m a r k e d b i r d s i n t h i s a r e a , t h e s e e s t i m a t e s w e r e n o t a s a c c u r a t e a s t h o s e i n t h e m a i n s t u d y a r e a . d) N e s t b o x e s D u r i n g t h e s t u d y , 42 n e s t b o x e s w e r e p u t u p . O f t h e s e , 3 3 w e r e h u n g i n t h e b u i l t - u p p a r t o f t h e s t u d y a r e a d u r i n g t h e f i r s t y e a r , t h e r e m a i n i n g n i n e w e r e a d d e d i n t h e f i r s t w e e k o f M a r c h 1 9 6 5 i n t h e w o o d s a f t e r t h e f e l l i n g o f a n a r r o w s t r i p o f m a t u r e A l d e r s w h i c h h a d h a d f o u r n e s t s - 8 -i n 19 6 4 . A l l n e s t b o x e s w e r e h a l f - f i l l e d w i t h s a w d u s t . O t h e r w o r k e r s h a v e f o u n d t h a t t h i s m a k e s t h e m m o r e a c c e p t a b l e t o c h i c k a d e e s ( K l u i j v e r , 1 9 6 1 ; D r u r y , 1 9 5 8 ) , s i n c e t h i s s p e c i e s n o r m a l l y e x c a v a t e s i t s o w n n e s t h o l e i n s o f t w o o d . T h e b o x e s w e r e p l a c e d a t v a r y i n g h e i g h t s ( m o s t b e t w e e n s e v e n a n d f i f t e e n f e e t ) a n d f a c e d i n v a r y i n g d i r e c t i o n s ; a l l w e r e a t t a c h e d t o t h e m a i n t r u n k o f a t r e e a t l e a s t f o u r i n c h e s i n d i a m e t e r . e ) S u r v i v o r s h i p T h e s e d a t a a r e p r e s e n t e d i n t h e f o r m o f l x t a b l e s a c c o r d i n g t o t h e m e t h o d s d e s c r i b e d b y A n d r e w a r t h a a n d B i r c h ( 1 9 5 4 ) . A s t h e c o u n t s w e r e c o m p l e t e f o r b a n d e d y o u n g b e t w e e n t h e t i m e t h e y l e f t t h e n e s t a n d f a m i l y f l o c k b r e a k - u p , n o s p e c i a l p r o b l e m s a r o s e f o r j u v e n i l e s u r v i v a l . H o w e v e r , i n t h e c a s e o f t h e a d u l t s , some i n d i v i d u a l s w e r e m i s s e d i n a l m o s t e v e r y f o r t n i g h t . T h i s i n t r o d u c e s c e r t a i n d i f f i c u l t i e s i n a r r i v i n g a t a f i g u r e f o r t h e p r o b a b i l i t y o f s u r v i v i n g a g i v e n t i m e i n t e r v a l ( C h i t t y , 1 9 5 2 ) . T h e r e f o r e l x c u r v e s f o r t h e a d u l t s w e r e c o m p i l e d f r o m m i n i m u m s u r v i v a l r a t e s b a s e d o n t h e i n d i v i d u a l f o r t n i g h t l y s a m p l e s . I f t h e m i n i m u m s u r v i v a l r a t e s w e r e m u c h b e l o w t h e t r u e r a t e s , t h e a n n u a l s u r v i v a l r a t e o b t a i n e d b y t h i s m e t h o d w o u l d b e g r o s s l y b e l o w t h e t r u e f i g u r e . T h e r e f o r e t h e d a t a h a v e b e e n e x a m i n e d f o r s u c h a b i a s . F o r e x a m p l e , - 9 -o f 1 1 b i r d s o b s e r v e d i n t h e f i r s t p e r i o d o f t h e s e c o n d y e a r ( 1 9 6 4 - 6 5 ) , t w o w e r e k n o w n t o b e a l i v e a l m o s t a y e a r l a t e r -a n o b s e r v e d m i n i m u m s u r v i v a l r a t e o f 0 . 1 8 . T h e r a t e c a l c u l a t e d f r o m t h e i n d i v i d u a l s a m p l e s i s s l i g h t l y g r e a t e r t h a n t h i s ( 0 . 2 3 , T a b l e 5 ) . O t h e r i n t e r v a l s h a v e b e e n e x a m i n e d i n t h e same f a s h i o n , a n d a n y b i a s t h a t m a y b e p r e s e n t a p p e a r s t o b e c o n c e a l e d b y e r r o r s o f s a m p l i n g . - 10 -RESULTS a ) N a t u r a l H i s t o r y i ) E s t a b l i s h m e n t o f P a i r s . I n t h i s s t u d y a l l p a i r s w e r e f o r m e d b e t w e e n m e m b e r s o f t h e s a m e f l o c k , a l t h o u g h Odum ( 1 9 4 1 ) r e p o r t e d a t l e a s t t w o i n s t a n c e s i n w h i c h p a i r s w e r e f o r m e d b e t w e e n b i r d s f r o m d i f f e r e n t f l o c k s , w h e n e v e r b o t h m e m b e r s o f a n o l d p a i r s u r v i v e d t h e y e a r , t h e y r e m a t e d , h a v i n g s t a y e d t o g e t h e r a l l w i n t e r . i i ) T e r r i t o r y F o r m a t i o n . T h e r e w a s a p e r i o d i n t h e s p r i n g n o t e x c e e d i n g t w o w e e k s i n e a c h y e a r w h e n t h e c h a n g e f r o m f l o c k i n g t o t e r r i t o r i a l b e h a v i o u r o c c u r r e d . P r i o r t o t h i s p e r i o d , t h e b i r d s w e r e i n w i n t e r f l o c k s ( F i g s . 