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A comparison of a cyclic and non-cyclic population of snowshoe hares in Kluane, Yukon Jardine, Claire 1995

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A COMPARISON OF A CYCLIC AND NON-CYCLIC POPULATION OF SNOWSHOE HARES IN KLUANE, YUKON by CLAIRE JARDINE B.Sc,  The U n i v e r s i t y of Guelph, 1992  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE  FACULTY OF GRADUATE STUDIES Department of Zoology  We accept t h i s t h e s i s as conforming t o t h e r e q u i r e d standard  THE  rJNjATERSITY OF BRITISH COLUMBIA June 1995 © C l a i r e J a r d i n e , 1995  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 department  or  by  his  scholarly purposes may be granted  or  her  representatives.  It  is  by the head of  understood  that  copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department of  Zoo.  lo  the University of British Columbia Vancouver, Canada  Date  DE-6 (2788)  AJUTM  1  ABSTRACT In t h i s study I compared a n o n - c y c l i c i s l a n d p o p u l a t i o n of snowshoe hares (Lepus  americanus)  with a c y c l i c mainland  population t o determine how the dynamics of the two populations d i f f e r e d f o l l o w i n g a p o p u l a t i o n d e c l i n e .  Both  populations had d e c l i n e d t o s i m i l a r low l e v e l s by the f a l l of 1992.  During t h i s study the Jacquot I s l a n d hare p o p u l a t i o n  increased 3.5  f o l d from the s p r i n g of 1993 t o the s p r i n g of  1994 while the c y c l i c mainland hare p o p u l a t i o n remained at low d e n s i t i e s . I monitored s u r v i v a l and r e p r o d u c t i o n t o determine the proximate causes f o r the d i f f e r e n t dynamics seen.  I  determined t h a t j u v e n i l e s u r v i v a l , overwinter a d u l t  survival  and r e p r o d u c t i o n were higher on Jacquot I s l a n d than the mainland from the s p r i n g of 1993 t o the s p r i n g o f  1994.  These were the key proximate f a c t o r s that allowed the Jacquot I s l a n d hare p o p u l a t i o n t o i n c r e a s e while the mainland population remained at low d e n s i t i e s .  There was  no  d i f f e r e n c e i n summer a d u l t s u r v i v a l between the two areas i n 1993. I a l s o i n v e s t i g a t e d the u l t i m a t e causes f o r the d i f f e r e n t dynamics seen i n the two areas.  Higher r e p r o d u c t i v e output,  and higher overwinter s u r v i v a l d i d not c o i n c i d e with b e t t e r hare c o n d i t i o n on Jacquot I s l a n d .  There were, however, fewer  mammalian predators on Jacquot Island than the mainland. Higher e a r l y j u v e n i l e s u r v i v a l on Jacquot I s l a n d c o i n c i d e d with lower numbers of small mammal p r e d a t o r s .  ii  TABLE OF CONTENTS Abstract  i i  Table of Contents  i i i  L i s t of Tables  v  L i s t of F i g u r e s  vi  Acknowledgments  viii  Introduction Survival Reproduction The Problem Previous Studies O b j e c t i v e s of Study  1 1  Study Area Jacquot I s 1 and Mainland  1° 10 11  Methods Hare Trapping Adult Hare S u r v i v a l Measurement of L i t t e r s Determination of Reproductive Parameters Predator Numbers Juvenile Survival Body Weights and C o n d i t i o n Index Predator Numbers S t a t i s t i c a l Procedures  1 11 13 14 16 16 16 17 17 18  Results Population Density Summer A d u l t Hare S u r v i v a l Overwinter Adult Hare S u r v i v a l Proximate Causes of M o r t a l i t y of A d u l t Hares E f f e c t of Maternity Cages on Reproductive Data Pregnancy Rates Timing of L i t t e r s L i t t e r Sizes S t i l l b o r n Rates Newborn Hare Body Weights Sex Ratios of Newborn Hares J u v e n i l e Breeding T o t a l Reproductive Output Evidence of a Fourth L i t t e r J u v e n i l e S u r v i v a l on Jacquot I s l a n d J u v e n i l e S u r v i v a l on the Mainland Comparison of J u v e n i l e S u r v i v a l on Jacquot I s l a n d the Mainland i n 1994  18 18 20 23 23 23 33 33 33 37 37 41 41 41 45 45 48  3 6  6 9  in  1  and  49  Comparison of J u v e n i l e S u r v i v a l over D i f f e r e n t L i t t e r G r o u p s i n 1994 49 O v e r w i n t e r S u r v i v a l o f J u v e n i l e H a r e s on J a c q u o t Island 49 P r o x i m a t e Causes of M o r t a l i t y of J u v e n i l e Hares 54 P r e d a t o r Numbers 54 A d u l t M a l e S p r i n g Body W e i g h t s and c o n d i t i o n I n d i c e s . . 5 7 Discussion 58 Survival •. 61 Adult Survival Following a Population Decline 61 Factors Influencing Adult Survival 62 J u v e n i l e S u r v i v a l on J a c q u o t I s l a n d 64 J u v e n i l e S u r v i v a l on J a c q u o t I s l a n d Compared w i t h the Mainland 65 Reproduction 68 The E f f e c t o f M a t e r n i t y Cages on R e p r o d u c t i v e d a t a . 6 8 Reproduction Following a Population Decline 70 Timing of Breeding. 72 T o t a l R e p r o d u c t i v e Output 72 L i t t e r S i z e and N e o n a t e W e i g h t s 73 Conclusion 75 Proximate Factors I n f l u e n c i n g the Jacquot I s l a n d Population Increase 76 U l t i m a t e C a u s e s o f H i g h e r S u r v i v a l on J a c q u o t I s l a n d . . 7 9 U l t i m a t e C a u s e s o f H i g h e r R e p r o d u c t i o n on J a c q u o t Island 81 Summary 81 Literature Cited  83  iv  L I S T OF TABLES Table 1. P r e d i c t i o n s of whether Jacquot Island would have lower o r higher values than the mainland f o r each f a c t o r examined d u r i n g t h i s study according t o the hypotheses..22 Table 2. 28-day s u r v i v a l rates of r a d i o - c o l l a r e d , a d u l t snowshoe hares (95% confidence l i m i t s i n parentheses and t o t a l hares c o l l a r e d beneath) 24 Table 3. Proximate causes of m o r t a l i t y of r a d i o - c o l l a r e d a d u l t snowshoe hares on Jacquot I s l a n d and the mainland.25 Table 4. Summary t a b l e of the e f f e c t of days a female spent i n a cage p r i o r t o p a r t u r i t i o n on l i t t e r s i z e and mean l e v e r e t weight per l i t t e r f o r 1993 and 1994 34 Table 5. Mean date of b i r t h (± S.D.) f o r Jacquot I s l a n d and mainland study s i t e s i n 1993 and 1994 (number of l i t t e r s i n parentheses) 35 Table 6. Mean l i t t e r Sizes a t b i r t h (± S.D.) f o r Jacquot Island and mainland study s i t e s i n 1993 and 1994 (number of l i t t e r s i n parentheses) 36 Table 7. Mean newborn weights a t b i r t h (± S.D.) f o r Jacquot I s l a n d and mainland study s i t e s i n 1993 and 1994 (number of l i t t e r s parentheses) 38 Table 8. Number of female hares born i n maternity cages on Jacquot I s l a n d and mainland study s i t e s i n 1993 and 1994 ( t o t a l number of newborn hares i n parentheses) 44 Table 9. Proximate causes of m o r t a l i t y of radio-tagged, j u v e n i l e snowshoe hares on Jacquot I s l a n d (JI) and the mainland i n 1994  55  Table 10. S i g h t i n g index of snowshoe hare predators on Jacquot I s l a n d and the mainland during the summers o f 1993 and 1994  56  Table 11. Mean body weights ± S.D. o f male snowshoe hares i n s p r i n g on study areas (sample s i z e i n parentheses)...59 Table 12. Mean c o n d i t i o n i n d i c e s + S.D. of male snowshoe hares i n s p r i n g on study areas (sample s i z e i n parentheses)  60  Table 13. Hypotheses and p r e d i c t i o n s examined during t h i s study and the r e s u l t s obtained 77  v  L I S T