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Breeding distribution, habitat selection and factors affecting coloniality in eared grebes in British… Breault, Andre Mario 1990

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BREEDING DISTRIBUTION, HABITAT SELECTION AND FACTORS AFFECTING COLONIALITY IN EARED GREBES IN BRITISH COLUMBIA By ANDRE MARIO BREAULT B.Sc, U n i v e r s i t y de Sherbrooke, 1984 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF ZOOLOGY We accept t h i s t h e s i s as conforming to the required standard May, 1990 © Andre* Mario Breault, 1990 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 The University of British Columbia Vancouver, Canada DE-6 (2/88) ABSTRACT In t h i s study, I f i r s t d e s c r i b e d i s t r i b u t i o n and abundance of b r e e d i n g Eared Grebes {Podiceps n i g r i c o l l i s ) i n B r i t i s h Columbia. Second, I c h a r a c t e r i z e and examine the r e l a t i o n s h i p s between n e s t i n g h a b i t a t and nest s i t e s e l e c t i o n on b r e e d i n g group s i z e . F i n a l l y , I. examine e f f e c t s of c o l o n y s i z e , n e s t i n g c h r o n o l o g y and n e s t i n g synchrony on r e p r o d u c t i v e success a t Eared Grebe c o l o n i e s . I surveyed 421 wetlands i n 1985 and 1986 and l o c a t e d 47 l a k e s used by n e s t i n g Eared Grebes. Those 47 l a k e s accomodated from a low e s t i m a t e o f 1761 t o a h i g h e s t i m a t e of 4474 p a i r s . B r e e d i n g abundance, c a l c u l a t e d from a d u l t , nest and young counts, ranged from s i n g l e p a i r s t o more than 590 p a i r s per l a k e . B r e e d i n g took p l a c e i n s h a l l o w l a k e s o f v a r i o u s s i z e s , s u b j e c t t o e x t e n s i v e v a r i a t i o n s i n water l e v e l s . B r e e d i n g abundance was p o s i t i v e l y c o r r e l a t e d w i t h l a k e a r e a . Fewer b r e e d i n g p a i r s u t i l i z e d n e s t i n g areas c l o s e t o shore ( i n s h a l l o w e r water) than n e s t i n g areas f a r from shore ( i n deeper w a t e r s ) . N e s t i n g areas c l o s e t o shore were found i n s m a l l e r l a k e s and were used l e s s o f t e n i n c o n s e c u t i v e y e a r s than n e s t i n g areas f a r from shore, presumably because of lower h a b i t a t p r e d i c t a b i l i t y . An experiment w i t h unattended a r t i f i c i a l n ests showed t h a t nest p r e d a t i o n was h i g h e r f a r from shore t h a n c l o s e t o shore. N e s t i n g areas c l o s e t o shore were used by s m a l l groups. These maximized concealment by b e i n g l o c a t e d i n denser v e g e t a t i o n . N e s t i n g areas f a r from shore were used by l a r g e r groups and were l o c a t e d i n more open areas. On both years, a d u l t s a r r i v e d at n e s t i n g lakes i n A p r i l and May, s t a r t e d l a y i n g on 27 May and departed from, n e s t i n g areas i n l a t e J u l y and- e a r l y August. Nesting was s i g n i f i c a n t l y e a r l i e r and reproductive success per p a i r was s i g n i f i c a n t l y higher i n 1985 than i n 1986. A .stepwise m u l t i p l e r e g r e s s i o n examined e f f e c t s of colony-s i z e , synchrony and chronology on n e s t i n g success. Only nesting chronology accounted f o r d i f f e r e n c e s i n n e s t i n g success. Late nesters were not b i r d s attempting to renest. Instead, there appeared to be q u a l i t a t i v e d i f f e r e n c e s across c o l o n i e s that were r e l a t e d to ages of breeders. Eared Grebe c o l o n i e s are l i k e l y not formed from passive aggregation at l i m i t i n g resources and there are l i k e l y no f o r a g i n g b e n e f i t s from c o l o n i a l n e s ting. Nesting c o l o n i e s could increase d e t e c t i o n and mobbing of predators, but no evidence supported t h i s . A n t i - p r e d a t o r b e n e f i t s of c o l o n i a l i t y might have been masked by d i f f e r e n c e s i n breeding chronology and synchrony, or were missed because of low sample s i z e . TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES v i i i LIST OF FIGURES " i x ACKNOWLEDGMENTS x i CHAPTER 1: General i n t r o d u c t i o n 1 1- Management concerns 3 2- T h e o r e t i c a l c o n s i d e r a t i o n s 6 CHAPTER 2: D i s t r i b u t i o n and abundance of Eared Grebes i n B r i t i s h Columbia 11 In t r o d u c t i o n 12 Methods 14 1- Surveys on abundance of breeders 14 2- E s t i m a t i n g abundance of breeders 20 3- S t a t i s t i c s 23 Results 24 1- Breeding d i s t r i b u t i o n and abundance 24 2- Number of breeding p a i r s 28 Di s c u s s i o n 30 1- D i s t r i b u t i o n and abundance i n B.C 30 2- Surveying techniques 32 Summary 33 CHAPTER 3: Habitat c h a r a c t e r i s t i c s , nest s i t e s e l e c t i o n and breeding group s i z e i n Eared Grebes 34 i v I n t r o d u c t i o n 35 1- Breeding h a b i t a t 35 2- E c o l o g i c a l c o r r e l a t e s of breeding group s i z e . . . . 36 3- Nest s i t e s e l e c t i o n 37 4- A n t i - p r e d a t o r value of nest s i t e s 38 Methods 40 1- Lake c h a r a c t e r i z a t i o n 40 2- E c o l o g i c a l c o r r e l a t e s of breeding abundance: . . . . 41 3- Nest s i t e s e l e c t i o n 42 4- A n t i - p r e d a t o r value of nest s i t e 43 Results 45 1- P h y s i c a l c h a r a c t e r i s t i c s of breeding lakes 45 2- E f f e c t s of a b i o t i c f a c t o r s on breeding d e n s i t y . . . 49 3- Nest s i t e s e l e c t i o n 50 4- A n t i - p r e d a t o r value of nest s i t e l o c a t i o n . . . . . 53 Di s c u s s i o n 56 1- Breeding h a b i t a t 56 2- C o r r e l a t e s of breeding group s i z e 57 3- Nest s i t e l o c a t i o n 59 4- A n t i p r e d a t o r value of nest s i t e s 60 Summary 64 CHAPTER 4: C o l o n i a l i t y and f a c t o r s a f f e c t i n g r eproductive success i n Eared Grebes c o l o n i e s 65 In t r o d u c t i o n 66 Methods 69 v 1- Study s i t e 69 2- Surveys 70 3- Colony s i z e 70 4- Reproductive b i o l o g y 70 5- C o r r e l a t e s of reproductive success 73 6- M u l t i p l e stepwise r e g r e s s i o n on reproductive success 74 7- I n d i v i d u a l q u a l i t y across c o l o n i e s 74 Results 75 1- Reproductive b i o l o g y 75 2- U n i v a r i a t e analyses of f a c t o r s a f f e c t i n g r eproductive success • 78 3- M u l t i p l e stepwise r e g r e s s i o n on f l e d g i n g success . . 83 4- I n d i v i d u a l q u a l i t y across c o l o n i e s 83 D i s c u s s i o n 86 1- Breeding chronology 86 2- Reproductive success 87 3- C o l o n i a l i t y and f a c t o r s a f f e c t i n g r e p r o d u c t i v e success 88 Summary 94 CHAPTER 5: General d i s c u s s i o n 95 1- Breeding b i o l o g y of Eared Grebes 96 A) D i s t r i b u t i o n and abundance 96 B) Nesting h a b i t a t 97 2- Importance of h a b i t a t p r e d i c t a b i l i t y 98 A) D i s t r i b u t i o n 99 B) P h i l o p a t r y 99 v i 3- C o l o n i a l i t y i n Eared Grebes 100 A) Resource l i m i t a t i o n hypothesis 101 B) Foraging b e n e f i t s 102 C) A n t i - p r e d a t i o n b e n e f i t s 103 4- Breeding chronology and synchrony 104 5- Conservation and management i 106 A) How to survey Eared Grebes 106 B) Management p r i o r i t i e s 107 LITERATURE CITED 110 Appendix 1. C a l c u l a t i o n of breeding abundance from chick counts 121 Appendix 2. Estimated number of Eared Grebe p a i r s i n the Northern Okanagan/Kamloops area 122 Appendix 3. Estimated number of Eared Grebe p a i r s i n the Peace River area 123 Appendix 4. Estimated number of Eared Grebe p a i r s i n the Southern I n t e r i o r area 124 Appendix 5. Estimated number of Eared Grebe p a i r s i n the C e n t r a l I n t e r i o r area 125 v i i 3- C o l o n i a l i t y i n Eared Grebes 100 A) Resource l i m i t a t i o n hypothesis 101 B) Foraging b e n e f i t s 102 C) A n t i - p r e d a t i o n b e n e f i t s 103 4- Breeding chronology and synchrony 104 5- Conservation and management 106 A) How to survey Eared Grebes 106 B) Management p r i o r i t i e s 107 LITERATURE CITED 110 Appendix 1. C a l c u l a t i o n of breeding abundance-from chick counts 121 Appendix 2. Estimated number of Eared Grebe p a i r s i n the Northern Okanagan/Kamloops area 122 Appendix 3. Estimated number of Eared Grebe p a i r s i n the Peace River area 123 Appendix 4. Estimated number of Eared Grebe p a i r s i n the Southern I n t e r i o r area 124 Appendix 5. Estimated number of Eared Grebe p a i r s i n the C e n t r a l I n t e r i o r area 125 v i i LIST OF TABLES Table r . Surveying e f f o r t at Eared Grebe breeding lakes i n B r i t i s h Columbia i n 1985 and 1986 18 Table I I . Lake morphology at selected Eared Grebe breeding lakes 46 Table I I I . Water chemistry c h a r a c t e r i s t i c s and lake area of Eared Grebe breeding lakes i n B.C 48 Table IV. Water chemistry readings on 3 June and 10 J u l y 1986 . 49 Table V. Habitat c h a r a c t e r i s t i c s (+se) of breeding lakes with Eared Grebe nests located close to and f a r from shore 51 v i i i LIST OF FIGURES F i g u r e 1: Zones with p o t e n t i a l breeding h a b i t a t f o r Eared Grebes 16 Figure 2: Areas surveyed i n 1985 and 1986 to l o c a t e Eared Grebe breeding lakes 17 Figure 3. Number of breeding p a i r s per lake and d i s t r i b u t i o n of the breeding p o p u l a t i o n (%) across lakes 29 Figure 4. Number of breeding p a i r s (a), b) lake area, c) hardness and d) water depth at nest (+SE) f o r lakes where n e s t i n g areas are l o c a t e d c l o s e and f a r from shore 52 Figure 5. Comparison of the number of eggs l e f t i n a r t i f i c i a l p latforms (+SE) a f t e r 4 days i n r e l a t i o n to a) nest l o c a t i o n f o r nests with covered eggs, b) egg cover f o r nests f a r from shore and c) nest concealment f o r nests f a r from shore 54 Figure 6. Comparison of the number of eggs l e f t i n a r t i f i c i a l p latforms (+SE) a f t e r 8 days i n r e l a t i o n to a) nest l o c a t i o n f o r nests with covered eggs, b) egg cover f o r nests f a r from shore and c) nest concealment f o r nests f a r from shore 55 Figure 7. Adu l t s surveys on breeding lakes i n the Riske Creek area i n 1985 and 1986 76 Figure 8. Date of c l u t c h i n i t i a t i o n f o r a l l n e s t i n g attempts i n the Riske-Creek area i n 1985 and 1986 77 Figure 9. C o r r e l a t i o n between number of young hatched and number of young f l e d g e d i n 1985 and 1986 79 i x Figure 10. R e l a t i o n s h i p s between c l u t c h i n i t i a t i o n date and a) c l u t c h s i z e , b) number of nests hatched per p a i r , c) number of eggs hatched per s u c c e s s f u l nest and d) number of young fledge d per p a i r i n 1985 80 Figu r e 11. R e l a t i o n s h i p s between c l u t c h i n i t i a t i o n date and a) c l u t c h s i z e , b) number of nests hatched per p a i r , c) number of eggs hatched per s u c c e s s f u l nest and d) number of young fledged per p a i r i n 1985 81 Figure 12. C o r r e l a t i o n between colony s i z e and a) c l u t c h s i z e , b) number of nests hatched per p a i r , c) number of eggs hatched per s u c c e s s f u l nest and d) number of young fledge d per p a i r i n 1985 84 Figure 13. C o r r e l a t i o n between colony s i z e and a) c l u t c h s i z e , b) number of nests hatched per p a i r , c) number of eggs hatched per s u c c e s s f u l nest and d) number of young fledge d per p a i r i n 1986 85 x ACKNOWLEDGMENTS Several people and o r g a n i z a t i o n s made t h i s study p o s s i b l e . I wish to thank volunteers and f i e l d a s s i s t a n t s : Catherine Choquette, Emma N e i l l , P h i l Ranson and one Canadian W i l d l i f e S e r v i c e summer student. Bob Emery volunteered surveying time i n the Peace River and Riske Creek areas. The Williams Lake N a t u r a l i s t Club and the B.C. Federation of N a t u r a l i s t s k i n d l y p r i n t e d a request f o r i n f o r m a t i o n on breeding d i s t r i b u t i o n of Eared Grebes i n t h e i r r e s p e c t i v e newsletters, while the B.C. Royal Museum allowed access to n e s t i n g records. I am t h a n k f u l to Ed Hennan, Murray Clarke, Ron Boychuck, Rori Brown, and Ian Barnett (Ducks U n l i m i t e d Canada) and to Sean Boyd and Dave Smith (Canadian W i l d l i f e Service) f o r s t i m u l a t i n g d i s c u s s i o n s on waterfowl ecology and access to unpublished wetland inventory reports and f i e l d surveys. S p e c i a l thanks go to Bryan N u t t a l l f o r extensive f i e l d a s s i s t a n c e and f o r making Williams Lake a more i n t e r e s t i n g p l a c e to be. I b e n e f i t e d from d i s c u s s i o n s and advice from the l a t e " P r e c o c i a l B i r d s D i s c u s s i o n Group" (J. Smith, K. Cheng, A. Somerville, P. Arcese, G. Gauthier, W. Hochachka, J . Eadie and J.P. Savard); from J. F j e l d s a , G. Nuechterlein, M. Buitron, C. Brown, A. M i l l e r ; J . Boe; C. N i c h o l s ; and from IARE t r a n s i e n t s who shared s p i r i t s , humor x i and new i n s i g h t s on o l d problems. I a l s o thank a 16th century philo s o p h e r (Don Marquis) f o r an obscure quote appropriate to advanced s t u d i e s . He wrote: " I f you make people b e l i e v e they think, they w i l l love you; i f you make them think, they w i l l curse you." I thank my supervisory committee, K. Cheng, J. Smith, L. Gass and N. Verbeek f o r advice, encouragement, support and s p e c i a l l y p a t i e n c e . I a l s o wish to thank the Canadian W i l d l i f e Service f o r supporting f i n a n c i a l l y and l o g i s t i c a l l y t h i s p r o j e c t . J-P. Savard was a d r i v i n g f o r c e behind t h i s study and he deserves s p e c i a l thanks. F i n a n c i a l support was provided by World W i l d l i f e Fund (Canada) , the Canadian W i l d l i f e S e r v i c e U n i v e r s i t y Research Support Fund and a Natura l Sciences and Engineering Research C o u n c i l of Canada grant to K. Cheng. x i i CHAPTER 1: GENERAL INTRODUCTION 1 Eared Grebes (Podiceps n i g r i c o l l i s ) breed c o l o n i a l l y throughout the Northern Hemisphere (Palmer 1962; Cramp and Simmons 1977) and i n Northern A f r i c a (Cramp and Simmons 1977). Small populations are al s o found i n South A f r i c a ( L i v e r s i d g e and McLachlan 1957; Broekhuisen 1963) and i n South America (Jehl 1988). The North American breeding range centers on the Northern Great P l a i n s and the Great Basin (Palmer 1962; J e h l 1988), with B r i t i s h Columbia at the northwestern l i m i t of the range. Although the breeding d i s t r i b u t i o n i s r e l a t i v e l y w e l l e s t a b l i s h e d i n North America, no q u a n t i t a t i v e s t u d i e s have yet focused on r e g i o n a l breeding p o p u l a t i o n s . In B r i t i s h Columbia, known breeding c o l o n i e s are concentrated over small i s o l a t e d areas (Munro 1941; 1942; M c A l l i s t e r 1956; 1958; Campbell and Garr i o c h 1978; Campbell et al. 1979; Campbell et al. i n press) i n or near areas of extensive a g r i c u l t u r a l , i n d u s t r i a l or r e c r e a t i o n a l use. The Canadian W i l d l i f e S e r v i c e ( P a c i f i c and Yukon Region) ranked Eared Grebes amongst the top 15 species l e a s t s t udied i n a p r i o r i t y migratory b i r d species l i s t (Boyd 1982). E f f e c t i v e management and p r o t e c t i o n of the species depends upon d e t a i l e d knowledge of d i s t r i b u t i o n , abundance and breeding b i o l o g y , which are a l l c u r r e n t l y l a c k i n g f o r B r i t i s h Columbia and the r e s t of North America. Breeding b i o l o g y of Eared Grebes presents i n t e r e s t i n g t h e o r e t i c a l problems. Although Eared Grebes are considered c o l o n i a l 2 nesters, breeding groups range from 1 to 2600 p a i r s (Palmer 1962). C o l o n i a l and s o l i t a r y nesters can be found i n the same general area, a l l o w i n g the study of cost and b e n e f i t s of c o l o n i a l n e s ting. Further, water l e v e l s on n e s t i n g grounds f l u c t u a t e widely w i t h i n and between years (Cramp and Simmons 1977), a f f e c t i n g food and nesti n g h a b i t a t • a v a i l a b i l i t y . The c o n s t r a i n t s ( i f any) that h a b i t a t v a r i a b i l i t y p laces on c o l o n i a l n e s t i n g are unknown. This study combines 1) management concerns and 2) t h e o r e t i c a l c o n s i d e r a t i o n s . The management o b j e c t i v e of t h i s study i s to c h a r a c t e r i z e breeding b i o l o g y , d i s t r i b u t i o n and abundance of Eared Grebes i n B.C. Known breeding areas are subject to h a b i t a t t h r e a t s (see below), whose p o t e n t i a l impacts on breeding populations cannot be assessed due to l a c k of information on d i s t r i b u t i o n and bi o l o g y of the sp e c i e s . The t h e o r e t i c a l o b j e c t i v e i s to c h a r a c t e r i z e c o l o n i a l i t y i n Eared Grebes. Each o b j e c t i v e w i l l be considered s e p a r a t e l y . 1- Management concerns Eared Grebes are not only c o l o n i a l nesters but a l s o h i g h l y gregarious i n winter and on var i o u s s t a g i n g p o i n t s d u r i n g migration. Concentrations of over 20,000 have been observed on Malheur Refuge, Oregon during s p r i n g migration (Palmer 1962). Each f a l l , some 3 750,000 b i r d s concentrate on Mono Lake, C a l i f o r n i a f o r t h e i r wing moult (Cooper et al. 1984; Storer and J e h l 1985; Winkler and Cooper 1986; J e h l 1988) . Over h a l f a m i l l i o n i n d i v i d u a l s winter on the Salton Sea i n C a l i f o r n i a (Palmer 1962). Gregariousness on breeding and w i n t e r i n g grounds r a i s e s the p o s s i b i l i t y of l o c a l i z e d i n c i d e n t s a f f e c t i n g l a r g e p o r t i o n s of populations (Jehl and Bond 1983). In B r i t i s h Columbia, lakes chosen f o r n e s t i n g are shallow, h i g h l y p r o d u c t i v e water bodies p r o v i d i n g nest cover and abundant aquatic i n v e r t e b r a t e food (Campbell et al. i n p r e s s ) . Major f a c t o r s a f f e c t i n g or t h r e a t e n i n g n e s t i n g h a b i t a t i n B.C. are: A- Natu r a l v a r i a t i o n s i n water l e v e l s Seasonal water l e v e l f l u c t u a t i o n s may f l o o d , destroy or expose whole Eared Grebe c o l o n i e s to pr e d a t i o n (Munro 1941, Cramp and Simmons 1977). B- Man-caused a l t e r a t i o n s of breeding h a b i t a t i ) - Impact of o i l e x p l o r a t i o n D r i l l i n g s i t e s have sometimes been l o c a t e d on Eared Grebe breeding lakes (e.g. Boundary Lake). O i l e x p l o r a t i o n a l s o i n v o l v e s c o n s t r u c t i o n of access roads, i n c r e a s e d a c c e s s i b i l i t y to nesting areas and sulphur gas re l e a s e s at d r i l l i n g s i t e s . No information i s 4 a v a i l a b l e on the frequency and impact of those disturbances. i i ) - A g r i c u l t u r a l p r a c t i c e s Ranching and farming p r a c t i c e s a f f e c t wetlands i n several ways. Most commonly, wetlands are drained to create sedge meadows, pasture areas or arable land, r e s u l t i n g i n l o s s of foraging and/or nesting areas. Water can also be used to i r r i g a t e f i e l d s , which can r e s u l t i n decreased water l e v e l s and could leave nests stranded on dry ground. i i i ) - Water l e v e l c o n t r o l s Organizations such as Ducks Unlimited preserve wetlands by a c q u i r i n g water r i g h t s and by c o n t r o l l i n g water l e v e l s . Water con t r o l s can have p o s i t i v e or negative e f f e c t s on plant and i n v e r t e b r a t e populations, depending on timing and water volumes a f f e c t e d (Kadlec 1962; Meeks 1969), and hence may a f f e c t Eared Grebes. Ducks Unlimited i s considering a c q u i r i n g water r i g h t s for d i f f e r e n t nesting lakes i n the Central and Southern I n t e r i o r regions (e.g. L i t t l e White, Elkhorn and McMurray Lakes); these are c u r r e n t l y used by a t o t a l of roughly 1000 nesting p a i r s . iv) - Composition of the vertebrate community Eared Grebes feed on aquatic and land i n s e c t s and t h e i r larvae (Munro 1941; Palmer 1962) . Eared Grebes do not nest on lakes where f i s h are present (pers. obs.). Introduction of f i s h for 5 r e c r e a t i o n a l purposes might g r e a t l y a f f e c t i n v e r t e b r a t e a v a i l a b i l i t y , as f i s h w i l l compete w i t h grebes f o r preys (Wetzel 1975; E r i k s s o n 1979; Anderson 1981a; Eadie and Keast 1982; Des Granges and Brodeur 1985). A p a r t from h a v i n g t h e i r b r e e d i n g h a b i t a t t h r e a t e n e d , Eared Grebes are a l s o s u s c e p t i b l e t o d i s t u r b a n c e by humans and ot h e r animals (Campbell et al. 1979) d u r i n g l a y i n g and i n c u b a t i o n . D i s t u r b a n c e s a t those times causes them t o l e a v e t h e i r n e s t s , and unattended n e s t s are s u b j e c t t o p r e d a t i o n (Riske 1975) . R e c r e a t i o n a l development a l o n g shores, i n c r e a s e d i n d u s t r i a l , a g r i c u l t u r a l or r e c r e a t i o n a l a c t i v i t i e s c l o s e t o b r e e d i n g areas may d i s t u r b i n c u b a t i n g b i r d s , and c o u l d e v e n t u a l l y reduce r e p r o d u c t i v e success or cause c o l o n y abandonment. 