1 a n d 2 ) , a n d w e r e n o t o b s e r v e d f i g h t i n g e v e n w h e n t w o f l o c k s m e t . ( F i g h t s a t f e e d i n g s t a t i o n s a r e n o t i n c l u d e d h e r e . ) D u r i n g t h i s p e r i o d f l o c k m e m b e r s w h i c h h a d f e d q u i e t l y t o g e t h e r a l l w i n t e r w e r e f r e q u e n t l y s e e n f i g h t i n g , a n d a f t e r t h i s p e r i o d a l l t h e c h i c k a d e e s r e m a i n i n g o n t h e a r e a w e r e p a i r e d , a n d d e f e n d e d a t e r r i t o r y ( e x c e p t f o r u n m a t e d f e m a l e s w h i c h w e r e t o l e r a t e d b y t e r r i t o r i a l p a i r s ) . T a b l e 1 s h o w s t h e s p r i n g p a t t e r n o f o b s e r v e d a g g r e s s i v e e n c o u n t e r s i n t h e s t u d y a r e a i n b o t h y e a r s . A n " a g r e s s i v e e n c o u n t e r " w a s n e a r l y a l w a y s a p r o l o n g e d c h a s e a c c o m p a n i e d b y " f i g h t i n g n o t e s " a n d " d o m i n a n c e n o t e s " (Odum, 1 9 4 2 ) ; a c t u a l c o n t a c t b e t w e e n f i g h t i n g c h i c k a d e e s w a s o b s e r v e d T A B L E 1. N u m b e r o f o b s e r v e d a g g r e s s i v e e n c o u n t e r s i n t h e s p r i n g : m a i n s t u d y a r e a . P e r i o d 1 9 6 4 1 9 6 5 P F . . 0 . 0 0 0 0 . 0 . 1 . 1 . 0 . . 0 . . 0 . . 0 0 0 . FM . . 3 . 1 4 . . . . 5 . . 6 . . 0 0 . . 0 . . 0 . 2 . . MM 3 . . 2 . . 4 6 . . 6 . . 8 . 2 Z . 1 . 3 2 . MM . 2 . 3 . 2 . . 2 . 0 1 . . 3 2 1 . 1 . 1 . 2 . . 1 . . MA . . . 1 . 1 1 . 1 . . . 1 2 . . 0 1 . . 1 2 . . . . 1 . A A . . . . 1 . 2 . . . . . 1 . 2 . . . 1 . . . . 1 . 0 . . AM 0 1 0 1 1 . 1 0 1 . . . 0 0 . . . 1 . . 1 MM 0 . 0 0 1 1 . 0 1 0 1 1 . 0 . . . 0 . . . 0 . . 0 . . 0 M J 0 0 0 0 0 0 . . 0 0 0 0 0 0 0 . 0 . 0 . . 0 0 0 0 . 0 . N o t e : f i g u r e s i n r e d a r e t h o s e a b o v e 3; t h i s f i g u r e w a s c h o s e n a r b i t r a r i l y t o i n d i c a t e t h e p e a k o f a g g r e s s i o n i n e a c h y e a r . F = F e b r u a r y ; M = M a r c h ; A = A p r i l ; M = M a y ; J = J u n e . P e r i o d = t w o - w e e k i n t e r v a l . T h e f i r s t b e g i n s F e b . 2 . - 12 -o n l y t w i c e d u r i n g t h e w h o l e s t u d y . I n m o s t c a s e s 4 b i r d s (2 p a i r s ) w e r e i n v o l v e d i n e a c h e n c o u n t e r . T h e p e a k i n n u m b e r s o f a g g r e s s i v e e n c o u n t e r s c o i n c i d e d w i t h t h e t w o - w e e k p e r i o d o f f l o c k b r e a k - u p a n d o n s e t o f t e r r i t o r i a l b e h a v i o u r i n b o t h y e a r s . T a b l e 2 s h o w s t h e c o r r e s p o n d i n g d a t a f r o m t h e c o n t r o l a r e a . A s o n t h e m a i n s t u d y a r e a , b e f o r e t h e p e a k o f a g g r e s s i o n t h e b i r d s w e r e o b s e r v e d i n f l o c k s , a n d a f t e r t h e p e a k t h e y w e r e i n p a i r s . T h e r e f o r e t h e b r e a k - u p o f w i n t e r f l o c k s a n d t e r r i t o r y f o r m a t i o n i n t h e c o n t r o l a r e a c o i n c i d e d w i t h t h a t o n t h e m a i n s t u d y a r e a i n b o t h y e a r s . T A B L E 2 . N u m b e r o f o b s e r v e d a g g r e s s i v e e n c o u n t e r s i n t h e s p r i n g : c o n t r o l s t u d y a r e a . 1 9 6 4 1 9 6 5 D a t e N o . D a t e N o . J a n . 30 0 F e b . 2 0 F e b . 13 0 F e b . 1 6 0 F e b . 2 7 4 M a r . 2 5 M a r . 12 2 M a r . 1 6 2 - 13 -b) Numerical Results i) Clutch Size. In the two years of the study the average clutch size was almost the same. In 19 64, seventeen clutches were l a i d (four were second attempts), f o r a t o t a l of 90 eggs, and an average of 5.3 i 0.42 eggs/ cl u t c h . In 1965, seven clutches were counted, giving a t o t a l of 38 eggs, or an average of 5.4 i 0.65 eggs/clutch. i i ) F e r t i l i t y and Hatching Success. The figures i n Table 3 used to calculate the f e r t i l i t y rate (observed totals) are only those obtained from nests where young fledged and were counted. This i s because the nests were opened only once, to band the young. To estimate the t o t a l mortality occurring on the study area up to the time of hatching, clutches had to be used which were deserted, or destroyed either as eggs or fledglings before I could count them. The average clutch sizes and f e r t i l i t y rates were used to get the unknown figures; these were then included to obtain the Hatching Success (corrected t o t a l s ) . In 1964, four clutches are added i n the Corrected t o t a l s : one of 6, one of 3, one of 2, and an uncounted one of 5.3. The hatching success for 1964 was thus 69/89.3, or 0.773. In 1965, three clutches were uncounted. Two of these hatched, and the other was destroyed before hatching. Applying average clutch size and f e r t i l i t y rate, the hatching success for 1965 was (35 + 5.4 + 5T) - (38 + 5.4 + TABLE 3. F e r t i l i t y Rate and Hatching Success. 19 64 1965 Week Eggs No. Proportion Eggs No. Proportion ending l a i d nests hatched l a i d nests hatched A p r i l 30 0 0 _ 7 1 0.86 May 7 20 3 1.00 11 3 0.91 14 25 5 0.96 7 1 1.00 21 7 1 1.00 13 2 0.92 28 3 1 1.00 0 0 — June 4 8 1 0.88 0 0 — 11 0 0 — 0 0 — 18 5 1 0.60 0 0 — 25 0 0 — 0 0 — • July 2 5 1 1.00 0 0 Observed t o t a l : 73 38 F e r t i l i t y : 0.945 0.921 Corrected t o t a l : 89 54 Hatching success: 0.773 0.833 5.4) = 4 5 $ / 5 4 . 