OF FIGURES Figure 1. Spring d e n s i t i e s (hares/lOOha) and the corresponding p o t e n t i a l n a t a l i t y ( l e v e r e t s produced per a d u l t female s u r v i v i n g the breeding season) of an A l b e r t a hare population from 1962 t o 1976 (from Carey and K e i t h 1979) 5 Figure 2. Population estimates (February-April) f o r snowshoe hares on Jacquot I s l a n d (north g r i d ) and the mainland ( s i l v e r c o n t r o l g r i d ) from 1978 t o 1992 7 Figure 3. Spring population estimates of snowshoe hares on Jacquot I s l a n d (north and south g r i d s ) and the mainland (sulphur and s i l v e r g r i d s ) , 1990-1994, (1991-1992, Zimmerling (1993); 1993-1994, t h i s study) 19 Figure 4. Population estimates with 95% confidence l i m i t s of snowshoe hares on Jacquot I s l a n d (north and south g r i d s ) and the mainland (sulphur and s i l v e r g r i d s ) i n the s p r i n g and f a l l from 1993-1994 21 Figure 5(a-b). The e f f e c t of time a female spent i n a cage p r i o r t o p a r t u r i t i o n on l i t t e r s i z e and average l e v e r e t weight per l i t t e r f o r a l l l i t t e r s i n 1993 on Jacquot Island 28 Figure 6 ( a - c ) . The e f f e c t of time a female spent i n a maternity cage p r i o r t o p a r t u r i t i o n on l i t t e r s i z e f o r l i t t e r groups 1, 2, and 3 of 1994 on Jacquot Island  30  Figure 7 ( a - c ) . E f f e c t of time a female spent i n a maternity cage p r i o r t o p a r t u r i t i o n on average l e v e r e t weight per l i t t e r , f o r l i t t e r groups 1, 2, and 3 of 1994 on Jacquot Island 32 Figure 8 ( a - c ) . C o r r e l a t i o n between l i t t e r s i z e and average l e v e r e t weight per l i t t e r f o r l i t t e r groups 1,2, and 3 of 1994 on Jacquot I s l a n d 40 Figure 9 ( a - c ) . The e f f e c t of l i t t e r s i z e on the t o t a l weight of a l i t t e r f o r l i t t e r groups 1, 2, and 3 of 1994 on Jacquot I s l a n d 43 Figure 10. T o t a l reproductive output (number of l e v e r e t s produced per a d u l t female s u r v i v i n g the breeding season) i n r e l a t i o n t o population peaks and lows f o r an A l b e r t a population of snowshoe hares from 1962 t o 1976 (Carey and K e i t h 1979), a Yukon population of snowshoe hares from 1989 t o 1990 (O'Donoghue 1991) and 1994, and the Jacquot I s l a n d population of snowshoe hares from 1991 t o 1992 (Zimmerling 1993) and 1993 t o 1994 47  vi  Figure 11. S u r v i v o r s h i p curves with 95% confidence l i m i t s f o r f i r s t l i t t e r radio-tagged j u v e n i l e s on Jacquot I s l a n d and the mainland, 1994 50 Figure 12. S u r v i v o r s h i p curves with 95% confidence l i m i t s f o r second l i t t e r radio-tagged j u v e n i l e s on Jacquot I s l a n d and the mainland, 1994 51 Figure 13. S u r v i v o r s h i p curves with 95% confidence l i m i t s f o r t h i r d l i t t e r radio-tagged j u v e n i l e s on Jacquot I s l a n d and the mainland, 1994 52 Figure 14. S u r v i v a l r a t e s with 95% confidence l i m i t s f o r the f i r s t 30 days of l i f e f o r l i t t e r groups 1, 2, and 3 on Jacquot I s l a n d and the mainland i n 1994 53  vii  ACKNOWLEDGMENTS I would l i k e t o thank my s u p e r v i s o r C. J . Krebs f o r g i v i n g me the o p p o r t u n i t y t o work on Jacquot I s l a n d and f o r h i s i n v a l u a b l e suggestions throughout t h i s p r o j e c t . to thank my research committee,  I would  like  T.P. S u l l i v a n , J . Myers, and  A.R.E. S i n c l a i r f o r t h e i r advice on a l l aspects o f my project. I thank L. Preston, M. Joyce, A. Kalousek, and S. Armstrong f o r t h e i r help with f i e l d work on the i s l a n d and M. O'Donoghue, C. Doyle, F. Doyle and C. Olsen f o r t h e i r a d v i c e i n the f i e l d .  I would a l s o l i k e t o thank C. Doyle f o r  c o l l e c t i n g mainland j u v e n i l e data and K. Madsen f o r determining the home ranges of hares on Jacquot I s l a n d .  M.  O'Donoghue helped with bear problems and mainland data analysis. get  I would l i k e t o thank I . Wingate f o r h e l p i n g me  organized and A. Williams, base manager  I n s t i t u t e , f o r l o g i s t i c a l support.  o f the A r c t i c  T. Zimmerling provided  valuable comments on e a r l i e r d r a f t s of the t h e s i s .  I would  e s p e c i a l l y l i k e t o thank Brendan Delehanty f o r the help and encouragement he has given me throughout t h i s p r o j e c t . This study was funded by a grant from the N a t u r a l Sciences and E n g i n e e r i n g Research C o u n c i l of Canada t o C.J. Krebs, grants from the Northern Sciences T r a i n i n g program, and a grant from Sigma X i .  viii  INTRODUCTION Snowshoe hares (Lepus americanus)  exhibit a characteristic  "10-year" p o p u l a t i o n c y c l e throughout most of t h e i r range (Keith 1990, Krebs et al. 1986).  Various hypotheses have  been proposed t o help e x p l a i n the c y c l e i n c l u d i n g food l i m i t a t i o n , predation, and genotypic s h i f t s i n the p o p u l a t i o n (Keith et al. 1984, T r o s t e l et al. 1987, C h i t t y  1967).  Despite numerous studies there i s s t i l l no c l e a r consensus as to the causes of the hare population c y c l e (Green and Evans 1940, Krebs et al. 1986, K e i t h et al. 1984).  Snowshoe hares  do not e x h i b i t p o p u l a t i o n c y c l e s at the southern p e r i p h e r y of t h e i r range ( S i e v e r t and K e i t h 1985, C h i t t y 1950, Dolbeer and C l a r k 1975).  Comparisons of reproduction and s u r v i v a l of  c y c l i c and n o n - c y c l i c snowshoe hare populations may  a l l o w us  t o determine what proximate f a c t o r s are necessary f o r c y c l e s t o occur. Survival There i s some disagreement about how a d u l t changes during the hare c y c l e .  survival  Green and Evans  (1940)  claimed t h a t adult s u r v i v a l was constant over the c y c l e . Subsequent s t u d i e s by K e i t h and Windberg  (1978) showed t h a t  winter s u r v i v a l of a d u l t s was reduced during the d e c l i n e and low phases and was c o r r e l a t e d with the annual r a t e of population change (Keith 1990).  In the Yukon, a d u l t s u r v i v a l  i n the f a l l and winter was c o r r e l a t e d with the annual r a t e of population change, with s u r v i v a l d e c l i n i n g g r a d u a l l y over the peak and d e c l i n e phases  (Krebs et al. 1986).  1  Studies of.non-  c y c l i c populations  have a l l been short-term  (see K e i t h 1990),  but s u r v i v a l r a t e s have been s i m i l a r t o those found during c y c l i c population  declines  (Keith 1990,  Kuvlesky and  Keith  1983). U n l i k e a d u l t s u r v i v a l , there i s l i t t l e debate t h a t changes i n overwinter j u v e n i l e s u r v i v a l are c l o s e l y a s s o c i a t e d with the population changes seen i n the 10-year c y c l e of snowshoe hares.  Green and Evans (1940) concluded t h a t poor overwinter  j u v e n i l e s u r v i v a l i n i t i a t e d and  sustained the  d e c l i n e i n a Minnesota hare population. from f a l l t o mid-winter was of population  population  Juvenile survival  h i g h l y c o r r e l a t e d with the  change i n the Yukon (Krebs et al.  rate  1986).  In  A l b e r t a , K e i t h and Windberg (1978) found j u v e n i l e s u r v i v a l from August t o December was population changes.  