2- T h e o r e t i c a l c o n s i d e r a t i o n s B i r d c o l o n i e s are p l a c e s where a number o f i n d i v i d u a l s o r p a i r s nest a t a more or l e s s c e n t r a l i z e d l o c a t i o n which they r e c u r r e n t l y d epart t o fo r a g e (Wittenberger 1985; K h a r i t o n o v and Siegel - C a u s e y 1988). P a s s i v e a g g r e g a t i o n at l i m i t i n g r e s o u r c e s and b e n e f i t s d e r i v e d from t h e presence o f c o n s p e c i f i c s can b o t h l e a d t o the f o r m a t i o n o f b i r d c o l o n i e s . F i r s t , c o l o n i e s can form when i n d i v i d u a l s a re i n d e p e n d e n t l y a t t r a c t e d t o s p e c i f i c l o c a t i o n s such as s a f e n e s t i n g s i t e s . T h i s i s thought t o be t h e case w i t h s p e c i e s 6 such as seabirds (Lack 1968; Nelson 1970; Ashmole 1971). However, because colonies are u s u a l l y more compact than s c a r c i t y of nests alone d i c t a t e s [Coulson (1971); Birkhead (1976) i n Wittenberger and Hunt 1985], there must also be other b e n e f i t s to nesting at high d e n s i t i e s . B e n e fits and cost associated with c o l o n i a l nesting have been d e t a i l e d i n various reviews (see Ward and Zahavi 1973; Wittenberger and Hunt 1985; Kharitonov and Siegel-Causey 1988). Costs of l i v i n g i n colonies include increased competition- f o r mates, food and space, increased r i s k of depredation and diseases, and increased r i s k of transmission of ectoparasites (Alexander 1974; Wittenberger and Hunt 1985). I n t r a s p e c i f i c nest p a r a s i t i s m and i n f a n t i c i d e can also occur (Hoogland and Sherman 1976). Benefits r e s u l t from e i t h e r increased food access, s o c i a l f a c i l i t a t i o n , or lower predation r i s k s (Wittenberger and Hunt 1985; Kharitonov and Siegel-Causey 1988). The key hypothesis I t e s t i n t h i s t h e s i s i s that Eared Grebe colonies are an anti-predator adaptation. I f colony s i z e o f f e r s major anti-predator advantages (to decrease predation on eggs), reproductive success (number of young fledged per pair) should increase with colony s i z e (see Hoogland and Sherman 1976, Andersson and Wiklund 1978; Wiklund and Andersson 1980; Wiklund 1982). Other studies, however, have f a i l e d to demonstrate a r e l a t i o n s h i p between colony s i z e and breeding success (e.g. Snapp 1976; Hoogland and 7 Sherman 1976; Brown and Brown 1987; Shields and Crook 1987) D i f f e r e n t mechanisms can also act to decrease predation at nesting c o l o n i e s . Breeding chronology i s known to a f f e c t reproductive success (see reviews i n Burger 1979; Wittenberger and Hunt 1985), with e a r l y nesters u s u a l l y enjoying higher reproductive success. Higher within-colony breeding synchrony was r e l a t e d to increased breeding success i n Bank Swallows (Riparia riparia) (Emlen and Demong 1975; Parsons 1976), but other studies have not found any c o r r e l a t i o n between synchrony and colony s i z e (see Burger 1979). Synchronized breeding could be advantageous by 1) decreasing the number of days during which a c t i v e nests are exposed to predators; 2) p r o v i d i n g more food than predators can consume (predator swamping e f f e c t ) ; 3) helping s o c i a l - f e e d i n g b i r d s get information on the l o c a t i o n of food sources from other foraging i n d i v i d u a l s ; 4) inc r e a s i n g capture success by cooperative hunting; or 5) using the group to decrease chances of an i n d i v i d u a l being preyed upon ( s e l f i s h herd e f f e c t ) (from Wittenberger 1985). Although group s i z e , synchrony w i t h i n colony and breeding chronology have a l l been r e l a t e d to breeding success, e f f e c t s of each f a c t o r have u s u a l l y been i n v e s t i g a t e d separately. Because group s i z e , synchrony and breeding chronology can be c o r r e l a t e d to one another (Burger 1979), those 3 v a r i a b l e s deserve to be studied simultaneously to understand the r e l a t i o n s h i p s between them. 8 Studies of c o l o n i a l i t y have commonly q u a n t i f i e d costs and b e n e f i t s a s s o c i a t e d with c o l o n i a l n e s t i n g f o r c o l o n i e s of d i f f e r e n t s i z e s (see above reviews). Most wi d e l y - s t u d i e d species (e.g. g u l l s , t e r n s , swallows and herons) have i n common: 1) nest s i t e s that are s t a b l e and p r e d i c t a b l e across years; 2) parents that f l y to and from f o r a g i n g grounds and 3) f o r a g i n g areas with no obvious p h y s i c a l or geographical boundaries. Eared Grebes d i f f e r from the above species i n a l l these p o i n t s . F i r s t , n e s t i n g h a b i t a t i s u n p r e d i c t a b l e and f l u c t u a t e s widely w i t h i n and across years (Cramp and Simmons 1977). F l u c t u a t i o n s i n water l e v e l s probably a f f e c t nest s i t e a v a i l a b i l i t y , food abundance and p o s s i b l y p h i l o p a t r y and d i s p e r s a l . Secondly, a d u l t s r a r e l y f l y during the breeding season. Nesting and r e a r i n g of young takes p l a c e i n a l i m i t e d and w e l l - d e f i n e d area (the breeding l a k e ) , which provides both nest s i t e s and foods used during the breeding season (Cramp and Simmons 1977). Eared Grebes provide an i d e a l system f o r studying how p h y s i c a l resources a f f e c t h a b i t a t s e l e c t i o n and c o l o n i a l n e s t i n g . They a l s o provide an opportunity to study i f and how c o l o n i a l n e s t i n g can be adaptive i n unpredictable or h i g h l y v a r i a b l e a q u a t i c environments. I expected attachment to nest s i t e s and c o l o n i e s to be minimal i n s p a t i a l l y and temporally f l u c t u a t i n g environments. Nesting requirements should a l s o be f l e x i b l e , to allow f o r v a r i a b i l i t y i n n e s t i n g c o n d i t i o n s . 9 My t h e s i s i s organized as follows. I examine f i r s t d i s t r i b u t i o n , abundance and habitat s e l e c t i o n of breeding Eared Grebes i n B r i t i s h Columbia. Secondly, I c h a r a c t e r i z e breeding habitat and nest s i t e s e l e c t i o n . T h i r d l y , I determine 1 ) i f there are net reproductive b e n e f i t s to nesting i n colonies and 2 ) how group s i z e , breeding chronology and breeding synchrony contribute to v a r i a t i o n s i n breeding success across colo n i e s . My study of c o l o n i a l i t y focuses on current cost (in terms of predation) and b e n e f i t s (breeding success) of c o l o n i a l nesting; I then i n t e r p r e t my r e s u l t s from an evolutionary perspective. Chapter 2 covers d i s t r i b u t i o n , abundance and breeding biology of Eared Grebes i n B r i t i s h Columbia. Chapter 3 c h a r a c t e r i z e s breeding ha b i t a t (morphology of breeding lakes, water chemistry and seasonal v a r i a b i l i t y i n water l e v e l s ) , and r e l a t e s h abitat c h a r a c t e r i s t i c s to breeding group s i z e . The anti-predator value of nest s i t e l o c a t i o n i s a l s o covered. Chapter 4 uses a m u l t i v a r i a t e approach to study the e f f e c t s of group s i z e , breeding chronology and breeding synchrony on breeding success. Chapter 5 i s a general d i s c u s s i o n . 1 0 CHAPTER 2: DISTRIBUTION AND ABUNDANCE OF EARED GREBES IN BRITISH COLUMBIA I n t r o d u c t i o n Eared Grebes are c o n s i d e r e d abundant breeders i n some areas of B r i t i s h Columbia (Munro 1941/ 1942; Campbell et al. i n p r e s s ) , w i t h b r e e d i n g c o n c e n t r a t i o n s r a n g i n g from i s o l a t e d p a i r s t o about 2500 p a i r s per l a k e (e.g. C e c i l Lake) (Munro 1941; Campbell et al. i n p r e s s ) . I n f o r m a t i o n on p a s t b r e e d i n g d i s t r i b u t i o n i n B r i t i s h Columbia was o b t a i n e d from McTaggart-Cowan (1939); Munro (1941; 1942); Guiguet (1954); Palmer (1962); Campbell and G a r r i o c h (1978); Campbell et al. (1979; i n press) and the B r i t i s h Columbia Nest Record Scheme. For v a r i o u s reasons, those r e c o r d s are o f l i t t l e use i n a s s e s s i n g c u r r e n t d i s t r i b u t i o n o r p a s t abundance. F i r s t , b r e e d i n g groups o f t e n s h i f t l o c a t i o n between y e a r s because of e c o l o g i c a l i n s t a b i l i t y o f n e s t i n g h a b i t a t (Cramp and Simmons 1977). Because p a s t surveys were spread over a 50-year p e r i o d , w i t h o n l y a few l a k e s surveyed on any g i v e n y e a r , we cannot t e l l whether abundance and d i s t r i b u t i o n r e c o r d s are addi,tive or r e f l e c t changes i n b r e e d i n g d i s t r i b u t i o n . More s e r i o u s l y , t h e r e i s l i t t l e i n f o r m a t i o n on how d a t a were c o l l e c t e d . The p r e c i s i o n of b r e e d i n g abundance e s t i m a t e s depends on the number, t i m i n g , and q u a l i t y of s u r v e y s . I n f o r m a t i o n d e r i v e d from m u l t i p l e surveys conducted on a s i n g l e year i s l i k e l y t o be more a c c u r a t e t h a n i n c i d e n t a l o b s e r v a t i o n s . Timing o f surveys i s a l s o c r i t i c a l , as surveys of 12 a d u l t s conducted d u r i n g i n c u b a t i o n are l i k e l y t o miss i n c u b a t i n g b i r d s . I n f o r m a t i o n on survey type and i n t e n s i t y i s c r i t i c a l , as i t i s the o n l y way t o s e p a r a t e a n e c d o t a l o b s e r v a t i o n s from e x h a u s t i v e s u r v e y s . F i n a l l y , i n f o r m a t i o n i s needed on how b r e e d i n g abundance was e s t i m a t e d , because the e s t i m a t e s can v a r y depending on d i f f e r e n t ways o f c a l c u l a t i o n (see below). B r e e d i n g abundance can be e s t i m a t e d by c o u n t i n g a d u l t s , n e s t s , or young; each method has b i a s e s and l i m i t a t i o n s (Cooperidder et al. 1986). A d u l t counts can be b i a s e d by the presence o f non-breeders, by the absence of i n c u b a t i n g a d u l t s , and by b i r d s f o r a g i n g underwater at the time o f the o b s e r v a t i o n s . A d u l t movements between b r e e d i n g areas are r a r e (Palmer 1962), so counts conducted on d i f f e r e n t l a k e s l i k e l y r e p r e s e n t d i f f e r e n t b i r d s . Q u a l i t y of nest counts depends on survey t i m i n g and degree of n e s t i n g synchrony ( B u l l 1981). Nest counts w i l l u n d e r e s t i m a t e t r u e n e s t numbers i f b r e e d i n g i s not f u l l y s y n c h r o n i z e d . Each p a i r o f Eared Grebes can a l s o b u i l d more than one p l a t f o r m (Palmer 1962), i n which case p l a t f o r m counts o v e r e s t i m a t e t r u e nest number. C h i c k counts p r e s e n t 2 problems; how t o count c h i c k s , and how t o r e l a t e c h i c k counts t o number of b r e e d e r s . Chick v i s i b i l i t y v a r i e s w i t h age and c h i c k f o r a g i n g b e h a v i o u r (Palmer 1962, Cramp and Simmons 1976). I f i n f o r m a t i o n i s a v a i l a b l e on a g e - s p e c i f i c c h i c k s u r v i v a l , c h i c k counts can be t r a n s f o r m e d i n t o number of b r e e d i n g p a i r s . However, such t r a n s f o r m a t i o n s are l i m i t i n g i n t h a t they assume t h a t c h i c k 13 s u r v i v a l i s s i m i l a r across lakes, which i s l i k e l y not to be the case. Population estimates should be accompanied by both an error term and a d e s c r i p t i o n of c a l c u l a t i o n methods. So f a r , t h i s has not been the case. This chapter w i l l : 1) summarize past breeding d i s t r i b u t i o n of Eared Grebes i n B r i t i s h Columbia, and 2) assess current d i s t r i b u t i o n and abundance. Extensive information on past and current breeding d i s t r i b u t i o n i n B r i t i s h Columbia has been given by Breault et al. (1988), so only general conclusions w i l l be presented here. Note that number of breeding p a i r s per lake i s not the same as colony s i z e , because some lakes support more than 1 colony (pers. obs.) . This chapter w i l l s o l e l y discuss o v e r a l l breeding abundance. C o l o n i a l i t y w i l l be tr e a t e d i n Chapter 4. Methods 1- Surveys on abundance of breeders H i s t o r i c records on d i s t r i b u t i o n and number of p a i r s of Eared Grebes nesting i n B r i t i s h Columbia were obtained from: 1) the B.C. Nest Records Scheme (housed at the Royal B r i t i s h Columbia Museum), 2) graduate theses, 3) published l i t e r a t u r e , 4) Canadian W i l d l i f e Service surveys, 5) Ducks Unlimited surveys and 6) B r i t i s h Columbia 14 M i n i s t r y of Environment surveys. Also, a survey form was d i s t r i b u t e d i n 1986 along with the newsletters of the B.C. Federation of N a t u r a l i s t s and the Williams Lake N a t u r a l i s t Club to s o l i c i t f u r t h e r information on past and present breeding records. No new information was c o l l e c t e d from the newsletters. Breeding records were grouped i n t o four geographical areas i n c l u d i n g s u i t a b l e nesting h a b i t a t : Central I n t e r i o r , Southern I n t e r i o r , Okanagan/Kamloops and Peace River regions (see F i g . 1 for area l o c a t i o n s ) . New surveys were conducted i n those areas from May to August i n 1985 and 1986 (see F i g . 2 f o r area surveyed i n 1985 and/or 1986) and covered 421 lakes (36 lakes f o r which there were h i s t o r i c a l breeding records and 385 new lakes) (see Table I f o r surveying e f f o r t per area). Lakes not p r e v i o u s l y surveyed were selected from 1:50,000 topographic maps based on the f o l l o w i n g c r i t e r i a : a) being a c c e s s i b l e by road, b) being located i n open habitat ( p r a i r i e or parkland), c) having part of t h e i r shoreline devoid of f o r e s t and d) showing signs of marshy areas or emergent vegetation. Those c r i t e r i a were select e d because a l l known breeding lakes i n B r i t i s h Columbia met conditions b) , c) and d) . Condition a) was added to increase the number of lakes that could be surveyed per u n i t of time. The f o l l o w i n g information was recorded f o r most lakes: number of adu l t s , number and age of chicks and number of nests and eggs 15 Figure 1: Zones with p o t e n t i a l breeding habitat f o r Eared Grebes i n B r i t i s h Columbia. 16 It Area Surveyed 0 100 200 300km jTTT Fort St-John jj Dawson Creek , Prince George Quesnel ^Williams Lake ' 100 Mile House Figure 2: Areas surveyed i n 1985 and 1986 to l o c a t e Eared Grebe breeding lakes. 17 Table I. Surveying e f f o r t at Eared Grebe breeding lakes i n B r i t i s h Columbia i n 1985 and 1986. LAKES IDENTIFIED FROM OTHER HISTORIC RECORDS LAKES TOTAL1 Region n l o c a t a b l e 2 v i s i t e d a c t i v e a c t i v e v i s i t e d a c t i v e (n) Northern Okanagan /Kamioops 17 8 3 2 4 66 6 (69) Southern I n t e r i o r 5 4 3 3 4 34 7 (37) Peace River 12 11 10 8 2 25 10 (35) C e n t r a l I n t e r i o r 28 25 20 7 17 260 24 (280) TOTAL 62 48 36 20 27 385 47 (421) 1 n = number of lakes v i s i t e d 2 Lakes a c c e s s i b l e or lakes which could be l o c a t e d on topographic maps. observed. Not a l l types of counts were conducted on each lake. Type and frequency of counts v a r i e d with lake l o c a t i o n and a c c e s s i b i l i t y . Only lakes with confirmed breeding records (nests with eggs, eg g s h e l l s or presence of unfledged chicks) were used to study 18 breeding d i s t r i b u t i o n . Empty n e s t i n g platforms or presence of a d u l t s alone or fledged chicks was not considered evidence of breeding attempts. Breeding abundance was s t u d i e d r e g i o n a l l y . A) Counts of a d u l t s and chicks Adults and chicks were counted from vantage p o i n t s on the shore with b i n o c u l a r s and/or a s p o t t i n g scope. Counts were repeated at l e a s t twice on lakes <26 ha and the maximum count was recorded. On l a r g e r lakes, a d u l t s were counted only once, but slowly enough to take i n t o account d i v i n g and r e s u r f a c i n g b i r d s . Age and number of chicks were recorded on audio tapes. Aging was done according to Gollop and M a r s h a l l ' s system of plumage development i n waterfowl (Gollop and M a r s h a l l 1954; B e l l r o s e 1978) . No e f f o r t s were made to f l u s h b i r d s from emergent v e g e t a t i o n so counts represent minimum values. When chicks fed a c t i v e l y , s e v e r a l counts were conducted c o n s e c u t i v e l y and the highest count was used. Breeding a d u l t s are not known to move between lakes (Palmer 1962), so there i s l i t t l e chance of repeated counting and overestimating a d u l t numbers. B- Counts of nests Nests were counted while wading through emergent v e g e t a t i o n on each lake. A c t i v e nests (with eggs or signs of hatching such as presence of v a s c u l a r i z e d membranes and small pieces of s h e l l ) were d i s t i n g u i s h e d from empty platforms. In areas of high nest density, counted nests were i d e n t i f i e d with small pieces of rope (2-3cm long) 19 to avoid double counting. The number of eggs i n each nest was recorded f o r each v i s i t . 