2 o r 0.845". i i i ) F l e d g i n g S u c c e s s . I n e a c h y e a r , e v e r y b r o o d e x c e p t o n e w a s t o t a l l y f l e d g e d . S i n c e i n e a c h c a s e o f l o s s t h e w h o l e b r o o d a s w e l l a s a p a r e n t d i s a p p e a r e d a t t h e s a m e t i m e , t h i s w a s p r e s u m a b l y d u e t o p r e d a t i o n . F l e d g i n g s u c c e s s w a s 0.94 i n 1 9 6 4 a n d 0.89 i n 1 9 6 5 . N i v ) J u v e n i l e S u r v i v a l . U n t i l t h e f a m i l y g r o u p s b r o k e u p t h r e e t o f o u r w e e k s a f t e r f l e d g i n g , t h e s u r v i v a l o f t h e y o u n g b i r d s c o u l d b e f o l l o w e d ( T a b l e 4 ) . I n 1 9 6 4 , o f 61 b a n d e d j u v e n i l e s , 50 s u r v i v e d u n t i l t h e b r e a k - u p . A l l e l e v e n o f t h e b i r d s w h i c h d i s a p p e a r e d d i d s o i n t h e f i r s t w e e k a f t e r f l e d g i n g : n o n e w a s s e e n a f t e r a p a r t i c u l a r l y s e v e r e s t o r m o n 2 1 M a y . W i t h t h i s e x c e p t i o n , a l l s u r v i v e d . I n 1 9 6 5 , n o s e v e r e s t o r m s o c c u r r e d i m m e d i a t e l y a f t e r a n y b r o o d h a d f l e d g e d . One b i r d d i s a p p e a r e d 7 d a y s a f t e r i t h a d l e f t t h e n e s t ; a l l o t h e r s w e r e o b s e r v e d u n t i l t h e f a m i l y g r o u p s b r o k e u p . A s i n o t h e r s p e c i e s o f P a r u s ( G o o d b o d y , 1 9 5 2 ) , t h e y o u n g s u d d e n l y d i s p e r s e s ome t h r e e t o f o u r w e e k s a f t e r f l e d g i n g . On t h e s t u d y a r e a t h i s w a s s e e n p r e c i s e l y w i t h o n e f a m i l y : o n 1 4 J u n e a l l s i x y o u n g w e r e s e e n a c c o m p a n i e d b y t h e p a r e n t s ; o n 15 J u n e t h e p a r e n t s w e r e a l o n e i n t h e i r t e r r i t o r y , a n d t w o o f t h e y o u n g w e r e s e e n s e p a r a t e l y , n e i t h e r o f t h e m i n t h e o r i g i n a l t e r r i t o r y . S i n c e t h e n n o n e o f t h e s i x y o u n g h a s b e e n s e e n . TABLE 4. Survival of banded young on the study area from the day of fledging. 1964 1965 Week aft e r fledging No. seen during week Proport-ion surviving lx No. seen during week Proport-ion surviving lx 0 61 0.8197 1000.0 33 1.0000 1000.0 1 50 1.0000 819.7 33 1.0000 1000.0 2 50 0.9200 819.7 33 0.8788 1000.0 3 46 0.4348 753.1 29 0.5517 878.8 4 20 0.4500 327.4 16 0.2500 484.8 5 9 0.5556 147.3 4 1.0000 121.2 6 5 1.0000 81.8 4 1.0000 121.2 7 5 1.0000 81.8 4 1.0000 121.2 8 5 1.0000 81.8 4 1.0000 121.2 9 5 1.0000 81.8 4 1.0000 121.2 10 5 1.0000 81.8 4 1.0000 121.2 - 17 -At the time when the banded young l e f t the study area, there was an i n f l u x of unhanded b i r d s . These were almost 100% young; they could be distinguished from adults by t h e i r unworn plumage and by t h e i r c a l l s (Odum, 1942). This exchange of birds was very extensive: of 61 banded young i n 19 64, only f i v e remained i n the study area by September. In 1965, of 35 marked young only four remain i n area to date (Fig. 3). However, without a much more extensive marking programme, no accurate measure of juvenile s u r v i v a l a f t e r family break-up can be made. v) Adult Survival. The rate of s u r v i v a l of chickadees from September to the next autumn i n the study area was not constant (Table 5; Figs. 4-6). When the su r v i v a l rate i s calculated for two-week periods throughout the year, there i s one period when the rate i s s i g n i f i c a n t l y lower than those i n any adjacent periods. The s t a t i s t i c a l t e s t used here was to obtain 95% binomial confidence i n t e r v a l s ) on the f o r t n i g h t l y s u r v i v a l rates. These were taken from Table A.15A (p. 458) of Steel and Torrie (1960). As the confidence i n t e r v a l for the c r i t i c a l fortnight's rate does not overlap those of adjacent rates i n either year, i t can thus be said to be s i g n i f i c a n t l y d i f f e r e n t from adjacent rates (Figs. 4 and 5). In 1964 t h i s two-week period was the end of February; i n 1965 i t was the f i r s t two weeks i n March. In both years the period of loss was correlated exactly with the onset of t e r r i t o r i a l behaviour (Tables 1 and - 1 8 -T A B L E 5 . S u r v i v a l o f m a r k e d b i r d s o n t h e s t u d y a r e a f r o m 1 S e p t e m b e r . 1 9 6 3 - 6 4 1 9 6 4 - 6 5 N o . s e e n P r o p o r t - N o . s e e n P r o p o r t -TWo w e e k d u r i n g i o n d u r i n g i o n p e r i o d p e r i o d s u r v i v i n g l x p e r i o d s u r v i v i n g l x S S 1 1 0 . 9 0 9 1 0 0 0 S S 10 1 . 0 0 0 9 0 9 SO 4 1 . 0 0 0 9 0 9 0 0 12 1 . 0 0 0 9 0 9 ON 9 1 . 0 0 0 9 0 9 NN 1 1 0 . 9 1 7 9 0 9 ND 4 1 . 0 0 0 1 0 0 0 13 1 . 0 0 0 8 3 4 DD 8 1 . 0 0 0 1 0 0 0 3 0 0 . 9 0 9 8 3 4 D J 13 1 . 0 0 0 1 0 0 0 20 0 . 9 0 9 7 5 8 J J 2 1 0 . 8 7 5 1 0 0 0 2 6 0 . 9 2 9 6 8 9 J F 2 9 0 . 9 3 5 8 7 5 37 1 . 0 0 0 6 4 0 F F 3 4 1 . 0 0 0 8 1 8 4 4 0 . 9 7 8 6 4 0 F M 23 0 . 6 7 6 8 1 8 4 8 0 . 9 4 1 6 2 6 MM 2 6 1 . 0 0 0 5 5 3 2 8 0 . 