s t r o n g l y c o r r e l a t e d with  For c y c l i c populations  overwinter  j u v e n i l e s u r v i v a l i s low i n the peak and d e c l i n e years and Windberg 1978,  Krebs et al.  n o n - c y c l i c populations  1986).  (Keith  Short term s t u d i e s of  i n d i c a t e t h a t overwinter j u v e n i l e  s u r v i v a l r a t e s were s i m i l a r t o those found during the d e c l i n e phase of the c y c l e (Keith 1990). The e f f e c t of e a r l y j u v e n i l e s u r v i v a l , between b i r t h  and  weaning at 28 days, on c y c l i c population changes i s l e s s clear.  Based on i n d i c e s of e a r l y j u v e n i l e s u r v i v a l , K e i t h  and Windberg (1978) concluded t h a t e a r l y j u v e n i l e s u r v i v a l was  not r e l a t e d t o rates of population growth w h i l e Krebs et  al.  (1986) concluded, based on a c a l c u l a t e d  recruitment  index, t h a t changes i n e a r l y j u v e n i l e s u r v i v a l were a cause  2  of the hare c y c l e .  O'Donoghue (1994) measured e a r l y  s u r v i v a l d i r e c t l y during  a population  juvenile  peak and found s u r v i v a l  to 14 days of age was approximately 0.55, 0.19, and 0.47 f o r f i r s t , second, and t h i r d l i t t e r groups, r e s p e c t i v e l y . (unpublished) c o l l e c t e d s u r v i v a l data f o r the same  Sovell  population  during one year o f the d e c l i n e phase of the c y c l e and found 14-day s u r v i v a l rates o f 0.20 and 0.05 f o r f i r s t and second l i t t e r s , respectively. Early juvenile survival i n a c y c l i c population  appears t o change as the population  more data are r e q u i r e d t o describe  changes, but  the r e l a t i o n s h i p between  e a r l y j u v e n i l e s u r v i v a l and population  trends.  No s t u d i e s  have examined e a r l y j u v e n i l e s u r v i v a l i n n o n - c y c l i c populations a t the southern range boundary (but see Zimmerling 1993). Despite the d i f f e r e n c e s i n a d u l t and j u v e n i l e s u r v i v a l r a t e s , the main proximate cause of death i n both c y c l i c and non-cyclic al.  populations i s predation  1986, S i e v e r t and K e i t h 1985).  increase  the r i s k of predation  (Keith 1990, Boutin et Poor body c o n d i t i o n can  f o r hares, and f a c t o r s  that  reduce body c o n d i t i o n , such as food shortage and disease, can u l t i m a t e l y be r e s p o n s i b l e The  ultimate  f o r poor s u r v i v a l (Keith 1990).  causes of the d i f f e r e n c e s seen i n the s u r v i v a l  rates remain  uncertain.  Reproduction Changes i n reproductive the 10 year population  output are c l o s e l y a s s o c i a t e d  c y c l e of snowshoe hares.  year study i n Rochester A l b e r t a , Carey and K e i t h  3  with  During a 16 (1979) found  that n a t a l i t y the breeding  (number of young produced per female s u r v i v i n g season) changed 2.4  f o l d during the c y c l e .  These changes i n n a t a l i t y had a s i m i l a r p e r i o d i c i t y t o the c y c l e i n hare numbers but the low i n n a t a l i t y preceded the population low by three years  (Carey and K e i t h 1979,  Figure  1). Few  s t u d i e s have looked at the reproduction of n o n - c y c l i c  populations  and,  of these, none have been more than three  years i n d u r a t i o n (see K e i t h 1990).  From these s t u d i e s i t  appears t h a t changes i n the reproductive output of n o n - c y c l i c populations  have not been so dramatic  and have not been  u s e f u l f o r p r e d i c t i n g subsequent population trends 1990).  Dolbeer and C l a r k (1975) s t u d i e d two  populations of snowshoe hares.  (Keith  non-cyclic  During t h e i r s t u d i e s the  population d e n s i t y i n both areas remained s t a b l e .  The  average annual n a t a l i t y r a t e (number of young produced per female s u r v i v i n g the breeding season) v a r i e d 1.3  f o l d over  the three year study i n Colorado and v a r i e d only 1.1 during the two year study i n Utah.  fold  Kuvlesky and K e i t h (1983)  recorded n a t a l i t y rates f o r a n o n - c y c l i c p o p u l a t i o n i n c e n t r a l Wisconsin  and found t h a t n a t a l i t y r a t e s remained  constant while the population d e n s i t y decreased  32%.  From  these s t u d i e s i t appears t h a t n a t a l i t y , i n n o n - c y c l i c populations l o c a t e d i n the southern p a r t of the hare's geographical range, remains f a i r l y s t a b l e compared t o the n a t a l i t y of c y c l i c  populations.  4  (1)  •fj* ro c O C  ro T3 C  i-S ° ro ro ro ,  to WI  <u cn £  ..  a) cn ro r-l to .c * — < > — Q. —-«—  ^-  I  + ro  rot 4->  <  ro c  ro  ,9 °~> ro '  aj cn to «—  "a a) -Q QJ  ro  J  T3 C  ro >^  <4-  to • a> to ro CD E  ro CD  lis c IL  a>  C 3 C T3 Q. O CO jr  c  o 3 Q. O  0)  ( M00L/S9JBL|) B  Aiisusp 6uuds  5  a.  The  Problem Most comparisons of c y c l i c and n o n - c y c l i c populations  been between southern  have  n o n - c y c l i c populations and more  northerly c y c l i c populations.  Comparisons between these  g e o g r a p h i c a l l y d i s p a r a t e hare populations are d i f f i c u l t t o make because of d i f f e r e n c e s i n c l i m a t e , h a b i t a t , v e g e t a t i o n , predators, and p o t e n t i a l competitors.  Jacquot I s l a n d ,  l o c a t e d i n the northern b o r e a l f o r e s t , has been s t u d i e d s i n c e 1977  and does not e x h i b i t c y c l i c f l u c t u a t i o n s i n p o p u l a t i o n  d e n s i t y (Figure 2, Krebs e t al. 1986, T r o s t e l 1986, Zimmerling 1993).  Jacquot I s l a n d , t h e r e f o r e , provides a r a r e  opportunity t o examine a n o n - c y c l i c i s l a n d p o p u l a t i o n of snowshoe hares and compare i t with a nearby c y c l i c mainland population. Previous  Studies  Two previous s t u d i e s compared the p o p u l a t i o n dynamics of snowshoe hares on Jacquot I s l a n d with the mainland.  Trostel  (1986) examined t r a p p i n g data from 1977 t o 1984 and d i d a one year r a d i o - t e l e m e t r y study on a d u l t hares t o determine s u r v i v a l and recruitment r a t e s .  During  1991 and 1992  Zimmerling (1993) c a r r i e d out a d e t a i l e d study o f the demographic f a c t o r s a f f e c t i n g hares on Jacquot I s l a n d . T r o s t e l (1986) found no d i f f e r e n c e s i n recruitment between Jacquot I s l a n d and the mainland.  rates  Recruitment  encompasses n a t a l i t y and e a r l y j u v e n i l e s u r v i v a l which Zimmerling (1993) examined s e p a r a t e l y . 1991  During the summer of  j u v e n i l e s u r v i v a l was found t o be higher on Jacquot  6  TJ C  HC  To  u  c  o o T3 C  ro  " ° ro <u ro  ro c^-  —>  ro^2. (NJ CD CT)  TJ C  O cn  CO  J 2 4-1  O CT O CO  -J CO  oo cn  c o  OT 0) i_  CO - C (Nl  cn o cn 0)  -C (/)  to CO cn  o c  o  +J 00  CO r-s.  o cn  vi—  CL  00 CT)  < (0 3 L_  'E  o  vi-  C O 0)  co  "o  Cl) +J 1LL c CNJ CO  cn  (0 0)  o o  •M TJ CO c E CO 10  c 'co  o  JZ  <D E c <D •4-"  CO  opul and  o oo cn  CL  ,»•—>,  TJ  i 'L.  (Nl D) Cl) . C  + d BU/S8JBH  cn  q °  7  L_ 3  _D) LL.  t  no  CO  Island than the mainland of  (Zimmerling 1993).  