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The role of spatial pattern learing in hummingbird foraging Sutherland, Glenn D. 1986

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THE ROLE OF SPATIAL PATTERN LEARNING IN HUMMINGBIRD FORAGING by GLENN D. SUTHERLAND B . S c , U n i v e r s i t y Of M a n i t o b a W i n n i p e g , M a n i t o b a 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT THE REQUIREMENTS FOR .THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Z o o l o g y ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA O c t o b e r 1986 © G l e n n D. S u t h e r l a n d , 1986 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of ZoO The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date IE-6 (3/81) i i ABSTRACT F o r a g i n g e f f i c i e n t l y r e q u i r e s t h a t a n i m a l s o r g a n i z e t h e i r b e h a v i o u r i n r e l a t i o n t o s p a t i a l and t e m p o r a l p a t t e r n s o f f o o d d i s t r i b u t i o n and a b u n d a n c e . T h i s t h e s i s e x a m i n e s how h u mmingbirds use i n f o r m a t i o n a b o u t s p a t i a l f o o d d i s t r i b u t i o n s i n t h e i r f o r a g i n g b e h a v i o u r . I u s e d l a b o r a t o r y t e s t s w i t h l a r g e a r r a y s o f f e e d e r s t o c l a r i f y t h e r o l e o f l e a r n i n g and memory f o r s p a t i a l l o c a t i o n i n hummingbird - f o r a g i n g and t o i d e n t i f y c o n s t r a i n t s on t h e s e a b i l i t i e s . The main q u e s t i o n s were: "What c h a r a c t e r i s t i c s o f t h e s p a t i a l p a t t e r n i n g of f o o d s u p p l y c o n s t r a i n hummingbird f o r a g i n g s u c c e s s ? " ; and "To what e x t e n t a r e l e a r n i n g and s p a t i a l memory i m p o r t a n t i n d e t e r m i n i n g where hummingbirds f o r a g e ? " . Hummingbirds l e a r n e d t o v i s i t t h e most p r o f i t a b l e f e e d e r s i n l a r g e two d i m e n s i o n a l a r r a y s i n w h i c h t h e o n l y s o u r c e o f i n f o r m a t i o n t o f e e d e r q u a l i t y was p r o v i d e d by s p a t i a l l o c a t i o n . T h e s e a r r a y s had e q u a l numbers o f p r o f i t a b l e f e e d e r s and t h e same t o t a l e n e r g y a v a i l a b l e ; t h e y d i f f e r e d i n t h e s p a t i a l a r r a n g e m e n t o f f o o d . B i r d s l e a r n e d more q u i c k l y and r e a c h e d somewhat h i g h e r l e v e l s o f p e r f o r m a n c e on a r r a y s o f a few l a r g e g r o u p s o f f e e d e r s t h a n on t h o s e w i t h a l a r g e r number o f s m a l l e r g r o u p s . However, hummingbirds a l s o l e a r n e d t o p e r f o r m w e l l e v e n i n complex a r r a y s , but t h e y p e r f o r m e d c o n s i s t e n t l y w e l l o n l y i f t h e f e e d e r s were r e g u l a r l y d i s t r i b u t e d . Memory f o r t h e l o c a t i o n o f f e e d e r g r o u p s was more i m p o r t a n t i n a c c o u n t i n g f o r p e r f o r m a n c e i n t h e s e e x p e r i m e n t s t h a n l e a r n i n g i n d i v i d u a l l o c a t i o n s o r s i m p l e movement r u l e s . I n e x p e r i m e n t s i n w h i c h I s w i t c h e d t h e d i s t r i b u t i o n o f f o o d t o i t s m i r r o r - i m a g e a f t e r b i r d s had r e a c h e d a s y m p t o t i c p e r f o r m a n c e , a l l b i r d s showed a l a g i n r e d i s t r i b u t i n g t h e i r f o r a g i n g e f f o r t . T h e r e was l i t t l e e v i d e n c e t h a t t h e b i r d s r e - l e a r n e d t h e new d i s t r i b u t i o n f a s t e r a f t e r t h e s w i t c h t h a n i n t h e i n i t i a l l e a r n i n g p h a s e . A d e t a i l e d a n a l y s i s of movements made i n a complex a r r a y s u g g e s t s t h a t hummingbirds a v o i d e d v i s i t s t o bad f e e d e r s by o r g a n i z i n g t h e i r v i s i t s w i t h i n and among s m a l l p a t c h e s . T h e s e r e s u l t s a r e c o n s i s t e n t w i t h a model o f hummingbird s p a t i a l i n f o r m a t i o n - p r o c e s s i n g i n w h i c h f e e d e r q u a l i t y i s "mapped" i n t o a c o a r s e - g r a i n e d s e t of e x p e c t a t i o n s t h a t becomes s t a b l e and c a n p e r s i s t i n s p i t e o f c h a n g e s i n t h e u n d e r l y i n g d i s t r i b u t i o n of f o o d . The p r i n c i p a l e f f e c t o f c o m p l e x i t y i s t o r e d u c e t h e r a t e o f l e a r n i n g d i s t r i b u t i o n s of f e e d e r q u a l i t y ; a l l of t h e p a t t e r n s I u s e d c o u l d be l e a r n e d by t h e b i r d s a l t h o u g h b i r d s d i d r e a c h h i g h e r l e v e l s o f p e r f o r m a n c e on t h e s i m p l e s t t h a n on o t h e r p a t t e r n s . TABLE OF CONTENTS ABSTRACT i i L I S T OF TABLES v i L I S T OF FIGURES v i i ACKNOWLEDGEMENTS v i i i C h a p t e r 1 GENERAL INTRODUCTION 1 S t u d y System and O b j e c t i v e s 4 C h a p t e r 2 LEARNING AND MEMORY IN HUMMINGBIRD FORAGING: SPATIAL PATTERNS OF FOOD DISTRIBUTION 9 E x p e r i m e n t 1: The E f f e c t of P a t t e r n C o m p l e x i t y 11 Methods 12 T r a i n i n g 13 E x p e r i m e n t a l P r o c e d u r e s 13 R e s u l t s 17 O v e r a l l P e r f o r m a n c e 17 S p a t i a l P a t t e r n s of F o r a g i n g E f f o r t 27 E x p e r i m e n t 2: The E f f e c t of E x p e c t a t i o n s a b o u t F e e d e r Q u a l i t y 36 Methods 37 R e s u l t s 38 D i s c u s s i o n 43 V C h a p t e r 3 SPATIAL PATTERN LEARNING BY HUMMINGBIRDS IN COMPLEX PATTERNS OF PROFITABILITY 49 Methods 51 T r a i n i n g 52 E x p e r i m e n t a l P r o c e d u r e s 52 R e s u l t s 54 O v e r a l l P e r f o r m a n c e 54 B e h a v i o u r a l Components o f P e r f o r m a n c e 62 S p a t i a l O r g a n i z a t i o n o f B e h a v i o u r a l Components ... 75 D i s c u s s i o n 81 C h a p t e r 4 GENERAL DISCUSSION 7 88 C o n c l u d i n g Remarks 96 LITERATURE CITED 98 v i L I S T OF TABLES T a b l e 2.1. Numbers o f v i s i t s t o good and bad f e e d e r s i n e a r l y and l a t e t r i a l s on e a c h p a t t e r n 20 T a b l e 2.2. R e v i s i t s t o good f e e d e r s w i t h i n t r i a l s i n e a r l y and l a t e t r i a l s on e a c h p a t t e r n 23 T a b l e 2.3. F o r e a c h p a t t e r n , t h e p r o p o r t i o n o f f i r s t v i s i t s o f e a r l y and l a t e t r i a l s t h a t began w i t h a v i s i t t o a good f e e d e r 31 T a b l e 2.4. D u r a t i o n s o f f i r s t v i s i t s t o f e e d e r s b e f o r e and a f t e r t h e s w i t c h 42 T a b l e 3.1. Development o f f o u r m e a s u r e s of p e r f o r m a n c e on t h e C h e c k e r b o a r d and Random p a t t e r n s 57 T a b l e 3.2. R u n l e n g t h i n good and bad p a t c h e s on t h e C h e c k e r b o a r d p a t t e r n b e f o r e and a f t e r t h e s w i t c h 66 T a b l e 3.3. Rate o f improvement i n t h e f o u r components o f p e r f o r m a n c e among and w i t h i n p a t c h e s 68 T a b l e 3.4. F r e q u e n c i e s o f t h e t h r e e p o s s i b l e p a t t e r n s o f r u n s o f 4 good f e e d e r s t h a t i n c l u d e no r e v i s i t s 80 v i i L I S T OF FIGURES F i g u r e 2.1. The f o u r s p a t i a l p a t t e r n s o f f e e d e r q u a l i t y p r e s e n t e d t o t h e b i r d s 14 F i g u r e 2.2. O v e r a l l p e r f o r m a n c e on a l l f o u r p a t t e r n s 18 F i g u r e 2.3. Mean p e r c e n t a g e o f r e v i s i t i n g o p p o r t u n i t i e s t a k e n a t s u c c e s s i v e i n t e r v i s i t i n t e r v a l s f o r a l l p a t t e r n s 25 F i g u r e 2.4. S p a t i a l d i s t r i b u t i o n s o f v i s i t s on e a c h p a t t e r n 28 F i g u r e 2.5. V e c t o r f i e l d s e x p r e s s i n g t h e d i s t r i b u t i o n of a l l d e p a r t u r e s f r o m e a c h f e e d e r 32 F i g u r e 2.6. O v e r a l l p e r f o r m a n c e on t h e Q u a r t e r s p a t t e r n i n t h e s w i t c h e x p e r i m e n t 39 F i g u r e 3.1. O v e r a l l p e r f o r m a n c e on t h e C h e c k e r b o a r d and Random p a t t e r n s 55 F i g u r e 3.2. O v e r a l l p e r f o r m a n c e o f e a c h i n d i v i d u a l b i r d on t h e l a s t day o f t h e e x p e r i m e n t on t h e C h e c k e r b o a r d and Random p a t t e r n s 59 F i g u r e 3.3. Changes i n f o u r component measures o f p e r f o r m a n c e b e f o r e t h e s w i t c h 64 F i g u r e 3.4. D i s t r i b u t i o n of r u n l e n g t h s on f i r s t v i s i t s t o good and bad p a t c h e s 70 F i g u r e 3.5. R e l a t i o n s h i p between number o f r e v i s i t s and t o t a l number o f v i s i t s d u r i n g f i r s t b o u t s i n good p a t c h e s , f o r 25 t r i a l s b e f o r e t h e s w i t c h 72 v i i i F i g u r e 3.6. F r e q u e n c y and d i r e c t i o n o f p r e d o m i n a n t moves between good p a t c h e s 76 F i g u r e 4.1. Summary o f p e r f o r m a n c e on a l l f o u r p a t t e r n s u s e d i n t h e s t u d y 90 i x ACKNOWLEDGEMENTS I w o u l d l i k e t o thank Lee Gass f o r h i s s u p p o r t t h r o u g h o u t t h e e v o l u t i o n o f t h i s s t u d y . He has a l w a y s been t h e r e w i t h i d e a s , e ncouragement and e n t h u s i a s m , and n e v e r h e s i t a t e d t o c h a l l e n g e my t h i n k i n g or my w r i t i n g when e i t h e r showed s i g n s of o s s i f i c a t i o n . F o r much o f t h e t i m e he has been more of a c o l l a b o r a t o r t h a n a s u p e r v i s o r , and a l l o w e d me t h e f r e e d o m t o p u r s u e many o t h e r q u e s t i o n s and b r a n c h o u t i n t o o t h e r p r o j e c t s . F o r a l l o f t h a t I am v e r y g r a t e f u l . My r e s e a r c h c o m m i t t e e , J a m i e S m i t h , Don W i l k i e and Lee Gass e a c h p r o v i d e d h e l p and a d v i c e a t c r i t i c a l t i m e s , and c o n s t r u c t i v e l y c r i t i c i z e d d r a f t s o f t h i s t h e s i s . R i c k M i l l e r a l s o commented on e a r l y d r a f t s o f C h a p t e r 2. Lee G a s s , Dave B e r n a r d and D i a n n a C o l n e t t h e l p e d w i t h d r a f t i n g f i g u r e s , and Gwen E i s l e r t y p e d some of t h e t a b l e s . I n t e r a c t i o n s w i t h t h e s t u d e n t s and f a c u l t y o f t h e I n s t i t u t e o f A n i m a l R e s o u r c e E c o l o g y p r o v i d e d me w i t h a s t i m u l a t i n g and c h a l l e n g i n g i n t e l l e c t u a l a t m o s p h e r e and a deepened a p p r e c i a t i o n f o r t h e s c i e n c e and p r a c t i s e o f e c o l o g y . S t e f a n Tamm n o t o n l y c o n t r i b u t e d c o n s t r u c t i o n s k i l l s , and computer p r o g r a m s f o r d a t a c o l l e c t i o n , b u t was a l s o a t i r e l e s s s o u r c e of i d e a s , c r i t i c i s m , and humour. P e t e r Cahoon, Dave Z i t t i n , Don Ludwig and Don W i l k i e a l l h e l p e d w i t h a n a l y s i s . P e t e r Cahoon c o n t r i b u t e d i n t e l l e c t u a l l y t o many a s p e c t s o f t h i s p r o j e c t ; i n p a r t i c u l a r t o t h e q u e s t i o n s and t e c h n i q u e s t h a t u n d e r l y t h e a n a l y s e s i n C h a p t e r 3. Ken L e r t z m a n , S h e i l a F i t z p a t r i c k , Tom G e t t y , Zena X T o o z e , Doug A r m s t r o n g , S t e v e P a t o n , K a a r e n L e w i s , G a y l e Brown and R i c k M i l l e r a l l w i l l i n g l y s h a r e d i d e a s and f r i e n d s h i p . My w o n d e r f u l c o l l e a g u e s a t ESSA L t d . n o t o n l y p a t i e n t l y b o r e my n e u r o s e s a s a s t u d e n t / c o n s u l t a n t (and a b s e n c e s from t h e j o b ) , b u t p r o v i d e d much needed e n c o u r a g e m e n t t o g e t i t f i n i s h e d . F o r m o r a l s u p p o r t , encouragement and s a i n t l y p a t i e n c e , I am d e e p l y g r a t e f u l t o J o a n S u t h e r l a n d . R e s e a r c h f u n d s were p r o v i d e d by NSERC o p e r a t i n g g r a n t 58-9876 t o C.L. G a s s . R i c k M i l l e r p r o v i d e d a d d i t i o n a l s u p p o r t f o r t h e a n a l y s e s p r e s e n t e d i n C h a p t e r 3. P e r s o n a l s u p p o r t was p r o v i d e d by an NSERC p o s t g r a d u a t e s c h o l a r s h i p , a 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 G r a d u a t e F e l l o w s h i p , and a t e a c h i n g a s s i s t a n t s h i p . 1 CHAPTER 1 GENERAL INTRODUCTION Any g l o b a l n o t i o n of how p a t t e r n s a r e d e t e c t e d and s t o r e d i s u n l i k e l y t o be c o r r e c t i n t h e p r e s e n t s t a t e o f knowledge b e c a u s e we s i m p l y do n o t have enough e v i d e n c e , b u t t h a t does n o t make s p e c u l a t i o n w o r t h l e s s . T h e r e i s an o b v i o u s d e a r t h o f s e n s i b l e h y p o t h e s e s t o t e s t , but t h e y a r e c e r t a i n l y n e e d ed i f one i s g o i n g t o make t h e b e s t o f hard-won e x p e r i m e n t a l e v i d e n c e ( B a r l o w , 1985). The f o o d r e s o u r c e s of a l l m o b i l e a n i m a l s v a r y i n q u a l i t y and a v a i l a b i l i t y i n b o t h s p a c e and t i m e ( M a c A r t h u r and P i a n k a 1966). F o r most a n i m a l s , a component of f o r a g i n g e f f e c t i v e n e s s i s t o g a t h e r i n f o r m a t i o n a b o u t t h e p a t t e r n s of v a r i a t i o n i n f o o d d i s t r i b u t i o n , and a c t on t h a t i n f o r m a t i o n ( K r e b s e t a l . 1983; Pyke 1984; Lima 1984, 1985). T h i s r e q u i r e s t h e a b i l i t y t o g a t h e r , o r g a n i z e , and remember t h i s i n f o r m a t i o n i n o r d e r t o use i t l a t e r . However, e n v i r o n m e n t s a l s o v a r y a t s e v e r a l s c a l e s ( e . g. home r a n g e s , p a t c h e s , p a r t i c u l a r f o o d i t e m s ) and f o o d a v a i l a b i l i t y may a l s o depend on t h e b e h a v i o u r of o t h e r a n i m a l s , o r on o t h e r f a c t o r s . The p r o b l e m f a c i n g an a n i m a l i s t o d e t e c t p e r t i n e n t and r e l i a b l e i n f o r m a t i o n from among many p o t e n t i a l s o u r c e s . Q u e s t i o n s a b o u t t h e k i n d s o f i n f o r m a t i o n t o w h i c h a n i m a l s a r e s e n s i t i v e , and how t h e y l e a r n a b o u t and use s u c h i n f o r m a t i o n a r e becoming i n c r e a s i n g l y i m p o r t a n t t o p i c s i n t h e a n a l y s i s o f b e h a v i o u r . In r e c e n t y e a r s a s y n t h e t i c a p p r o a c h c o m b i n i n g t e c h n i q u e s f r o m b e h a v i o u r a l e c o l o g y and c o m p a r a t i v e p s y c h o l o g y has been 2 s u c c e s s f u l l y a p p l i e d i n s t u d i e s o f t h e s e q u e s t i o n s . T h i s a p p r o a c h , now g e n e r a l l y known a s t h e e c o l o g i c a l s t u d y o f l e a r n i n g ( J o h n s t o n 1985), u s e s d e s c r i p t i o n s o f b e h a v i o u r o c c u r r i n g i n an e c o l o g i c a l c o n t e x t t o ask "What do a n i m a l s l e a r n ? " , and p s y c h o l o g i c a l a n a l y s e s o f t h a t b e h a v i o u r t o ask "How i s t h i s b e h a v i o u r l e a r n e d ? " . As f o r a g i n g t h e o r i s t s i n c r e a s i n g l y come t o view a n i m a l s as d e c i s i o n - m a k e r s who r e q u i r e i n f o r m a t i o n a b o u t t h e i r e n v i r o n m e n t s t o f o r a g e e f f i c i e n t l y , a p p l i c a t i o n s of t h i s a p p r o a c h have become i n c r e a s i n g l y w i d e s p r e a d ( K a m i l and Y o e r g 1982). E x p e r i m e n t a l s t u d i e s of f o r a g i n g b e h a v i o u r p r o v i d e c l e a r examples of how s u c h an a p p r o a c h has been u s e d i n t h e s t u d y o f how a n i m a l s use s p a t i a l i n f o r m a t i o n i n d e c i d i n g how t o a l l o c a t e t h e i r e f f o r t among t h e a v a i l a b l e o p p o r t u n i t i e s . S e v e r a l s p e c i e s o f b i r d s c a n l e a r n and remember p a t c h e s of p r o f i t a b l e p r e y ( S m i t h and Dawkins 1971; S m i t h and Sweatman 1974; Zach and F a l l s 1977). More r e c e n t l y , e x t e n s i v e s t u d i e s w i t h f o o d - h o a r d i n g b i r d s s u c h a s marsh t i t s , n u t c r a c k e r s and crows ( B a l d a 1980; K a m i l and B a l d a 1985; S h e r r y e t a l . 1982; V a n d e r W a l l 1982; James and V e r b e e k 1983) show t h a t t h e s e b i r d s c a n remember t h e l o c a t i o n s o f c a c h e d f o o d i t e m s weeks o r months a f t e r t h e y h i d e them. A wide v a r i e t y o f n o n - h o a r d i n g a n i m a l s a l s o use s p a t i a l memory i n t h e i r f o r a g i n g . In a c l a s s i c s t u d y , M e n z e l (1973) f o u n d t h a t c h i m p a n z e e s a c c u r a t e l y remembered where f o o d i t e m s were l o c a t e d , and r e t r i e v e d them i n ways t h a t s u g g e s t e d t h e y were u s i n g a "map" o f l o c a t i o n s w i t h w h i c h t o o r i e n t . G o u l d (1986) showed t h a t honey b e e s n a v i g a t e as i f t h e y e f f e c t i v e l y 3 c o n s t r u c t "maps" o f l a n d m a r k s t h a t t h e y use when f o r a g i n g among p r e f e r r e d f e e d i n g l o c a t i o n s , and when r e t u r n i n g t o t h e home h i v e . T h u s , t h e i d e a t h a t a n i m a l s use i n f o r m a t i o n about t h e s p a t i a l l o c a t i o n o f h i g h q u a l i t y f o r a g i n g s i t e s t o g u i d e t h e i r f o r a g i n g i s n o t new. However, few t h e o r e t i c a l s t u d i e s of f o r a g i n g b e h a v i o u r s p e c i f y how a n i m a l s a c q u i r e or use t h a t i n f o r m a t i o n , p e r h a p s b e c a u s e t h a t would r e q u i r e an i n t e g r a t i o n of f o r a g i n g e c o l o g y and t h e s t u d y o f i n f o r m a t i o n - p r o c e s s i n g mechanisms f o r i n d i v i d u a l a n i m a l s . I f s e n s i t i v i t y t o t h e s p a t i a l c h a r a c t e r i s t i c s o f t h e i r e n v i r o n m e n t s i s an i m p o r t a n t and b a s i c component o f a n i m a l s ' i n f o r m a t i o n - p r o c e s s i n g c a p a b i l i t i e s , t h e n a n a l y s e s o f t h e c h a r a c t e r i s t i c s and c o n s t r a i n t s on a n i m a l s ' use of t h i s component a r e n e c e s s a r y t o our u n d e r s t a n d i n g of t h e p r o x i m a t e b a s e s o f f o r a g i n g b e h a v i o u r . The r e s e a r c h d e s c r i b e d i n t h i s t h e s i s was d e s i g n e d t o e x p l o r e t h e r o l e o f s p a t i a l memory i n hummingbird f o r a g i n g . I became i n t e r e s t e d i n s p a t i a l memory w h i l e p a r t i c i p a t i n g i n a f i e l d e x p e r i m e n t on hummingbird t e r r i t o r i a l i t y and f o r a g i n g (Gass and S u t h e r l a n d 1985). I n t h a t s t u d y , e v i d e n c e t h a t h u mmingbirds l e a r n e d t h e l o c a t i o n s o f a t l e a s t h i g h q u a l i t y p a t c h e s o f f l o w e r s s u g g e s t e d t h a t a b r o a d e r a n a l y s i s of s p a t i a l memory c a p a b i l i t i e s of hummingbirds ( i n c l u d i n g c o n s t r a i n t s on t h o s e c a p a b i l i t i e s ) w o u l d be v a l u a b l e i n u n d e r s t a n d i n g t h e i r b e h a v i o u r . Here I d e f i n e some r e c u r r e n t t e r m s u s e d i n t h i s t h e s i s t h a t 4 c o u l d be s u b j e c t t o c o n f u s i o n . S p a t i a l memory i s t h e p r o c e s s by w h i c h a n i m a l s p e r c e i v e , r e c o g n i z e and remember t h e s p a t i a l o r g a n i z a t i o n of o b j e c t s and e v e n t s . S p a t i a l l y d i s t r i b u t e d  e x p e c t a t i o n s r e f e r s t o b i r d s b e h a v i n g a s i f t h e y have p r i o r e x p e c t a t i o n s a b o u t p a r t i c u l a r l o c a t i o n s o r g r o u p s o f l o c a t i o n s d i s t r i b u t e d o v e r t h e a r r a y . S i m p l e p a t t e r n s can be c h a r a c t e r i z e d by few d e s c r i p t o r s , whereas complex p a t t e r n s r e q u i r e many more d e s c r i p t o r s . In my e x p e r i m e n t s , p a t t e r n s a r e t w o - d i m e n s i o n a l a r r a n g e m e n t s o f f e e d e r q u a l i t y . S t u d y System and O b j e c t i v e s Much i s known of t h e f o r a g i n g e c o l o g y of t e m p e r a t e zone hummingbirds, i n c l u d i n g : mechanisms o f e n e r g y r e g u l a t i o n ( H a i n s w o r t h ejb a l . 