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Advantages to late breeding in Ruddy ducks Somerville, Alison Joan 1985

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ADVANTAGES TO LATE BREEDING IN RUDDY DUCKS by ALISON JOAN SOMERVILLE B.Sc . (Hons. ) , U . B . C , V a n c o u v e r , 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Dep a r t m e n t o f Z o o l o g y ) We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA O c t o b e r 1985 © A l i s o n J o a n S o m e r v i l l e , 1985 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Zoology  The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date October 15, 1985 i i ABSTRACT Ruddy Ducks i n t h e C h i l c o t i n p a r k l a n d s of B r i t i s h C o l u m b i a n e s t i n l a t e J u n e , J u l y and e a r l y A u g u s t , l a t e r t h a n most o t h e r w a t e r f o w l s p e c i e s b r e e d i n g i n s o u t h w e s t e r n B r i t i s h C o l u m b i a , Canada. T h i s t h e s i s c o n s i d e r s f a c t o r s t h a t may a f f e c t t h e t i m i n g o f b r e e d i n g i n Ruddy Ducks by c o m p a r i n g Ruddy Ducks t o B a r r o w ' s G o l d e n e y e and B u f f l e h e a d ( s p e c i e s t h a t b r e e d e a r l y but do n o t r e n e s t ) and t o A m e r i c a n C o o t (a s p e c i e s t h a t b r e e d s e a r l y and i s a b l e t o r e n e s t ) . T h e s e f a c t o r s i n c l u d e p r e d a t i o n , f l o o d i n g and d e s e r t i o n of n e s t s , f e e d i n g b e h a v i o r of d u c k l i n g s , a bundance of f o o d , a v a i l a b i l i t y of g r e e n v e g e t a t i o n and f l u c t u a t i o n s i n t e m p e r a t u r e . P o s s i b l e a d v a n t a g e s of l a t e b r e e d i n g i n c l u d e r e d u c e d n e s t p r e d a t i o n and h i g h e r a m bient t e m p e r a t u r e d u r i n g i n c u b a t i o n . L o n g e r d i v e d u r a t i o n s and more f r e q u e n t f e e d i n g and r e s t i n g by Ruddy d u c k l i n g s may e n a b l e d u c k l i n g s t o m a x i m i z e e n e r g y f o r g r o w t h . Reduced n e s t f l o o d i n g l a t e i n t h e s e a s o n , dependence on g r e e n v e g e t a t i o n f o r n e s t i n g and g r e a t e r abundance o f f o o d f o r young i n summer were not d e m o n s t r a t e d by t h i s s t u d y . T h e r e f o r e , t h e s e f a c t o r s a p p a r e n t l y do n o t e x p l a i n t h e t i m i n g o f b r e e d i n g i n Ruddy Ducks i n s o u t h w e s t e r n B r i t i s h C o l u m b i a . D e s p i t e i n s u f f i c i e n t t i m e t o r e n e s t and s h o r t e r t i m e f o r d u c k l i n g s t o mature b e f o r e ponds f r e e z e , t h e a v e r a g e number o f 2B age c l a s s young p r o d u c e d p e r p a i r o f Ruddy Ducks was s i m i l a r t o t h a t o f A m e r i c a n C o o t s . F o r t y p e r c e n t of n e s t i n g Ruddy f e m a l e s d i d n o t h a t c h any young, whereas a l m o s t a l l n e s t i n g C o o t f e m a l e s s u c c e s s f u l l y h a t c h e d young; however, s u r v i v a l of Ruddy i i i ducklings to 2B age class (four weeks old) was higher than that of American Coots, Barrow's Goldeneye and Bufflehead. i v TABLE OF CONTENTS ABSTRACT i i L I S T OF TABLES v i i L I S T OF FIGURES i x ACKNOWLEDGEMENTS x CHAPTER ONE: G e n e r a l I n t r o d u c t i o n 1 CHAPTER TWO: N e s t S u c c e s s and B r e e d i n g C h r o n o l o g y 4 I n t r o d u c t i o n 4 Methods 6 R e s u l t s 11 Nest S u c c e s s 11 -Nest P r e d a t i o n 11 Nest S i t e and N e s t i n g C o v e r 12 P r e d a t o r B e h a v i o r 20 Nest F l o o d i n g 22 S e a s o n a l Water L e v e l F l u c t u a t i o n s 25 Nest D e s e r t i o n 27 D i s c u s s i o n 28 Nest S u c c e s s and R e n e s t i n g 28 Nest P r e d a t i o n 31 Ne s t F l o o d i n g . 32 Nest D e s e r t i o n 33 C o v e r , P r e d a t o r B e h a v i o r and Water L e v e l F l u c t u a t i o n s 34 C o n c l u s i o n s 35 V CHAPTER THREE: F e e d i n g B e h a v i o r and S u r v i v a l o f D u c k l i n g s . 37 I n t r o d u c t i o n 37 Methods 39 R e s u l t s 45 D u c k l i n g S u r v i v a l 45 Female B e h a v i o r 45 Time Budget o f D u c k l i n g s 49 D i v i n g D u r a t i o n and F e e d i n g I n t e n s i t y o f D u c k l i n g s .. 52 D i s c u s s i o n 54 Time Budget of D u c k l i n g s 57 D i v i n g D u r a t i o n and F e e d i n g I n t e n s i t y of D u c k l i n g s .. 58 C o n c l u s i o n s 59 CHAPTER FOUR: F o o d f o r Ruddy D u c k l i n g s 61 I n t r o d u c t i o n 61 Methods 62 R e s u l t s 64 Food of Ruddy D u c k l i n g s 64 S e a s o n a l Abundance o f C h i r o n o m i d a e and Z y g o p t e r a .... 68 Food D e n s i t y and C h o i c e o f P a t c h e s w i t h i n Ponds 70 Food d e n s i t y and C h o i c e o f Ponds 70 D i s c u s s i o n 72 Food o f Ruddy D u c k l i n g s 72 S e a s o n a l Abundance o f C h i r o n o m i d a e and Z y g o p t e r a .... 73 Food D e n s i t y and C h o i c e o f P a t c h e s w i t h i n Ponds 74 Fo o d D e n s i t y and C h o i c e o f Ponds 75 C o n c l u s i o n s 76 CHAPTER F I V E : G e n e r a l D i s c u s s i o n 77 R e f e r e n c e s C i t e d 80 APPENDIX ONE: D e s c r i p t i o n o f Study S i t e 86 APPENDIX TWO: Ambient T e m p e r a t u r e and L a t e B r e e d i n g 88 C o m p a r i s o n o f Ambient T e m p e r a t u r e i n S p r i n g and Summer 89 Ruddy Duck and A m e r i c a n Coot N e s t T e m p e r a t u r e s 91 C o n c l u s i o n s 92 APPENDIX THREE: P r e d a t i o n of F l a g g e d and C o n c e a l e d N e s t s .. 95 C o n c l u s i o n s 96 APPENDIX FOUR: Gree n v e g e t a t i o n i n Ruddy N e s t s 98 Ne s t C o m p o s i t i o n 98 L a y i n g C h r o n o l o g y 99 S e a s o n a l P a t t e r n s i n V e g e t a t i o n Growth 101 N e s t P a r a s i t i s m . 103 C o n c l u s i o n s 103 v i i L I S T OF TABLES TABLE 1: V e g e t a t i o n and N e s t S i t e Measurement D e s c r i p t i o n s 7 TABLE 2: V e g e t a t i o n Measurements i n S p r i n g and Summer 14 TABLE 3: C o m p a r i s o n o f A m e r i c a n C o o t and Ruddy Duck N e s t S i t e s 16 TABLE 4: C o n c e a l m e n t a t A m e r i c a n C o o t and Ruddy Duck N e s t S i t e s 19 TABLE 5: C o m p a r i s o n of S u c c e s s f u l and D e s t r o y e d Ruddy N e s t S i t e s 21 TABLE 6: C o m p a r i s o n o f S u c c e s s f u l and D e s t r o y e d A m e r i c a n C o o t N e s t S i t e s 21 TABLE 7: A v i a n P r e d a t o r s i n S p r i n g and Summer 23 TABLE 8: Raven B e h a v i o r i n S p r i n g and Summer 24 TABLE 9: Water L e v e l F l u c t u a t i o n s i n S p r i n g and Summer .... 26 TABLE 10: N e s t S u c c e s s o f Ruddy Ducks R e p o r t e d i n Other-S t u d i e s 30 TABLE 11: N e s t S u c c e s s o f A m e r i c a n C o o t s R e p o r t e d i n O t h e r S t u d i e s 30 TABLE 12: Mean D u c k l i n g Age f o r Age C l a s s e s 1A t o 2C 41 TABLE 13: A l e r t B e h a v i o r of Fema l e s w i t h B r o o d s 48 TABLE 14: F r e q u e n c y t h a t Broods were O b s e r v e d i n B u l r u s h C o v e r 50 TABLE 15: R e s t i n g and F e e d i n g B e h a v i o r o f D u c k l i n g s 51 TABLE 16: D i v i n g D u r a t i o n s of D u c k l i n g s 53 TABLE 17: F e e d i n g I n t e n s i t i e s of D u c k l i n g s 53 v i i i TABLE 18: R e p r o d u c t i v e S u c c e s s o f Ducks and C o o t s 56 TABLE 19: F o o d H a b i t s o f Ruddy D u c k l i n g s 65 TABLE 20: I n v e r t e b r a t e s and Seeds i n E s o p h a g i o f Ruddy D u c k l i n g s C o l l e c t e d a t Ponds 26 and 54 67 TABLE 21: D e n s i t y of I n v e r t e b r a t e s a t Ponds 26 and 54 67 i x L I S T OF FIGURES FIGURE 1: P r e d a t i o n and P a r a s i t i s m of Dummy N e s t s 13 FIGURE 2: V e g e t a t i o n H e i g h t and D e n s i t y i n S p r i n g and Summer 18 FIGURE 3: S u r v i v a l f r o m Egg t o 2B Age C l a s s f o r Young o f Ducks and C o o t s . 46 FIGURE 4: D u c k l i n g S u r v i v a l f r o m H a t c h i n g t o 2B Age C l a s s . 47 FIGURE 5: D e n s i t i e s of C h i r o n o m i d L a r v a and Z y g o p t e r a N a i a d s i n A r e a s where F e m a l e s Ruddy Ducks F e d Most and L e a s t 69 FIGURE 6: D e n s i t i e s o f C h i r o n o m i d L a r v a and Z y g o p t e r a N a i a d s on a Pond where Ruddy Ducks d i d not B r e e d 71 FIGURE 7: Map o f t h e S t u d y A r e a 87 FIGURE 8: A v e r a g e Minimum and Maximum T e m p e r a t u r e s i n S p r i n g and Summer 90 FIGURE 9: P r e d a t i o n of U n f l a g g e d , F l a g g e d and C o n c e a l e d Dummy N e s t s 97 FIGURE 10: C h r o n o l o g y o f C l u t c h I n i t i a t i o n i n Ruddy Ducks .100 FIGURE 11: P a t t e r n s of V e g e t a t i o n Growth i n 1983 and 1984 .102 X ACKNOWLEDGEMENTS I w i s h t o thank Dr. A.R.E. S i n c l a i r ( s u p e r v i s o r ) , J.N.M. S m i t h ( c o m m i t t e e member), D r . W.E. N e i l l ( c o m m i t t e e member), and J . P . S a v a r d ( C a n a d i a n W i l d l i f e S e r v i c e b i o l o g i s t ) who have s u p p o r t e d me t h r o u g h t h e s i s t o p i c 'changes, p e r m i t d i f f i c u l t i e s and o t h e r d i s a s t e r s . My f r i e n d s G i l l e s G a u t h i e r , J o h n and J a n e E a d i e , H o l l y D u b l i n , John F r y x e l l , W i l f Leudke, Juan M e r k t , John W e r r i n g , A l y r e C h i a s s o n , K a t e Mesa, Dave B e r n a r d , Rob P o w e l l , Mark Cheesman, J o y Bowerman, F l o r e n c e DeLannoy, and D a v i d M c A l a r y p r o v i d e d encouragement o f t e n , t h o u g h t h e y may not have r e a l i z e d i t . They c e r t a i n l y d e s e r v e my t h a n k s , as do Susan E r t i s , S h i r l e y G r a y s t o n e and A l i s t a i r B l a c h f o r d who have s u c c e s s f u l l y d i f f u s e d my computer a n x i e t i e s . U s e f u l s u g g e s t i o n s and h e l p w i t h f i e l d work came from John G a r r e a u , A n d r e B r e a u l t , Bob Emery, Shawn Boyd (CWS), Rory Brown (Ducks U n l i m i t e d ) , and Ron Boychuck (Ducks U n l i m i t e d ) . I ' d s t i l l be i n t h e l a b c o u n t i n g i n v e r t e b r a t e s a m p l e s i f i t we r e n ' t f o r t h e a s s i s t a n c e of B r y c e S o m e r v i l l e and I would be l o s t i n t h e i n p e n e t r a b l e f o r e s t o f m i s p l a c e d m o d i f i e r s , m i s s p e l l e d words and o t h e r n i g h t m a r e s w i t h o u t t h e e d i t i n g a d v i c e of C h r i s t i n e S o m e r v i l l e . F i n a n c i a l a s s i s t a n c e f o r t h i s p r o j e c t came from t h e C a n a d i a n W i l d l i f e S e r v i c e R e s e a r c h S u p p o r t Fund and p e r s o n a l s u p p o r t from t h e James R o b e r t Thompson F e l l o w s h i p . F i n a l l y , I w i s h t o ac k n o w l e d g e t h e f i n a n c i a l and m o r a l s u p p o r t g i v e n t o me by my f a t h e r , R i c h a r d S o m e r v i l l e , so I am d e d i c a t i n g t h i s t h e s i s t o him. 1 CHAPTER ONE G e n e r a l , I n t r o d u c t i o n B i r d s b r e e d i n r e s t r i c t e d s e a s o n s t h a t a r e c h a r a c t e r i s t i c f o r a p a r t i c u l a r g e o g r a p h i c a r e a ( L a c k , 1968). In t e m p e r a t e c l i m a t e s , most b i r d s b r e e d i n s p r i n g and summer ( L a c k , 1954); m o r e o v e r , i n f o r m a t i o n from v a r i o u s s t u d i e s s u g g e s t s t h a t t h e t i m i n g of b r e e d i n g a f f e c t s r e p r o d u c t i v e s u c c e s s . F o r example, c o m p a r i s o n s w i t h i n s p e c i e s show h i g h e r s u r v i v a l r a t e s f o r young t h a t h a t c h e a r l y t h a n f o r young t h a t h a t c h l a t e ( L a c k , 1954; P e r r i n s , 1965, 1966). B r e e d i n g l a t e r i n t h e s e a s o n may r e d u c e t h e number o f n e s t i n g a t t e m p t s t h a t a r e p o s s i b l e and a l l o w l e s s t i m e f o r young t o grow and f l e d g e b e f o r e w i n t e r . D e s p i t e t h e s e p o t e n t i a l d r a w b a c k s , Ruddy Ducks e x h i b i t h i g h n e s t s u c c e s s ( p r o p o r t i o n of c l u t c h e s t h a t p r o d u c e one or more h a t c h e d young) and h i g h d u c k l i n g s u r v i v a l (Low, 1941; M c K n i g h t , 1974; S i e g f r i e d , 1977), t h o u g h t h e y n e s t a month o r more l a t e r t h a n most w a t e r f o w l i n N o r t h A m e r i c a ( B e l l r o s e , 1980). The aim of t h i s s t u d y i s t o examine some of t h e f a c t o r s t h a t may a f f e c t t h e t i m i n g of b r e e d i n g i n Ruddy Ducks (Oxyura j a m a i c e n s i s ) and c o n s i d e r how h i g h r e p r o d u c t i v e s u c c e s s i s a c h i e v e d . D i s c u s s i o n s of t h e f a c t o r s t h a t d e t e r m i n e r e p r o d u c t i v e s u c c e s s a l m o s t a l w a y s r e f e r t o D a v i d L a c k ' s h y p o t h e s i s t h a t b i r d s b r e e d when f o o d f o r young i s most abundant ( L a c k , 1954, 1 9 6 8). O f t e n t h i s i d e a i s p r e s e n t e d a s i f i t were a f a c t r a t h e r t h a n a t h e o r y . W h i l e f o o d f o r young i s an i m p o r t a n t f a c t o r t o c o n s i d e r , i t i s c l e a r l y n o t t h e o n l y f a c t o r t h a t c a n v a r y s e a s o n a l l y , i n f l u e n c e r e p r o d u c t i v e s u c c e s s and t h u s , a f f e c t 2 t i m i n g o f b r e e d i n g . R e s e a r c h has shown t h a t p r e d a t i o n ( B r a e s t r u p , 1940), f o o d f o r f e m a l e s ( L a c k , 1966; P e r r i n s , 1966) and t i m i n g o f m o u l t ( H a r r i s , 1969) c a n a l s o i n f l u e n c e t i m i n g of b r e e d i n g . Thus, a c o m p r e h e n s i v e a p p r o a c h t o s t u d 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 i m i n g of b r e e d i n g must c o n s i d e r more t h a n j u s t f o o d f o r young. The q u e s t i o n of what d e t e r m i n e s t h e t i m i n g of b r e e d i n g i n Ruddy Ducks has r e c e i v e d l i t t l e a t t e n t i o n i n t h e l i t e r a t u r e . B i o l o g i s t s c o n d u c t i n g r e s e a r c h on t h e m a t i n g s y s t e m ( G r a y , 1980), and b r e e d i n g b i o l o g y ( S i e g f r i e d , 1976a) of Ruddy Ducks have b r i e f l y d i s c u s s e d t h i s q u e s t i o n . G r a y (1980) s u g g e s t e d t h a t f o o d f o r Ruddy young was most abundant l a t e i n t h e s e a s o n and t h u s s u p p o r t e d L a c k ' s h y p o t h e s i s . S i e g f r i e d (1976a) o b s e r v e d t h a t Ruddy f e m a l e s a l m o s t a l w a y s i n c o r p o r a t e d g r e e n v e g e t a t i o n i n t o t h e i r n e s t s and s u g g e s t e d t h a t Ruddy Ducks d e l a y b r e e d i n g b e c a u s e t h e y r e q u i r e g r e e n v e g e t a t i o n f o r n e s t i n g . S i e g f r i e d a l s o d i s c u s s e d t h e h y p o t h e s i s t h a t f e m a l e s have i n s u f f i c i e n t e n e r g y r e s e r v e s t o b r e e d i n t h e s p r i n g , b u t r e j e c t e d i t b e c a u s e f e m a l e s a r r i v i n g a t t h e b r e e d i n g g r o u n d s e x h i b i t e d s u b s t a n t i a l f a t s t o r e s . I a t t e m p t e d t o u n d e r s t a n d why Ruddy Ducks b r e e d l a t e i n t h e s e a s o n by c o m p a r i n g : 1) c o n d i t i o n s e x i s t i n g i n t h e s p r i n g t o t h o s e e x i s t i n g l a t e r when Ruddy Ducks b r e e d , 2) c o n d i t i o n s e x i s t i n g i n a r e a s u s e d by b r e e d i n g Ruddy Ducks w i t h t h o s e e x i s t i n g i n a r e a s t h a t t h e y do n o t u s e , 3) b i o l o g y o f e a r l y b r e e d i n g s p e c i e s i n c l u d i n g B a r r o w ' s 3 G o l d e n e y e ( B u c e p h a l a c l a n g u l a ) , B u f f l e h e a d ( B u c e p h a l a  a l b e o l a ) and A m e r i c a n C o o t ( F u l i c a a m e r i c a n a ) t o t h a t of Ruddy D u c k s . I c o n s i d e r v a r i o u s c a u s e s of n e s t l o s s i n C h a p t e r One and f e e d i n g b e h a v i o r o f Ruddy d u c k l i n g s i n C h a p t e r Two, s i n c e s u r v i v a l of t h e f i r s t c l u t c h and r a p i d g r o w t h of young i s e s s e n t i a l f o r l a t e b r e e d i n g s p e c i e s . I a l s o d i s c u s s the' abundance o f f o o d f o r d u c k l i n g s i n C h a p t e r T h r e e , ambient t e m p e r a t u r e i n A p p e n d i x Two and g r e e n v e g e t a t i o n i n A p p e n d i x F o u r t o examine t h e i n f l u e n c e of t h e s e f a c t o r s on t i m i n g of b r e e d i n g . The s t u d y was c o n d u c t e d i n t h e C h i l c o t i n p a r k l a n d s of B r i t i s h C o l u m b i a , Canada i n an a r e a c a l l e d B e c h e r ' s P r a i r i e . A d e s c r i p t i o n of t h e a r e a i s g i v e n i n A p p e n d i x One. 4 CHAPTER TWO N e s t S u c c e s s and B r e e d i n g C h r o n o l o g y i n Ruddy Ducks and C o o t s I n t r o d u c t i o n A m e r i c a n C o o t s n e s t i n t h e s p r i n g i n emergent v e g e t a t i o n when n e s t i n g c o v e r i s o f t e n poor and water l e v e l s on ponds may f l u c t u a t e . As a r e s u l t , t h e y m ight be e x p e c t e d t o l o s e n e s t s t o p r e d a t o r s o r f l o o d i n g . However, t h e y can n e s t a s e c o n d t i m e i f t h e f i r s t n e s t i s l o s t ( i e . r e n e s t ) and C o o t n e s t s u c c e s s r e p o r t e d i n t h e l i t e r a t u r e i s t y p i c a l l y h i g h ( M i l l e r and C o l l i n s , 1954; K i e l , 1955). In c o n t r a s t , Ruddy Ducks b r e e d l a t e r t h a n A m e r i c a n C o o t s t h o u g h i n s i m i l a r s i t e s i n emergent v e g e t a t i o n . N e s t i n g c o v e r a t t h i s t i m e would l i k e l y be t a l l e r and d e n s e r . A l t h o u g h b r e e d i n g l a t e p r e c l u d e s t h e p o s s i b i l i t y o f r e n e s t i n g , Ruddy Ducks e x h i b i t f a i r l y h i g h n e s t i n g s u c c e s s r e l a t i v e t o o t h e r w a t e r f o w l ( B e l l r o s e , 1980). N e s t s u c c e s s o f Ruddy Ducks i s n o t as h i g h as t h a t o f C o o t s . The c h a p t e r w i l l f o c u s on two q u e s t i o n s : 1) How does t h e n e s t s u c c e s s o f Ruddy Ducks i n t h e C h i l c o t i n compare t o t h a t o f A m e r i c a n C o o t s ? 2) What a r e t h e a d v a n t a g e s f o r Ruddy Ducks o f b r e e d i n g l a t e ? I t examines how s e a s o n a l d i f f e r e n c e s i n f a c t o r s s u c h as p r e d a t i o n , f l o o d i n g and d e s e r t i o n o f n e s t s m i g h t d i f f e r e n t i a l l y a f f e c t t h e t i m i n g o f b r e e d i n g i n t h e s e two s p e c i e s . In a d d i t i o n , i t c o n s i d e r s c h a r a c t e r i s t i c s o f e a c h s p e c i e s t h a t may i n f l u e n c e when t h e y b r e e d . S e v e r a l f a c t o r s s u g g e s t t h a t n e s t p r e d a t i o n i s l o w e r i n t h e summer t h a n i n t h e s p r i n g . F i r s t , c o v e r may i n c r e a s e l a t e r i n 5 t h e s e a s o n and t h u s fewer Ruddy Duck n e s t s t h a n C o o t n e s t s may be d e s t r o y e d by p r e d a t o r s ( S c h r a n k , 1972). Second, p r e d a t o r b e h a v i o r may d i f f e r between s p r i n g when C o o t s n e s t and summer when Ruddy Ducks n e s t . P r e d a t o r s may v i s i t ponds t o s e a r c h f o r n e s t s l e s s o f t e n i n t h e summer t h a n i n t h e s p r i n g . N e s t d e n s i t y may be l o w e r i n t h e summer, t h e r e f o r e s e a r c h i n g f o r n e s t s w o u l d l e a d t o fewer r e w a r d s , and p r e d a t o r s may c o n c e n t r a t e on o t h e r s o u r c e s of f o o d ( J o n e s and H u n g e r f o r d , 1972). S i n c e C o o t a r e t e r r i t o r i a l ( R y d e r , 1959), and b o t h s e x e s i n c u b a t e and d e f e n d t h e n e s t s i t e , whereas Ruddy Ducks a r e not t e r r i t o r i a l and o n l y Ruddy f e m a l e s i n c u b a t e t h e eggs,- Ruddy Ducks may be more v u l n e r a b l e t o p r e d a t i o n and t h e r e f o r e e x c l u d e d from b r e e d i n g e a r l i e r . F l o o d i n g may a l s o be l e s s common i n summer t h a n i n s p r i n g when r a i n f a l l may be g r e a t e r . B e c a u s e Ruddy Ducks and C o o t s n e s t above t h e w a t e r , t h e y a r e more v u l n e r a b l e t o f l o o d i n g t h a n o t h e r d u c k s t h a t n e s t on t h e g r o u n d o r i n c a v i t i e s . F i n a l l y , n e s t d e s e r t i o n may a l s o be l e s s common i n summer t h a n i n s p r i n g . The c o s t of i n c u b a t i o n i n l i k e l y t o be a f f e c t e d by a mbient t e m p e r a t u r e . In a c o l d s p r i n g , C o o t s may d e s e r t n e s t s b e c a u s e t h e y have i n s u f f i c i e n t e n e r g y r e s e r v e s t o c o m p l e t e i n c u b a t i o n . By b r e e d i n g l a t e r when t e m p e r a t u r e s a r e warmer, Ruddy f e m a l e s may r e d u c e i n c u b a t i o n c o s t s . F u r t h e r , Tome (1984) f o u n d t h a t Ruddy f e m a l e s f e e d more o f t e n d u r i n g i n c u b a t i o n t h a n e a r l y b r e e d i n g d u c k s . Thus, Ruddy f e m a l e s may r e q u i r e l e s s s t o r e d e n e r g y t h a n C o o t s t o c o m p l e t e i n c u b a t i o n and m a i n t a i n n e s t t e m p e r a t u r e s as h i g h o r h i g h e r t h a n t h o s e of C o o t s ( s e e 6 A p p e n d i x Two). In t h i s c h a p t e r , I d e s c r i b e n e s t s i t e s o f Ruddy Ducks and C o o t s and compare t h e s e t o t h e marsh v e g e t a t i o n a v a i l a b l e t o a s s e s s t h e d i f f e r e n c e i n c o v e r a v a i l a b l e t o A m e r i c a n C o o t s and Ruddy D u c k s . Water l e v e l c h a n g e s a r e d e s c r i b e d , and b e h a v i o r of p r e d a t o r s e a r l y and l a t e i n t h e s e a s o n i s compared