2- Estimating abundance of breeders Depending on the number and timing of surveys, up to 3 estimates of the number of breeding p a i r s per lake were derived from: A) Adult counts An estimate was obtained by d i v i d i n g the maximum number of adults seen during the April-August period by 2. B) Nest counts The highest recorded number of a c t i v e nests during each breeding season was used as the minimum number of breeding p a i r s per lake (because nesting i s not n e c e s s a r i l y synchronized). Empty platforms (before l a y i n g , a f t e r hatching or a f t e r predation at nest) were recorded separately but t r e a t e d as a c t i v e nests. Platform counts were used only f o r lakes where no or incomplete a c t i v e nest counts were a v a i l a b l e . A l l platforms from previous years were presumed to have been destroyed by i c e , wind and wave a c t i o n unless they were located i n abnormally sheltered area (e.g. McMurray Lake). C) Chick counts This estimate was obtained by d i v i d i n g the observed number of 20 chicks of a given age by the mean number of chicks per p a i r s u r v i v i n g to that age. The period from hatching to f l e d g i n g was d i v i d e d i n t o 3 periods, based on chick v i s i b i l i t y and behaviour. The f i r s t p e r i o d covered from hatching to 2 weeks of age. Chicks are poorly v i s i b l e at that age and spend most of t h e i r time under the folded wings of t h e i r parents (Cramp and Simmons 1976). The second period was from 2 weeks to 1 month o l d . Chicks of that age are not found under t h e i r parent's wings, but they are s t i l l fed by them. From 1 month of age to f l e d g i n g , chicks are r a r e l y accompanied by parents and are e a s i l y detectable when not d i v i n g f o r food. The equation used to estimate breeding abundance from chick counts i s presented i n Appendix 1. D) O v e r a l l estimate of breeding p a i r abundance When a v a i l a b l e , maximum nest counts (complete or incomplete) were used as an o v e r a l l estimate of the abundance of breeding p a i r s . When nest counts were not a v a i l a b l e or when estimates based on incomplete nest counts were lower than estimates based on chick counts, I used estimates based on chick counts. Estimates of the number of breeding p a i r s per lake thus took the form of s i n g l e values or ranges. Single values were obtained from m u l t i p l e nest surveys, or when the estimate based on adult counts was i d e n t i c a l to the estimate derived from nest counts. In a l l other cases, abundance i s presented as a range c o n s i s t i n g of 21 both minimum and maximum estimates as c a l c u l a t e d by the above methods. Estimates from both 1985 and 1986 were used to derive the range. Regional estimates of breeding abundance were derived by adding minimum and minimum estimates from each lake. For cases where only 1 or a few surveys were conducted l a t e i n the year (e.g. surveys i n the Peace River region i n 1985), a subjective c o r r e c t i o n f a c t o r was used. The c o r r e c t i o n f a c t o r was based on comparisons with lakes used by known numbers of breeding p a i r s also surveyed l a t e i n the summer. Size of reg i o n a l populations was obtained by separately adding lowest and highest estimates of breeding populations f o r a l l lakes. E r r o r s inherent to each method and the f a c t that minimum and maximum estimates were u s u a l l y derived from d i f f e r e n t methods (minimum counts from nests, maximum counts from adult surveys) are l i k e l y responsible f o r the wide range between maximum and minimum estimates. Adult counts are biased downwards by missing incubating or feeding adults and upwards by i n c l u d i n g non-breeders. Nest counts are a l s o biased downwards, because egg-laying i s r a r e l y f u l l y synchronized and nests are l o s t to predators, and upwards by the presence of empty platforms. M u l t i p l e surveys could compensate for those biases, but t h i s was r a r e l y p o s s i b l e . Biases associated with chick counts mostly depend on how chick counts are adjusted to number of breeders. I f a g e - s p e c i f i c s u r v i v a l r a t e s of chi c k s are high, chick counts w i l l underestimate true p o p u l a t i o n s i z e . Conversely, i f a g e - s p e c i f i c s u r v i v a l rates are low, numbers of breeding p a i r s w i l l be overestimated. P r e c i s i o n of chick counts i n c r e a s e s with chick age and s i z e (because chicks cease to be t r a n s p o r t e d under t h e i r parents' wings), but plumage c h a r a c t e r i s t i c s on which aging i s based are a f f e c t e d by p r e f e r e n t i a l feeding by the parents. The number of breeding p a i r s per lake and the d i s t r i b u t i o n of the p o p u l a t i o n across lakes was i n v e s t i g a t e d i n 1985 and 1986. Breeding lakes were a r b i t r a r i l y grouped i n t o 5 c a t e g o r i e s based on the number of breeding p a i r s using a lake: 1-25, ' 26-50, 51-75, 76-100 and 101+ breeding p a i r s per lake. Breeding abundance was d e f i n e d as the highest estimate from a d u l t , chick and nest counts when m u l t i p l e surveys were a v a i l a b l e or as the mean of the range f o r each lake. 3- S t a t i s t i c s S t a t i s t i c a l analyses presented i n t h i s t h e s i s were done with SYSTAT (Wilkinson 1989). Normality of data sets was a s c e r t a i n e d with a L i l l i e f o r s t e s t . Most measurements shown i n the t h e s i s are accompanied by t h e i r standard e r r o r (S.E.). 23 Results 1- Breeding d i s t r i b u t i o n and abundance Surveys conducted on 421 lakes i n 1985 and 1986 i d e n t i f i e d 47 lakes used by breeding Eared Grebes i n 4 regions of B.C. (Table I ) . Eared Grebes were known to breed on 20 of those 47 lakes p r i o r to 1985. The other 27 breeding lakes were i d e n t i f i e d i n a survey of 385 lakes not p r e v i o u s l y surveyed. Sixteen of the 36 lakes (44.4%) that I surveyed where breeding had taken place p r i o r to 1985 were not used f o r breeding i n 1985 and 1986. The most recent estimates of breeding abundance f o r those lakes i n d i c a t e that a l l 16 lakes were each l a s t used by 35 p a i r s or l e s s . O v e r a l l , I located from 1761 to 4474 breeding p a i r s on those lakes. The number of breeding lakes and breeding p a i r s i n each region was as follows (see Breault et al. 1988 f o r more d e t a i l s ) . A) Northern Okanagan/Kamloops P r i o r to 1985, 17 breeding lakes had been i d e n t i f i e d i n the area. The 1985 and 1986 surveys covered 3 of those lakes and i d e n t i f i e d 4 new breeding lakes. O v e r a l l , only Stump Lake was used by a large number (70-100) of breeding p a i r s . Assuming that lakes with h i s t o r i c a l records that were not surveyed i n 1985 and 1986 are s t i l l used by the same number of 24 breeders, estimated breeding population i n the area ranges from 109 to 280 p a i r s (Appendix 2), or 6.2 to 6.3% of the p r o v i n c i a l population. B) Peace River Region At one time, t h i s region included the 2 lakes with the l a r g e s t number of breeding p a i r s i n B r i t i s h Columbia: C e c i l Lake, with more than 1000 p a i r s i n 1978 and 1981 and Boundary Lake, with 600 to 800 p a i r s i n 1978 ( B r i t i s h Columbia Nest Record Scheme). O v e r a l l , 12 lakes i n the region supported breeders p r i o r to 1985. A l l but 2 lakes were v i s i t e d in. 1985 and 1986, with 8 out of the remaining 10 lakes used by breeding p a i r s . The number of p a i r s nesting on Boudreau and C e c i l lakes i n 1985 and 1986 was l e s s than previously reported. This could be due i n part to l a t e surveying i n both years or i t may r e f l e c t a c t u a l decreases i n . numbers. Further surveys are needed to confirm the p o s s i b l e d e c l i n e . The Peace River region accounted f o r 342 to 1775 breeding p a i r s (Appendix 3), or 19.4 to 39.7 % of the estimated p r o v i n c i a l population. Breeders were concentrated on 3 lakes: C e c i l , Boundary and Boudreau Lakes. C) Southern I n t e r i o r H i s t o r i c a l l y , 5 breeding lakes were known i n the area. Three of them were r e v i s i t e d i n 1985 and 1986, and few changes were observed 25 i n breeding numbers. P r i o r to the 1985-86 surveys, only Meadow Lake was known to be used by more than 50 breeding p a i r s , and my surveys i n d i c a t e d that breeding population there remained the same or p o s s i b l y increased, even though non-breeders were also observed throughout the breeding season. Nesting ha b i t a t i s l i m i t e d to the northeast shore of the lake, and t h i s area was completely searched f o r nests. Adult surveys conducted at the time of the nest searches accounted f o r more than the number of p a i r s p r e d i c t e d from nest counts. Large groups of adults were observed away from the shore, which i s contrary to usual breeding behaviour. Those b i r d s were c l a s s i f i e d as non-breeders. Four new breeding lakes were located i n 1985 and 1986. L i t t l e White Lake was used by approximately 500 p a i r s i n 1986. However, a higher population was suspected, because 1) the estimate was derived from a chick count conducted on 18 Jul y 1988, and chick counts are c e r t a i n l y underestimates on l a r g e r lakes because of problems with v i s i b i l i t y , feeding behaviour, high chick density, e t c . ; 2) no nest searches were conducted on the lake, thus any incubating b i r d s would have been missed; 3) counting young on that lake took twice as long as on another lake of s i m i l a r s i z e used by 440 p a i r s with chicks of the same age, suggesting the presence of more young; and 4) a 1986 survey conducted by Ducks Unlimited during peak breeding time (June) reported 1600 adults on the lake. 26 O v e r a l l , the Southern I n t e r i o r accommodated from 676 to 940 breeding p a i r s (Appendix 4), or roughly 38.4 to 21.0% of the estimated p r o v i n c i a l population. Breeding b i r d s were mostly concentrated on L i t t l e White Lake and Meadow Lake. D) Central I n t e r i o r More than h a l f the h i s t o r i c a l l y - k n o w n breeding lakes i n the province were located i n t h i s region. The l a r g e s t populations were found on Westwick Lake (419 nests and 50 platforms i n 1978), Rock Lake (160 nests i n 1978) and Sorenson Lake (50+ p a i r s i n 1949). Surveys conducted i n 1985 and 1986 covered 20 of the 28 lakes used i n the past. Changes i n breeding abundance were observed on some lakes. For example, Eared Grebes s t i l l bred on Westwick and Rock Lakes i n 1985 and 1986, but the numbers were down compared to 1978. My surveys also found lower numbers of Eared Grebes on Sorenson Lake, probably because of a c t i v e drainage of the lake f o r i r r i g a t i o n purposes. Seventeen new breeding lakes were i d e n t i f i e d i n the region during t h i s study, the most notable being McMurray Lake (2 bodies of water connected by a narrow channel of open water) , used by more than 400 p a i r s both i n 1985 and 1986. Elkhorn Lake was used by roughly 260 p a i r s i n 1985, whereas Lake 8432 North was used by between 80 and 100 p a i r s i n 1986. No other lakes were used by more 27 than 40 p a i r s . The Central I n t e r i o r accounted f o r 634 to 1479 breeding p a i r s (Appendix 5), or 36.0 to 33.1 % of the estimated breeding population i n B.C. 2- Number of breeding p a i r s Breeding abundance per lake ranged from s i n g l e p a i r s to more than 590 p a i r s i n 1985 and 1986 (Appendices 2, 3, 4 and 5). Higher estimates of breeding abundance are a v a i l a b l e from h i s t o r i c records, the highest being f o r C e c i l Lake (Peace River Region), with an estimated 2500 nests i n 1962. More lakes were used by few (<25 pairs) breeders than by many (>100 pairs ) breeders (Fig. 3) . However, lakes used by many breeders accounted f o r more than 60% of the surveyed population i n both years. Lakes used by l e s s than 51 p a i r s accounted f o r roughly 14% (1986) to 23% (1985) of a l l estimated breeding p a i r s . 28 30-1 CO tu < u. O cc UJ CD 5 3 25-20-15-10-5-(12.1%) (3.2%) 1985 (n=36 lakes) (60.7%) (12.8%) X CO UJ < cc UJ CD Z 30-1 25-20-15-10-5-(8.2%) (5.6%) (9.1%) T 1986 (n = 43 lakes) (73.6%) (3.5%) X T T 1-25 26-50 51-75 76-100 101 + NUMBER OF BREEDING PAIRS PER LAKE Figure 3. Number of breeding p a i r s per lake and d i s t r i b u t i o n of the breeding population (%) across lakes. 29 D i s c u s s i o n 1- D i s t r i b u t i o n and abundance i n B.C. In B r i t i s h Columbia, the 4 areas where Eared Grebes nest include the most productive wetlands f o r waterfowl i n the province (Waterfowl production areas i n B r i t i s h Columbia, Canadian Land Use survey map, Environment Canada). The known Eared Grebe population n e s t i n g on the 47 lakes I surveyed i n those 4 areas was estimated at between 1761 and 4474 breeding p a i r s i n 1985 and 1986. The p r o v i n c i a l p o p u l a t i o n i s undoubtedly much higher, as only a p o r t i o n of the s u i t a b l e breeding h a b i t a t was surveyed. Areas showing the highest p o t e n t i a l f o r undiscovered breeding lakes are the Southern and C e n t r a l I n t e r i o r , which i n c l u d e many wetlands, few of which have been surveyed. Old breeding records were u s e f u l i n the study of d i s t r i b u t i o n of breeding Eared Grebes, but methodological l i m i t a t i o n s kept them from p r o v i d i n g r e l i a b l e i nformation on past abundance. Past records do, however, i l l u s t r a t e c o n t i n u i t y of use of breeding areas. Breeding d e n s i t i e s v a r i e d widely i n amplitude on c e r t a i n lakes, and a large number of breeding areas were not c o n s i s t e n t l y used across years. For example, the number of breeding p a i r s on Westwick Lake went from 0 i n 1931 to 228 p a i r s i n 1941 (Munro 1942) . V a r i a b i l i t y i n d i s t r i b u t i o n and abundance appears to be inherent to the species 30 (Palmer 1962, Cramp and Simmons 1977) Breeding abundance v a r i e d widely both seasonally and across lakes. Even though few lakes were used by more than 100 nesting p a i r s , these accounted f o r more than 60% of the known p r o v i n c i a l population. Those lakes should be protected because of t h e i r s i g n i f i c a n c e . Groups of l e s s than 50 p a i r s accounted f o r 15 to 22% of the o v e r a l l number of p a i r s surveyed, but the occurrence of nesting by small groups i s l i k e l y higher than reported here. Lakes used by few breeders are l e s s known to b i o l o g i s t s and n a t u r a l i s t s than large breeding concentrations. Detection a l s o increases with group s i z e , favoring l o c a l i z a t i o n of large breeding groups. E c o l o g i c a l c o r r e l a t e s of group s i z e w i l l be i n v e s t i g a t e d i n Chapter 3. One aim of t h i s study was to provide a data base against which future changes i n d i s t r i b u t i o n and abundance could be measured. The information I c o l l e c t e d achieves that purpose. There i s no strong evidence that abundance has declined. Breeding lakes previously supporting large numbers of p a i r s were found to be s t i l l a c t i v e , even though breeding abundance sometimes v a r i e d . Differences i n abundance between my surveys and o l d records could be accounted for by d i f f e r e n c e s i n surveying techniques such as survey timing. Surveys conducted during peak breeding time i n the Peace River region could determine whether the apparent de c l i n e there i s r e a l . 31 2- Surveying techniques Methods used to determine breeding abundance are h i g h l y relevant to the understanding of breeding biology, as q u a n t i t a t i v e data on ha b i t a t use are a p r e r e q u i s i t e to good studies of h a b i t a t s e l e c t i o n (Woolhead 1987). From the 3 techniques a v a i l a b l e to estimate breeding abundance, repeated nest counts are l e a s t biased, provided that nesting i s synchronized. Nest counts, however, are time-consuming and d i s t u r b incubating b i r d s . Non-systematic nest counts are of l i m i t e d value to assess breeding abundance, but can be use f u l i n d i s t r i b u t i o n studies. Adult surveys are the e a s i e s t to conduct. They provide p r e c i s e estimates i f m u l t i p l e surveys are a v a i l a b l e , e s p e c i a l l y i f they are conducted r i g h t before the onset of l a y i n g (early June i n c e n t r a l B r i t i s h Columbia). A f t e r that time, they underestimate true breeding numbers because incubating a d u l t s , non-breeders and adults that have f a i l e d w i l l be missed. There are so many problems with chick counts that they should not be used to assess breeding abundance. Extensive information on techniques used to survey c o l o n i a l waterbirds can be found i n Cooperidder et a l . (1986) . Assessment of the number of breeding grebes has been studied i n Great Crested Grebes (Podiceps cristatus) i n Europe. This f a c u l t a t i v e l y - c o l o n i a l species nest i n emergent vegetation (Cramp and Simmons 197 6). Counting nests i s not easy, as nests are l o c a t e d i n dense rushes or 32 reeds (Cramp and Simmons 1976). Leys and de Wilde (1971) therefore concluded that chick counts i n Jul y and August were the best method to count Great Crested Grebes. Woolhead (1987) pointed out that chick counts are biased by nest f a i l u r e s and predation on chicks, and suggested using adult counts p r i o r to nesting. Other studies also i d e n t i f i e d the s t a r t of the breeding season as the optimum period to estimate the number of breeding p a i r s from adult counts (Green 1985; N i l s s o n 1981; Woolhead 1987). I recommend the use of nest counts to determine breeding abundance. I f nest counts are not p o s s i b l e , abundance of Eared Grebes would be best determined from m u l t i p l e adult surveys conducted p r i o r to nesting. Summary I determined breeding d i s t r i b u t i o n and abundance from h i s t o r i c a l records and f i e l d surveys. H i s t o r i c a l nesting records were found f o r 62 lakes i n B.C. I surveyed 36 of those lakes and another 385 lakes i n 1985 and 1986. I found 47 lakes used by breeding Eared Grebes. The breeding population of the 47 lakes was estimated at 17 61 to 4 47 4 p a i r s , with breeding abundance per lake ranging from s i n g l e p a i r s to more than 590 p a i r s i n 1985 and 1986. . 33 CHAPTER 3: HABITAT CHARACTERISTICS, NEST SITE SELECTION AND BREEDING GROUP SIZE IN EARED GREBES 34 Introduction: D i f f e r e n t e c o l o g i c a l f a c t o r s a f f e c t breeding d i s t r i b u t i o n and habi t a t use: 1) i n t e r - and i n t r a s p e c i f i c competition, 2) resource d i s t r i b u t i o n (e.g.food), and 3) predation (Buckley and Buckley 1980) . This chapter w i l l focus on resource - d i s t r i b u t i o n and predation. My approach i s to quantify Eared Grebe breeding habitat at the lake and nest s i t e l e v e l s , and then consider e c o l o g i c a l f a c t o r s associated with group s i z e and nest s i t e s e l e c t i o n . 1- Breeding ha b i t a t Eared Grebes breed worldwide i n "highly productive" wetlands (Cramp and Simmons 1977) . In North America, o v e r a l l breeding d i s t r i b u t i o n (Palmer 1962) coincides with presence of shallow productive wetlands. Breeding p a i r s are found i n sheltered, shallow and reedy portions of medium-size or l a r g e r wetlands (Palmer 1962). Although general breeding habitat d e s c r i p t i o n s are a v a i l a b l e from observations i n Washington State (Yocom et al. 1958), B r i t i s h Columbia (Munro 1941; 1942; Guiguet 1954; Campbell et a l . i n press), and from general accounts (e.g. Bent 1919; Cramp and Simmons 1977), d e t a i l e d information on breeding habitat i s only a v a i l a b l e for i s o l a t e d lakes i n B.C. (e.g. McTaggart-Cowan 1939; M c A l l i s t e r 1956; 1958; Munro 1941; 1942; Forbes 1985) and North Dakota (Faaborg, 1976) . Only Faaborg (1976) has so f a r studied h a b i t a t s e l e c t i o n 35 q u a n t i t a t i v e l y , and he found that Eared Grebes nest on large semi-permanent open ponds. Because of seasonal and annual f l u c t u a t i o n s i n water l e v e l s , breeding habitat i s known to be somewhat unpredictable (Cramp and Simmons 1977), but hab i t a t p r e d i c t a b i l i t y and i t s e f f e c t s on habitat s e l e c t i o n have not been studied. 