1981; T o o z e and Gass 1985; Diamond e_t a l . 1986), f o r a g i n g t a c t i c s (Wolf and H a i n s w o r t h 1983; G a s s and S u t h e r l a n d 1985; Tamm jin p r e s s ) and f e e d i n g t e r r i t o r i a l i t y (Gass e t a l . 1976; K o d r i c - B r o w n and Brown 1978; H i x o n e t a l . 1983; P a t o n and C a r p e n t e r 1984). I s t u d i e d t h e c h a r a c t e r i s t i c s of s p a t i a l l e a r n i n g i n hummingbirds f o r two major r e a s o n s : 1) e n e r g e t i c a c c o u n t a b i l i t y i n t h e i r b e h a v i o u r ; and 2) e m p i r i c a l e v i d e n c e t h a t s p a t i a l l e a r n i n g i s i m p o r t a n t i n t h e i r f o r a g i n g . The hummingbird s p e c i e s u s e d i n t h i s s t u d y , t h e r u f o u s h u m mingbird ( S e l a s p h o r u s r u f u s ) has h i g h d a i l y r e q u i r e m e n t s f o r e n e r g y ( T o o z e and G a s s 1985). R u f o u s hummingbirds c a n l o s e up t o 20% o f t h e i r body w e i g h t e a c h day ( p e r s . o b s . ) . F i e l d s t u d i e s show t h a t m i g r a t i n g r u f o u s hummingbirds r e g u l a t e t h e 5 numbers o f f l o w e r s i n t h e i r t e r r i t o r i e s t o p r o v i d e a t l e a s t t h e i r d a i l y e n e r g y r e q u i r e m e n t s ( G a s s e t a_l. 1976; K o d r i c - B r o w n and Brown 1978; G a s s 1979; H i x o n e t a l . 1983) and t o a c c u m u l a t e f a t r e s e r v e s a t s u s t a i n e d h i g h r a t e s ( C a r p e n t e r e_t a l . 1983; H i x o n p e r s . comm. ). I t h e r e f o r e e x p e c t e d t h a t t h e s e a n i m a l s t o be s e n s i t i v e t o e x p e r i m e n t a l m a n i p u l a t i o n o f t h e i r f o o d s u p p l y and i t s d i s t r i b u t i o n . N e c t a r i v o r e s g e n e r a l l y f e e d ,on n e c t a r f r o m s t a t i o n a r y f l o w e r s w h i c h i s s l o w l y r e p l e n i s h e d i n s e v e r a l h o u r s . F o r t h e s e a n i m a l s , t h e f o r a g e r ' s own a c t i v i t y o f t e n p r o d u c e s a s i g n i f i c a n t p r o p o r t i o n of t h e v a r i a t i o n i n n e c t a r a v a i l a b i l i t y t h a t i t e x p e r i e n c e s (Zimmerman 19B1). N e c t a r i v o r e s c a n a v o i d r e v i s i t i n g i n d i v i d u a l f l o w e r s w i t h i n p a t c h e s f o r a t l e a s t s e v e r a l h o u r s ( G i l l and Wolf 1977; K a m i l 1978), p o s s i b l y by remembering where t h e y have f o r a g e d . O t h e r s t u d i e s show more e x p l i c i t l y t h a t h ummingbirds do use s p a t i a l i n f o r m a t i o n i n f o r a g i n g . B i r d s q u i c k l y and e a s i l y l e a r n t o v i s i t o n l y p r o f i t a b l e f e e d e r s i n s m a l l a r r a y s c o n t a i n i n g m o s t l y u n p r o f i t a b l e f e e d e r s ( C o l e e t a l . 1982; M i l l e r e t a l . 1985), and t h e y c a n a l s o l e a r n t o p r e f e r e n t i a l l y v i s i t t h e most p r o f i t a b l e p a t c h e s o f f l o w e r s i n t h e i r t e r r i t o r i e s (Gass and S u t h e r l a n d 1985). I t h e r e f o r e e x p e c t e d t o be a b l e t o use t h i s s p a t i a l a b i l i t y t o e x p e r i m e n t a l l y t e s t f o r t h e f a c t o r s t h a t i n f l u e n c e t h e r a t e and d e g r e e o f s p a t i a l d i s c r i m i n a t i o n and l e a r n i n g i n complex e n v i r o n m e n t s . W i t h i n t h i s c o n t e x t , I d e f i n e d t h e f o l l o w i n g r e s e a r c h 6 o b j e c t i v e s : 1 . To c l a r i f y t h e r o l e o f l e a r n i n g and memory i n hummingbirds f o r a g i n g i n e n v i r o n m e n t s w i t h e c o l o g i c a l l y r e l e v a n t s p a t i a l v a r i a t i o n i n f o o d q u a l i t y ; and 2. To i d e n t i f y c o n s t r a i n t s on hummingbirds' a b i l i t i e s t o r e s p o n d t o s p a t i a l l y complex p a t t e r n s of p r o f i t a b i l i t y . To meet t h e s e o b j e c t i v e s , I c a r r i e d o ut a s e r i e s of e x p e r i m e n t s on i n d i v i d u a l hummingbirds f o r a g i n g i n s p a t i a l l y h e t e r o g e n e o u s a r r a y s i n t h e l a b o r a t o r y . In C h a p t e r 2 I u s e d two l a b o r a t o r y e x p e r i m e n t s t o i n v e s t i g a t e how hummingbirds use s p a t i a l l y d i s t r i b u t e d i n f o r m a t i o n t o l e a r n f e e d e r p r o f i t a b i l i t y p a t t e r n s . In p a r t i c u l a r , I w i s h e d t o d i s c o v e r how t h e c o m p l e x i t y o f p a t t e r n s of f e e d e r q u a l i t y i n f l u e n c e d how q u i c k l y and how w e l l h u m m i n g b i r d s l e a r n e d f e e d e r l o c a t i o n s . E x p e r i m e n t a l s t u d i e s have s u g g e s t e d t h a t l e a r n i n g s p a t i a l l o c a t i o n s o f f o o d i s i m p o r t a n t b o t h w i t h i n and between f o r a g i n g b o u t s i n t h e s e a n i m a l s . However, most o f t h i s work has u s e d e i t h e r s m a l l , s i m p l e a r r a y s ( e . g. C o l e e t a l . 1982) o r u n r e a l i s t i c a l l y m a n i p u l a t e d p a t c h q u a l i t i e s ( e . g. Ga s s and S u t h e r l a n d 1985), and l i t t l e i s known a b o u t t h e i m p o r t a n c e of s p a t i a l memory i n 7 day t o day f o r a g i n g i n more t y p i c a l e n v i r o n m e n t s . I u s e d f e e d e r a r r a y s o f s u f f i c i e n t s i z e t o a l l o w me t o p r e s e n t s e v e r a l t y p e s o f p a t t e r n s , and t o a l l o w e a c h f e e d e r t o c o n t a i n r e a l i s t i c a l l y low amounts o f f o o d ( C a r p e n t e r 1983; Pyke 1980). The f e e d e r s l a c k e d v i s i b l e c u e s t o t h e amount o f n e c t a r t h e y c o n t a i n e d . Thus i n f o r m a t i o n a b o u t t h e e n e r g e t i c v a l u e o f any l o c a t i o n c o u l d be o b t a i n e d o n l y by v i s i t i n g i t , o r by remembering i t s v a l u e f r o m p r e v i o u s v i s i t s . The major aims o f t h e s e e x p e r i m e n t s were t o ask i f : 1. Hummingbirds c o u l d l e a r n t o p r e f e r e n t i a l l y v i s i t h i g h e r q u a l i t y f e e d e r l o c a t i o n s even i n l a r g e a r r a y s ; 2. The r a t e and a c c u r a c y o f t h e i r l e a r n i n g i s a d i r e c t f u n c t i o n of t h e c o m p l e x i t y o f s p a t i a l o r g a n i z a t i o n of f e e d e r q u a l i t y ; and 3. S p a t i a l memory f o r l o c a t i o n i s an i m p o r t a n t component o f t h i s l e a r n i n g . T h a t i s , do b i r d s d e v e l o p e x p e c t a t i o n s a b o u t p a t c h q u a l i t y and behave as i f t h e y have c o n s t r u c t e d a "map" o f t h e a r r a y , r a t h e r t h a n u s i n g s i m p l e r u l e s f o r d i r e c t i n g t h e i r f o r a g i n g movements. In C h a p t e r 3 I c a r r i e d out a l o n g e r - t e r m e x p e r i m e n t w i t h t h e two complex p a t t e r n s o f f e e d e r q u a l i t y u s e d i n C h a p t e r 2. I 8 u s e d them t o i n v e s t i g a t e t h e c a p a c i t y o f h ummingbirds t o l e a r n complex d i s t r i b u t i o n s o f s p a t i a l i n f o r m a t i o n and t o d e t e r m i n e i f b i r d s c a n l e a r n l o c a t i o n s o f s m a l l , r e g u l a r l y , d i s t r i b u t e d p a t c h e s . In C h a p t e r 4 I e v a l u a t e my r e s e a r c h i n v i e w o f o t h e r work on s p a t i a l b e h a v i o u r o f hummingbirds and p o i n t o u t p o s s i b l e d i r e c t i o n s f o r f u t u r e r e s e a r c h . I c o n c l u d e w i t h a r e e v a l u a t i o n of t h e a p p r o a c h t a k e n i n t h i s s t u d y t o d e t e r m i n e i f t h e e x p e r i m e n t a l p a r a d i g m u s e d o f f e r s v a l u e i n t h e a n a l y s i s of s p a t i a l c a p a b i l i t i e s i n h ummingbirds and i n c r o s s - d i s c i p l i n a r y s t u d i e s o f s p a t i a l a b i l i t i e s . 9 CHAPTER 2 LEARNING AND MEMORY IN HUMMINGBIRD FORAGING: SPATIAL PATTERNS OF FOOD DISTRIBUTION S e v e r a l s p e c i e s o f f o o d - h o a r d i n g b i r d s c a n remember t h e s p a t i a l l o c a t i o n s o f many s c a t t e r e d f o o d i t e m s f o r h o u r s , d a y s o r even months ( B a l d a 1980; K a m i l and B a l d a 1985; S h e r r y e_t a l . 1981; S h e t t l e w o r t h and K r e b s 1982, 1986; Tomback 1980; V a n d e r W a l l 1982). S p a t i a l memory c a p a b i l i t i e s have a l s o been s t u d i e d i n a few o t h e r s p e c i e s , i n c l u d i n g r a t s ( O l t o n and Samuelson 1976; R o b e r t s 1979, 1982), g e r b i l s ( W i l k i e and S l o b i n 1983), c h i m p a n z e e s ( M e n z e l 1973, 1978), marmosets ( M e n z e l and Juno 1982), p i g e o n s ( W i l k i e 1984) and d o v e s ( W i l k i e e t a l . 1981). Some a u t h o r s b e l i e v e t h a t i n g e n e r a l , t h e a b i l i t y t o l e a r n and remember t h e l o c a t i o n s of good f o r a g i n g s i t e s c o u l d be v e r y i m p o r t a n t i n t h e f o r a g i n g b e h a v i o u r of many a n i m a l s ( S h e r r y 1984b), but d e t a i l e d s t u d i e s a r e few ( s e e S m i t h and Sweatman 1974; Zach and F a l l s 1977a, 1977b f o r e x a m p l e s ) . Hummingbirds and o t h e r n e c t a r i v o r o u s a n i m a l s f e e d f r o m c o n s p i c u o u s , s t a t i o n a r y , s l o w l y r e n e w i n g f o o d s o u r c e s ( p r i n c i p a l l y f l o r a l n e c t a r ) and s e v e r a l s t u d i e s s u g g e s t t h a t memory f o r s p a t i a l l o c a t i o n s i s i m p o r t a n t i n t h e i r f o r a g i n g b e h a v i o u r . E u g l o s s i n e bees r e p e a t e d l y r e t u r n t o t h e l o c a t i o n s o f p a r t i c u l a r p l a n t s a l o n g t h e i r f o r a g i n g r o u t e s , even a f t e r t h o s e p l a n t s have been removed ( J a n t z e n , 1971). Honeybees n a v i g a t e between t h e i r home h i v e s and f o r a g i n g s i t e s as i f t h e y use "landmark maps" ( G o u l d 1986). H o n e y c r e e p e r s and s u n b i r d s 10 c a n a v o i d r e v i s i t i n g i n f l o r e s c e n c e s t h e y have p r e v i o u s l y d e p l e t e d and t h e y may do t h i s by u s i n g memory ( G i l l and Wolf 1977; K a m i l 1978). Hummingbirds r a p i d l y l e a r n i n d i v i d u a l f e e d e r l o c a t i o n s i n s m a l l l a b o r a t o r y a r r a y s of 2 t o 16 f e e d e r s , w i t h or w i t h o u t c u e s s u c h a s c o l o u r (Gass 1978; C o l e e t a l . 1982) and i n one s t u d y t h i s a b i l i t y was more s t r o n g l y i n f l u e n c e d by s p a t i a l p o s i t i o n t h a n by c o l o u r c u e s ( M i l l e r e t a l . 1985). On a c o a r s e r s p a t i a l s c a l e , hummingbirds a l s o l e a r n w h i c h p a t c h e s o f f l o w e r s i n t h e i r t e r r i t o r i e s a r e most p r o f i t a b l e and use them p r e f e r e n t i a l l y even i f t h o s e p a t c h e s a r e s m a l l and d i s t r i b u t e d among a l a r g e number o f o t h e r s (Gass and S u t h e r l a n d 1985). T h i s s u g g e s t s t h a t hummingbirds have a g e n e r a l c a p a b i l i t y f o r l e a r n i n g s p a t i a l p a t t e r n s of f o o d d i s t r i b u t i o n . How q u i c k l y and how w e l l do hummingbirds l e a r n s p a t i a l d i s t r i b u t i o n s of f o o d ? Do t h e y l e a r n some k i n d s o f d i s t r i b u t i o n s b e t t e r t h a n o t h e r s ? How l o n g do t h e y remember t h e l o c a t i o n s o f f o o d , and how q u i c k l y do t h e y l e a r n new d i s t r i b u t i o n s i f t h e y m i g r a t e o r e n v i r o n m e n t s change? What k i n d s o f i n f o r m a t i o n a r e most v a l u a b l e t o them as t h e y l e a r n s p a t i a l d i s t r i b u t i o n s ? These q u e s t i o n s a b o u t s p a t i a l memory f o c u s on e c o l o g i c a l i s s u e s ; t h e y do not d i r e c t l y a d d r e s s p h y s i o l o g i c a l or p s y c h o l o g i c a l mechanisms i n v o l v e d i n s p a t i a l memory p r o b l e m s . A c c o r d i n g l y , I d e s i g n e d a s e r i e s o f l a b o r a t o r y e x p e r i m e n t s t h a t p r o v i d e d a r a n g e o f c o m p l e x i t y of g e o m e t r i c p a t t e r n s of e n e r g e t i c p r o f i t a b i l i t y i n l a r g e a r r a y s of v i s u a l l y i d e n t i c a l 11 f e e d e r s . I p r o v i d e d no v i s i b l e c u e s t o f e e d e r q u a l i t y o t h e r t h a n l o c a t i o n . A r r a y s were l a r g e enough and i n d i v i d u a l f l o w e r s c o n t a i n e d l i t t l e enough n e c t a r t h a t i n d i v i d u a l s must l e a r n t h e l o c a t i o n s o f p r o f i t a b l e f e e d e r s t o m a i n t a i n n e u t r a l o r p o s i t i v e e n e r g y b a l a n c e o v e r a s e r i e s o f t r i a l s . E x p e r i m e n t j _ : The E f f e c t o f P a t t e r n C o m p l e x i t y In t h i s e x p e r i m e n t , I a s k e d how t h e d i s t r i b u t i o n of p r o f i t a b i l i t y a f f e c t e d how q u i c k l y and t o what e x t e n t i n d i v i d u a l h u mmingbirds l e a r n e d t o v i s i t p r o f i t a b l e f e e d e r s and a v o i d v i s i t i n g u n p r o f i t a b l e o n e s . In p a r t i c u l a r , I a s k e d how t h e c o m p l e x i t y o f t h e p a t t e r n i n g o f f e e d e r q u a l i t i e s a f f e c t e d t h e d i s c r i m i n a t i o n between t h e l o c a t i o n s of p r o f i t a b l e and u n p r o f i t a b l e f e e d e r s . T h e o r e t i c a l and e m p i r i c a l s t u d i e s of a n i m a l p r o b l e m - s o l v i n g s u g g e s t t h a t i f complex p r o b l e m s c a n be decomposed i n t o a s e t o f s i m p l e r p r o b l e m s , a n i m a l s w i l l be a b l e t o l e a r n f a s t e r and p e r f o r m b e t t e r (Simon 1974, 1979; Gass 1985). In t h i s c a s e , h ummingbirds t h a t d i s c o v e r and use s p a t i a l r e l a t i o n s h i p s among f e e d e r s t o d e v e l o p e x p e c t a t i o n s a b o u t f e e d e r p r o f i t a b i l i t y s h o u l d p e r f o r m b e t t e r on s i m p l e p a t t e r n s . However, i f t h e y c a n l e a r n t h e p r o f i t a b i l i t i e s o f many i t e m s of i n f o r m a t i o n i n d e p e n d e n t l y w i t h o u t u s i n g t h e i r p a t t e r n i n g , o r i f r e c o g n i t i o n o f s p a t i a l p a t t e r n s i s n o t an i m p o r t a n t component of t h e i r l e a r n i n g , t h e n t h e y s h o u l d p e r f o r m i d e n t i c a l l y on a l l s p a t i a l d i s t r i b u t i o n s o f f e e d e r q u a l i t y r e g a r d l e s s of 12 c o m p l e x i t y . I u s e d f o u r a r r a y s o f t h e same s i z e and number of p r o f i t a b l e f e e d e r s , but w h i c h d i f f e r e d i n t h e d i s t r i b u t i o n of f e e d e r q u a l i t y . T h e r e were t h r e e r e g u l a r p a t t e r n s t h a t d i f f e r e d i n t h e s i z e and number of p a t c h e s , and one i r r e g u l a r p a t c h y p a t t e r n . In none of t h e a r r a y s were t h e r e v i s i b l e c u e s t o f e e d e r q u a l i t y . I u s e d s e v e r a l m e asures of t h e t e n d e n c y by b i r d s t o v i s i t p r o f i t a b l e l o c a t i o n s as i n d i c a t o r s of t h e e x t e n t t o w h i c h t h e y l e a r n e d t h e a r r a y s . Methods I u s e d f o u r n a i v e a d u l t f e m a l e r u f o u s hummingbirds i n t h i s e x p e r i m e n t . A l l b i r d s were c a p t u r e d i n t h e f i e l d , t h e n m a i n t a i n e d communally i n a l a r g e a v i a r y f o r 6 months p r i o r t o t e s t i n g ( p h o t o p e r i o d 13.5 L: 10.5 D ) . T h e i r m a i n t e n a n c e f o o d was s u c r o s e s o l u t i o n of 22% mass/mass c o n c e n t r a t i o n ( B o l t e n e t a l . 1979) w i t h a d d e d p r o t e i n powder (95 % s o y a p r o t e i n ) , m i n e r a l s ( A v i m i n ) , v i t a m i n s ( A v i t r o n ) , f a t t y a c i d s ( L i n a t o n e ) and wheat germ o i l on weekdays, and a 35% s u c r o s e s o l u t i o n on weekends. U n l i m i t e d a d u l t D r o s o p h i l a were a v a i l a b l e a t a l l t i m e s e x c e p t d u r i n g t r a i n i n g s e s s i o n s and t r i a l s . I p e r f o r m e d a l l t r a i n i n g and e x p e r i m e n t a l s e s s i o n s i n an e x p e r i m e n t a l chamber, (3.5 x 8.1 x 2.5 m). The room had a p e r c h i n t h e c e n t e r , and a p a i n t e d wooden p a n e l (1.07 x 1.24 m) o f 64 f e e d e r s was mounted on one w a l l . The f e e d e r s were p l a s t i c s y r i n g e n e e d l e s p l u g g e d w i t h epoxy, and mounted on r e m o v a b l e 13 c o r k s i n a r e g u l a r o r t h o g o n a l a r r a y o f h o l e s i n t h e p a n e l 11.0 cm a p a r t i n b o t h h o r i z o n t a l and v e r t i c a l d i r e c t i o n s . W i t h t h i s a r r a n g e m e n t I c o u l d r e f i l l f e e d e r s w i t h a r e p e a t i n g d i s p e n s e r ( H a m i l t o n No. PB-600-1) w i t h o u t e n t e r i n g t h e chamber by r e m o v i n g t h e c o r k s from b e h i n d t h e p a n e l . T r a i n i n g E a c h b i r d was t r a i n e d f o r t h r e e d a y s i m m e d i a t e l y p r i o r t o t e s t i n g . On e a c h day, i t r e c e i v e d 4 h o u r s (20 t r i a l s ) of t r a i n i n g i n t h e e x p e r i m e n t a l p r o c e d u r e . On t h e f i r s t day, a l l 64 f e e d e r s c o n t a i n e d 2 u l o f s u c r o s e s o l u t i o n a t t h e b e g i n n i n g of e a c h t r i a l . On d a y s 2 and 3 o n l y 32 f e e d e r s , d i s t r i b u t e d i n a r a n d o m l y - g e n e r a t e d p a t t e r n ( d i f f e r e n t e a c h d a y ) , c o n t a i n e d f o o d . I u s e d t h e s e random p a t t e r n s t o a c c u s t o m t h e b i r d s t o t h e f a c t t h a t o n l y 50% of t h e f e e d e r s w o u l d c o n t a i n f o o d i n e x p e r i m e n t s , and t o " e r a s e " o r s t a n d a r d i z e any s p a t i a l b i a s e s w i t h w h i c h t h e b i r d s may have begun t h e e x p e r i m e n t s . Between t r a i n i n g s e s s i o n s t h e b i r d s were r e t u r n e d t o t h e i r communal h o l d i n g c a g e . E x p e r i m e n t a l P r o c e d u r e s B e g i n n i n g a t t h e same t i m e on e a c h o f f o u r c o n s e c u t i v e d a y s , e a c h b i r d was g i v e n 40 t r i a l s on one o f f o u r s p a t i a l p a t t e r n s o f p r o f i t a b l e and u n p r o f i t a b l e f e e d e r s ( F i g . 2 . 1 ) . The p a t t e r n r e m a i n e d c o n s t a n t d u r i n g a l l 40 t r i a l s o f a day, but was made more complex e a c h day as f o l l o w s : Day 1: H a l v e s ; Day 2: 14 F i g u r e 2.1. The f o u r s p a t i a l p a t t e r n s o f f e e d e r q u a l i t y p r e s e n t e d t o t h e b i r d s . S o l i d c i r c l e s r e p r e s e n t "good" f e e d e r l o c a t i o n s ( i . e. f e e d e r s c o n t a i n i n g f o o d a t t h e b e g i n n i n g o f e a c h t r i a l ) ; open c i r c l e s r e p r e s e n t "bad" f e e d e r s ( i . e. f e e d e r s n o t c o n t a i n i n g f o o d ) . 