i n o r d e r t o d e t e r m i n e t h e r i s k of f l o o d i n g and p r e d a t i o n a t t h e s e t i m e s . F i n a l l y , dummy n e s t e x p e r i m e n t s t h a t compare e x p e r i m e n t a l l y n e s t p r e d a t i o n e a r l y and l a t e i n t h e s e a s o n a r e d i s c u s s e d . Methods N e s t S u c c e s s In 1983, I s e a r c h e d t h e emergent v e g e t a t i o n band and s h o r e l i n e o f e a c h o f s e v e n t e e n ponds once between J u l y 1 and August 9. In 1984, e a c h o f twenty ponds was s e a r c h e d p e r i o d i c a l l y between May 1 and A u g u s t 5. Most ponds were s e a r c h e d a t i n t e r v a l s o f two weeks, f o r a t o t a l of s e v e n t i m e s i n a l l . P onds were s e a r c h e d l e s s f r e q u e n t l y when a l l p a i r s of d u c k s and C o o t s were i n c u b a t i n g and t h e l o c a t i o n s of t h e i r n e s t s were known. When a n e s t was d i s c o v e r e d , i t s l o c a t i o n was n o t e d on a map. A l l eggs were c o u n t e d and e a c h egg was l a b e l e d i n f e l t pen w i t h a number u n i q u e i n t h a t n e s t . E a c h n e s t s i t e was c h a r a c t e r i z e d by m e a s u r i n g s e v e r a l measurements d e s c r i b e d i n T a b l e 1. N e s t s i t e s were r e v i s i t e d a t l e a s t once between t h e t i m e o f d i s c o v e r y and h a t c h i n g t o d e t e r m i n e i f n e s t s were 7 TABLE J_ V e g e t a t i o n and N e s t S i t e Measurement D e s c r i p t i o n s DEPTH AT NEST - water d e p t h a t n e s t DEGREES OPEN - # of d e g r e e s (0-360) i n t h e v e r t i c a l p l a n e of t h e n e s t c i r c l e w h i c h were f r e e o f c o v e r (an e s t i m a t e of c o n c e a l m e n t of eggs when t h e n e s t was v i e w e d from t h e s i d e ) # OF NEST ENTRANCES - # of ramps of v e g e t a t i o n a l l o w i n g e n t r a n c e t o and e x i t from n e s t NEST CONCEALMENT - v i s i b i l i t y of n e s t s from above (2 c a t e g o r i e s : open and c o n c e a l e d ) . WIDTH OF VEGETATION - s h o r t e s t d i s t a n c e , f r o m s h o r e t o t h e edge o f t h e marsh (where open water began) MAXIMUM VEGETATION HEIGHT - h e i g h t ( w a t e r l i n e t o apex of stem) of t a l l e s t s c i r p u s stem GREEN VEGETATION HEIGHT - h e i g h t o f 1.0 g r e e n s c i r p u s stems w i t h i n a meter o f t h e n e s t DEAD VEGETATION HEIGHT - a s above, e x c e p t h e i g h t o f p r e v i o u s y e a r s ' dead stems were measured GREEN VEGETATION DENSITY - # of g r e e n s c i r p u s stems i n a 0.30 X 0.30 m q u a d r a t p l a c e d w i t h i n 1 m o f n e s t ( o r a t m i d p o i n t of w i d t h i f e x t e n s i v e v e g e t a t i o n measurement) DEAD VEGETATION DENSITY - a s above e x c e p t t h e # o f dead s c i r p u s stems was r e c o r d e d TOTAL DENSITY - t h e sum of g r e e n and dead v e g . d e n s i t i e s 8 d e s t r o y e d by p r e d a t o r s , and a l s o t o e n s u r e t h a t a l l eggs l a i d i n a n e s t were c o u n t e d . N e s t s were r e v i s i t e d a t t h e p r e d i c t e d h a t c h i n g d a t e a n d examined f o r u n h a t c h e d e g g s . Ponds were c h e c k e d f o r new b r o o d s a t t h i s t i m e a l s o . N e s t s s u c c e s s , and n e s t l o s s t o p r e d a t i o n o f Coot and Ruddy Duck were compared u s i n g c h i - s q u a r e d t e s t s . N e s t i n g C o v e r To compare n e s t s i t e s a v a i l a b l e when C o o t s n e s t e d w i t h t h o s e a v a i l a b l e when Ruddy Ducks n e s t e d , n i n e l a k e s were m o n i t o r e d d u r i n g two p e r i o d s : l a t e May t o e a r l y June 1984, and a g a i n i n m i d - J u l y o f 1984. (Th e s e w i l l be r e f e r r e d t o as t h e e x t e n s i v e v e g e t a t i o n measurements.) Emergent v e g e t a t i o n was measured a t t h i r t y s i t e s on e a c h pond, t h e l o c a t i o n o f e a c h s i t e b e i n g i n d i c a t e d by m a r k e r s on t h e s h o r e . Rocks s p r a y - p a i n t e d f l u o r e s c e n t o r a n g e i n d i c a t e d t h e t h i r t y s t a t i o n s . At odd-numbered s t a t i o n s , I measured maximum h e i g h t , dead v e g e t a t i o n h e i g h t , g r e e n v e g e t a t i o n h e i g h t , w i d t h , g r e e n v e g e t a t i o n d e n s i t y , and d e a d v e g e t a t i o n d e n s i t y . A t even-numbered s t a t i o n s , o n l y w i d t h was measured. (More samples were needed t o e s t a b l i s h whether s t a t i s t i c a l d i f f e r e n c e s e x i s t e d between s p r i n g and summer emergent v e g e t a t i o n w i d t h . ) Mean v a l u e s f o r n e s t s i t e measurements were compared by t - t e s t s . 9 Ne s t P r e d a t i o n E x p e r i m e n t s I compared p r e d a t i o n o f n e s t s p l a c e d i n s p r i n g when C o o t s n e s t and summer when Ruddy Ducks n e s t . ( T h i s e x p e r i m e n t w i l l be r e f e r r e d t o as dummy n e s t e x p e r i m e n t A.) B e g i n n i n g on May 27,1984, t h i r t y dummy n e s t s were c o n s t r u c t e d f r o m d e a d s c i r p u s b u l r u s h a t s i t e s w i t h measurement v a l u e s w i t h i n t h e range measured a t Ruddy Duck n e s t s i t e s d i s c o v e r e d i n 1983. (These a r e r e f e r r e d t o as f l a g g e d - u n c o n c e a l e d dummy n e s t s . ) T h e s e n e s t s were a r r a n g e d a t a d e n s i t y o f one o r two per pond, and were l o c a t e d w i t h i n t h e emergent v e g e t a t i o n ; s m a l l ponds had o n l y one dummy n e s t , and l a r g e r ponds had two. Nest l o c a t i o n s were marked by s e c u r i n g f l a g g i n g t a p e on o r n e a r t h e s h o r e a t a d i s t a n c e o f f i v e o r more m e t e r s from t h e n e s t ( s e e Appendix T h r e e ) . F i v e c h i c k e n eggs were p l a c e d i n e a c h n e s t . ( C h i c k e n eggs were w h i t e l i k e Ruddy Duck e g g s b u t were s l i g h t l y s m a l l e r . ) Dummy n e s t s were v i s i t e d two d a y s a f t e r c o n s t r u c t i o n and s u b s e q u e n t l y a t wee k l y i n t e r v a l s . The f i n a l v i s i t was made when th e n e s t s were t w e n t y - f o u r d a y s o l d . ( A c c o r d i n g t o B e l l r o s e ( 1 9 8 0 ) , t w e n t y - f o u r d a y s i s t h e l e n g t h of t h e a v e r a g e i n c u b a t i o n p e r i o d of a Ruddy Duck.) Egg l o s s f r o m e a c h n e s t was r e c o r d e d a t ea c h v i s i t . B e g i n n i n g J u l y 14, t h e p r o c e d u r e was r e p e a t e d . N e s t s were c o n s t r u c t e d and d i s t r i b u t e d a s b e f o r e , b u t new s i t e s were c h o s e n t o e n s u r e t h a t no b i a s was i n t r o d u c e d b e c a u s e p r e d a t o r s had l e a r n e d t o a s s o c i a t e a n e s t l o c a t i o n w i t h e g g s . N e s t p r e d a t i o n was compared s t a t i s t i c a l l y by t h e c h i - s q u a r e d t e s t . 10 I d e n t i f i c a t i o n of N e s t P r e d a t o r s To d e t e r m i n e what s p e c i e s m i g h t be r e s p o n s i b l e f o r n e s t p r e d a t i o n , t h e l o c a t i o n and b e h a v i o r of p o t e n t i a l a v i a n p r e d a t o r s were n o t e d whenever t h e y were seen c l o s e t o a pond. O n l y Common Ravens ( C o r v u s c o r a x ) , R e d - t a i l e d Hawks ( B u t e o  j a m a i c e n s i s ) , N o r t h e r n H a r r i e r s ( C i r e u s c y a n e u s ) , and B a l d E a g l e s ( H a l i a e e t u s l e u c o c e p h a l u s ) were o b s e r v e d . B e h a v i o r s r e c o g n i z e d i n c l u d e d : a) w a l k i n g on t h e g r o u n d , b) f l y i n g low and s l o w ( l o w e r t h a n 15 m.- f l a p p i n g and g l i d i n g ) , c) f l y i n g h i g h and f a s t (15 m. o r h i g h e r - f l a p p i n g ) , d) c a l l i n g , and e) p r e y i n g upon n e s t s ( o b s e r v e d c o n s u m i n g an egg o r c a r r y i n g i t away). I compared t h e numbers and k i n d s of a v i a n p r e d a t o r s and t h e b e h a v i o r s o b s e r v e d d u r i n g t h e t w e n t y - f o u r day p e r i o d s of t h e e a r l y and l a t e s e a s o n p r e d a t i o n e x p e r i m e n t . C h i - s q u a r e d t e s t s were a p p l i e d t o d e t e r m i n e s t a t i s t i c a l d i f f e r e n c e s between t h e number of a v i a n p r e d a t o r s e a r l y and l a t e i n t h e s e a s o n and a l s o t h e b e h a v i o r o f p r e d a t o r s e a r l y and l a t e . N e s t D e n s i t y N e s t d e n s i t y p e r pond e a r l y and l a t e i n t h e s e a s o n was e s t i m a t e d by c o u n t i n g t h e number of C o o t and Ruddy Duck n e s t s on 14 ponds t w i c e : once d u r i n g peak Coot n e s t i n g (May 27-June 19) and once d u r i n g peak Ruddy Duck n e s t i n g ( J u l y 14-Aug 6 ) . B o t h Ruddy Ducks and C o o t s n e s t e d on a l l o f t h e 14 ponds s t u d i e d . 11 Water L e v e l F l u c t u a t i o n s F l u c t u a t i o n s i n d e p t h o f ponds u s e d by Ruddy Ducks and C o o t s were measured w i t h d e p t h m o n i t o r i n g s t a k e s i n s t a l l e d on t w e n t y - t h r e e ponds on May 10, 1984. Changes i n d e p t h were r e c o r d e d May 28, June 15, J u l y 10 and Aug. 4. R e s u l t s N e s t S u c c e s s A c h i - s q u a r e d t e s t showed t h a t f r e q u e n c i e s of s u c c e s s f u l and u n s u c c e s s f u l n e s t s of Ruddy Ducks were n o t s i g n i f i c a n t l y d i f f e r e n t from t h o s e of A m e r i c a n C o o t s . N e s t s u c c e s s of Ruddy Ducks was 60.9% (n=46), whereas n e s t s u c c e s s of A m e r i c a n C o o t s was 70.0% (n=146). N e s t s u c c e s s was c a l c u l a t e d by d i v i d i n g t h e t o t a l number o f n e s t s i n w h i c h a t l e a s t one egg h a t c h e d by t h e t o t a l number of n e s t s i n w h i c h a t l e a s t one egg was l a i d . N e s t P r e d a t i o n A c h i - s q u a r e d t e s t showed t h a t fewer Ruddy n e s t s were d e s t r o y e d by p r e d a t o r s t h a n were Coot n e s t s (p<.005; t o t a l Ruddy n e s t s = 4 6 , t o t a l Coot n e s t s = 1 4 6 ) . E l e v e n p e r c e n t of Ruddy n e s t s were d e s t r o y e d by p r e d a t o r s , whereas t w e n t y - e i g h t p e r c e n t o f C o o t n e s t s were d e s t r o y e d . 1 2 E x p e r i m e n t s s u g g e s t e d t h a t n e s t l o s s t o p r e d a t o r s v a r i e d w i t h t h e s e a s o n ( s e e a l s o A p p e n d i x T h r e e ) . In dummy n e s t e x p e r i m e n t A, p r e d a t i o n o f dummy n e s t s e s t a b l i s h e d e a r l y was compared t o p r e d a t i o n l a t e i n t h e s e a s o n ( F i g u r e 1 ) . The p r o p o r t i o n of dummy n e s t s d e s t r o y e d i n s p r i n g was s i g n i f i c a n t l y d i f f e r e n t from t h a t i n summer ( p < . 0 0 l ; c h i - s q u a r e d t e s t ; n=30). In t h e s p r i n g a l l but 2 n e s t s were c o m p l e t e l y d e s t r o y e d ( a l l 5 eggs m i s s i n g ) w i t h i n t h e f i r s t 2 d a y s of t h e e x p e r i m e n t , whereas i n t h e summer o n l y one n e s t was c o m p l e t e l y d e s t r o y e d w i t h i n t h e f i r s t 2 d a y s . S e v e n t e e n p e r c e n t o f dummy n e s t s were p a r a s i t i z e d by f e m a l e Ruddy Ducks i n t h e summer. My dummy n e s t s l i k e l y were m i s t a k e n f o r Ruddy n e s t s by p a r a s i t i c f e m a l e s , s i n c e Ruddy Ducks r a r e l y p a r a s i t i z e n e s t s o f o t h e r w a t e r f o w l ( J o y n e r , 1973). N e s t S i t e and N e s t i n g C o v e r N e s t i n g c o v e r may be g r e a t e r i n t h e summer t h a n i t i s i n t h e s p r i n g and t h u s , m i g h t e x p l a i n why p r e d a t i o n o f Ruddy n e s t s was l e s s t h a n p r e d a t i o n of Coot n e s t s . C h a r a c t e r i s t i c s o f emergent v e g e t a t i o n p r e s e n t e a r l y and l a t e i n t h e se a s o n were compared t o t e s t t h i s i d e a . The a v e r a g e v a l u e s and 95% c o n f i d e n c e i n t e r v a l s of measurements t a k e n e a r l y and l a t e i n t h e 1984 s e a s o n a r e shown i n T a b l e 2. F o r a l l measurements e x c e p t w i d t h of emergent v e g e t a t i o n , mean v a l u e s t a k e n e a r l y i n t h e s e a s o n were 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 t h o s e t a k e n l a t e i n t h e s e a s o n ( t - t e s t , p v a l u e s i n T a b l e 2 ) . Maximum h e i g h t o f 13 O o o CO I -z UJ CJ QC UJ 0. o o o (VI n = 30 o J LATE EARLY nr 30 n =30 n =30 NESTS DESTROYED BY PREDATORS NESTS PARASITIZED FIGURE j_ : Comparison of the p r o p o r t i o n s of dummy nest p r e d a t i o n , egg pr e d a t i o n and nest p a r a s i t i s m i n the e a r l y and l a t e season 14 TABLE 2 E x t e n s i v e V e g e t a t i o n M easurements: T h e s e measurements were t a k e n a t a t i m e when most A m e r i c a n C o o t s began t o l a y eggs (EARLY) and compared t o t h o s e t a k e n a t t h e t i m e when most Ruddy Ducks began t o l a y ( L A T E ) . EARLY LATE VEGETATION MEASUREMENTS MEAN 95% MEAN 95% C.I . C.I . ***Maximum V e g e t a t i o n H e i g h t 1 .2 0.05 1 .7 0.04 * * * G r e e n V e g e t a t i o n H e i g h t 0.21 0.018 1.21 0.121 ***Dead V e g e t a t i o n H e i g h t 0.79 0.051 0.46 0.043 W i d t h of V e g e t a t i o n 6.3 0.33 6.3 0.29 ***Dead V e g e t a t i o n D e n s i t y 21 1 . 5 6 0.9 * * * G r e e n V e g e t a t i o n D e n s i t y 17 1 . 1 26 1 . 1 * * * T o t a l D e n s i t y 37 1 .7 31 1 .2 * * * s i g n i f i c a n t d i f f e r e n c e p<.00! 1 5 v e g e t a t i o n , h e i g h t of g r e e n v e g e t a t i o n and g r e e n v e g e t a t i o n d e n s i t y were s i g n i f i c a n t l y g r e a t e r l a t e r i n t h e s e a s o n when Ruddy Ducks n e s t e d . T h e s e r e s u l t s were 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 s e a s o n a l d i f f e r e n c e s i n c o v e r r e s u l t e d i n d i f f e r e n t n e s t p r e d a t i o n r a t e s f o r C o o t s and Ruddy D u c k s . S i n c e , c o v e r was t a l l e r , and d e n s e r when Ruddy Ducks n e s t e d t h a n i n s p r i n g , c o v e r may have c a m o u f l a g e d n e s t s f r o m p r e d a t o r s r e d u c i n g t h e r i s k of p r e d a t i o n . Not a l l measurements t a k e n s u p p o r t t h e h y p o t h e s i s t h a t c o v e r was g r e a t e r l a t e r i n t h e s e a s o n . Dead v e g e t a t i o n d e n s i t y , t o t a l d e n s i t y and dead v e g e t a t i o n h e i g h t were g r e a t e r e a r l i e r i n t h e s e a s o n . T h i s r e s u l t s u g g e s t e d t h a t c o v e r was t a l l e r and d e n s e r e a r l i e r when C o o t s n e s t e d r a t h e r t h a n l a t e r when Ruddy Ducks n e s t e d . C h a r a c t e r i s t i c s o f n e s t s i t e s must a l s o be c o n s i d e r e d i n o r d e r t o u n d e r s t a n d t h e i n f l u e n c e o f c o v e r on n e s t p r e d a t i o n . T a b l e 3 shows mean v a l u e s and c o n f i d e n c e l i m i t s o f measurements t a k e n a t Ruddy Duck and Coot n e s t s i t e s . A l t h o u g h t h e n e s t s i t e s of t h e two s p e c i e s were q u i t e s i m i l a r , c a r e f u l measurement showed t h a t t h e n e s t s i t e s d i f f e r e d s i g n i f i c a n t l y i n 8 of t h e 10 measurements t a k e n . The dead v e g e t a t i o n h e i g h t , and dead v e g e t a t i o n d e n s i t y were s i g n i f i c a n t l y l e s s a t Ruddy Duck n e s t s i t e s t h a n a t Coo t n e s t , s i t e s . The g r e e n v e g e t a t i o n d e n s i t y and g r e e n v e g e t a t i o n h e i g h t were s i g n i f i c a n t l y g r e a t e r a t Ruddy Duck n e s t s i t e s ( t - t e s t , see T a b l e 3 f o r p v a l u e s ) . Thus, n e s t s i t e s o f Ruddy D u c k s , l i k e t h e e x t e n s i v e v e g e t a t i o n measurements l a t e i n t h e s e a s o n ( T a b l e 2 ) , e x h i b i t e d s h o r t e r , l e s s d e n s e dead 16 TABLE 3 C o m p a r i s o n o f Ruddy Duck and A m e r i c a n C o o t N e s t S i t e Measurements AMERICAN COOT RUDDY DUCK NEST SITE MEASUREMENTS MEAN 95 % C.I . MEAN 95 C. % I . ***Number of N e s t E n t r a n c e s 1.12 0.069 0.68 0. 216 • D e g r e e s Open 60.0 7.84 40.2 1 3 .71 * * * D e p t h a t N e s t 0.43 0.018 0.33 0. 049 ***Maximum V e g e t a t i o n H e i g h t 0.87 0.066 1 .68 0. 106 * * * G r e e n V e g e t a t i o n H e i g h t 0.46 0.069 1 .30 0. 092 *Dead V e g e t a t i o n H e i g h t 0.82 0.052 0.61 0. 123 W i d t h of V e g e t a t i o n 11.85 1 .543 1 1 .84 2. 465 **Dead V e g e t a t i o n D e n s i t y 22.4 1 .80 14.8 3 .92 * * * G r e e n V e g e t a t i o n D e n s i t y 16.6 2.16 -25.1 3 .52 T o t a l D e n s i t y 39.0 2.10 39.9 3 .90 s i g n i f i c a n t d i f f e r e n c e p<.05 s i g n i f i c a n t d i f f e r e n c e p<.0l s i g n i f i c a n t d i f f e r e n c e p<.00! 1 7 v e g e t a t i o n and t a l l e r , d e n s e r g r e e n v e g e t a t i o n . S i g n i f i c a n t d i f f e r e n c e s e x i s t e d between t h e a v e r a g e emergent v e g e t a t i o n v a l u e s and t h e a v e r a g e n e s t s i t e v a l u e s . C o o t s s e l e c t e d n e s t s i t e s w i t h t a l l e r g r e e n v e g e t a t i o n , w h i l e Ruddy Ducks s e l e c t e d n e s t s i t e s w i t h g r e a t e r t h a n t h e a v e r a g e a v a i l a b l e dead v e g e t a t i o n d e n s i t y ( t - t e s t , p<.005; see F i g u r e 2 ) . B o t h s p e c i e s s e l e c t e d s i t e s w i t h g r e a t e r c o v e r t h a n t h e a v e r a g e a v a i l a b l e when t h e y n e s t e d . Ruddy Duck and C o o t n e s t s i t e s a r e t h u s more a l i k e t h a n a r e t h e a v e r a g e v e g e t a t i o n s i t e s e a r l y and l a t e i n t h e s e a s o n . The c o n s t r u c t i o n and p o s i t i o n of t h e n e s t w i t h i n t h e v e g e t a t i o n s u g g e s t e d o t h e r d i f f e r e n c e s between C o o t and Ruddy Duck n e s t s i t e s . The number o f n e s t e n t r a n c e s , and d e g r e e s open (se e T a b l e 1 f o r d e f i n i t i o n ) were s i g n i f i c a n t l y l e s s a t Ruddy Duck n e s t s i t e s t h a n a t Coot n e s t s i t e s ( t - t e s t s ; see T a b l e 3 f o r p v a l u e s ) . These measurement e s t i m a t e d t h e v i s i b i l i t y of t h e n e s t t o p r e d a t o r s a p p r o a c h i n g t h e marsh from any s i d e . F o r n e s t s w i t h more e n t r a n c e s and d e g r e e s open, t h e r e may have been a g r e a t e r c h a n c e t h a t a p r e d a t o r w o u l d a p p r o a c h from an a n g l e where t h e n e s t and eggs were v i s i b l e . C o m p a r i s o n of n e s t c o n c e a l m e n t g i v e s a s i m i l a r r e s u l t . N e s t c o n c e a l m e n t i s an e s t i m a t e of t h e v i s i b i l i t y o f a n e s t t o a v i a n p r e d a t o r s . Open n e s t s were t h o s e j u d g e d t o be most v i s i b l e t o a v i a n p r e d a t o r s . The f r e q u e n c y o f c o n c e a l e d C o o t n e s t s was s i g n i f i c a n t l y d i f f e r e n t from t h a t of c o n c e a l e d Ruddy Duck n e s t s ( t a b l e 4; c h i -s q u a r e d t e s t ; p<.05). T h i s e v i d e n c e s u g g e s t s t h a t Ruddy Duck n e s t s may be l e s s v u l n e r a b l e t o a v i a n p r e d a t o r s . 18 Coot Nest aito Spring Veg. 8lto Ruddy Noat Site Sumac Vflfl. 81ta FIGURE 2 : a) C o m p a r i s o n of g r e e n v e g e t a t i o n h e i g h t a t Ruddy Duck and A m e r i c a n Coot n e s t s i t e s w i t h g r e e n v e g e t a t i o n h e i g h t a t e x t e n s i v e v e g e t a t i o n measurement s i t e s i n t h e s p r i n g and summer b) C o m p a r i s o n o f dead v e g e t a t i o n d e n s i t y a t Ruddy Duck and A m e r i c a n C o o t n e s t s i t e s w i t h d ead v e g e t a t i o n d e n s i t y a t e x t e n s i v e v e g e t a t i o n measurement s i t e s i n t h e s p r i n g and summer 19 TABLE 4 C o m p a r i s o n o f Ruddy Duck and A m e r i c a n Coot N e s t C o n c e a l m e n t RUDDY DUCK NESTS AMERICAN COOT NESTS C o n c e a l e d 26 46 Open 4 21 20 F i n a l l y , i f c o v e r a t t h e n e s t s i t e d i d i n c r e a s e t h e p r o b a b i l i t y of a n e s t b e i n g d e s t r o y e d by a p r e d a t o r , one would e x p e c t d i f f e r e n c e s between n e s t s i t e s of s u c c e s s f u l and d e s t r o y e d n e s t s . Such d i f f e r e n c e s m ight i n c l u d e t a l l e r and d e n s e r c o v e r ( e s p e c i a l l y g r e e n v e g e t a t i o n ) , fewer n e s t e n t r a n c e s and d e g r e e s open, and g r e a t e r n e s t c o n c e a l m e n t a t s u c c e s s f u l n e s t s i t e s t h a n a t n e s t s i t e s d e s t r o y e d by p r e d a t o r s . T a b l e s 5 and 6 show mean v a l u e s and c o n f i d e n c e l i m i t s of measurements d e s c r i b i n g s u c c e s s f u l Ruddy Duck and Coot n e s t s and Ruddy Duck and Coot n e s t s t h a t were d e s t r o y e d by p r e d a t o r s . D e s t r o y e d Ruddy n e s t s may have been l o c a t e d i n p o o r e r c o v e r . Most measurement v a l u e s were l o w e r f o r d e s t r o y e d n e s t s t h a n f o r s u c c e s s f u l o n e s , but o n l y t h e d i f f e r e n c e s between v e g e t a t i o n h e i g h t s and water "depths a t n e s t s were s i g n i f i c a n t l y d i f f e r e n t . S u c c e s s f u l and d e s t r o y e d Coot n e s t s a p p e a r e d t o be more s i m i l a r t h a n s u c c e s s f u l and d e s t r o y e d Ruddy Duck n e s t s . O n l y d e ad v e g e t a t i o n h e i g h t was s i g n i f i c a n t l y d i f f e r e n t , t h e t a l l e r d e a d v e g e t a t i o n b e i n g f o u n d a t d e s t r o y e d C o o t n e s t s i t e s . Thus, c o v e r was t a l l e r , not s h o r t e r , a t C o o t n e s t s t h a t were d e s t r o y e d by p r e d a t o r s . P r e d a t o r B e h a v i o r P r e d a t o r b e h a v i o r may be d i f f e r e n t e a r l y i n t h e s e a s o n when C o o t s n e s t as compared t o l a t e r when Ruddy Ducks n e s t . P r e d a t o r s may v i s i t ponds t o s e a r c h f o r n e s t s l e s s f r e q u e n t l y l a t e r i n t h e s e a s o n and t h u s r a r e l y d e s t r o y Ruddy n e s t s . T a b l e 21 TABLE 5 C o m p a r i s o n o f S u c c e s s f u l and D e s t r o y e d Ruddy Duck N e s t S i t e s DESTROYED NESTS SUCCESSFUL NESTS VEGETATION MEASUREMENTS MEAN 95% C.I . MEAN 95% C.I . # of n e s t e n t r a n c e s 0.3 0.65 0.7 0.26 D e g r e e s Open 29 11.5 67 69.0 *D e p t h a t N e s t 0 .10 0.095 0.32 0.055 Maximum V e g e t a t i o n H e i g h t 1 .10 0.020 1.71 0. 