2- E c o l o g i c a l c o r r e l a t e s of breeding group s i z e The taxonomic d i s t r i b u t i o n and e c o l o g i c a l c o r r e l a t e s of avian c o l o n i a l i t y have been documented by Crook (1964, 1965) and Lack (1968). E c o l o g i c a l f a c t o r s r e l a t e d to breeding group s i z e include s i z e of breeding h a b i t a t , d i s t r i b u t i o n and use of e s s e n t i a l resources such as food (Crook 1972; Cody 1971; Horn 1968) and v u l n e r a b i l i t y to predation (Hamilton 1971). Studies of i s l a n d biogeography have shown that l a r g e r land b i r d populations are found on bigger or more productive i s l a n d s (see Simberloff 1974; P i e l o u 1979; Anderson 1981b; Bengston and Bloch 1983). Eared Grebes breed i n groups of extremely v a r i a b l e s i z e (from 1 p a i r to more than 590 p a i r s i n B.C.) (see Chapter 1), and breeding lake s i z e i s also h i g h l y v a r i a b l e (Munro 1941; 1942; Palmer 1962; Faaborg 1976; Cramp and Simmons 1982). Their d i e t c o n s i s t s of t i n y i n s e c t s or in s e c t larvae (Palmer 1976) , whose abundance and d i s t r i b u t i o n i s c o r r e l a t e d to water chemistry (Lancaster 1985). I 36 w i l l examine the extent to which breeding group s i z e i n Eared Grebes i s r e l a t e d to habitat p r o d u c t i v i t y (e.g. food and cover). I estimated habitat p r o d u c t i v i t y from water chemistry analyses. Animal zooplankton standing crop i s p o s i t i v e l y and l i n e a r l y c o r r e l a t e d to Dissolved S o l i d Content (DSC), which a f f e c t s nutrient a v a i l a b i l i t y and growth rate i n aquatic systems (Northcote and Lark i n 1956; Wetzel 1975; Topping 1985), and DSC can be qui c k l y evaluated from water c o n d u c t i v i t y (Northcote and Lar k i n 1956). I use water c o n d u c t i v i t y as an index of wetland p r o d u c t i v i t y (see Lancaster 1985 f o r more d e t a i l s ) . 3- Nest s i t e s e l e c t i o n D i f f e r e n t types of nest s i t e s are used by Eared Grebes. Nests are e i t h e r anchored to bulrush (Scirpus spp.), c a t t a i l {Typha spp.) (Palmer 1976), or are exposed and f r e e - f l o a t i n g (Bent 1919; Munro 1941) . C a t t a i l and bulrush stands are u s u a l l y l i m i t e d to shore l i n e s , while exposed nests can be seen at quite a distance from shore (pers. obs.). Using vegetation to anchor nests might be b e n e f i c i a l , as bulrush and c a t t a i l could decrease nest v i s i b i l i t y and detection by predators. Being close to shore would, however, increase nest a c c e s s i b i l i t y , and large breeding groups could q u i c k l y lose b e n e f i t s from nest concealment. Use of both types of nest s i t e s might i n d i c a t e t r a d e - o f f s between nest-concealment, distance 37 from shore ( a f f e c t i n g nest a c c e s s i b i l i t y to predators), group s i z e , and nest predation rates. 4- Anti-predator value of nest s i t e s One of the most important aspects of nest s i t e s e l e c t i o n i n b i r d s i s safety from predators (Buckley and Buckley 1980). Predation on b i r d nests can have a major i n f l u e n c e on young production (Lack 1968; R i c k l e f s 1969) . Predation rates are a f f e c t e d by h a b i t a t type (Burger 1973), nest substrate and nest height ( R i c k l e f s 1969), habitat l o c a t i o n ( L o i s e l l e and Hoppes 1983) and nest p o s i t i o n w i t h i n a colony (Patterson 1965; Coulson 1968, Dexheimer and Southern 1974). Two primary defenses can be used against nest predation: 1) locate nests i n s i t e s i n a c c e s s i b l e to predators or 2) conceal nests from predators (Wittenberger and Hunt 1985). Use of i n a c c e s s i b l e nest s i t e s i s most obvious with marine seabirds nesting on small i s l a n d s or rocks devoid of predators (Lack 1968) and with c a v i t y -nesting b i r d s (Sonerud 1985). These s i t e s are, however, l i m i t e d i n number. Concealment i s e f f e c t i v e only i f body s i z e i s small and breeding density i s low. Experiments have suggested that concealment i s most e f f e c t i v e when nests are widely dispersed and uncommon (Tinbergen et al. 1967, Croze 1970). Beyond a c e r t a i n 38 group s i z e , concealment becomes l e s s e f f e c t i v e , as nesting a c t i v i t i e s betray colony and nest s i t e l o c a t i o n . I designed an experiment to t e s t f o r t r a d e - o f f s between nest concealment, nest a c c e s s i b i l i t y and predation on eggs. A r t i f i c i a l platforms were used to represent d i f f e r e n t nesting c o n d i t i o n s : nests were concealed or exposed, close to or f a r from shore and with eggs exposed or concealed. My p r e d i c t i o n s were that 1) nest predation should be lower on concealed platforms and on nests close to shore; and 2) exposed platforms close to shore should s u f f e r the heaviest predation because of increased detection and a c c e s s i b i l i t y to predators. Eared Grebes normally cover t h e i r eggs before l e a v i n g the nest, but not always so (Broekhuisen 1963). I repeatedly observed uncovered Eared Grebe eggs during v i s i t s to nesting areas. M c A l l i s t e r (1956) suggested 2 non-exclusive functions of egg cover: keep eggs warm while untended or/and conceal eggs from predators. A r t i f i c i a l platforms were used to determine whether predation rates d i f f e r e d between covered and uncovered eggs. The chapter i s d i v i d e d i n 4 sections: 1) a d e s c r i p t i o n of p h y s i c a l and chemical c h a r a c t e r i s t i c s of breeding lakes; 2) a study of r e l a t i o n s h i p s between p h y s i c a l and chemical c h a r a c t e r i s t i c s and 39 number of breeding p a i r s per lake; 3) a d e s c r i p t i o n of nest s i t e s e l e c t i o n ; and 4) a study of the anti-predator value of nest s i t e s . Methods 1- Lake c h a r a c t e r i z a t i o n : The f o l l o w i n g v a r i a b l e s were studied on lakes used by breeding Eared Grebes: lake morphology (area, mean and maximum depth), water chemistry (pH, c o n d u c t i v i t y , s a l i n i t y and hardness), and water l e v e l f l u c t u a t i o n s w i t h i n and across years. Lake area was determined f o r 28 lakes by t r a c i n g lake contours on 1:50,000 topographic maps with an IBM-PC graphics t a b l e t , then c a l c u l a t i n g area by program. Information on mean and maximum depths was obtained f o r 17 and 15 lakes from e i t h e r Ducks Unlimited surveys, Boyd and Savard (1987), or from f i e l d surveys. Water depth at nest was estimated from water height on chest waders or measured with a meter s t i c k i n 1986. Water samples were c o l l e c t e d on 27 lakes i n June 1986 (methods i n Boyd and Savard 1987). Samples were frozen at the f i e l d camp and analyzed i n e a r l y August. Conductivity, s a l i n i t y and hardness were 40 measured on a S-C-T Meter (Yellow Springs Instruments L t d . ) . PH was measured on DUAL-TINT pH t e s t paper (graduation 0.3). Water l e v e l f l u c t u a t i o n s were studied on 11 lakes i n 1985 and 1986 i n the Riske-Creek, B.C. area. Submerged permanent stakes were set as f a r away as p o s s i b l e from Eared Grebe nesting areas. Readings were taken weekly from May to J u l y with a 30cm r u l e r p o s i t i o n e d at the end of the stake. Stakes were submerged under at l e a s t 15cm of water, to keep them from being destroyed by i c e i n the winter. Two e x t r a lakes were measured i n 1985. 2- E c o l o g i c a l c o r r e l a t e s of breeding abundance: Data on lake area, pH, c o n d u c t i v i t y , s a l i n i t y and hardness were c o l l e c t e d f o r 27 lakes. Number of breeding p a i r s using those lakes, hardness and c o n d u c t i v i t y were log-transformed to normalize the data. A stepwise m u l t i p l e regression a n a l y s i s was conducted on normalized data to r e l a t e number of breeding p a i r s per lake to the above c h a r a c t e r i s t i c s . Alpha values f o r entering v a r i a b l e s were set at 0.15, on the basis of Monte Carlo studies of stepwise regression (Bendel and A f i f i 1977, i n Wilkinson 1989). 41 3- Nest s i t e s e l e c t i o n : Nest s i t e s were located on 29 lakes where m u l t i p l e nest surveys were made (see Chapter 1 f o r survey methods) . Breeding areas were mapped and c l a s s i f i e d as e i t h e r close to shore (within 5m from the shore) or f a r from shore (more than 5m from shore). P h y s i c a l (lake area; maximum, minimum and mean lake depths; seasonal and annual water l e v e l f l u c t u a t i o n s ) and chemical (pH, co n d u c t i v i t y , s a l i n i t y , hardness) c h a r a c t e r i s t i c s of wetlands were compared f o r lakes with nesting areas close to and f a r from shore with p a i r e d t - t e s t s . Data on nest s i t e s e l e c t i o n were standardized and t e s t e d f o r normality. Log transformations produced normally-d i s t r i b u t e d values f o r number of breeding p a i r s , lake area, and hardness. S t a t i s t i c a l transformations d i d not normalize the d i s t r i b u t i o n of pH data, so pH was analyzed with non-parametric s t a t i s t i c s . Because some of the information u t i l i z e d was obtained from other studies, sample s i z e s v a r i e d from a n a l y s i s to a n a l y s i s . I used 15 lakes with nesting areas close to shore and 10 lakes with nesting areas f a r from shore to determine the e f f e c t of nest s i t e l o c a t i o n on lake use on consecutive years. I only used lakes f o r which m u l t i p l e adult surveys and nest searches were a v a i l a b l e f o r both 1985 and 1986. Those lakes were c l a s s i f i e d as e i t h e r used by breeders (presence of nesting platforms) or not used by breeders 42 (absence of adults or absence of nesting platforms) on each year. I compared the r a t i o of lakes unused/total number of lakes surveyed on consecutive years f o r nests located close to and f a r from shore. 4- Anti-predator value of nest s i t e : A r t i f i c i a l platforms were used to r e l a t e nest predation i n small breeding groups (3 nests) to: 1) distance from the shore (close vs. f a r ) , 2) nest concealment (exposed vs. p a r t i a l l y - c o n c e a l e d platforms) and 3) egg concealment (exposed vs. concealed eggs). I b u i l t platforms representing each combination of f a c t o r s except the f o l l o w i n g : concealed nests close to shore with exposed eggs and exposed nests close to shore with exposed eggs. Each combination of f a c t o r s ( i n v o l v i n g 3 nests each) was r e p l i c a t e d twice on each of 8 d i f f e r e n t lakes i n the Riske-Creek area, f o r ' a t o t a l of 288 a r t i f i c i a l platforms. A l l lakes were i n a 4 km2 area and unused by Eared Grebes, but adjacent to lakes used by breeding grebes. My experiment assumed that experimental lakes were subject to s i m i l a r predator pressure as neighbouring lakes used by Eared Grebes. A r t i f i c i a l nests were b u i l t from decomposing bulrush placed on square wooden platforms (roughly 400-625cm2) set between 1 June and 15 June 1986. Platforms were attached to three poles to keep them from swaying and to provide support f o r p o t e n t i a l predators. The platforms were estimated to be as stable as n a t u r a l nests. Each 43 nest was provisioned with 3 Japanese Quail (Coturnix japonica) eggs. The eggs I used were pale creamy-buff, with f i n e o v e r - a l l speckling and sparser i r r e g u l a r s p o t t i n g and b l o t c h i n g buffish-brown or dark brown (Harrison 1978). Quail eggs are markedly smaller and l i k e l y more c r y p t i c than Eared Grebes eggs. Quail eggs were a v a i l a b l e i n large q u a n t i t i e s , and have been used s u c c e s s f u l l y i n other studies of nest predation (e.g. Schaeff and Pieman 1988, Pieman and B e l l e s -I s l e s 1988). Nests close to shore were set w i t h i n 2 m from shore i n water 0.5m deep, whereas nests away from shore were set w i t h i n 2 to 3 m from shore, i n water 1.3m deep. Nests were concealed by d r i l l i n g 6cm-diameter holes on 3 sides of each wooden platform, and i n s e r t i n g dead and fresh bulrush stems c o l l e c t e d i n the area i n t o the holes u n t i l a l l holes were f i l l e d . Eggs were covered with palm-s i z e d p a t t i e s of decaying vegetation and mud, equivalent i n s i z e , texture and c o l o r a t i o n to that used by Eared Grebes. Egg losses were measured a f t e r 4 and 8 days. Predator type was i d e n t i f i e d from egg remains (Rearden 1951; Green 1987) . Avian predators produce t r i a n g u l a r punctures on the egg side and push the eggshell inwards. Mammalian predators make a small hole out of one end or break eggshells, i n t o small pieces, but the edges of some s h e l l s may show f i n e tooth marks. The area beneath each platform was searched f o r eggshell fragments or f o r eggs that had f a l l e n o f f . Eggs that disappeared from the platforms were presumed to be preyed upon unless they were found on the lake bottom. Platform s o l i d i t y 44 and amount of vegetation l e f t on the platform were al s o noted, and that information was used to assess whether egg losses could have been caused by wave a c t i o n . Cases where wave a c t i o n was thought to be the cause of egg a t t r i t i o n were removed from analyses. I conducted u n i v a r i a t e analyses of variance between egg losses and 1) distance from shore, 2) nest concealment and 3) egg cover. Because the number of eggs l e f t i n each nest a f t e r 4 and 8 days (ranging from 0 i f a l l eggs were preyed upon to 3 i f no eggs were preyed upon) d i d not f o l l o w a normal d i s t r i b u t i o n , I used a Kruskal-W a l l i s a n a l y s i s of variance to analyze the data. Results 1- P h y s i c a l c h a r a c t e r i s t i c s of breeding lakes: Morphological data was c o l l e c t e d on 23 lakes (see Table II) . A l l breeding lakes were quite shallow, with maximum lake depth ranging from 1.0 to 3.4m. .Lake depth averaged 1.0m (+0.1) (n=17), while maximum depths averaged 1.8m (+0.2) (n=15). Water depth at nest s i t e s averaged 0.9m (+0.1) (n=19). Mean water l e v e l s decreased by 5.6cm ( + 0.3) (n=12) between 15 May and 31 J u l y 1985 and 15.9cm (+0.7) f o r the same period i n 1986. Decreases i n water l e v e l were s i g n i f i c a n t l y d i f f e r e n t between years (paired t - t e s t , t=15.1, df=9, 45 Table I I . Lake morphology at selected Eared Grebe breeding lakes. WATER DEPTH FLUCTUATIONS IN WATER LEVELS LAKE MEAN MAX AT NEST 1985 1986 1985-1986 (m) (m) (m) (cm) (cm) (cm) 6 1.4 2.5 0.8 -4.5 -11.0 -16.7 11 0.9 1.9 0.8 -4.5 - -10 .3 12 0.8 1.5 1.0 -5.5 -18.8 8.2 16 1.0 1.0 1.0 -4.7 -16. 6 -16.7 24 1.3 2.1 0.5 -4.8 -16.8 -26 0.8 1.5 0.8 -5.1 -15.0 -14.3 28 0.7 2.5 0.5 - -14 .7 -55 0.6 1.0 0.5 -6.6 -18.9 -17 . 9 42 1.0 2.0 0.8 -6.0 - -8.1 53 1.9 3.4 0.6 -5.7 -13.7 -8.1 50 0.8 1.2 1.0 -5.7 -16.2 -8.9 McMRY 1.5 2.2 1.4 -8.6 -17.1 -11.5 WESTW 1.0 - 1.5 -5.9 -15.8 -11.8 NL1 1.0 - 1.0 - - -NL2 - - 1.0 - - -NL3 - - 1.2 - - -NL4 0.6 1.2 - - - -NL5 - - 0.5 - - -NL6 1.1 2.0 - - - -NL7 - 1.0 - - -NL8 - - 1.0 - - -NL9 0.7 - - - - -NL10 — — 1.0 - - -MEAN 1.0 1.8 0.9 -5. 6 -15. 9 -10.6 SE 0.1 0.2 0.1 0.3 0.7 2.2 (n) (17) (15) (19) (12) (11) (11) 46 p<0.01), with water l e v e l s on 15 May 1986 averaging 10.56cm (+2.16) l e s s than on the same date i n 1985. Water chemistry analyses were performed on samples o r i g i n a t i n g from 27 lakes (Table I I I ) . A l l lakes were a l k a l i n e , with pH averaging 8.3 (+0.1). Conductivity averaged 2518.4 (+437.4) umhs/sec, while s a l i n i t y averaged 1.7 (+0.3) ppt. Hardness readings averaged 380.6 (+74.8). Many-fold v a r i a t i o n s i n magnitude were observed f o r a l l water chemistry v a r i a b l e s . Breeding lakes ranged i n s i z e from 0.7ha to 716.3ha, the average being 103.6ha (+35.5). Breeding abundance per lake ranged from 1 to 440 p a i r s . Eight lakes i n the Riske-Creek area were sampled on both 3 June and 10 J u l y 1986 to determine seasonal v a r i a t i o n s i n water chemistry (see Table IV f o r data). A Wilcoxon Signed Ranks Test showed no s i g n i f i c a n t d i f f e r e n c e s between June and J u l y readings, although a l l readings were on average higher i n Ju l y than i n June (see Table IV). Evaporation was l i k e l y responsible f o r higher readings i n l a t e summer. 47 Table I I I . Water chemistry c h a r a c t e r i s t i c s and lake area of Eared Grebe breeding lakes i n B.C. LAKE NO, , BREEDING PH CONDUCTIVITY SALINITY HARDNESS AREA PAIRS (umhs/ sec) (PPt) (ppm) (ha) COYOTE 6 8 . 5 4050 .0 2. 9 307 . 8 16 .0 McMURRAY 440 8 .8 7200 . 0 3. 5 153. 9 162 . 0 8432 21 8 . 6 800 .0 1. 0 547 . 2 19 .5 UPPERDRY 28 7 .9 148 .0 0. 0 119. 7 27 . 1 JAMIESON 8 7 .6 320 .0 0. 3 256. 5 17 .9 3-DRY 2 8 .2 165 .0 0. 0 102 . 6 10 .0 55 4 8 .5 2050 .0 1. 7 649. 8 1 .3 12 20 8 .8 990 .0 0. 8 102 . 6 3 .0 11 35 8 . 6 3730 .0 3. 0 290 . 7 7 .0 GREEN-B 6 8 . 6 8000 .0 6. 5 340 . 2 . 4 .0 MCQUEEN 25 7 . 3 450 .0 0. 2 256. 5 152 .3 BOUNDARY 175 6 .2 260 .0 0 . 0 171. 0 460 .0 GREEN-A 3 8 .5 2750 .0 2. 0 615. 6 39 .3 BOUDREAU 100 8 .2 180 .0 0. 0 119. 7 453 . 8 CECIL 400 8 .5 328 .0 0. 0 171. 0 716 .3 4403 36 8 .2 1820 .0 1. 3 837. 9 73 . 4 LITLWHIT 400 8 .5 5100 .0 4 . 0 171. 0 166 . 7 SLOANESL 3 7 .4 165 .0 0. 0 85. 5 10 .0 42 17 8 .5 1750 .0 1. 0 546. 3 4 .8 24 2 8 . 6 5500 .0 3. 5 1915. 2 3 . 4 6 85 8 . 5 3220 .0 2. 0 153 . 9 27 .2 53 4 8 . 4 1270 .0 0. 8 307. 8 3. .3 16 28 8 . 5 5800 .0 3. 7 153. 9 11 . 6 26 7 8 . 5 3300 .0 2. 2 889. 2 2 .7 28 1 8 .5 3200 .0 2. 0 222. 3 5. .1 50 5 8 .2 1950 .0 1. 2 649. 8 . 7 MEADOW 37 8 . 5 3500 .0 2. 3 102. 6 496 . 6 ELKHORN 200 - 90 .8 WESTWICK 220 - 40. . 6 MEAN= 79.9 8 .3 2518 . 4 1. 7 380. 6 103 . 6 SE = 24.1 0 . 1 437 . 4 0. 3 74 . 8 34 .5 (n) = (29) (27) (27) (27) (27) (29) 48 Table IV. Water chemistry readings on 3 June and 10 J u l y 1986. CONDUCTIVITY SALINITY PH HARDNESS (umhs/sec) (ppt) (ppm) LAKE 3 June 10 Jul y 3 June 10 Jul y 3 June 10 J u l y 3 June 10 July 24 3200 5500 2 . 1 3.5 8.2 8.6 410.4 1915.2 50 1600 1950 1 1.2 8.1 8.2 427. 5 649.8 26 2550 3300 1 .8 2.2 8.2 8.5 666. 9 889.2 6 2420 3220 1 . 6 2 8.5 8.5 119.7 153.9 42 1370 1750 0 . 8 1 8.3 8.5 239. 4 546.3 40 1530 1480 1 1 8.2 8.6 393. 3 410.4 28 3430 3200 2 .2 2 8.5 8.5 102.6 223.3 55 1650 2050 1 1.7 8.2 8.5 530.1 649.8 MEAN 2218.8 • 2806.3 1 . 44 1.83 8 .28 8.49 361.24 679.74 SE 282.9 463.0 .20 .29 .05 .04 69.42 195.81 2- E f f e c t s of a b i o t i c f a c t o r s on breeding density The stepwise m u l t i p l e regression i d e n t i f i e d only lake area as a p r e d i c t o r of the number of breeding p a i r s , with l a r g e r lakes supporting s i g n i f i c a n t l y l a r g e r breeding populations than smaller ones (r 2 = 0.60, t=6.36, p<0.01). Lake p r o d u c t i v i t y (as estimated by water conductivity) d i d not s i g n i f i c a n t l y a f f e c t number of breeding p a i r s . 