15 Halves Quarters o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o • • • • o o o o • • • • o o o o • • • • o o o o • • • • • • • • o o o o • • • • o o o o • • • • o o o o • • • • o o o o • • o o • • o o o • • o • o • • • • o o • • o o • • o • • o • o o o • • o o • • • o o • o • o • o o • • o o • • o • o • • • o • • • o o • • o o • o • o • o • o • • o o • • o o o o o • o o • o o o • • o o • • • • o o o • o • o o • • o o • • o o • • • o o o Checkerboard Random 16 Q u a r t e r s ; Day 3: C h e c k e r b o a r d ; Day 4: Random (a d i f f e r e n t p a t t e r n f r o m t h e t r a i n i n g p a t t e r n ) . At t h e b e g i n n i n g of e a c h t r i a l on any p a t t e r n , 32 "good f e e d e r s " c o n t a i n e d 2 u l of 25% s u c r o s e s o l u t i o n , and 32 "bad f e e d e r s " c o n t a i n e d 2 u l of w a t e r . T h i s volume i s w i t h i n t h e n o r m a l r a n g e of n e c t a r volumes f o u n d i n t y p i c a l hummingbird f l o w e r s (Pyke 1980; C a r p e n t e r 1983; A r m s t r o n g 1986). In p i l o t e x p e r i m e n t s , hummingbirds a t e about 60 - 70 u l of s u c r o s e s o l u t i o n e v e r y 10 min and i n t h e f i e l d n o r m a l meal s i z e s a p p r o x i m a t e 70 u l (Diamond e_t a_l. 1986). E a c h i n d i v i d u a l was k e p t i n t h e e x p e r i m e n t a l chamber w i t h o u t f o o d f o r 15-20 m i n u t e s b e f o r e t h e s t a r t of e a c h e x p e r i m e n t a l day. T r i a l s were 1 min i n l e n g t h , but b i r d s c o u l d s t o p f e e d i n g and r e t u r n t o t h e p e r c h a t any t i m e . I o b s e r v e d t r i a l s from o u t s i d e t h e chamber t h r o u g h a one-way m i r r o r . I r e c o r d e d e a c h f e e d e r v i s i t o r a l l y w i t h a t a p e r e c o r d e r , and l a t e r t r a n s c r i b e d t h e s e r e c o r d s i n t o a c o m p u t e r . O c c a s i o n a l r e c o r d i n g e q u ipment m a l f u n c t i o n s r e s u l t e d i n t h e p a r t i a l or c o m p l e t e l o s s o f d a t a from 15 of a t o t a l of 640 t r i a l s , and I e l i m i n a t e d t h e s e t r i a l s f r o m a n a l y s i s . At t h e end o f e a c h t r i a l I p u l l e d a b l i n d o v e r t h e p a n e l , r e p l e n i s h e d t h e a r r a y , and t h e n began t h e n e x t t r i a l 9 m i n u t e s l a t e r . B i r d s removed a l l n e c t a r from f e e d e r s , as t h e y do from f l o w e r s i n t h e f i e l d (Gass and M o n t g o m e r i e 1981; C a r p e n t e r i n  p r e s s ) . I c o n f i r m e d t h i s i n a p i l o t e x p e r i m e n t by m e a s u r i n g amounts o f s u c r o s e r e m a i n i n g i n f e e d e r s a f t e r v i s i t s by a b i r d . O n l y 1 o f 40 v i s i t e d f e e d e r s c o n t a i n e d any m e a s u r a b l e r e s i d u a l 17 s o l u t i o n , so I assumed t h a t a l l r e v i s i t s d u r i n g t r i a l s were u n p r o f i t a b l e . R e s u l t s O v e r a l l P e r f o r m a n c e In t h i s s e c t i o n I use t h e f o l l o w i n g d e f i n i t i o n s i n a n a l y z i n g p e r f o r m a n c e . I d e f i n e a s , " c o r r e c t " a l l v i s i t s t o good f e e d e r s , whether t h e y were f i r s t ( p r o f i t a b l e ) v i s i t s o r u n p r o f i t a b l e r e v i s i t s d u r i n g t h e same t r i a l . L a t e r I w i l l c o n s i d e r how r e v i s i t s i n f l u e n c e d t h e o v e r a l l e n e r g e t i c e f f e c t i v e n e s s of b o u t s . " E a r l y t r i a l s " r e f e r s t o t h e f i r s t 5 t r i a l s on e a c h p a t t e r n ( T r i a l s 1-5); " l a t e t r i a l s " t o t h e l a s t 5 t r i a l s ( T r i a l s 3 6 - 4 0 ) . In g e n e r a l , p e r f o r m a n c e i m p r o v e d o v e r t r i a l s on e v e r y p a t t e r n . I n d i v i d u a l s began e a c h day a t a p p r o x i m a t e l y 50% c o r r e c t c h o i c e s . On s u c c e e d i n g t r i a l s , t h e y v i s i t e d i n c r e a s i n g p r o p o r t i o n s of good f e e d e r s ( F i g . 2 . 2 ) . In p a r t i c u l a r , t h e y i n c r e a s e d t h e number o f v i s i t s t h e y made t o good f e e d e r s , and d e c r e a s e d t h e numbers o f v i s i t s made t o bad f e e d e r s ( T a b l e 2.1) a l t h o u g h t h e s e c h a n g e s were s i g n i f i c a n t o n l y f o r H a l v e s and Q u a r t e r s . The p a t t e r n o f f e e d e r q u a l i t y w i t h i n a r r a y s d r a m a t i c a l l y a f f e c t e d b o t h t h e r a t e of improvement and t h e maximum p e r f o r m a n c e r e a c h e d a f t e r 40 t r i a l s . On t h e H a l v e s p a t t e r n , a l l i n d i v i d u a l s e x c e e d e d 90% c o r r e c t c h o i c e s w i t h i n 10 t r i a l s ; 18 F i g u r e 2.2. O v e r a l l performance on a l l four p a t t e r n s . Closed c i r c l e s represent r e s u l t s from Halves (top) and Checkerboard (bottom) p a t t e r n s ; open c i r c l e s from Quarters (top) and Random (bottom) p a t t e r n s . V e r t i c a l bars represent 95% c o n f i d e n c e i n t e r v a l s f o r each p o i n t . Each p o i n t i s an average f o r four b i r d s over four t r i a l s . The broken l i n e i n d i c a t e s chance performance (50%). T h i s f i g u r e summarizes 38,399 v i s i t s to feeders in 625 t r i a l s . 19 r— O UJ cc cc o o I -z 111 o cc LU D. 9 0 8 0 7 0 6 0 5 0 4 . 8 12 16 2 0 2 4 2 8 3 2 3 6 TRIAL NUMBER T a b l e 2 . 1 . N u m b e r s o f v i s i t s t o g o o d a n d b a d f e e d e r s i n e a r l y a n d l a t e t r i a l s ( s e e t e x t f o r d e f i n i t i o n s ) f o r e a c h p a t t e r n . V a l u e s a r e means p e r t r i a l f o r a l l b i r d s ( 9 5 % c o n f i d e n c e i n t e r v a l s ) o n e a c h p a t t e r n . R e s u l t s o f a t h r e e f a c t o r K r u s k a l - W a l l i s a n a l y s i s o f v a r i a n c e a r e a l s o s h o w n . Means s i g n i f i c a n t l y d i f f e r e n t a t t h e 0.05 l e v e l a r e i n d i c a t e d w i t h a "*"; i n s i g n i f i c a n t d i f f e r e n c e s a r e i n d i c a t e d a s " n . s . " ( T u k e y ' s t e s t ) . S a m p l e s i z e s ( n u m b e r o f t r i a l s i n e a c h c o m p a r i s o n ) a r e g i v e n b e l o w e a c h mean. E a r l y L a t e C o m p a r i s o n o f M e a n s H a l v e s P a t t e r n G o od F e e d e r s 3 1 . 2 ( 2 2 . 8 -n = 18 4 0 . 7) 45.9 ( 3 9 . 5 -n = 19 5 2 . 3) * B a d F e e d e r s 12. 8 ( 9.0 -n = 18 16. 7) 5.7 ( 3.7 -n = 19 7 . 6) * Q u a r t e r s P a t t e r n G o od F e e d e r s 35. 5 (29.4 -n = 20 4 1 . 5) 42 . 8 (3 7 . 7 -n = 20 47. 8) * B a d F e e d e r s 18.0 (13.4 -n = 20 2 2 . 5) 8.8 ( 6.2 -n = 20 1 1 . 3) * C h e c k e r b o a r d P a t t e r n Good F e e d e r s 35 . 1 ( 2 8 . 2 -n = 15 4 2 . 0) 40.9 ( 3 4 . 2 -n = 20 4 7 . 7) n . s . B a d F e e d e r s * 32. 8 (2 5 . 8 -n = 15 38. 3) 26. 3 ( 2 0 . 3 -n = 20 32. 2) n . s . Random P a t t e r n G ood F e e d e r s 33.0 ( 2 5 . 3 -n = 20 40 . 8) 38.2 ( 3 3 . 9 -n = 20 4 2 . 4) n . s . B a d F e e d e r s 28.8 ( 2 2 . 1 -n = 20 35. 5) 24 . 4 (20.4 -n = 20 28 . 4) n . s . 21 s u b s e q u e n t improvement was i n s i g n i f i c a n t (Spearmann rank c o r r e l a t i o n c o e f f i c i e n t Rs = 0.30 f o r t r i a l s 11-40; n= 120 t r i a l s ; p = 0 . 3 ) . T h r e e o f t h e f o u r b i r d s r e a c h e d 100% c o r r e c t c h o i c e s a t l e a s t once i n t h e f i r s t 20 t r i a l s , and no i n d i v i d u a l a c h i e v e d l e s s t h a n 80% c o r r e c t i n any o f t h e l a s t t e n t r i a l s . P e r f o r m a n c e was s i m i l a r on t h e Q u a r t e r s p a t t e r n . I n d i v i d u a l s a v e r a g e d 82% c o r r e c t c h o i c e s by t r i a l 10, t h e n i m p r o v e d s l o w l y b u t s i g n i f i c a n t l y a f t e r t h a t (Rs = 0.84 f o r t r i a l s 11-40; n=120; p < 0.001). O n l y two b i r d s e v e r a c h i e v e d 100% c o r r e c t c h o i c e s on any t r i a l on Q u a r t e r s , but no i n d i v i d u a l a c h i e v e d l e s s t h a n 65% a f t e r t r i a l 20. O v e r a l l p e r f o r m a n c e on t h e H a l v e s and Q u a r t e r s p a t t e r n s was i n s i g n i f i c a n t l y d i f f e r e n t d u r i n g t h e l a s t 5 t r i a l s ( H a l v e s : 89%; Q u a r t e r s : 85%; Mann-Whitney U t e s t ; p > 0 . 05). P e r f o r m a n c e i m p r o v e d s i g n i f i c a n t l y on b o t h t h e C h e c k e r b o a r d and Random p a t t e r n s , but much more s l o w l y t h a n on t h e o t h e r two p a t t e r n s ( C h e c k e r b o a r d : Rs = 0.75 f o r t r i a l s 1-40; n = 155 t r i a l s ; Random: Rs = 0.79; n = 158; p < 0.0001 f o r b o t h ) . In s p i t e of t h e d i f f e r e n c e i n t h e c o m p l e x i t y of t h e s e two p a t t e r n s , o v e r a l l p e r f o r m a n c e on them was i n d i s t i n g u i s h a b l e by t h i s a n a l y s i s . B i r d s a c h i e v e d an a v e r a g e o f 60% c o r r e c t c h o i c e s on t h e l a s t 5 t r i a l s on b o t h p a t t e r n s ( F i g . 2 . 2 ) . The b e s t p e r f o r m a n c e a t t a i n e d on any t r i a l on e i t h e r p a t t e r n was 74% (on Random); no i n d i v i d u a l a c h i e v e d l e s s t h a n 50% c o r r e c t a f t e r t r i a l 26. B e c a u s e t h e measure o f p e r f o r m a n c e as d e f i n e d above ( i . e. " c o r r e c t " = a v i s i t t o a good f e e d e r r e g a r d l e s s o f whether i t 22 c o n t a i n s f o o d a t t h e t i m e ) i n c l u d e s r e v i s i t s , i t o v e r e s t i m a t e s s u c c e s s o f t h e hummingbirds i n 2 ways. R e v i s i t s t o good f e e d e r s w i t h i n t r i a l s a r e u n p r o f i t a b l e e n e r g e t i c a l l y , and t h e y p r o v i d e c o n t r a d i c t o r y i n f o r m a t i o n a b o u t t h e p r o f i t a b i l i t y o f t h e l o c a t i o n . In g e n e r a l , b i r d s d i d n o t l e a r n t o s i g n i f i c a n t l y a v o i d r e v i s i t s t o good f e e d e r s w i t h i n t r i a l s f r o m e a r l y t o l a t e t r i a l s ( T a b l e 2 . 2 ) . In f a c t , on t h e Q u a r t e r s p a t t e r n t h e r e was a s l i g h t b ut s i g n i f i c a n t t e n d e n c y t o i n c r e a s e t h e number of r e v i s i t s o v e r t i m e . One component o f s p a t i a l memory t h a t may d e t e r m i n e how q u i c k l y b i r d s f i n d t h o s e f e e d e r s c o n t a i n i n g f o o d i s t h e c a p a c i t y of t h e i r " w o r k i n g memory" f o r l o c a t i o n s t h e y have v i s i t e d w i t h i n t h e c u r r e n t t r i a l . I f t h e b i r d s c a n remember w h i c h f e e d e r s t h e y have a l r e a d y v i s i t e d and a v o i d them, i t might be e x p e c t e d t h a t f e e d e r s v i s i t e d r e l a t i v e l y l o n g ago would be r e v i s i t e d more t h a n f e e d e r s v i s i t e d r e l a t i v e l y more r e c e n t l y i n t h e t r i a l . T h i s e x p e c t a t i o n i s known as a " r e c e n c y e f f e c t " f o r s p a t i a l i n f o r m a t i o n ( O l t o n and Samuelson 1976; O l t o n e_t a_l. 1977), and can be u s e d a s a measure o f w o r k i n g memory c a p a c i t y ( S h e t t l e w o r t h and K r e b s 1982). To examine t h e c h a r a c t e r i s t i c s o f w i t h i n - t r i a l w o r k i n g memory of t h e b i r d s i n t h e s e e x p e r i m e n t s , I s t u d i e d t h e t e m p o r a l s p a c i n g between r e v i s i t s w i t h i n t r i a l s f o r e a c h p a t t e r n . In a s e quence o f n v i s i t s t h e r e a r e n-1 o p p o r t u n i t i e s f o r r e p e a t v i s i t s t o f e e d e r s t o be one v i s i t l a t e r ( i n t e r v i s i t i n t e r v a l of 0 v i s i t s ) whereas t h e r e i s o n l y one o p p o r t u n i t y f o r an i n t e r v i s i t i n t e r v a l o f n-1 v i s i t s ( S h e t t l e w o r t h and K r e b s 1982). 23 Table 2.2. Revisits to good feeders within t r i a l s in early and late t r i a l s on each pattern. Values are mean percentage of r e v i s i t s among v i s i t s to good feeders (SD). Results of Mann-Whitney U tests (two-tailed) are also shown; i n s i g n i f i c a n t differences at the 0.05 l e v e l are indicated as "n.s.". Numbers of t r i a l s are shown in brackets below each mean. Early Late p Halves 37.6 (13.9) 34.3 (15.0) n.s. n = = 19 n = 1 7 Quarters 31 .1 (15.6) 39.7 (12.0) < 0.04 n = = 20 n = 19 Checkerboard 34.4 (11.2) 35.5 (13.3) n.s. n = = 18 n = 20 Random 27.8 (12.6) 27.4 ( 9.9) n.s. n = -• 17 n = 20 24 F o r a l l p a t t e r n s t h e r e was a s i g n i f i c a n t o v e r a l l e f f e c t of i n t e r v i s i t i n t e r v a l l e n g t h ( K r u s k a l - W a l l i s two-way a n a l y s i s of v a r i a n c e ; p < 0.05 f o r e a c h p a t t e r n ) w i t h r e v i s i t s a f t e r a b o u t 30-35 i n t e r v e n i n g v i s i t s more f r e q u e n t t h a n r e v i s i t s a f t e r any s h o r t e r i n t e r v a l s ( F i g . 2 . 3 ) . O t h e r s p a t i a l memory s t u d i e s have f o u n d t h a t a n i m a l s can remember a t l e a s t 15, and up t o o v e r 30 l o c a t i o n s w i t h i n t r i a l s b e f o r e p e r f o r m a n c e d e c l i n e s t o c h a n c e l e v e l s ( O l t o n and Samuelson 1976; O l t o n e t a l . 1977; S h e t t l e w o r t h and K r e b s 1982; W i l k i e e t a l . 1981). A l t h o u g h i n t h e s e e x p e r i m e n t s hummingbirds t e n d e d t o make r e p e a t v i s i t s t o f e e d e r s more o f t e n a t i n t e r v a l s l o n g e r t h a n 30 v i s i t s ( c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t t h e i r w o r k i n g memory f o r l o c a t i o n s t h e y have v i s i t e d i s a p p r o x i m a t e l y 30 l o c a t i o n s ) , i t i s a l s o p o s s i b l e t h a t t h i s h i g h p e r f o r m a n c e i s a f u n c t i o n o f t h e o r g a n i z a t i o n o f movements d u r i n g t r i a l s , and n o t s i m p l y w o r k i n g memory p e r s e . I examine some o f t h e c h a r a c t e r i s t i c s o f t h e i r movement p a t t e r n s l a t e r . P e r f o r m a n c e as measured by g r o s s e n e r g y i n t a k e f o r e a c h t r i a l was d i r e c t l y r e l a t e d t o p e r f o r m a n c e as measured by c o r r e c t c h o i c e s (Rs = 0.63; n = 625 t r i a l s ; p < 0.001). B i r d s h a r v e s t e d more t o t a l e n e r g y by t h e end o f 40 t r i a l s on t h e two s i m p l e p a t t e r n s ( a v e r a g e t o t a l i n t a k e : H a l v e s = 10.1 k J ; Q u a r t e r s = 10.2 k J ; C h e c k e r b o a r d = 9.1 k J ; Random = 8.9 k J ; K r u s k a l - W a l l i s t e s t ; p < 0. 0 5 ) . On a v e r a g e , t h e y a l s o t e r m i n a t e d b o u t s of f o r a g i n g e a r l i e r and t h e r e f o r e s p e n t l e s s t i m e and e n e r g y on t h e two s i m p l e p a t t e r n s t h a n on t h e two complex ones ( K r u s k a l - W a l l i s t e s t ; H = 10.96; p < 0.001). B o t h f a c t o r s s u g g e s t t h a t the 25 F i g u r e 2.3. Mean p e r c e n t a g e o f r e v i s i t i n g o p p o r t u n i t i e s t a k e n a t s u c c e s s i v e i n t e r v i s i t i n t e r v a l s f o r a l l p a t t e r n s . F o r e a c h b i r d t h e number of o p p o r t u n i t i e s i t had t o r e v i s i t f e e d e r s f o r e a c h i n t e r v i s i t i n t e r v a l ( s e e t e x t f o r e x p l a n a t i o n ) was c a l c u l a t e d from t h e t o t a l number of v i s i t s i n e a c h o f t h e l a s t 10 t r i a l s f o r e a c h p a t t e r n . The t o t a l number o f r e v i s i t s a nd o p p o r t u n i t i e s t o r e v i s i t were e a c h summed o v e r b l o c k s o f f i v e i n t e r v i s i t i n t e r v a l s and e x p r e s s e d as a p e r c e n t a g e . 27 b i r d s a c h i e v e d h i g h e r n e t e n e r g y i n t a k e r a t e s on b o u t s on the two s i m p l e p a t t e r n s . The above r e s u l t s c l e a r l y i n d i c a t e t h a t o v e r whole t r i a l s , and o v e r whole 40 t r i a l s e s s i o n s , t h e s p a t i a l p a t t e r n i n g o f good and bad f e e d e r s had an i m p o r t a n t e f f e c t on hummingbirds' a b i l i t i e s t o l o c a t e f o o d i n t h e t i m e a v a i l a b l e , and on t h e i r r a t e s o f e n e r g y i n t a k e w h i l e f o r a g i n g . I n c r e a s i n g t h e c o m p l e x i t y of t h e p a t t e r n i n g o f f e e d e r q u a l i t y d e c r e a s e d t h e i r a b i l i t y t o f o r a g e e f f e c t i v e l y . Spat i a l P a t t e r n s o f F o r a g i n g E f f o r t I c a r r i e d out more d e t a i l e d a n a l y s e s of two components of f o r a g i n g b e h a v i o u r i n t h e a r r a y s i n an e f f o r t t o c l a r i f y t h e f a c t o r s t h a t c o n t r i b u t e d t o t h e o v e r a l l r e s p o n s e s d e s c r i b e d a b o v e : where b i r d s c o n c e n t r a t e d t h e i r v i s i t s , and how t h e y o r g a n i z e d movements between f e e d e r s w i t h r e s p e c t t o t h e p a t t e r n of p r o f i t a b i l i t y o f t h e a r r a y . D i s t r i b u t i o n o f e f f o r t . In g e n e r a l , t h e s p a t i a l d i s t r i b u t i o n of f o r a g i n g e f f o r t r e f l e c t e d t h e u n d e r l y i n g d i s t r i b u t i o n of p r o f i t a b i l i t y on a l l 4 p a t t e r n s ( F i g . 2 . 4 ) . E v e r y b i r d v i s i t e d e v e r y good f e e d e r more t h a n any bad f e e d e r on t h e H a l v e s p a t t e r n , even i n c l u d i n g e a r l y t r i a l s when p e r f o r m a n c e was n e a r 50% c o r r e c t . R e s u l t s were s i m i l a r f o r t h e Q u a r t e r s p a t t e r n b u t l e s s d r a m a t i c . On b o t h p a t t e r n s , most of the i n c o r r e c t v i s i t s were made o n l y t o t h o s e f e e d e r s i m m e d i a t e l y 28 F i g u r e 2.4. S p a t i a l d i s t r i b u t i o n s of v i s i t s on e a c h p a t t e r n . I n d i v i d u a l f e e d e r s a r e i n d i c a t e d by a h o r i z o n t a l s q u a r e composed o f 9 s m a l l e r s q u a r e s ; good f e e d e r s a r e s h a d e d . E a c h d i s t r i b u t i o n i s an a g g r e g a t e d summary o v e r f o u r b i r d s f o r a l l 40 t r i a l s on t h e g i v e n p a t t e r n . E a c h f i g u r e i s s c a l e d i n h e i g h t t o t h e maximum f r e q u e n c y a t any l o c a t i o n on any p a t t e r n . 30 a d j a c e n t t o t h e p a t c h ( e s ) o f good f e e d e r s a f t e r t r i a l 10 ( H a l v e s : 87% of 673 i n c o r r e c t c h o i c e s f o r a l l b i r d s p o o l e d ; Q u a r t e r s : 88% o f 1334 i n c o r r e c t c h o i c e s ) . I n c o n t r a s t , w h i l e t h e d i s t r i b u t i o n o f f o r a g i n g among good and bad f e e d e r s was s t i l l c l e a r l y d i f f e r e n t on C h e c k e r b o a r d and Random, t h i s d i f f e r e n c e was much l e s s d i s t i n c t ( F i g . 2 . 4 ) . Not o n l y d i d o v e r a l l e f f o r t q u i c k l y c o n c e n t r a t e on good f e e d e r s i n H a l v e s and Q u a r t e r s , b u t " b i r d s i n c r e a s i n g l y t e n d e d t o b e g i n t r i a l s a t good f e e d e r s ( T a b l e 2 . 3 ) . T h i s i n c r e a s e was s i g n i f i c a n t o n l y f o r t h e H a l v e s and Q u a r t e r s p a t t e r n s ( b i n o m i a l t e s t ; p < 0.001 f o r t h e H a l v e s and Q u a r t e r s c o m p a r i s o n s ; p > 0.1 f o r t h e C h e c k e r b o a r d and Random c o m p a r i s o n s ) . P a t t e r n s o f Movement. I e x p r e s s e d a l l d e p a r t u r e s f r o m e a c h f e e d e r l o c a t i o n o v e r a l l b i r d s and a l l t r i a l s a s a v e c t o r i n d i c a t i n g mean d e p a r t u r e d i r e c t i o n and i t s v a r i a n c e and p l o t t e d a l l s i g n i f i c a n t v e c t o r s . Thus o v e r a l l t r e n d s of movement on ea c h p a t t e r n a p p e a r as a f i e l d o f 64 v e c t o r s ( F i g . 2.5) 1 . These v e c t o r f i e l d s summarize s i g n i f i c a n t f i r s t - o r d e r t r a n s i t i o n s between l o c a t i o n s and i l l u s t r a t e o v e r a l l p a t t e r n i n g of movement. 