1 32 *Green V e g e t a t i o n H e i g h t 0 .93 0. 1 29 1.41 0.115 ***Dead V e g e t a t i o n H e i g h t 0 .30 0.024 0.65 0.121 W i d t h of V e g e t a t i o n 6.7 9.34 12.0 3.81 Dead V e g e t a t i o n D e n s i t y 0 1 5 4.3 Gree n V e g e t a t i o n D e n s i t y 1 5 10.1 28 4. 1 * s i g n i f i c a n t d i f f e r e n c e p<.05 *** s i g n i f i c a n t d i f f e r e n c e p<.00l TABLE 6 C o m p a r i s o n o f S u c c e s s f u l and U n s u c c e s s f u l A m e r i c a n Coot N e s t S i t e s DESTROYED NESTS SUCCESSFUL NESTS VEGETATION MEASUREMENTS MEAN 95% MEAN 95% C.I . C.I . # of N e s t E n t r a n c e s 1.1 0.17 1 . 1 0.08 D e g r e e s Open 56 10.8 66 21.8 D e p t h a t N e s t 0.41 0 .036 0.43 0.024 Maximum V e g e t a t i o n H e i g h t 0.79 0 . 1 50 0.88 0.083 G r e e n V e g e t a t i o n H e i g h t 0.45 0 . 1 54 0.45 0.081 *Dead V e g e t a t i o n H e i g h t 0.90 0 .089 0.78 0.071 W i d t h 9.7 2.18 1 2 1 .78 Dead V e g e t a t i o n D e n s i t y 23 3.3 21 2.2 Gr e e n V e g e t a t i o n D e n s i t y 18 5.4 1 7 2.6 * s i g n i f i c a n t d i f f e r e n c e p<.05 22 7 shows t h a t s i g n i f i c a n t l y fewer Ravens were o b s e r v e d i n t h e s p r i n g t h a n i n t h e summer ( c h i - s q u a r e d t e s t ; p<.005). Ravens were a l s o o b s e r v e d p r e y i n g upon n e s t s i n t h e emergent v e g e t a t i o n on 3 s e p a r a t e o c c a s i o n s . The numbers of R e d - t a i l e d Hawks o b s e r v e d i n c r e a s e d from s p r i n g t o summer; however, t h i s d i f f e r e n c e was n o t s i g n i f i c a n t , and a l t h o u g h R e d - t a i l e d Hawks were o b s e r v e d a t t e m p t i n g t o p r e y upon a d u l t b i r d s , t h e y were n o t o b s e r v e d t o p r e y upon n e s t s . In T a b l e 8, t h e b e h a v i o r of Ravens e a r l y and l a t e i n t h e s e a s o n i s compared. The b e h a v i o r ' f l y i n g low and s l o w l y ' was o b s e r v e d s i g n i f i c a n t l y l e s s f r e q u e n t l y l a t e i n t h e s e a s o n . T h i s b e h a v i o r and n e s t p r e d a t i o n were o n l y o b s e r v e d e a r l y i n t h e s e a s o n . The b e h a v i o r ' w a l k i n g on t h e g r o u n d ' was o n l y o b s e r v e d l a t e i n t h e s e a s o n . The Ravens seen ' w a l k i n g on t h e g r o u n d ' may have been f e e d i n g on g r a s s h o p p e r s t h a t were abundant d u r i n g J u l y and A u g u s t . The a v e r a g e d e n s i t y of Coot and w a t e r f o w l n e s t s i n em e r g e n t v e g e t a t i o n was 5.9 n e s t s p e r pond when A m e r i c a n C o o t s n e s t e d and 1.9 n e s t s p e r pond when Ruddy Ducks n e s t e d . N e s t F l o o d i n g T w e l v e p e r c e n t of Ruddy Duck n e s t s (n=46) were f o u n d f l o o d e d i n 1984, but no f l o o d e d Coot n e s t s (n=146) were f o u n d . F l o o d i n g of Ruddy n e s t s was a p p a r e n t l y c a u s e d by two m a j o r w i n d s t o r m s t h a t swamped and o v e r t u r n e d n e s t s i n t h e em e r g e n t v e g e t a t i o n . A l m o s t a l l Coot c l u t c h e s had a l r e a d y h a t c h e d when TABLE 7 C o m p a r i s o n of A v i a n P r e d a t o r s : T h e s e o b s e r v a t i o n s were made a t a t i m e when most A m e r i c a n C o o t s began t o l a y eggs (EARLY) and compared t o t h o s e t a k e n a t t h e t i m e when most Ruddy Ducks began t o l a y ( L A T E ) . SPECIES EARLY LATE **Raven R e d - t a i l e d Hawk N o r t h e r n H a r r i e r B a l d E a g l e T o t a l 20 3 6 8 3 0 16 24 ** s i g n i f i c a n t d i f f e r e n c e p<.0l TABLE 8 Raven B e h a v i o r : T h e s e o b s e r v a t i o n s were made a t a t i m e when most A m e r i c a n C o o t s began t o l a y eggs (EARLY) and compared t o t h o s e t a k e n a t t h e tim e when most Ruddy Ducks began t o l a y ( L A T E ) . BEHAVIOR PEAK COOT NESTING PEAK RUDDY NESTING P r e y i n g Upon N e s t s 3 0 * F l y i n g Low and S l o w l y 13 0 F l y i n g H i g h and F a s t 3 1 W a l k i n g on t h e Ground 0 2 C a l l i n g 1 3 * s i g n i f i c a n t d i f f e r e n c e p<.005 25 t h e s e s t o r m s o c c u r r e d but some Coot n e s t s were s t i l l b e i n g i n c u b a t e d . Wind s t o r m s and t h e r e s u l t i n g n e s t l o s s e s were n o t o b s e r v e d i n 1983 f o r e i t h e r Ruddy Ducks o r A m e r i c a n C o o t s . N e s t f l o o d i n g due t o heavy r a i n was not o b s e r v e d i n e i t h e r 1983 o r 1 984. S e a s o n a l Water L e v e l F l u c t u a t i o n s Water l e v e l f l u c t u a t i o n s i n ponds i n 1984 a r e d e s c r i b e d i n T a b l e 9. Most ponds became s h a l l o w e r as t h e s e a s o n p r o g r e s s e d . W h i l e t h e p r e d i c t i o n t h a t f l o o d i n g of ponds w o u l d o c c u r l e s s o f t e n l a t e i n t h e s e a s o n may y e t be t r u e of some b r e e d i n g a r e a s , f l o o d i n g i n b o t h s p r i n g and summer i s a p p a r e n t l y uncommon i n t h e C h i l c o t i n . B r e e d i n g l a t e may be a d i s a d v a n t a g e w i t h r e s p e c t t o water l e v e l d y n a m i c s . Fewer n e s t s i t e s i n d eep water may have been a v a i l a b l e t o Ruddy D u c k s . Water l e v e l s i n ponds were l o w e r l a t e r i n t h e s e a s o n and T a b l e 5 s u g g e s t s t h a t Ruddy Duck n e s t s d e s t r o y e d by p r e d a t o r s t e n d e d t o be a t s h a l l o w e r d e p t h s . T h e r e was no s i g n i f i c a n t d i f f e r e n c e between water d e p t h a t s u c c e s s f u l o r d e s t r o y e d C o o t n e s t s ( T a b l e 6 ) . D e p t h of w a t e r may o n l y be c o r r e l a t e d w i t h n e s t d e s t r u c t i o n by p r e d a t o r s , however; t h e r e i s no p r o o f t h a t t h e r e d u c e d w a t e r l e v e l s c a u s e d n e s t s t o be more v u l n e r a b l e t o p r e d a t i o n . I n d e e d , d r y l a n d n e s t i n g by Ruddy Ducks has been r e p o r t e d by M c K n i g h t (1974) and n e s t s u c c e s s was 80%. He s p e c u l a t e d t h a t most n e s t s were s u c c e s s f u l o n l y b e c a u s e a v i a n p r e d a t o r s were r a r e ; however, t h e p r e d a t o r s r e s p o n s i b l e 26 TABLE 9 C o m p a r i s o n of Water L e v e l Changes E a r l y and L a t e i n t h e S e a s o n MAY 12 -JUNE 15 JULY 1-AUG. 4 MEAN 95% C.I . MEAN 95% C.I . * * A v e r a g e D e c l i n e i n Water L e v e l (m) 0.023 0.0032 0.096 0.0357 A v e r a g e I n c r e a s e i n Water L e v e l (m) 0.021 0.0079 0.019 0.0153 % of O b s e r v a t i o n s where Water L e v e l I n c r e a s e d 30 NA 26 NA *% o f O b s e r v a t i o n s where Water L e v e l Remained Unchanged 22 NA 0 NA % of O b s e r v a t i o n s where 48 NA 74 NA Water L e v e l D e c l i n e d * s i g n i f i c a n t d i f f e r e n c e p<.05 ** s i g n i f i c a n t d i f f e r e n c e p<.01 27 f o r t h e 20% n e s t l o s s were unknown. A v i a n p r e d a t o r s ( e s p e c i a l l y R avens) a r e n o t r a r e i n t h i s s t u d y a r e a ; however, e x a m i n a t i o n of d e s t r o y e d n e s t s s u g g e s t e d t h a t mammals n o t b i r d s p r e y e d upon Ruddy Duck n e s t s . N e s t D e s e r t i o n F i f t e e n p e r c e n t o f Ruddy Duck n e s t s were d e s e r t e d . A l l but one of t h e s e n e s t s were f o u n d d u r i n g l a y i n g or j u s t a f t e r t h e c l u t c h was c o m p l e t e d . T h e s e n e s t s were not known t o have been i n c u b a t e d . When eggs were opened, t h e r e was no s i g n of embryo d e v e l o p m e n t . One n e s t was d e s e r t e d 10 days a f t e r i n c u b a t i o n had begun. T h i s - n e s t s i t e was v e r y c l o s e . t o a t e m p e r a t u r e m o n i t o r i n g s i t e ( s e e A p p e n d i x Two) and d e s e r t i o n may have been c a u s e d by t h e d a i l y d i s t u r b a n c e when I c h e c k e d t h e t h e r m o m e t e r . N e s t d e s e r t i o n by C o o t s was not o b s e r v e d , a l t h o u g h d e s e r t e d n e s t s m i g h t have been r a p i d l y d e s t r o y e d by p r e d a t o r s and so n e v e r f o u n d . S e v e r a l Ruddy and C o o t n e s t s were i n c u b a t e d but s u b s e q u e n t l y abandoned when t h e f e m a l e d i e d . T h e s e n e s t s were n o t i n c l u d e d i n t h e n e s t d e s e r t i o n c a t e g o r y . 28 D i s c u s s i o n N e s t S u c c e s s and R e n e s t i n g N e s t s u c c e s s of Ruddy Ducks was f o u n d not t o be s i g n i f i c a n t l y d i f f e r e n t from t h a t o f C o o t s . However, s i n c e C o o t s n e s t a s e c o n d t i m e i f t h e f i r s t n e s t i s l o s t , t h i s measurement does not r e f l e c t t h e p r o p o r t i o n of p a i r s t h a t h a t c h e d y o ung. One h u n d r e d and f o r t y - s i x C o o t n e s t s were d i s c o v e r e d , y e t c e n s u s e s of t h e ponds showed t h a t t h e r e were a p p r o x i m a t e l y 105 p a i r s of C o o t s . S i n c e 70% o f Coot n e s t s ( i e . 100 n e s t s ) were s u c c e s s f u l , a l m o s t a l l C o o t s s u c c e s s f u l l y h a t c h e d y o ung. Thus, a l t h o u g h n e s t l o s s of C o o t s was h i g h , p a i r s t h a t l o s t t h e i r f i r s t n e s t were a b l e on a v e r a g e t o r e n e s t s u c c e s s f u l l y . In c o n t r a s t , Ruddy Ducks were n o t o b s e r v e d t o r e n e s t , and fewer n e s t s t h a n f e m a l e s were c o u n t e d on b r e e d i n g p o n d s . ( I t was not p o s s i b l e t o c o u n t b r e e d i n g p a i r s s i n c e f e m a l e Ruddy Ducks i n my s t u d y a r e a t e n d e d t o be a c c o m p a n i e d by s e v e r a l m a l e s . ) A l t h o u g h Gray (1980) s u g g e s t e d t h a t t h e Ruddy Ducks i n C a l i f o r n i a r e n e s t e d , t h e b r e e d i n g s e a s o n was c o n s i d e r a b l y l o n g e r t h e r e . When she g r a p h e d t h e number of n e s t s i n i t i a t e d (one egg l a i d i n t h e n e s t ) v e r s u s t h e c a l e n d a r d a t e , G r a y f o u n d two d i s t i n c t p e a k s of n e s t i n i t i a t i o n . She c o n c l u d e d t h a t t h e s e c o n d peak r e p r e s e n t e d n e s t s o f f e m a l e s t h a t r e n e s t e d . M i s t e r e k (1974) n o t e d t h e same phenomenon; however, he a t t r i b u t e d i t t o f e m a l e age s i n c e f o r many b i r d s p e c i e s , y o u n g e r f e m a l e s n e s t l a t e r t h a n t h e more e x p e r i e n c e d o l d e r o nes 29 (Klomp,1970; P e r r i n s , 1 9 7 0 ) . S i e g f r i e d ( 1 9 7 6 a ) , and J o y n e r (1976a) f o u n d no e v i d e n c e o f r e n e s t i n g i n Ruddy Duck p o p u l a t i o n s i n Canada and t h e U n i t e d S t a t e s . W h i l e i t i s p o s s i b l e t h a t 1983 and 1984 were p a r t i c u l a r l y p o o r b r e e d i n g s e a s o n s f o r Ruddy Ducks, and so Ruddy Ducks l o s t more n e s t s t h a n u s u a l , i t seems u n l i k e l y t h a t Ruddy Ducks l o s e n e s t s so r a r e l y t h a t a l m o s t a l l f e m a l e s h a t c h y o u ng. H i g h n e s t i n g s u c c e s s f o r t h i s s p e c i e s has been r e p o r t e d i n o t h e r s t u d i e s ( T a b l e 10); however, n e s t s u c c e s s o f Ruddy Ducks t e n d s t o be l o w e r t h a n t h a t o f C o o t s ( T a b l e 11) and C o o t s c an r e p l a c e n e s t s t h a t a r e l o s t . N e s t s u c c e s s of Ruddy Ducks was n o t s i g n i f i c a n t l y l e s s t h a n t h a t of two w a t e r f o w l s p e c i e s t h a t b r e e d e a r l y . J . P. S a v a r d ( p e r s . comm.) e s t i m a t e d t h a t 43% of Ba r r o w ' s G o l d e n e y e p a i r s h a t c h e d young i n t h e C h i l c o t i n i n 1984 and G. G a u t h i e r ( p e r s . comm.) f o u n d t h a t 64% o f B u f f l e h e a d p a i r s h a t c h e d young i n t h e C h i l c o t i n i n 1984. N e i t h e r B u f f l e h e a d nor B a r r o w ' s G o l d e n e y e r e n e s t e d i n t h i s a r e a . Thus, s p e c i e s t h a t do n o t r e n e s t ( B a r r o w ' s G o l d e n e y e , B u f f l e h e a d and Ruddy Duck) a p p e a r t o h a t c h fewer young p e r p a i r t h a n t h o s e t h a t do r e n e s t ( A m e r i c a n C o o t ) . S p e c i a l c o n s i d e r a t i o n must be g i v e n t o t h e i m p l i c a t i o n s o f t h i s r e s u l t . T h e s e d i f f e r e n c e s do not n e c e s s a r i l y mean r e n e s t i n g b i r d s have h i g h e r o v e r a l l r e p r o d u c t i v e s u c c e s s . F o r example, newly h a t c h e d C o o t young a r e l e s s p r e c o c i o u s t h a n newly h a t c h e d d u c k l i n g s . They a r e u n a b l e t o f o r a g e f o r t h e m s e l v e s ( F r e d r i c k s o n , 1 9 7 0 ) , h a v e l e s s down t h a n d u c k l i n g s , and a r e l e s s 30 TABLE j_0 C o m p a r i s o n of N e s t S u c c e s s o f Ruddy Ducks r e p o r t e d i n V a r i o u s S t u d i e s % NESTS SAMPLE SUCCESSFUL S I Z E B e n n e t t (1938) 77.0 22 Low (1941) 73.2 71 M i l l e r and C o l l i n s (1954) 32.0 25 R i e n e c k e r and A n d e r s o n (1960) 54.7 64 M i s t e r e k (1974) 53.3 30 M c k n i g h t (1974) 80.0 1 5 J o y n e r (1977) 31 .3 1 50 TABLE 11 C o m p a r i s o n o f N e s t S u c c e s s o f S t u d i e s A m e r i c a n C o o t r e p o r t e d i n V a r i o u s % NEST SUCCESS SAMPLE SI ZE M i l l e r and C o l l i n s (1954) 94.6 149 K i e l (1955) 97.0 380 R i e n e c k e r and A n d e r s o n ( i 9 6 0 ) 93.0 94 G o r e n z e l e t a l . (1982) 78.9 330 31 c o o r d i n a t e d , s l o w e r swimmers ( p e r s . o b s . ) . Thus, t h e y may be more v u l n e r a b l e t o s t a r v a t i o n , c o l d , and p r e d a t o r s t h a n a r e d u c k l i n g s . H i g h m o r t a l i t y of newly h a t c h e d C o o t young was f o u n d by A l l e y a nd Boyd (1947) and Ryder ( 1 9 6 1 ) . C l e a r l y , i t i s n e c e s s a r y t o c o n s i d e r s u r v i v a l o f young ( s e e C h a p t e r 2) i n o r d e r t o d e t e r m i n e r e p r o d u c t i v e s u c c e s s . N e s t P r e d a t i o n C o m p a r i s o n of n e s t l o s s due t o p r e d a t i o n of A m e r i c a n C o o t s and Ruddy Ducks s u g g e s t s t h a t l a t e b r e e d e r s e x p e r i e n c e l o w e r p r e d a t i o n . T h i s h y p o t h e s i s i s a l s o s u p p o r t e d by t h e dummy n e s t e x p e r i m e n t , s i n c e a l m o s t a l l n e s t s e s t a b l i s h e d i n t h e s p r i n g were d e s t r o y e d by p r e d a t o r s , whereas a l m o s t none o f t h e n e s t s e s t a b l i s h e d i n t h e summer were d e s t r o y e d . A s i m i l a r r e s u l t was a l s o f o u n d by K l a m b a c h ( 1 9 3 7 ) , who compared w a t e r f o w l n e s t l o s s t o crow p r e d a t i o n i n s p r i n g v e r s u s summer. S e a s o n a l d i f f e r e n c e s i n i n t e n s i t y of n e s t p r e d a t i o n may o n l y e x i s t f o r n e s t s i n emergent v e g e t a t i o n . N a g e l (1969) compared p r e d a t i o n of g r o u n d and c a v i t y n e s t s e a r l y and l a t e i n th e s e a s o n and f o u n d no s i g n i f i c a n t d i f f e r e n c e . A l s o , n o t a l l s p e c i e s t h a t b r e e d e a r l y i n s o u t h w e s t e r n B r i t i s h C o l u m b i a e x p e r i e n c e h i g h e r n e s t p r e d a t i o n . G i l l e s G a u t h i e r ( p e r s . comm.) s t u d i e d B u f f l e h e a d i n t h e C a r i b o o a r e a of B. C. and f o u n d o n l y 6.8% of n e s t s were d e s t r o y e d by p r e d a t o r s . N e s t p r e d a t i o n may be low b e c a u s e B u f f l e h e a d , u n l i k e Ruddy Ducks and C o o t s , n e s t i n t r e e c a v i t i e s . C a v i t y n e s t i n g b i r d s t e n d t o e x p e r i e n c e low n e s t 32 p r e d a t i o n e x c e p t where r a c c o o n s and o t h e r mammalian p r e d a t o r s a r e common ( F r e t w e l l , 1972). Barrow's G o l d e n e y e , w h i c h a l s o n e s t i n c a v i t i e s , e x p e r i e n c e d h i g h n e s t p r e d a t i o n (31.6%) i n B e c h e r ' s P r a i r i e , b e c a u s e b e a r s p r e y e d upon eggs i n n e s t boxes ( J . P . S a v a r d p e r s . comm.). Ne s t F l o o d i n g N e s t l o s s t o f l o o d i n g a p p e a r e d t o be g r e a t e r f o r Ruddy Ducks t h a n f o r C o o t s i n t h e C h i l c o t i n p a r k l a n d s ; however, few Ruddy n e s t s were f l o o d e d . A s u r v e y of t h e l i t e r a t u r e s u g g e s t s t h a t f l o o d i n g i s a s i g n i f i c a n t c a u s e of Ruddy Duck n e s t l o s s i n some a r e a s ; however, f l o o d i n g does not seem t o be a major c a u s e of A m e r i c a n C o o t n e s t l o s s . M i l l e r _ . and C o l l i n s (1954) and R i e n e c k e r and A n d e r s o n (1960) s t u d y i n g w a t e r f o w l a t T u l e Lake, C a l i f o r n i a r e p o r t e d t h a t more t h a n 18% o f t h e Ruddy Duck n e s t s t h a t t h e y s t u d i e d were f l o o d e d , whereas Low ( 1 9 4 1 ) , M c K n i g h t ( 1 9 7 4 ) , M i s t e r e k (1974) and J o y n e r (1977) f o u n d fewer t h a n 9% of Ruddy n e s t s were f l o o d e d . M i l l e r and C o l l i n s (1954) and R i e n e c k e r and A n d e r s o n (1960) a l s o s t u d i e d Coot n e s t l o s s and fo u n d t h a t f l o o d i n g t e n d e d t o o c c u r a f t e r C o o t s had n e s t e d . They r e p o r t e d fewer t h a n 7% of Coot n e s t s were f l o o d e d and K i e l (1955) f o u n d no Coot n e s t s were l o s t due t o f l o o d i n g . Thus, i t a p p e a r s t h a t f l o o d i n g i n marshes may be more common l a t e r i n t h e s e a s o n . 33 N e s t D e s e r t i o n C o m p a r i s o n of t h e c a u s e s o f n e s t l o s s s u g g e s t s t h a t Ruddy Ducks had l o w e r n e s t s u c c e s s r e l a t i v e t o C o o t s b e c a u s e Ruddy Ducks d e s e r t e d n e s t s , r a t h e r t h a n b e c a u s e t h e y l o s t n e s t s t o p r e d a t o r s or f l o o d i n g . J . P . S a v a r d and G. G a u t h i e r ( p e r s . comm.) a l s o f o u n d a h i g h p r o p o r t i o n of n e s t s d e s e r t e d by Ba r r o w ' s G o l d e n e y e (25.7%) and B u f f l e h e a d ( 2 9 . 5 % ) . ( T h e r e was no s i g n i f i c a n t d i f f e r e n c e between t h e f r e q u e n c y of d e s e r t e d and s u c c e s s f u l Ruddy Duck and B a r r o w ' s G o l d e n e y e o r B u f f l e h e a d n e s t s when t h e y were compared by c h i - s q u a r e d t e s t s . ) More t h a n 15% of n e s t s were d e s e r t e d i n o t h e r p o p u l a t i o n s of Ruddy Ducks ( J o y n e r , 1977; M i s t e r e k , 1974), and B u f f l e h e a d ( E r s k i n e , 1972). Ruddy Ducks, Barrow's G o l d e n e y e and B u f f l e h e a d a l l e x h i b i t f a c u l t a t i v e n e s t p a r a s i t i s m whereas C o o t s a r e r a r e l y p a r a s i t i c ( W e l l e r , 1 9 5 9 ; F r e d r i c k s o n , 1 9 6 9 ) . Thus, h i g h r a t e s of n e s t p a r a s i t i s m may e x p l a i n n e s t d e s e r t i o n and t h e d i f f e r e n c e between Coo t and Ruddy Duck i n t h e p r o p o r t i o n of p a i r s t h a t s u c c e s s f u l l y h a t c h young. J o y n e r (1977) s t u d i e d n e s t p a r a s i t i s m i n Ruddy Ducks e x t e n s i v e l y , but c o n c l u d e d t h a t n e s t d e s e r t i o n was a r e s p o n s e t o " r a p i d f l u c t u a t i o n s i n water d e p t h " and " r a p i d d e t e r i o r a t i o n and l o s s of s u i t a b l e n e s t i n g c o v e r " r a t h e r t h a n n e s t p a r a s i t i s m . T h i s i n t e r p r e t a t i o n seems odd s i n c e n e s t s were d e s e r t e d p r i o r t o f l o o d i n g , and J o y n e r s u g g e s t s t h a t Ruddy Ducks p r o b a b l y r e s p o n d e d t o t h e f l u c t u a t i n g w a ter l e v e l s by i n c r e a s i n g i n t r a s p e c i f i c n e s t p a r a s i t i s m . F u r t h e r m o r e , f l o o d i n g a p p a r e n t l y does not e x p l a i n n e s t d e s e r t i o n by Ruddy Ducks i n t h e B e c h e r ' s P r a i r i e s t u d y a r e a s i n c e n e s t d e s e r t i o n d i d not o c c u r when 34 w i n d s t o r m s o c c u r r e d . S i m i l a r l y , f l o o d i n g c a n n o t e x p l a i n n e s t d e s e r t i o n i n Barrow's G o l d e n e y e and B u f f l e h e a d s i n c e t h e y n e s t i n t r e e c a v i t i e s . Thus, n e s t p a r a s i t i s m seems a more b e t t e r e x p l a n a t i o n of n e s t d e s e r t i o n . C o v e r , P r e d a t o r B e h a v i o r and Water L e v e l F l u c t u a t i o n s A l t h o u g h b o t h Ruddy Ducks and C o o t s n e s t i n emergent v e g e t a t i o n , t h e same c o n d i t i o n s d i d not e x i s t d u r i n g t h e p e r i o d t h a t Ruddy Ducks n e s t e d as e x i s t e d d u r i n g t h e p e r i o d t h a t C o o t s n e s t e d . The n e s t s i t e s c h o s e n by t h e two s p e c i e s and t h e c o v e r a v a i l a b l e when e a c h s p e c i e s n e s t e d were s i g n i f i c a n t l y d i f f e r e n t . R avens were f o u n d l e s s f r e q u e n t l y n e a r ponds l a t e i n t h e . s e a s o n (when Ruddy Ducks n e s t e d ) as compared t o e a r l i e r (when C o o t s n e s t e d ) , and Ravens were n o t seen t o d e s t r o y n e s t s l a t e i n t h e s e a s o n as t h e y d i d e a r l i e r . A l s o , t h e t o t a l n e s t i n g d e n s i t y , d u r i n g t h e s p r i n g when C o o t s n e s t e d , was c o n s i d e r a b l y h i g h e r t h a n n e s t i n g d e n s i t y i n t h e summer when Ruddy Ducks n e s t e d . From t h e s e r e s u l t s , I c o u l d n ot d i s t i n g u i s h between s e v e r a l p o s s i b l e e x p l a n a t i o n s of why Ruddy Duck n e s t s s u f f e r l e s s p r e d a t i o n t h a n C o o t s . N e s t i n g c o v e r a v a i l a b l e i n t h e summer may have made n e s t s d i f f i c u l t t o f i n d and c a u s e d p r e d a t o r s t o s t o p a c t i v e l y s e a r c h i n g f o r them. Reduced n e s t i n g d e n s i t y may have made n e s t p r e d a t i o n l e s s p r o d u c t i v e . A l s o , o t h e r s o u r c e s o f f o o d p r e f e r r e d by Ravens ( e g . i n s e c t s s u c h as g r a s s h o p p e r s ) may be a v a i l a b l e when Ruddy Ducks n e s t , b u t n o t when C o o t s n e s t . P o s s i b l y n e s t i n g c o v e r , n e s t i n g d e n s i t y and a l t e r n a t e s o u r c e s o f 35 f o o d f o r Ravens a l l i n t e r a c t t o p r o d u c e r e d u c e d p r e d a t i o n of Ruddy Duck n e s t s . C o n c l u s i o n s 1. A l t h o u g h 30% o f A m e r i c a n C o o t s were u n s u c c e s s f u l i n t h e f i r s t n e s t i n g a t t e m p t , most n e s t e d a s e c o n d t i m e s u c c e s s f u l l y . In c o n t r a s t , The 40% of Ruddy f e m a l e s t h a t were u n s u c c e s s f u l i n n e s t i n g d i d n o t r e p l a c e n e s t s . T h e s e r e s u l t s i n d i c a t e t h a t t h e r e may be a c o s t t o n e s t i n g l a t e b e c a u s e Ruddy Ducks have i n s u f f i c i e n t t i m e t o r e n e s t . 