49 3- Nest s i t e s e l e c t i o n Twenty-nine lakes were used to cha r a c t e r i z e n e s t - s i t e l o c a t i o n . Three lakes had nesting areas both close and f a r from shore and were not included i n the f o l l o w i n g analyses. Of the remaining 26, 10 lakes had nesting areas close to shore, and 16 had nesting areas f a r from shore. P h y s i c a l and chemical c h a r a c t e r i s t i c s of lakes with nesting areas close to and f a r from shore are presented i n Table V. The number of breeding p a i r s was s i g n i f i c a n t l y lower when nests were close to shore than when nests were f a r from shore (t=-5.50, p<0.01) (Fig. 4a). Lake area (t=-5.53, p<0.01), hardness (t=-2.57, p=0.02) and water depth at nest (t=-4.79, p<0.01) also d i f f e r e d on lakes where nests were close and f a r from shore (see F i g . 4b, c and d) . Nesting areas close to shore were found i n smaller lakes with higher hardness readings, and nesting areas were located i n shallower water. Other than s i z e , there were 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 lake morphology (mean and maximum depth) between lakes with nesting areas close to and f a r from shore, and both types of lakes e x h i b i t e d s i m i l a r seasonal and annual f l u c t u a t i o n s i n water l e v e l s . Lakes with nesting areas close to shore were used l e s s c o n s i s t e n t l y (10 out of 15) than lakes with nesting areas f a r from shore (10 of 10) . 50 Table V. Habitat c h a r a c t e r i s t i c s (+se) of breeding lakes with Eared Grebe nests located close to and f a r from shore. NEST SITE LOCATION VARIABLE CLOSE TO SHORE FAR FROM SHORE No. Breeding p a i r s Lake area (ha) Water chemistry: - PH - Conductivity (umhos/sec) • - S a l i n i t y (ppt) - Hardness (ppm) (log scale) Lake depth: - Average (m) - Maximum (m) - At nest (m) Fluc t u a t i o n s i n water l e v e l (cm) : - May/July 1985 - May/July 1986 - May 1985/May 1986 No. of lakes used i n consecutive years 6.9 + 3.2 (n=10) 5.3 + 3.8 (n=10) 8.5 + 0.1 (n=10) 2796.5 + 479.6 (n=10) 1.9 + 0.3 (n=10) 6.1 +0.1 (n=10) 1.00 + 0.17 (n=7) 1.94 + 0.31 (n=7) 0.6 + 0.1 (n=9) 5.4 + 0.3 (n=6) 15.9 + 0.8 (n=6) 11.9 + 1.8 (n=6) 10 (n=15) 138.0 + 38.2 *(n=16) 182.4 + 55.5 * (n=16) 8.1 + 0.2 (n=14) 2651.9 + 756.5 (n=14) 1.8 + 0.5 (n=14) 5.3 +.2*(n=14) 1.03 + 0.11 (n=8) 1.64 + 0.27 (n=6) 1.1 + 0.1 *(n=9) 5.9 + 0.9 (n=4) 15.1+ 1.4 (n=4) 14.2 + 1.5 (n=4) 10 (n=10) *p<0.05, determined by t - t e s t a n a l y s i s 51 5-r a) 3 4-J CO tr < Q. LL O cr LU 2 3 Z C L O S E —I— FAR ~ 4 CO < LU tr < LU < 3. b) " C L O S E — r FAR 6.2-c) E a a « 5.8 H CO LU z Q 5.6-< X 5.4H 5.2« E 1.2-t-co LU z 1.0-1-< z t-Q. LU 0.8-Q CC LU 1- 0.6-< 0.4-d) C L O S E FAR C L O S E — r FAR Figure 4. Number of breeding p a i r s (a), b) lake area, c) hardness and d) water depth at nest (+SE) f o r lakes where ne s t i n g areas are l o c a t e d c l o s e and f a r from shore. 52 4- Anti-predator value of nest s i t e l o c a t i o n On nests with covered eggs, predation caused more losses (x2=11.67, p<0.01, n=190 nests) f a r from shore than close to shore (Fig. 5a) . The e f f e c t s of egg cover and nest concealment were only-measured on nests f a r from shore. For those nests, covered eggs suffered l e s s predation (x2=21.22, p<0.01, n=192 nests) than exposed eggs (Fig 5b), but concealed nests d i d not have s i g n i f i c a n t l y lower egg predation rates than exposed nests (x2=0.27, p=0.60, n=190 nests) (Fig. 5c). S i m i l a r r e s u l t s were obtained f o r egg predation a f t e r 8 days. On nests with covered eggs, predation was higher away from shore (x2=9.54, p<0.01, n=181 nests) than close to shore (Fig. 6a). On nests f a r from shore, nests with exposed eggs su f f e r e d higher predation (x2=27.15, p<0.01, n=173) than nests with covered eggs (Fig. 6b), while there were 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 rates of egg l o s s between concealed and non-concealed nests (x2=0.89, p=0.34, n=173 nests) (Fig. 6c). The type of predation observed on q u a i l eggs was s i m i l a r to that observed on eggs of grebes and other waterbirds nesting i n the Riske-Creek area (pers. obs.). Many eggs showed roughly t r i a n g u l a r -shaped punctures on the side of the eggs, i n d i c a t i n g avian predation (Rearden 1951). American Coots were observed puncturing some eggs. 53 H II) Ul Z u. Ul .1 CO C9 o Ul K CD Ul z 0) a o Ul CO Ul z u. Ul -I CO o o Ul 2.8' 2.4-2.0 1.6 1.2-a) 0.8 2.8 2.4 2.0-1.6 1.2-0.8' 2.8 2.4 2.0' 1.8-1.2-b) 0.8 c) m96 mS4 FAR -7" CLOSE n:04 m92 COVERED N 0 T COVERED m93 n>83 CONCEALED NOT CONCEALED Figure 5. Comparison of the number of eggs l e f t i n a r t i f i c i a l platforms (+SE) a f t e r 4 days i n r e l a t i o n to a) nest l o c a t i o n f o r nests with covered eggs, b) egg cover f o r nests f a r from shore and c) nest concealment f o r nests f a r from shore. 54 (0 Ul z M a a 01 Ul co o o Ul CO Ul CO o o Ul 2.8 2.4-2.0 1.6 1.2 0.8 a) 2.8 2.4 2.0-1.6-1.2-0.8 2.8' 2.4 2.0 1.6 1.2 b) 0.8-c) n:96 n>94 FAR CLOSE n:94 n:32 COVERED N 0 T COVERE0 r>:93 n:93 CONCEALED NOT CONCEALED Figure 6. Comparison of the number of eggs l e f t i n a r t i f i c i a l p latforms (+SE) a f t e r 8 days i n r e l a t i o n to a) nest l o c a t i o n f o r nests with covered eggs, b) egg cover f o r nests f a r from shore and c) nest concealment f o r nests f a r from shore. 55 Muskrats (Ondatra zibethicus) were repeatedly observed eating bulrush on Eared Grebe nests, which sometimes r e s u l t e d i n crushed grebe eggs. Discussion 1- Breeding habitat General d e s c r i p t i o n s of Eared Grebe breeding h a b i t a t i n d i c a t e that they nest i n small productive lakes i n Europe (Cramp and Simmons 1977) and mostly i n medium-sized or l a r g e r lakes i n North America (Palmer 1962) . Previous d e s c r i p t i o n s f o r B r i t i s h Columbia show that Eared Grebes nest i n marshy habitat on lakes of moderate s i z e (Munro 1941). Habitat c h a r a c t e r i s t i c s were not q u a n t i f i e d i n these studies. In North Dakota, Eared Grebes p r e f e r shallow large ponds (>19.4ha) with abundant emergent vegetation over small ponds (Faaborg 197 6) . I found that Eared Grebes i n B r i t i s h Columbia also nest i n shallow, productive lakes with emergent cover. However, breeding lake s i z e v a r i e d widely. Twelve out of 27 breeding lakes were small (<10 ha) . Nesting on small lakes i s l i k e l y more common than p r e v i o u s l y suspected f o r the f o l l o w i n g reasons. F i r s t , l a r g e r lakes contain l a r g e r breeding populations and are thus more known 56 and e a s i l y detected than smaller lakes. Breeding records may also be biased i n favor of l a r g e r lakes or concentrations of b i r d s . Furthermore, l a r g e r lakes are used more continuously than smaller lakes. 2- Correlates of breeding group s i z e a) h a b i t a t s i z e Habitat s i z e a f f e c t s habitat s e l e c t i o n i n various ways. F i r s t , l a r g e r lakes may provide more diverse h a b i t a t s than smaller lakes, and thus support more i n d i v i d u a l s (Faaborg 1976). Although I d i d not study t h i s , I b e l i e v e that increased h a b i t a t d i v e r s i t y i s not important f o r the number of breeding p a i r s , because: 1) breeding p a i r s used s i m i l a r nesting habitats on wetlands of d i f f e r e n t s i z e s , and 2) foraging success d i d not d i f f e r s i g n i f i c a n t l y across lakes (unpubl. data). A second hypothesis i s that l a r g e r lakes provide l a r g e r amounts of resources (food or nest s i t e s ) than smaller lakes, and that breeding abundance i s res o u r c e - l i m i t e d . Nest s i t e a v a i l a b i l i t y i s not l i k e l y l i m i t i n g breeding abundance, as most breeding lakes are bordered with extensive bulrush stands. I used water c o n d u c t i v i t y as an index of food abundance and I compared adult foraging rates and foraging success on d i f f e r e n t lakes. Wetland p r o d u c t i v i t y was not s i g n i f i c a n t l y r e l a t e d to breeding density, but t h i s i s not 57 conclusive, as p r o d u c t i v i t y was not adjusted f o r lake s i z e . Also, there i s a hyperbolic r e l a t i o n s h i p between water c o n d u c t i v i t y and wetland p r o d u c t i v i t y (Northcote and L a r k i n 1956). b) Habitat p r e d i c t a b i l i t y Extensive seasonal and annual v a r i a t i o n s i n water l e v e l s were observed on a l l breeding lakes. On a lm-deep lake, I found 25% decreases i n water l e v e l s over a 12-month per i o d i n c l u d i n g a " t y p i c a l " summer and a low snowpack winter. F l u c t u a t i o n s i n water l e v e l s are r e l a t e d to v a r i a t i o n s i n water chemistry, plant growth and i n v e r t e b r a t e food abundance (see Lancaster 1985). For Eared Grebes, t h i s may t r a n s l a t e i n t o v a r i a t i o n s i n food abundance and nest s i t e a v a i l a b i l i t y . Winter snow pack and summer weather have a major infl u e n c e on water l e v e l s . Because both are unpredictable, d i s t r i b u t i o n and q u a l i t y of breeding habitat are also unpredictable. Temporary losses of nesting habitat because of f l u c t u a t i o n s i n water l e v e l s have been recognized by Palmer (1962) and Cramp and Simmons (1977). My study q u a n t i f i e d those losses and found that 20% of the wetlands surveyed on consecutive years were not used by breeders on both years. This f i n d i n g has important i m p l i c a t i o n s f o r the species management. 58 Larger breeding groups were found i n more p r e d i c t a b l e h a t i t a t . Nests close to shore i n shallow water were used by fewer p a i r s than nests f a r from shore i n deeper water. Decreases i n water l e v e l would most severely a f f e c t nests located i n shallower water i n areas close to shore, as I observed. However, species nesting i n unpredictable environments should not be h i g h l y p h i l o p a t r i c , because p r i o r reproductive success cannot be used to p r e d i c t future prospects (Shields et al. 1988). Lower p h i l o p a t r y could r e s u l t i n smaller group s i z e s i n lakes with nests located i n shallower water. Even though I cannot d i s c a r d the hypothesis that low p h i l o p a t r y explains small breeding group s i z e s when nests are close to shore, I suspect that breeding group s i z e i s b e t t e r explained by tr a d e - o f f s between nest concealment and predation (see below). 3- Nest s i t e l o c a t i o n Nest close and f a r from shore were found at d i f f e r e n t l o c a t i o n s on otherwise s i m i l a r lakes. Nests close to shore were found on smaller lakes, used by fewer breeders and had nests located i n shallower water than lakes with nesting areas f a r from shore. The r e l a t i o n s h i p between lake s i z e and nest l o c a t i o n was probably because emergent vegetation was only found close to shore on small lakes (pers. obs.). A l l lake s i z e s considered, b i r d s nested f a r from shore when vegetation was a v a i l a b l e both close to and f a r from 59 shore i n a l l but 3 cases. Those 3 cases, however, are i n t e r e s t i n g and show that lake s i z e cannot f u l l y account f o r nest l o c a t i o n . 4- Antipredator value of nest s i t e s The experiment I conducted showed that, f o r nests with covered eggs, predation rates inherent to nest s i t e l o c a t i o n were lower close to shore than f a r from shore. On nests f a r from shore, covered eggs were l e s s preyed upon than exposed eggs, while nest concealment d i d not appear to a f f e c t predation rates. I f predation i s lowest close to shore, why are most bi r d s nesting f a r from shore? I hypothesized that predation close to shore was by both mammalian and avian predators, while predation away from shore was s o l e l y by avian predators. I f both predator types occur as frequently and have the same impact on nesting b i r d s , predation would be minimized by nesting f a r from shore, where nests are only exposed to avian predators. I found the opposite, i . e . predation i s lower close to shore than away from shore. This i n d i c a t e s e i t h e r : 1) an e f f e c t i v e parental defense of the nest against avian predators but not against mammalian predators (I d i d not measure nest attendance and nest defense) or 2) frequency of occurrence and impact of predators are d i f f e r e n t close to and f a r from shore. 60 In my study area, Somerville (1985) repeatedly observed corvids preying upon eggs. Mammalian predators such as Mink (Mustela vison) consume eggs and-adults (Arnold and F r i t z e l l 1987), and t h e i r impact i s l i k e l y greater than avian predators preying s o l e l y upon eggs. A Mink k i l l e d 51 out of 200 Eared Grebes breeding close to shore on Westwick Lake, B.C. i n 1986, while a second breeding group of the same s i z e nesting near the center of the same lake was l e f t untouched (Breault and Cheng 1988) . The colony nesting close to shore was subsequently abandoned. I also observed coyotes (Canis Latrans) searching emergent vegetation close to shore. Those observations suggest that, i n c e n t r a l B.C., mammalian predation i s r a r e r but has more severe impact than avian predation. Because of t h i s , l arge breeding groups would not b e n e f i t from nesting close to shore, as large numbers of breeders a t t r a c t more predators (see Wittenberger 1985). Since l a r g e r groups are more conspicuous by nature, nesting f a r from shore might reduce mammalian predation on adult and eggs. For nests f a r from shore, no dif f e r e n c e s were observed i n rates of egg l o s s between concealed and exposed nests. E i t h e r 1) vegetation does not a f f e c t predation, or 2) a c r i t i c a l amount of emergent vegetation must be present to o f f e r e f f e c t i v e nest concealment. 61 I suggest that nest concealment i s not important to Eared Grebes, f o r the f o l l o w i n g reasons. F i r s t , adults often nested s u c c e s s f u l l y i n the absence of emergent vegetation. Secondly, adults d i d not nest i n dead vegetation, even though dense stands were a v a i l a b l e . Instead, they delayed nest b u i l d i n g u n t i l green shoots appeared. Nest concealment could be equally provided by dead vegetation. Preference f o r green shoots suggests that nest s i t e s require greater support than can be provided by dead emergent vegetation alone. F i n a l l y , parental v i g i l a n c e might reduce egg predation rates by avian predators. In the course of my study, I never observed avian predators preying upon Eared Grebe eggs. My experiment disagrees with studies that showed that nests i n increased vegetative cover are l e s s preyed upon than more exposed nests (Bider 1968, Bowman and Harris 1980, Chasko and Coates 1982, Redmond et al. 1982). In my study, a c c e s s i b i l i t y of nests and impact of predators v a r i e d with vegetative cover. In wetlands, exposed nests i n a c c e s s i b l e to predators may experience lower predation rates than concealed nests i n more a c c e s s i b l e h a b i t a t s . Nest predation rates should be i n t e r p r e t e d with respect to impact and a c c e s s i b i l i t y of nests to predators. There are probably anti-predator b e n e f i t s derived from anchoring nests to emergent vegetation, but my experiment f a i l e d to document them. D i f f e r e n t t e s t s could be conducted to determine i f vegetation 62 reduces nest predation. F i r s t , one could place a r t i f i c i a l nesting platforms with and without vegetation on breeding lakes. Because a r t i f i c i a l platforms with and without emergent vegetation provide the same nest support, the type of platforms s e l e c t e d by nesting p a i r s would i n d i c a t e the importance of emergent vegetation. A d i f f e r e n t approach would cons i s t i n repeating my experiment with a r t i f i c i a l platforms with d i f f e r e n t l e v e l s of emergent vegetation, to determine i f and when nest concealment decreases predation rates on eggs. O v e r a l l , I i n t e r p r e t nest s i t e c h a r a c t e r i s t i c s i n terms of a tr a d e - o f f between predation and group s i z e . Nests close to shore are more concealed and used by fewer p a i r s , but are more a f f e c t e d by nest predation. Nests f a r from shore are l e s s concealed and used by l a r g e r numbers of breeders, and they are l e s s a f f e c t e d by nest predation. I f nest attendance deters avian predators, nest s i t e s e l e c t i o n would thus act to decrease exposure to predators. 63 Summary P h y s i c a l and chemical c h a r a c t e r i s t i c s of breeding lakes were studied at 27 breeding lakes and were r e l a t e d to number of breeding p a i r s . Breeding took place i n shallow lakes of various s i z e s , subject to extensive v a r i a t i o n s i n water l e v e l s . Lake s i z e was the only s i g n i f i c a n t f a c t o r r e l a t e d ( p o s i t i v e l y ) to breeding abundance. Nest s i t e s were c l a s s i f i e d i n t o 2 categories: nest s i t e s close to and f a r from shore. Nests close to shore were associated with shallower waters, smaller lakes and fewer breeding p a i r s than nests f a r from shore. A v a i l a b i l i t y of . nesting areas close to shore i s l e s s p r e d i c t a b l e than f a r from shore, and lakes with breeding areas close to shore were l e s s c o n s i s t e n t l y used than lakes with nesting areas f a r from shore. For unattended nests, nest predation was higher f a r from shore than close to shore. I f nest attendance can decrease avian predation rates, lower frequency of occurrence and lower impact of predators away from shore might e x p l a i n why most b i r d s nested f a r from shore. Nest s i t e s e l e c t i o n can thus be approached as a t r a d e - o f f between breeding group s i z e , nest concealment and nest predation, with nests close to shore maximizing concealment by nesting i n small groups i n dense vegetation, while nests f a r from shore decrease exposure to mammalian predators by nesting i n large groups away from shore. 64 CHAPTER 4: COLONIALITY AND FACTORS AFFECTING REPRODUCTIVE SUCCESS IN EARED GREBES COLONIES 65 Introduction Nesting colonies are s i t e s where groups of i n d i v i d u a l s or p a i r s nest at a more or l e s s c e n t r a l i z e d l o c a t i o n from which they r e c u r r e n t l y depart i n search of food (Wittenberger and Hunt 1985). Three ideas have been used to e x p l a i n avian c o l o n i a l i t y : 1) colonies form from aggregation at l i m i t e d resources; 2) i n d i v i d u a l s nesting i n colonies enjoy foraging b e n e f i t s ; and 3) colonies form to decrease predation (Alexander 1971; Krebs 1978; Wittenberger and Hunt 1985; Kharitonov and Siegel-Causey 1988) . C o l o n i a l i t y can r e s u l t from aggregation at l i m i t i n g resources such as breeding s i t e s (Lack 1968) . Nest s i t e s are often more densely packed than required by nest s i t e a v a i l a b i l i t y alone [see Coulson (1971) and Birkhead (1976) i n Wittenberger and Hunt 1985], so other advantages (such as increased foraging success and lower predation) may be associated to nesting close to c o n s p e c i f i c s . C o l o n i a l i t y could enhance foraging i n d i f f e r e n t ways. I f food a v a i l a b i l i t y v a r i e s both s p a t i a l l y and temporally, i n d i v i d u a l s would minimize distances to foraging s i t e s by nesting i n c e n t r a l l o c a t i o n s (Horn 1968). Foragers might also use colonies to obtain information on food l o c a t i o n and abundance (Ward and Zahavi 1973) . There i s l i t t l e evidence to support the l a t t e r hypothesis [Wittenberger and Hunt 1985, but see Brown (1986; 1988a)]. 