1 B e c a u s e s t a t i s t i c a l c o m p a r i s o n s i n v o l v i n g mean v e c t o r s a r e s t r o n g l y i n f l u e n c e d by t h e sample s i z e , and b e c a u s e numbers of movements f r o m d i f f e r e n t f e e d e r s d i f f e r e d by a s much a s an o r d e r of m a g n i t u d e , a l l mean v e c t o r s a r e s e c o n d - o r d e r means. T h a t i s , I c a l c u l a t e d one mean v e c t o r f o r e a c h f e e d e r l o c a t i o n f o r e a c h t r i a l . T h e s e t r i a l means c o n s t i t u t e t h e sample v a l u e s f o r p l o t t i n g and a n a l y s i s , and sample s i z e s a r e e q u a l t o t h e number of t r i a l s . The r a t i o n a l e f o r u s i n g s e c o n d - o r d e r means i s g i v e n i n B a t s c h e l e t ( 1 9 8 1 ) . Table 2.3. For each pattern, the proportion of early and late t r i a l s that begin with a v i s i t to a good feeder. Early Late Halves 0.40 0.90 Quarters 0.25 0.75 Checkerboard 0.50 0.60 Random 0.60 0.65 32 F i g u r e 2.5. V e c t o r f i e l d s e x p r e s s i n g t h e d i s t r i b u t i o n o f a l l d e p a r t u r e s f r o m e a c h f e e d e r . E a c h a r r o w r e p r e s e n t s t h e mean d e p a r t u r e d i r e c t i o n f r o m t h e l o c a t i o n , and i t s l e n g t h r e p r e s e n t s t h e t h e v a r i a n c e i n d e p a r t u r e d i r e c t i o n ; g r e a t e r v a r i a n c e r e s u l t s i n s h o r t e r a r r o w s . O n l y v e c t o r s s i g n i f i c a n t l y d i f f e r e n t f r o m z e r o (p < 0.05) a r e p l o t t e d ( R a y l e i g h ' s t e s t f o r r a n d o m n e s s ) . 33 H A L V E S Q U A R T E R S 34 C H E C K E R B O A R D \ \ \\ \ 1 / \ * j * / ; / I • „ ' / Illllll 1 / 4 / / t l l i i l l l f t \ / / X R A N D O M X ^ \ • V :::x::::::::::::::::::::::::'':-:'>:^:-:v:::v::: ^:$S$: ;: :: :: :>: :: •X; \ 1 - / 35 D e p a r t u r e d i r e c t i o n s were r e m a r k a b l y o r d e r l y on a l l p a t t e r n s ( F i g . 2 . 5 ) . On H a l v e s and Q u a r t e r s , movements were c l e a r l y o r g a n i z e d w i t h r e s p e c t t o t h e p a t t e r n s o f p r o f i t a b i l i t y ; b i r d s moved i n t o f i e l d s o f p r o f i t a b i l i t y and t e n d e d t o remain t h e r e . The l o n g e r v e c t o r s i n f i e l d s o f u n p r o f i t a b i l i t y i n d i c a t e low v a r i a n c e i n d e p a r t u r e d i r e c t i o n , and t h e i r g e n e r a l o r i e n t a t i o n i n d i c a t e s t h a t b i r d s moved t o w a r d f i e l d s of p r o f i t a b i l i t y . The s h o r t e r v e c t o r s i n f i e l d s o f p r o f i t a b i l i t y and t h e c o n c e n t r a t i o n o f i n s i g n i f i c a n t v e c t o r s i n t h e c e n t e r s o f t h e s e f i e l d s i n d i c a t e h i g h e r v a r i a n c e i n d e p a r t u r e d i r e c t i o n t h e r e ( l e s s s t a b l e p a t t e r n s o f movement). On C h e c k e r b o a r d and Random, movements were o r g a n i z e d w i t h r e s p e c t t o t h e a r r a y i t s e l f r a t h e r t h a n t o t h e p a t t e r n s o f p r o f i t a b i l i t y w i t h i n i t ; b i r d s moved t o w a r d t h e c e n t r e o f t h e a r r a y , and t h e r e were few s i g n i f i c a n t t r e n d s i n d e p a r t u r e d i r e c t i o n f r o m most c e n t r a l f e e d e r s . The good p e r f o r m a n c e on t h e H a l v e s and Q u a r t e r s p a t t e r n s shows t h a t hummingbirds c a n l e a r n t o f o r a g e e f f e c t i v e l y i n p a t t e r n e d a r r a y s o f p r o f i t a b l e and u n p r o f i t a b l e f e e d e r s w i t h no v i s i b l e c o r r e l a t e s t o f e e d e r q u a l i t y t h a t c o u l d g u i d e f o r a g i n g . In p a r t i c u l a r , t h e p o o r o v e r a l l p e r f o r m a n c e and t h e l a c k of e f f e c t i v e o r g a n i z a t i o n o f movement on C h e c k e r b o a r d and Random p a t t e r n s s u g g e s t s t h a t hummingbirds may n o t be a b l e t o l e a r n a l a r g e number of s p a t i a l l o c a t i o n s i n d e p e n d e n t l y of e a c h o t h e r ; i n s t e a d t h e y may r e q u i r e s t r u c t u r e o f some k i n d t o h e l p them o r g a n i z e t h e i r l e a r n i n g . T h a t i s , hummingbirds can d i s c o v e r and use t h e s p a t i a l s t r u c t u r e of t h e i r e n v i r o n m e n t s , b ut t h e y do 36 t h i s more e f f e c t i v e l y and more q u i c k l y i n s i m p l y s t r u c t u r e d e n v i r o n m e n t s . E x p e r i m e n t 2: The E f f e c t o f E x p e c t a t i o n s a b o u t F e e d e r Q u a l i t y E x p e r i m e n t 1 d e m o n s t r a t e s t h a t hummingbirds c a n f o r a g e s u c c e s s f u l l y from l a r g e p a t t e r n e d a r r a y s , b u t i t does not d i s t i n g u i s h between two p l a u s i b l e mechanisms t h a t c o u l d a c c o u n t f o r t h e o b s e r v e d p a t t e r n s o f p e r f o r m a n c e . On one hand, b i r d s may have l e a r n e d t h e e n t i r e p a t t e r n o r t h e s p a t i a l r e l a t i o n s h i p s among f e e d e r s i n t h e a r r a y a s a "map" ( M e n z e l and Wyers 1981). On t h e o t h e r hand, t h e y may have l e a r n e d non-mapping mechanisms s u c h a s s i m p l e movement r u l e s t h a t k e p t them i n p a t c h e s of good f e e d e r s ( i . e. a r e a - r e s t r i c t e d s e a r c h ) , o r a l l o w e d them t o r e c o v e r f r o m " e r r o r s " ( i . e. g o t them out o f p a t c h e s of bad f e e d e r s ) w i t h o u t n e c e s s a r i l y l e a r n i n g t h e s p a t i a l r e l a t i o n s h i p s between f e e d e r q u a l i t y and l o c a t i o n ( K r e b s e t a_l. 1983; W i l k i e and Summers 1983; S u t h e r l a n d and Dyck 1984; M e l l g r e n and Roper 1986) . To d i s t i n g u i s h between t h e s e e x p l a n a t i o n s , I e x p e r i m e n t a l l y " s w i t c h e d " t h e Q u a r t e r s p a t t e r n t o i t s m i r r o r image midway t h r o u g h t h e e x p e r i m e n t . I f h i g h p e r f o r m a n c e r e s u l t s from s p a t i a l l y u n d i f f e r e n t i a t e d movement r u l e s w i t h i n t r i a l s , t h e same r u l e s s h o u l d a p p l y a f t e r t h e s w i t c h a s b e f o r e , and b i r d s s h o u l d c o n t i n u e a t h i g h p e r f o r m a n c e . I f h i g h p e r f o r m a n c e r e s u l t e d f r o m l e a r n i n g t h e p o s i t i o n s of good f e e d e r s , whether i n d e p e n d e n t l y or as a p a t t e r n , t h e n p e r f o r m a n c e s h o u l d 37 d e t e r i o r a t e s h a r p l y a f t e r t h e s w i t c h , u n t i l b i r d s s t o p u s i n g t h e o l d d i s t r i b u t i o n and l e a r n t h e new one. Methods I u s e d f o u r n a i v e a d u l t f e m a l e and two a d u l t male r u f o u s h u mmingbirds i n t h i s e x p e r i m e n t . Methods f o r m a i n t a i n i n g t h e b i r d s and f o r t r a i n i n g them p r i o r t o e a c h e x p e r i m e n t were s i m i l a r t o t h o s e u s e d i n E x p e r i m e n t 1. I m o d i f i e d t h e f e e d e r a r r a y and method o f d a t a c o l l e c t i o n a s f o l l o w s . F e e d e r s were p l a s t i c t u b i n g (1.67 mm i n s i d e d i a m e t e r X 20 mm l o n g ) w i t h open r e s e r v o i r s a t one end. They were mounted 11.0 cm a p a r t i n b o t h h o r i z o n t a l and v e r t i c a l d i r e c t i o n s b e h i n d 2.4 mm d i a m e t e r h o l e s i n a m e t a l p a n e l on one w a l l of a 3.5 X 2.5 X 2.5 m chamber. On t h e s i d e o f t h e p a n e l f a c i n g t h e b i r d s , f e e d e r p o s i t i o n s were marked w i t h 19 mm r e d d i s k s w i t h 6.4 mm h o l e s p u nched i n t h e i r c e n t e r s f o r t h e f e e d e r t u b e s . F e e d e r s were n o t v i s i b l e t o t h e b i r d s ; t h e y saw an 8 X 8 a r r a y o f p e r f o r a t e d r e d d i s k s e q u a l l y s p a c e d 11.0 cm a p a r t . V i s i t s t o f e e d e r s were m o n i t o r e d by a m i c r o c o m p u t e r w h i c h r e c o r d e d s i g n a l s from p h o t o d a r l i n g t o n p h o t o c e l l s t r i g g e r e d by t h e b i r d s ' b i l l s on a r r i v a l and d e p a r t u r e , p r o v i d i n g a r e c o r d o f t h e t i m i n g and d u r a t i o n o f e a c h v i s i t . On t h e day f o l l o w i n g t r a i n i n g , e a c h b i r d had 60 t r i a l s , e a c h o f 40 s d u r a t i o n , on t h e Q u a r t e r s p a t t e r n ( s e e F i g . 2 . 1 ) . A f t e r 30 t r i a l s , I " s w i t c h e d " t h e p a t t e r n t o i t s m i r r o r image f o r t h e r e m a i n i n g 30 t r i a l s ; a l l good f e e d e r s s u d d e n l y became 38 bad, and v i c e v e r s a . A t t h e s w i t c h , I r e p l a c e d a l l f e e d e r s i n t h e a r r a y w i t h c l e a n ones b e f o r e a d d i n g n e c t a r . R e s u l t s P e r f o r m a n c e b e f o r e t h e s w i t c h was v e r y s i m i l a r t o t h e r e s u l t s o f E x p e r i m e n t 1 (compare F i g . 2.2 and F i g . 2 . 6 ) . B i r d s began a t t h e c h a n c e l e v e l of 50% c o r r e c t , i m p r o v e d q u i c k l y a t f i r s t , and t h e n i m p r o v e d more s l o w l y . As b e f o r e , b i r d s were s t i l l i m p r o v i n g by t r i a l 30 but t h e y had been p e r f o r m i n g a t a p p r o x i m a t e l y 80% c o r r e c t f o r a t l e a s t 15 t r i a l s by t h a t t i m e . A f t e r t h e s w i t c h , e v e r y b i r d d r o p p e d below 50% c o r r e c t f o r a t l e a s t t h e f i r s t t h r e e t r i a l s . P e r f o r m a n c e r e c o v e r e d q u i c k l y ; by 10 t r i a l s a f t e r t h e s w i t c h , b i r d s were a v e r a g i n g 75% p e r f o r m a n c e . The v e r y b e g i n n i n g o f e a c h t r i a l j u s t b e f o r e and j u s t a f t e r t h e s w i t c h i l l u s t r a t e s t h i s d r a m a t i c s h i f t i n p e r f o r m a n c e . F o r 5 t r i a l s b e f o r e t h e s w i t c h 80% of t h e 20 f i r s t v i s i t s were c o r r e c t ( i . e. good f e e d e r s ) ; f o r 5 t r i a l s a f t e r t h e s w i t c h , a l l 20 of t h e f i r s t v i s i t s were i n c o r r e c t ( i . e. p r e v i o u s l y good f e e d e r s ) . S i m i l a r l y , w h i l e 87% of t h e f i r s t 6 v i s i t s i n e a c h o f t h e 5 t r i a l s b e f o r e t h e s w i t c h were c o r r e c t , 75% of t h e f i r s t 6 v i s i t s were i n c o r r e c t i n e a c h of t h e 5 t r i a l s a f t e r t h e s w i t c h . C l e a r l y , b i r d s c o n t i n u e d t o v i s i t l o c a t i o n s t h e y had l e a r n e d were p r o f i t a b l e even t h o u g h t h e s e no l o n g e r p r o v i d e d f o o d a f t e r t h e s w i t c h . At t h e same t i m e , t h e y f a i l e d t o v i s i t t h e f e e d e r s t h a t d i d c o n t a i n f o o d . 39 F i g u r e 2.6. O v e r a l l p e r f o r m a n c e on t h e Q u a r t e r s p a t t e r n i n t h e s w i t c h e x p e r i m e n t . The p a t t e r n was s w i t c h e d t o i t s m i r r o r image a f t e r t r i a l 30 ( i n d i c a t e d by a v e r t i c a l l i n e ) . The b r o k e n l i n e i n d i c a t e s c h a n c e p e r f o r m a n c e ( 5 0 % ) . E a c h p o i n t i s an a v e r a g e f o r 6 b i r d s f o r e a c h t r i a l . The f i g u r e summarizes t h e r e s u l t s of 13,341 v i s i t s t o f e e d e r s i n 360 t r i a l s . 40 41 Not o n l y d i d t h e h ummingbirds p e r s i s t i n r e t u r n i n g t o p r e v i o u s l y good l o c a t i o n s a f t e r t h e s w i t c h , but t h e y a l s o s p e n t an u n e x p e c t e d l y l o n g t i m e h a n d l i n g p r e v i o u s l y good f e e d e r s . The t i m e r e q u i r e d f o r a hummingbird t o p r o c e s s f l o w e r s or f e e d e r s i n c r e a s e s w i t h t h e amount o f n e c t a r t h e y c o n t a i n , a l t h o u g h some minimum t i m e i s r e q u i r e d even i f t h e y c o n t a i n no n e c t a r (Gass and M o n t g o m e r i e 1981). I e x p e c t e d t h e n t h a t a t h i g h p e r f o r m a n c e b o t h b e f o r e and a f t e r t h e s w i t c h , b i r d s would s p e n d l o n g e r on f i r s t v i s i t s t o good f e e d e r s w i t h i n t r i a l s ( i . e. t o f e e d e r s t h a t c o n t a i n e d n e c t a r ) t h a n t o bad f e e d e r s , and t h e y d i d ( T a b l e 2.4; Mann-Whitney U t e s t ; p < 0 . 001). On t h e f i r s t t r i a l a f t e r t h e s w i t c h , t h e y s p e n t as l o n g h a n d l i n g f i r s t v i s i t s t o good ( i . e. p r e v i o u s l y bad) f e e d e r s as t h e y had b e f o r e t h e s w i t c h , but t h e y s p e n t s i g n i f i c a n t l y more t i m e h a n d l i n g bad ( i . e. p r e v i o u s l y good) f e e d e r s t h a n e x p e c t e d , even t h o u g h t h e s e c o n t a i n e d no f o o d a t a l l ( T a b l e 2 . 4 ) . T h i s e f f e c t was s i g n i f i c a n t f o r t h e b i r d s t a k e n t o g e t h e r (Mann-Whitney U t e s t ; p < 0.02), and s i g n i f i c a n t f o r 3 o f t h e 6 b i r d s a s i n d i v i d u a l s (p < 0.03 f o r e a c h ) . The e f f e c t d e c a y e d d u r i n g t h a t f i r s t t r i a l ( c o r r e l a t i o n o f v i s i t s e q u e n c e w i t h v i s i t d u r a t i o n ; Rs = -0.44; n=l04; p < 0.05), and was n o t d e t e c t a b l e a f t e r t h e f i r s t t r i a l (Mann-Whitney U t e s t ; p > 0 . 2 ) . B e c a u s e I r e p l a c e d a l l f e e d e r s w i t h c l e a n ones a t t h e s w i t c h , t h e r e s u l t c o u l d n o t have been due t o r e s i d u a l n e c t a r i n t h e bad f e e d e r s . P e r s i s t e n c e o f f o r m e r l y p r o f i t a b l e p a t t e r n s o f f o r a g i n g i n t h e f a c e of i n v e r t e d p a t t e r n s o f o p p o r t u n i t y d e m o n s t r a t e s t h a t l e a r n i n g o f s i m p l e a r r a y s does n o t r e s u l t e n t i r e l y f r o m l e a r n i n g 42 T a b l e 2 . 4 . D u r a t i o n s o f f i r s t v i s i t s t o f e e d e r s b e f o r e a n d a f t e r t h e m i r r o r i m a g e s w i t c h . V a l u e s a r e mean s e c o n d s s p e n t h o v e r i n g (SD) f o r a l l b i r d s f o r e a c h t r i a l . The s w i t c h o c c u r r e d b e t w e e n t r i a l 30 a n d 3 1 . S a m p l e s i z e s a r e g i v e n b e l o w e a c h m e a n . T r i a l 29 T r i a l 30 T r i a l 31 T r i a l 32 G o o d 0 . 4 7 ( 0 . 2 1 ) 0 . 5 0 ( 0 . 2 2 ) 0 . 5 1 ( 0 . 0 9 ) 0 . 4 9 ( 0 . 1 7 ) F e e d e r s n = 114 n = 120 n = 81 n = 74 B a d 0 . 2 9 ( 0 . 0 7 ) 0 . 2 9 ( 0 . 0 8 ) 0 . 3 9 ( 0 . 3 1 ) 0 . 2 9 ( 0 . 1 0 ) F e e d e r s n = 49 n = 57 n = 105 n = 110 43 of s p a t i a l l y u n d i f f e r e n t i a t e d r u l e s f o r r e s p o n d i n g t o good and bad f e e d e r s . W h i l e r u l e s o f t h i s k i n d may be i n v o l v e d , p a r t i c u l a r l y i n t h e e a r l y s t a g e s o f p a t t e r n i n d u c t i o n , t h e y a r e i n s u f f i c i e n t t o e x p l a i n t h e r e s u l t s o f t h i s e x p e r i m e n t . To the c o n t r a r y , w i t h i n 30 t r i a l s a t most, hummingbirds behave as i f t h e y "know" p r o f i t a b l e f e e d e r l o c a t i o n s and p e r s i s t i n u s i n g t h i s knowledge i_n s p i t e o f immediate e x p e r i e n c e o f f e e d e r q u a l i t y and i n s p i t e of e n e r g e t i c s h o r t f a l l s t h a t c o n t r a d i c t i t . D i s c u s s i o n Hummingbirds f e e d i n g i n l a r g e a r r a y s of v i s u a l l y i d e n t i c a l f e e d e r s l e a r n e d t o p r e f e r e n t i a l l y v i s i t p r o f i t a b l e l o c a t i o n s w i t h i n one day. The c o m p l e x i t y of t h e s p a t i a l d i s t r i b u t i o n of f e e d e r q u a l i t y imposed i m p o r t a n t c o n s t r a i n t s on t h i s c a p a b i l i t y . O n l y i n c a s e s i n w h i c h p a t t e r n s o f p r o f i t a b i l i t y were s i m p l e , i n which g r o u p s o f p r o f i t a b l e f e e d e r s were few, l a r g e , and r e g u l a r l y d i s t r i b u t e d , d i d b i r d s p e r f o r m w e l l . They p e r f o r m e d p o o r l y on more complex p a t t e r n s i n w h i c h g r o u p s of f e e d e r s were many and s m a l l o r i r r e g u l a r i n t h e i r s i z e and d i s t r i b u t i o n . S w i t c h i n g t h e Q u a r t e r s p a t t e r n t o i t s m i r r o r image a d v e r s e l y and d r a m a t i c a l l y a f f e c t e d p e r f o r m a n c e and d e m o n s t r a t e d t h a t an i m p o r t a n t component of l e a r n i n g was t h e d e v e l o p m e n t of e x p e c t a t i o n s a b o u t f e e d e r q u a l i t y . B e c a u s e e n e r g y i n t a k e d e p ended on p e r f o r m a n c e as I measured i t , t h e s e o b s e r v a t i o n s i l l u s t r a t e t h e i m p o r t a n c e o f q u e s t i o n s a b o u t how a n i m a l s d i s c o v e r and l e a r n a b o u t s p a t i a l v a r i a t i o n i n p r o f i t a b i l i t y as t h e y f o r a g e , and how t h e y use t h i s i n f o r m a t i o n l a t e r (Pyke e t 44 a l . 1977; K r e b s e t a l . 1983; G e t t y and K r e b s 1985). What d i d t h e b i r d s l e a r n a b o u t t h e s e a r r a y s ? E x a m i n a t i o n o f p r o p e r t i e s o f t h e i r r e s p o n s e s h e l p e d t o c l a r i f y how t h e y o r g a n i z e complex s p a t i a l i n f o r m a t i o n about t h e i r e n v i r o n m e n t s i n d e v e l o p i n g p a t t e r n s of a c t i o n t h a t a f f o r d h i g h p e r f o r m a n c e . T h i s a n a l y s i s d i d n o t a l l o w d e s c r i p t i o n of t h e a c t u a l mechanisms u s e d i n p e r c e p t i o n , p r o c e s s i n g , o r s t o r a g e o f i n f o r m a t i o n , or i n g e n e r a t i o n o f b e h a v i o u r ; t h e s e i s s u e s a r e beyond t h e s c o p e of my s t u d y . However, t h i s k i n d of a n a l y s i s d i d a l l o w some s i m p l e c o n c l u s i o n s a b o u t c o n s t r a i n t s under w h i c h t h e s e mechanisms must f u n c t i o n . Two i m p o r t a n t and r e l a t e d p r o p e r t i e s of t h e s p a t i a l l e a r n i n g o b s e r v e d h e r e a r e w h o l e n e s s of s p a t i a l l y d i s t r i b u t e d b e h a v i o u r p a t t e r n s , and p e r s i s t e n c e o f t h e s e p a t t e r n s even when t h e y a r e i n a p p r o p r i a t e and e n e r g e t i c a l l y c o s t l y . By w h o l e n e s s , I mean t h a t b i r d s l e a r n e d e n t i r e p a t t e r n s o f f e e d e r q u a l i t y , and not j u s t t h e q u a l i t y of i n d i v i d u a l l o c a t i o n s i n d e p e n d e n t l y . S e v e r a l a s p e c t s o f t h e i r b e h a v i o u r p o i n t t o w h o l e n e s s . F i r s t , t h e r e g u l a r i t y and symmetry o f movement p a t t e r n s i l l u s t r a t e d by t h e v e c t o r f i e l d s f o r t h e H a l v e s and Q u a r t e r s p a t t e r n s ( F i g . 2.4) s u p p o r t s t h i s n o t i o n . Second, I a r g u e d above t h a t l o c a l r u l e s f o r movement i n t h e a r r a y s c a n n o t a c c o u n t f o r t h e low p e r f o r m a n c e a f t e r t h e s w i t c h . The t h i r d and c l e a r e s t k i n d o f e v i d e n c e i s i n d i r e c t . I n d i v i d u a l s p e r s i s t e d i n making up t o 80% o f t h e i r v i s i t s t o p r e v i o u s l y good f e e d e r s f o r t h e f i r s t few t r i a l s a f t e r t h e s w i t c h ; t h e y v i s i t e d m a i n l y bad f e e d e r s 45 ( F i g . 2 . 6 ) . T h e s e bad f e e d e r s were p a t t e r n e d i n a p a r t i c u l a r way ( i . e . t h e way i n w h i c h t h e good f e e d e r s had been p a t t e r n e d b e f o r e t h e s w i t c h ) , and b i r d s p e r s i s t e d i n v i s i t i n g them i n s p i t e o f d r a m a t i c a l l y r e d u c e d e n e r g y i n t a k e . I f i t were n o t f o r t h e f a c t t h a t p e r f o r m a n c e was much lower on t h e two complex p a t t e r n s t h a n on t h e two s i m p l e o n e s , i t p l a u s i b l y c o u l d be a r g u e d t h a t b i r d s d i d not l e a r n 80% of t h e whole p a t t e r n a t a l l , b u t l e a r n e d 80% of i t s p a r t s i n d e p e n d e n t l y . But p o o r p e r f o r m a n c e on t h e complex p a t t e r n s a r g u e s s t r o n g l y t h a t hummingbirds have o n l y l i m i t e d a b i l i t y t o l e a r n p l a c e s i n d e p e n d e n t l y under t h e s e c o n d i t i o n s . I s u g g e s t t h a t v i e w i n g t h e l e a r n i n g as d e v e l o p m e n t of e x p e c t a t i o n s about whole p a t t e r n s of l o c a t i o n s i s t h e most p a r s i m o n i o u s i n t e r p r e t a t i o n o f t h e r e s u l t s . I t i s w e l l known t h a t s e v e r a l s p e c i e s of b i r d s c a n remember good f o r a g i n g s i t e s and p r e f e r e n t i a l l y r e t u r n t o them ( K r e b s et. a_l. 1974; S m i t h and Sweatman 1974; Zach and F a l l s 1977a; S h e r r y 1984a, 1984b), and b o t h o v e n b i r d s ( Z a c h and F a l l s 1977b) and t i t m i c e ( S m i t h and Sweatman 1974) a p p e a r t o be a b l e t o l e a r n d i s t r i b u t i o n s o f f o o d a s o p p o s e d t o s i m p l y remembering i n d i v i d u a l f o o d l o c a t i o n s . P e r s i s t e n c e o f s p a t i a l l y s t r u c t u r e d e x p e c t a t i o n s was c l e a r l y e v i d e n t i n b i r d s ' c h o i c e s of f e e d e r s t o v i s i t . I t was a l s o e v i d e n t i n t h e way t h e y t r e a t e d t h o s e f e e d e r s when t h e y v i s i t e d them; p a r t i c u l a r l y i n how l o n g t h e y s p e n t h a n d l i n g f e e d e r s i n t h e f i r s t t r i a l a f t e r t h e s w i t c h . T h r e e o f t h e s i x b i r d s s p e n t n e a r l y as l o n g h a n d l i n g p r e v i o u s l y good f e e d e r s as 46 t h e y had s p e n t h a n d l i n g t h o s e same f e e d e r s p r i o r t o t h e s w i t c h . Even t h o u g h t h i s e f f e c t d e c a y e d d u r i n g t h e f i r s t t r i a l , i t was s t a t i s t i c a l l y c l e a r f o r t h o s e 3 i n d i v i d u a l s ( T a b l e 2 . 