2. I p r e d i c t e d t h a t l o w e r n e s t p r e d a t i o n i n summer m i g h t be an a d v a n t a g e o f l a t e b r e e d i n g . T h i s h y p o t h e s i s was s u p p o r t e d by s e v e r a l r e s u l t s . F i r s t , s i g n i f i c a n t l y more A m e r i c a n C o o t n e s t s and dummy n e s t s e s t a b l i s h e d i n s p r i n g were d e s t r o y e d by p r e d a t o r s t h a n Ruddy Duck n e s t s and dummy n e s t s e s t a b l i s h e d i n summer. S i n c e n e s t d e n s i t y i n t h e emergent v e g e t a t i o n was g r e a t e r e a r l i e r i n t h e s e a s o n , more p r e d a t o r s may have been a t t r a c t e d t o n e s t s t h e n . S e c o n d , maximum h e i g h t o f v e g e t a t i o n and a v e r a g e h e i g h t and d e n s i t y o f g r e e n v e g e t a t i o n were s i g n i f i c a n t l y g r e a t e r l a t e r i n t h e s e a s o n when Ruddy Ducks n e s t . V a r i o u s measurements d e s i g n e d t o a s s e s s v i s i b i l i t y o f n e s t s t o p r e d a t o r s s u g g e s t e d t h a t n e s t s i t e s s e l e c t e d by C o o t s were more v i s i b l e t o p r e d a t o r s t h a n n e s t s i t e s c h o s e n by Ruddy D u c k s . T h i r d , Ravens were o b s e r v e d f l y i n g low and s l o w l y o v e r marsh v e g e t a t i o n and p r e y i n g upon eggs i n s p r i n g b u t n o t i n summer. 36 3. I p r e d i c t e d t h a t l o w e r n e s t l o s s t o f l o o d i n g i n summer m i g h t be an a d v a n t a g e t o l a t e b r e e d i n g . The data, showed t h a t i n summer when Ruddy Ducks n e s t e d , f l o o d i n g o c c u r r e d a s a r e s u l t of wind s t o r m s ; however, i n s p r i n g when C o o t s n e s t e d , heavy r a i n f a l l and s u b s e q u e n t f l o o d i n g d i d n o t o c c u r . A l t h o u g h t h e r e s u l t s d i d n o t c o n f i r m t h e p r e d i c t i o n , o n l y a l o n g term s t u d y c o u l d a c c u r a t e l y a s s e s s whether n e s t l o s s t o f l o o d i n g was more common i n t h e s p r i n g t h a n i n t h e summer. 4. D u r i n g i n c u b a t i o n , Ruddy f e m a l e s r e l y l e s s on s t o r e d e n e r g y t h a n do e a r l y b r e e d e r s (Tome, 1981). S i n c e a m bient t e m p e r a t u r e i s a l s o h i g h e r when Ruddy Ducks n e s t , I p r e d i c t e d t h a t t h e y m i g h t l o s e fewer n e s t s t o d e s e r t i o n t h a n would A m e r i c a n C o o t s . The r e s u l t s d i d not s u p p o r t t h i s h y p o t h e s i s . F i f t e e n p e r c e n t o f Ruddy Duck n e s t s were d e s e r t e d b ut no Coot n e s t s were d e s e r t e d . D e s e r t i o n of Ruddy Duck n e s t s may have been c a u s e d by i n t r a s p e c i f i c n e s t p a r a s i t i s m , a r a r e phenomenon i n C o o t s . 3 7 CHAPTER THREE F e e d i n g B e h a v i o r and S u r v i v a l of D u c k l i n g s I n t r o d u c t i o n F o r n o r t h t e m p e r a t e b i r d s s u c h a s B a r r o w ' s G o l d e n e y e , B u f f l e h e a d and A m e r i c a n C o o t , b r e e d i n g o c c u r s soon a f t e r p a i r s a r r i v e a t t h e b r e e d i n g g r o u n d s ( B e l l r o s e , 1 9 8 0 ) . By b r e e d i n g e a r l y , t h e s e s p e c i e s a l l o w t i m e f o r t h e young t o grow and f l e d g e b e f o r e f a l l when b i r d s m i g r a t e s o u t h . In c o n t r a s t , Ruddy Ducks d e l a y b r e e d i n g a month or more a f t e r a r r i v a l ( G r a y , 1980; Tome, 1981). In t h e C h i l c o t i n p a r k l a n d ( s o u t h w e s t e r n B r i t i s h C o l u m b i a ) , Ruddy Ducks a r r i v e a t t h e b r e e d i n g g r o u n d i n l a t e A p r i l , w i t h o t h e r w a t e r f o w l s p e c i e s , but t h e y r a r e l y b r e e d u n t i l a t l e a s t s i x weeks l a t e r . Thus, Ruddy d u c k l i n g s h a t c h i n mid t o l a t e summer more t h a n a month l a t e r t h a n most o t h e r w a t e r f o w l s p e c i e s and o n l y 7 t o 9 weeks b e f o r e ponds f r e e z e i n t h e f a l l . T h i s c h a p t e r f o c u s e s on r e s e a r c h d e s i g n e d t o answer two q u e s t i o n s : 1) I s t h e s u r v i v a l r a t e o f Ruddy d u c k l i n g s s i m i l a r t o t h a t o f d u c k l i n g s of e a r l y b r e e d i n g s p e c i e s ? 2) How do Ruddy d u c k l i n g s grow t o r e a c h t h e f l e d g i n g s t a g e i n t h e s h o r t t i m e a v a i l a b l e ? B e c a u s e b r e e d i n g l a t e a f f o r d s l e s s t i m e f o r d u c k l i n g s t o f l e d g e , low r e p r o d u c t i v e s u c c e s s m i g h t be p r e d i c t e d i n t h e Ruddy Duck. When ponds f r e e z e , d u c k l i n g s t h a t h a t c h e d f r o m t h e l a s t Ruddy b r o o d s may not have f l e d g e d or a t t a i n e d s u f f i c i e n t r e s e r v e s t o e n s u r e s u c c e s s f u l m i g r a t i o n . F u r t h e r m o r e , Ruddy f e m a l e s t e n d t o abandon b r o o d s e a r l i e r t h a n f e m a l e s o f o t h e r 38 s p e c i e s . Even s o , h i g h s u r v i v a l o f Ruddy d u c k l i n g s , p a r t i c u l a r l y when b r o o d s a r e young, has been r e p o r t e d ( B e l l r o s e , 1980). S i n c e young b r o o d s a r e a l m o s t a l w a y s a c c o m p a n i e d by t h e f e m a l e , m a t e r n a l p r o t e c t i o n may i n f l u e n c e s u r v i v a l of d u c k l i n g s . Ruddy f e m a l e s may be more p r o t e c t i v e of b r o o d s t h a n f e m a l e s of e a r l y b r e e d i n g s p e c i e s . M o r e o v e r , Ruddy f e m a l e s may be more a l e r t t o t h e p r e s e n c e of p r e d a t o r s and may l e a d b r o o d s t o dense c o v e r b e f o r e d a n g e r i s imminent. J . P. S a v a r d ( p e r s . comm.) has f o u n d Ruddy b r o o d s more d i f f i c u l t t o c e n s u s t h a n o t h e r w a t e r f o w l s p e c i e s b e c a u s e t h e y s p e n t much o f t h e i r t i m e i n dense c o v e r o u t of v i e w . S i n c e Ruddy d u c k l i n g s have 7 t o 9 weeks i n w h i c h t o f l e d g e , whereas o t h e r s p e c i e s s u c h as B a r r o w ' s G o l d e n e y e and B u f f l e h e a d have 12 t o 14 weeks, Ruddy Duck young a p p a r e n t l y grow t o f l e d g i n g f a s t e r t h a n t h e young o f e a r l y b r e e d e r s . R a p i d growth c o u l d be a c c o m p l i s h e d by s e v e r a l mechanisms. F i r s t , Ruddy d u c k l i n g s may f e e d and r e s t more and p r e e n and swim l e s s t h a n d u c k l i n g s of e a r l y b r e e d i n g s p e c i e s . T h e s e b e h a v i o r s would e n a b l e Ruddy d u c k l i n g s t o m a x i m i z e t h e amount of e n e r g y d i r e c t e d t o w a r d g r o w t h and so f l e d g e more q u i c k l y t h a n d u c k l i n g s o f e a r l y b r e e d i n g s p e c i e s . S e c o n d , Ruddy d u c k l i n g s may g a t h e r more f o o d p e r f e e d i n g b out t h a n d u c k l i n g s of e a r l y b r e e d e r s . W h i l e I d i d not d e t e r m i n e d i r e c t l y how much f o o d was c o l l e c t e d i n e a c h d i v e , f e e d i n g i n t e n s i t y ( t i m e t a k e n t o make a g i v e n number o f d i v e s ) o r d i v e d u r a t i o n ( t i m e s p e n t u n d e r w a t e r ) were p o s s i b l e i n d i r e c t measurement o f f o o d g a t h e r e d . The r e l a t i o n s h i p between d i v e 39 d u r a t i o n o r f e e d i n g i n t e n s i t y and f o o d g a t h e r e d may seem t e n u o u s s i n c e d u c k l i n g s t h a t d i v e l o n g e r o r more f r e q u e n t l y may be l e s s e f f i c i e n t a t swimming u n d e r w a t e r , or f i n d i n g f o o d . However, Ruddy Ducks have t h e l a r g e s t p a d d l e s i z e ( a r e a of webbed f e e t ) r e l a t i v e t o body w e i g h t o f a l l w a t e r f o w l and t h e r e f o r e , t h e y a r e l i k e l y t o be more r a t h e r t h a n l e s s e f f i c i e n t swimmers (Raikow, 1973). A l s o , f o o d was v e r y abundant i n t h e ponds where d u c k l i n g s a r e r e a r e d . Thus, i t was u n l i k e l y t h a t f o o d was d i f f i c u l t t o f i n d . In t h i s c h a p t e r , I compare Ruddy Ducks t o e a r l y b r e e d i n g s p e c i e s ( B a r r o w ' s G o l d e n e y e , B u f f l e h e a d and A m e r i c a n C o o t ) i n t h r e e c a t e g o r i e s : s u r v i v a l of young, b e h a v i o r of f e m a l e s and b e h a v i o r o f d u c k l i n g s . I measure t i m e b u d g e t s of f e m a l e s and t i m e b u d g e t s , d i v e d u r a t i o n and f e e d i n g i n t e n s i t y of d u c k l i n g s . Methods D e t e r m i n i n g Age o f D u c k l i n g s To e s t i m a t e s u r v i v a l r a t e s and c o n t r o l f o r c h a n g e s i n b e h a v i o r as d u c k l i n g s m ature, i t was n e c e s s a r y t o c l a s s i f y b r o o d s a c c o r d i n g t o age. O f t e n age c o u l d be d e t e r m i n e d d i r e c t l y ; however, t h i s i n f o r m a t i o n was n o t a v a i l a b l e f o r a l l B u f f l e h e a d and B a r r o w ' s G o l d e n e y e b r o o d s . Thus, a g e s of t h e s e b r o o d s were d e t e r m i n e d a c c o r d i n g t o t h e i r plumage d e v e l o p m e n t ( L a r s o n and T a b e r , 1980). A l l d u c k l i n g s c l a s s i f i e d w i t h i n a g i v e n age c l a s s were a t a p p r o x i m a t e l y t h e same s t a g e of 40 d e v e l o p m e n t but d u c k l i n g s of d i f f e r e n t s p e c i e s a r e known t o mature a t d i f f e r e n t r a t e s . T h u s , n o t a l l d u c k l i n g s c l a s s i f i e d w i t h i n an age c l a s s were the same c h r o n o l o g i c a l age ( s e e T a b l e 12). D u c k l i n g S u r v i v a l S u r v i v a l of d u c k l i n g s was a s s e s s e d by 2 d i f f e r e n t methods. In t h e f i r s t t e c h n i q u e , s u r v i v a l o f d u c k l i n g s between h a t c h i n g and age c l a s s 2B was a s s e s s e d . T h i s e s t i m a t e was b a s e d on d a t a t h a t J . P. S a v a r d and I c o l l e c t e d i n 1984. A l l i n f o r m a t i o n was b a s e d on d u c k l i n g b r o o d s f o r w h i c h n e s t l o c a t i o n and c l u t c h s i z e was known ( s e e c h a p t e r 2 ) . As soon as a b r o o d a p p e a r e d on a pond, t h e n e s t was c h e c k e d t o d e t e r m i n e i f a l l eggs, had h a t c h e d . The number of young r e m a i n i n g i n t h e b r o o d was r e c o r d e d when t h e d u c k l i n g s r e a c h e d t h e 2B age c l a s s . A c h i -s q u a r e d c o n t i n g e n c y t e s t was u s e d t o compare t h e number of Ruddy d u c k l i n g s t h a t s u r v i v e d and d i d n o t s u r v i v e t o t h e 2B age c l a s s w i t h t h a t of B a r r o w's G o l d e n e y e and B u f f l e h e a d d u c k l i n g s t h a t s u r v i v e d and d i d n o t s u r v i v e . The s e c o n d t e c h n i q u e e s t i m a t e d t h e p e r c e n t a g e o f eggs l a i d t h a t u l t i m a t e l y became 2B young. T h i s e s t i m a t e was made b e c a u s e of t h e d i f f i c u l t y o f a s s e s s i n g h a t c h i n g s u c c e s s o f A m e r i c a n C o o t s . ( U n h a t c h e d eggs and egg s h e l l a r e q u i c k l y removed from the n e s t by t h e p a r e n t s . ) 41 TABLE j_2 C o m p a r i s o n o f C h r o n o l o g i c a l Age ( i n d a y s ) of Ruddy, B a r r o w ' s G o l d e n e y e , and B u f f l e h e a d d u c k l i n g s f o r age c l a s s 1A t h r o u g h 2C MEAN AGE (IN DAYS) FOR DUCKLINGS IN A GIVEN SPECIES AGE CLASS ;* 1A 1B 1C 2A 2B 2C Ruddy Duck 3 8 1 4 21 28 35 B a r r o w ' s G o l d e n e y e 5 13 22 31 40 50 B u f f l e h e a d 3 8 1 4 21 28 35 *- a s t a n d a r d c l a s s i f i c a t i o n scheme f o r a g i n g d u c k l i n g s when h a t c h i n g d a t e s a r e unknown. The method i n v o l v e s i d e n t i f i c a t i o n of plumage c h a r a c t e r i s t i c s w h i c h change as d u c k l i n g s d e v e l o p ( L a r s o n and T a b e r , 1980). +- mean age e s t i m a t e s f r o m u n p u b l i s h e d Ducks U n l i m i t e d R e p o r t (1983) 42 Female B e h a v i o r B e h a v i o r o f f e m a l e Ruddy Duck, B a r r o w ' s G o l d e n e y e , and B u f f l e h e a d was compared t o a s s e s s how t h e s e s p e c i e s d i f f e r e d i n b r o o d d e f e n s e . F e m a l e s w i t h c l a s s one young were c o n s i d e r e d s e p a r a t e l y f r o m t h o s e w i t h c l a s s two young s i n c e y o u n g e r d u c k l i n g s ( c l a s s one) may be more v u l n e r a b l e t o p r e d a t o r s ( B a l l e t a l . , 1975; T a l e n t e t a l . , 1983). To a s s e s s t h e f r e q u e n c y of a l e r t b e h a v i o r r e l a t i v e t o a l l o t h e r b e h a v i o r s , f e m a l e s were o b s e r v e d a t a d i s t a n c e t h r o u g h a B u s h n e l l s p o t t i n g s c o p e . B e h a v i o r was r e c o r d e d a t t e n m i n u t e i n t e r v a l s and e a c h f e m a l e was o b s e r v e d f o r a t l e a s t one h o u r . The f r e q u e n c i e s of a l e r t b e h a v i o r o f Ruddy f e m a l e s were compared t o t h o s e of t h e o t h e r two s p e c i e s , by c h i - s q u a r e d c o n t i n g e n c y t e s t s . I a l s o , u s e d t h i s t e s t t o compare t h e f r e q u e n c i e s t h a t f e m a l e Ruddy Ducks and b r o o d s were o u t of s i g h t w i t h t h e f r e q u e n c i e s t h a t B a r r o w's G o l d e n e y e a n d B u f f l e h e a d f e m a l e s and b r o o d s were o u t of s i g h t . A f e m a l e was c o n s i d e r e d t o be ' a l e r t ' when i t was e i t h e r swimming o r r e s t i n g , w i t h i t s head up.and e y e s open, ne a r i t s b r o o d . Time b u d g e t o f d u c k l i n g s Time b u d g e t of d u c k l i n g s was a s s e s s e d by o b s e r v a t i o n o f b i r d s t h r o u g h a B u s h n e l l s p o t t i n g t e l e s c o p e . B e h a v i o r of d u c k l i n g b r o o d s was r e c o r d e d e v e r y t e n m i n u t e s . C a t e g o r i e s o f b e h a v i o r t h a t were r e c o r d e d i n c l u d e d : r e s t i n g , p r e e n i n g , swimming, an d f e e d i n g . B r o o d s o f age c l a s s 1A, 1B, 1C, 2A, 2B, 43 and 2C were o b s e r v e d and b r o o d s i n e a c h age c l a s s were compared o n l y w i t h o t h e r s o f t h e same age c l a s s . S i n c e most i n d i v i d u a l s i n a b r o o d t e n d e d t o a c t as a u n i t ( i e . when one d u c k l i n g f e d , a l l d u c k l i n g s f e d ) , b e h a v i o r of e a c h d u c k l i n g i n t h e b r o o d was n o t c o n s i d e r e d t o be i n d e p e n d e n t . Thus, e a c h o b s e r v a t i o n c o n s i s t e d o f s c o r e s f o r t h e f o u r b e h a v i o r c a t e g o r i e s whose sum was e q u a l t o one ( i e . L a r g e b r o o d s were n o t more h e a v i l y w e i g h t e d i n a n a l y s i s t h a n s m a l l o n es.) T h r e e o r more d i f f e r e n t b r o o d s were o b s e r v e d and e a c h b r o o d was o b s e r v e d f o r a t l e a s t 3 h o u r s . W i t h i n e a c h age c l a s s , t h e r e s u l t s were ad d e d t o g e t h e r and c o n v e r t e d i n t o a p e r c e n t a g e of b e h a v i o r o b s e r v a t i o n s of f e e d i n g and r e s t i n g b e h a v i o r . (The number of o b s e r v a t i o n s t h a t showed d u c k l i n g s out of s i g h t of t h e o b s e r v e r were e x c l u d e d f r o m t h i s c a l c u l a t i o n . ) D i v i n g d u r a t i o n and f e e d i n g i n t e n s i t y o f d u e k l i n q s I e s t i m a t e d d i v i n g d u r a t i o n ( t i m e d u c k l i n g s p e n d s u n d e r w a t e r d u r i n g a s i n g l e d i v e ) and f e e d i n g i n t e n s i t y ( t h e t i m e t a k e n f o r a s i n g l e d u c k l i n g t o d i v e f i v e t i m e s i n s u c c e s s i o n ) o f Ruddy, B a r r o w ' s G o l d e n e y e and B u f f l e h e a d by o b s e r v i n g i n d i v i d u a l d u c k l i n g s t h a t were 2 m e t e r s o r more from o t h e r d u c k l i n g s . I marked t h e l o c a t i o n of f e e d i n g on a map o f t h e pond and l a t e r I d e t e r m i n e d t h e d e p t h a t t h a t l o c a t i o n from pond d e p t h p r o f i l e s t a k e n by Shaun Boyd ( C a n a d i a n W i l d l i f e S e r v i c e ) . O c c a s i o n a l l y , t h e r e was some doubt a s t o w h i c h d u c k l i n g was t h e one under o b s e r v a t i o n s i n c e d u c k l i n g s were unmarked. T h i s p r o b l e m may have c o n t r i b u t e d e r r o r t o measurements o f d i v i n g d u r a t i o n and 44 f e e d i n g i n t e n s i t y ; however, t h e t e n d e n c y f o r s y n c h r o n y between n e a r e s t n e i g h b o u r s i n t h e t i m e of d i v i n g and s u r f a c i n g p r o b a b l y k e p t t h i s e r r o r t o a minimum. I f a b r o o d c o n s i s t e d of more t h a n a s i n g l e d u c k l i n g , an a t t e m p t was made t o sample as many d i f f e r e n t d u c k l i n g s i n . t h e b r o o d a s p o s s i b l e . F o r e a c h b r o o d o f a g i v e n age c l a s s , d i v e d u r a t i o n was a s s e s s e d by u s i n g a s t o p w a t c h t o t i m e a t o t a l of twenty d i v e s . The a v e r a g e o f t h e s e was t h e n t a k e n t o r e p r e s e n t t h a t b r o o d f o r t h a t age c l a s s . F o r most age c l a s s e s , t h r e e b r o o d s of e a c h s p e c i e s were s t u d i e d . A median t e s t was made t o d e t e r m i n e i f d i f f e r e n c e s between d i v i n g d u r a t i o n s o f v a r i o u s s p e c i e s were s i g n i f i c a n t ( Z a r , 1984). M e d i a n d i v i n g d u r a t i o n s f o r e a c h age c l a s s were d e t e r m i n e d by p l o t t i n g mean d i v i n g d u r a t i o n s f o r d u c k l i n g s o f a l l t h r e e s p e c i e s . Then, t h e number of a v e r a g e d i v i n g d u r a t i o n s f a l l i n g a bove t h e median was a s s e s s e d f o r Ruddy d u c k l i n g s . T h e s e numbers f o r a l l age c l a s s e s were ad d e d t o g e t h e r and compared t o t h a t o f B u f f l e h e a d and B a r r ow's G o l d e n e y e d u c k l i n g s by c h i -s q u a r e d c o n t i n g e n c y t e s t s . To a s s e s s f e e d i n g i n t e n s i t y , I s t a r t e d t h e s t o p w a t c h when a d u c k l i n g dove and s t o p p e d t h e c l o c k when t h e same d u c k l i n g r e s u r f a c e d a f t e r c o m p l e t i n g t h e f i f t h d i v e . Whenever p o s s i b l e , I t o o k f i v e s u c h s a m p l e s , e a c h t a k e n on d i f f e r e n t d u c k l i n g s f o r e a c h b r o o d o f a p a r t i c u l a r age c l a s s . ( I n s u f f i c i e n t d a t a were a v a i l a b l e on f e e d i n g i n t e n s i t y o f 2C b r o o d s so t h e s e were o m i t t e d . ) I t o o k f e e d i n g i n t e n s i t y measurements on a t l e a s t two d i f f e r e n t b r o o d s of e a c h s p e c i e s - , and age c l a s s ( 1 A - 2 B ) . R e s u l t s f o r Ruddy d u c k l i n g s were compared t o t h o s e f o r B a r r o w ' s 45 G o l d e n e y e and B u f f l e h e a d d u c k l i n g s by a median t e s t . R e s u l t s D u c k l i n g S u r v i v a l C o m p a r i s o n of s u r v i v a l of young s u g g e s t s t h a t Ruddy d u c k l i n g s have h i g h e r s u r v i v a l t h a n do t h e young of t h e o t h e r t h r e e s p e c i e s ( s e e f i g . 