5 8 3 5 8 9 MM 2 5 1 . 0 0 0 5 5 3 2 6 0 . 9 2 9 3 4 3 MA 2 4 1 . 0 0 0 5 5 3 2 4 1 . 0 0 0 3 1 9 A A 22 0 . 9 5 6 5 5 3 20 0 . 9 5 2 3 1 9 A M 2 4 0 . 9 6 0 5 2 9 19 0 . 9 5 0 3 0 4 MM 2 1 0 . 9 5 0 5 0 8 1 6 0 . 9 4 1 2 8 9 M J 1 9 0 . 9 0 5 4 8 2 1 5 0 . 9 3 7 2 7 2 J J 1 0 0 . 8 3 3 4 3 6 15 1 . 0 0 0 2 5 5 J J 7 0 . 8 7 5 3 6 3 1 1 0 . 9 1 7 2 5 5 j j 9 1 . 0 0 0 3 1 8 7 1 . 0 0 0 2 3 4 J A 1 1 1 . 0 0 0 3 1 8 9 1 . 0 0 0 2 3 4 A A 12 0 . 8 5 7 3 1 8 A A 6 0 . 8 5 7 2 7 3 A S 8 0 . 8 8 9 2 3 4 SS 9 1 . 0 0 0 2 0 8 SO 4 1 . 0 0 0 2 0 8 0 0 9 1 . 0 0 0 2 0 8 ON 5 1 . 0 0 0 2 0 8 NN 9 0 . 9 0 0 2 0 8 ND 8 1 . 0 0 0 1 8 7 N o t e : S = S e p t e m b e r ; 0 = 0 c t o b e r ; N = N o v e m b e r ; e t c . - 19 -2): before t h i s period the birds were a l l i n winter flocks, and afterward they were i n t e r r i t o r i a l p a i r s . Throughout th i s period and the following week over 20 unhanded birds were seen i n the study area i n 1964, and over 15 i n 1965. As f a r as I could t e l l , none of these unmarked birds remained to breed; that I s , each banded b i r d that remained to breed with an unhanded b i r d was associating with an unhanded b i r d i n the winter flo c k before spring break-up. This then indicates that the same process was occurring i n surrounding areas. I cannot assume that a l l the birds which disappeared from the study area died - e s p e c i a l l y not those which disappeared during the c i r t i c a l f ortnight i n the spring. A l l I know i s that they remained neither i n the area, nor did they own t e r r i t o r i e s immediately surrounding i t . Thus, they no longer survived on my study area. The proportion of adults found a f t e r the breeding season was also low, e s p e c i a l l y i n 1964. This drop was not as sudden as that i n either spring. I t i s known that adult chickadees go through a period of moult a f t e r breeding, and i t i s suggested that t h i s i s a time of considerable physiological s t r a i n f or the in d i v i d u a l s . However beyond th i s c o r r e l a t i o n there i s no d i r e c t evidence supporting the idea that the moult was responsible for thi s period of l o s s . I suspect that a l l birds disappearing during t h i s time did indeed die, although I cannot prove t h i s . Evidence supporting i t , however, i s that no unhanded birds - 20 -were recorded as entering the study area at t h i s time. This was based on differences i n plumage and i n voice. vi) Excess Birds During Breeding. In each year of the study there was one unmated female i n the study area during the breeding season. These birds were allowed to range over several t e r r i t o r i e s , and i n a l l observed cases when the owners were encountered, the unmated b i r d gave the begging c a l l (Odum, 1942). No excess males were recorded during either breeding season. Evidence that there was none i s that i n both years at l e a s t one male died early i n the breeding season (just before or during incubation) and i n each case the t e r r i t o r y was not claimed by a new male, and the female remained unmated for the res t of the year. - 21 -DISCUSSION Three assumptions have been made i n t h i s study. The study area was assumed to be favourable habitat, i . e . production of young was expected to exceed adult losses, thus r e s u l t i n g i n surplus b i r d s . This condition was necessary for t h i s study. Also, i t was assumed that the study population was a representative sample of populations of t h i s species i n favourable habitats. F i n a l l y , populations of Black-capped Chickadees were assumed to behave s i m i l a r l y to those of other passerine species of s i m i l a r ecology, such as ti t m i c e . Adult losses during the following summer, autumn and winter were considerably less than the number of young fledged i n the study area. Although almost a l l of these young disappeared from the area during juvenile dispersal, subsequent banding data indicate that t h e i r place was taken by an apparently s i m i l a r number of unhanded young. (It i s peculiar that i n 1964 the number of immigrants was so close to the number of emigrants. Nothing i s known of any mechanism that might have been responsible for t h i s r e s u l t , indeed, i n 19 65 immigration may have exceeded production^ However, the study area can s t i l l be c a l l e d "favourable" habitat, for not only was a surplus of young produced i n the area, there was also a surplus present at the beginning of autumn. The drop i n numbers which effected the removal of the surplus birds and thus regulated the breeding - 22 -d e n s i t y o f t h e s t u d y p o p u l a t i o n o c c u r r e d i n t h e s p r i n g , a n d w a s c o r r e l a t e d w i t h t h e b r e a k - u p o f w i n t e r f l o c k s a n d t h e o n s e t o f t e r r i t o r i a l b e h a v i o u r . T h i s c h a n g e i n b e h a v i o u r i s a g e n e r a l f a c t