4 ) . B e c a u s e h o v e r i n g a t f e e d e r s i n v o l v e s p e r f o r m a n c e o f many component b e h a v i o u r s ( i n c l u d i n g a t l e a s t f l a p p i n g t h e wings and l i c k i n g ) , t h e r e s u l t s u g g e s t s t h a t t h e s e components a r e a l s o i n f l u e n c e d by e x p e c t a t i o n s a b o u t t h e q u a l i t y o f f e e d e r s . Thus t h e b e h a v i o u r o f t h e whole a n i m a l , from s e q u e n c e s of c h o i c e s among f e e d e r s t o t i m e s p e n t h a n d l i n g them i s i n t e g r a t e d t o g e t h e r . F u r t h e r , t h i s syndrome o f b e h a v i o u r s i s d i r e c t e d by e x p e c t a t i o n s a b o u t t h e u t i l i t y o f v i s i t i n g s p a t i a l l o c a t i o n s . T h i s t e n d e n c y t o c o n t i n u e r e t u r n i n g t o f o r m e r l y p r o f i t a b l e s p a t i a l l o c a t i o n s even a f t e r t h e e n v i r o n m e n t has been c h a n g e d has a l s o been d e m o n s t r a t e d i n t i t m i c e ( S m i t h and Sweatman 1974). In t h a t s t u d y , i n d i v i d u a l s w i t h t h e h i g h e s t d e g r e e of s p e c i a l i z a t i o n on h i g h q u a l i t y p r e y p a t c h e s t e n d e d most s t r o n g l y t o p e r s i s t i n v i s i t i n g t h o s e l o c a t i o n s a f t e r t h e s w i t c h ( S m i t h and Sweatman 1974). In t h i s s t u d y , I f o u n d l i t t l e r e a s o n t o suppose t h a t h u mmingbirds c a n d i s c r i m i n a t e between i n d i v i d u a l l o c a t i o n s i n a r r a y s or r e s p o n d t o them i n d e p e n d e n t l y . T h i s s u g g e s t s t h a t t h e i r a b i l i t y t o r e s o l v e s p a t i a l l o c a t i o n s i s l i m i t e d i n some way; t h e y behave a s i f t h e y use a " c o a r s e - g r a i n e d " r e p r e s e n t a t i o n o f t h e i r e n v i r o n m e n t . T h i s c o n c l u s i o n i s i n agreement w i t h t h a t o f M i l l e r e t a_l. (1985) who f o u n d t h a t w i t h o u t o t h e r c u e s i n a d d i t i o n t o s p a t i a l l o c a t i o n , hummingbirds showed o n l y l i m i t e d a b i l i t y t o l e a r n and remember i n d i v i d u a l 47 l o c a t i o n s even i n much s m a l l e r l i n e a r a r r a y s of 6 f e e d e r s . The r e l a t i v e l y c o a r s e - g r a i n e d r e s p o n s e s o b s e r v e d i n t h e s e s t u d i e s seem p a r a d o x i c a l i n r e l a t i o n t o s u g g e s t i o n s from f i e l d work t h a t t h e s e and o t h e r a n i m a l s c a n remember many i n d i v i d u a l l o c a t i o n s . F o r example, o b s e r v a t i o n s t h a t n e c t a r i v o r o u s a n i m a l s c a n a v o i d p r e v i o u s l y v i s i t e d i n f l o r e s c e n c e s has been a t t r i b u t e d t o a b i l i t y t o remember t h e i r l o c a t i o n s ( e . g. G i l l and Wolf 1977; K a m i l 1978), a l t h o u g h s u c h " c a p a b i l i t y h a s y e t t o be c o n c l u s i v e l y d e m o n s t r a t e d . F o o d - h o a r d i n g b i r d s s u c h as marsh t i t s o r n u t c r a c k e r s c a n r e a d i l y d i s t i n g u i s h and remember t h e l o c a t i o n s of h u n d r e d s o r t h o u s a n d s o f i n d i v i d u a l c a c h e s i t e s f o r weeks or months ( S h e r r y 1984a; K a m i l and B a l d a 1985). T h i s p a r a d o x may be a t l e a s t p a r t i a l l y r e s o l v e d by c o n s i d e r i n g t h a t c a p a c i t y t o d i s t i n g u i s h and remember i n d i v i d u a l p l a c e s may be s t r o n g l y d e p e n d e n t on h a v i n g i n f o r m a t i o n t h a t c an be a s s o c i a t e d w i t h t h e p l a c e s ( L i e b l i c h and A r b i b 1982). T h i s o t h e r i n f o r m a t i o n c an i n c l u d e s i z e , shape or c o l o u r c o r r e l a t e s of q u a l i t y ( L a v e r t y 1980; G e o r g e 1980; Gass and Montgomerie 1981; M i l l e r e t a l . 1985) o r l a n d m a r k s . Vander W a l l (1982) f o u n d t h a t n u t c r a c k e r s i n t h e l a b o r a t o r y r e l o c a t e c a c h e d s e e d s by u s i n g s p a t i a l r e l a t i o n s h i p s between n e a r b y o b j e c t s w h i c h t h e y use a s l a n d m a r k s . Even s m a l l d i s p l a c e m e n t s of t h e s e " l a n d m a r k s " r e s u l t e d i n t h e b i r d s m i s s i n g t h e i r c a c h e s by s i m i l a r d i s p l a c e m e n t s . S e v e r a l s t u d i e s w i t h r a d i a l arm mazes y i e l d s i m i l a r c o n c l u s i o n s : r a t s l o c a t e t h e m s e l v e s r e l a t i v e t o b o t h n e a r b y and more d i s t a n t o b j e c t s ( S u z u k i e t a l . 1980; DeWeer e t 48 a l . 1980), and t h e fewer t h e l a n d m a r k s t h e l e s s w e l l t h e y p e r f o r m ( R o b e r t s 1982). Hummingbirds have much r i c h e r s e t s of i n f o r m a t i o n a v a i l a b l e t o them i n t h e f i e l d t h a n i n s i m p l e l a b o r a t o r y e n v i r o n m e n t s i n w h i c h I i n t e n t i o n a l l y removed a l l i n f o r m a t i o n b u t s p a t i a l l o c a t i o n . U s i n g t h e s e i n f o r m a t i o n s o u r c e s t o g e t h e r w i t h s p a t i a l l o c a t i o n c o u l d a l l o w much f i n e r d i s c r i m i n a t i o n s . 49 CHAPTER 3 SPATIAL PATTERN LEARNING BY HUMMINGBIRDS IN COMPLEX PATTERNS OF PROFITABILITY F o r a g i n g a n i m a l s t e n d t o s e l e c t r e l a t i v e l y h i g h q u a l i t y r e s o u r c e s from t h e c h o i c e s a v a i l a b l e t o them i n t h e i r e n v i r o n m e n t s ( s e e Pyke e t a l . 1977; K r e b s 1978; K r e b s e t a l . 1983 f o r r e v i e w s ) . S u c c e s s f u l f o r a g e r s must be a t t h e r i g h t p l a c e a t t h e a p p r o p r i a t e t i m e s . - B e c a u se f o o d r e s o u r c e s t y p i c a l l y v a r y i n q u a l i t y and a v a i l a b i l i t y i n b o t h s p a c e and t i m e , a n i m a l s must be a b l e t o r e s p o n d e f f e c t i v e l y t o t h i s v a r i a t i o n ( M a c A r t h u r and P i a n k a 1966; K r e b s 1978). F o r n e c t a r i v o r o u s a n i m a l s , s p a t i a l v a r i a t i o n i n f o o d a v a i l a b i l i t y e x i s t s a t s e v e r a l c o a r s e - g r a i n e d s p a t i a l s c a l e s , i n c l u d i n g whole g e o g r a p h i c r e g i o n s , h a b i t a t s , and i n d i v i d u a l home r a n g e s i n t h o s e h a b i t a t s (Gass and Mon t g o m e r i e 1981). But much of t h i s v a r i a t i o n a l s o o c c u r s a t r e l a t i v e l y f i n e - g r a i n e d s p a t i a l s c a l e s where i n d i v i d u a l s may be e x p o s e d t o i t r e g u l a r l y and r e p e a t e d l y (Wolf and H a i n s w o r t h 1983). F o r a g i v e n f o r a g e r , s u c h as a t e r r i t o r i a l h ummingbird, t h e d i s t r i b u t i o n and abundance o f n e c t a r a v a i l a b l e t o i t a t any p a r t i c u l a r t i m e i s i n f l u e n c e d by t h e d i s p e r s i o n and n e c t a r p r o d u c t i o n r a t e s o f p l a n t s , and by t h e s p a t i a l and t e m p o r a l d i s t r i b u t i o n of f o r a g i n g a c t i v i t i e s of i t s e l f a nd i t s c o m p e t i t o r s (Zimmerman 1981; Wolf and H a i n s w o r t h 1983; A r m s t r o n g e t a_l. 1986). Q u e s t i o n s a b o u t a b i l i t i e s o f n e c t a r i v o r e s t o t r a c k p o t e n t i a l l y complex p a t t e r n s of v a r i a t i o n a t s e v e r a l d i f f e r e n t s p a t i a l and t e m p o r a l s c a l e s 50 a r e b e coming i n c r e a s i n g l y f r e q u e n t ( K a m i l 1978; C o l e et. a l . 1982; G a s s 1985). A l t h o u g h hummingbirds c o u l d use v i s i b l e c o r r e l a t e s of f l o w e r q u a l i t y or landmark c u e s t o g u i d e t h e i r f o r a g i n g , s e v e r a l s t u d i e s have shown t h a t l e a r n i n g and remembering t h e s p a t i a l l o c a t i o n s o f p a t c h e s o f f l o w e r s , i n d i v i d u a l f e e d e r s , and p o s s i b l y i n d i v i d u a l f l o w e r s i s an i m p o r t a n t component of h ummingbird f o r a g i n g b e h a v i o u r ( K a m i l 1978; M i l l e r e t a l . 1985; Gass and S u t h e r l a n d 1985). In C h a p t e r 2 I showed t h a t i n t h e a b s e n c e o f v i s i b l e i n d i c e s t o f e e d e r q u a l i t y , hummingbirds can l e a r n t o f o r a g e e f f e c t i v e l y i n l a r g e , v a r i o u s l y p a t t e r n e d a r r a y s of f e e d e r s by d e v e l o p i n g and u s i n g s p a t i a l l y d i f f e r e n t i a t e d e x p e c t a t i o n s about p a t t e r n s of p r o f i t a b i l i t y , and not j u s t by u s i n g movement r u l e s t h a t have no s p a t i a l s t r u c t u r e . F u r t h e r , I c o n c l u d e d t h a t i t i s u n l i k e l y t h a t t h e y c a n l e a r n e a c h l o c a t i o n i n d e p e n d e n t l y ; t h e y a p p a r e n t l y r e q u i r e r e l a t i v e l y c o a r s e - g r a i n e d s p a t i a l s t r u c t u r e t o l e a r n a r r a y s o f t h e n u m e r i c a l s i z e I u s e d . But a r e hummingbirds a c t u a l l y l i m i t e d i n t h e way t h a t I s u g g e s t e d i n C h a p t e r 2? C o u l d t h e y l e a r n f i n e - g r a i n e d s p a t i a l p a t t e r n s t h a n t h e y d i d i n t h o s e e x p e r i m e n t s i f I gave them more t i m e ? L e a r n i n g f i n e - g r a i n e d p a t t e r n s would r e q u i r e d i s c r i m i n a t i o n and memory of l a r g e r numbers of u n i t s t h a n t o l e a r n c o a r s e - g r a i n e d p a t t e r n s , and l e a r n i n g r e l a t i o n s h i p s among them. One a p p r o a c h t o t h i s p r o b l e m of n u m e r i c a l s i z e would be t o decompose a whole p a t t e r n i n t o a s e t o f p o s s i b l y s i m p l e r p a t t e r n s and t h e n c o m b i n i n g t h e i r s o l u t i o n s i n p r a c t i c e ( M i l l e r 51 1956; Simon 1974). The two complex p a t t e r n s I u s e d i n C h a p t e r 2 d i f f e r e d i n two i m p o r t a n t ways. Good f e e d e r s were i n g r o u p s o r p a t c h e s o f f o u r f e e d e r s e a c h i n t h e C h e c k e r b o a r d p a t t e r n , but p a t c h e s v a r i e d i n s i z e i n t h e Random p a t t e r n . Good p a t c h e s were d i s c r e t e and s p a c e d r e g u l a r l y i n t h e C h e c k e r b o a r d p a t t e r n but n o t i n t h e Random p a t t e r n . The p r o b l e m o f l e a r n i n g t h e C h e c k e r b o a r d p a t t e r n i s e a s i l y -decomposable i n t o s e p a r a t e p r o b l e m s of l e a r n i n g t h a t f e e d e r s a r e i n p a t c h e s of f o u r and t h a t p a t c h e s a r e r e g u l a r l y d i s t r i b u t e d w i t h a c e r t a i n s p a c i n g . I t i s n o t so e a s y t o see how t o decompose t h e p r o b l e m of l e a r n i n g t h e Random p a t t e r n . To c l a r i f y t h e r o l e of p a t t e r n s t r u c t u r e i n p e r f o r m a n c e of a complex s p a t i a l t a s k , I a l l o w e d t h e b i r d s more t i m e t o l e a r n t h e C h e c k e r b o a r d and Random p a t t e r n s t h a n I a l l o w e d i n C h a p t e r 2 ( s e e F i g . 2 . 1 ) . I f hummingbirds a r e s e n s i t i v e t o f i n e - g r a i n e d s p a t i a l p a t t e r n s t h e n t h e y s h o u l d be a b l e t o l e a r n t h e C h e c k e r b o a r d p a t t e r n more q u i c k l y t h a n t h e Random p a t t e r n . M ethods I u s e d f i v e n a i v e a d u l t S e l a s p h o r u s r u f o u s hummingbirds ( t h r e e f e m a l e s and two m a l e s ) i n t h e e x p e r i m e n t . A l l were w i l d -c a u g h t , and m a i n t a i n e d i n i n d i v i d u a l c a g e s f o r two months p r i o r t o t h e e x p e r i m e n t . T h e i r m a i n t e n a n c e f o o d was N e k t a r - P l u s c o m m e r c i a l hummingbird f o o d ( N e k t o n U.S.A., I n c . ) f o r 5 days e a c h week, and 35% s u c r o s e on weekends d i s p e n s e d from a c e n t r a l 52 h a n g i n g f e e d e r . A d u l t D r o s o p h i l a s p . were a v a i l a b l e ad l i b i t u m a t a l l t i m e s . The f e e d e r a r r a y a p p a r a t u s , method o f d a t a c o l l e c t i o n , and e x p e r i m e n t a l p r o t o c o l were i d e n t i c a l t o t h o s e u s e d i n E x p e r i m e n t 2 o f C h a p t e r 2 w i t h t h e e x c e p t i o n t h a t I d i d no t c o l l e c t d u r a t i o n s o f v i s i t s t o f e e d e r s . T r a i n i n g T r a i n i n g p r o c e d u r e s were s i m i l a r t o t h o s e u s e d i n C h a p t e r 2, e x c e p t t h a t I e x t e n d e d t h e t h r e e d a i l y t r a i n i n g s e s s i o n s t o 6 h o u r s i n s t e a d of 4. E a c h b i r d l i v e d i n t h e e x p e r i m e n t a l chamber from t h e b e g i n n i n g o f i t s t r a i n i n g t o t h e end o f e a c h e x p e r i m e n t . Between t r a i n i n g s e s s i o n s t h e a r r a y was c o v e r e d , and 35% s u c r o s e s o l u t i o n was a v a i l a b l e ad l i b i t u m f r o m a h a n g i n g f e e d e r . Between e x p e r i m e n t s b i r d s were r e t u r n e d t o t h e i r home c a g e s . E x p e r i m e n t a l P r o c e d u r e s B e g i n n i n g on t h e f i r s t day a f t e r i t s t r a i n i n g , I t e s t e d e a c h b i r d on t h e C h e c k e r b o a r d p a t t e r n . Two t o f o u r weeks l a t e r , a f t e r a n o t h e r t h r e e d a y s o f t r a i n i n g , I t e s t e d e a c h b i r d on t h e Random p a t t e r n . F o r e a c h s e r i e s , e a c h i n d i v i d u a l had 125 t o 165 o p p o r t u n i t i e s t o f o r a g e on t h e a r r a y d u r i n g s e v e r a l c o n s e c u t i v e d a y s i n t h e f o l l o w i n g b a s i c d e s i g n : 1. A s e q u e n c e o f two o r more d a y s o f 40 t r i a l s e a c h , on w h i c h I k e p t t h e C h e c k e r b o a r d o r 53 Random p a t t e r n c o n s t a n t o v e r t h e p e r i o d ; and 2. A f i n a l day o f 45 t r i a l s , on w h i c h I " s w i t c h e d " t h e p a t t e r n t o i t s m i r r o r image a f t e r t r i a l 25. At t h e s w i t c h , I r e p l a c e d a l l f e e d e r s w i t h c l e a n ones b e f o r e a d d i n g n e c t a r t o them. The e x p e r i m e n t a l s e r i e s on t h e C h e c k e r b o a r d p a t t e r n l a s t e d 3 d a y s f o r f o u r b i r d s , w i t h t h e s w i t c h a f t e r t r i a l 25 on day 3. B i r d 4 i m p r o v e d more s l o w l y t h a n t h e o t h e r s , so I k e p t i t on t h e c o n s t a n t p a t t e r n f o r an a d d i t i o n a l day and s w i t c h e d t h e p a t t e r n a f t e r t r i a l 25 on day 4. The s e r i e s l a s t e d 4 days on t h e Random p a t t e r n , w i t h t h e s w i t c h a f t e r t r i a l 25 on day 4. B i r d 3 v i s i t e d t h e a r r a y on l e s s t h a n h a l f o f i t s t r i a l s , f o r c i n g a p r e m a t u r e t e r m i n a t i o n of t h e s e r i e s ; I e x c l u d e d i t s d a t a f r o m a l l a n a l y s e s o f t h e Random p a t t e r n . I a l s o e x c l u d e d i n d i v i d u a l t r i a l s on w h i c h any b i r d v i s i t e d l e s s t h a n 8 f e e d e r s (66 of 1325 t r i a l s o r 5%) b e c a u s e of p o t e n t i a l b i a s e s i n t r o d u c e d by s u c h s h o r t c h o i c e s e q u e n c e s . 54 R e s u l t s O v e r a l l P e r f o r m a n c e I use t h e f o l l o w i n g d e f i n i t i o n s i n a n a l y z i n g p e r f o r m a n c e . " P e r c e n t c o r r e c t c h o i c e s " i s t h e p e r c e n t a g e o f a l l v i s i t s w i t h i n t r i a l s t h a t were t o good f e e d e r s , whether t h e y were f i r s t ( p r o f i t a b l e ) v i s i t s o r u n p r o f i t a b l e r e v i s i t s d u r i n g t h e same t r i a l . " P e r c e n t r e v i s i t s " i s t h e p e r c e n t a g e of c o r r e c t c h o i c e s t h a t were u n p r o f i t a b l e r e v i s i t s i n t h e same t r i a l . " E a r l y t r i a l s " r e f e r s t o t h e f i r s t 5 t r i a l s o f t h e e x p e r i m e n t ; " l a t e t r i a l s " t o t h e l a s t 5 t r i a l s b e f o r e t h e s w i t c h , " t r i a l s j u s t a f t e r t h e s w i t c h " t o t h e n e x t 5 t r i a l s , and " l a s t t r i a l s " t o t h e l a s t 5 t r i a l s o f t h e e x p e r i m e n t . I f I s t a t e t h a t a b i r d " i n c r e a s e d " o r " d e c r e a s e d " ( e . g . i t s c o r r e c t c h o i c e s ) , I r e f e r t o a c o m p a r i s o n of i t s p e r f o r m a n c e by t h a t measure on e a r l y and l a t e t r i a l s , u n l e s s I s p e c i f i c a l l y s t a t e o t h e r w i s e . C o m p a r i s o n s were made w i t h Mann-Whitney U t e s t s u n l e s s o t h e r w i s e i n d i c a t e d . In g e n e r a l , a l l b i r d s s i g n i f i c a n t l y i m p r o v e d t h e i r p e r f o r m a n c e on b o t h p a t t e r n s ( F i g . 3.1; T a b l e 3 . 1 ) . On t h e C h e c k e r b o a r d p a t t e r n , t o t a l f e e d e r v i s i t s p e r t r i a l r e m a i n e d a p p r o x i m a t e l y c o n s t a n t t h r o u g h t i m e , b ut number o f p r o f i t a b l e v i s i t s and g r o s s e n e r g y i n t a k e p e r t r i a l i n c r e a s e d s i g n i f i c a n t l y ( T a b l e 3.1; p < 0.05 f o r e v e r y b i r d ) . C o r r e c t c h o i c e s i n c r e a s e d f r o m a b o u t 50% t o o v e r 80% f o r a t l e a s t 4 of t h e 10 t r i a l s b e f o r e t h e s w i t c h (p < 0.01 f o r e v e r y b i r d ) and r e v i s i t s d e c r e a s e d (p < 0.05 f o r 2 b i r d s ; d e c r e a s e d i n s i g n i f i c a n t l y f o r 3 55 F i g u r e 3.1. O v e r a l l p e r f o r m a n c e on t h e C h e c k e r b o a r d and Random p a t t e r n s . E a c h p o i n t i s an a v e r a g e f o r a s i n g l e t r i a l : f o r C h e c k e r b o a r d t h i s i s f o r t h e f o u r b i r d s t h a t c o m p l e t e d t h e e x p e r i m e n t i n 3 d a y s ; f o r Random i t i s f o r t h e f o u r b i r d s t h a t c o m p l e t e d t h e e x p e r i m e n t . The a s t e r i s k i n d i c a t e s a m i r r o r - i m a g e s w i t c h i n p r o f i t a b i l i t y of t h e a r r a y . The b r o k e n h o r i z o n t a l l i n e i n d i c a t e s c h a n c e p e r f o r m a n c e <50%). Note t h a t t h e f i n a l day o f e a c h e x p e r i m e n t has an a d d i t i o n a l 5 t r i a l s . D A Y 1 D A Y 2 D A Y 3 D A Y 4 . C H E C K E R B O A 1 R D » 1 1. q i 1 1 1 1 i ' • ' • * 1 1 1 — i — i — i i i r ^ * • i i R A N D O M ft* SLMI 1 J 1 1 1 1 L 1 1—. 1 1 i i — , i i — i i — i — i 1 1 1 1 1 1 1 - 1 0 2 0 4 0 2 0 4 0 2 0 4 0 2 0 4 0 TRIAL Table 3.1. Development of four measures of o v e r a l l performance on Checkerboard and Random.Values are means f o r a l l f i r s t v i s i t s t o patches by b i r d s over 5 t r i a l s (95% c . i . ) . Results of a three f a c t o r K r u s k a l - W a l l i s a n a l y s i s of v a r i a n c e are a l s o shown. Means s i g n i f i c a n t l y d i f f e r e n t at the 0.05 l e v e l are i n d i c a t e d with a "*"; i n s i g n i f i c a n t d i f f e r e n c e s are i n d i c a t e d as "n.s." (Tukey's t e s t ) . Checkerboard E a r l y Late Comparison of Means Feeder V i s i t s 31. 