3 ) . T h i r t y - e i g h t p e r c e n t of t h e Ruddy Duck eggs l a i d i n n e s t s became 2B d u c k l i n g s (31 n e s t s were e x a m i n e d ) . Fewer B a r r o w ' s G o l d e n e y e (26.9%, 149 n e s t s ) , B u f f l e h e a d (22.6%, 17 n e s t s ) and A m e r i c a n Coot (29.2%, 126 n e s t s ) eggs became 2B d u c k l i n g s . S u r v i v a l from h a t c h i n g t o 2B age c l a s s was a l s o h i g h e s t i n Ruddy d u c k l i n g s ( s e e f i g . • 4 ) . S e v e n t y - f o u r p e r c e n t o f Ruddy d u c k l i n g s w h i c h h a t c h e d became 2B young, whereas o n l y s i x t y - t h r e e p e r c e n t of B a r r o w's G o l d e n e y e and t h i r t y - t h r e e p e r c e n t o f B u f f l e h e a d h a t c h l i n g s became 2B young. C h i - s q u a r e d c o n t i n g e n c y t e s t s showed t h a t s u r v i v a l of Ruddy d u c k l i n g s f r o m h a t c h i n g t o t h e 2B age c l a s s was s i g n i f i c a n t l y g r e a t e r t h a n t h a t o f Barrow's G o l d e n e y e (p<.05) and B u f f l e h e a d ( p < . 0 0 l ) . Female B e h a v i o r The f r e q u e n c y o f a l e r t b e h a v i o r i n Ruddy, Barrow's G o l d e n e y e and B u f f l e h e a d f e m a l e s i s p r e s e n t e d i n T a b l e 13. The c h i - s q u a r e d c o n t i n g e n c y t e s t was u s e d t o compare t h e f r e q u e n c y 46 to CO < -J (J U l to < m CM CO CD UJ o rr u . < > > r r 3 CO o _ to o _ 10 o •fl-ea o 01 o _ o -» n = 1 8 9 n = 8 3 6 n = 1 3 7 8 n = 1 3 7 RUOOY COOT BARROWS BUFFLE FIGURE 3_ : Comparison of Ruddy, Barrow's Goldeneye, B u f f l e h e a d and American Coot s u r v i v a l from egg to 2B age c l a s s d u c k l i n g s ( T h i s measure was c a l c u l a t e d by d i v i d i n g the t o t a l eggs l a i d by the t o t a l number of young which s u r v i v e d to the 2B age c l a s s ) 4 7 CO CO < o CO n=96 n=588 o to o n=93 o OJ RU00Y BARROWS BUFFLE FIGURE 4 : Comparison of Ruddy, Barrow's Goldeneye and Bufflehead duckling survival from hatching to 2 B age cla s s . 48 TABLE 21 P r o p o r t i o n s o f O b s e r v a t i o n s Showing A l e r t B e h a v i o r i n Ruddy, Barrow's G o l d e n e y e and B u f f l e h e a d f e m a l e s w i t h Young PROPORTION OF OBSERVATIONS OF ALERT BEHAVIOR SPECIES FEMALES WITH CLASS ONE FEMALES WITH CLASS TWO YOUNG ( i e . 1a,1b,1c) YOUNG ( i e . 2a,2b,2c) Ruddy Duck 59. 1 51 .7 (n= 39 h r s ) (n = 12 h r s ) B arrow's G o l d e n e y e 67. 6 65 .2 (n= 19 h r s ) (n= 22 h r s ) B u f f l e h e a d 70. 3 61 .5 (n= 16 h r s ) (n = 29 h r s ) 49 of a l e r t b e h a v i o r r e c o r d e d f o r Ruddy f e m a l e s , w i t h t h a t f o r f e m a l e s o f t h e o t h e r two s p e c i e s . No s i g n i f i c a n t d i f f e r e n c e s were f o u n d . A l e r t b e h a v i o r was n o t more o f t e n o b s e r v e d i n Ruddy f e m a l e s w i t h c l a s s one o r two young t h a n i n B a r r o w ' s G o l d e n e y e and B u f f l e h e a d f e m a l e s w i t h c l a s s one o r two young. A l s o , when t h e i n c i d e n c e of a l e r t b e h a v i o r was compared w i t h i n a s p e c i e s ( i e . f e m a l e s w i t h c l a s s one young v e r s u s f e m a l e s w i t h c l a s s two y o u n g ) , no s i g n i f i c a n t d i f f e r e n c e s were f o u n d . The p r o p o r t i o n of o b s e r v a t i o n s t h a t f e m a l e s were out of s i g h t o f t h e o b s e r v e r i s p r e s e n t e d i n T a b l e 14. C h i - s q u a r e d c o n t i n g e n c y t e s t s shows t h e p r o p o r t i o n o f o b s e r v a t i o n s t h a t f e m a l e Ruddy Ducks, B a r r o w ' s G o l d e n e y e and B u f f l e h e a d were out of s i g h t o f t h e o b s e r v e r . These t e s t s showed t h a t Ruddy f e m a l e s w i t h c l a s s two young were more o f t e n o u t of s i g h t o f t h e o b s e r v e r t h a n B u f f l e h e a d w i t h c l a s s two young; however, t h e r e were no s i g n i f i c a n t d i f f e r e n c e s between Ruddy and Barrow's G o l d e n e y e f e m a l e s , and Ruddy f e m a l e s w i t h c l a s s one young and B u f f l e h e a d f e m a l e s w i t h c l a s s one young. Time Budget o f D u c k l i n g s T a b l e 15 p r e s e n t s t h e p r o p o r t i o n o f o b s e r v a t i o n s of r e s t i n g and f e e d i n g f o r Ruddy, B a r r o w ' s G o l d e n e y e , and B u f f l e h e a d d u c k l i n g s . Ruddy d u c k l i n g s were o b s e r v e d f e e d i n g and r e s t i n g more o f t e n t h a n 1A, 1B, 2B and 2C B u f f l e h e a d and 1A, 2A, 2B, and 2C B a r r o w ' s G o l d e n e y e young; however, t h e d i f f e r e n c e s between Ruddy d u c k l i n g s and d u c k l i n g s of t h e o t h e r two s p e c i e s may not 50 TABLE J_4 P r o p o r t i o n of O b s e r v a t i o n s Showing Ruddy, Barrow's G o l d e n e y e and B u f f l e h e a d F e m a l e s and Young Out o f S i g h t of t h e O b s e r v e r PROPORTION OF OBSERVATIONS WHERE BIRDS WERE OUT OF SIGHT FEMALES WITH CLASS ONE FEMALES WITH CLASS TWO YOUNG YOUNG Ruddy Duck (n= 35 39 .0 h r s ) (n = 16.7 12 h r s ) Barrow's G o l d e n e y e (n= 40 19 .4 h r s ) (n= 18.1 22 h r s ) B u f f l e h e a d (n= 33 16 .3 h r s ) (n = 7.5 29 h r s ) 51 TABLE 15 P r o p o r t i o n o f O b s e r v a t i o n s Showing R e s t i n g and F e e d i n g Ruddy, B a r r o w ' s G o l d e n e y e and B u f f l e h e a d D u c k l i n g s PROPORTION OF OBSERVATIONS OF FEEDING OR RESTING BEHAVIOR SPECIES TOTAL DUCKLING AGE CLASS OVERALL N 1A 1B 1C 2A 2B 2C AVERAGE ( h r s ) B a r r o w ' s G o l d e n e y e 39 22.2 73.6 71.5 48.0 61.1 58.4 55.8 Ruddy Duck 63 64.8 50.6 39.3 51.0 67.2 70.8 57.3 B u f f l e h e a d 47 24.6 37.9 55.5 54.0 56.5 61.0 48.1 52 r e f l e c t r e a l d i f f e r e n c e s i n t h e t i m e d u c k l i n g s of e a c h s p e c i e s s p e n t f e e d i n g and r e s t i n g . The b e h a v i o r of d u c k l i n g s when t h e y were o u t of s i g h t was unknown and may n o t be t h e same as what was o b s e r v e d when t h e y were v i s i b l e . T hus, a c t u a l f r e q u e n c y of f e e d i n g and r e s t i n g , by d u c k l i n g s o f a l l t h r e e s p e c i e s , c o u l d have been e q u a l . D i v i n g D u r a t i o n and F e e d i n g I n t e n s i t y o f D u c k l i n g s A b r o a d r a n g e of d i v i n g d u r a t i o n s was o b s e r v e d f o r d u c k l i n g s of e a c h age c l a s s ( s e e T a b l e 16). To compare Ruddy d u c k l i n g d i v e s t o t h o s e of t h e o t h e r two s p e c i e s , t h e number of d i v i n g d u r a t i o n s f a l l i n g above t h e median ( f o r e a c h s p e c i e s ) was compared. Ruddy d u c k l i n g s had s i g n i f i c a n t l y l o n g e r d i v i n g d u r a t i o n s t h a n B a r r o w ' s G o l d e n e y e (median t e s t , p < .0l) and B u f f l e h e a d (median t e s t , p<.005). T h e r e was no o b v i o u s d i f f e r e n c e i n pond d e p t h a t l o c a t i o n s where d i v i n g d u r a t i o n and f e e d i n g i n t e n s i t y measurements were t a k e n . T a b l e 17 shows t h e f e e d i n g i n t e n s i t i e s o f 1A t o 2C Ruddy, Barrow's G o l d e n e y e and B u f f l e h e a d d u c k l i n g s . A median t e s t showed t h a t f e e d i n g i n t e n s i t y o f Ruddy d u c k l i n g s was not 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 f e e d i n g i n t e n s i t y of d u c k l i n g s of t h e o t h e r two s p e c i e s . 53 TABLE j_6 The Range o f A v e r a g e D i v i n g D u r a t i o n s O b s e r v e d f o r V a r i o u s Age C l a s s e s of Ruddy, B a r r o w ' s G o l d e n e y e and B u f f l e h e a d D u c k l i n g s SPECIES (MINIMUM AND MAXIMUM VALUES FOR EACH AGE CLASS) 1 A 1B 1C 2A 2B 2C Ruddy MINIMUM 8.4 9.9 9.2 11.2 15.2 16.4 MAXIMUM 16.1 17.6 17.3 16.9 19.7 17.8 Barrows MINIMUM 3.6 5.6 10.6 8.6 15.2 14.3 MAXIMUM 4.4 13.0 15.0 11.2 19.5 16.8 B u f f l e MINIMUM 5.7 8.5 7.0 8.1 9.2 10.9 MAXIMUM 9.5 11.6 9.7 10.8 14.2 15.6 TABLE 17 The Range of A v e r a g e F e e d i n g I n t e n s i t i e s O b s e r v e d F o r V a r i o u s Age C l a s s e s of Ruddy, Barrow's G o l d e n e y e and B u f f l e h e a d D u c k l i n g s SPECIES (MINIMUM AND MAXIMUM VALUES FOR EACH AGE CLASS) 1A 1B 1C 2A 2B Ruddy MINIMUM 59.3 92.9 91 .6 119.1 130.8 MAXIMUM 71.8 142.0 109.7 138.5 1 39. 1 Barrows MINIMUM 76.5 69.2 31.1 102.5 121.5 MAXIMUM 78.0 94.3 132.6 1 26.3 185.5 B u f f i e MINIMUM 88.0 76.4 117.3 88.5 91 .8 MAXIMUM 100.6 94.4 118.7 1 06. 1 . 95.8 54 D i s c u s s i o n R e s u l t s of t h i s s t u d y s u g g e s t t h a t Ruddy d u c k l i n g s had h i g h e r s u r v i v a l r a t e s t o age c l a s s 2B t h a n d i d d u c k l i n g s of Barrow's G o l d e n e y e , B u f f l e h e a d , and A m e r i c a n C o o t . A l t h o u g h L i b b y (1972) f o u n d low s u r v i v a l o f Ruddy d u c k l i n g s (2B a v e r a g e b r o o d s i z e a p p r o x i m a t e l y 50% o f 1A b r o o d s i z e ) , h i g h s u r v i v a l r a t e s f o r Ruddy d u c k l i n g s have been f o u n d i n o t h e r s t u d i e s . J o y n e r (1976b) f o u n d t h a t d u c k l i n g b r o o d s of 2A age c l a s s were 75% t h e s i z e of 1A b r o o d s , w h i l e S i e g f r i e d (1977) f o u n d t h a t d u c k l i n g b r o o d s of 2B age c l a s s were 84% t h e s i z e of 1A b r o o d s . G r a y (1980) f o u n d h i g h s u r v i v a l r a t e s of c l a s s one d u c k l i n g s (no s i g n i f i c a n t d i f f e r e n c e between 1A and 2A a v e r a g e b r o o d s i z e ) , a l t h o u g h i n one y e a r of. h e r s t u d y , bad weather c a u s e d h i g h m o r t a l i t y i n o l d e r b r o o d s . H i g h s u r v i v a l r a t e s o f Ruddy d u c k l i n g s do n o t a p p e a r t o r e s u l t from g r e a t e r a l e r t n e s s of f e m a l e Ruddy D u c k s . A l t h o u g h th e t r e n d was not s t a t i s t i c a l l y s i g n i f i c a n t , Ruddy f e m a l e s were a l e r t l e s s o f t e n t h a n B a r r ow's G o l d e n e y e o r B u f f l e h e a d . S i m i l a r l y , t h e f r e q u e n c y t h a t Ruddy f e m a l e s l e d t h e i r b r o o d s i n t o c o v e r does n o t e x p l a i n why Ruddy d u c k l i n g s u r v i v a l was h i g h e r . A l t h o u g h Ruddy b r o o d s were out o f s i g h t o f t h e o b s e r v e r more o f t e n t h a n B u f f l e h e a d , t h i s r e s u l t was o n l y o b s e r v e d f o r c l a s s two b r o o d s . T h e r e was no s i g n i f i c a n t d i f f e r e n c e between th e f r e q u e n c y t h a t Ruddy b r o o d s were o u t o f s i g h t of t h e o b s e r v e r and t h e f r e q u e n c y t h a t c l a s s one B a r r o w ' s G o l d e n e y e b r o o d s and c l a s s one and two B u f f l e h e a d b r o o d s were o u t of s i g h t of t h e o b s e r v e r . 55 S e v e r a l e x p l a n a t i o n s o f h i g h s u r v i v a l i n R u d d y d u c k l i n g s a r e p o s s i b l e . F i r s t , R u d d y d u c k l i n g s m a y b e b e t t e r a b l e t o e s c a p e p r e d a t i o n t h a n t h e y o u n g o f m o s t w a t e r f o w l . S e c o n d , d u c k l i n g m o r t a l i t y t o p r e d a t i o n m a y b e h i g h e r e a r l i e r i n t h e s e a s o n , j u s t l i k e n e s t p r e d a t i o n . T h i r d , t h e w a r m e r w e a t h e r t y p i c a l w h e n R u d d y d u c k l i n g s h a t c h m a y r e d u c e d u c k l i n g m o r t a l i t y t o e x p o s u r e . F u r t h e r r e s e a r c h w o u l d b e r e q u i r e d t o e x p l a i n d i f f e r e n c e s i n s u r v i v a l o f R u d d y , B a r r o w ' s G o l d e n e y e a n d B u f f l e h e a d d u c k l i n g s . T h e r e s u l t s o f t h i s t h e s i s d o n o t d e m o n s t r a t e t h a t h i g h s u r v i v a l o f R u d d y d u c k l i n g s i s a d i r e c t c o n s e q u e n c e o f b r e e d i n g l a t e r i n t h e s e a s o n . H o w e v e r , s u r v i v a l i s h i g h w h i c h s u g g e s t s t h a t b r e e d i n g l a t e c a n b e a s s u c c e s s f u l a s b r e e d i n g e a r l y . U n f o r t u n a t e l y , w i t h o u t a r a d i o - t a g g e d p o p u l a t i o n , i t i s d i f f i c u l t t o d e t e r m i n e t h e m a g n i t u d e o f d u c k l i n g m o r t a l i t y w h e n p o n d s f r e e z e i n t h e f a l l . ( F e m a l e s h a v e a b a n d o n e d b r o o d s b y t h i s t i m e , s o b r o o d c o h e s i o n t e n d s t o b r e a k d o w n . W h e n d u c k l i n g s d i s a p p e a r , t h e y m a y h a v e d i e d o r f l e d g e d . ) E s t i m a t e s o f d u c k l i n g s u r v i v a l t o 2 B a g e c l a s s , s u g g e s t t h a t r e p r o d u c t i v e s u c c e s s o f R u d d y D u c k s m a y b e s u f f i c i e n t l y h i g h t o a b s o r b s o m e m o r t a l i t y o f d u c k l i n g s w h e n p o n d s f r e e z e . B a r r o w ' s G o l d e n e y e h a v e s l i g h t l y h i g h e r r e p r o d u c t i v e s u c c e s s t h a n R u d d y D u c k s , b u t t h e r e p r o d u c t i v e s u c c e s s o f B u f f l e h e a d a n d A m e r i c a n C o o t s i s l o w e r ( s e e T a b l e 18). T h e G o l d e n e y e p o p u l a t i o n i n t h e C a r i b o u s t u d y a r e a , m a d e e x t e n s i v e u s e o f n e s t b o x e s w h i c h m a y h a v e a l l o w e d s l i g h t l y l a r g e r c l u t c h e s t o b e s u c c e s s f u l l y i n c u b a t e d t h a n i s p o s s i b l e i n n a t u r a l c a v i t i e s . TABLE J_8 R e p r o d u c t i v e 2B Age C l a s s S u c c e s s i n Ducks and C o o t s -Young P r o d u c e d p e r P a i r p e r The A v e r a g e Number of Year CLUTCH S I Z E AVERAGE 2B SPECIES FOUND IN YOUNG SURVIVING THIS STUDY PER CLUTCH Ruddy Duck 6.10 2.29 A m e r i c a n C o o t 6.63 1.93 Ba r r o w ' s G o l d e n e y e 9.77 2.62 B u f f l e h e a d 8.05 1.82 57 ( B e l l r o s e (1980) r e p o r t s a l o w e r a v e r a g e c l u t c h s i z e f o r B a r r o w ' s G o l d e n e y e t h a n t h a t r e p o r t e d i n t h i s s t u d y ) . T h u s , r e p r o d u c t i v e s u c c e s s o f B a r r o w ' s G o l d e n e y e i n t h i s s t u d y may be h i g h e r t h a n t h a t t y p i c a l o f p o p u l a t i o n s n e s t i n g n o r m a l l y i n t r e e c a v i t i e s , a s s u m i n g t h a t s u r v i v a l d o e s not d e c l i n e w i t h i n c r e a s i n g c l u t c h s i z e . S i m i l a r l y , c l u t c h s i z e o f Ruddy Ducks r e p o r t e d i n o t h e r s t u d i e s t e n d s t o be h i g h e r t h a n t h a t o f t h i s s t u d y ( G r a y , 1980- 7 e g g s ; J o y n e r , 1975- 7.8-9.8 eggs; Tome, 1981- 7.6 e g g s ) . T h i s d i f f e r e n c e may be due t o g e o g r a p h i c v a r i a t i o n i n c l u t c h s i z e ( o t h e r p o p u l a t i o n s o f Ruddy Ducks s t u d i e d were f u r t h e r s o u t h ) or h i g h e r n e s t p a r a s i t i s m i n o t h e r s t u d i e s . C l u t c h s i z e i s g e n e r a l l y h i g h e r i n n o r t h e r n p o p u l a t i o n s o f b i r d s ( H e s s e ' s R u l e ) , however L a c k (1968) s u g g e s t e d t h a t t h e c l u t c h s i z e f o r ' s o u t h e r n p o p u l a t i o n s may sometimes be g r e a t e r t h a n n o r t h e r n p o p u l a t i o n s i f f o o d i s most ab u n d a n t i n t h e s o u t h . Time Budget o f D u c k l i n g s Time budget s t u d i e s of Ruddy, Barrow's G o l d e n e y e and B u f f l e h e a d s u g g e s t t h a t Ruddy d u c k l i n g s ( e s p e c i a l l y c l a s s 2 d u c k l i n g s ) f e e d and r e s t more t h a n B u f f l e h e a d and B a r r o w's G o l d e n e y e d u c k l i n g s ; however, t h e s e r e s u l t s a r e d i f f i c u l t t o i n t e r p r e t b e c a u s e b r o o d s o f a l l s p e c i e s were f r e q u e n t l y out o f s i g h t o f t h e o b s e r v e r i n b u l r u s h c o v e r . S i e g f r i e d (1976b) f o u n d t h a t a d u l t Ruddy Ducks f e d p r i m a r i l y i n open w a t e r a t l e a s t 2 m e t e r s from emergent v e g e t a t i o n . N e l s o n (1983) f o u n d t h a t Ruddy 58 Ducks t e n d e d t o f e e d i n d e e p e r water and L i b b y (1972) f o u n d Ruddy b r o o d s more o f t e n i n d e e p e r water h a b i t a t . Thus, when Ruddy b r o o d s a r e i n t h e emergent v e g e t a t i o n o u t of s i g h t of t h e o b s e r v e r , t h e y may not f e e d e x t e n s i v e l y . I a l s o n o t e d t h a t b r o o d s o f t h e s e two s p e c i e s t e n d e d t o e n t e r emergent v e g e t a t i o n i m m e d i a t e l y a f t e r f e e d i n g , o r when a g g r e s s i v e i n t e r a c t i o n s between b r o o d s o c c u r r e d . They a l s o t e n d e d t o f e e d i m m e d i a t e l y a f t e r l e a v i n g emergent c o v e r . P o s s i b l y , b r o o d s o f a l l s p e c i e s r e s t e d most of t h e t i m e t h e y s p e n t i n emergent c o v e r . D i v i n g D u r a t i o n and F e e d i n g I n t e n s i t y o f D u c k l i n g s A p r e l i m i n a r y , c o m p a r i s o n of d i v i n g d u r a t i o n of Ruddy d u c k l i n g s s u g g e s t s t h a t t h e i r d i v e s were l o n g e r t h a n t h o s e of e i t h e r B a r r o w ' s G o l d e n e y e or B u f f l e h e a d . F u r t h e r m o r e , l o n g e r d i v e s a p p a r e n t l y do not mean t h a t Ruddy d u c k l i n g s d i v e l e s s f r e q u e n t l y s i n c e f e e d i n g i n t e n s i t y o f a l l t h r e e s p e c i e s was n o t s i g n i f i c a n t l y d i f f e r e n t . T h e s e r e s u l t s may be i n t e r p r e t e d i n s e v e r a l ways. F i r s t , l o n g e r d i v e s may mean more c a l o r i e s ( f o o d ) a r e c o l l e c t e d . Thus, Ruddy d u c k l i n g s may f l e d g e r a p i d l y by f e e d i n g more i n t e n s i v e l y . S e c o n d , d i v i n g d u r a t i o n s may r e f l e c t d i f f e r e n c e s between d e p t h where d u c k l i n g s f e e d . F o r example, Ruddy d u c k l i n g s might have f e d on c h i r o n o m i d s i n t h e mud, whereas B u f f l e h e a d and B a r r o w ' s G o l d e n e y e m i g h t have f e d on amphipods n e a r t h e s u r f a c e . T h i r d , Ruddy d u c k l i n g s may t a k e l o n g e r t o c a p t u r e p r e y . F u r t h e r r e s e a r c h i s r e q u i r e d t o 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 . 59 C o n c l u s i o n s 1. The young o f Ruddy Ducks had h i g h e r s u r v i v a l r a t e s t h a n t h o s e of A m e r i c a n C o o t , B a r r ow's G o l d e n e y e , o r B u f f l e h e a d . 2. R e s u l t s o f t h i s s t u d y d i d n o t u n i l a t e r a l l y s u p p o r t t h e h y p o t h e s i s t h a t Ruddy f e m a l e s were more p r o t e c t i v e of t h e i r b r o o d s t h a n were Barrow's G o l d e n e y e or B u f f l e h e a d f e m a l e s . A l t h o u g h Ruddy f e m a l e s w i t h c l a s s two young were . f o u n d s i g n i f i c a n t l y more f r e q u e n t l y i n b u l r u s h c o v e r t h a n B u f f l e h e a d f e m a l e s w i t h c l a s s two young, t h e r e was no s i g n i f i c a n t d i f f e r e n c e between Ruddy and B u f f l e h e a d f e m a l e s w i t h c l a s s one b r o o d s . S i m i l a r l y , Ruddy f e m a l e s w i t h b r o o d s were n o t more f r e q u e n t l y o b s e r v e d i n b u l r u s h c o v e r t h a n were B a r r o w ' s G o l d e n e y e f e m a l e s . A l s o , Ruddy f e m a l e s w i t h b r o o d s were not f o u n d t o be more a l e r t t h a n B a r r o w's G o l d e n e y e o r B u f f l e h e a d f e m a l e s w i t h b r o o d s . 3. P r e l i m i n a r y d a t a s u g g e s t e d t h a t Ruddy d u c k l i n g s may grow f a s t e r t h a n B u f f l e h e a d or Barrow's G o l d e n e y e d u c k l i n g s by f e e d i n g and r e s t i n g more; however, t h i s t r e n d was o n l y e v i d e n t i n c l a s s II d u c k l i n g s . 4. P r e l i m i n a r y d a t a a l s o showed t h a t d i v e d u r a t i o n s of Ruddy d u c k l i n g s were s i g n i f i c a n t l y l o n g e r t h a n t h o s e of B u f f l e h e a d o r Barrow's G o l d e n e y e w h i l e t h e t i m e t a k e n t o c o m p l e t e 5 d i v e s i n se q u e n c e was s i m i l a r f o r a l l t h r e e s p e c i e s . T h e s e r e s u l t s s u p p o r t t h e h y p o t h e s i s t h a t Ruddy d u c k l i n g s may grow f a s t e r t h a n d u c k l i n g s o f t h e o t h e r s p e c i e s (by g a t h e r i n g more- food- p e r f e e d i n g b o u t ) . N e v e r t h e l e s s , t h e d a t a may s i m p l y r e f l e c t 6 0 d i f f e r e n c e s i n t h e d epth'where e a c h s p e c i e s f e d o r t h e t i m e t a k e n t o c a p t u r e p r e y . 61 CHAPTER FOUR S e a s o n a l Abundance of Food f o r Ruddy D u c k l i n g s I n t r o d u c t i o n L a c k ( 1 9 5 4 ) , Moreau ( 1 9 5 0 ) , F r e t w e l l (1972) and o t h e r s have c o n s i d e r e d t h e f a c t o r s w h i c h d e t e r m i n e t h e t i m i n g of b r e e d i n g . They s u g g e s t e d t h a t b i r d s t y p i c a l l y c o o r d i n a t e b r e e d i n g so t h a t h a t c h i n g o c c u r s when f o o d f o r young i s most a b u n d a n t . ( H e r e a f t e r t h i s w i l l be c a l l e d L a c k ' s h y p o t h e s i s . ) Much of t h e r e s e a r c h on Ruddy Ducks i s c o n s i s t e n t w i t h t h e i d e a t h a t f o o d f o r Ruddy d u c k l i n g s i s more abundant l a t e i n t h e summer. Gra y ( 1 9 8 0 ) , S i e g f r i e d (1973) and o t h e r s have c o l l e c t e d Ruddy d u c k l i n g s and a n a l y z e d t h e i r f o o d h a b i t s by e x a m i n i n g e s o p h a g u s , c r o p and g i z z a r d c o n t e n t s . Most s t u d i e s showed t h a t l a r v a l c h i r o n o m i d s (midge f l i e s ) were t h e most a b u n d a n t i t e m i n t h e d i e t . G r a y a l s o d e t e r m i n e d t h e peak h a t c h i n g d a t e o f Ruddy d u c k l i n g s and showed t h a t peak c h i r o n o m i d d e n s i t y o c c u r r e d a p p r o x i m a t e l y t h r e e weeks l a t e r . She s u g g e s t e d t h a t h a t c h i n g was c o o r d i n a t e d w i t h c h i r o n o m i d d e n s i t y , d e s p i t e t h e t h r e e week l a g between peak h a t c h and peak c h i r o n o m i d d e n s i t y ; however, G r a y ' s r e s e a r c h does not d e m o n s t r a t e t h a t Ruddy d u c k l i n g s h a t c h l a t e b e c a u s e of h i g h c h i r o n o m i d d e n s i t y l a t e i n t h e s e a s o n . Ruddy d u c k l i n g s may s i m p l y e a t c h i r o n o m i d s b e c a u s e c h i r o n o m i d s a r e more abundant when Ruddy d u c k l i n g s h a t c h . In o r d e r t o d e t e r m i n e whether f o o d d e n s i t y i n f l u e n c e s when Ruddy Ducks b r e e d , i t i s n e c e s s a r y t o d e t e r m i n e whether f o o d l i m i t s r e p r o d u c t i v e s u c c e s s of Ruddy D u c k s . I f f o o d d o e s l i m i t 62 r e p r o d u c t i v e s u c c e s s , we would e x p e c t Ruddy f e m a l e s t o a s s e s s f o o d d e n s i t y and s e l e c t t h e f e e d i n g a r e a s w i t h maximum f o o d . To a s s e s s whether f o o d f o r d u c k l i n g s d e t e r m i n e s when Ruddy Ducks b r e e d , t h i s c h a p t e r w i l l f o c u s on t h r e e q u e s t i o n s : 1) What do Ruddy d u c k l i n g s e a t ? 