66 There i s extensive evidence that c o l o n i a l i t y reduces nest predation. Colonies can 1) enhance predator d e t e c t i o n , 2) "swamp" predators by p r o v i d i n g s p a t i a l l y and temporally overabundant food supply, 3) provide communal mobbing of predators and 4) increase the p r o b a b i l i t y that predators w i l l attack other group members (from reviews i n Caraco et al. 1980; Findlay and Cooke 1982; Shields 1984; Wittenberger and Hunt 1985; Brown and Hoogland 1986; Brown and Brown 1987). F i n a l l y , nest l o c a t i o n w i t h i n colonies has been shown to have an e f f e c t on predation rates (e.g. Patterson 1965; Coulson 1968; Tenaza 1971; Dexheimer and Southern 1974; Gross and McMillan 1981). Eared Grebes are good f o r studying c o l o n i a l i t y and breeding success. F i r s t , the grebe family shows a range of breeding s o c i a l i t y (see Palmer 1962) . Secondly, Eared Grebes nest at d i f f e r e n t d e n s i t i e s i n B.C. (Chapter 2), with breeding abundance ranging from 1 p a i r to 590 p a i r s per lake i n 1985 and 1986. Small breeding groups are common and c o n s t i t u t e a non-negligible p o r t i o n of the breeding population. F i n a l l y , breeding chronology v a r i e s widely from colony to colony (Munro 1941; M c A l l i s t e r 1956;- 1958). Because colonies are found close to one another, i t can be assumed that neighbouring colonies are subject to s i m i l a r pressure from predators. Differences i n reproductive success across colonies 67 should then s o l e l y r e f l e c t d i f f e r e n c e s i n group s i z e and habitat s e l e c t i o n and not d i f f e r e n c e s i n predator abundance. My r e s u l t s (Chapter 3) suggest that nest s i t e a v a i l a b i l i t y i s not l i m i t i n g and that there are few foraging advantages to nesting i n groups. This chapter w i l l focus on nest predation rates and reproductive success at Eared Grebe c o l o n i e s . I assume that b e n e f i t s from c o l o n i a l nesting are t r a n s l a t e d i n t o higher reproductive success (and not i n t o higher adult s u r v i v a l ) , and I i n v e s t i g a t e c o r r e l a t e s of reproductive success. Because e a r l y -nesters often enjoy higher reproductive success than l a t e - n e s t e r s (Lack 1968), I consider how chronology a f f e c t s reproductive success. There i s a l s o evidence that percentage of s u c c e s s f u l nests increases with nesting synchrony (e.g. D a r l i n g 1938; Veen 1977; Emlen and Demong 1975; Gochfeld 1980). I also looked f o r t h i s . Components of reproductive success are used to determine which part(s) of the breeding cycle i s ( a r e ) responsible f o r d i f f e r e n c e s i n reproductive success. Three hypotheses w i l l be considered: higher reproductive success i s r e l a t e d to 1) higher c l u t c h s i z e ; 2) higher nest p r o d u c t i v i t y ; or 3) to greater post-hatching s u r v i v a l . I f i r s t describe breeding chronology and breeding success. Then I i n v e s t i g a t e r e l a t i o n s h i p s between breeding success and: 1) nesting chronology, 2) nesting synchrony and 3) colony s i z e . I then use a 68 m u l t i v a r i a t e approach to determine the r e l a t i v e importance of these 3 influences on reproductive success. F i n a l l y , I use observations on marked i n d i v i d u a l s to discuss colony s e l e c t i o n i n Eared Grebes. P a i r s breeding alone are r e f e r r e d to as colonies of 1 p a i r . Methods 1- Study s i t e Breeding .phenology was studied at Riske-Creek, B.C. The study area covered roughly 10 km2. The area i s part of the Cariboo-Aspen-Lodgepole Pine-Douglas F i r Parkland biogeoclimatic Zone of K r a j i i n a (1969; 1973), and c o n s i s t s of r o l l i n g savannah upland dominated by Agropyron spicatum and stands of Populus tremuloides and Pinus contorta (Cannings and Scudder 1978). The area i s also under the inf l u e n c e of the rainshadow e f f e c t of the Coast Mountains ( B e i l 1974). My study area included 10 lakes used by breeding Eared Grebes i n 1985 and 9 lakes i n 1986. Lakes ranged i n s i z e from 0.7 to 27.2 ha, and were used by 1 to 81 p a i r s per lake. Together they accounted f o r approximately 200 nesting p a i r s each year. 69 2- Surveys In both 1985 and 1986, shore counts of adults and young were conducted every 2 to 4 days from l a t e A p r i l to e a r l y August. Nesting areas were searched every 4 days, s t a r t i n g when adults were repeatedly seen c a r r y i n g vegetation i n t h e i r b i l l s . Nesting areas were mapped during each v i s i t except on the lake used by 81 p a i r s i n 1985, where too much disturbance would have been caused by long v i s i t s to the nesting area. V i s i t s to nests stopped a f t e r a l l eggs had hatched or when adults stopped v i s i t i n g t he.nesting area. Eggs were i n d i v i d u a l l y marked with permanent f e l t markers, and t h e i r presence was recorded at each v i s i t . 3- Colony s i z e Colony s i z e was defined as the maximum number of a c t i v e nests observed simultaneously during a breeding season. On most colonies, maximum a c t i v e nest count agreed ex a c t l y with h a l f the maximum number of adults surveyed throughout the summer. 4- Reproductive biology Nesting chronology, nesting synchrony, c l u t c h s i z e and reproductive performance were measured i n 1985 and 1986. Laying date was derived from the number of eggs at the nest and s h e l l 70 c o l o r . Laying i n t e r v a l between consecutive eggs i s roughly 1 day, and average c l u t c h s i z e i s 3.48 eggs ( M c A l l i s t e r 1958). V i s i t s every 4 days were therefore s u f f i c i e n t to estimate l a y i n g by back-dating one day f o r each egg present i n the nest. Sequences of l a y i n g were determined from egg c o l o r . Fresh eggs are pale blue and become q u i c k l y stained by nesting m a t e r i a l as they get older ( M c A l l i s t e r 1958; Palmer 1962). I c a l c u l a t e d l a y i n g dates f o r both f i r s t and a l l nesting attempts. Date of i n i t i a t i o n of f i r s t and a l l l a y i n g attempts were r e s p e c t i v e l y obtained by averaging i n i t i a t i o n dates of the f i r s t (n) nests i n a colony [where (n) i s the number of p a i r s breeding i n the colony] and of a l l nesting attempts recorded during a breeding season. Comparisons between f i r s t and a l l nesting attempts were used to assess frequency of nest losses and renesting i n colonies. Nesting synchrony was defined as the Standard Deviation (SD) of 'the mean l a y i n g date of f i r s t nesting attempts i n a colony. For each colony, I measured i n d i v i d u a l reproductive performance (clutch s i z e and number of young hatched per successful nest) and determined the number of successful nests and young fledged per colony. Fledging success could not be measured f o r i n d i v i d u a l p a i r s , because chicks are c a r r i e d under the parent's wings f o r t h e i r 71 f i r s t 3 weeks (van Ijzendoorn 1944 i n Palmer 1962) and forage independently past that age (Palmer 1962, Cramp and Simmons 1976). Clutch s i z e was defined as the highest number of marked eggs (see Chapter 2 f o r d e t a i l s ) observed on 3 consecutive v i s i t s . Egg h a t c h a b i l i t y was determined from c l u t c h s u r v i v a l . For c a l c u l a t i o n s , disappearances of clutches were presumed to happen halfway between v i s i t s . Although Eared Grebes incubate f o r 20 to 21.5 days ( M c A l l i s t e r 1956) , a nest was presumed to have hatched i f at le a s t one egg survived a minimum of 19 days. The d i f f e r e n c e ( i . e . 1-2 days) aimed at compensating f o r p o t e n t i a l e r r o r s i n estimating egg age and egg s u r v i v a l . The proportion of nests that s u c c e s s f u l l y hatched eggs per colony was c a l c u l a t e d by d i v i d i n g the number of nests where at l e a s t one egg was hatched by colony s i z e . The number of young hatched per p a i r was defined as the number of eggs present at the l a s t v i s i t p r i o r to the expected hatching date minus the number of unhatched eggs observed past i t . Fledging success was estimated from chick surveys. For each colony, f l e d g i n g success was defined as the maximum number of young more than 1 month o l d observed throughout the breeding season d i v i d e d by colony s i z e . Because chicks become f u l l y independent from t h e i r parents at 3 weeks of age (Palmer 1962), f l e d g i n g success 72 could not be measured f o r i n d i v i d u a l p a i r s . I used l i n e a r regressions to determine the r e l a t i o n s h i p between number of young hatched and number of young fledged. Differences across years f o r any of those parameters were studied with e i t h e r K ruskal-Wallis analyses or t - t e s t s . 5- Correlates of reproductive success I used separate analyses to r e l a t e reproductive performance (clutch s i z e , number of young hatched per successful nest, r a t i o of successful nest per p a i r and number of young fledged per pair) to 1) nesting chronology, 2) nesting synchrony and 3) colony s i z e . Depending on the analyses, I used e i t h e r observations from i n d i v i d u a l nests or mean values per colony. A l l v a r i a b l e s or t h e i r log-transformations were normally d i s t r i b u t e d , except f o r c l u t c h s i z e i n 1985 and 1986; mean c l u t c h i n i t i a t i o n date i n 1986 and nesting synchrony i n 1985. The r a t i o of successful nests per p a i r was arcsine-transformed. I used K r u s k a l - W a l l i s t e s t s f o r the analyses i n v o l v i n g non-no r m a l l y - d i s t r i b u t e d v a r i a b l e s . Analyses of variance and/or l i n e a r regressions were used with the remaining analyses. 73 6- M u l t i p l e stepwise r e g r e s s i o n on reproductive success A m u l t i p l e stepwise r e g r e s s i o n a n a l y s i s was used to a s c e r t a i n the r e l a t i v e importance of breeding chronology, n e s t i n g synchrony and colony s i z e on the number of young fledged' per colony. A l l values were normalized, except f o r c l u t c h i n i t i a t i o n date i n .1986 and n e s t i n g synchrony i n 1985, which were considered normally-d i s t r i b u t e d f o r the purpose of the a n a l y s i s . Separate analyses were conducted f o r 1985 and 1986. Analyses were conducted f o r both f i r s t n e s t i n g attempts and o v e r a l l n e s t i n g attempts. 7- I n d i v i d u a l q u a l i t y across c o l o n i e s I captured (Breault and Cheng i n press) and used c o l o r e d nasal d i s c s on 69 a d u l t Eared Grebes i n 1985 and 1986. Surveys conducted i n 1985, 1986 and 1987 were used to determine the l o c a t i o n , breeding status and breeding success of 54 i n d i v i d u a l s observed a f t e r banding and on subsequent years (n=14 a d u l t s ) . I used a Chi-Square t e s t to determine whether previous breeding success a f f e c t e d a d u l t r e t u r n and a l s o determined whether a d u l t s returned t o the colony they were banded on or moved to other c o l o n i e s . 74 R e s u l t s 1- R e p r o d u c t i v e b i o l o g y A) N e s t i n g chronology S m a l l numbers o f b i r d s were p r e s e n t on b r e e d i n g l a k e s when f i e l d work s t a r t e d i n A p r i l 1985 and 1986, but most b i r d s a r r i v e d i n May ( F i g u r e 7) . Nests were f i r s t observed on 27 May i n both 1985 and 1986 ( F i g u r e 8 ) , but f i r s t n e s t i n g attempts began l a t e r i n 1986 than 1985 [medians r e s p e c t i v e l y 6 J u l y (n=139) and 7 June (n=184) ] ( K r u s k a l - W a l l i s t e s t , p<0.01). The shape o f t h e d i s t r i b u t i o n s was a l s o d i f f e r e n t a c r o s s y e a r s . Median dates o f c l u t c h i n i t i a t i o n f o r a l l n e s t i n g attempts were r e s p e c t i v e l y 12 June i n 1985 (n=341 nests) and 30 June i n 1986 (n=195), 1986 b e i n g s i g n i f i c a n t l y l a t e r ( K r u s k a l - W a l l i s t e s t , p<0.01). A d u l t s d e p a r t e d from n e s t i n g l a k e s from m i d - J u l y on ( F i g . 7 ) , but d e p a r t u r e s were most apparent i n August. A d u l t s departed s e p a r a t e l y from young. Non-breeders and u n s u c c e s s f u l breeders l e f t n e s t i n g l a k e s a t an e a r l i e r date. Whether a d u l t s s t a y e d i n the area or m i g r a t e d southwards i s unknown. B) C l u t c h s i z e Mean c l u t c h s i z e was 3.14 +0.06 eggs p e r nest i n 1985 (n=191 nests) and was s i g n i f i c a n t l y s m a l l e r (p<0.01, K r u s k a l - W a l l i s t e s t ) 75 400-1 300H CO _j Q < u- 2 0 0 H cc LU m 2 Z 100H a) 1985 1 ••—r 1 1 r APRIL MAY JUNE JULY AUGUST CO 3 o < LU o OC LU CD Z 400-1 300H 200H 100H b) 1986 OH—• 1 1— 1 —l r APRIL MAY JUNE JULY AUGUST Figure 7. Adults surveys on breeding lakes i n the Riske Creek area i n 1985 and 1986. 76 150-1 CO I-co Ul z u. o cc UJ m s CD Z 100H 5<H 150 - t b) 1 9 8 6 MAY JUNE JULY AUGUST Figure 8. Date of c l u t c h i n i t i a t i o n f o r a l l nesting attempts i n the Riske-Creek area i n 1985 and 1986. 77 than i n 1986 (3.31 +0.06, n=99 nests). C) Hatching success Fewer young hatched per successful nest i n 1985 (2.84 +0.08, n=152 nests) than i n 1986 (3.07 +0.11, n=46 nes t s ) , but the d i f f e r e n c e between years was not s i g n i f i c a n t (Kruskal-Wallis t e s t , p=0.08). D) Fledging success The number of young fledged per p a i r i n 1985 (1.09 + 0.04, n=187 nests) was s i g n i f i c a n t l y higher than i n 1986 (0.53 + 0.06, n=139 nests) ( t - t e s t , p<0.01). Fledging success was hi g h l y c o r r e l a t e d with number of young hatched i n both 1985 (r2=0.99, n=7, p<0.01) and 1986 (r2=0.77, n=6, p=0.01) (Fig. 9). About 47% of eggs hatched survived to f l e d g i n g (slope on F i g . 9) on both 1985 and 1986, but there was much more v a r i a t i o n i n 1986. 2- Un i v a r i a t e analyses of fa c t o r s a f f e c t i n g reproductive success A) Breeding chronology E a r l i e r clutches were s i g n i f i c a n t l y l a r g e r than l a t e clutches i n 1985 (Kruskal-Wallis t e s t , n=191, p=0.02) (Fig. 10a), but not i n 1986 (Kruskal-Wallis t e s t , n=99, p=0.13) (Fig. 11a). The number of nests s u c c e s s f u l l y hatching eggs per p a i r was i n v e r s e l y c o r r e l a t e d with mean date-of f i r s t c l u t c h i n i t i a t i o n i n 1985 (r2=0.40, n=10, 78 YOUNG HATCHED Figure 9. C o r r e l a t i o n between number of young hatched and number young fledged i n 1985 and 1986. 79 Figure 10. R e l a t i o n s h i p s between c l u t c h i n i t i a t i o n date and a) c l u t c h s i z e , b) number of nests hatched per p a i r , c) number of eggs hatched per s u c c e s s f u l nest and d) number of young fledged per p a i r i n 1985. 80 4 • 2-1 -a) 150 - r T 160 170 180 190 200 NEST INITIATION DATE 2.0-1 150 160 170 180 190 200 NEST INITIATION DATE 7 6 i 5 4 • 3 -2 1 -I c) 150 — I — 160 T T 1 170 180 190 200 NEST INITIATION DATE tr • < a. tr LU to. Q LU CD O LU O z o 150 160 170 180 190 200 NEST INITIATION DATE Figure 11. R e l a t i o n s h i p s between c l u t c h i n i t i a t i o n date and a) c l u t c h s i z e , b) number of nests hatched per p a i r , c) number of eggs hatched per s u c c e s s f u l nest and d) number of young fledged per p a i r i n 1986. 81 p=0.05) (Fig. 10b), but not i n 1986 (r2=.27, n=9, p=0.16) (Fig. l i b ) . The number of young hatched per successful nest d i d not vary s i g n i f i c a n t l y with mean c l u t c h i n i t i a t i o n date of successful nests i n 1985 (Kruskal-Wallis t e s t , n=152, p=0.15) (Fig. 10c) and 1986 (Kruskal-Wallis t e s t , n=46, p=0.80) (Fig. 11c). E a r l y nests fledged s i g n i f i c a n t l y more young per p a i r than l a t e nests i n 1985 (r2=.90, p<0.00) (Fig. lOd), but not i n 1986 (Kruskal-Wallis t e s t , p=0.43) (Fig. l i d ) . B) Synchrony No s i g n i f i c a n t r e l a t i o n s h i p s were observed between nesting synchrony and c l u t c h s i z e i n 1985 (Kruskal-Wallis t e s t , n=8, p=0.43) and 1986 ' (r 2=.55, n=7, p=0.06), even though higher synchrony appeared to be c o r r e l a t e d with l a r g e r clutches i n 1986. There were no d i f f e r e n c e s between nesting synchrony and 1) the number of nests hatched per p a i r i n 1985 (Kruskal-Wallis t e s t , n=9, p=0.43) and 1986 (r2=0.16, n=8, p=0.33); 2) the number of young hatched per successful nest i n 1985 (Kruskal-Wallis t e s t , n=7, p=0.42) and 1986 (r2=0.13, n=5, p=0.56) and 3) the number of young fledged per p a i r i n 1985 (Kruskal-Wallis t e s t , n=9, p=0.43) and 1986 (r2=0.08, n=8, p=0.51). C) Colony s i z e Clutch s i z e was s i g n i f i c a n t l y smaller i n nests from smaller colonies than i n l a r g e r ones i n 1985 (Kruskal-Wallis t e s t , n=191, 82 p<0.01) (Fig. 12a) but not s i g n i f i c a n t l y so i n 1986 (Kruskal-Wallis t e s t , n=99, p=0.09) (Fig. 13a). The d i s t r i b u t i o n of l a y i n g dates was d i f f e r e n t across colony s i z e s . There were no r e l a t i o n s h i p s between colony s i z e and 1) the number of nests s u c c e s s f u l l y hatched per p a i r i n 1985 (r2=0.05, n=10, p=0.53) (Fig. 12b) and 1986 (r2=0.00, n=9, p=0.97) (Fig. 13b); 2) the number of young hatched per successful nest i n 1985 (r2=0.00, n=7, p=0.95) (Fig. 12c) and 1986 (r2=0.57, n=5, p=0.14) (Fig. 13c); and 3) f l e d g i n g success per p a i r i n 1986 (r 2 =0.02, n=9, p=0.75) (Fig. 13d). Fledging success per p a i r i n 1985 was p o s i t i v e l y c o r r e l a t e d to colony s i z e (r2=0.56, n=10, p=0.01) (Fig. 12d). 3- M u l t i p l e stepwise regression on f l e d g i n g success Mean c l u t c h i n i t i a t i o n date was the only p r e d i c t o r of fl e d g i n g success i n 1985 (r2=0.89, n=9, p<0.01), and no s i g n i f i c a n t p r e d i c t o r s were found f o r the 198 6 data. 4- I n d i v i d u a l q u a l i t y across colonies Of the 54 marked i n d i v i d u a l s f o r which s u f f i c i e n t data was a v a i l a b l e , adults that had a brood on the previous year were more l i k e l y to return (6 of 14) than adults without broods (8 of 46) (X2=3.85, p<0.05). Marked i n d i v i d u a l s were repeatedly observed on the same breeding lakes p r i o r to onset of l a y i n g , i n d i c a t i n g that 83 7-i ~ 2.0-1 a) 6 -5 -4-2 -1 • 0 C — I — 1.0 —r— 1.5 0.5 COLONY SIZE ( l o g ) —I 2.0 CD c "3 o cc < Q . cc LU 0 . Q LU Z o I-< z CO I-co LU z b) 1.5-1.0-0 .5-0.0 I • I I ' I I 0 0 0.5 1.0 1-6 2.0 COLONY SIZE ( l o g ) 5 i c) 4-> 3-' 2-> 0.6 —I— 0.8 —1— 1.0 —1— 1.2 —I— 1.4. T.6 COLONY SIZE ( l o g ) 2.0-t COLONY SIZE ( l o g ) F i g u r e 12.- C o r r e l a t i o n between col o n y s i z e and a) c l u t c h s i z e , b) number o f n e s t s hatched per p a i r , c) number o f eggs hatched per s u c c e s s f u l nest and d) number o f young f l e d g e d p e r p a i r i n 1985. 84 Figure 13. C o r r e l a t i o n between colony s i z e and a) c l u t c h s i z e , b) number of nests hatched per p a i r , c) number of eggs hatched per s u c c e s s f u l nest and d) number of young fledged per p a i r i n 1986. 