1 ( 28. 4 - 33. 8) 29. 0 ( 26. 9 - 31. 1) n.s. Energy Intake (J) 113. 8 (103. 7 - 122. 9) 171. 1 (155. 6 - 186. 6) * Percent C o r r e c t 56. 7 ( 54. 8 - 59. 5) 81. 4 ( 79. 0 - 84. 0) * Percent R e v i s i t s 25. 6 ( 21. 9 - 29. 4) 21. 1 ( 17. 9 - 23. 2) * Random E a r l y Late Comparison of Means Feeder V i s i t s 27. 9 ( 23. 4 - 31. 7) 25. 1 ( 23. 0 - 27. 1) n.s. Energy Intake (J) 97. 6 ( 83. 3 - 111. 9) 116. 1 (101. 5 - 130. 9) n.s. Percent C o r r e c t 52. 0 ( 47. 5 - 56. 6) 66. 2 ( 60. 0 - 72. 4) * Percent R e v i s i t s 22. 5 ( 18. 3 - 26. 7) 22. 8 ( 18. 7 - 26. 9) n.s. 58 b i r d s ) . In c o n t r a s t , b i r d s p e r f o r m e d l e s s w e l l on Random t h a n on C h e c k e r b o a r d ( T a b l e 3.1; F i g . 3 . 1 ) . E n e r g y i n t a k e p e r t r i a l i n c r e a s e d s i g n i f i c a n t l y f o r o n l y one b i r d (p < 0.02 f o r B i r d 4 ) , and b o t h t h e mean and maximum r a t e s of e n e r g y i n t a k e i n l a t e t r i a l s were c o n s i d e r a b l y l e s s t h a n f o r C h e c k e r b o a r d (means: T a b l e 3.1; maxima: 273.0 J / t r i a l ( C h e c k e r b o a r d ) ; 200.2 J / t r i a l (Random)). A l t h o u g h c o r r e c t c h o i c e s i n c r e a s e d s i g n i f i c a n t l y on a v e r a g e ( T a b l e 3.1), o n l y 2 o f t h e 4 b i r d s a c t u a l l y i m p r o v e d . B i r d s 4 and 5 a v e r a g e d o v e r 80% c o r r e c t c h o i c e s i n l a t e t r i a l s ; B i r d s 1 and 2 a v e r a g e d o n l y 52.0% c o r r e c t c h o i c e s . No b i r d s i g n i f i c a n t l y c h a n g e d t h e p e r c e n t a g e o f r e v i s i t s t o good f e e d e r s t h e y made w i t h i n t r i a l s on Random ( T a b l e 3 . 1 ) . In g e n e r a l , b i r d s p e r f o r m e d s i g n i f i c a n t l y worse i m m e d i a t e l y a f t e r I s w i t c h e d t h e p a t t e r n t o i t s m i r r o r image ( F i g . 3.1; F i g . 3 . 2 ) . T h i s e f f e c t was more d r a m a t i c f o r C h e c k e r b o a r d , where e a c h b i r d had a c h i e v e d h i g h e r p e r f o r m a n c e b e f o r e t h e s w i t c h . C o r r e c t c h o i c e s on C h e c k e r b o a r d d r o p p e d from 83% (+ 8% SD) i n l a t e t r i a l s t o o n l y 28% (+ 13% SD) i n t h e f i r s t t r i a l a f t e r t h e s w i t c h . A f t e r t h e s w i t c h , a l l 5 b i r d s r e m a i n e d below 50% c o r r e c t c h o i c e s f o r a t l e a s t 5 t r i a l s . S i m i l a r l y , t h e g r o s s e n e r g y i n t a k e o f a l l 5 b i r d s d e c l i n e d d r a m a t i c a l l y ( l a t e t r i a l s : 163.1 + 56.1 J / t r i a l ; t r i a l s a f t e r s w i t c h : 98.6 + 30.0 J / t r i a l ; p < 0.04 f o r e v e r y b i r d ) . In c o n t r a s t , o n l y two o f t h e 4 b i r d s ( B i r d s 4 and 5) d e c r e a s e d s i g n i f i c a n t l y i n p e r f o r m a n c e a f t e r t h e s w i t c h on 59 F i g u r e 3.2. O v e r a l l p e r f o r m a n c e o f e a c h i n d i v i d u a l b i r d on t h e l a s t day o f t h e e x p e r i m e n t on t h e C h e c k e r b o a r d and Random p a t t e r n s . B i r d 3 d i d n o t c o m p l e t e t h e e x p e r i m e n t on Random. E a c h p o i n t i s an a v e r a g e o v e r 5 t r i a l s . The a s t e r i s k i n d i c a t e s t h e m i r r o r - i m a g e s w i t c h i n t h e p a t t e r n a f t e r t r i a l 25. The b r o k e n h o r i z o n t a l l i n e i n d i c a t e s c h a n c e p e r f o r m a n c e ( 5 0 % ) . 61 Random ( F i g . 3 . 2 ) . C o r r e c t c h o i c e s by t h o s e two i n d i v i d u a l s d e c r e a s e d f r o m 78% + 12.1% i n l a t e t r i a l s t o 16% + 15.9% i n t h e f i r s t t r i a l a f t e r t h e s w i t c h , and r e m a i n e d below 50% f o r a t l e a s t 4 t r i a l s . C o r r e s p o n d i n g l y , t h e i r g r o s s e n e r g y i n t a k e d e c r e a s e d s i g n i f i c a n t l y a f t e r t h e s w i t c h ( l a t e t r i a l s : 139.5 + 48.0 J / t r i a l ; t r i a l s a f t e r s w i t c h : 76.8 + 47.3 J / t r i a l ; p < 0.05 f o r b o t h b i r d s ) . B i r d s 1 and 2 made s l i g h t l y but i n s i g n i f i c a n t l y fewer c o r r e c t c h o i c e s i n t r i a l s a f t e r t h e s w i t c h ( l a t e t r i a l s : 51.1% + 6.8%; t r i a l s a f t e r s w i t c h : 47.5% + 9.3%). They a l s o h a r v e s t e d s l i g h t l y but i n s i g n i f i c a n t l y l e s s g r o s s e n e r g y ( l a t e t r i a l s : 105.6 + 29.1 J / t r i a l ; t r i a l s a f t e r s w i t c h : 83.7 + 40.0 J / t r i a l ; p > 0.3 f o r a l l c o m p a r i s o n s ) . On b o t h C h e c k e r b o a r d and Random, e v e r y b i r d whose p e r f o r m a n c e was s i g n i f i c a n t l y d i s r u p t e d by t h e s w i t c h r e c o v e r e d t o o v e r 50% c o r r e c t c h o i c e s w e l l b e f o r e t h e end o f t h e e x p e r i m e n t ( F i g . 3 . 2 ) . However, no b i r d on e i t h e r p a t t e r n r e a c h e d t h e maximum p e r f o r m a n c e i t had a t t a i n e d b e f o r e t h e s w i t c h , and e n e r g y i n t a k e i n t h e l a s t 5 t r i a l s o f t h e e x p e r i m e n t r e m a i n e d s i g n i f i c a n t l y below t h a t f o r t h e 5 t r i a l s b e f o r e t h e s w i t c h (p < 0.03 f o r a l l c o m p a r i s o n s ) . In summary, p e r f o r m a n c e as m e a s u r e d by e n e r g y i n t a k e , by v i s i t s t o good f e e d e r s , and by a v o i d a n c e o f r e v i s i t s was b e t t e r and l e s s v a r i a b l e among i n d i v i d u a l s on t h e C h e c k e r b o a r d t h a n on th e Random p a t t e r n . B i r d s i m p r o v e d more q u i c k l y and r e a c h e d h i g h e r l e v e l s of p e r f o r m a n c e on C h e c k e r b o a r d t h a n on Random. H i g h p e r f o r m a n c e on b o t h p a t t e r n s ( a l l 5 i n d i v i d u a l s on 62 C h e c k e r b o a r d ; 2 of 4 i n d i v i d u a l s on Random) was s t r o n g l y d i s r u p t e d by t h e s w i t c h , i n d i c a t i n g t h a t l e a r n e d e x p e c t a t i o n s of s p a t i a l p a t t e r n i n g of good f e e d e r s was an i m p o r t a n t component of p e r f o r m a n c e . B e h a v i o u r a l Components o f P e r f o r m a n c e To u n d e r s t a n d how b i r d s c o u l d have p e r f o r m e d so much b e t t e r on C h e c k e r b o a r d t h a n t h e y d i d on Random, I c a r r i e d out d e t a i l e d a n a l y s e s of p e r f o r m a n c e on t h a t p a t t e r n . P e r f o r m a n c e on C h e c k e r b o a r d has two components: s e l e c t i o n o f p a t c h e s , and f o r a g i n g w i t h i n e a c h p a t c h . B e c a u s e C h e c k e r b o a r d has two t y p e s of p a t c h e s , good and bad, t h e s e two components can be f u r t h e r decomposed and a n a l y z e d f o r e a c h t y p e o f p a t c h . F o r example, p e r f e c t e n e r g e t i c p e r f o r m a n c e would r e q u i r e moving d i r e c t l y among a l l good p a t c h e s on t h e a r r a y w i t h o u t v i s i t i n g any bad p a t c h e s , and v i s i t i n g a l l f o u r good f e e d e r s i n e a c h o f t h o s e p a t c h e s w i t h o u t any r e v i s i t s . I f o c u s e d t h i s a n a l y s i s e x c l u s i v e l y on t h e C h e c k e r b o a r d p a t t e r n and made no d i r e c t c o m p a r i s o n s w i t h Random, f o r two r e a s o n s . F i r s t , b e c a u s e f e e d e r q u a l i t y on C h e c k e r b o a r d was d i s t r i b u t e d a s a l t e r n a t i n g g r o u p s of f o u r f e e d e r s e a c h , I c o u l d e a s i l y o r g a n i z e a n a l y s e s of b e h a v i o u r p a t t e r n s w i t h i n and among t h e s e r e c o g n i z a b l e p a t c h e s . In most c a s e s I c o u l d c l e a r l y i d e n t i f y no d i s c r e t e p a t c h e s o f good f e e d e r s i n t h e Random p a t t e r n ( s e e F i g . 2 . 1 ) . S e c o n d , b e c a u s e fewer b i r d s p e r f o r m e d w e l l on Random t h a n on C h e c k e r b o a r d and t h o s e p e r f o r m e d l e s s 63 well, there was less reason to expect clear organization of behaviour on that pattern. I used four p r i n c i p a l measures to examine how the component structure of foraging within and among patches developed. Two measures of organization of foraging within patches are the lengths of sequences of feeders v i s i t e d on bouts in good patches and bad patches (termed "runlength"). Runlength on f i r s t bouts in good patches during t r i a l s should increase toward but not beyond four feeders as performance improves. Similarly, runlength in any bad patches v i s i t e d should decrease towards one feeder. Birds should also increasingly v i s i t good feeders and good patches in sequences that minimize the time and energy costs of foraging. Two measures of organization of foraging among patches are the numbers of the two kinds of patches v i s i t e d on each t r i a l . As performance improves, birds should tend to v i s i t more of the good patches, to a maximum of 8, and fewer of the bad patches, to a minimum of 0. In summary, these four components of behavioural organization are runlengths in good and in bad patches, and numbers of good and bad patches v i s i t e d in each t r i a l . In the analyses below, I present the res u l t s for f i r s t bouts in patches during t r i a l s . A l l four components of performance improved as predicted above. Both runlength in good patches and number of good patches v i s i t e d increased asymptotically from early to late t r i a l s (Fig. 3.3; Table 3.2; runlength: p < 0.05; good patches: p < 0.01). S i m i l a r l y , both runlength in bad patches and number 64 F i g u r e 3.3. Changes i n f o u r component measures o f p e r f o r m a n c e b e f o r e t h e s w i t c h . Top p a n e l shows mean r u n l e n g t h s i n f i r s t v i s i t s t o good and bad p a t c h e s ; b o t t o m p a n e l shows number o f good and bad p a t c h e s v i s i t e d p e r t r i a l . E a c h p o i n t i s an a v e r a g e o v e r 15 t r i a l s f o r a l l b i r d s ( t h e a v e r a g e f o r t h e f i r s t and l a s t t r i a l s a r e a l s o shown). C l o s e d c i r c l e s and s o l i d l i n e s i n d i c a t e good p a t c h e s ; open c i r c l e s and b r o k e n l i n e s i n d i c a t e bad p a t c h e s . 65 => 2 . 0 i DC 1 . 5 • ""-cu. ^ T R I A L Table 3.2. Runlength in good and bad patches on the Checkerboard pattern before and after the switch. Values are means for a l l f i r s t v i s i t s to patches by a l l birds for 5 t r i a l s (SD). Sample sizes (number of t r i a l s ) are shown below each mean. Before Switch After Switch T r i a l s 1-5 T r i a l s 101-105 T r i a l s 106-110 T r i a l s 121-125 Good Patches 2.3 (1.2) n = 113 3.1 (1.3) n = 120 1.8 (0.9) 2.7 (1.4) n = 114 n = 124 Bad 1.9 (0.9) 1.2 (0.4) 2.5 (1.2) 1.7 (0.9) Patches n = 121 n = 63 n = 147 n = 112 67 of bad patches v i s i t e d s i g n i f i c a n t l y decreased over the same period (runlength: p < 0.05; good patches: p < 0.05). Performance improved more quickly in early t r i a l s , both within and among good patches, than the same measures of performance on bad patches (Fig 3.3). On average, birds took 2.4 times as many t r i a l s to reach 50% of their best performance within bad patches as within good patches, and 3.9 times as many t r i a l s to reach 50% of their best performance among bad patches as among good ones (Table 3.3). However, birds' reached peak performance on both measures of organization among patches before they reached peak performance within patches (Fig. 3.3). In fact, birds were s t i l l improving within both kinds of patches at the time of the switch. These results establish that a l l four components of performance contributed to improvement. Clearly, learning to forage e f f e c t i v e l y in the Checkerboard pattern involved organization of behaviour at both within patch and among patch sp a t i a l scales. The hummingbirds organized their behaviour with respect to pr o f i t a b l e patches faster than with respect to unprofitable ones. This organization allowed them to v i s i t most of the good feeders and avoid most of the bad feeders by the time of the switch. A more detailed examination of these four components provides additional information about the processes underlying the development of overall performance. F i r s t , analysis of the frequencies of di f f e r e n t runlengths in good and bad patches .68 Table 3.3. Rates of improvement in the four components of ov e r a l l performance among and within patches. Values are t r i a l s on which birds reached the spe c i f i e d l e v e l of performance for each component, estimated by linear interpolation of the data used in constructing Figure 3.3. Percentage of Best Observed Performance Component 25 50 75 Good Patches per t r i a l 8 15 21 Bad Patches per t r i a l 41 59 66 Runlength in Good Patches 9 15 35 Runlength in Bad Patches 14 36 59 69 r e v e a l s t h a t b i r d s d e v e l o p e d t h e p r e d i c t e d modes o f r u n l e n g t h i n good and bad p a t c h e s ( F i g . 3 . 4 ) , b o t h b e f o r e ( T r i a l s 101-105) and a f t e r t h e s w i t c h ( T r i a l s 121-125). In good p a t c h e s , modal r u n l e n g t h i n c r e a s e d f r o m 2 v i s i t s p e r p a t c h i n e a r l y t r i a l s t o 4 v i s i t s i n l a t e t r i a l s , when 37% o f a l l c o r r e c t v i s i t s were made i n r u n s of 4 v i s i t s . Over t h e same p e r i o d , t h e modal r u n l e n g t h i n bad p a t c h e s d e c r e a s e d from 2 v i s i t s t o o n l y 1 v i s i t i n l a t e t r i a l s , when o n l y 1 9 . 8 % o f a l l v i s i t s t o bad p a t c h e s were i n r u n s o f more t h a n one. Second, e x a m i n a t i o n of r u n l e n g t h s on f i r s t v i s i t s t o good p a t c h e s r e v e a l s t h a t b i r d s made s i g n i f i c a n t l y fewer r e v i s i t s t h a n would be e x p e c t e d i f t h e y had been v i s i t i n g f e e d e r s w i t h i n them a t random ( F i g . 3 . 5 ) . In f a c t , t h e y m a i n t a i n e d r e v i s i t s n e a r z e r o f o r a l l r u n s o f f o u r v i s i t s o r f e w e r . Note t h a t r e v i s i t s must i n c r e a s e i n r u n l e n g t h s o f f i v e o r g r e a t e r , b e c a u s e p a t c h e s have o n l y 4 f e e d e r s . T h i s r e s u l t d e m o n s t r a t e s t h a t b i r d s o r g a n i z e d r u n s of v i s i t s w i t h i n b o u t s i n a way t h a t e f f e c t i v e l y m i n i m i z e d r e v i s i t s . I w i l l examine t h i s i s s u e i n more d e t a i l below. T h i r d , c o m p a r i s o n o f r u n l e n g t h s b e f o r e and a f t e r t h e s w i t c h c l e a r l y r e v e a l s t h a t b i r d s d e v e l o p e d s p a t i a l l y s t r u c t u r e d e x p e c t a t i o n s a b o u t p a t c h q u a l i t y , and t h a t t h e s e e x p e c t a t i o n s p e r s i s t e d a f t e r t h e y were no l o n g e r r e i n f o r c e d by f e e d e r q u a l i t y . I showed above t h a t modal r u n l e n g t h i n good p a t c h e s was t h r e e f o l d l o n g e r t h a n i n bad p a t c h e s i n l a t e t r i a l s ; mean r u n l e n g t h s a l s o d i f f e r e d i n t h e same d i r e c t i o n ( T a b l e 3.2; p < 70 F i g u r e 3.4. D i s t r i b u t i o n of r u n l e n g t h s on f i r s t v i s i t s t o good and bad p a t c h e s . T h e s e a r e summed o v e r a l l b i r d s f o r t h e 5 t r i a l i n t e r v a l s i n d i c a t e d . The d i s t r i b u t i o n s f o r bad p a t c h e s a r e s h a d e d . 71 8 0 4 0 -> o 2 LU => o LU CC 8 0 4 0 8 0 4 0 0 8 0 4 0 0 3 T r i a l s 1 - 5 T r i a l s 1 0 1 - 1 0 5 T r i a l s 1 0 6 - 1 1 0 T r i a l s 1 2 1 - 1 2 5 1 2 3 4 5 6 7 R U N L E N G T H IN V I S I T E D P A T C H E S 72 F i g u r e 3.5. R e l a t i o n s h i p between number o f r e v i s i t s and t o t a l number of v i s i t s d u r i n g f i r s t b o u t s i n good p a t c h e s , f o r 25 t r i a l s b e f o r e t h e s w i t c h . The b r o k e n l i n e i n d i c a t e s e x p e c t e d number o f r e v i s i t s under c h a n c e e x p e c t a t i o n . The shaded band i n d i c a t e s t h e 95% c o n f i d e n c e r e g i o n a b o u t t h i s e x p e c t a t i o n b a s e d on 100 Monte C a r l o s i m u l a t i o n s . The v e r t i c a l b a r s i n d i c a t e 95% c o n f i d e n c e l i m i t s a b o u t t h e o b s e r v e d means. 74 0.0001). T h i s c l e a r d i f f e r e n c e between r u n s i n good and bad p a t c h e s r e v e r s e d a f t e r t h e s w i t c h (p < 0.01), a l t h o u g h i t r e c o v e r e d by t h e l a s t t r i a l s o f t h e e x p e r i m e n t (p < 0.001). The r e v e r s a l r e s u l t e d from c h a n g e s i n r u n l e n g t h i n b o t h good and bad p a t c h e s , and t h e s e c h a n g e s a r e d i r e c t e v i d e n c e f o r t h e d e v e l o p m e n t o f e x p e c t a t i o n s a b o u t b o t h k i n d s o f p a t c h e s . R u n l e n g t h i n bad ( p r e v i o u s l y good) p a t c h e s was l o n g e r t h a n i n bad p a t c h e s b e f o r e t h e s w i t c h (p < 0.0001), and r u n l e n g t h i n good ( p r e v i o u s l y bad) p a t c h e s was s h o r t e r t h a n i n good p a t c h e s b e f o r e t h e s w i t c h (p < 0.005). The f a c t t h a t t h e d i f f e r e n c e i n r u n l e n g t h s d i d not c o m p l e t e l y r e v e r s e a f t e r t h e s w i t c h shows t h a t a l t h o u g h r u n l e n g t h i s c l e a r l y i n f l u e n c e d by e x p e c t a t i o n s a b o u t p a t c h e s , i t i s a l s o i n f l u e n c e d by immediate e x p e r i e n c e of p a t c h q u a l i t y ; b i r d s " c o r r e c t " t h e i r e x p e c t a t i o n w i t h e x p e r i e n c e of t h e r e v e r s e d p a t t e r n . F o u r t h , c o m p a r i s o n o f t h e number o f good and bad p a t c h e s v i s i t e d b e f o r e and a f t e r t h e s w i t c h p r o v i d e s a d d i t i o n a l e v i d e n c e t h a t b i r d s d e v e l o p e d s p a t i a l l y d i s t r i b u t e d e x p e c t a t i o n s a b o u t p a t c h q u a l i t y . Whereas t h e y v i s i t e d many more good p a t c h e s t h a n bad p a t c h e s i n l a t e t r i a l s ( F i g . 3.3; p < 0.0001), t h e y v i s i t e d more bad p a t c h e s t h a n good p a t c h e s i n t r i a l s j u s t a f t e r t h e s w i t c h (p < 0.005). 75 S p a t i a l O r g a n i z a t i o n of B e h a v i o u r a l Components Among good p a t c h e s . By t h e 25 t r i a l s b e f o r e t h e s w i t c h , e a c h b i r d s t r o n g l y t e n d e d t o b e g i n t r i a l s i n a p a r t i c u l a r good p a t c h , a l t h o u g h d i f f e r e n t i n d i v i d u a l s began t r i a l s i n d i f f e r e n t p a t c h e s ( F i g . 3 . 6 ) . T h i s c a n a l i z a t i o n d e v e l o p e d w i t h e x p e r i e n c e , u n t i l e a c h b i r d began a t l e a s t 5 o f t h e l a s t 10 t r i a l s b e f o r e t h e s w i t c h i n one p a r t i c u l a r good p a t c h , and b i r d 3 began e v e r y t r i a l i n one good p a t c h . I n d i v i d u a l s not o n l y t e n d e d t o b e g i n t r i a l s i n t h e same good p a t c h , b u t t h e y t e n d e d t o b e g i n a t t h e same f e e d e r i n t h a t p a t c h . F o r example, B i r d 3 began 15 of t h e l a s t 25 t r i a l s b e f o r e t h e s w i t c h i n t h e upper l e f t f e e d e r o f t h e upper l e f t p a t c h ( i . e . t h e c o r n e r f e e d e r o f t h e a r r a y ) . I n d i v i d u a l s a l s o d e v e l o p e d u n i q u e "pathways" t h r o u g h t h e a r r a y , a s measured by t h e s e q u e n c e s o f good p a t c h e s t h e y v i s i t e d d u r i n g t h e 25 t r i a l s b e f o r e t h e s w i t c h ( F i g . 3 . 