2) I s f o o d f o r Ruddy d u c k l i n g s most abundant l a t e i n t h e summer when d u c k l i n g s h a t c h ? 3) Do f e m a l e Ruddy Ducks s e l e c t a r e a s of h i g h e s t d u c k l i n g f o o d d e n s i t y f o r f e e d i n g ? In t h i s c h a p t e r , f o o d c h o i c e of Ruddy d u c k l i n g s i s d e s c r i b e d and compared t o t h e d e n s i t i e s o f i n v e r t e b r a t e s measured i n a r e a s where d u c k l i n g s f e d . The s e a s o n a l p a t t e r n s of d e n s i t y c h a n g e s , i n i n v e r t e b r a t e s p e c i e s consumed by Ruddy d u c k l i n g s , a r e a l s o p r e s e n t e d t o e s t i m a t e w h i c h i n v e r t e b r a t e s were most a b u n d a n t when Ruddy d u c k l i n g s h a t c h e d . The r e l a t i o n s h i p between m a t e r n a l c h o i c e of f e e d i n g a r e a and d u c k l i n g f o o d d e n s i t y i s a l s o e x p l o r e d , and t h e c h o i c e of b r o o d r e a r i n g ponds and f e e d i n g a r e a s w i t h i n t h o s e ponds by f e m a l e s i s d i s c u s s e d . Methods To a s s e s s f o o d h a b i t s of d u c k l i n g s , s i x d u c k l i n g s , f r o m age c l a s s 1C t o 2C, were c o l l e c t e d from ponds 26, 54 and 66 ( s e e A p p e n d i x One) i n August 1984. The d i g e s t i v e t r a c t s were removed i m m e d i a t e l y and p r e s e r v e d i n 70% i s o p r o p y l a l c o h o l . L a t e r , t h e number and t a x a o f i n v e r t e b r a t e s c o n t a i n e d i n t h e e s o p h a g i were r e c o r d e d and t h e l e n g t h of e a c h i n v e r t e b r a t e m e asured (+ o r 63 0.5 mm). E s o p h a g u s c o n t e n t s o n l y a r e p r e s e n t e d h e r e . S i n c e s o f t - b o d i e d i n v e r t e b r a t e s c o n t a i n e d i n t h e g i z z a r d and c r o p a r e r a p i d l y d i g e s t e d , a s s e s s m e n t s o f d i e t b a s e d on g i z z a r d and c r o p c o n t e n t s t e n d t o u n d e r e s t i m a t e t h e i m p o r t a n c e o f s o f t - b o d i e d i n v e r t e b r a t e s i n d i e t (Swa nson and B a r t o n e k , 1970). Dry w e i g h t s f o r e a c h i n v e r t e b r a t e t a x a were d e t e r m i n e d by e s t a b l i s h i n g s i z e c l a s s e s w h i c h spanned 0.5 cm. c h a n g e s i n l e n g t h ( i e . 0-0.5 cm., 0.5-1.0 cm., 1-1.5 cm. e t c . ) , and oven d r y i n g a t l e a s t 10 i n v e r t e b r a t e s i n e a c h s i z e c l a s s . The t o t a l w e i g h t of t h e s e i n v e r t e b r a t e s was d i v i d e d by t h e t o t a l number of i n v e r t e b r a t e s d r y e d t o g i v e t h e a v e r a g e d r y w e i g h t p e r a n i m a l f o r a p a r t i c u l a r s i z e c l a s s and t a x a . D u c k l i n g d i e t i n f o r m a t i o n was p r e s e n t e d u s i n g t h e c o n v e n t i o n of Swanson e t a l . (1974) e x c e p t t h a t d r y w e i g h t was s u b s t i t u t e d f o r volume i n c a l c u l a t i o n s . D u c k l i n g s c o l l e c t e d f o r f o o d h a b i t s d a t a were t a k e n f r om t h r e e p o n d s . I n v e r t e b r a t e d e n s i t i e s on two o f t h e s e ponds ( b r e e d i n g ponds 26 and 54) were measured t h e day a f t e r d u c k l i n g s were c o l l e c t e d : 10 m o d i f i e d G e r k i n g t r a p samples ( K a m i n s k i , 1981) and 15 c o r e s a m p l e s (4 cm d i a m e t e r , Swanson, 1978) a t e a c h l a k e . Samples were t a k e n a t t h e l o c a t i o n on e a c h pond where f e e d i n g d u c k l i n g s had been c o l l e c t e d . To d e t e r m i n e t h e i n f l u e n c e of i n v e r t e b r a t e d e n s i t y on c h o i c e o f f e e d i n g a r e a by f e m a l e Ruddy Ducks, samples were t a k e n a t two ponds ( b r e e d i n g pond 68 and n o n b r e e d i n g pond 6 0 ) , once i n e a c h o f t h e s p r i n g and summer months of 1983 (mid-May, mid-June, m i d - J u l y and e a r l y A u g u s t ) . B o t h ponds had emergent c o v e r s u i t a b l e f o r n e s t i n g ; however, one pond was u s e d e x t e n s i v e l y by 64 b r e e d i n g Ruddy Ducks ( b r e e d i n g pond 6 8 ) , w h i l e t h e o t h e r was r a r e l y v i s i t e d by Ruddy Ducks ( n o n b r e e d i n g pond 6 0 ) . E a c h l a k e was d i v i d e d i n t o t w e l v e q u a d r a t s , e a c h o f an a p p r o x i m a t e l y 5 0 0 s q u a r e m e ter a r e a . 10 G e r k i n g t r a p s a m p l e s and 10 c o r e s a m p l e s were t a k e n i n e a c h of two of t h e q u a d r a t s . On t h e l a k e w i t h b r e e d i n g Ruddy Ducks (pond 6 8 ) , t h e two q u a d r a t s were c h o s e n by s t u d y i n g t h e f e e d i n g b e h a v i o r o f Ruddy f e m a l e s . F e m a l e s were o b s e r v e d f o r two t w e l v e hour s e s s i o n s e a c h month ( 6 A.M. t o 6 P.M. and 6 P.M. t o 6 A.M.) and l o c a t i o n o f f e e d i n g f e m a l e s was r e c o r d e d a t 15- m i n u t e i n t e r v a l s . I s a m p l e d t h e i n v e r t e b r a t e s i n t h e q u a d r a t where most f e e d i n g Ruddy f e m a l e s were o b s e r v e d and t h e q u a d r a t where t h e f e w e s t f e e d i n g Ruddy f e m a l e s were o b s e r v e d . On t h e pond w i t h o u t b r e e d i n g Ruddy Ducks (pond 6 0 ) , q u a d r a t s were s e l e c t e d a t random. F e e d i n g and n o n f e e d i n g q u a d r a t s and b r e e d i n g and n o n b r e e d i n g ponds were compared by t - t e s t s . R e s u l t s F o o d o f Ruddy D u c k l i n g s D a t a on d u c k l i n g d i e t a r e summarized i n T a b l e 19. A g g r e g a t e w e i g h t , a g g r e g a t e p e r c e n t and p e r c e n t o c c u r r e n c e of i n v e r t e b r a t e s and s e e d s a r e compared. E s t i m a t e s of p e r c e n t o c c u r r e n c e ( t h e number o f b i r d s t h a t consume a p a r t i c u l a r f o o d i t e m d i v i d e d by t h e number o f b i r d s i n t h e sample) i n d i c a t e t h a t c h i r o n o m i d s and s e e d s o c c u r r e d most f r e q u e n t l y i n Ruddy d u c k l i n g TABLE j_9 Foods of Ruddy D u c k l i n g s ITEMS IN ESOPHAGI AGGREGATE AGGREGATE PERCENT OF DUCKLINGS PERCENT WEIGHT OCCURRENCE D i p t e r a : C h i r o n o m i d a e 49 91 50 O d o n a t a : Z y g o p t e r a 23 5 33 H e m i p t e r a : C o r i x i d a e 9 2 17 C o l e o p t e r a : D y t i s c i d a e 1 t r a c e 17 Seeds 18 2 5066 d i e t s (50% o f t h e d u c k l i n g e s o p h a g i c o n t a i n e d t h e s e ) . M easurements o f a g g r e g a t e p e r c e n t ( t h e p r o p o r t i o n o f t h e d i e t o f an i n d i v i d u a l b i r d w h i c h a g i v e n f o o d i t e m o c c u p i e s a v e r a g e d o v e r a l l b i r d s ) show t h a t t h e d r y w e i g h t o f s e e d s i n e a c h d u c k l i n g was low, whereas t h e d r y w e i g h t of c h i r o n o m i d s was h i g h . P o s s i b l y , s e e d s were not s e l e c t e d s p e c i f i c a l l y f o r f o o d but r a t h e r were consumed a l o n g w i t h c h i r o n o m i d s when d u c k l i n g s f o r a g e d i n t h e mud. The i m p o r t a n c e o f c h i r o n o m i d s i n t h e d i e t o f Ruddy d u c k l i n g s may be d i s t o r t e d by measurements o f a g g r e g a t e w e i g h t ( t h e t o t a l d r y w e i g h t o f a p a r t i c u l a r f o o d i t e m consumed by a l l b i r d s d i v i d e d by t h e t o t a l d r y w e i g h t o f a l l f o o d i t e m s consumed by a l l b i r d s ) . Most o f t h e d r y w e i g h t of i n v e r t e b r a t e s i n e s o p h a g i of d u c k l i n g s i s c o n c e n t r a t e d i n c h i r o n o m i d s ( 9 1 % ) ; however, t h i s r e s u l t was due t o one d u c k l i n g whose e s o p h a g u s was f i l l e d w i t h c h i r o n o m i d l a r v a . Z y g o p t e r a n a i a d s may a l s o be i m p o r t a n t i n t h e d i e t o f d u c k l i n g s . W h i l e o n l y two of t h e s i x d u c k l i n g e s o p h a g i c o n t a i n e d Z y g o p t e r a n a i a d s , f o u r g i z z a r d s c o n t a i n e d n a i a d s . I n f o r m a t i o n a b o u t d u c k l i n g d i e t and p r e f e r e n c e can be a l s o be g a t h e r e d from i n v e r t e b r a t e s a m p l i n g i n a r e a s where d u c k l i n g s f e e d , and c o m p a r i n g t h i s w i t h e s o p h a g a e l c o n t e n t s o f d u c k l i n g s . I c h o s e pond 54 and 26 f o r t h i s c o m p a r i s o n b e c a u s e t h e d i e t o f d u c k l i n g s on t h e s e ponds was d i f f e r e n t ( s e e T a b l e 2 0 ) . D u c k l i n g s a t pond 54 f e d on c h i r o n o m i d s o n l y , w h i l e t h o s e a t l a k e 26 f e d on a v a r i e t y o f o t h e r i n v e r t e b r a t e s ( z y g o p t e r a n a i a d s , c o r i x i d s , d y t i s c i d l a r v a ) and s e e d s . I n v e r t e b r a t e d e n s i t i e s on ponds 26 and 54 a r e compared i n T a b l e 21. 67 TABLE 2 0 C o m p a r i s o n of Dry Weight of I n v e r t e b r a t e s and Se e d s i n t h e E s o p h a g i o f Ruddy D u c k l i n g s C o l l e c t e d a t Ponds 2 6 a n d 5 4 J A K E D U C K L I N G S E X A G E D R Y W E I G H T # W E I G H T C L A S S C H I R O . Z Y G O P . C O R I X . D Y T I S . S E E D S 2 6 5 4 0 M A L E 2 C 0 0 . 0 1 0 4 0 0 . 0 0 0 9 0 . 0 0 0 1 2 6 2 8 5 M A L E 2 B 0 0 . 0 0 5 2 0 . 0 0 6 3 0 0 2 6 2 4 0 M A L E 2 A - B 0 0 0 0 0 . 0 0 2 0 5 4 1 5 5 M A L E 1 C 0 . 0 2 6 4 0 0 0 0 5 4 1 4 0 M A L E 1 C 0 . 2 1 0 7 0 0 0 0 TABLE 2_1_ C o m p a r i s o n of A v e r a g e Dry Weight of I n v e r t e b r a t e T a x a p e r Sample on Ponds 2 6 and 5 4 I N V E R T E B R A T E T A X A L A K E 5 4 M E A N 9 5 % C . l L A K E 2 6 M E A N 9 5 % C.I C r u s t a c e a : Amphipoda H e m i p t e r a : C o r i x i d a e C o l e o p t e r a : D y t i s c i d a e O d o n a t a : Z y g o p t e r a D i p t e r a : * C h i r onomidae D i p t e r a : * * C h i ronomidae 0 . 8 8 0 0 0 . 0 1 2 1 0 . 0 0 1 9 0 . 0 0 1 9 0 . 0 0 0 7 0 . 0 2 2 3 0 . 5 3 0 0 0 . 0 1 3 1 0 . 0 0 1 9 0 . 0 0 2 1 0 . 0 0 1 3 0 . 0 1 0 5 0 . 4 3 2 0 0 . 0 5 0 6 0 . 0 0 0 5 0 . 0 0 9 5 0 . 0 3 2 0 0 . 0 1 1 3 0 . 3 5 0 0 0 . 0 3 3 8 0 . 0 0 0 5 0 . 0 0 8 1 0 . 0 3 7 8 0 . 0 0 4 1 *-mean d r y w e i g h t e s t i m a t e s f r o m m o d i f i e d G e r k i n g t r a p samples **-mean d r y w e i g h t e s t i m a t e s from c o r e s a m p l e s 68 Amphipods were c o n s i d e r a b l y more abundant t h a n any o t h e r i n v e r t e b r a t e , y e t t h e s e d i d not a p p e a r i n t h e d i e t of d u c k l i n g s c o l l e c t e d on e i t h e r pond. C h i r o n o m i d d e n s i t y i n t h e water column ( a s measured i n G e r k i n g samples w h i c h g a t h e r l a r v a a s s o c i a t e d w i t h m a c r o p h y t e s and pupae near t h e s u r f a c e ) was lower on pond 54, where Ruddy d u c k l i n g s f e d on c h i r o n o m i d s , t h a n i t was on pond 26 where c h i r o n o m i d s were a v o i d e d . However, t h e c h i r o n o m i d d e n s i t y i n t h e mud (as measured i n c o r e samples) was h i g h e r on pond 54 t h a n on pond 26. S e a s o n a l Abundance of C h i r o n o m i d a e and Z y g o p t e r a F i g u r e 5 compares, t h e c h a n g e s i n c h i r o n o m i d and z y g o p t e r a d e n s i t i e s f r o m May t h r o u g h A u g u s t on b r e e d i n g pond 68... Two q u a d r a t s were sampled t o p r o v i d e i n f o r m a t i o n on i n v e r t e b r a t e d e n s i t y where Ruddy f e m a l e s f e d most and l e a s t o f t e n ( s e e 'Food D e n s i t y and C h o i c e of P a t c h e s w i t h i n P o n d s ' ) ; i n t h i s s e c t i o n , t h e two q u a d r a t s a r e s i m p l y t r e a t e d as r e p l i c a t e s f o r a p a r t i c u l a r month. C h i r o n o m i d d e n s i t y i n t h e w a t e r column ( F i g . 5A) was h i g h e s t i n A u g u s t , when most Ruddy b r o o d s i n t h e s t u d y a r e a h a t c h e d . In c o n t r a s t , z y g o p t e r a d e n s i t y ( F i g 5B) i n t h e water column and c h i r o n o m i d d e n s i t y ( F i g . 5C) i n t h e mud was h i g h e s t i n May. O n l y one b r o o d was r e a r e d on t h i s pond i n 1983. U n l i k e Ruddy b r o o d s t y p i c a l o f t h e s t u d y a r e a , i t h a t c h e d i n l a t e J u n e . I t was a l s o r e a r e d s u c c e s s f u l l y (3 o u t of 5 young f l e d g e d ) a l t h o u g h , when t h e d u c k l i n g s were young, c h i r o n o m i d s , and DRY WT. OF CHIRONOMIO LARVA PER GERKING SAMPLE-BREEOING PONO (g) 0.05 I 0.10 0.1S 0.20 »-» f i l -« ta •-> o > ••J re e 0) e »v I t Ml — *-* 0. a HI 01 CI tn C L n tn a n U l i O a r r o r r o r r c o » 0> g a 9 01 o pi r r pa r r "8 a 9 3 U l pa 3 in 3 M TJ l o i O n O M. O DI 3 •rf* 3 !-»• 3 r r " I C tn M I C cn Ml cn 19 rr O re 3 " O re U l •—• re re 3 re ffl 3 re a o o a . a 1 a. _r 3 o re O re O **• re 3 3 M I 3 Ml 3 »-i O Ml U 3 ia I D re Ml M« SB r— » N a. >Q c U .Q c •< i O w h-» re C a n C a U 3 C c 01 3 01 a < cv a O 01 a . n n C L s. a •< •o a a < re n r r ri •< 01 Ol o> re DI t-" M > r r M I n r r Ml r-l r r Ml 3 in (» 3 " cn re 01 U l re o r r i 9 9 zr re 5 CD 3 01 M« •I CB • O Di l-» 01 01 I - 1 r i < r r re 3 r r l» r r re o DI cn O tn 01 U l 3 I—1 tr 9 tr a tr o U l 1 M. Mi 9 re Ml a. re Ml a re re 01 re A it re re re Q. a M. a. a Q . a a 3 a. 9 re re U l a. 3 9 3 3 9 3 o re to O CO l O o r r tQ IA 3 U l cn cn »— r r U l e v •o rt r r •o r r ft •o !-«• —-*• o »— o CA o •**»• r r 3 re 3 3 Mi a ui a Ml »-•• a re re ft re 3 re tn o> n *-»• a* IB cr* a . ro di 3 OD a ae CO 3 3 »*• 3 n 3 »->• v O 3 l O or 3 >o yr 3 i O ge . x> re . •Q 3 —• c n c U 3 c l O VO DI vr CD to cn CD DI CO a. H' U a Q> LO a U l u> 3 n 9 n 01 01 l O DI •o 01 9 r r r f I— r r •o CA U l CA 19 t n •—' 01 •v. Ut - re 9 tn •o a ca 01 r— 3 o 3 o 3 re a Ml a Ml a . cn IJ^IIIIIIIIIIIIIIIIIIIJIIIIIIIIIIIIIIIIIIIIIIII n + i o 0RY MT. OF ZYGOPTERA LARVA PER GERKING SAMPLE-BREEDING PONO (g) °-° 0-1 0.2 0.3 0.4 0.5 —' 1 1 I —I o> ro DRY WT. OF CHIRONOMID LARVA PER CORE SAMPLE-BREEOING PONO (g) 0.0 O.00S 0.010 0.015 0.020 ' 1 — l M-4-i 69 70 z y g o p t e r a d e n s i t i e s were low r e l a t i v e t o t h o s e i n May and A u g u s t . Food D e n s i t y and C h o i c e o f P a t c h e s w i t h i n Ponds F i g u r e 5 a l s o compares t h e d e n s i t y of c h i r o n o m i d s and z y g o p t e r a i n a r e a s where f e m a l e s f e d most ( f e e d i n g q u a d r a t s ) and l e a s t ( n o n f e e d i n g q u a d r a t s ) . In J u l y and A u g u s t , d e n s i t y o f t h e s e c h i r o n o m i d s t e n d e d t o be l o w e r i n f e e d i n g q u a d r a t s t h a n i n n o n f e e d i n g q u a d r a t s , whereas i n May and J u n e , d e n s i t y t e n d e d t o be h i g h e r i n f e e d i n g q u a d r a t s t h a n i n n o n f e e d i n g q u a d r a t s . S i g n i f i c a n t d i f f e r e n c e s were o b s e r v e d between f e e d i n g and n o n f e e d i n g q u a d r a t s i n A u g u s t c h i r o n o m i d d e n s i t y measured by c o r e s a m p l e s ( t - t e s t ; p<0.05), and J u l y and A u g u s t c h i r o n o m i d d e n s i t y m e asured by G e r k i n g s a m p l e s ( t - t e s t ; J u l y p < 0 . 0 l , A u g u s t P<.001). No s i g n i f i c a n t d i f f e r e n c e s i n z y g o p t e r a n a i a d d e n s i t i e s were o b s e r v e d between f e e d i n g and n o n f e e d i n g q u a d r a t s , but d e n s i t i e s i n f e e d i n g q u a d r a t s t e n d e d t o be s l i g h t l y h i g h e r . Food d e n s i t y and C h o i c e o f Ponds F i g u r e 6 p r e s e n t s t h e c h a n g e s i n d e n s i t i e s of c h i r o n o m i d l a r v a and z y g o p t e r a n a i a d s f r o m May t h r o u g h A u g u s t on n o n b r e e d i n g pond 60. C o m p a r i s o n o f F i g u r e s 5 and 6 shows t h a t d e n s i t y o f t h e s e i n v e r t e b r a t e s was on a v e r a g e much h i g h e r a t b r e e d i n g pond 68. Z y g o p t e r a d e n s i t y i n b o t h q u a d r a t s a t t h e DRY HT. OF CHIRONOMIO LARVA PER GERKING SAMPLE-N0N8REE0ING POND (g) 0.0 0.05 0. 15 0.20 rt n f t a O > C 3 * — • 3 wi — »-* o o O o O n Cl 3 3 n 3 a tr .a o tr .O o tr r t o w « c o »n c 3 C 3 re 01 re 01 •o re o •o IT. re a •6 re a 01 re 01 o> a n a n Q> n »*• 01 M> •O 3 r t M> 3 r t VI 3 c in tO in U) lO in o lO 0> o -O 3 a 3 o •o UI 3 •a cn •a n. o o QI o 01 O o 01 O 3 3 o 3 3 rn 3 r t Mi a •a rt. a T> a. in »-•• t—' N t-» a a* re l-» re •< tr. 01 o a. a o a lO o in n. O o> < n <: H . . •o 3 01 3 01 3 r t •o »-• 3 t-> 3 re 3 *-* re o D . 01 o —» 01 01 —• a. 3- rf 3- IO n OD O0 3 aj UJ •o n W •v 01 L J M- o < 0 O 0 M> 3 3 3 3 3 01 O r-« a O a a 0> 3 tA 3 a •o a CJ •n a re o a 0) 3 3 a rn ti a i UI a re re re re 3 VO t-« 3 r t n in Ui »< UI 01 <#> re n r t rr ID n e c t-> re tn n UI >< in rt VI re 3 a a c M- lO U) 3 3 re re tr tr H . a U3 s: O •< *• re O tr t| 3 50 re w lO c c » 3 a in a VI c lO. a 01 Cb 01 a 3 >< 3 a •o •o >< in i-» >—1 01 • re o re o 3 c UI c UI c •o o n o o o ?r re VI tn Ml in in 3n 7 DRY HT. OF ZYGOPTERA LARVA PER GERKING SAMPLE-N0N8REE0 ING P0NO (g) 0.0 0.1 0.2 0.3 0.4 0.5 I I I I 1 I 3H DRY WT. OF CHIRONOMID LARVA PER CORE SAMPLE-NONBREEDING POND (g) 0.0 0.005 0.010 0.015 0.020 I l I I z O TL 72 n o n b r e e d i n g pond was s i g n i f i c a n t l y l o w e r t h a n t h a t i n b o t h q u a d r a t s a t t h e b r e e d i n g pond f o r a l l f o u r months ( t - t e s t s ; ,p<0.05). C h i r o n o m i d d e n s i t y i n t h e w a t e r column was s i g n i f i c a n t l y l o w e r i n most of t h e c o m p a r i s o n s between q u a d r a t s of t h e b r e e d i n g and n o n b r e e d i n g pond; however, c h i r o n o m i d d e n s i t y i n t h e mud was s i m i l a r a t t h e two ponds. Where s i g n i f i c a n t d i f f e r e n c e s were o b s e r v e d t h e l a r g e r d e n s i t y o c c u r r e d a t t h e n o n b r e e d i n g pond. F o r example, A u g u s t c h i r o n o m i d d e n s i t y i n t h e mud was s i g n i f i c a n t l y g r e a t e r i n b o t h q u a d r a t s of t h e n o n b r e e d i n g pond t h a n i n t h e f e e d i n g q u a d r a t of t h e b r e e d i n g pond ( t - t e s t s ; p < 0 . 0 0 l ) . D i s c u s s i o n F o o d o f Ruddy D u c k l i n g s C h i r o n o m i d l a r v a were b o t h consumed i n t h e g r e a t e s t b i o m a s s and a l s o t h e most commonly o c c u r r i n g i n v e r t e b r a t e i n t h e e s o p h a g i of Ruddy d u c k l i n g s c o l l e c t e d i n t h i s s t u d y and t h u s a p p e a r e d t o be t h e most i m p o r t a n t component i n d i e t o f Ruddy d u c k l i n g s s a m p l e d . Z y g o p t e r a n a i a d s were p e r h a p s o f s e c o n d a r y i m p o r t a n c e s i n c e t h e y r e p r e s e n t e d o n l y 5% o f t h e t o t a l b i o m a s s c o n t a i n e d i n d u c k l i n g e s o p h a g i ; however, t r a c e s of z y g o p t e r a n a i a d s were d i s c o v e r e d i n t h e d i g e s t i v e t r a c t s o f f o u r o f t h e s i x d u c k l i n g s c o l l e c t e d . T hus, i n l a k e s where h i g h d e n s i t y o f z y g o p t e r a n a i a d s o c c u r s , t h e s e i n v e r t e b r a t e s may be t h e s t a p l e f o o d i t e m . 