o r a n d i s c h a r a c t e r i s t i c o f a l l B l a c k - c a p p e d C h i c k a d e e p o p u l a t i o n s w h i c h h a v e b e e n s t u d i e d ( B r e w e r , 1 9 6 1 ; T a n n e r , 1 9 5 2 ; Odum, 1 9 4 1 a ; M c C a m e y , 19 6 2 ) . I t i s a l s o c h a r a c t e r i s t i c o f some o t h e r P a r i d a e ( T a n n e r , 1 9 5 2 ; B r e w e r , 1 9 6 1 ; a n d D i x o n , 1 9 6 3 : C a r o l i n a C h i c k a d e e ; R o o t , 1 9 6 4 : C h e s t n u t - b a c k e d C h i c k a d e e ; K l u y v e r , & T i n b e r g e n , 1 9 5 3 ; G i b b , 1 9 6 0 : G r e a t T i t ; G i b b , 1 9 6 0 : B l u e a n d C o a l T i t s ) . I t h a s l o n g b e e n s u s p e c t e d t h a t t e r r i t o r i a l b e h a v i o u r i n s p r i n g r e g u l a t e s t h e s i z e o f c e r t a i n s p e c i e s ' b r e e d i n g p o p u l a t i o n s . Tompa ( 1 9 6 2 ) f o u n d t h a t t e r r i t o r i a l b e h a v i o u r d i d r e g u l a t e t h e b r e e d i n g n u m b e r s o f S o n g S p a r r o w s o n a s m a l l i s l a n d ( M a n d a r t e I s l a n d , B . C . ) . J e n k i n s , W a t s o n & M i l l e r ( 1 9 6 3 ) s h o w e d t h a t i n t h e i r s t u d y a r e a s i n n o r t h e a s t S c o t l a n d t e r r i t o r i a l b e h a v i o u r r e g u l a t e d t h e s i z e o f t h e b r e e d i n g p o p u l a t i o n o f R e d G r o u s e . W a t s o n ( 1 9 6 5 ) w o r k i n g o n P t a r m i g a n i n t h e C a i r n g o r m s , S c o t l a n d , w r o t e , " D u r i n g 5 y e a r s w h e n w i n t e r c o u n t s w e r e d o n e , n u m b e r s s t a y e d f a i r l y c o n s t a n t f r o m a u t u m n t i l l s p r i n g , b u t d e c r e a s e d s u d d e n l y i n M a r c h o r A p r i l , f o l l o w i n g t h e b r e a k - u p o f f l o c k s a n d t h e o n s e t o f v i g o r o u s t e r r i t o r y d e f e n c e . " C o n c e r n i n g t e r r i t o r i e s i n g e n e r a l , H i n d e ( 1 9 5 6 ) w r o t e , "... t h e o b s e r v a t i o n s t h a t t e r r i t o r y o w n e r s a r e - 23 -forced to defend t h e i r t e r r i t o r i e s from encroach-ment, that some attempts to s e t t l e are unsuccessful, and that some individuals are forced to breed i n sub-optimal habitats, strongly suggest that t e r r i t o r y regulates the density of many species i n the most favoured areas. Proof i s lacking." (p. 354) Yet as f a r as titmice are concerned, i t seems that no attempt has been made to prove or disprove Hinde's supposition. Although i t has been demonstrated i n some species, Gibb, and Perrins seem to have ignored i t . If t e r r i t o r i a l behaviour i s indeed the variable which l i m i t s the breeding density of chickadees, i t ought to apply to some titmice as w e l l . Let us now consider the studies on titmice population ecology, to see i f t e r r i t o r i a l behaviour seems to be a relevant variable i n those populations too. Gibb (1960) claims to have shown that the t i t populations i n Thetford Chase were cont r o l l e d by winter food shortage. There are several objections to t h i s conclusion. His populations were not marked, and apparently no allowance was made for the f a c t that nearby populations were not t o t a l l y stable (Gibb, 1950). Also, h i s counts were only monthly: "... the monthly census i n winter should be s u f f i c i e n t l y accurate to indicate the general l e v e l of the population and to reveal major seasonal changes i n the number of each species." (Gibb, 1960; p. 168) His graphs on pp. 170 and 191 (both Coal and Blue Tits) show a drop i n the l a s t month before breeding i n almost every year; t h i s drop, he claims, i s the r e s u l t of lack of food at that time, although he has no d i r e c t evidence for t h i s . - 24 -F i n a l l y , he bases h i s conclusions to a great extent on a graph (1960; p. 195) which shows the c o r r e l a t i o n between minimum winter invertebrate food stock and "percent s u r v i v a l " of the Coal T i t . Actually he did not have any s u r v i v a l data; a l l he had was the proportion of f a l l numbers present i n the spring, based on two counts: one at the end of September and the other i n A p r i l . Yet he says of t h i s c o r r e l a t i o n that i t "... i s so s t r i k i n g that i t seems almost unnecessary to look for a l t e r n a t i v e s . " (1960; p. 195). In f a c t he i s so convinced by t h i s corre-l a t i o n that he has accepted i t without looking seriously for alternative explanations. The second major hypothesis was f i r s t proposed by Perrins (1963), when he showed that i n Marley Wood the higher the proportion of juvenile Great T i t s i n the winter population, the higher the breeding population the following year. However, the actual winter counts from Marley Wood were not given, and numbers apparently were not measured, the proportion of juveniles having been obtained by sampling. Thus, a low