6 ) . Note t h a t t h i s measure i s c o a r s e - g r a i n e d . I t u n d e r - r e p r e s e n t s t h e d e g r e e s of f r e e d o m of movement of t h e b i r d s between good p a t c h e s i n two ways. B e c a u s e e a c h p a t h r e p r e s e n t s a d i r e c t i o n a l t r a n s i t i o n between two good p a t c h e s , e a c h o f w h i c h has f o u r f e e d e r s , e a c h p a t h c o u l d o c c u r i n 16 p o s s i b l e p e r m u t a t i o n s . In a d d i t i o n , b e c a u s e e a c h arrow r e p r e s e n t s a p a t h between good p a t c h e s w i t h o u t c o n s i d e r i n g any v i s i t s t o bad f e e d e r s t h a t may have o c c u r r e d a l o n g t h e way, e a c h of t h e 16 p e r m u t a t i o n s has even more p o s s i b l e p e r m u t a t i o n s . N e v e r t h e l e s s , t h e measure a l l o w s d e s c r i p t i o n o f much o f t h e o r g a n i z a t i o n of among-patch movement 76 F i g u r e 3.6. F r e q u e n c y and d i r e c t i o n of p r e d o m i n a n t moves between good p a t c h e s . The w i d t h of e a c h a r r o w i s p r o p o r t i o n a l t o t h e t o t a l number of e v e n t s o b s e r v e d i n t h e l a s t 25 t r i a l s b e f o r e t h e s w i t c h . A l l p a t h s shown a c c o u n t e d f o r a t l e a s t 5% of a l l moves between good p a t c h e s , w h i c h i s 6.4 t i m e s t h e f r e q u e n c y e x p e c t e d from t h e a s s u m p t i o n o f random movement. A s t e r i s k s i n d i c a t e p a t c h e s i n w h i c h t h e b i r d s most f r e q u e n t l y began t r i a l s . BIRD 1 \ c v \ N * P BIRD 4 BIRD 3 H P O B S / E X P H mmmt^ 11.5-14.0 » 9.0-11.4 p • 6.5-8.9 LEGEND 78 t h a t t h e b i r d s e x h i b i t e d . S i n c e t h e r e a r e 8 good p a t c h e s , t h e r e a r e 64 p o s s i b l e p a t h s between them, and s i n c e e a c h p a t h can o c c u r i n b o t h d i r e c t i o n s , t h e n u l l e x p e c t e d f r e q u e n c y o f each p a t h i s 0.78% of a l l p a t h s between good f e e d e r s . I w i l l c o n s i d e r t h e s e a d d i t i o n a l d e g r e e s of f r e e d o m of movement s e p a r a t e l y . I n s p e c t i o n of F i g u r e 3.6 c o n f i r m s t h e f o l l o w i n g a s s e r t i o n s a b o u t o r g a n i z a t i o n o f among-patch movement. F i r s t , t h e 5 i n d i v i d u a l s d e v e l o p e d 5 c l e a r l y d i f f e r e n t p a t h w a y s . Second, i n d i v i d u a l s a l s o d i f f e r e d i n t h e s t r e n g t h , o r dominance, of t h e i r p a t h w a y s . E a c h e x h i b i t e d a t l e a s t 8 p a t h s w i t h more t h a n 6.4 t i m e s t h e e x p e c t e d f r e q u e n c y , and 4 o f B i r d 1's p a t h s had more t h a n 11.5 t i m e s t h e e x p e c t e d f r e q u e n c y . T h i r d , p a t h s t e n d e d t o be d i a g o n a l and t o j o i n a d j a c e n t good p a t c h e s . O n l y 8 of t h e 46 dominant p a t h s were h o r i z o n t a l or v e r t i c a l , and none l i n k e d good p a t c h e s t h a t were more t h a n one bad p a t c h a p a r t . In f a c t , o n l y 3 of 49 p a t h s w i t h more t h a n 3.8 t i m e s t h e e x p e c t e d f r e q u e n c y were l o n g e r t h a n t h i s . D i s r e g a r d i n g v i s i t s t o bad f e e d e r s d u r i n g movements between good p a t c h e s f o r t h e moment, i n d i v i d u a l s e x h i b i t e d o n l y few of t h e 16 p o s s i b l e p e r m u t a t i o n s of t h e most s t r o n g l y d e v e l o p e d p a t h s among good p a t c h e s . They a l s o t e n d e d t o c o n c e n t r a t e t h e i r movements i n t o o n l y one o f t h e 16 p o s s i b i l i t i e s . F o r 5 o f t h e 12 p a t h s w i t h more t h a n 11.5 t i m e s e x p e c t e d f r e q u e n c y ( F i g . 3 . 6 ) , more t h a n 75% o f a l l movements were o f o n l y one t y p e , and f o r o n l y two p a t h s were l e s s t h a n 50% o f movements of 79 o n l y one t y p e . On a v e r a g e , 63% o f t h e 276 movements a l o n g t h e s e 18 p a t h s were o f o n l y one t y p e , and f o r no i n d i v i d u a l was t h i s a v e r a g e l e s s t h a n 50%. The maximum number o f o b s e r v e d p e r m u t a t i o n s of any p a t h was 6, and t h e modal number was 3. As i n d i v i d u a l s g a i n e d e x p e r i e n c e i n moving between p a i r s of good p a t c h e s , t h e y v i s i t e d fewer bad f e e d e r s a l o n g t h e way. The number o f bad f e e d e r s v i s i t e d p e r movement d u r i n g t h e 25 t r i a l s b e f o r e t h e s w i t c h was s t r o n g l y and n e g a t i v e l y r e l a t e d t o t h e t o t a l number o f o c c u r r e n c e s o f t h a t movement a c c u m u l a t e d by t h e t i m e o f t h e s w i t c h (Rs = -0.44; n = 111 p a t h s ; p < 0.01). In a d d i t i o n , b i r d s t e n d e d i n c r e a s i n g l y t o move d i r e c t l y between good p a t c h e s w i t h o u t v i s i t i n g any bad f e e d e r s a l o n g t h e way (Rs = 0.46 t o 0.77 ( r a n g e ) ; n = 5 b i r d s ; p < 0.05 f o r e a c h ) . T h e s e r e s u l t s s u g g e s t t h a t t h e t e n d e n c y t o c a n a l i z e movements a l o n g p a r t i c u l a r pathways and t h e t e n d e n c y t o p e r f e c t t h o s e pathways a r e r e l a t e d f u n c t i o n a l l y . W i t h i n good p a t c h e s I s u g g e s t e d e a r l i e r t h a t b i r d s o r g a n i z e d t h e i r w i t h i n - p a t c h v i s i t s i n ways t h a t m i n i m i z e d r e v i s i t s ( F i g . 3 . 5 . ) . To examine t h i s o r g a n i z a t i o n more c l o s e l y , I examined a l l r u n s o f 4 ( F i g . 3.4) t h a t c o n t a i n e d no r e v i s i t s . T h e r e were t h r e e p o s s i b l e p a t t e r n s ( T a b l e 3 . 4 ) : r u n s w i t h 0 d i a g o n a l moves ( t h a t i s , b i r d s v i s i t e d a d j a c e n t f e e d e r s i n t h e p a t c h by t u r n i n g 90 d e g r e e s i n t h e same d i r e c t i o n a f t e r e a c h f e e d e r ; U i n t h e t a b l e ) ; r u n s w i t h 1 d i a g o n a l move (Z i n t h e t a b l e ) ; and r u n s w i t h 2 d i a g o n a l moves (X i n t h e t a b l e ) . T h e s e p a t t e r n s i n c r e a s e Table 3.4. Frequencies of the three possible patterns among runs of 4 with no r e v i s i t s in good patches (see text for d e f i n i t i o n s ) . Values are pooled for a l l 5 birds for the 25 t r i a l s before the switch. Pattern Frequency (runs) U 107 Z 6 X 1 Total 81 from U t o X i n b o t h t o t a l d i s t a n c e and c o m p l e x i t y o f movement r u l e s . B i r d s c l e a r l y a d o p t e d t h e f i r s t p a t t e r n i n p r e f e r e n c e o v e r any o t h e r . In summary, b o t h w i t h i n and among p a t c h e s , b i r d s d e v e l o p e d c l e a r o r g a n i z a t i o n of t h e i r s e q u e n c e s of movements t h a t r e f l e c t e d t h e s p a t i a l p a t t e r n i n g o f f e e d e r q u a l i t i e s . T h e r e were s e v e r a l i n d i c a t i o n s t h a t b i r d s l e a r n e d t h e q u a l i t i e s of good and bad p a t c h e s , and p e r s i s t e d i n t h e i r e x p e c t a t i o n s even a f t e r t h e s w i t c h . B i r d s i m p r o v e d f a s t e r a t good p a t c h e s , and good f e e d e r s w i t h i n t h o s e p a t c h e s , t h a n t h e y d i d a t bad p a t c h e s . In p a r t i c u l a r , t h e y i m p r o v e d most q u i c k l y i n terms o f l o c a t i n g t h e good p a t c h e s ; o n l y l a t e r d i d t h e y b e g i n t o a v o i d v i s i t i n g bad p a t c h e s . D i s c u s s i o n In an a r r a y w i t h f o o d d i s t r i b u t e d among f e e d e r s i n s i m p l e , r e g u l a r s p a t i a l p a t t e r n s , hummingbirds l e a r n e d r e l a t i v e l y q u i c k l y t o v i s i t most of t h e good f e e d e r s and a v o i d most o f t h e bad o n e s . They l e a r n e d more s l o w l y on a l e s s s i m p l y p a t t e r n e d a r r a y . A l t h o u g h l e s s t h a n h a l f (two o u t o f f i v e ) o f t h e b i r d s l e a r n e d t h i s more complex p a t t e r n t o any m e a s u r a b l e e x t e n t , t h o s e who d i d l e a r n e v e n t u a l l y f o r a g e d n e a r l y as w e l l a s th e y d i d on t h e s i m p l e r p a t t e r n . As w i t h t h e two s i m p l e p a t t e r n s I s t u d i e d i n C h a p t e r 2, t h e d i s t r i b u t i o n o f b e h a v i o u r i n t h e s e a r r a y s a t h i g h p e r f o r m a n c e was v e r y s i m i l a r t o t h e d i s t r i b u t i o n of e n e r g y i n t h e a r r a y . T h i s c o r r e s p o n d e n c e o f t h e a n i m a l s ' 82 b e h a v i o u r and t h e s p a t i a l s t r u c t u r e of t h e e n v i r o n m e n t was c l e a r a t s e v e r a l s p a t i a l and t e m p o r a l s c a l e s ; f o r example, I saw i t b o t h w i t h i n and among p a t c h e s and w i t h i n and among t r i a l s . E v e r y i n d i v i d u a l who r e a c h e d h i g h p e r f o r m a n c e and s t r o n g s p a t i a l s t r u c t u r i n g o f b e h a v i o u r was s t r o n g l y a f f e c t e d by a sudden s w i t c h i n t h e d i s t r i b u t i o n o f f o o d i n i t s e n v i r o n m e n t . In e v e r y c a s e , t h e i n d i v i d u a l s c o n t i n u e d t o r e t u r n t o t h e l o c a t i o n s a t w h i c h t h e y had c o n c e n t r a t e d t h e i r e f f o r t b e f o r e t h e s w i t c h and t o behave a t them i n s i m i l a r ways, even t h o u g h t h i s was no l o n g e r p r o f i t a b l e t o do. The e x p e r i m e n t s I r e p o r t e d i n C h a p t e r 2 d i d not a l l o w me t o c o n c l u d e t h a t hummingbirds c a n n o t l e a r n complex p a t t e r n s , a l t h o u g h t h e y d i d n o t under t h e c o n d i t i o n s o f t h a t s t u d y . T h i s s t u d y was d e s i g n e d t o e x p l o r e c o n s t r a i n t s o r l i m i t s on t h e amount of s p a t i a l i n f o r m a t i o n t h a t hummingbirds c a n l e a r n , remember, and u s e . I d i d n o t f i n d a c l e a r l i m i t on t h e c a p a c i t y o f hummingbirds t o remember l o c a t i o n s , a l t h o u g h I showed t h a t t h e c o m p l e x i t y o f t h e p a t t e r n i n f l u e n c e s t h e r a t e of l e a r n i n g . T h i s f a i l u r e t o o b s e r v e l i m i t s t o c a p a c i t y i s i n agreement w i t h many o t h e r s p a t i a l memory s t u d i e s ; many a n i m a l s can remember more s p a t i a l i n f o r m a t i o n t h a n t y p i c a l e x p e r i m e n t s have o f f e r e d them. F o r example, r a t s i n r a d i a l arm maze t a s k s can p e r f o r m w e l l i n mazes of o v e r 30 p l a c e s ( R o b e r t s 1979). Food h o a r d i n g b i r d s c a n remember d o z e n s , h u n d r e d s o r t h o u s a n d s of i n d i v i d u a l l o c a t i o n s i n b o t h l a b o r a t o r y and f i e l d e x p e r i m e n t s ( S h e t t l e w o r t h a n d K r e b s 1982, 1986; S h e r r y 1984b). One p o s s i b l e c o n c l u s i o n f r o m t h i s body o f work i s t h a t a n i m a l s ' c a p a c i t y t o remember t h e 83 i n f o r m a t i o n s e t s t h e y have been o f f e r e d t o d a t e may not be s t r o n g l y l i m i t e d i n an a b s o l u t e a n a t o m i c a l or s t o r a g e c a p a c i t y s e n s e . R a t h e r i t may be c o n s t r a i n e d more by t h e way t h e y o r g a n i z e i n f o r m a t i o n f o r s t o r a g e , and t h e r e s o l u t i o n o f t h e s y s t e m o f s t o r a g e and r e c a l l (Simon 1974; R o b e r t s 1982; Gass 1985). The r e s u l t s o f d e t a i l e d a n a l y s i s o f t h e components of b e h a v i o u r a l o r g a n i z a t i o n a l l o w me t o e x t e n d my c o n c l u s i o n from C h a p t e r 2 t h a t hummingbirds d e v e l o p s p a t i a l l y s t r u c t u r e d e x p e c t a t i o n s a b o u t t h e i r e n v i r o n m e n t s ; t h e y e x h i b i t t h o s e e x p e c t a t i o n s i n t h e o r g a n i z a t i o n of t h e i r b e h a v i o u r a t s e v e r a l s p a t i a l s c a l e s . Hummingbirds l e a r n "where t o go", and t h e y l e a r n "what, t o do"; t h e s t u d y d e m o n s t r a t e s t h a t "what t o do" d e v e l o p s w i t h e x p e r i e n c e , and t h a t i t i s r e s i s t a n t t o cha n g e . I c o n c l u d e t h a t s p a t i a l p a t t e r n l e a r n i n g i s an i n t e g r a l p a r t o f hum m i n g b i r d f o r a g i n g . T h e o r i e s of f o r a g i n g i n s p a t i a l l y s t r u c t u r e d e n v i r o n m e n t s must a c c o u n t f o r t h i s c a p a b i l i t y , i n c l u d i n g i t s l i m i t a t i o n s and i t s c o n s e q u e n c e s ( s e e a l s o M e n z e l and Wyers 1981; K a m i l and Y o e r g 1982), b ut no p r e s e n t f o r a g i n g t h e o r i e s embrace t h e i s s u e i n e x p l i c i t t e r m s . Two models of s p a t i a l memory do m i n a t e e m p i r i c a l and t h e o r e t i c a l s t u d i e s o f s p a t i a l memory o r g a n i z a t i o n . The f i r s t i s a " l i s t - s e a r c h i n g " m o d el, i n w h i c h i n f o r m a t i o n about a l o c a t i o n i s s t o r e d a s a s e t o f c u e s i n a l i s t ( O l t o n 1978). A n i m a l s make c h o i c e s among p o t e n t i a l s p a t i a l l o c a t i o n s by s e a r c h i n g t h i s l i s t f o r a match between c u r r e n t p e r c e p t i o n s and 84 s e t s of c u e s a l r e a d y s t o r e d i n t h e l i s t . Most r e c e n t s t u d i e s of s p a t i a l memory i n a n i m a l s , i n c l u d i n g t h i s s t u d y , l e n d l i t t l e s u p p o r t f o r t h e f i r s t model ( s e e R o b e r t s 1982 f o r a r e v i e w ) . The s e c o n d , " s p a t i a l mapping" o r " c o g n i t i v e mapping" model v i e w s a n i m a l s as l e a r n i n g and remembering l o c a t i o n s o f p l a c e s i n t h e e n v i r o n m e n t and r e l a t i o n s h i p s between them ( M e n z e l 1973; O'Keefe and N a d e l 1978; R o b e r t s 1982). Most r e c e n t work i s c o n s i s t e n t w i t h t h e mapping model ( M o r r i s 1981; S u t h e r l a n d and Dyck 1984; G o u l d 1986), and two r e s u l t s s u g g e s t t h a t t h i s model may a c c o u n t f o r hummingbird p e r f o r m a n c e i n t h i s s t u d y . F i r s t , b e c a u s e a s p a t i a l mapping model i s a r e p r e s e n t a t i o n o f s p a t i a l r e l a t i o n s h i p s between p l a c e s , and n o t j u s t a c o l l e c t i o n of u n r e l a t e d l o c a t i o n s , a n i m a l s c o u l d c r e a t e " s h o r t -c u t s " between l o c a t i o n s t h e y have v i s i t e d b e f o r e ( G o u l d 1986). T h a t i s , a map i s not j u s t a l i s t o f pathways between p l a c e s ; i t i s an e n t i r e s u r f a c e c o n t a i n i n g r e p r e s e n t a t i o n s of p l a c e s , and new pathways c a n e a s i l y be added w i t h o r w i t h o u t t r a v e r s i n g them f i r s t . In my e x p e r i m e n t , t h e f a c t t h a t hummingbirds b o t h d i s t r i b u t e d t h e i r e f f o r t i n c l o s e c o r r e s p o n d e n c e w i t h t h e d i s t r i b u t i o n o f good p a t c h e s i n t h e a r r a y , and f o l l o w e d a v a r i e t y o f d e t a i l e d pathways i n d o i n g so i s c o n s i s t e n t w i t h t h i s i d e a : t h e b i r d s d i r e c t e d t h e i r movements between p l a c e s i n v a r i a b l e b u t i n c r e a s i n g l y e f f i c i e n t ways. Se c o n d , L i e b l i c h and A r b i b (1982) p r o p o s e d a model of s p a t i a l memory i n w h i c h a n i m a l s n o t o n l y remember i m p o r t a n t p l a c e s i n t h e i r e n v i r o n m e n t and s p a t i a l r e l a t i o n s h i p s between 85 them, but t h e y a l s o remember what t o do o r what n o t t o do i n t h o s e p l a c e s and s t o r e t h e s e t o g e t h e r . In o t h e r words t h e y p r o p o s e d t h a t t h e c o g n i t i v e map i s a "World G r a p h " c o n t a i n i n g b o t h k i n d s o f i n f o r m a t i o n . My o b s e r v a t i o n s o f hummingbird b e h a v i o u r i n t h e C h e c k e r b o a r d p a t t e r n p r o v i d e s s e v e r a l k i n d s of e v i d e n c e t h a t hummingbirds do remember t h e s e two k i n d s o f i n f o r m a t i o n . The b i r d s f i r s t l e a r n e d where t h e good p a t c h e s were, and t h e n how b e s t t o f o r a g e i n them. F u r t h e r m o r e , t h e y c o n t i n u e d t o f o r a g e i n s i m i l a r ways i n t h e same p a t c h e s a f t e r t h e s w i t c h . T h i s i s c o n s i s t e n t w i t h t h e i m p l i c a t i o n i n t h e L i e b l i c h and A r b i b (1982) model t h a t "what t o do" becomes a s s o c i a t e d w i t h "where t o go" i n memory. However, c l e a r i d e a s a b o u t how i n t e r n a l r e p r e s e n t a t i o n s o f t h e e n v i r o n m e n t s u c h a s s p a t i a l maps a r e c o n s t r u c t e d , m o d i f i e d and u s e d by a n i m a l s a r e f a r f r o m f u l l y d e v e l o p e d ( s e e L e i b l i c h and A r b i b 1982), and c o n s i d e r a t i o n of t h e s e i s s u e s i s b e y o n d the s c o p e o f t h i s s t u d y . The major c o n c l u s i o n from t h i s s t u d y , and f r o m C h a p t e r 2, t h a t how f a s t and how w e l l hummingbirds l e a r n and remember l o c a t i o n s i n an e n v i r o n m e n t i s d e p e n d e n t on t h e i r s p a t i a l a r r a n g e m e n t or o r g a n i z a t i o n makes two r e l a t e d p r e d i c t i o n s . F i r s t , a n i m a l s s h o u l d a c h i e v e h i g h e r l e v e l s of p e r f o r m a n c e w i t h a g i v e n number of p l a c e s t o remember i f t h o s e p l a c e s a r e s i m p l y p a t t e r n e d t h a n i f t h e y a r e n o t , a s s u m i n g t h a t t h e a n i m a l can p e r c e i v e t h a t p a t t e r n i n g . S e c o n d , a n i m a l s s h o u l d be a b l e t o a c h i e v e a g i v e n l e v e l of p e r f o r m a n c e w i t h more p l a c e s t o remember i f t h e y c a n o r g a n i z e i n f o r m a t i o n a b o u t t h o s e p l a c e s i n t o s i m p l e r s u b s e t s t h a n i f t h e y c a n n o t , f o r example by u s i n g 86 c u e s s u c h a s l a n d m a r k s . How a n i m a l s - use t h e p a t t e r n i n g of s p a t i a l l y d i s t r i b u t e d i n f o r m a t i o n t o p e r f o r m s u c c e s s f u l l y i n a complex e n v i r o n m e n t i s s t i l l p o o r l y known. One well - k n o w n s y s t e m may o f f e r good o p p o r t u n i t i e s f o r e x p l o r i n g t h i s q u e s t i o n . F o o d - h o a r d i n g b i r d s , s u c h a s marsh t i t s , c h i c k a d e e s , n u t c r a c k e r s and j a y s use v i s u a l i n f o r m a t i o n t o remember and r e l o c a t e c a c h e s i t e s b u t v e r y l i t t l e work has been done on how t h e y s e l e c t among t h e many c u e s t h a t c o u l d p o t e n t i a l l y be u s e d as l a n d m a r k s ( S h e r r y 1984b). N u t c r a c k e r s t e n d t o p l a c e t h e i r c a c h e s a r o u n d p r o m i n e n t o b j e c t s , s u c h as r o c k s , l o g s and t r e e stumps ( B a l d a 1980; Tomback 1980) and t h e y a r e s e n s i t i v e t o d i s p l a c e m e n t s i n n e a r b y l a n d m a r k s when r e c o v e r i n g t h e i r c a c h e s (Vander W a l l 1982). One p o s s i b i l i t y i s t h a t t h e s e b i r d s may t e n d t o use s i m i l a r s e t s of l a n d m a r k s i n d i f f e r e n t l o c a t i o n s , a l t h o u g h d i f f e r e n t b i r d s m i g h t use d i f f e r e n t s e t s . O b s e r v a t i o n s o f i n d i v i d u a l s i t e p r e f e r e n c e s ( i . e. s t o r i n g f o o d i n o n l y a few t y p e s of p l a c e s ) i n b o t h n u t c r a c k e r s ( B a l d a 1980) and c h i c k a d e e s ( S h e t t l e w o r t h and K r e b s 1982) i s c o n s i s t e n t w i t h t h i s p r e d i c t i o n . A s e c o n d p r e d i c t i o n t h a t has n o t y e t been t e s t e d i s whether b i r d s t e n d t o s e l e c t c l a s s e s o f l a n d m a r k s t h a t t e n d t o be f o u n d i n s i m p l e g e o m e t r i c r e l a t i o n s h i p s t o e a c h o t h e r . Not a l l e n v i r o n m e n t s p r o v i d e o b v i o u s p r o x i m a t e c u e s t o t h e q u a l i t y o f l o c a t i o n s . But many a n i m a l s c a n l e a r n and remember p a t c h e s of p r o f i t a b l e f o o d i t e m s even i f c u e s a r e n o t r e a d i l y a v a i l a b l e ( S m i t h and Sweatman 1974; Zach and F a l l s 1977; Gass 87 and S u t h e r l a n d 1985); i n some c a s e s w i t h h i g h a c c u r a c y and f o r l o n g p e r i o d s ( e . g. M e l l g r e n and Roper 1986). B e cause t h i s s t u d y d e m o n s t r a t e d t h a t t h e p a t t e r n i n g o f f o o d d i s t r i b u t i o n s i s an i m p o r t a n t d e t e r m i n a n t of how w e l l hummingbirds can l e a r n them, a t t e n t i o n may u s e f u l l y be s h i f t e d t o c l a r i f y i n g t h e p r o c e s s e s t h a t u n d e r l i e r e c o g n i t i o n and memory o f s p a t i a l p a t t e r n s of i n f o r m a t i o n . 