8 5 late-breeders are not b i r d s attempting renesting. Six of the b i r d s caught i n colonies of more than 25 p a i r s returned to the same colony, while 7 i n d i v i d u a l s caught i n smaller colonies moved to l a r g e r colonies on subsequent years, even though the colonies where they were o r i g i n a l l y banded were s t i l l a c t i v e . One i n d i v i d u a l moved repeatedly between lakes. No b i r d s moved to smaller c o l o n i e s . Discussion 1- Breeding chronology Extensive v a r i a t i o n s i n breeding chronology have been reported across North America. Clutches are l a i d from l a t e A p r i l on i n the southern t h i r d of the U.S.; from e a r l y May w e l l i n t o June i n the northern U.S.; and w e l l i n t o June i n Canada (Palmer 1962). In Washington State, nesting begins i n mid-May and the bulk of the nests are s t a r t e d near 1 June (Yocom et al. 1958). In B r i t i s h Columbia, clutches were begun on 27 June i n 1955; 22 June i n 1956 ( M c A l l i s t e r 1956); on 20 May 1941; and on 16 J u l y 1940 (Munro 1941). Breeding chronology i n c e n t r a l B r i t i s h Columbia f i t with the data a v a i l a b l e f o r Washington State and B.C., with nests i n i t i a t e d from 27 May on i n 1985 and 1986, and median f i r s t c l u t c h i n i t i a t i o n date of 7 June i n 1985 and 6 J u l y i n 1986. However, l a y i n g was observed 86 i n t o August i n both 1985 and 1986 (Fig. 8), l a t e r than reported elsewhere. 2- Reproductive success P r o p o r t i o n a l l y fewer renesting attempts were i n i t i a t e d i n 1986 than i n 1985. Clutch s i z e s from both years are s t i l l smaller than the 3.48 eggs per nest reported by M c A l l i s t e r (1958). This might be because c l u t c h s i z e can vary with colony s i z e , and M c A l l i s t e r studied colonies l a r g e r than the ones used i n t h i s study. Other p o s s i b l e explanations include d i f f e r e n c e s i n breeding chronology, i n the number of renesting attempts or d i f f e r e n c e s i n nest p a r a s i t i s m . No q u a n t i t a t i v e information on breeding success i s a v a i l a b l e f o r the Western P a l e a r c t i c (Cramp and Simmons 1977) . Of 223 eggs l a i d i n South A f r i c a , only 12 young l e f t the nest (Broekhuisen and Frost 1968b). In North America, accounts of reproductive success c o n s i s t of estimates of young per adult during the breeding season. Yocom et al. (1958) estimated roughly one young per adult i n l a t e J u l y i n Washington State colonies. Munro (1941) presented young counts at selec t e d lakes throughout the summer, but young were not aged, so i t i s d i f f i c u l t to assess the number of young s u r v i v i n g to f l e d g i n g . Young counts do not however i n d i c a t e true reproductive success, because they do not consider f a i l e d breeding attempts. My 87 study appears to be the f i r s t one q u a n t i f y i n g both reproductive f a i l u r e and reproductive success i n Eared Grebe co l o n i e s . My study could not f i n d consistent d i f f e r e n c e s i n nest p r o d u c t i v i t y across colonies. However, d i f f e r e n c e s i n the number of nests hatched per p a i r suggest that nest predation i s the major f a c t o r a f f e c t i n g d i f f e r e n c e s i n reproductive success. Some of that d i f f e r e n c e could be due to d i f f e r e n c e s i n nest s i t e s e l e c t i o n (see Chap. 3) . Although nest predation can be reduced through communal mobbing (Gotmark and Andersson 1984), I could not f i n d any f i e l d or published evidence of communal mobbing i n Eared Grebes. I suggest that d i f f e r e n c e s i n nesting habitat are responsible f o r differences i n nest predation rates. 3- C o l o n i a l i t y and f a c t o r s a f f e c t i n g reproductive success A) E f f e c t s of colony s i z e This study d i d not support the hypothesis that group s i z e a f f e c t s reproductive success. Reproductive success i s only higher f o r c o l o n i a l than f o r s o l i t a r y b i r d s i n species with communal defense (Andersson and Wiklund 1978; Wiklund and Andersson 1980; Gotmark and Andersson 1984). My r e s u l t s showed that reproductive success increased with colony s i z e i n 1985, but there i s no evidence from f i e l d observations or from the l i t e r a t u r e that communal mobbing takes place i n Eared Grebes. 88 B) M u l t i v a r i a t e approach to reproductive success Because of e f f e c t s of both colony s i z e and chronology on nesting success, I used a m u l t i p l e stepwise regression to show that only c l u t c h i n i t i a t i o n date accounted f o r v a r i a t i o n s i n nesting success. E a r l y nesters d i d b e t t e r than l a t e ones, i r r e s p e c t i v e of colony s i z e . O v e r a l l , l a y i n g took place roughly 2 weeks l a t e r than i n 1985 than i n 1985, and there was a trend f o r l a t e nesters i n 1986 to do be t t e r than e a r l y nesters. This seems to i n d i c a t e that b e n e f i t s of e a r l y nesting are not consistent across years. Even though d i f f e r e n c e s i n reproductive success have been associated with breeding chronology (Burger 1979; Spaans et al. 1987), only one study has considered chronology e f f e c t s on reproductive success across colonies (Haas 1985). Haas argued that colony s i z e has d i f f e r e n t e f f e c t s on nesting success with changes i n environmental conditions (e.g. vegetative cover). E a r l y broods b e n e f i t only from colony s i z e , while l a t e broods are a f f e c t e d by both d i f f e r e n c e s i n vegetative cover and predator behavior. Comparative studies of c o l o n i a l i t y should t e s t f o r e f f e c t s of chronology, synchrony and group s i z e on nesting success. Absence of c o r r e l a t i o n s between group s i z e and reproductive success i n other studies might be explained by dif f e r e n c e s i n nesting chronology (Haas 1985). For example, swallows have been shown to have 89 extensive v a r i a t i o n s i n nesting chronology and nesting success (Snapp 1976; Brown and Brown 1987; M i l l e r 1987) . The study by Emlen and Demong (1975) on the r e l a t i o n s h i p between synchrony and reproductive success could have not taken i n t o consideration c o r r e l a t i o n s between chronology and synchrony. This r a i s e s the p o s s i b i l i t y that many studies on b e n e f i t s of group s i z e could have been biased by e f f e c t s of chronology or synchrony. C) Anti-predator b e n e f i t s of c o l o n i a l i t y D i f f e r e n t mechanisms have been proposed to e x p l a i n how c o l o n i a l nesting could decrease predation rates. Colonies could enhance predator detection (e.g. Pu l l i a m 1973; Hoogland and Sherman 1976; Hoogland 1979; Caraco et a l . 1980; Brown and Brown 1987); predators could be "swamped" by s p a t i a l l y and temporally overabundant food supply (Kruuk 1964; Nisbet 1975; Findlay and Cooke 1982); colonies could be defended through communal mobbing (e.g. Kruuk 1964; Lubcke 1975; Hoogland and Sherman 1976; Andersson and Wiklund 1978; Shields 1984) ; groups could form to d i l u t e predation (Hamilton 1971; Burger 1979); or to avoid peak of predator a c t i v i t y (Wittenberger and Hunt 1985) . Although my study d i d not e x p l i c i t l y consider any of those mechanisms, I w i l l use i n c i d e n t a l observations to discuss them. Eared Grebes colonies might be n e f i t from increased predator detection i n 2 ways: because of increased group s i z e (more eyes to detect predators), and because l e s s dense vegetation i n larger 90 colonies (away from shore) makes predators more v i s i b l e . Increased group s i z e and increased predator v i s i b i l i t y may both play a r o l e i n i n c r e a s i n g predator detection. I do not b e l i e v e that predator swamping or d i l u t i o n e f f e c t occurs i n Eared Grebe colonies, as predation can r e s u l t i n large egg losses (see Somerville 1985) or adult c a s u a l t i e s (Breault et al. 1988). Mobbing behaviour was not observed i n my study, and there i s no published evidence that i t occurs. Peaks of predator a c t i v i t y might not avoided by nesting e a r l y . I observed higher nest losses e a r l y i n the season than l a t e , and work done i n the Riske-Creek area by Somerville (1985) also i n d i c a t e d lower predation rates f o r l a t e nesters. I suggest that anti-predator b e n e f i t s of c o l o n i a l i t y i n Eared Grebes are mostly r e l a t e d to increased predator detection. Some p r e d i c t i o n s from the anti-predator hypothesis were not supported. The number of nests hatched per p a i r and the number of young hatched per successful nest d i d not increase with group s i z e nor with nesting synchrony. The absence of documented a n t i -predation b e n e f i t s of colony s i z e might have been caused by the low number of colonies i n v e s t i g a t e d . Data c o l l e c t e d on nest predation rates i n various nesting habitats (see chapter 3) suggested a n t i -predation b e n e f i t s from nesting i n large groups, but I was unable to document those b e n e f i t s . 91 D) Net b e n e f i t s of e a r l y nesting E a r l y nesters enjoyed higher reproductive success than l a t e nesters. I f there are reproductive b e n e f i t s to be gained from nesting e a r l y , why nest l a t e ? Three f a c t o r s could produce l a t e nesters: h a b i t a t d i f f e r e n c e s , renesting attempts and v a r i a t i o n s i n i n d i v i d u a l q u a l i t y (such as age or previous breeding experience). Habitat d i f f e r e n c e s could cause d i f f e r e n c e s i n food a v a i l a b i l i t y and d i s t r i b u t i o n across breeding lakes and a f f e c t breeding chronology. Eared Grebe breeding lakes i n the Peace River region could be used to study the e f f e c t of hab i t a t d i f f e r e n c e s , as colonies of d i f f e r e n t s i z e s are found on some lakes. The breeding synchrony observed among colonies on the same lake (colonies sharing the same resources) i n d i c a t e s that breeding chronology i s l i k e l y to be a fu n c t i o n of h a b i t a t . Conversely, d i f f e r e n c e s i n nesting chronology between colonies suggest v a r i a t i o n s i n i n d i v i d u a l q u a l i t y . That study has not yet been conducted. E) I n d i v i d u a l q u a l i t y i n d i f f e r e n t colonies Differences i n b i r d q u a l i t y across colonies could explain d i f f e r e n c e s i n breeding chronology and colony composition (Veen 1977). Observations on marked adults i n d i c a t e d that l a t e breeders were not b i r d s attempting renesting. Only b i r d s from large colonies stayed i n the colonies where they were o r i g i n a l l y banded, while b i r d s from smaller colonies moved to l a r g e r ones. This suggests age-92 r e l a t e d d i f f e r e n c e s between colonies of d i f f e r e n t s i z e s . Banding returns were i n s u f f i c i e n t to consider e f f e c t s of previous breeding experience and reproductive success on colony s e l e c t i o n . Further adult and young marking i s needed to understand q u a l i t a t i v e d i f f e r e n c e s across colonies. 93 Summary Adults a r r i v e d to nesting lakes i n A p r i l and May i n 1985 and 1986; s t a r t e d nesting on 27 May on both years and most departed from nesting lakes i n J u l y and August. Median c l u t c h i n i t i a t i o n date was l a t e r i n 1986. Number of young fledged per p a i r declined with l a y i n g date i n 1985, but tended to increase with l a y i n g date i n 1986. Number of young fledged per p a i r increased with colony s i z e i n 1985. Nest predation was the major cause of nest l o s s e s . Number of young fledged per p a i r was p o s i t i v e l y c o r r e l a t e d with the number of eggs hatched. In a m u l t i p l e stepwise regression, only nesting chronology c o r r e l a t e d with d i f f e r e n c e s i n reproductive performance, with e a r l y nesters enjoying higher reproductive success. I discuss 3 hypotheses to e x p l a i n the presence of l a t e nesters: l a t e nesters are 1) adjusted to l o c a l resource a v a i l a b i l i t y ; 2) b i r d s attempting renesting and 3) i n d i v i d u a l s that cannot nest e a r l y . Observations on marked adults showed that l a t e nesters were not renesters, but were consistent with q u a l i t a t i v e d i f f e r e n c e s r e l a t e d to age across colo n i e s . 94 CHAPTER 5: GENERAL DISCUSSION In t h i s t h e s i s , I describe breeding biology and c o l o n i a l i t y of Eared Grebes nesting i n B r i t i s h Columbia. I discuss f i n d i n g s i n 5 sections: 1) breeding biology; 2) h a b i t a t p r e d i c t a b i l i t y ; 3) models of c o l o n i a l i t y ; 4) nesting chronology and synchrony and 5) conservation and management. 1- Breeding biology of Eared Grebes This s e c t i o n summarizes information on breeding d i s t r i b u t i o n , abundance, and breeding biology of Eared Grebes i n B r i t i s h Columbia. A) D i s t r i b u t i o n and abundance My surveys located 1761-4474 breeding p a i r s d i s t r i b u t e d over 47 lakes i n B.C. Breeders were concentrated i n the c e n t r a l I n t e r i o r and the Peace River regions, with the Southern I n t e r i o r and Northern Okanagan/Kamloops regions supporting s u b s t a n t i a l l y smaller breeding populations. Breeding abundance ranged from 1 to roughly 500 p a i r s per lake and was p o s i t i v e l y c o r r e l a t e d to lake s i z e . This i s probably because l a r g e r lakes provide more abundant or d i f f e r e n t resources (Faaborg 1976) than smaller ones. My study on d i s t r i b u t i o n and abundance of Eared Grebes (Breault et al. 1988) c o n s t i t u t e s a baseline against which future f l u c t u a t i o n s i n breeding abundance can be measured. However, 96 because I surveyed only 421 wetlands, f u r t h e r surveys are necessary to c h a r a c t e r i z e status and abundance of r e g i o n a l populations. Surveying should focus on the Central and Southern I n t e r i o r regions, which were l e a s t surveyed. These 2 regions include the highest number of productive wetlands i n B r i t i s h Columbia (Canadian Land Use survey map, Environment Canada). Most s u i t a b l e wetlands found i n the Peace River and Northern Okanagan/Kamloops regions were surveyed and/or monitored by Ducks Unlimited, so f u r t h e r surveys should not be conducted i n those areas. B) Nesting h a b i t a t Nesting took place on shallow, h i g h l y productive lakes of various s i z e s . Most nests were anchored to emergent vegetation, presumably because of increased support and re s i s t a n c e to wave ac t i o n (Broekhuisen and Frost 1968b). Two types of nest s i t e s were observed: nests close to shore and nests f a r from shore. Nests close to shore were located i n shallower water and associated with smaller, shallower lakes than nests f a r from shore. Nesting lakes were subject to extensive seasonal and annual environmental changes. Water l e v e l s decreased by roughly 25% between 1985 and 1986, perhaps a f f e c t i n g food abundance and d e f i n i t e l y a f f e c t i n g a v a i l a b i l i t y of nesting h a b i t a t . Environmental changes have been l i n k e d to s h i f t s of colony l o c a t i o n across years (Werschkul 1979, P r a t t and Winkler 1985). In Eared Grebes, 20% of 97 breeding lakes surveyed on 2 consecutive years (n=25) were not used on both years. A l l lakes not used on consecutive years had nesting areas located i n shallow water near shore, where nest s i t e s are subject to the most extreme v a r i a t i o n s i n water l e v e l s . My data suggest that Eared Grebes use 2 types of breeding lakes: i s o l a t e d lakes supporting large breeding populations (not e x t e n s i v e l y studied i n t h i s work) and areas with a high density of smaller lakes supporting smaller breeding populations (e.g. Riske-Creek area). Large lakes appeared able to b u f f e r environmental v a r i a t i o n s and Eared Grebes using them probably show high p h i l o p a t r y (see below). Habitat v a r i a b i l i t y has a more severe impact on smaller breeding lakes, and grebes nesting there are l i k e l y l e s s p h i l o p a t r i c . Differences i n breeding biology and reproductive success between large lakes and small wetland systems remain to be documented. 2- Importance of habitat p r e d i c t a b i l i t y Many authors have discussed the importance of habitat v a r i a b i l i t y and p r e d i c t a b i l i t y on c o l o n i a l nesting, mostly with respect to resource d i s t r i b u t i o n and s o c i a l foraging (see Wittenberger and Hunt 1985; Kharitonov and Siegel-Causey 1988) . I b e l i e v e that habitat p r e d i c t a b i l i t y i s also important at a deeper 98 l e v e l , and I w i l l discuss i t s i m p l i c a t i o n s f o r d i s t r i b u t i o n and p h i l o p a t r y i n Eared Grebes. A) D i s t r i b u t i o n Habitat p r e d i c t a b i l i t y can a f f e c t d i s t r i b u t i o n i n d i f f e r e n t ways. F i r s t , i t d i r e c t l y a f f e c t s habitat a v a i l a b i l i t y . In Eared Grebes, lakes subject to higher decreases i n water l e v e l s were less c o n s i s t e n t l y used than l e s s a f f e c t e d lakes. I n d i r e c t e f f e c t s could also take place. As s u i t a b l e habitat s i z e decreases, species become l o c a l l y e x t i n c t (Pielou 1979). For Eared Grebes, t h i s would t r a n s l a t e i n t o small populations or populations using small habitats running greater r i s k s of becoming l o c a l l y e x t i n c t . Small i s o l a t e d populations should be rare, as small l o c a l populations would become e x t i n c t f a s t e r than large populations. I r a r e l y observed i s o l a t e d small colonies of Eared Grebes, even though groups of small connected colonies were repeatedly observed. Large i s o l a t e d colonies (used by hundreds of breeding p a i r s ) were repeatedly observed. B) P h i l o p a t r y P h i l o p a t r y should increase with habitat p r e d i c t a b i l i t y . Species with p r e d i c t a b l e nest s i t e s (e.g. swallows, terns, g u l l s , herons, marine birds) are hi g h l y p h i l o p a t r i c (Wittenberger and Hunt 1985). Conversely, i f nest s i t e s are not p r e d i c t a b l e , there should be low p h i l o p a t r y to nesting areas. This suggests that, w i t h i n 99 populations, gradients i n nest s i t e p r e d i c t a b i l i t y are c o r r e l a t e d to gradients i n p h i l o p a t r y , which i s supported by my observations on marked i n d i v i d u a l s . Low p h i l o p a t r y could influence community s t r u c t u r e , which could i n t u rn i n f l u e n c e reproductive success and breeding chronology. Colonies formed of e x c l u s i v e l y young b i r d s would l i k e l y nest l a t e r and experience lower reproductive success than colonies made of older b i r d s . This could occur i f breeding adults group themselves based on t h e i r readiness to l a y , where age would be c o r r e l a t e d with readiness to l a y . There i s evidence that breeding chronology v a r i e s with age (see Coulson and White 1960). Anti-predator and foraging b e n e f i t s would l i k e l y favor h i g h l y synchronized nesting, with l a t e nesters subject to more resource depletion. Extensive adult movements p r i o r to nesting might have r e s u l t e d i n adult grouping based on body co n d i t i o n or some other q u a l i t a t i v e f a c t o r . 