Lower d e n s i t i e s  a main predator of j u v e n i l e snowshoe hares, the red  s q u i r r e l (Tamiasciurus  hudsonicus;  O'Donoghue 1994),  and  areas of dense understory cover on Jacquot I s l a n d were thought t o c o n t r i b u t e t o the d i f f e r e n c e s i n j u v e n i l e s u r v i v a l (Zimmerling 1993). J u v e n i l e s u r v i v a l data were not c o l l e c t e d in  1992.  I t remains t o be seen whether j u v e n i l e s u r v i v a l i s  c o n s i s t e n t l y higher on Jacquot Island and i f i t p l a y s an important r o l e i n determining the p o p u l a t i o n dynamics of snowshoe hares on Jacquot I s l a n d . Zimmerling  (1993) and T r o s t e l (1986) both concluded that  adult hare p r e d a t i o n on Jacquot I s l a n d and the mainland  was  d i f f e r e n t , with p r e d a t i o n on the mainland showing a p r e d i c t a b l e delayed density-dependent p a t t e r n not e v i d e n t on Jacquot I s l a n d .  Reproductive data, such as l i t t e r s i z e and  b i r t h weights, were s i m i l a r between mainland and i s l a n d g r i d s in  1991;  however, l i t t l e data were c o l l e c t e d on Jacquot  I s l a n d i n 1992 because both pregnancy females was  poor (Zimmerling 1993).  numbers on the mainland i n 1992  r a t e s and s u r v i v a l of Because of low hare  (Zimmerling 1993)  only one  f u l l year of r e p r o d u c t i v e data has been c o l l e c t e d c o n c u r r e n t l y on Jacquot Island and the mainland. Both Jacquot I s l a n d and mainland populations experienced d e c l i n e s from the f a l l of 1991  t o the f a l l of 1992  and  reached s i m i l a r low l e v e l s . C y c l i c populations are c h a r a c t e r i z e d by a long d e c l i n e and p e r i o d of low d e n s i t y which l a s t s approximately 4 years d e s p i t e the apparent  8  abundance o f food and s c a r c i t y o f predators d u r i n g t h i s time (Keith  1990).  O b j e c t i v e s o f Study The o b j e c t i v e o f my study was t o compare the p o p u l a t i o n dynamics o f hares on Jacquot I s l a n d with t h a t o f hares on the mainland d u r i n g the low phase o f the p o p u l a t i o n c y c l e from 1993-1994 and b u i l d on the i n f o r m a t i o n c o l l e c t e d d u r i n g Zimmerling's  (1993) study of Jacquot I s l a n d .  Specifically, I  compare a d u l t s u r v i v a l , j u v e n i l e s u r v i v a l and r e p r o d u c t i o n on Jacquot I s l a n d with the mainland t o determine how these f a c t o r s d i f f e r between the two areas.  I a l s o compare hare  body c o n d i t i o n and a predator s i g h t i n g i n d i c e s on Jacquot I s l a n d and the mainland t o determine i f these two f a c t o r s are c o r r e l a t e d with any d i f f e r e n c e s i n s u r v i v a l o r r e p r o d u c t i v e output. Three main hypotheses Hypothesis  1  are examined i n t h i s study:  Differences i n reproduction explain  the d i f f e r e n c e s seen i n the p o p u l a t i o n dynamics o f snowshoe hares on Jacquot I s l a n d and the mainland. Hypothesis  2  D i f f e r e n c e s i n m o r t a l i t y e x p l a i n the  d i f f e r e n c e s seen i n the p o p u l a t i o n dynamics o f snowshoe hares on Jacquot Island and t h e mainland. Hypothesis 2a Only j u v e n i l e m o r t a l i t y d i f f e r s between the i s l a n d and the mainland. Hypothesis 2b  Only adult m o r t a l i t y d i f f e r s  between the i s l a n d and the  9  mainland.  Hypothesis 2c  Both a d u l t and j u v e n i l e m o r t a l i t y  d i f f e r between the i s l a n d and the mainland. Hypothesis  3  D i f f e r e n c e s i n both r e p r o d u c t i o n and  m o r t a l i t y e x p l a i n the d i f f e r e n c e s seen i n the p o p u l a t i o n dynamics o f snowshoe hares on Jacquot I s l a n d and t h e mainland. The s p e c i f i c p r e d i c t i o n s a s s o c i a t e d with the above hypotheses depend on the p o p u l a t i o n trends observed on Jacquot I s l a n d during t h i s study and as a r e s u l t are presented the p o p u l a t i o n d e n s i t y r e s u l t s  section.  STUDY AREA Jacquot  Island  Jacquot I s l a n d i s l o c a t e d i n Kluane Lake i n t h e southwestern Yukon (61°N, 138°W).  The i s l a n d i s approximately  5 km and c o n s i s t s o f two s e c t i o n s j o i n e d by a 30 m wide 2  isthmus.  The southern s e c t i o n i s approximately 54 ha and i s  separated from the mainland by a t l e a s t 3 km.  The northern  s e c t i o n i s much l a r g e r (approximately 400 ha) and i s separated from the mainland by a minimum o f 1.5 km.  From the  end o f November u n t i l the end o f May the i s l a n d i s connected t o the mainland by i c e .  During the summer, however, access  to and from the i s l a n d by t e r r e s t r i a l animals i s l i m i t e d because o f the l a k e . The understory o f the i n t e r i o r i s l a n d i s dominated by willow (Salix  spp.)  and Shepherdia  (Shepherdia  The canopy i s predominantly white spruce (Picea some stands o f aspen  (Populus  tremuloides)  10  canadensis).  glauca)  with  and balsam p o p l a r  (Populus  balsamifera)  on h i l l s i d e s .  On the outer edges of  the i s l a n d there are a number of windswept b l u f f s where the v e g e t a t i o n c o n s i s t s mainly of herbs and low shrubs.  For a  more d e t a i l e d d e s c r i p t i o n of the h a b i t a t on Jacquot I s l a n d see Krebs et al.  (1986) and Zimmerling  (1993).  Mainland The mainland areas used i n t h i s study are the c o n t r o l areas of the Kluane B o r e a l Forest Ecosystem P r o j e c t al.  (Krebs et  1992), l o c a t e d i n the Shakwak Trench, approximately 60  km  southeast of Jacquot I s l a n d . Willow (Salix  gluaca)  and Shepherdia dominate the  understory of the mainland g r i d s .  U n l i k e the i s l a n d t h e r e  are some mainland areas with a high p r o p o r t i o n of shrub b i r c h (Betula  glandulosa).  White spruce f o r e s t , v a r y i n g from very  dense t o sparse, i s present on a l l g r i d s . small areas of balsam poplar and aspen.  There are a l s o For a more d e t a i l e d  d e s c r i p t i o n of the mainland areas see Krebs et al.  (1986).  METHODS Hare  Trapping  This study was  conducted from the end of A p r i l t o the end  of August during 1993 and 1994.  Two  t r a p p i n g g r i d s were used  on Jacquot I s l a n d , one on the north s e c t i o n of the i s l a n d and one on the south.  The o r i g i n a l g r i d s were 10 X 10 with 30 m  between s t a t i o n s on the north and 40 m between s t a t i o n s on the south.  These g r i d s were spaced d i f f e r e n t l y due t o  previous s t u d i e s on the i s l a n d .  I used these t r a p p i n g g r i d s  f o r the p o p u l a t i o n estimates, except f o r the f i n a l s e s s i o n of  11  1993  when I used a 12 X 15 g r i d on the north and a 10 X 16  g r i d on t h e south.  This was done t o cover a l a r g e r area f o r  the removal of r a d i o c o l l a r s . A l l g r i d s had a checkerboard arrangement of t r a p s with one Tomahawk l i v e t r a p placed a t every other s t a t i o n .  Despite the  d i f f e r e n c e s i n g r i d spacing between s t a t i o n s on t h e 10 X 10 north and south g r i d s , t h e e f f e c t i v e t r a p p i n g areas were quite s i m i l a r .  