88 CHAPTER 4 GENERAL DISCUSSION The r e s e a r c h p r e s e n t e d i n t h i s t h e s i s e x t e n d s e a r l i e r work on use of memory i n hummingbird f o r a g i n g t o i n c l u d e a) t h e c a p a b i l i t y f o r l e a r n i n g complex p a t t e r n s o f s p a t i a l i n f o r m a t i o n ; and b) s u g g e s t i o n s f o r how hummingbird s p a t i a l memory m i g h t be o r g a n i z e d . The r e s u l t s i n t u r n p o i n t t o o t h e r q u e s t i o n s about t h e c h a r a c t e r i s t i c s o f s p a t i a l memory i n hummingbirds i n p a r t i c u l a r , and a b o u t t h e r o l e o f l e a r n i n g s p a t i a l l o c a t i o n s and d i s t r i b u t i o n of r e s o u r c e s i n t h e f o r a g i n g b e h a v i o u r o f t h e s e and o t h e r a n i m a l s . In t h i s c h a p t e r , I r e v i e w t h e p r i n c i p a l r e s u l t s of t h e e x p e r i m e n t s , i n t e g r a t e t h e s e w i t h r e c e n t work on hummingbird b e h a v i o u r and p o i n t o u t p o s s i b l e d i r e c t i o n s f o r f u t u r e r e s e a r c h . The e x p e r i m e n t s i n C h a p t e r 2 showed t h a t i n s i t u a t i o n s i n w h i c h s p a t i a l l o c a t i o n was t h e p r i m a r y cue t o f e e d e r q u a l i t y , h u m mingbirds q u i c k l y l e a r n t o f o r a g e i n l a r g e a r r a y s i f t h e q u a l i t y o f f e e d e r s was s i m p l y p a t t e r n e d . They l e a r n complex a r r a y s much more s l o w l y . The r e s u l t s i n d i c a t e t h a t an i m p o r t a n t component of l e a r n i n g i n t h e s e a r r a y s was t h e d e v e l o p m e n t of c o a r s e - g r a i n e d e x p e c t a t i o n s a b o u t t h e q u a l i t y of g r o u p s of f e e d e r s ; t h e r e was l i t t l e e v i d e n c e t h a t t h e b i r d s depended p r i m a r i l y on a r e a - r e s t r i c t e d s e a r c h mechanisms t o p e r f o r m i n t h e s e a r r a y s . S i m i l a r l y , t h e r e was l i t t l e c l e a r e v i d e n c e t h a t t h e b i r d s l e a r n e d t h e q u a l i t i e s o f i n d i v i d u a l l o c a t i o n s i n d e p e n d e n t l y of o t h e r l o c a t i o n s . The r e s u l t s s u p p o r t 89 observations that hummingbirds have good memory for locations of highly p r o f i t a b l e feeders or patches of flowers (Miller et a l . 1985; Gass and Sutherland 1985) and that t h i s c a p a b i l i t y may be an important factor in use of available resources. However, the re s u l t s also imply that, under conditions of highly variable nectar q u a l i t i e s among plants, birds may not be able to remember locations of previous bouts or individual v i s i t s to flowers. The experiment in Chapter 3 confirms that hummingbirds learn locations of good feeders by developing expectations about the quality of feeder locations. Even in complex d i s t r i b u t i o n s of feeder quali t y , hummingbirds learn to use r e g u l a r i t i e s in the patterning of feeders in foraging. Given enough time, they can learn r e l a t i v e l y complex, regular patterned arrays, and remember patches of good feeders within those patterns. Slow and variable improvement on a non-regularly distributed pattern of feeders reinforces the conclusion that patterning of s p a t i a l d i s t r i b u t i o n s i s an important factor in sp a t i a l learning in th i s species. Analysis of movements within and among patches suggested that the birds may have been using a map-like representation to guide their return to good patches. To summarize the general relationship between complexity of s p a t i a l pattern and rate of improvement and le v e l of performance, I i l l u s t r a t e the primary result from each experiment in the study in F i g . 4.1. The ef f e c t of s p a t i a l patterning of food d i s t r i b u t i o n in this study can be considered as primarily a r a t e - l i m i t i n g phenomenon. Performance began at 90 F i g u r e 4.1. Summary of p e r f o r m a n c e on a l l f o u r p a t t e r n s u s e d i n t h e s t u d y . C l o s e d c i r c l e s r e p r e s e n t 4 - t r i a l a v e r a g e s from H a l v e s (H) and C h e c k e r b o a r d (C) p a t t e r n s ; open c i r c l e s from Q u a r t e r s (Q) and Random (R) p a t t e r n s . V a l u e s f o r H a l v e s a r e from E x p e r i m e n t 1 ( F i g . 2 . 2 ) ; f o r Q u a r t e r s f r o m E x p e r i m e n t 2 ( F i g . 2 . 6 ) . V a l u e s f o r C h e c k e r b o a r d and Random a r e from E x p e r i m e n t 3 ( F i g . 3 . 1 ) . O n l y d a t a f r o m b e f o r e t h e s w i t c h and f o r Random o n l y t h e two b i r d s who im p r o v e d a r e i l l u s t r a t e d . The smooth c u r v e s a r e f i t t e d by eye t h r o u g h t h e p o i n t s shown i n t h e f i g u r e . PERCENT CORRECT 16 92 c h a n c e l e v e l s , and e v e n t u a l l y r e a c h e d a p p r o x i m a t e l y t h e same l e v e l on a l l f o u r p a t t e r n s ; o n l y r a t e o f improvement showed a c o n s i s t e n t and r e p e a t a b l e d i f f e r e n c e between p a t t e r n t y p e s . A l t h o u g h n o t e v e r y i n d i v i d u a l t e s t e d i m p r o v e d i t s p e r f o r m a n c e on t h e Random p a t t e r n , I c a n n o t c o n c l u d e t h a t p a t t e r n s of t h i s c o m p l e x i t y a r e beyond t h e c a p a b i l i t y o f t h e s e a n i m a l s t o l e a r n . T h e s e r e s u l t s p o i n t t o q u e s t i o n s a b o u t t h e f e a t u r e s i n an e n v i r o n m e n t t h a t c o n s t r a i n an a n i m a l ' s a b i l i t y t o l e a r n about t h e q u a l i t y and d i s t r i b u t i o n of r e s o u r c e s . M o d e l s o f human i n f o r m a t i o n p r o c e s s i n g c l e a r l y p o i n t t o c o n s i s t e n c y and r e g u l a r i t y i n p a t t e r n s of i n f o r m a t i o n a s key f a c t o r s i n l e a r n i n g t o s o l v e complex t a s k s ( S c h n e i d e r and S h i f f r i n 1977; Simon 1979). I f r e g u l a r i t y o f s p a t i a l p a t t e r n i n g i s an i m p o r t a n t and g e n e r a l d e t e r m i n a n t of s p a t i a l memory c a p a c i t y and l e a r n i n g r a t e s , t h e n i d e n t i f y i n g how a n i m a l s r e c o g n i z e t h e s e p a t t e r n s becomes i m p o r t a n t i n s p e c i f y i n g t h e c o n s t r a i n t s on a n i m a l memory f o r s p a t i a l l o c a t i o n s . Q u e s t i o n s a b o u t t h e e x t e n t t o w h i c h hummingbirds can l e a r n and remember l o c a t i o n s o f f o o d , and how t h e o r g a n i z a t i o n and d i s t r i b u t i o n of f o o d a f f e c t s t h e r a t e of s p a t i a l l e a r n i n g i n h u mmingbirds i n i t i a l l y a r o s e f r o m f i e l d o b s e r v a t i o n s of h u m mingbird f o r a g i n g b e h a v i o u r . I i n t e n d e d t h i s s t u d y of s p a t i a l l e a r n i n g i n hummingbirds t o b r i d g e t h e gap between e x p e r i m e n t a l work done i n s m a l l a r r a y s o f 2 t o 16 f e e d e r s (Gass 1977; C o l e e t a l . 1982; M i l l e r e t a l . 1985) and s t u d i e s done a n a l y z i n g hummingbirds' use of p a t c h e s of f l o w e r s o r movements o v e r whole t e r r i t o r i e s (Gass and S u t h e r l a n d 1985). How do t h e 93 r e s u l t s c o n t r i b u t e t o t h e u n d e r s t a n d i n g o f t h e r o l e o f s p a t i a l l e a r n i n g i n hummingbird f o r a g i n g ? N e c t a r i v o r o u s b i r d s i n c l u d i n g hummingbirds a r e known t o a v o i d r e v i s i t i n g i n f l o r e s c e n c e s t h e y have p r e v i o u s l y v i s i t e d ( G i l l and Wolf 1977; K a m i l 1978; S u t h e r l a n d , Tamm and G a s s u n p u b l . o b s . ) . A l t h o u g h t h e s e o b s e r v a t i o n s a r e u s u a l l y t a k e n as e v i d e n c e f o r a p o s s i b l y f i n e l y d e t a i l e d s p a t i a l memory i n t h e s e a n i m a l s ( K a m i l 1982; S h e r r y I 9 8 4 b ) , t h e mechanisms by w h i c h t h e y c o u l d a v o i d r e v i s i t s have n o t been e x p l o r e d i n d e t a i l . The o b s e r v a t i o n s i n t h i s s t u d y do n o t s u p p o r t t h e h y p o t h e s i s t h a t h u mmingbirds use memory f o r l a r g e numbers o f i n d i v i d u a l f l o w e r s t o a v o i d r e v i s i t s ; t h e y do s u g g e s t t h a t hummingbirds have t h e c a p a b i l i t y t o remember p a t c h l o c a t i o n s and t o o r g a n i z e t h e i r v i s i t s w i t h i n p a t c h e s t o r e d u c e r e v i s i t s i f t h o s e p a t c h e s a r e s m a l l enough ( s e e C h a p t e r 3 ) . Thus t h e mechanisms f o r a v o i d i n g r e v i s i t s may r e l y on two s c a l e s o f o r g a n i z a t i o n : t h e c o a r s e r -g r a i n e d (and l o n g - t e r m ) s c a l e of l o c a t i o n s o f b o u t s and t h e f i n e r - g r a i n e d (and s h o r t - t e r m ) s c a l e o f w i t h i n b out v i s i t s . A computer s i m u l a t i o n ( A r m s t r o n g e t al. 1986) p r o v i d e d p a r t i a l s u p p o r t f o r t h e b e n e f i t s o f t h i s t y p e of o r g a n i z a t i o n . M odel hummingbirds t h a t g i v e up q u i c k l y i n l o w - q u a l i t y p a t c h e s b e n e f i t more from o r g a n i z a t i o n o f v i s i t s w i t h i n p a t c h e s ( i . e. a v o i d r e v i s i t s t o f l o w e r s w i t h i n b o u t s i n p a t c h e s ) t h a n t h e y do by remembering and a v o i d i n g r e v i s i t s t o p a t c h e s . D e c r e a s i n g t h e e f f i c i e n c y of g i v i n g - u p r u l e s o r i n c r e a s i n g t h e v a r i a b i l i t y i n q u a l i t y of p a t c h e s i n c r e a s e s t h e b e n e f i t s o f remembering t h e l o c a t i o n s of p r e v i o u s b o u t s . F u r t h e r e m p i r i c a l work on t h e 94 f o r a g i n g movements o f hummingbirds s h o u l d c o n c e n t r a t e on q u a n t i f y i n g t h e s e q u e n c i n g of movements w i t h i n and between b o u t s , and on i d e n t i f y i n g t h e f a c t o r s t h a t d e t e r m i n e t h e r e l a t i v e b e n e f i t s o f remembering p a t c h e s , and remembering l o c a t i o n s w i t h i n p a t c h e s . Hummingbirds' good memory f o r l o c a t i o n s of h i g h q u a l i t y p a t c h e s o f f l o w e r s i n t h e i r t e r r i t o r i e s , as d e m o n s t r a t e d by f i e l d e x p e r i m e n t s (Gass and S u t h e r l a n d 1985), l e a v e s open t h e q u e s t i o n o f t h e r o l e o f memory i n e n v i r o n m e n t s w i t h n o r m a l v a r i a t i o n i n p a t c h o r f l o w e r q u a l i t y . R e s u l t s o f one s t u d y o f f o r a g i n g movements by t e r r i t o r i a l hummingbirds i n u n m a n i p u l a t e d t e r r i t o r i e s r e v e a l e d no c l e a r e v i d e n c e t h a t t h e b i r d s remembered t h e l o c a t i o n s o f p r e v i o u s b o u t s (Wolf and H a i n s w o r t h 1983). These a u t h o r s h y p o t h e s i z e d t h a t b i r d s c o u l d use a r u l e s u c h as a l t e r n a t i o n between b o u t s i n a r b i t r a r y s u b s e c t i o n s of t h e i r t e r r i t o r i e s t o a v o i d p r e v i o u s l y v i s i t e d bout l o c a t i o n s . In t h e i r s t u d y t h e y f o u n d no e v i d e n c e f o r s u c h a r u l e , and c o n c l u d e d t h a t memory f o r p r e v i o u s bout l o c a t i o n s was i n s i g n i f i c a n t . However G a s s and S u t h e r l a n d (1985) a r g u e d t h a t a more a c c u r a t e c o n c l u s i o n may be t h a t s u c h a r u l e may n o t o p e r a t e a t t h e s c a l e measured by Wolf and H a i n s w o r t h . In any c a s e , t h e sample s i z e o f t h e Wolf and H a i n s w o r t h d a t a s e t (1 day of o b s e r v a t i o n s on a s i n g l e t e r r i t o r i a l i n d i v i d u a l ) i s t o o s m a l l t o d e t e c t any but t h e s i m p l e s t p a t t e r n i n g o f b o u t s . The r e s u l t s of my s t u d y s u g g e s t t h a t b i r d s can remember l o c a t i o n s o f s e v e r a l p r o f i t a b l e p a t c h e s even when n e c t a r amounts i n e a c h f l o w e r i n t h o s e p a t c h e s a p p r o x i m a t e t h e a v e r a g e r e w a r d p e r f l o w e r i n 95 t y p i c a l h a b i t a t s . To what e x t e n t hummingbirds a c t u a l l y use t h i s c a p a b i l i t y under n o r m a l c o n d i t i o n s i s s t i l l n o t c l e a r . T h i s s t u d y f o c u s e d a t t e n t i o n on one p r i n c i p a l s o u r c e of i n f o r m a t i o n a v a i l a b l e t o hummingbirds ( s p a t i a l l o c a t i o n ) and a s k e d how t h e s e b i r d s use t h a t p a r t i c u l a r s o u r c e of i n f o r m a t i o n i n d i s t r i b u t i n g t h e i r f o r a g i n g e f f o r t s . However, hummingbirds and o t h e r n e c t a r i v o r e s can use s e v e r a l o t h e r t y p e s of i n f o r m a t i o n i n g u i d i n g t h e i r f o r a g i n g b e h a v i o u r . V i s i b l e c h a r a c t e r i s t i c s of f l o w e r s s u c h a s c o l o u r , s i z e and shape a r e u s e d as p r o x i m a t e c u e s t o t h e p r o f i t a b i l i t y o f f o o d i t e m s i n bees and i n hummingbirds ( H e i n r i c h 1976; L a v e r t y 1980; G e o r g e 1980). F o r example, i n d i v i d u a l bumblebees "major" on p a r t i c u l a r s p e c i e s of f l o w e r s , even when t h e y a r e i n t e r s p e r s e d w i t h o t h e r s p e c i e s ( H e i n r i c h 1976, 1979). Hummingbirds d i s c r i m i n a t e c o l o u r s w i t h a h i g h d e g r e e o f s p e c t r a l s e n s i t i v i t y ( G o l d s m i t h and G o l d s m i t h 1979) and r e a d i l y a s s o c i a t e c h a n g e s i n f l o w e r a p p e a r a n c e w i t h t h e p r e s e n c e o f n e c t a r r e w a r d s ( e . g. G e o r g e 1980). O n l y one s t u d y has a t t e m p t e d t o d e t e r m i n e t h e r e l a t i v e i m p o r t a n c e o f s p a t i a l l o c a t i o n and o t h e r c u e s ( s u c h as c o l o u r ) i n d e t e r m i n i n g t h e f e e d i n g p a t t e r n s of h ummingbirds ( M i l l e r e t a l . 1985). In t h a t s t u d y , b i r d s i n i t i a l l y l o c a t e d a r t i f i c i a l f e e d e r s . E m p i r i c a l s t u d i e s t h a t u s e d a m u l t i - v a r i a b l e a p p r o a c h t o p a r t i t i o n out t h e r e l a t i v e c o n t r i b u t i o n o f c u e s s u c h as v i s i b l e c h a r a c t e r i s t i c s of f l o w e r s , n e a r b y l a n d m a r k s , and s p a t i a l l o c a t i o n o f s i n g l e o r p a t c h e s o f f l o w e r s would be v a l u a b l e i n i n t e r p r e t i n g t h e f a c t o r s i n f l u e n c i n g f o r a g i n g movements i n h u m m i n g b i r d s . 96 C o n c l u d i n g Remarks F o r a g i n g i n n a t u r e i n v o l v e s complex i n t e r a c t i o n s between b e h a v i o u r and e n v i r o n m e n t t h a t o c c u r on d i f f e r e n t s p a t i a l and t e m p o r a l s c a l e s (Simon 1979; Ga s s and M o n t g o m e r i e 1981). The p s y c h o l o g i c a l p r o c e s s e s t h a t g e n e r a t e b e h a v i o u r , and t h e k i n d s o f i n f o r m a t i o n we p o s t u l a t e t h e y m a n i p u l a t e a r e o f t e n u n a v a i l a b l e t o d i r e c t s c i e n t i f i c a n a l y s i s (Shaw and M i n g o l l a 1982). F o r example, l e a r n i n g p r o c e s s e s a r e n o t d i r e c t l y o b s e r v a b l e ; t h e i r n a t u r e c a n o n l y be i n f e r r e d f r o m c h a n g e s i n b e h a v i o u r . I t i s o f t e n d i f f i c u l t t o d e t e r m i n e whether a d i f f e r e n c e i n b e h a v i o u r i s due t o d i f f e r e n t p r o c e s s e s , o r t o a d i f f e r e n c e i n t h e e x p r e s s i o n o f t h e same p r o c e s s i n d i f f e r e n t s e t t i n g s ( K a m i l and Y o e r g , 1982). Few t h e o r i e s y e t e x i s t about how many o f t h e s e p r o c e s s e s t h e r e a r e o r how t h e y i n t e r a c t w i t h e a c h o t h e r o r w i t h t h e e n v i r o n m e n t a l v a r i a b l e s t h a t d r i v e them (Simon 1979). E x p e r i m e n t a l p a r a d i g m s f o r s t u d y i n g t h e i n t e r a c t i o n s between component p r o c e s s e s , s u c h a s p e r c e p t i o n , l e a r n i n g and memory mechanisms a r e s t i l l i n t h e i r i n f a n c y . T h i s r e s e a r c h was an e x p l i c i t a t t e m p t t o s t r a d d l e t h e i n t e r a c t i o n between e c o l o g y and p s y c h o l o g y . I a s k e d an e c o l o g i c a l q u e s t i o n : "How do hummingbirds f i n d f o o d i n complex e n v i r o n m e n t s ? " . I s t u d i e d some component mechanisms ( s p a t i a l memory and o r g a n i z a t i o n o f t h a t memory) t h a t seemed i m p o r t a n t i n a n s w e r i n g t h a t q u e s t i o n u s i n g an e x p e r i m e n t a l p a r a d i g m t h a t e m p h a s i z e d t h e c o m p l e x i t y o f s p a t i a l i n f o r m a t i o n t h a t h u m m i n g b i r d s must cope w i t h . A c r i t i c m i g h t a r g u e t h a t t o adopt 97 s u c h a c r o s s - d i s c i p l i n a r y a p p r o a c h might be i n c o n c l u s i v e a t b e s t and m i s l e a d i n g a t w o r s t . On t h e one hand a p s y c h o l o g i s t might r e m a i n u n s a t i s f i e d b e c a u s e t h e a p p r o a c h d o e s not o f f e r t h e c a p a b i l i t y t o f i n e l y d i s c r i m i n a t e between a l t e r n a t i v e mechanisms and t h u s c l a i m t h a t t h e r e s u l t s have no p r e d i c t i v e power. On t h e o t h e r hand, an e c o l o g i s t m i g h t f e e l t h a t b e c a u s e i m p o r t a n t v a r i a b l e s a r e i n e v i t a b l y i g n o r e d , he c a n n o t u s e f u l l y i n t e r p r e t t h e r e s u l t s i n t e r m s o f f i e l d s i t u a t i o n s . D e s p i t e some j u s t i f i c a t i o n f o r b o t h t h e s e a r g u m e n t s , I b e l i e v e t h i s g e n e r a l e x p e r i m e n t a l a p p r o a c h t o s t u d i e s o f complex s p a t i a l b e h a v i o u r does have good p o t e n t i a l , n o t o n l y f o r g e n e r a t i n g i n s i g h t s , h y p o t h e s e s and p r e d i c t i o n s a b o u t f o r a g i n g b e h a v i o u r , but a l s o f o r i l l u m i n a t i n g more f u n d a m e n t a l and p o s s i b l y g e n e r a l b e h a v i o u r a l p r o c e s s e s . S i g n i f i c a n t p r o g r e s s i n i n t e r p r e t i n g t h e f l e x i b i l i t y of f o r a g e r s i n c h a n g i n g e n v i r o n m e n t s r e q u i r e s a d e e p e r u n d e r s t a n d i n g o f how t h e i r e x p e c t a t i o n s a b o u t c u r r e n t and f u t u r e c o n d i t i o n s d e v e l o p , and how t h e y use new i n f o r m a t i o n t o u p d a t e t h e i r e x p e c t a t i o n s . However, f u t u r e s u c c e s s may d e p e n d c r i t i c a l l y upon d e v e l o p m e n t of t e c h n i q u e s c a p a b l e of a n a l y z i n g complex s t r e a m s of b e h a v i o u r a l d a t a , c a r e f u l i d e n t i f i c a t i o n o f c o n s t r a i n t s on i m p o r t a n t p r o c e s s e s , and s y s t e m a t i c e x p l o r a t i o n of t h e i r e f f e c t s . 98 LITERATURE CITED A r m s t r o n g , D.A. 1986. 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