3- C o l o n i a l i t y i n Eared Grebes I observed both c o l o n i a l and s o l i t a r y nesting i n Eared Grebes, with colonies ranging i n s i z e from 1 to 3'43 p a i r s . Many lakes (mostly i n the Peace River and Central I n t e r i o r regions) supported more than 1 colony. 100 Although evolutionary causes of c o l o n i a l i t y i n Eared Grebes are unknown, current f a c t o r s maintaining i t can be studied. I compared reproductive success i n a dense group of colonies i n the Central I n t e r i o r to assess current reproductive b e n e f i t s of c o l o n i a l i t y . As mentioned e a r l i e r , 3 groups of hypotheses have been proposed to e x p l a i n the e v o l u t i o n of c o l o n i a l nesting i n b i r d s : 1) colonies a r i s e from clumping at l i m i t i n g resources, 2) colonies increase the e f f i c i e n c y i n obtaining resources and 3) colonies help decrease predation (Alexander 1974; Wittenberger and Hunt 1985). Those 3 hypotheses w i l l be discussed with respect to my data. A) Resource l i m i t a t i o n hypothesis B i r d s might aggregate to take advantage of l i m i t i n g resources such as nest s i t e s (Wittenberger and Hunt 1985) . The nest s i t e l i m i t a t i o n hypothesis i s p a r t i a l l y supported by the f a c t that breeding abundance was p o s i t i v e l y c o r r e l a t e d with lake s i z e , but such a r e l a t i o n s h i p cannot by i t s e l f e x p l a i n why nests are aggregated at colonies as opposed to being uniformly or randomly d i s t r i b u t e d over the breeding area. I i n t e r p r e t the lack of r e l a t i o n s h i p s between lake c h a r a c t e r i s t i c s (other than nest s i t e l o c a t i o n ones) and breeding abundance as i n d i c a t i n g that breeding lakes are of s i m i l a r nature. The d i f f e r e n c e i n nest s i t e s e l e c t i o n on otherwise s i m i l a r lakes, combined with a s i g n i f i c a n t l y d i f f e r e n t number of breeders at each type of nest s i t e a l so support the resource l i m i t a t i o n hypothesis. 101 Nest s i t e s do not, however, appear to be l i m i t i n g . Although not q u a n t i t a t i v e l y studied, emergent vegetation was very abundant on most lakes, and could probably have supported more breeding p a i r s than observed. Colonies also r e g u l a r l y moved to new areas a f t e r nest f a i l u r e , and p a i r s often s u c c e s s f u l l y hatched eggs at the new l o c a t i o n . I f nest s i t e s are l i m i t i n g , r e l o c a t i o n should not take place, or reproductive success at new s i t e s should be low because adults s e t t l e d down i n suboptimal h a b i t a t . I suggest that nest s i t e l i m i t a t i o n cannot e x p l a i n c o l o n i a l nesting i n Eared Grebes. B) Foraging b e n e f i t s A second hypothesis i s that colonies can evolve i f i n d i v i d u a l s gain foraging b e n e f i t s from being i n groups. Foraging gains could a r i s e from i n d i v i d u a l s independently t a k i n g advantage of food d i s t r i b u t i o n and p r e d i c t a b i l i t y (Horn 1968) or from t r a n s f e r of information about foraging areas at colonies (Ward and Zahavi 1965). Neither argument i s l i k e l y to apply to Eared Grebes. Horn's geometrical model assumes a cost f o r g e t t i n g to and from patchy food. Eared Grebes forage s o l e l y on breeding lakes (pers. obs.), and foraging costs are probably low on mos t / a l l lakes. On regularly-shaped lakes, information t r a n s f e r could take place i n the absence of nesting colonies: nests evenly d i s t r i b u t e d on the lake edge would allow d i r e c t observation of foragers anywhere on the 102 lake. Further, Eared Grebes forage independently from one another (pers. obs.), while one would expect aggregation at good food patched i n the presence of information t r a n s f e r . I conclude from those observations that there are no foraging b e n e f i t s of c o l o n i a l i t y i n Eared Grebes. C) Ant i - p r e d a t i o n b e n e f i t s Nest predation i s a primary cause of nesting m o r t a l i t y i n many b i r d species ( R i c k l e f s 1969; Somerville 1985). My study showed that most of the v a r i a t i o n i n reproductive success across colonies occurred during incubation, showing the importance of predation at nest. Nest s i t e . l o c a t i o n i n fluenced nest predation rates. Attended a r t i f i c i a l nests close to shore were subject to more predation than attended a r t i f i c i a l nests f a r from shore, but predation rates on unattended nests were higher f a r from shore than close to shore. This suggests that attendance at nest or nest defense plays an important r o l e on nest predation rates, and that attendance at nest was more e f f e c t i v e on nests f a r from shore than on nests close to shore. My experiment could not f u l l y account f o r e f f e c t s of group s i z e on nest defense, even though i t was observed that nesting areas close to shore were used by fewer p a i r s than nesting areas f a r from shore. Avian predators (e.g. corvids, hawks, eagles) are common i n my study area (Somerville 1985; pers. obs.), but nest defense or 103 mobbing might be e f f e c t i v e against them. However, mobbing or nest defense by Eared Grebes have not been reported i n the l i t e r a t u r e . On the other hand, mammalian predators (e.g. Mink, Coyote) are u s u a l l y found at much lower d e n s i t i e s than avian predators, but t h e i r impact i s more severe and they cannot be fended o f f . Because of e a s i e r access to nests, impact of mammalian predation should be most severe close to shore. This could e x p l a i n why nests were more concealed close to shore than f a r from shore. Nest s i t e l o c a t i o n can be considered i n terms of trade o f f s between group s i z e , nest concealment, and exposure to predators. Larger groups might use exposed s i t e s (because concealment would be i n e f f e c t i v e ) where exposure to predators i s reduced. Smaller breeding groups, using s i t e s more a c c e s s i b l e to predators, would opt f o r maximum nest concealment. 4- Breeding chronology and synchrony On a year with normal ( i . e . non-drought) conditions ( i . e . 1985), reproductive success was higher f o r i n d i v i d u a l s nesting e a r l y . I f nesting e a r l y increases reproductive success, why nest l a t e ? I considered 3 hypotheses: l a t e nesters are 1) t a k i n g advantage of l o c a l h a b i t a t ; 2) renesting b i r d s from d i f f e r e n t colonies and 3) b i r d s that cannot nest e a r l y (because of body c o n d i t i o n , age or previous breeding experience). 104 E a r l i e r breeding has been reported i n older Kittiwakes (Rissa t r i d a c t y l a ) (Coulson and White 1958; 1960; 1968). Late-nesting young Kittiwakes and Shags (Phalacrocorax aristotelis) experienced lower reproductive success than o l d i n d i v i d u a l s (Coulson and White 1956, 1960, Snow 1960), while experienced g u l l p a i r s are more successful than newly e s t a b l i s h e d p a i r s (Coulson 1966, M i l l s 1973). Veen (1977) suggested that b i r d s seek out p a i r s that are at a s i m i l a r reproductive s t a t e . Colonies could breed l a t e because they contain a large proportion of young b i r d s with l i t t l e breeding experience (Coulson and White 1960). Breeding chronology could also be a f f e c t e d by resource d i s t r i b u t i o n . Separating e f f e c t s of' age and resource d i s t r i b u t i o n on breeding chronology could be accomplished by comparing chronology i n c olonies sharing s i m i l a r resources. In Eared Grebes, t h i s could be accomplished by studying lakes i n the Peace River region, which supports m u l t i p l e nesting colo n i e s . Because colonies on a given lake share the same set of resources, the resource d i s t r i b u t i o n hypothesis p r e d i c t s synchronized nesting across c o l o n i e s , while the i n d i v i d u a l q u a l i t y hypothesis . p r e d i c t s non-synchronized nesting across c o l o n i e s . The study remains to be conducted. Synchronization w i t h i n colonies can increase i n d i v i d u a l f i t n e s s by reducing the period f o r which vulnerable prey items are a v a i l a b l e to predators (Evans 1982). Higher synchrony w i t h i n colonies than 105 across colonies has been demonstrated i n Bank Swallows (Emlen and Demong 1975), and there i s evidence of a d d i t i o n a l synchrony i n neighbourhoods w i t h i n colonies (Hoogland and Sherman 1976) . Anti-predator b e n e f i t s of within-colony synchrony might not be detectable i f predation i s seasonal and nesting i s not synchronized. Synchronized colonies nesting at d i f f e r e n t times would s u f f e r d i f f e r e n t predation rates because of seasonal d i f f e r e n c e s i n predator a c t i v i t y . Seasonal v a r i a t i o n s i n predation rates have been observed with egg predators i n the Riske Creek area (Somerville 1985), and I showed that nesting chronology v a r i e d extensively across c o l o n i e s . This could e x p l a i n the apparent lack of a n t i -predator b e n e f i t s of within-colony synchrony. 5- Conservation and management Conservation and management of rare and endangered w i l d l i f e i s based on data on abundance, d i s t r i b u t i o n , h a b i t a t p r o t e c t i o n , reproductive success and n a t i o n a l and i n t e r n a t i o n a l s i g n i f i c a n c e of regio n a l populations [Committee On Status of Endangered W i l d l i f e i n Canada ranking c r i t e r i a ] . My study t r i e d to gather information on the above po i n t s . This s e c t i o n w i l l b r i e f l y discuss 1) surveying techniques used and 2) management p r i o r i t i e s derived from my work. A) How to survey Eared Grebes 106 M u l t i p l e adult, nest and young counts were used throughout the breeding season to derive number of breeding p a i r s per lake. The above surveys suggest that breeding abundance can be derived from a small number of surveys. The best method i s to conduct adult and nest counts from mid to l a t e June. Most p a i r s are nesting by then, and f a l l migration has not yet begun. Estimates based on adult and nest counts should match c l o s e l y . I f only one type of survey i s p o s s i b l e , e i t h e r adult or nest counts should be used. Adult surveys are most e f f i c i e n t i n l a t e May, p r i o r to nesting, because a l l spring migrants have a r r i v e d on the breeding lakes and breeding p a i r s spend t h e i r time on open water, where they can e a s i l y be counted. Nest counts are most e f f i c i e n t from mid-June to e a r l y J u l y , when most nests are a c t i v e . Surveys should not be conducted at times other than i n d i c a t e d above, due to biases associated with nest f a i l u r e s , predation, migrations, and d i f f e r e n c e s i n breeding chronology. B) Management p r i o r i t i e s I have provided extensive information on d i s t r i b u t i o n and biology of Eared Grebes i n B r i t i s h Columbia, and used i t to i d e n t i f y key breeding areas f o r p r o t e c t i o n (Breault et al. 1988). Conservation e f f o r t s should be d i r e c t e d towards lakes with large breeding populations, because these lakes comprise the bulk of the known breeding population, and they are l e s s a f f e c t e d by environmental f l u c t u a t i o n s than lakes with small breeding populations. 107 environmental f l u c t u a t i o n s than lakes with small breeding populations. I showed that f l u c t u a t i o n s i n water l e v e l play an important r o l e i n the reproductive biology of Eared Grebes. Because n e s t - s i t e a v a i l a b i l i t y i s unpredictable, many breeding areas s h i f t l o c a t i o n across years. Small lakes with nesting areas i n shallow water close to shore are most a f f e c t e d . P r o t e c t i n g those lakes would be l e s s e f f e c t i v e , because they are not c o n s i s t e n t l y used by breeders. However, i f smaller colonies contain younger i n d i v i d u a l s , as some of my data suggest, smaller colonies should be al s o protected. Water con t r o l s on major breeding lakes should not be considered at the moment, because t h e i r impact on emergent and submerged vegetation i s unknown. Emergent vegetation might provide concealment, p r o t e c t i o n and support f o r the nest. The presence of succe s s f u l s e l f - s u p p o r t i n g nests (not associated with emergent vegetation) suggests that emergent vegetation may merely support the nest. I f t h i s i s the case, a r t i f i c i a l s t ructures providing nest support might also be used by breeding p a i r s . I placed a t o t a l of 50 a r t i f i c i a l platforms on 5 lakes used by breeding Eared Grebes i n 1985. Eared Grebes b u i l t nests and l a i d eggs i n 5 of those platforms, while I observed p a r t i a l l y or completed nests (without eggs) on another 10 a r t i f i c i a l platforms (unpubl. data). A r t i f i c i a l nesting platforms might help 108 rare) , and could also be used to study nest s i t e s e l e c t i o n and c o l o n i a l i t y i n Eared Grebes. Most of the fi n d i n g s of t h i s study have management i m p l i c a t i o n s because l i t t l e was known on the breeding biology of Eared Grebes both l o c a l l y and world-wide. However, i t a l s o revealed further needs f o r research covering 1) status and s i z e of l o c a l populations; 3) e f f e c t s of resource abundance (food) on d i s t r i b u t i o n , breeding chronology and reproductive success; 4) p o t e n t i a l b e n e f i t s of c o l o n i a l i t y and 5) the suspected age d i f f e r e n c e s between colonies. Savard (1986) pointed out that studies of waterfowl ecology can address t h e o r e t i c a l questions, and that the answers to those questions have important management i m p l i c a t i o n s . I attempted to in t e g r a t e both t h e o r e t i c a l ( c o l o n i a l i t y ) and management considerations i n the design and implementation of t h i s p r o j e c t , because I b e l i e v e that Eared Grebe conservation depends on a good understanding of both aspects. 109 LITERATURE CITED Alexander, R.D. 1974. The evo l u t i o n of s o c i a l behaviour. Annu. Rev. E c o l . Syst. 5:325-383. Anderson, G. 1981a. 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A method f o r estimating the number of breeding p a i r s of Great Crested Grebes Podiceps cristatus on lakes. B i r d Study 34:82-86. 119 Yocom, C.R., S.W. Har r i s and H.A. Hansen. 1958. Status of grebes Eastern Washington. Auk 75:36-47. 120 Appendix 1. C a l c u l a t i o n of breeding abundance from chick counts Age s p e c i f i c s u r v i v a l rates were obtained from a d e t a i l e d study of 174 nests surveyed i n 1985 and 1986 at Riske-Creek. Clutch s i z e (3.48 eggs per nest) ( M c A l l i s t e r 1958) was assumed to i n d i c a t e the number of chicks hatched. The maximum number of chicks 2 weeks of age or older was compared to the number of eggs l a i d i n breeding lakes used by a known number of breeders. The s u r v i v a l rate f o r that p e r i o d was 32.4%. S u r v i v a l from 2 weeks to 1 month o l d was s i m i l a r l y derived by comparing the number of chicks 1 month o l d or older with the number of chicks 2 weeks o l d or more. S u r v i v a l was 84%. Fledging rates could not be measured d i r e c t l y due to movements of fledged chicks between lakes. Because of the short i n t e r v a l between 1 month o l d and f l e d g i n g , I assumed that s u r v i v a l from 2 weeks to 1 month was i d e n t i c a l to s u r v i v a l from 2 weeks to fle d g i n g . This information produced the f o l l o w i n g equation, used to obtain the number of breeding p a i r s from chick counts: BP = [ (Y1/S1) + (Y2/S2) ]/C. where BP = number of breeding p a i r s Y1 = number of chicks l e s s than 2 weeks o l d Y2 = number of chicks more than 2 weeks o l d 51 = s u r v i v a l from 0 to 2 weeks o l d (%) 52 = s u r v i v a l from 2 weeks o l d to f l e d g i n g (%) C3 = c l u t c h s i z e (3.48 eggs/nest) ( M c A l l i s t e r 1958) 121 Appendix 2. Estimated number of Eared Grebe p a i r s i n the Northern Okanagan/Kamloops area. Lake Location Estimate* (mercator coordinates) Separation South 10 .6918-56063 0-48 Separation North 10 .6917-56072 0-18 Stump 10 . 6845-55786 74- (100) Rawling 11 .3663-55705 4-24 Kamloops A (Mitchell) 10 .6934-56113 9-(10) Munson unknown 2-9 McKay's unknown 8-9 Lew (Campbell) 10 .7060-56040 6-22 Hamilton Corrals unknown 1 Douglas 10 .6990-55600 2 Round 11 .3345-55885 2-(10) Golden unknown 1-2 Deer unknown 1 Duck unknown 0-20 Osoyoos unknown 1 Spectacled 11 .3128-54390 1 White unknown 1 Tunkwa 10 .6528-56067 0-1 Total 109-280 * Presents the minimum and maximum estimates obtained from the 2 most recent years of surveys. Some maximum values are personal inferences and are presented i n parentheses. 122 Appendix 3. Estimated number of Eared Grebe p a i r s i n the Peace River area. Lake Location (mercator coordinates) Estimate* Fort St. John Potholes 10.6377-62383 0-33 Boundary 10.6850-62480 83-295 Boudreau A 10.6030-62250 120-(700) Cutbank 10.6840-61340 0-(50) German 10.6820-62520 0-11 C e c i l 10.6490-62450 62- (500) "Bob Emery" 10.6302-62655 33 Whispering Pine 10.6240-62725 0-24 McQueen's slough 10.6775-61872 23-63 Sloane's slough 10.6388-61868 0-7 Boudreau B 10.5970-62255 20- (50) C h a r l i e 10.6260-62400 1-5 Huhn's slough 10.6393-62465 0-2 Scott 10.6310-61965 0-2 Tota l 342-1775 * Presents the minimum and maximum estimates obtained from the 2 most recent years of surveys. Some maximum values are personal inferences and are presented i n parentheses. 123 Appendix 4. Estimated number of Eared Grebe p a i r s i n the Southern I n t e r i o r area. Lake Location (mercator coordinates) Estimate* Meadow Lake Green Lake A Green Lake B Green Lake C L i t t l e White Lake 4403 lakes 43 miles 10.5860-56910 10.6147-56858 10.6150- 56853 10.6151- 56856 10.5915-56815 10.5890-56906 unknown 37-164 3-4 9-19 0- 2 590-(700) 36-46 1- 5 Tota l 676-940 * Presents the minimum and maximum estimates obtained from the 2 most recent years of surveys. Some maximum values are personal inferences and are presented i n parentheses. 124 Appendix 5. Estimated number of Eared Grebe p a i r s i n the Central I n t e r i o r area. Lake Location (mercator coordinates) Estimate* 6 (Rock) 10.5400-57580 37- (82) 11 10.5387-57605 21-33 12 10.5390-57609 2-24 16 (Separating) 10.5344-57588 11-28 24 10.5386-57616 1-15 26 10.5387-57619 0-11 28 10 .5375-57615 0-3 S. of 40 10.5338-57639 5-15 SS. of 40 10.5337-57637 0-13 42 10.5332-57643 17-21 53 10.5380-57626 3-5 Westwick 10.5580-57600 206-243 Sorenson 10.5570-57610 0-19 Coyote 10.5445-57910 8-9 McMurray 10.5415-57877 358-(450) Elkhorn 10.4874-57386 96-262 8432 North 10.4817-57767 41-86 Upper Dry- 10.4995-57450 0-57 Lower Dry 10.5005-57445 0-35 Dry 3 10.4984-57452 0-5 Jamieson Meadow 10.5212-57353 6-19 Golden Pond 10.4887-57381 3 Soda I & J 10.6130-58369 5 Rush 10.7110-55710 1-5 5 mi East of 100 M i l e unknown 11 Stum 10.4990-57900 2 Tachick 10.4200-59780 2-7 Near Bonds unknown 1-3 Duncan unknown 2-3 A l k a l i 10.5500-57365 1-5 Tota l 634-1479 * Presents the minimum and maximum estimates obtained from the 2 most recent years of surveys. Some maximum values are personal inferences and are presented i n parentheses. 125 

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