73 C ottam ( 1 9 3 9 ) , C o l l i a s and C o l l i a s (1963) and S i e g f r i e d (1973) a l s o f o u n d c h i r o n o m i d s t o be t h e main s t a p l e o f Ruddy d u c k l i n g s . B o t h S i e g f r i e d and Cottam f o u n d amphipods were common i n t h e gut c o n t e n t s of Ruddy d u c k l i n g s , w h i l e o n l y Cottam f o u n d c o r i x i d s i n t h e d i e t o f d u c k l i n g s . A l t h o u g h z y g o p t e r a n a i a d s have been r e p o r t e d i n t h e d i e t of a d u l t Ruddy Ducks (Tome, 1981), t h e y have not been o b s e r v e d a s an i m p o r t a n t i t e m i n d u c k l i n g d i e t . S e a s o n a l Abundance of C h i r o n o m i d a e and Z y g o p t e r a I f Ruddy d u c k l i n g s e a t z y g o p t e r a n a i a d s and c h i r o n o m i d l a r v a p r i m a r i l y , L a c k ' s h y p o t h e s i s p r e d i c t s t h a t t h e d e n s i t y of t h e s e i n v e r t e b r a t e s would be h i g h e s t when Ruddy d u c k l i n g s h a t c h . N e s t i n g c h r o n o l o g y i s g i v e n i n Ap p e n d i x F o u r and s u g g e s t s t h a t most d u c k l i n g s i n t h e C h i l c o t i n h a t c h i n l a t e J u l y o r e a r l y A u g u s t . Thus, L a c k ' s h y p o t h e s i s p r e d i c t s t h a t d e n s i t y of Z y p o p t e r a n a i a d s and c h i r o n o m i d l a r v a would be h i g h e s t i n l a t e J u l y and A u g u s t . My r e s u l t s showed t h a t o n l y t h e d e n s i t y of c h i r o n o m i d l a r v a i n t h e water column was h i g h e s t i n A u g u s t . W h i l e i t i s p o s s i b l e t h a t Ruddy d u c k l i n g s c a n e x p l o i t t h e s e c h i r o n o m i d s , C o t t a m r e p o r t e d t h a t Ruddy d u c k l i n g s were b e t t e r a t s t r a i n i n g , a mode o f f e e d i n g t h a t he s u g g e s t e d was more s u i t e d t o c a p t u r i n g c h i r o n o m i d s i n t h e mud. F u r t h e r m o r e , on b r e e d i n g pond 54 where Ruddy d u c k l i n g s f e d on c h i r o n o m i d ' l a r v a o n l y , d e n s i t y of t h e s e i n v e r t e b r a t e s i n t h e water column was v e r y low, 74 whereas t h a t i n c o r e s was v e r y h i g h , s u g g e s t i n g t h a t d u c k l i n g s f e d on c h i r o n o m i d s i n t h e mud. T h u s , t h e L a c k h y p o t h e s i s i s not c l e a r l y s u p p o r t e d by t h e c o m p a r i s o n o f d u c k l i n g f o o d h a b i t s w i t h d a t a on i n v e r t e b r a t e d e n s i t i e s where d u c k l i n g s f e d . F i n a l l y , on t h e b r e e d i n g pond 68, t h e b r o o d r e a r i n g c h r o n o l o g y d i d n o t s u p p o r t L a c k ' s h y p o t h e s i s . A b r o o d of Ruddy d u c k l i n g s was r e a r e d and f l e d g e d s u c c e s s f u l l y on t h i s pond, even t h o u g h d e n s i t i e s of c h i r o n o m i d l a r v a and z y g o p t e r a n a i a d s were a t t h e low p o i n t measured f o r t h e May t o A u g u s t p e r i o d . A l t h o u g h t h i s b r o o d was not t y p i c a l of t h e Ruddy p o p u l a t i o n , i t does show t h a t t o r e p r o d u c e s u c c e s s f u l l y , Ruddy f e m a l e s do not have t o b r e e d when c h i r o n o m i d l a r v a and z y g o p t e r a n a i a d d e n s i t i e s a r e h i g h e s t . Food D e n s i t y and C h o i c e o f P a t c h e s w i t h i n Ponds Z y g o p t e r a n a i a d d e n s i t i e s were g r e a t e r i n t h e q u a d r a t s where f e m a l e s f e d most o f t e n ( f e e d i n g q u a d r a t s ) , , a l t h o u g h d i f f e r e n c e s between f e e d i n g and n o n f e e d i n g q u a d r a t s (where f e m a l e s f e d l e a s t ) were not s i g n i f i c a n t . S i n c e n a i a d d e n s i t y was h i g h e r i n t h e f e e d i n g q u a d r a t , f o o d d e n s i t y m i g h t have d e t e r m i n e d t h e c h o i c e o f p a t c h e s f o r f e e d i n g (and more samples were n e c e s s a r y t o e s t a b l i s h a s t a t i s t i c a l d i f f e r e n c e ) . However, l a r v a l c h i r o n o m i d d e n s i t i e s were s i g n i f i c a n t l y l o w e r i n f e e d i n g q u a d r a t s t h a n i n n o n f e e d i n g q u a d r a t s . T h i s s u g g e s t e d t h a t some o t h e r f a c t o r b e s i d e s f o o d d e t e r m i n e d where f e m a l e s and young f e d . S i n c e we do not know what f e m a l e s and d u c k l i n g s were 75 f e e d i n g on i t i s d i f f i c u l t t o i n t e r p r e t t h e s e r e s u l t s . C h i r o n o m i d l a r v a and z y g o p t e r a n a i a d d e n s i t i e s on b r e e d i n g pond 68 were h i g h e r t h a n t h o s e o f b r e e d i n g ponds where d i e t o f d u c k l i n g s was sampled ( b r e e d i n g pond 26 and 5 4 ) . T h i s r e s u l t s u g g e s t e d t h a t d u c k l i n g s on l a k e 68 c o u l d have been r e a r e d s u c c e s s f u l l y on e i t h e r c h i r o n o m i d s or z y g o p t e r a . Food D e n s i t y and C h o i c e of Ponds I f c h i r o n o m i d l a r v a and z y g o p t e r a n a i a d s a r e i m p o r t a n t i n d e t e r m i n i n g when d u c k l i n g s h a t c h , Ruddy Ducks s h o u l d b r e e d on ponds where d e n s i t y of t h e s e i n v e r t e b r a t e s was h i g h e s t . T h i s p r e d i c t i o n i s p a r t l y s u p p o r t e d by t h e d a t a c o m p a r i n g b r e e d i n g pond 68 w i t h n o n b r e e d i n g pond 60, s i n c e d e n s i t i e s i n t h e water column o f z y g o p t e r a n a i a d s and c h i r o n o m i d l a r v a t e n d e d t o be l o w e r i n n o n b r e e d i n g p o n d s . However, c h i r o n o m i d d e n s i t y i n c o r e samples was h i g h e r on n o n b r e e d i n g ponds i n J u l y and A u g u s t , t h e main t i m e f o r b r o o d r e a r i n g . T h e s e r e s u l t s may i n d i c a t e t h a t f o o d was n o t l i m i t e d on t h e s e ponds and t h e r e f o r e , t h a t pond c h o i c e by Ruddy f e m a l e s was not g o v e r n e d by i n v e r t e b r a t e d e n s i t y . A l t e r n a t e l y , f o o d may s t i l l have l i m i t e d r e p r o d u c t i v e s u c c e s s and i n f l u e n c e d pond c h o i c e , b u t some unknown f a c t o r may have c a u s e d Ruddy Ducks t o a v o i d u s i n g t h e n o n b r e e d i n g pond d e s p i t e t h e h i g h c h i r o n o m i d d e n s i t y t h e r e . A l a r g e r sample, i n c l u d i n g s e v e r a l more ponds, m i g h t have p r o d u c e d d i f f e r e n t c o n c l u s i o n s . When J o y n e r (1980) s t u d i e d 4 ponds u s e d e x t e n s i v e l y by d u c k s and 3 r a r e l y u s e d , he f o u n d t h a t t h e numbers o f i n v e r t e b r a t e s and i n v e r t e b r a t e t a x a were p o s i t i v e l y 76 c o r r e l a t e d w i t h duck use of ponds. C o n c l u s i o n s 1. C h i r o n o m i d l a r v a and z y g o p t e r a n a i a d s were the major components i n esophagi of d u c k l i n g s c o l l e c t e d i n t h i s s t u d y . 2. R e s u l t s of t h i s s tudy do not su p p o r t the h y p o t h e s i s t h a t Ruddy Ducks breed when food f o r young i s most abundant f o r t h r e e main r e a s o n s . F i r s t , z y g o p t e r a n a i a d d e n s i t i e s measured when d u c k l i n g s were p r e s e n t ( J u l y and August) were not s i g n i f i c a n t l y g r e a t e r than those measured b e f o r e d u c k l i n g s had h a t c h e d (May and J u n e ) . Second, d e n s i t i e s of l a r v a l c h i r o n o m i d s i n the mud were s i g n i f i c a n t l y l e s s when d u c k l i n g s were p r e s e n t i n August than they were b e f o r e d u c k l i n g s h a t c h e d " i n May. F i n a l l y , c h i r o n o m i d d e n s i t i e s tended t o be lower i n a r e a s where female Ruddy Ducks and young f e d than i n a r e a s they a v o i d e d . 77 CHAPTER F I V E G e n e r a l D i s c u s s i o n In t h i s s t u d y , I i n v e s t i g a t e a range of f a c t o r s t h a t p o t e n t i a l l y i n f l u e n c e t h e t i m i n g o f b r e e d i n g , r a t h e r t h a n f o c u s i n g on a s i n g l e h y p o t h e s i s . F a c t o r s I c o n s i d e r i n c l u d e n e s t p r e d a t i o n , a v a i l a b i l i t y of g r e e n v e g e t a t i o n , and abundance of f o o d f o r young. My r e s u l t s s u g g e s t t h a t a v a i l a b i l i t y of g r e e n v e g e t a t i o n f o r n e s t s and abundance o f f o o d f o r young do no t s i g n i f i c a n t l y d e l a y b r e e d i n g , b u t n e s t p r e d a t i o n may be an i m p o r t a n t d e l a y i n g f a c t o r . T h i s i n f o r m a t i o n s u g g e s t s r e a s o n s why Ruddy Ducks c o n t i n u e t o b r e e d l a t e but does n o t e x p l a i n why Ruddy Ducks e v o l v e d t o become l a t e b r e e d e r s . At l e a s t f o r Ruddy Ducks i n t h e C h i l c o t i n , an a d v a n t a g e of b r e e d i n g l a t e i s t h a t n e s t p r e d a t i o n i s low e r i n summer t h a n i n s p r i n g . S e v e r a l o b s e r v a t i o n s s u p p o r t t h i s c o n c l u s i o n . F i r s t , n e s t l o s s t o p r e d a t i o n f o r A m e r i c a n C o o t s (a s p e c i e s w h i c h b r e e d s e a r l y ) was s i g n i f i c a n t l y g r e a t e r t h a n f o r Ruddy D u c k s . S e c o n d , p r e d a t i o n o f s p r i n g dummy n e s t s was s i g n i f i c a n t l y g r e a t e r t h a n t h a t o f summer dummy n e s t s . F i n a l l y , Ravens were se e n p r e y i n g upon n e s t s i n s p r i n g but not i n summer and were f o u n d more o f t e n near ponds i n s p r i n g t h a n i n summer. E s t a b l i s h i n g t h e e x i s t e n c e of s u c h an a d v a n t a g e does n o t p r o v e t h a t Ruddy Ducks b r e e d l a t e t o a v o i d heavy n e s t p r e d a t i o n , but i t d oes i n d i c a t e t h a t n e s t p r e d a t i o n i n t h e s p r i n g may be a d e t e r r e n t a g a i n s t e a r l y b r e e d i n g by Ruddy Ducks. As w e l l a s e x a m i n i n g a d v a n t a g e s o f l a t e b r e e d i n g i n Ruddy D u c k s , t h i s s t u d y f o c u s e s on c h a r a c t e r i s t i c s of Ruddy Ducks t h a t 78 enhance t h e i r a b i l i t y t o b r e e d i n g l a t e s u c c e s s f u l l y . F i r s t , Ruddy d u c k l i n g s a r e a b l e t o f l e d g e more r a p i d l y t h a n d u c k l i n g s of e a r l y b r e e d i n g s p e c i e s . L o n g e r d i v e d u r a t i o n s , and more f r e q u e n t f e e d i n g and r e s t i n g may a l l o w Ruddy d u c k l i n g s t o grow more q u i c k l y ; however, o t h e r f a c t o r s not c o n s i d e r e d i n t h i s s t u d y , s u c h as a s s i m i l a t i o n e f f i c i e n c y and c a l o r i c c o n t e n t o f f o o d , may a f f e c t g r o w t h r a t e s . F u r t h e r r e s e a r c h on f e e d i n g r a t e and n u t r i t i o n i s n e c e s s a r y . S e c o n d , t h e r a t i o o f egg s i z e t o body w e i g h t i n Ruddy Ducks i s t h e l a r g e s t i n t h e a n a t i d a e ( L a c k , 1968). I t may a l l o w Ruddy d u c k l i n g s t o h a t c h a t a l a r g e r f r a c t i o n o f a d u l t w e i g h t t h a n young o f e a r l y b r e e d i n g d u c k s . L a c k (1968) s u g g e s t s t h a t eggs a r e l a r g e r i n c o n d i t i o n s where f o o d f o r young i s i n s h o r t s u p p l y . F o o d s h o r t a g e i n t h e b r o o d r e a r i n g p e r i o d does n o t a p p e a r t o be a p r o b l e m i n t h e C h i l c o t i n a r e a and i t seems more l i k e l y t h a t l a r g e egg s i z e i n Ruddy Ducks e n s u r e s t h a t l e s s g r o w t h i s r e q u i r e d between h a t c h i n g and f l e d g i n g . V a r i o u s f e a t u r e s o f Ruddy Ducks s u g g e s t t h a t t h e y w o u l d be u n s u c c e s s f u l i f t h e y b r e d e a r l i e r . Most w a t e r f o w l a n d c o o t s l a y e ggs of a d r a b c o l o u r and c o v e r them w i t h down o r v e g e t a t i o n . A m e r i c a n C o o t , f o r example, have brown s p e c k l e d eggs t h a t b l e n d w e l l w i t h t h e v e g e t a t i o n but Ruddy Duck eggs a r e b r i g h t w h i t e and a r e n o t c o v e r e d by down or v e g e t a t i o n . M o r e o v e r , Ruddy f e m a l e s do not a g g r e s s i v e l y d e f e n d t h e n e s t a g a i n s t i n t r u s i o n s by p r e d a t o r s u n l i k e c o o t s w h i c h d e f e n d t e r r i t o r i e s i n t h e v i c i n i t y o f n e s t s ( R y d e r , 1959). I have a n a l y z e d t h e q u e s t i o n of what d e t e r m i n e s t i m i n g o f 79 b r e e d i n g i n Ruddy Ducks, and s u g g e s t e d some o f t h e a d v a n t a g e s t o b r e e d i n g l a t e . F a c t o r s s u c h as r e d u c e d n e s t p r e d a t i o n have a d i r e c t e f f e c t on r e p r o d u c t i v e s u c c e s s , w h i l e c h a r a c t e r i s t i c s l i k e egg s i z e and d u c k l i n g b e h a v i o r have an i n d i r e c t e f f e c t by e n s u r i n g t h a t d u c k l i n g s grow s u f f i c i e n t l y t o f l e d g e b e f o r e ponds f r e e z e . C h a r a c t e r i s t i c s a p p r o p r i a t e t o e a r l y b r e e d i n g s p e c i e s and n o t f o u n d i n Ruddy Ducks ( e g . d u l l eggs c o v e r e d w i t h down) s u g g e s t t h a t Ruddy Ducks would be l e s s s u c c e s s f u l i f t h e y a t t e m p t e d t o b r e e d e a r l i e r . 80 REFERENCES CITED A l l e y , R. and H. Boyd. 1947. The h a t c h i n g and f l e d g i n g s u c c e s s of some c o o t . B r i t i s h B i r d s 40: 199-203. Ankney, C D . 1977. F e e d i n g and d i g e s t i v e organ s i z e i n b r e e d i n g L e s s e r Snow Geese. Auk 94: 275-282. 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W a s h i n g t o n . 143-202 pp. L i b b y , H.J. 1972. Ruddy Duck b r o o d d i s t r i b u t i o n i n r e l a t i o n t o marsh h a b i t a t . M.S. t h e s i s . U n i v . W i s e . ( M a d i s o n ) . 59 pp. Low, J.B. 1941. N e s t i n g of t h e Ruddy Duck i n Iowa. Auk 58: 506-517. 83 M c K n i g h t , D.E. 1974. D r y - l a n d n e s t i n g by Redheads and Ruddy D u c k s . J . W i l d l . Manage. 38: 112-119. M i l l e r , A.W. and B.D. C o l l i n s . 1954. A n e s t i n g s t u d y o f d u c k s and c o o t s on T u l e Lake and Lower K l a m a t h N a t i o n a l W i l d l i f e R e f u g e s . C a l i f . F i s h and Game 40: 17-37. M i s t e r e k , D. L. 1974. The b r e e d i n g e c o l o g y o f t h e Ruddy Duck ( O x y u r a j a m a i c e n s i s ) on Rush L a k e , Winnebago C o u n t y , W i s c o n s i n . M.S. t h e s i s . U n i v . W i s e . ( O s h k o s h ) . 82 pp. Moreau, R.E. 1950. The b r e e d i n g s e a s o n s of A f r i c a n b i r d s . I b i s 92: 223-267. Munro, J.A. 1945. The b i r d s of t h e C a r i b o o P a r k l a n d s , B r i t i s h C o l u m b i a . Can. J . Res. (D.) 23: 17-103. N a g e l , R.E. 1969. P r e d a t i o n on eggs i n s i m u l a t e d n e s t s and t r e e c a v i t y abundance i n wood duck n e s t i n g h a b i t a t . M.S. t h e s i s . Iowa S t a t e U n i v . (Ames). 94 pp. N e l s o n , C. 1983. U n p u b l i s h e d a b s t r a c t s o f D e l t a W a t e r f o w l C o n f e r e n c e , Summer 1983. N i c e , M.M. 1954. P r o b l e m s of i n c u b a t i o n p e r i o d s i n n o r t h a m e r i c a n b i r d s . Condor 56: 173-197. P e r r i n s , C M . 1965. P o p u l a t i o n f l u c t u a t i o n s and c l u t c h - s i z e i n t h e G r e a t T i t , P a r i s major . J . Anim. E c o l . 34:601-647. . 1966. S u r v i v a l of young Manx S h e a r w a t e r s P u f f i n u s p u f f i n u s i n r e l a t i o n t o t h e i r presumed d a t e o f h a t c h i n g . I b i s 108: 132-135. . 1970. The t i m i n g of b i r d s ' b r e e d i n g s e a s o n s . I b i s 112: 242-255. P i c o z z i , N. 1975. Crow p r e d a t i o n on marked n e s t s . J . W i l d l . Manage. 39: 151-155. 84 Raikow, R . J . 1973. Loc o m o t o r mechanism i n N o r t h A m e r i c a n d u c k s . W i l s o n B u l l . 85: 295-307. R y d e r , R.A. 1959. I n t e r s p e c i f i c i n t o l e r a n c e o f t h e Am e r i c a n C o o t i n U t a h . Auk 76: 424-442. . 1961. Coot and duck p r o d u c t i v i t y i n n o r t h e r n Utah, T r a n s . N o r t h Amer. W i l d l . C o n f . 26: 134-147. R i e n e c k e r , W.C. and W. A n d e r s o n . 1960. A w a t e r f o w l n e s t i n g s t u d y on T u l e Lake and Lower K l a m a t h N a t i o n a l W i l d l i f e R e f u g e s , 1957. C a l i f . F i s h and Game 46: 481-506. S c h r a n k , B.W. 1972. W a t e r f o w l n e s t c o v e r and some p r e d a t i o n r e l a t i o n s h i p s . J . W i l d l . 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N o t e s on b e h a v i o u r o f Ruddy Ducks d u r i n g t h e b r o o d p e r i o d . W i l d f o w l 28: 126-128. 85 S k u t c h , A.F. 1962. The c o n s t a n c y of i n c u b a t i o n . W i l s o n B u l l . 74: 115-152. Swanson, G.A. 1978. A s i m p l e l i g h t w e i g h t c o r e s a m p l e r f o r q u a n t i f y i n g w a t e r f o w l f o o d s . J . W i l d l . Manage. 42: 426-428. Swanson, G.A. and J . C . B a r t o n e k . 1970. B i a s a s s o c i a t e d w i t h f o o d a n a l y s i s i n g i z z a r d s o f B l u e - w i n g e d T e a l . J . W i l d l . Manage. 34: 739-746. Swanson, G.A., G.L. K r a p u , J . C . B a r t o n e k , J.R. S e r i e and D.H. J o h n s o n 1974. A d v a n t a g e s i n m a t h e m a t i c a l l y w e i g h t i n g w a t e r f o w l f o o d h a b i t s d a t a . J . W i l d l . Manage. 38: 302-307. T a l e n t , L.G., R.L. J a r v i s , and G.L. K r a p u . 1983. S u r v i v a l o f M a l l a r d b r o o d s i n s o u t h - c e n t r a l N o r t h D a k o t a . Condor 85: 74-78. Tome, M. 1981. R e p r o d u c t i v e b i o e n e r g e t i c s of f e m a l e Ruddy Ducks i n M a n i t o b a . M.S. t h e s i s . U n i v . Maine ( O r o n o ) . 67 pp. . 1984. Changes i n n u t r i e n t r e s e r v e s and o r g a n s i z e o f f e m a l e Ruddy Ducks b r e e d i n g i n M a n i t o b a . Auk 101: 830-837. W e l l e r , M.W. 1959. P a r a s i t i c egg l a y i n g i n t h e Redhead ( A y t h y a a m e r i c a n a ) and o t h e r N o r t h A m e r i c a n A n a t i d a e . E c o l . Monog. 29: 333-365. Z a r , J.H. 1984. Second e d . B i o s t a t i s t i c a l A n a l y s i s . P r e n t i c e -H a l l , Englewood C l i f f s , New J e r s e y . 718 pp. 86 APPENDIX ONE D e s c r i p t i o n o f S t u d y S i t e T h i s s t u d y was c o n d u c t e d a t B e e c h e r ' s P r a i r i e i n t h e C h i l c o t i n p a r k l a n d s o f B r i t i s h C o l u m b i a ( L o n g i t u t e : 122 d e g r e e s 31.5 m i n u t e s West, L a t i t u t e : 51 d e g r e e s 58 m i n u t e s N o r t h ) n e a r R i s k e C r e e k , 30 m i l e s s o u t h w e s t of W i l l i a m s L a k e . Much of t h e s t u d y s i t e was l o c a t e d w i t h i n a m i l i t a r y t r a i n i n g a r e a o f t h e C a n a d i a n Armed F o r c e s . The C h i l c o t i n r e g i o n i s d o m i n a t e d by r a n g e g r a s s l a n d w h i c h i s i n t e r s p e r s e d w i t h c o n i f e r g r o v e s and numerous s h a l l o w p o n d s . A map, F i g u r e 7, shows t h e ponds and m a j o r r o a d s t h r o u g h t h e s t u d y s i t e . Ponds a r e numbered a c c o r d i n g t o t h e s y s t e m u s e d by C a n a d i a n W i l d l i f e . S e r v i c e b i o l o g i s t s w o r k i n g i n t h i s a r e a . E x t e n s i v e r e s e a r c h has been c o n d u c t e d by CWS b i o l o g i s t s on t h e water c h e m i s t r y , f l o r a , f a u n a , d e p t h c h a r a c t e r i s t i c s and w a t e r f o w l use of t h e s e ponds. Water c o n d u c t i v i t y r a n g e s from 50-1500 (micromhos/cm a t 25 d e g r e e s ) . Ponds t e n d e d t o be s h a l l o w ( d e p t h was 3 m o r l e s s ) and most ponds were r i n g e d by emergent s c i r p u s . W a t e r f o w l w h i c h commonly use t h e ponds f o r b r e e d i n g i n c l u d e L e s s e r Scaup, Redhead, G r e e n - w i n g e d T e a l , B l u e -winged T e a l , A m e r i c a n Widgeon, and Cinnamon T e a l . Range g r a s s l a n d i s u s e d e x t e n s i v e l y f o r g r a z i n g c a t t l e , and c o n i f e r o u s f o r e s t a r e a s a r e b e i n g l o g g e d a f t e r i n f e s t a t i o n s of p i n e b a r k b e e t l e . F u r t h e r d e s c r i p t i o n s o f t h i s a r e a a r e p r o v i d e d by Munro ( 1 9 4 5 ) , S c u d d e r and Mann ( 1 9 6 8 ) , and S c u d d e r ( 1 9 6 9 ) . 88 APPENDIX TWO Ambient T e m p e r a t u r e and L a t e B r e e d i n g Most n o r t h t e m p e r a t e w a t e r f o w l s p e c i e s r e l y h e a v i l y on s t o r e d e n e r g y r e s e r v e s t o f u e l i n c u b a t i o n (Ankney, 1977; K o r s h k e n , 1977). In c o n t r a s t , Ruddy f e m a l e s f u e l 85% of t h e i r e n e r g y r e q u i r e m e n t s f o r i n c u b a t i o n by d i e t a r y i n t a k e (Tome, 1984). They a r e f r e q u e n t l y a b s e n t from t h e n e s t f o r s h o r t p e r i o d s o f t i m e d u r i n g w h i c h t h e y f e e d i n t e n s i v e l y ( S i e g f r i e d e t a l . , 1 9 7 6 c ) , y e t t h e y must be a b l e t o m a i n t a i n n e s t t e m p e r a t u r e s s u f f i c i e n t t o h a t c h eggs s u c c e s s f u l l y . Ambient t e m p e r a t u r e a p p e a r s t o i n f l u e n c e how much t i m e f e m a l e d u c k s s p e n d o f f t h e n e s t (Low, 1941; S k u t c h , 1962) and t h u s , how much t i m e i s a v a i l a b l e t o them f o r f e e d i n g . Female m a l l a r d s t e n d e d t o spend more t i m e on t h e n e s t when i t i s c o l d and r a i n y t h a n t h e y do when i t i s warm and sunny ( C a l d w e l l and C o r n w e l l , 1975). Thus, f e m a l e Ruddy Ducks may be a b l e t o f e e d e x t e n s i v e l y d u r i n g i n c u b a t i o n b e c a u s e t h e y b r e e d l a t e r when ambient t e m p e r a t u r e s a r e h i g h e r . In t h i s a p p e n d i x , t h e e f f e c t o f ambient t e m p e r a t u r e on n e s t t e m p e r a t u r e of Ruddy Ducks i s c o n s i d e r e d . The p o t e n t i a l i n f l u e n c e of ambient t e m p e r a t u r e on t h e t i m i n g o f b r e e d i n g and dep e n d e n c e o f t h e f e m a l e on endogenous e n e r g y f o r i n c u b a t i o n a r e a l s o d i s c u s s e d . Ambient t e m p e r a t u r e i n s p r i n g i s compared t o t h a t i n summer, and n e s t t e m p e r a t u r e of Ruddy Ducks i s compared t o t h a t o f A m e r i c a n C o o t s . 