I estimated the e f f e c t i v e t r a p p i n g area (ETA)  of the g r i d by adding a border equal t o the r a d i u s of the home range of the hares where p o s s i b l e ( K e i t h 1990). In the summer o f 1994 t h e home range of hares on t h e north and south i s l a n d s was 5.43 ha and 3.40 ha r e s p e c t i v e l y (Madsen 1994, Kluane Boreal Forest Ecosystem P r o j e c t , unpublished).  The  south i s l a n d g r i d was bounded on two opposite s i d e s by water so the ETA of the 10 X 10 south g r i d was 20.2 ha, and the ETA of the 10 X 15 south g r i d was 27.4 ha. The north g r i d was bounded on one s i d e by water so only a 30 m boundary c o u l d be added on one s i d e , making the ETA of the 10 X 10 north  grid  was 22.8 ha and the ETA o f the 12 X 15 g r i d was 31.3 ha. I trapped  at the end o f A p r i l and a t the end o f August t o  get s p r i n g and f a l l population estimates.  Each s e s s i o n  c o n s i s t e d o f 3-5 nights of t r a p p i n g on each g r i d , a l t e r n a t i n g between g r i d s . apple.  Traps were b a i t e d with a l f a l f a cubes and  When captured,  each hare was marked with a numbered  ear t a g and had i t s weight, sex, and r i g h t hind f o o t length recorded.  The reproductive c o n d i t i o n of males was noted as  s c r o t a l , t e s t e s receding o r abdominal, based on t e s t e s s i z e .  12  Females were noted as l a c t a t i n g or n o n - l a c t a t i n g .  I also  noted whether the females were pregnant or non-pregnant on weight change and abdominal  based  palpation.  I estimated the p o p u l a t i o n s i z e s on each g r i d u s i n g the j a c k k n i f e estimator from the CAPTURE program (Otis et al. 1978).  T h i s estimator was  found t o be most robust t o the  sampling v a r i a t i o n s found i n snowshoe hare p o p u l a t i o n s i n the Kluane area (Boulanger and Krebs  1994).  Population estimates f o r the mainland g r i d s were obtained during March and November a l s o using the j a c k k n i f e estimator (Otis et al. 1978).  For the p o p u l a t i o n estimates of the  mainland I use data from two mainland c o n t r o l g r i d s , and Sulphur.  Silver  For reproduction and s u r v i v a l i n f o r m a t i o n I  have combined the mainland c o n t r o l s f o r i n c r e a s e d sample size.  In those cases I r e f e r t o one mainland c o n t r o l area.  Adult  Hare  Survival  I r a d i o - c o l l a r e d between 10 and 20 hares on each during the summers of 1993  and 1994.  grid  I used Lotek, model  SMRC-3RB, m o r t a l i t y t r a n s m i t t e r s (mass=40g) attached t o e i t h e r a l e a t h e r or a nylon webbing c o l l a r .  These  t r a n s m i t t e r s doubled t h e i r pulse r a t e i f they remained f o r four hours and, although monitored every one o r two  still days,  needed t o be t r a c k e d only when the pulse r a t e doubled and the hare was  presumed t o be dead.  During the winter of 1992-93 there were 7 r a d i o c o l l a r e d adult hares and I used those i n d i v i d u a l s t o estimate overwinter s u r v i v a l .  S u r v i v a l rates f o r the summer and  13  s p r i n g were c a l c u l a t e d using the Kaplan-Meier method (KaplanMeier 1958, P o l l o c k et al.  1989a) which allows f o r the  censoring of data (owing t o l o s s or f a i l u r e of r a d i o s or animals l i v i n g beyond the d u r a t i o n of the study) and the staggered e n t r y of animals (Pollock et al. al.  1989b).  test  1989a, P o l l o c k et  S u r v i v a l r a t e s were compared u s i n g the log-rank  (Savage 1956, P o l l o c k et al.  1989b)  S i t e a n a l y s i s was used t o determine the cause of death f o r r a d i o - c o l l a r e d hares.  The cause of death was  determined  using the c r i t e r i a set out by the Kluane Boreal F o r e s t Ecosystem P r o j e c t (C. Doyle, unpublished).  The k i l l s i t e  examined f o r evidence of predators, such as whitewash, or t r a c k s and f o r the c h a r a c t e r i s t i c way with t h e i r prey.  was  scats,  some predators deal  S u r v i v a l of hares on the mainland  was  estimated using the same methods as used on Jacquot I s l a n d . Measurement o f  Litters  Female snowshoe hares do not make nests and nurse young only once per day (Severaid 1942, Rongstad and T e s t e r  1971).  This makes l i t t e r s very d i f f i c u l t t o l o c a t e i n the f i e l d  and  as a r e s u l t the f o l l o w i n g method f o r studying hare l i t t e r s was e s t a b l i s h e d by O'Donoghue (1992). attempted t o catch 10-15  In 1993 and 1994 I  pregnant female hares (on each  i s l a n d g r i d ) s h o r t l y before p a r t u r i t i o n and place each female i n a 60 X 60 X 120 cm, wire mesh cage, at t h e i r p o i n t of capture.  The back h a l f of each cage was covered i n b u r l a p  and spruce bows were woven through the sides and top of the wire mesh t o c r e a t e a concealed area f o r the hare.  14  Straw  was  placed on the bottom of the cage and food and water were provided once d a i l y .  Each hare r e c e i v e d one apple, 4 0-50  willow twigs, 400 ml of water and 100 ml of bunny chow. p a r t u r i t i o n the cage was opened and the hare was A f t e r the female l e f t the cage, the l i t t e r was  Upon  released. counted,  and each l e v e r e t was tagged with a numbered eartag,  weighed,  had i t s r i g h t hind foot measured and i t s sex recorded.  A  maximum of four l e v e r e t s from a l i t t e r had r a d i o t r a n s m i t t e r s (Biotrack, model SR-1; subsequent s u r v i v a l  mass= 2-3 g) attached f o r determining  (methods described below). The whole  l i t t e r was then placed i n a concealed area, u s u a l l y amongst d e a d f a l l , w i t h i n four meters of the place of b i r t h .  The cage  was removed from the area t o prevent l e v e r e t s from c r a w l i n g back i n and t o avoid a t t r a c t i n g or d e t e r r i n g predators from the  area. On the mainland 10-15  females were caught throughout  c o n t r o l areas of the study s i t e and were brought t o a c e n t r a l area with e l e c t r i c fencing t o prevent harassment predators. the  by  Upon p a r t u r i t i o n the females were removed from  cage, the l i t t e r s were processed as d e s c r i b e d f o r the  i s l a n d g r i d s , and then both female and young were t r a n s p o r t e d back t o the female's home range.  The l i t t e r was then placed  i n a concealed area and the female was s i t e and then r e l e a s e d .  introduced t o t h i s  A l l other aspects of the procedure  were the same except, on the mainland, a l l l e v e r e t s from a l i t t e r had r a d i o t r a n s m i t t e r s attached when p o s s i b l e .  15  D e t e r m i n a t i o n of R e p r o d u c t i v e  Parameters  To measure the t i m i n g of breeding f o r each area the mean date of p a r t u r i t i o n of females i n cages was c a l c u l a t e d . Testes r e g r e s s i o n of males was recorded while t r a p p i n g during the summer t o estimate the t i m i n g of the end o f t h e breeding p e r i o d f o r each area.  An estimate of pregnancy r a t e s was  made by counting the p r o p o r t i o n of pregnant pregnant  or recently  female hares during a 2 week p e r i o d around the mean  date of p a r t u r i t i o n f o r each area.  Juvenile Survival For determining e a r l y j u v e n i l e s u r v i v a l r a d i o t r a n s m i t t e r s (described i n the Measurement of L i t t e r s s e c t i o n ) were used. The r a d i o t r a n s m i t t e r s were glued t o a small area of trimmed fur  between the shoulder blades of each l e v e r e t .  