proportion may mean simply a high adult s u r v i v a l . It i s possible that adults are more aggressive than yearlings at the onset of t e r r i t o r i a l behaviour, so that the more adults there are, the fewer t e r r i t o r i e s there are. This i s borne out by my data: the three largest t e r r i t o r i e s i n the study woods i n 1965 were held by the only three i n t a c t pairs surviving from the 1964 season. Thus, u n t i l actual winter counts are made, i t i s unknown whether the juvenile - 2 5 -o r t h e a d u l t s u r v i v a l i s o f m o r e i m p o r t a n c e i n M a r l e y Wood, a n d f i n a l l y , s i n c e n o w i n t e r c e n s u s e s w e r e made a t a l l i n M a r l e y W o o d, • t h e r e a r e n o d a t a o n t h e t e m p o r a l p a t t e r n o f w i n t e r m o r t a l i t y i n t h i s s t u d y . T h e t h i r d h y p o t h e s i s s u g g e s t s t h a t s p r i n g t e r r i t o r i a l b e h a v i o u r l i m i t s b r e e d i n g d e n s i t i e s . T h i s i s b y n o m e a n s a new i d e a , a n d h a s b e e n d e m o n s t r a t e d i n s p e c i e s o f some o t h e r f a m i l i e s . I t w a s f i r s t p u t f o r t h i n r e f e r e n c e t o t i t m i c e i n 1 9 5 3 b y K l u y v e r & T i n b e r g e n , w h i l e t h e y w e r e p r o p o s i n g a b u f f e r m e c h a n i s m o f p o o r h a b i t a t s f o r e x c e s s b i r d s , a n d h a s u p t i l l now n o t b e e n p r o p e r l y i n v e s t i g a t e d i n t h e g e n u s P a r u s . L a c k ( 1 9 6 4 ) w r i t e s t h a t i n M a r l e y Wood, t e r r i t o r i a l b e h a v i o u r p l a y s n o e f f e c t i v e p a r t i n t h e r e g u l a t i o n o f t h e b r e e d i n g d e n s i t y o f t h e G r e a t T i t , a l t h o u g h h e w r i t e s , " U n t i l 2 y e a r s a g o , o n e m i g h t p o s s i b l y h a v e a r g u e d t h a t t e r r i t o r i a l b e h a v i o u r s e t a l i m i t t o t h e n u m b e r o f g r e a t t i t s b r e e d i n g i n M a r l e y ..." ( p . 1 7 2 ) . T h e r e a s o n h e r e j e c t s t e r r i t o r i a l c o n t r o l i s t h a t 8 6 p a i r s , a l m o s t t w i c e a s m a n y a s u s u a l , b r e d i n M a r l e y W o o d i n 1 9 6 1 . T h e a s s u m p t i o n L a c k m a k e s h e r e i s t h a t t e r r i t o r i e s a r e a f i x e d s i z e r e g a r d l e s s o f o t h e r v a r i a b l e s . H o w e v e r , w h a t c o n t r o l s t h e s i z e o f t e r r i t o r i e s i s u n k n o w n . T h e f a c t t h a t d i f f e r e n t n u m b e r s o f t e r r i t o r i e s a r e e s t a b l i s h e d i n d i f f e r e n t y e a r s i s i r r e l e v a n t ; t h e r e l e v a n t p o i n t i s w h e t h e r o r n o t t h e r e a r e l o s s e s a s s o c i a t e d w i t h t e r r i t o r i a l b e h a v i o u r . L a c k g i v e s t h e e s t i m a t e d m a x i m u m p o p u l a t i o n f o r t h e p r e v i o u s w i n t e r : 3 0 4 i n d i v i d u a l s . A s - 26 -only 86 pairs bred the next spring, the estimated loss i s 132, which i s more than the maximum number believed to have been present i n f i v e of the ten winters quoted. These excess birds must have disappeared between October and A p r i l ; but again there are no data on the time these losses occurred. Lack therefore has no evidence against the view that many birds disappeared with the onset of t e r r i t o r i a l behaviour i n spring. The l a s t theory has one great merit: i t i s more general than the other two put f o r t h . The change from fl o c k i n g to t e r r i t o r i a l behaviour has been reported i n every population of chickadees studied, whereas severe winter food shortage, or severe summer conditions r e s u l t i n g i n low juvenile s u r v i v a l , happen only some years i n some areas. I t i s true that i f a l l excess birds are removed by these or other factors before spring, t h i s change i n behaviour w i l l s t i l l occur although i t w i l l have no numerical e f f e c t . An hypothesis i s of very l i t t l e use i f i t cannot be tested. The hypothesis that t e r r i t o r i a l behaviour regulates breeding densities i n favourable habitats has withstood the f i r s t t e s t of being confirmed over two successive years. However, i t i s necessary that further tests be possible. One possible method i s a series of experiments using several plots from which birds are removed at d i f f e r e n t times of year. The predictions of t h i s hypothesis are that i f the birds are removed a f t e r - 27 -the s t a r t of laying, the only invasion w i l l r e s u l t from neighbouring p a i r s ' expanding t h e i r t e r r i t o r i e s . However, i f the birds are removed from a plot during the time of change from f l o c k i n g to t e r r i t o r i a l behaviour, or within a period of roughly two to three weeks thereafter, there should be an invasion by excess birds driven o f f from surrounding areas (providing there has been good s u r v i v a l i n these areas) and some of these invading birds should claim t e r r i t o r i e s and remain to breed, as Stewart & A l d r i c h (1951) and Hensley & Cope (1951) found with wood warblers. - 28 -CONCLUSIONS The factor preventing continual increase i n the study population i n a favourable habitat was the change i n behaviour from flo c k i n g to t e r r i t o r i a l , with the re s u l t i n g increase i n aggressivity of i n d i v i d u a l s . Because t h i s change i n behaviour i s a general factor which has been observed i n a l l studied populations of Black-capped Chickadees and also i n those of many other species, i t i s suggested that this factor may be the one c o n t r o l l i n g the breeding densities of other species of sim i l a r ecology as well, providing they are i n favourable environments. - 2 9 -L I T E R A T U R E C I T E D ANDREWARTHA, H. G. a n d L . C. B I R C H . 1 9 5 4 . T h e d i s t r i b u t i o n a n d a b u n d a n c e o f a n i m a l s . U n i v e r s i t y o f C h i c a g o P r e s s , C h i c a g o . B E N T , A . C. 1 9 4 6 . L i f e h i s t o r i e s o f N o r t h A m e r i c a n j a y s , c r o w s a n d t i t m i c e . U . S . N a t l . M u s . , B u l l N o . 1 9 1 : 1 - 4 9 5 . BREWER, R. 1 9 6 1 . C o m p a r a t i v e n o t e s o n t h e l i f e h i s t o r y o f t h e C a r o l i n a C h i c k a d e e s . W i l s o n B u l l 7 3 : 3 4 8 - 3 7 3 . BREWER, R. 1 9 6 3 . E c o l o g i c a l a n d r e p r o d u c t i v e r e l a t i o n s h i p s o f B l a c k - c a p p e d a n d C a r o l i n a C h i c k a d e e s . A u k 8 0 : 9 - 4 7 . C H I T T Y , D. 1 9 5 2 . M o r t a l i t y a m o n g v o l e s ( M i c r o t u s a g r e s t i s ) a t L a k e V y r n w y , M o n t g o m e r y s h i r e i n 1 9 3 6 - 9 . P h i l T r a n s . R o y a l S o c . B . 2 3 6 : 5 0 5 - 5 5 2 . D I X O N , K. L . 19 6 2 . N o t e s o n t h e m o l t s c h e d u l e o f t h e P l a i n T i t m o u s e . C o n d o r 6 4 : 1 3 4 - 1 3 9 . D I X O N , K. L . 1 9 6 3 . Some a s p e c t s o f s o c i a l o r g a n i z a t i o n i n t h e C a r o l i n a C h i c k a d e e . P r o c . X l l l t h I n t e r n . O r n i t h . C o n g r . .-240-258. D RURY, W. H. J r . 1 9 5 8 . C h i c k a d e e s a n d n e s t b o x e s . M a s s a c h u s e t t s A u d u b o n S o c i e t y B u l l e t i n , N o v e m b e r : l . G I B B , J . A . 1 9 5 0 . T h e b r e e d i n g b i o l o g y o f t h e G r e a t a n d B l u e T i t m i c e . I b i s 9 2 . : 5 0 7 - 5 3 9 . G I B B , J . A . 1 9 5 4 a . P o p u l a t i o n c h a n g e s o f t i t m i c e 1 9 4 7 - 5 1 . B i r d S t u d y . L : 4 0 - 4 8 . G I B B , J . A . 1 9 5 6 . T e r r i t o r y i n t h e g e n u s P a r u s . I b i s 9 8 : 4 2 0 - 4 2 9 . G I B B , J . A . 1 9 5 8 . P r e d a t i o n b y t i t s a n d s q u i r r e l s o n t h e E u c o s m i d E r n a r m o n i a c o n i c o l a n a ( H e y l . ) . J . A n i m . E c o l . 2 7 : 3 7 5 - 3 9 6 . G I B B , J . A . 1 9 6 0 . P o p u l a t i o n s o f t i t s a n d G o l d c r e s t s a n d t h e i r f o o d s u p p l y i n p i n e p l a n t a t i o n s . I b i s 1 0 2 : 1 6 3 - 2 0 8 . G I B B , J . A . 1 9 6 2 . T i t s a n d t h e i r f o o d s u p p l y i n E n g l i s h p i n e w o o d s : a p r o b l e m i n a p p l i e d o r n i t h o l o g y . P p . 5 8 - 6 6 i n F e s t s c h r i f t 1 9 3 7 - 1 9 6 2 d e r V o g e l -s c h u t z w a r t e f u r H e s s e n , R h e i n l a n d - P f a l z u n d S a a r l a n d ( S . P f e i f e r a n d W. K e i l , e d s ) F r a n k f u r t . - 30 -G I B B , J . A . a n d M. M. B E T T S . 1 9 6 3 . F o o d a n d f o o d s u p p l y o f n e s t l i n g t i t s ( P a r i d a e ) i n B r e c k l a n d p i n e . J . A n i m . E c o l . 3 2 : 4 8 9 - 5 3 3 . G 0 0 D B 0 D Y , I . M. 1 9 5 2 . T h e p o s t - f l e d g i n g d i s p e r s a l o f j u v e n i l e t i t m i c e . B r i t , b i r d s 4 5 : 2 7 9 - 2 8 5 . H E N S L E Y , M. M. a n d J . B . C O P E . 1 9 5 1 . F u r t h e r d a t a o n r e m o v a l a n d r e p o p u l a t i o n o f t h e b r e e d i n g b i r d s i n a s p r u c e - f i r f o r e s t c o m m u n i t y . A u k 6 8 : r 4 8 3 - 4 9 3 . H I N D E , R. A . 1 9 5 6 . T h e b i o l o g i c a l s i g n i f i c a n c e o f t h e t e r r i t o r i e s o f b i r d s . I b i s 9 8 : 3 4 0 - 3 6 9 . J E N K I N S , D., A . WATSON a n d G. R. M I L L E R . 19 6 3 . P o p u l a t i o n s t u d i e s o n R e d G r o u s e , L a g o p u s l a g o p u s s c o t i c u s ( L a t h . ) i n n o r t h - e a s t S c o t l a n d . J . A n i m . E c o l . 3 2 . : 3 1 7 - 3 7 6 . K L U I J V E R , H. N . 1 9 5 1 . T h e p o p u l a t i o n e c o l o g y o f t h e G r e a t T i t , P a r u s m. m a j o r L . A r d e a 3 9 : 1 - 1 3 5 . K L U Y V E R , H . N . 1 9 6 1 . F o o d c o n s u m p t i o n i n r e l a t i o n t o h a b i t a t i n b r e e d i n g c h i c k a d e e s . A u k 7 8 . : 5 3 2 - 5 5 0 . K L U Y V E R , H . N . a n d N . T I N B E R G E N . 