89 C o m p a r i s o n o f Ambient T e m p e r a t u r e i n S p r i n g and Summer In 1984, an e x p e r i m e n t was c o n d u c t e d t o d e s c r i b e t h e d i f f e r e n c e between ambient ( a i r ) t e m p e r a t u r e s i n t h e s p r i n g when C o o t s n e s t and t h e summer when Ruddy Ducks n e s t . F i f t e e n permanent n e s t s i t e s were e s t a b l i s h e d w i t h i n t h e emergent v e g e t a t i o n of e i g h t ponds. The s i t e s s e l e c t e d f e l l w i t h i n t h e measured range of e a c h measurement f o r Ruddy Duck n e s t s i t e s i n 1983. At e a c h s i t e , a S p r i n g f i e l d maximum-minimum thermometer was f i x e d t o a wooden p o l e a n c h o r e d i n t h e marsh, a t a d i s t a n c e of n o t more t h a n 40 cm from t h e n e s t b o w l . At e a c h s i t e , maximum and minimum t e m p e r a t u r e s were r e c o r d e d d a i l y t h r o u g h o u t two t w e n t y - f o u r day p e r i o d s . The f i r s t e x t e n d e d from May 27 t o June 19 and was c h o s e n t o encompass t h e t i m e of peak Co o t i n c u b a t i o n . The s e c o n d was from J u l y 10 t o A u g u s t 2 and was c h o s e n t o c o i n c i d e w i t h t h e t i m e of peak Ruddy Duck i n c u b a t i o n . A v e r a g e minimum and maximum t e m p e r a t u r e s were compared by S t u d e n t ' s t - t e s t . The t o t a l number of r e c o r d s below f r e e z i n g i n s p r i n g - were compared by c h i - s q u a r e d c o n t i n g e n c y t e s t t o t h o s e i n summer. A l s o , t h e t o t a l number o f r e c o r d s above 34 d e g r e e s C. i n s p r i n g were compared by c h i - s q u a r e d c o n t i n g e n c y t e s t t o t h o s e i n summer. (H u g g i n s (1949) f o u n d t h e a v e r a g e i n c u b a t i o n t e m p e r a t u r e of b i r d s t o be 34 d e g r e e s C.) S p r i n g and summer minimum and maximum t e m p e r a t u r e s a r e compared i n F i g u r e 8. A v e r a g e summer minimum t e m p e r a t u r e was s i g n i f i c a n t l y h i g h e r t h a n t h e s p r i n g minimum ( p < . 0 0 l ) and a v e r a g e summer maximum t e m p e r a t u r e was s i g n i f i c a n t l y h i g h e r t h a n t h e s p r i n g maximum (p<.001). S i x p e r c e n t of t h e r e c o r d e d 90 L A T E M I N I M U M M A X I M U M FIGURE 8 : Comparison of average maximum and minimum ambient temperatures early (when most Coots nest) and late in the season (when most Ruddy Ducks nest) 91 minimum t e m p e r a t u r e r e c o r d s i n s p r i n g were below f r e e z i n g , whereas t h e r e were no minimum t e m p e r a t u r e r e c o r d s a t or below f r e e z i n g i n t h e summer. T h i s d i f f e r e n c e was s i g n i f i c a n t t i t -t e s t , p<.001 . Ruddy Duck and A m e r i c a n C o o t N e s t T e m p e r a t u r e s T e m p e r a t u r e s of n e s t s known t o be i n t h e i n c u b a t i o n s t a g e were t a k e n d u r i n g t h e p e r i o d s when a m b i e n t t e m p e r a t u r e s were b e i n g m o n i t o r e d . T e m p e r a t u r e s of C o o t n e s t s were measured d u r i n g t h e May 27 t o June 19 p e r i o d , w h e r e a s t h e t e m p e r a t u r e s o f Ruddy Duck n e s t s were t a k e n d u r i n g t h e J u l y 10 t o A u g u s t 2 p e r i o d . T e m p e r a t u r e s were t a k e n , by p l a c i n g t h e b u l b of a m e r c u r y thermometer i n t h e c e n t e r of t h e n e s t and r e c o r d i n g t h e t e m p e r a t u r e a f t e r f i v e m i n u t e s . O f t e n C o o t s were f o u n d s i t t i n g on n e s t s and had t o be e n c o u r a g e d t o l e a v e so t h a t t e m p e r a t u r e measurements c o u l d be t a k e n . Ruddy f e m a l e s were n e v e r d i s c o v e r e d on t h e n e s t . A v e r a g e t e m p e r a t u r e of Ruddy Duck and A m e r i c a n Coot n e s t s were compared by S t u d e n t ' s t - t e s t . A v e r a g e Coot n e s t t e m p e r a t u r e was 24.1 d e g r e e s C , 6.6 d e g r e e s l e s s t h a n t h a t o f Ruddy Ducks (30.7 d e g r e e s C.) and s i g n i f i c a n t l y d i f f e r e n t a t p<.0005. 92 C o n c l u s i o n s Eggs warmed by i n c u b a t i o n c o o l e d more r a p i d l y i n t h e c o l d t e m p e r a t u r e s of s p r i n g t h a n i n summer. D a i l y minimum t e m p e r a t u r e s a t o r below f r e e z i n g o c c u r r e d more f r e q u e n t l y i n t h e s p r i n g and d a i l y maximum t e m p e r a t u r e s a p p r o a c h i n g i n c u b a t i o n t e m p e r a t u r e s o c c u r l e s s f r e q u e n t l y . Measurements of n e s t t e m p e r a t u r e when t h e f e m a l e was o f f t h e n e s t showed t h a t t h e a v e r a g e Ruddy Duck n e s t t e m p e r a t u r e was s i g n i f i c a n t l y h i g h e r t h a n t h e a v e r a g e C o o t s n e s t t e m p e r a t u r e . Such a d i f f e r e n c e d oes n o t mean t h a t Coot n e s t s were a l l o w e d t o c o o l t o l o w e r t e m p e r a t u r e s t h a n Ruddy Ducks, s i n c e b o t h m a l e s and f e m a l e s i n c u b a t e d and t h e n e s t was r a r e l y u n a t t e n d e d d u r i n g i n c u b a t i o n i f t h e y were l e f t u n d i s t u r b e d ; however, i f i n c u b a t i n g d u c k s o r C o o t s were d i s t u r b e d on t h e n e s t , r e d u c e d h a t c h i n g s u c c e s s i n t h e s p r i n g , due t o e x p o s u r e o f eggs t o c o l d , m i g h t r e s u l t . ( B a t t and C o r n w e l l (1972) showed t h a t some m o r t a l i t y o c c u r r e d when M a l l a r d eggs were e x p o s e d t o f r e e z i n g t e m p e r a t u r e s . ) In c o n t r a s t , s u c h d i s t u r b a n c e i n summer would be u n l i k e l y t o have t h e same e f f e c t on Ruddy Ducks b e c a u s e i t i s warmer when t h e y n e s t . I f a f e m a l e l e a v e s t h e n e s t u n a t t e n d e d f o r e x t e n d e d p e r i o d s of t i m e t o s e a r c h f o r f o o d , b r e e d i n g l a t e r i n t h e s e a s o n when t e m p e r a t u r e s a r e warmer c o u l d r e d u c e egg m o r t a l i t y . Ruddy f e m a l e s do l e a v e t h e n e s t more o f t e n t h a n o t h e r w a t e r f o w l s p e c i e s (Tome, 1981) p e r h a p s o u t o f n e c e s s i t y t o a v o i d s t a r v a t i o n . T h e r e i s c o n v i n c i n g e v i d e n c e t h a t Ruddy Ducks, u n l i k e o t h e r 93 w a t e r f o w l , u n d e r g o a wing m o l t p r i o r t o s p r i n g m i g r a t i o n ( J o y n e r , 1978). Ruddy f e m a l e s a l s o l a y v e r y l a r g e , eggs f o r a duck, of t h e i r body s i z e ( L a c k , 1968). A c l u t c h o f Ruddy eggs o f t e n w e i g hs more t h a n t h e f e m a l e w h i c h l a i d i t (Tome,1981). T h u s , t h e c o m b i n e d c o s t o f m o l t i n g , m i g r a t i n g , l a y i n g a c l u t c h of e g gs, and i n c u b a t i n g i t m i g h t be p r o h i b i t i v e , i f Ruddy f e m a l e s were u n a b l e t o f e e d b e c a u s e t h e y had t o s i t on t h e i r n e s t s c o n s t a n t l y t o a v o i d egg m o r t a l i t y . C o l d t e m p e r a t u r e s do not n e c e s s a r i l y r e s u l t i n egg m o r t a l i t y . When a b s e n c e s from t h e n e s t a r e f r e q u e n t but s h o r t and n e s t s a r e w e l l i n s u l a t e d w i t h down, eggs l i k e l y w ould n o t c o o l t o a m b i e n t t e m p e r a t u r e i n t h e a b s e n c e o f t h e f e m a l e . However, i n c u b a t i o n p e r i o d (number of d a y s eggs must be warmed b e f o r e h a t c h i n g o c c u r s ) may be a f f e c t e d by t h e t e m p e r a t u r e of t h e eggs ( N i c e , 1954). I f a m b i e n t t e m p e r a t u r e s a r e l o w e r , m a i n t a i n i n g a h i g h i n c u b a t i o n t e m p e r a t u r e p r o b a b l y becomes more d i f f i c u l t and d e v e l o p m e n t may s l o w when f e m a l e s l e a v e t h e n e s t and eggs c o o l . Thus, i t m i g h t be p o s s i b l e t o f u e l i n c u b a t i o n i n t h e e a r l y s p r i n g by t a k i n g f r e q u e n t s h o r t f e e d i n g b o u t s , b u t i n c u b a t i o n p e r i o d would l i k e l y be l e n g t h e n e d . S i n c e n e s t p r e d a t i o n a p p e a r s h e a v i e r i n t h e s p r i n g , l o n g e r i n c u b a t i o n p e r i o d s would mean p r o l o n g e d e x p o s u r e t o p r e d a t i o n . F i n a l l y , b e c a u s e Ruddy f e m a l e s i n c u b a t e when t e m p e r a t u r e s a r e warmer, t h e y may have h i g h e r s u r v i v a l r a t e s t h r o u g h t h e i n c u b a t i o n p e r i o d t h a n e a r l y b r e e d i n g s p e c i e s . F e m a l e s may be most v u l n e r a b l e t o p r e d a t o r s w h i l e s i t t i n g on t h e n e s t ( L a c k , 1954). S i n c e Ruddy Ducks spend l e s s t i m e s i t t i n g on t h e n e s t , 94 there w i l l be fewer opportunities for predators to attack them on the nest. 95 APPENDIX THREE Ne s t P r e d a t i o n o f F l a g g e d and C o n c e a l e d Dummy N e s t s E a r l y r e s u l t s o f t h e s p r i n g r e p l i c a t e of dummy n e s t e x p e r i m e n t A ( s e e C h a p t e r One) s u g g e s t e d t h a t p r e d a t o r s m i g h t have l o c a t e d dummy n e s t s by i n v e s t i g a t i n g marsh a r e a s n e a r t h e f l a g g i n g t a p e . (The a b i l i t y of crows t o a s s o c i a t e c o l o u r banded c a n e s w i t h t h e p r e s e n c e of eggs was d e m o n s t r a t e d by P i c o z z i ( 1 9 7 5 ) . ) A l t e r n a t e l y , p r e d a t o r s m i g h t have o b s e r v e d me i n t h e marsh when I was c o n s t r u c t i n g n e s t s and come t o i n v e s t i g a t e a f t e r I had l e f t . Heavy p r e d a t i o n o f dummy n e s t s i n t h e s p r i n g m ight have been c a u s e d by one o r b o t h o f t h e s e f a c t o r s , and t h e i r e f f e c t m i g h t have been g r e a t e r i n t h e s p r i n g when c o v e r was l e s s d e n s e . The e f f e c t on n e s t p r e d a t i o n , of f l a g g i n g t a p e and my p r e s e n c e i n t h e marsh d u r i n g n e s t b u i l d i n g i s d i s c u s s e d i n t h i s a p p e n d i x . A dummy n e s t e x p e r i m e n t ( e x p e r i m e n t B) was c o n d u c t e d f o r twe n t y f o u r d a y s b e g i n n i n g May 31, 1984, a week a f t e r e x p e r i m e n t A b e g a n . E i g h t dummy n e s t s ( r e f e r r e d t o h e r e a s u n f l a g g e d -u n c o n c e a l e d dummy n e s t s ) were c o n s t r u c t e d and m o n i t o r e d a s i n t h e f i r s t e x p e r i m e n t . The p o s i t i o n s o f t h e s e n e s t s were not marked by f l a g g i n g t a p e . I f f l a g g i n g t a p e p r o v i d e d a c l u e t o n e s t l o c a t i o n , i t was p r e d i c t e d t h a t p r e d a t o r s would f i n d t h e s e u n f l a g g e d n e s t s l e s s f r e q u e n t l y t h a n f l a g g e d n e s t s ( c o n s t r u c t e d i n dummy n e s t e x p e r i m e n t A ) . In a d d i t i o n , e i g h t dummy n e s t s ( r e f e r r e d t o h e r e a s u n f l a g g e d - c o n c e a l e d dummy n e s t s ) were b u i l t a t s i t e s w h i c h a f f o r d e d good o v e r h e a d c o v e r t o c o n c e a l eggs from b i r d s f l y i n g a b o v e . An u n f l a g g e d - c o n c e a l e d n e s t w o u l d be 96 d i f f i c u l t f o r a p r e d a t o r t o f i n d u n l e s s t h e p r e d a t o r h a d seen me b u i l d t h e n e s t . One c o n c e a l e d and one u n c o n c e a l e d n e s t were l o c a t e d on e a c h o f e i g h t ponds. B o t h u n f l a g g e d - u n c o n c e a l e d and u n f l a g g e d - c o n c e a l e d n e s t s c o n t a i n e d f i v e eggs and were l i k e t h e dummy n e s t s c o n s t r u c t e d i n e x p e r i m e n t A i n a l l o t h e r r e s p e c t s . R e s u l t s a r e p r e s e n t e d i n F i g u r e 9. P r e d a t i o n of u n f l a g g e d - u n c o n c e a l e d and u n f l a g g e d - c o n c e a l e d n e s t s i s compared t o p r e d a t i o n of f l a g g e d - u n c o n c e a l e d n e s t s ( i e . n e s t s c o n s t r u c t e d i n t h e s p r i n g p o r t i o n o f e x p e r i m e n t A ) . T h e r e was no s i g n i f i c a n t d i f f e r e n c e i n number o f n e s t s t h a t were p r e y e d upon between u n f l a g g e d - u n c o n c e a l e d and f l a g g e d - u n c o n c e a l e d dummy n e s t s . The number of c o n c e a l e d n e s t s t h a t were p r e y e d upon was s i g n i f i c a n t l y l o w e r t h a n t h e number o f u n c o n c e a l e d n e s t s t h a t t h a t were p r e y e d upon ( c h i - s q u a r e d c o n t i n g e n c y t e s t , p < . 0 0 l ) . C o n c l u s i o n s R e s u l t s o f e x p e r i m e n t B s u g g e s t e d t h a t n e i t h e r f l a g g i n g t a p e p l a c e d a t a d i s t a n c e from t h e n e s t n o r my- b e h a v i o r d u r i n g n e s t c o n s t r u c t i o n was r e s p o n s i b l e f o r t h e h i g h n e s t p r e d a t i o n r a t e s o b s e r v e d i n t h e s p r i n g . I f p r e d a t o r s f o u n d n e s t s by s e a r c h i n g a r e a s n e a r f l a g g i n g t a p e , I p r e d i c t e d t h a t fewer u n f l a g g e d t h a n f l a g g e d n e s t s would be d e s t r o y e d by p r e d a t o r s . S i m i l a r l y , i f p r e d a t o r s f o u n d n e s t s s o l e l y by i n v e s t i g a t i n g a r e a s n e a r where t h e y o b s e r v e d me b u i l d i n g dummy n e s t s , I p r e d i c t e d t h a t n e s t p r e d a t i o n o f c o n c e a l e d and u n c o n c e a l e d n e s t s w o u l d be s i m i l a r . N e i t h e r of t h e s e p r e d i c t i o n s was c o n f i r m e d by t h e e x p e r i m e n t s . 97 O O -i n =30 o CO n r 8 a ID a *9 n = 8 o (VI o -J-FLA66E0 UNFLAGGED UNFLA66E0 UNCONCEALED UNCONCEALEO CONCEALEO FIGURE 9 : Comparison of the e f f e c t of f l a g g i n g and nest concealment on the p r o p o r t i o n s of dummy nest p r e d a t i o n 98 APPENDIX FOUR Gr e e n V e g e t a t i o n and t h e C l u t c h I n i t i a t i o n of Ruddy Ducks S i e g f r i e d (1976a) f o u n d t h a t t h e t i m i n g of n e s t i n g i n Ruddy Ducks was c o r r e l a t e d w i t h t h e a v a i l a b i l i t y o f g r e e n n e s t i n g c o v e r . He s u g g e s t e d t h a t f e m a l e s were p h y s i o l o g i c a l l y r e a d y t o l a y e a r l y i n t h e s p r i n g , but r e q u i r e d g r e e n v e g e t a t i o n f o r n e s t b u i l d i n g . Thus, t h e y d e l a y e d n e s t i n g u n t i l g r e e n v e g e t a t i o n was a v a i l a b l e o r l a i d eggs p a r a s i t i c a l l y i n t h e n e s t s of o t h e r b i r d s . D a t a t h a t r e f u t e S i e g f r i e d ' s i d e a s a r e p r e s e n t e d i n t h i s a p p e n d i x . I d i s c u s s i n f o r m a t i o n on n e s t c o m p o s i t i o n , n e s t i n i t i a t i o n , and t h e t i m i n g of n e s t p a r a s i t i s m o f Ruddy Ducks i n t h e C h i l c o t i n r e g i o n of B r i t i s h C o l u m b i a i n 1983 and 1984. •Data on s e a s o n a l v a r i a t i o n i n g r e e n v e g e t a t i o n h e i g h t a r e a l s o p r e s e n t e d . N e s t C o m p o s i t i o n A l l Ruddy Duck n e s t s I d i s c o v e r e d i n t h e B e e c h e r ' s P r a i r i e s t u d y a r e a were examined t o d e t e r m i n e whether t h e y were c o n s t r u c t e d of g r e e n or dead v e g e t a t i o n . On a v e r a g e , f o r t y -s e v e n p e r c e n t o f t h e s e n e s t s were c o n s t r u c t e d c o m p l e t e l y f r o m dead v e g e t a t i o n (1983: 38.5% n=13 n e s t s ; 1984: 50.0% n=30). T h e r e was no t e n d e n c y f o r n e s t s c o n s t r u c t e d o f d e ad v e g e t a t i o n t o o c c u r more f r e q u e n t l y e i t h e r e a r l y o r l a t e i n t h e s e a s o n . 99 L a y i n g C h r o n o l o g y The d a t e t h a t t h e f i r s t egg was l a i d i n e a c h n e s t ( c l u t c h i n i t i a t i o n ) was e s t a b l i s h e d by s u b t r a c t i n g f r o m t h e h a t c h i n g d a t e , t h e i n c u b a t i o n p e r i o d (24 d a y s - B e l l r o s e , 1980) and t h e t o t a l number of eggs i n t h e c l u t c h (eggs a r e l a i d a t a r a t e of one p e r d a y ) . H i s t o g r a m s c o m p a r i n g number of n e s t s v e r s u s week i n t h e b r e e d i n g s e a s o n a r e g i v e n f o r 1983 and 1984 i n F i g u r e 10. In 1983, t h e e a r l i e s t Ruddy Duck c l u t c h i n i t i a t i o n was May 22 and t h e l a t e s t was J u l y 18 and most Ruddy c l u t c h e s were i n i t i a t e d between June 18 and J u l y 5. In 1984, t h e e a r l i e s t Ruddy n e s t was i n i t i a t e d on June 17 w h i l e t h e l a t e s t was J u l y 24 and n e s t i n i t i a t i o n was q u i t e e v e n l y d i s t r i b u t e d between t h e s e two d a t e s . E x c e p t f o r t h e e a r l y c l u t c h - , ( i n i t i a t e d i n May, 1983), l a y i n g c h r o n o l o g y i n t h e two y e a r s was s i m i l a r . A l t h o u g h s m a l l sample s i z e may have m i s r e p r e s e n t e d t h e t r u e t i m i n g o f c l u t c h e s i n 1983, l a r g e samples i n 1984 e l i m i n a t e d t h i s p o s s i b i l i t y . C o n s i d e r a b l e v a r i a t i o n i n l a y i n g c h r o n o l o g y e x i s t s between p o p u l a t i o n s o f Ruddy Ducks. J o y n e r (1975) s t u d i e d Ruddy Ducks i n U t a h and f o u n d t h a t l a y i n g began i n l a t e A p r i l and c e a s e d i n l a t e J u n e . In c o n t r a s t , Hudson (1976) r e p o r t e d t h a t Ruddy d u c k l i n g s i n E n g l a n d were u s u a l l y r a i s e d i n J u l y and A u g u s t , as t h e y a r e i n B r i t i s h C o l u m b i a . 100 09 -| m o 01 a UJ CO r-ul Ul z li. o or tu co X Z ro at a ui u r-0) (E Ul ffl X 10 -o J- 1 1 2 3 4 5 6 7 8 9 10 WEEK IN THE NESTING SEASON LEGEND WEEK 1- MAY 20-26 WEEK 2- MAY 27-JUNE 2 WEEK 3- JUNE 3-9 WEEK 4- JUNE 10-16 WEEK 5- JUNE 17-23 WEEK 6- JUNE 24-30 WEEK 7- JULY 1-7 WEEK 8- JULY 8-14 WEEK 9- JULY 15-21 WEEK 10- JULY 22-28 1 2 3 4 5 6 7 8 9 10 WEEK IN THE NESTING SEASON FIGURE 10 : C o m p a r i s o n of Ruddy Duck c l u t c h i n i t i a t i o n i n 1983 and 1984. 101 S e a s o n a l P a t t e r n s i n V e g e t a t i o n Growth In 1983, a v e r a g e h e i g h t of g r e e n v e g e t a t i o n was e s t a b l i s h e d by m e a s u r i n g t h e h e i g h t above w a t e r o f f i v e b u l r u s h ( s c i r p u s ) s h o o t s a t e a c h o f e l e v e n s t a t i o n s on a s i n g l e pond. D a t a were g a t h e r e d f i v e t i m e s d u r i n g t h e b r e e d i n g s e a s o n : May 13, May 30, June 30, J u l y 12, and J u l y 25. In 1984, t h e same pond was s t u d i e d but t h e number o f s t a t i o n s m o n i t o r e d was i n c r e a s e d t o 30 and s e v e n s h o o t s were measured a t e a c h s t a t i o n . D a t a were c o l l e c t e d f o u r t i m e s : May 13, May 31, June 15, J u l y 17. In F i g u r e 11, a v e r a g e h e i g h t of g r e e n v e g e t a t i o n i s p l o t t e d a g a i n s t c a l e n d a r d a t e f o r t h e s p r i n g and summer of 1983 and 1984. W h i l e g r e e n v e g e t a t i o n s h o o t s emerged above t h e w a t e r s u r f a c e by mid-May i n b o t h y e a r s , t h e s e s h o o t s were p r o b a b l y n o t t a l l enough f o r n e s t b u i l d i n g u n t i l m i d - J u n e . In b o t h y e a r s , Ruddy f e m a l e s began l a y i n g when g r e e n v e g e t a t i o n h e i g h t a v e r a g e d 70 t o 80 cm; however, g r e e n v e g e t a t i o n h e i g h t l i k e l y does n o t d e t e r m i n e when c l u t c h e s a r e i n i t i a t e d . F e m a l e s must have a s s e s s e d green- v e g e t a t i o n h e i g h t s e v e r a l weeks b e f o r e l a y i n g o c c u r r e d , s i n c e t i m e i s r e q u i r e d f o r t h e a p p r o p r i a t e p h y s i o l o g i c a l c h a n g e s w h i c h b r i n g f e m a l e s i n t o r e p r o d u c t i v e c o n d i t i o n . B e c a u s e g r e e n v e g e t a t i o n h e i g h t p r i o r t o l a y i n g was c o n s i d e r a b l y l o w e r i n 1984 (between 20 and 40 cm l o w e r ) , w h i l e c l u t c h i n i t i a t i o n began i n t h e same week i n b o t h y e a r s , i t seems l i k e l y t h a t some o t h e r f a c t o r d e t e r m i n e s when Ruddy Ducks b r e e d . 102 10 CV X So S-z o M rn ¥— . ? ° UJ CO UJ > ID Z O UJ UJ cc CO ^ < o 2 - * X • • X • X X X • MAY 1 1 JUNE 1 I JULY 1 j AUG 1 F I G U R E 11 Comparison of seasonal changes in average green v e g e t a t i o n height in 1983 (X) and 1984 (sq u a r e s ) . 1 03 N e s t P a r a s i t i s m N e s t p a r a s i t i s m was not d e t e c t e d p r i o r t o t h e o n s e t of Ruddy Duck l a y i n g i n e i t h e r y e a r . Dummy n e s t s , s e t up t o m o n i t o r n e s t p r e d a t i o n r a t e s and am b i e n t t e m p e r a t u r e s i n 1984 ( s e e c h a p t e r one and A p p e n d i x Two), a p p a r e n t l y d i d not s t i m u l a t e p a r a s i t i c l a y i n g e a r l y i n t h e s e a s o n , s i n c e no Ruddy eggs were f o u n d i n t h e s p r i n g dummy n e s t s . In c o n t r a s t , some summer dummy n e s t s were p a r a s i t i z e d s u g g e s t i n g t h a t p a r a s i t i c n e s t i n g and n o r m a l n e s t i n g o c c u r r e d s i m u l t a n e o u s l y , r a t h e r t h a n t h e f o r m e r p r e c e d i n g t h e l a t t e r . A s i m i l a r r e s u l t was r e p o r t e d by J o y n e r ( 1 9 8 3 ) . C o n c l u s i o n s B e c a u s e n e a r l y 50% o f a l l Ruddy Duck n e s t s were c o n s t r u c t e d w i t h dead v e g e t a t i o n o n l y , t h e s u g g e s t i o n t h a t g r e e n v e g e t a t i o n d e l a y s b r e e d i n g i n t h i s s p e c i e s seems u n l i k e l y . T h i s s t u d y shows t h a t w h i l e most Ruddy Ducks b r e e d when g r e e n v e g e t a t i o n i s abundant ( a f t e r June 1 5 ) , many Ruddy Ducks do not use g r e e n v e g e t a t i o n f o r c o n s t r u c t i n g t h e n e s t and one Ruddy f e m a l e n e s t e d b e f o r e most g r e e n v e g e t a t i o n i n t h e marsh had emerged more t h a n 20 cm above t h e water ( c l u t c h i n i t i a t e d i n mid t o l a t e May 1983). M i s t e r e k (1974) and J o y n e r (1975) a l s o r e p o r t e d t h a t some Ruddy f e m a l e s began l a y i n g eggs b e f o r e g r e e n v e g e t a t i o n was a v a i l a b l e f o r n e s t b u i l d i n g . F u r t h e r m o r e , nest' p a r a s i t i s m a p p e a r s t o be most p r e v a l e n t a f t e r g r e e n v e g e t a t i o n i s abu n d a n t 1 04 ( l a t e June and J u l y ) and thus, the lack of s u i t a b l e n e s t i n g m a t e r i a l e a r l y i n the season cannot e x p l a i n why Ruddy females la y p a r a s i t i c a l l y r a ther than n e s t i n g normally. 

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