This  procedure kept t h e t r a n s m i t t e r s attached f o r approximately 35 weeks.  Radio-tagged  j u v e n i l e hares were t r a c k e d f o r a  v i s u a l s i g h t i n g d a i l y t o determine  i f they were a l i v e .  If a  l e v e r e t was found dead, the cause of m o r t a l i t y was determined using the same procedure as d e s c r i b e d f o r a d u l t hares.  I  counted a l i t t e r as abandoned when 1) the whole l i t t e r was found dead i n a r e l a t i v e l y open area c l o s e t o the b i r t h spot, 2) the bodies were whole and there was no evidence of predation and,  3) when autopsied t h e i r stomachs were empty.  S u r v i v o r s h i p curves f o r the radio-tagged l e v e r e t s were c a l c u l a t e d using the Kaplan-Meier a d u l t hares.  procedure  as d e s c r i b e d f o r  Comparisons of the s u r v i v o r s h i p curves were  made using the log-rank t e s t  (Savage 1956, P o l l o c k e t a l .  16  1989b).  The same procedures were used on the mainland except  that a l l l e v e r e t s from a l i t t e r were radio-tagged when possible. J u v e n i l e hares t h a t were caught i n the August t r a p p i n g s e s s i o n and weighed more than 1000 g were f i t t e d with a d u l t mortality c o l l a r s .  On Jacquot Island I monitored overwinter  j u v e n i l e s u r v i v a l using t r a p p i n g data and 3 r a d i o - c o l l a r e d j u v e n i l e hares.  On the mainland overwinter j u v e n i l e s u r v i v a l  was measured using 8 r a d i o - c o l l a r e d hares.  Body Weights and C o n d i t i o n  Index  Body c o n d i t i o n can be estimated by measuring s k e l e t a l and weight  ( B a i l e y 1968).  size  I estimated body c o n d i t i o n by  measuring r i g h t hind foot length (RHF; i n mm)  and body mass  ( i n grams) of male snowshoe hares i n A p r i l and e a r l y May. The mean r i g h t hind foot length f o r each hare was used i n the c a l c u l a t i o n s t o reduce observer e r r o r .  Only males were used  because most females were already pregnant when the measurements were obtained.  The f o l l o w i n g equation was used:  P r e d i c t e d Weight = 738.9 +  (RHF)  This equation was c a l c u l a t e d by O'Donoghue  1-3  (1992), and was  used t o o b t a i n a p r e d i c t e d weight f o r each i n d i v i d u a l .  The  r a t i o of observed weight t o p r e d i c t e d weight was used as the c o n d i t i o n index.  P r e d a t o r Numbers To get an index of predator numbers a s i g h t i n g index was used on both Jacquot I s l a n d and the mainland.  Each  researcher recorded the number of hours spent i n the f i e l d  17  and the number and type of species seen d u r i n g t h i s time.  An  index of predators seen per 100 hrs i n t h e f i e l d was c a l c u l a t e d from t h i s i n f o r m a t i o n . Red s q u i r r e l numbers were estimated on each of the Jacquot I s l a n d g r i d s by a c t i v e midden counts and v i s u a l s i g h t i n g s o f s q u i r r e l s u s i n g middens.  parryii)  A r c t i c ground s q u i r r e l s (Spermophilus  numbers were estimated by o b s e r v a t i o n of burrows. On the mainland r e d and ground s q u i r r e l s numbers were estimated through l i v e - t r a p p i n g on c o n t r o l g r i d s .  Statistical  Procedures  I pooled the data from Jacquot I s l a n d north and south g r i d s t o i n c r e a s e the sample s i z e .  To determine i f the data  from the two i s l a n d g r i d s could be pooled I used t - t e s t s . Because of the small sample s i z e s on Jacquot I s l a n d and the l a c k of data f o r the mainland i n 1993, comparisons  of l i t t e r  s i z e and average l e v e r e t weight per l i t t e r were made with 1994 data o n l y . all  A 0.05 l e v e l of s i g n i f i c a n c e was used f o r  tests.  RESULTS Population  Density  During t h i s study the hare p o p u l a t i o n on Jacquot I s l a n d was higher than the mainland p o p u l a t i o n a t a l l times 3).  (Figure  Jacquot I s l a n d reached low p o p u l a t i o n d e n s i t i e s i n the  s p r i n g of 1993 as d i d the mainland p o p u l a t i o n .  The average  population d e n s i t y on Jacquot Island increased 3.5 f o l d  from  0.4 hares/ha i n the s p r i n g of 1993 t o 1.4 hares/ha i n the  18  o OO  o  Z  4-> 4->  o  o  CT U  CT CJ CO  3  (0  3  oo  L75  + +H CD  CD C Q.  00  CNJ  rth  vf cn  cn cn  o  *—  TJ  cn  CO JO  —'  v  •  c ' CT) — C i—  cn O cn 3  4->  cn cn D)  c  Q.  00  o cn  c  v—  o  cn c  *L_  CL OO  CO  o  cn cu c cn  o d BL|/S9JBH  19  >—  i  CO  cu cn 3 - C cn  pop and  CO  CD Q.  00  /<s  CD .C  CO  cn cn cn c  ro" 4-> CD O CD 3 10 F LL  CO  iiu;  CL 00  '(0  o E  igun  CD C  *-> CO  TJ C  sp  cn cn  3  Q-  10 (0  UjJ  o  >,  TJ  nd  CL 00  'lO  c CO  c  c  CD  <4—  E cn cn  cn  ates ow (sul hur and this  cn cn  •  oe Ive  CO  (NJ  ^-  CT O CO -)  es ids  CO  s p r i n g o f 1994, w h e r e a s t h e a v e r a g e p o p u l a t i o n d e n s i t y o f t h e mainland c o n t r o l g r i d s remained  c o n s t a n t a t 0.08 h a r e s / h a  (Figure 3 ) . B o t h J a c q u o t I s l a n d and m a i n l a n d p o p u l a t i o n s i n c r e a s e d o v e r t h e summer o f 1993;  however, J a c q u o t I s l a n d showed a  7.3 f o l d i n c r e a s e compared t o a 1.8 f o l d i n c r e a s e f r o m t o October on t h e m a i n l a n d .  April  D u r i n g t h e summer o f 1994 t h e  Jacquot I s l a n d hare p o p u l a t i o n i n c r e a s e d about 5 f o l d .  The  m a i n l a n d c o n t r o l g r i d s i n c r e a s e d b e t w e e n 5 and 23 f o l d  from  t h e s p r i n g o f 1994 t o t h e f a l l o f 1994 ( F i g u r e 4 ) . Based on t h e s e r e s u l t s , p r e d i c t i o n s f o r each o f t h e hypotheses  p r e s e n t e d i n t h e i n t r o d u c t i o n c a n be made.  These  a r e shown i n T a b l e 1. Summer A d u l t  Hare  Survival  T h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n a d u l t  hare  s u r v i v a l d u r i n g t h e summer o n t h e n o r t h and s o u t h g r i d s o f J a c q u o t I s l a n d i n e i t h e r y e a r (1993, l o g - r a n k t e s t s t a t i s t i c = l . 5 0 , p=0.13; 1994, 100% s u r v i v a l o n b o t h  grids).  As a r e s u l t , f o r c o m p a r i n g w i t h t h e m a i n l a n d , I p o o l e d t h e d a t a from both i s l a n d g r i d s t o i n c r e a s e t h e sample s i z e . Twenty-eight day a d u l t s u r v i v a l d i d n o t d i f f e r s i g n i f i c a n t l y b e t w e e n J a c q u o t I s l a n d and t h e m a i n l a n d i n 1993 ( l o g - r a n k t e s t s t a t i s t i c = l . 1 3 , p=0.26) b u t was 10% h i g h e r o n J a c q u o t I s l a n d t h a n t h e m a i n l a n d i n 1994 ( l o g - r a n k t e s t s t a t i s t i c = 3 . 0 4 , p=0.002).  A d u l t s u r v i v a l on J a c q u o t  Island  was 10% h i g h e r i n 1994 t h a n 1993 ( l o g - r a n k t e s t s t a t i s t i c = 3 . 