1 9 5 3 . T e r r i t o r y a n d t h e r e g u l a t i o n o f d e n s i t y i n t i t m i c e . A r c h , n e e r l . Z o c i l . 1 0 : 2 6 5 - 2 8 9 . L A C K , D. 1 9 5 8 . A q u a n t i t a t i v e b r e e d i n g s t u d y o f B r i t i s h t i t s . A r d e a 4 6 : 9 1 - 1 2 4 . L A C K , D. 19 6 4 . A l o n g - t e r m s t u d y o f t h e G r e a t T i t ( P a r u s  m a j o r ) . J . A n i m . E c o l . 3 3 , J u b i l e e S y m p o s i u m S u p p l . .-159-173. L A C K , D., J . G I B B a n d D. F . OWEN. 1 9 5 7 . S u r v i v a l i n r e l a t i o n t o b r o o d - s i z e i n t i t s . P r o c . Z o o l . S o c . L o n d o n 1 2 8 : 3 1 3 - 3 2 6 . LAWRENCE, L . d e K . 1 9 5 8 . On r e g i o n a l m o v e m e n t s a n d b o d y w e i g h t s o f B l a c k - c a p p e d C h i c k a d e e s i n w i n t e r . A u k 7 5 : 4 1 5 - 4 4 3 . M c C A M E Y , F . J r . 1 9 6 2 . S u r v i v a l a n d a g e s t r u c t u r e i n a s a m p l e p o p u l a t i o n o f t h e B l a c k - c a p p e d C h i c k a d e e . P h . D . d i s s e r t a t i o n , U n i v e r s i t y o f C o n n e c t i c u t . MUNRO, J . A . a n d I . MCT. COWAN. 1 9 4 7 . A r e v i e w o f t h e b i r d f a u n a o f B r i t i s h C o l u m b i a . B.C. P r o v i n c i a l M u s e u m S p e c i a l P u b l i c a t i o n N o . 2 : 1 - 2 8 5 . - 3 1 -ODUM, E . P. 1 9 4 1 a . A n n u a l c y c l e o f t h e B l a c k - c a p p e d C h i c k a d e e . 1 . A u k 5 8 : 3 1 4 - 3 3 3 . ODUM, E . P. 1 9 4 1 b . A n n u a l c y c l e o f t h e B l a c k - c a p p e d C h i c k a d e e . 2. A u k 5 8 : 5 1 8 - 5 3 5 . ODUM, E . P. 1 9 4 2 . A n n u a l c y c l e o f t h e B l a c k - c a p p e d C h i c k a d e e . 3. A u k 5 9 : 4 9 9 - 5 3 1 . P E R R I N S , C. 1 9 6 3 . S u r v i v a l i n t h e G r e a t T i t , P a r u s m a j o r . P r o c . X l l l t h I n t e r n . O r n i t h . C o n g r . : 7 1 7 - 7 2 8 . P E T E R S O N , R. T. 1 9 6 1 . A F i e l d G u i d e t o W e s t e r n B i r d s . H o u g h t o n M i f f l i n C o . , B o s t o n . ROOT, R. B . 1 9 6 4 . E c o l o g i c a l i n t e r a c t i o n s o f t h e C h e s t n u t -b a c k e d C h i c k a d e e f o l l o w i n g a r a n g e e x t e n s i o n . C o n d o r 6 6 : 2 2 9 - 2 3 8 . S P E I R S , J . M. 1 9 6 3 . S u r v i v a l a n d p o p u l a t i o n d y n a m i c s w i t h p a r t i c u l a r r e f e r e n c e t o B l a c k - c a p p e d C h i c k a d e e s . B i r d - b a n d i n g 34_: 8 7 - 9 3 . S T E E L , R. G. a n d J . H . T O R R I E . 1 9 6 0 . P r i n c i p l e s a n d P r o c e d u r e s o f S t a t i s t i c s . M c G r a w - H i l l B o o k C o . I n c . , T o r o n t o . STEWART, R. E . a n d J . W. A L D R I C H . 1 9 5 1 . R e m o v a l a n d r e p o p u l a t i o n o f b r e e d i n g b i r d s i n a s p r u c e - f i r f o r e s t c o m m u n i t y . A u k 6 8 _ : 4 7 1 - 4 8 2 . TANNER, J . T. 1 9 5 2 . B l a c k - c a p p e d a n d C a r o l i n a C h i c k a d e e s i n t h e s o u t h e r n A p p a l a c h i a n M o u n t a i n s . A u k 6 9 : 4 0 7 - 4 2 4 . TOMPA, F . S. 1 9 6 2 . T e r r i t o r i a l b e h a v i o u r : t h e m a i n c o n t r o l l i n g f a c t o r o f a l o c a l s o n g s p a r r o w p o p u l a t i o n . A u k 7 9 : 6 8 7 - 6 9 7 . WATSON, A d a m . 1 9 6 5 . A p o p u l a t i o n s t u d y o f P t a r m i g a n ( L a c f o p u s m u t u s ) i n S c o t l a n d . J . A n i m . E c o l . 3 4 : 1 3 5 - 1 7 2 . FIGURE 1. Flock ranges (A) and breeding t e r r i t o r i e s (B) on the study area* 1963-64. Numbers: banded b i r d s a l i v e in each flock Feb. 12, 1964. FIGURE 2. Flock ranges (A) and breeding t e r r i t o r i e s (B) on the study area: 1964-65. Numbers: banded birds a l i v e in each flock Feb. 14, 1965. 1 100 00-80 70 60-• o 7 ^ 50 | 40 e ; 30 c ! 2 i • 1 20 10 1 • o e i- - i -! l-i j i r I i ! t i " • 1 • J . ! i T r • • • • * I i N D O S J F P M M M A A M M J J J J A A A S S O O N fl O O J J F F M M M A A M M J J J j A A A 8 S o O N N D . : -| l Tima: two week periods ; : ' . . . ' i ; FIGURE 4!. Minimum; su r v i v a l 1 rates and 95% confidence | int e r v a l s for each two week period i n 1963-64. •. ' • T 9 7 i 1 i i it .••II • ! oo 90 80 70 o r • • ? 9 • T » o > E E c 60-50 40-30 20 IO T 0 T mi . )-. U ..I. .1 1 ; i T e o 7 • .1 •;-S S S O O N N D D J J F F M M M A A M M J j i J 5 S 0 0 N N 0 D J J F P M M M A A M M J J J J A i Time: two week periods FIGURE 51 Minimum;survival rates and .95% confidence i n t e r v a l s for each -two week period i n 1964-65 J I i t i 1 4 ~ ; . fj.!:.! | ;j;;J:i.:!.!:l i ' i ; • + ' 1 1 ' , • ! • : • ' <- T i l i • .! • 1... i li-M-li ' ! * ' t • ' - , 1 S O M D J F M A M j j A 3 O N D Time two week periods FIGURE 6. Survival of marked birds on the study area from Sept. 1st. 

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