1 1 , p=0.002). On t h e m a i n l a n d t h e r e was no  20  3 % o o Z  CO  o  o  CT O w  CT O ro  —) —)  ^  Q. -=•  <D >  .5 CO  CO  .2  4-  cn  5" S  JS cn ^ c  o a. CO <"  d) d> CO 4_*  c <u — 10  T3  §  ' RA C  0 C  CD CD  Dl C O. CO  ito a)  V4-  >  In  "5  12 —  3  c  C  o  C3  ^.S CO CD CD  ro CD  ^  I  ± ! ±3 5 -D s  —' c to CO  1-2 \p O) CO CD CD  D) C  "i—  Q. CO  CO CO "O  3  C CD Q . CD CD  o x: . — CD  °5  EL|/SaJBH  21  2  1  CO CD  E  J5 O LT J2 it D5  o d  %  TJ C CO  c o  •+J  u 3  TJ  -I cu  or*  cu  -G  t. o E co  CD  cu  cu  o  <:  cu  cu  o  o  o  TJ  i £  i ! re t! 3  "8  5  SI  C  _  cu  ^  >  c\j  .5,  CU  E  CO 10  c o 3  TJ CO  C\J  CO  t E  cu  cu  co  co  E ro  E ro  cu  o  M o cu  > ~  3 ro CNJl  <3  i  cu  cu  E ro  cu  co  o  E CO  cu  cu  cu  co  CO  CO  c o  CO LU OO LU X  ho CL >-  '4-1  u 3  TJ O  L.  Q. CU  H  E re  CD  o  (0  CU > CtC  O o <  t o _0) E  U  43 2 a. Q.  *  £  O  0)  > 3  22  E CO  f*> CO  £ o E 3  TJ CO  s i g n i f i c a n t d i f f e r e n c e i n s u r v i v a l r a t e s between 1993 and 1994  (log-rank t e s t s t a t i s t i c = 0 . 8 0 , p=0.42; Table 2 ) .  Overwinter  A d u l t Hare  Survival  During the winter of 1993-1994 (September t o A p r i l ) there were 7 r a d i o - c o l l a r e d a d u l t hares on Jacquot I s l a n d (approximately 54% of the a d u l t s i n the p o p u l a t i o n ) . Two of the hares d i e d , one due t o an unknown predator, the other due to unknown causes.  There was no d i s p e r s a l of r a d i o - c o l l a r e d  hares o f f the i s l a n d during t h i s p e r i o d .  Based on t r a p p i n g  r e s u l t s , s u r v i v a l of a d u l t hares from September 1993 t o May 1994 was 83% over e i g h t months. On the mainland 38 hares were c o l l a r e d from September t o April.  The s u r v i v a l r a t e f o r t h i s p e r i o d was 12.6% over  e i g h t months (95% confidence i n t e r v a l 8-17%).  Proximate Causes of M o r t a l i t y of A d u l t  Hares  During the summers of 1993 and 1994 on Jacquot I s l a n d there were only 6 m o r t a l i t i e s out of 55 c o l l a r e d hares. m a j o r i t y of deaths were due t o p r e d a t i o n .  The  On the mainland  there were 19 m o r t a l i t i e s out of 54 c o l l a r e d hares and the majority of deaths were due t o unknown causes and unknown predators (Table 3 ) .  Effect  of M a t e r n i t y  Cages on R e p r o d u c t i v e  Data  Females were kept i n maternity cages and s u p p l i e d with food p r i o r t o p a r t u r i t i o n . of  To determine the p o s s i b l e impact  t h i s procedure on the young I d i d r e g r e s s i o n s o f days a  female spent i n the maternity cage p r i o r t o p a r t u r i t i o n on l i t t e r s i z e and average l e v e r e t weight per l i t t e r .  23  In 1993  Table 2. 28-day survival rates of radio-collared, adult snowshoe hares (95% confidence limits in parentheses and total hares collared beneath).  Summer 1993  Summer 1994  Jacquot Island  0.90 (0.83-0.96) 23  1.00 * (1.00-1.00) 32  Mainland  0.85 (0.68-0.94) 12  0.90 (0.85-0.95) 42  * significantly different from Jacquot Island summer 1993 (log rank test statistic=3.11, p=0.002); and mainland 1994 (logranktest statistic=3.04, p=0.002).  24  Table 3. Proximate causes of mortality of radio-collared adult snowshoe hares on Jacquot Island and the mainland.  Percentage of Mortalities  Mortality Factors Lynx Coyote Unknown Mammal Goshawk Great-Horned Owl Unknown Avian Unknown Predator Unknown  Total Killed Total Radio-Collared  Island 0.0 0.0 16.7 0.0 0.0 0.0 66.7 16.7  Mainland 0.0 0.0 16.7 0.0 0.0 16.7 16.7 50.0  Island 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  Mainland 7.7 0.0 0.0 15.4 0.0 0.0 30.7 46.2  6 23  6 12  0 32  13 42  25  females were held i n cages an average of 5.8 days d e v i a t i o n of ± 2.9 days) p r i o r t o p a r t u r i t i o n .  (standard  The time a  female spent i n a maternity cage p r i o r t o p a r t u r i t i o n had no s i g n i f i c a n t e f f e c t on l i t t e r s i z e (Figure 5a; r e g r e s s i o n , Y=0.10X + 5.59, R =0.04, p=0.53) o r average l e v e r e t weight per 2  litter  (Figure 5b; r e g r e s s i o n , Y=-0.36X + 60.03, R =0.02, 2  p=0.63). For the f i r s t l i t t e r of 1994 females were h e l d i n maternity cages an average of 5.2 days (standard d e v i a t i o n of ±3.7  days). The time a female spent i n a maternity cage  p r i o r t o p a r t u r i t i o n was s i g n i f i c a n t l y c o r r e l a t e d t o l i t t e r s i z e (Figure 6a; r e g r e s s i o n , Y=0.14X + 3.36, R =0.2, p=0.05) 2  and s i g n i f i c a n t l y , n e g a t i v e l y c o r r e l a t e d t o average l e v e r e t weight per l i t t e r  (Figure 7a; r e g r e s s i o n , Y=-1.32X + 67.49,  R =0.22, p=0.04). 2  For the second l i t t e r of 1994 females were h e l d i n cages and average o f 7.2 days (standard d e v i a t i o n of ± 3.9 days). The time a female spent i n a maternity cage p r i o r t o p a r t u r i t i o n was s i g n i f i c a n t l y c o r r e l a t e d t o l i t t e r s i z e (Figure 6b; r e g r e s s i o n , Y=0.18X +5.3, R =0.27, p=0.05) but 2  not t o average l e v e r e t weight per l i t t e r  (Figure 7b;  r e g r e s s i o n , Y=-0.58X + 71.47, R =0.10, p=0.27). 2  For the t h i r d l i t t e r of 1994 females were h e l d i n maternity cages an average of 5.0 days (standard d e v i a t i o n of ±2.8  days). The time a female spent i n a maternity cage  p r i o r t o p a r t u r i t i o n was not s i g n i f i c a n t l y c o r r e l a t e d t o l i t t e r s i z e (Figure 6a; r e g r e s s i o n , Y=0.09X + 7.21, R =0.01, 2  26  F i g u r e 5 ( a - b ) . The e f f e c t of time a female spent i n a cage p r i o r t o p a r t u r i t i o n on l i t t e r s i z e and average l e v e r e t weight per l i t t e r f o r a l l l i t t e r s i n 1993 on Jacquot I s l a n d .  27  (a) 1993 all litters 8 7+ 6 5 4 3 2+ 1 0 0  Litter size  (b) Average  R = 0.04 p=0.53  10  15  1 993 all litters 80  leveret  70  weight  50  60 •  •  1 »  »  40  per  30  litter  10  R = 0.02 p=0.63 2  20 + 0 0  10  15  (9)  Time in cage prior to parturition (days)  28  F i g u r e 6 ( a - c ) . The e f f e c t of time a female spent i n a maternity cage p r i o r t o p a r t u r i t i o n on l i t t e r s i z e f o r l i t t e r groups 1, 2, and 3 of 1994 on Jacquot I s l a n d .  29  (a) 1994 first litter 10 8  litter size = 0.1423 Days + 3.36 R = 0.20 p=0.05  6  2  4 2 0 10  15  20  (b) 1994 second litter 10 8 6  litter size = 0.1 848Days+ 5.3358 R = 0.27 p=0.05 2  4 2 0 10  15  20  (C) 1994 third litter 14 -r 12 10 + 8 6 4 2 0  • R = 0.01 p=0.69 2  10  15  20  Time in cage prior to parturition (days)  30  F i g u r e 7 ( a - c ) . E f f e c t of time a female spent i n a maternity cage p r i o r t o p a r t u r i t i o n on average l e v e r e t weight per l i t t e r , f o r l i t t e r groups 1, 2, and 3 of 1994 on Jacquot Island.  31  (a) 1994 first litter 100 80 60 40 20 0  Weight = -1.33Days +67.49 R =0.22 p=0.04 2  10  20  15  (b) 1994 second litter 100 80 60 40 20 0  It  •  10  15  R =0.10 p=0.27 2  20  (C)  1994 third litter 100 80 60  R =0.01 p=0.68 2  40 20 0 10  15  20  Time in cage prior to parturition (days)  32  p=0.68) o r l i t t e r weights (Figure 7c; r e g r e s s i o n , Y=-0.41X + 74.99, R =0.01, p=0.68). The e f f e c t of time a female spent i n 2  a maternity cage p r i o r t o p a r t u r i t i o n on l i t t e r s i z e and average l e v e r e t weight per l i t t e r i s summarized i n Table 4.  Pregnancy  Rates  Pregnancy r a t e s (proportion of females pregnant during each l i t t e r group) v a r i e d between 89% and 94% with an average of  92% (standard d e v i a t i o n of ± 1.7%) on Jacquot I s l a n d  during 1993 and 1994. for  The mainland hares t h a t were trapped  maternity cages were a l l pregnant o r had r e c e n t l y given  birth.  Timing of  Litters  The mean dates of b i r t h were s i m i l a r between years and between the mainland and the i s l a n d f o r each l i t t e r (Table 5 ) .  group  In 1994 the i n t e r v a l between l i t t e r s , based on  mean p a r t u r i t i o n dates, v a r i e d between 36 and 38 days, with an average of 37 days.  Litter  Sizes  L i t t e r s i z e data were not analyzed i n 1993 due t o small sample s i z e s and l a c k o f mainland data.  In 1994 mean l i t t e r  s i z e s were 17% l a r g e r on Jacquot I s l a n d than t h e mainland (Table 6; two-way ANOVA, p=0.008). e f f e c t between l o c a t i o n  There was no i n t e r a c t i o n  (Jacquot I s l a n d and the mainland) and  l i t t e r group (two-way ANOVA, p=0.89).  For both the i s l a n d  and the mainland i n 1994 the f i r s t l i t t e r was s i g n i f i c a n t l y smaller than second and t h i r d l i t t e r s  (Tukey t e s t , p<0.001 i n  each case) and there was no d i f f e r e n c e between l i t t e r s two  33  Table 4. Summary table of the effect of days a female spent in a cage prior to parturition on litter size and mean leveret weight per litter for 1993 and 1994.  The effect of days in cage prior to parturition on:  Litter size  Mean newborn weights  litter  Days in cage prior to parturition  Year  group  + (S.D.)  R value  p value  R value  p value  1993  all  5.8 (2.9)  0.04  0.53  0.02  0.63  1994  1  5.2 (3.7)  0.20  0.05*  0.22  0.04*  1994  2  7.2 (3.9)  0.27  0.05*  0.10  0.27  1994  3  5.0 (2.8)  0.01  0.69  0.01  0.68  2  2  * significant effect of days a female spent in cage prior to parturition  34  Table 5. Mean date of birth (+ S.D.) for Jacquot Island and mainland study sites in 1993 and 1994 (number of litters in parentheses).  Mean date of birth  1993 Litter  Jacquot Island  1994 Mainland  Jacquot Island  Mainland  (D  May 12 + 3.3 (20)  May 13 +2.6 (11)  2  June 18+ 2.6 (4)  June 19 + 5.5 (15)  June 19 ± 3 . 4 (9)  3  July 22 ± 2 . 8 (7)  July 26 ± 7 . 3 (14)  July 25 ± 3 . 8 (10)  1  May 17  35  Table 6. Mean litter sizes at birth (+ S.D.) for Jacquot Island and mainland Study Sites in 1993 and 1994 (number of litters in parentheses).  Mean litter Size  1993  1994  Litter  Jacquot Island  Mainland  Jacquot Island  1  4.0  -  4.1 + 1.2 (20)  (D 2  3  1  2  7.3 + 0.5 (4)  -  5.9+1.5 (7)  -  1  2  Mainland 3.2±0.8  2  (11)  6.7 + 1.4 (14)  5.8 ± 1 . 1  7.6 + 2.1 (14)  6.4+1.2 (10)  (9)  significantly larger litter sizes on Jacquot Island (2-way ANOVA p=0.008) significantly larger than litter groups 2 and 3 (2-way ANOVA, Tukey test p<0.001)  36  and one (Tukey t e s t p=0.502).  During the t h i r d l i t t e r one  female on Jacquot Island had 14 l e v e r e t s which i s l a r g e r than any l i t t e r Stillborn  s i z e I have found recorded i n the l i t e r a t u r e . Rates  S t i l l b o r n rates were very low on both the i s l a n d and the mainland f o r 1993 and 1994. On Jacquot i s l a n d t h e r e was no incidence o f s t i l l b i r t h s i n 1993 and the f i r s t l i t t e r of 1994 and s t i l l b o r n r a t e s were only 1.0% f o r second and t h i r d l i t t e r s i n 1994. On the mainland the s t i l l b o r n r a t e s were 2.9% f o r f i r s t l i t t e r ,  0.0% f o r second l i t t e r ,  and 4.7% f o r  t h i r d l i t t e r of 1994. Newborn H a r e Body  Weights  Mean newborn weight data were not analyzed i n 1993 due t o small sample s i z e s and the l a c k o f data from the mainland. In  1994 the average weights of newborn hares were 12% g r e a t e r  on Jacquot I s l a n d than the mainland (Table 7; two way ANOVA, p=0.02).  There was no s i g n i f i c a n t i n t e r a c t i o n between  l o c a t i o n (Jacquot I s l a n d and the mainland) and l i t t e r (two-way ANOVA, p=0.96). the  group  On both the i s l a n d and the mainland  newborn weights f o r f i r s t l i t t e r s were s i g n i f i c a n t l y  smaller than t h i r d l i t t e r s  (Tukey t e s t p<0.001), however  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 between the weights of l i t t e r groups one and two (Tukey t e s t p=0.08) and l i t t e r groups two and three (Tukey t e s t p=0.25). For  the f i r s t and t h i r d l i t t e r s of 1994 the average  l e v e r e t weight per l i t t e r was s i g n i f i c a n t l y n e g a t i v e l y c o r r e l a t e d with l i t t e r s i z e ( F i r s t l i t t e r ;  37  Figure 8a, R =0.30, 2  Table 7. Mean newborn weights at birth (+ S.D.) for Jacquot Island and mainland study sites in 1993 and 1 994 (number of litters in parentheses).  Mean newborn weights (g)  1993  1994  Litter  Jacquot Island  Mainland  Jacquot Island  Mainland  1  47.4  -  60.6 +10.3 (20)  54.3 + 7.0 (9)  (D.  1  2  2  2  56.4 + 5.0 (4)  -  67.3 + 7.5 (14)  60.4 ± 4 . 8 (9)  3  60.3 + 6.7 (7)  -  72.9 ± 9 . 8 (14)  64.5 + 4.6 (10)  1  significanlty heavier mean newborn weights on Jacquot Island (2-way ANOVA, p=0.02)  2  significantly lighter than litter 3 (2-way ANOVA, Tukey test, p=0.001)  38  Figure 8 ( a - c ) . C o r r e l a t i o n between l i t t e r s i z e and average l e v e r e t weight per l i t t e r f o r l i t t e r groups 1,2, and 3 of 1994 on Jacquot I s l a n d .  39  (b)  1994 second litter 90 80 70 60 50 40 30 20 10 0  R = 0.20 p=0.08 2  10  1994 third litter  (C) 100 90 + 80 70 60 50 40 30 20 10 0  R = 0.60 p=0.001 2  10  Litter size  40  15  p=0.01; T h i r d l i t t e r ;  Figure 8c, R =0.60, p=0.001). 2  s i g n i f i c a n t c o r r e l a t i o n was found f o r second l i t t e r  (Figure  9  8b; R =0.20, p=0.08). 2  For  No  a l l l i t t e r groups the t o t a l weight o f a l i t t e r  increased with l i t t e r s i z e (Figure 9a-c; F i r s t  litter,  R =0.67, p<0.001; Second l i t t e r , R =0.72, p<0.001; T h i r d 2  2  l i t t e r , R =0.86, p<0.001). 2  Sex R a t i o s o f Newborn Hares Sex r a t i o s were s t a t i s t i c a l l y d i f f e r e n t than 1:1 i n two cases (Table 8; G - t e s t ) .  On the north g r i d of Jacquot I s l a n d  f o r f i r s t l i t t e r there was a d i s p r o p o r t i o n a t e number of female newborns and on the mainland f o r t h i r d l i t t e r t h e r e was a d i s p r o p o r t i o n a t e number of male newborns.  Juvenile  Breeding  On Jacquot I s l a n d i n 1993 there were 2 s c r o t a l l i t t e r males caught i n mid-July.  first  In 1994 t h e r e were 3  s c r o t a l f i r s t l i t t e r males caught on the mainland and 4 caught on the i s l a n d d u r i n g mid-July.  There was no evidence  of any j u v e n i l e females being pregnant o r l a c t a t i n g d u r i n g e i t h e r year o f the study.  Total  R e p r o d u c t i v e Output  T o t a l r e p r o d u c t i v e output per female s u r v i v i n g the breeding season can be estimated by m u l t i p l y i n g  pregnancy  r a t e s by mean l i t t e r s i z e and ( 1 - s t i l l b o r n r a t e s ) and adding these over the t h r e e l i t t e r groups  (O'Donoghue 1991). This  value corresponds t o p o t e n t i a l n a t a l i t y (Carey and K e i t h 1979, O'Donoghue  1992).  No s t a t i s t i c a l t e s t s c o u l d be done  41  F i g u r e 9 ( a - c ) . The e f f e c t of l i t t e r s i z e on the t o t a l weight of a l i t t e r f o r l i t t e r groups 1, 2, and 3 of 1994 on Jacquot Is1and.  42  (b)  1994 second litter  600  T  500 400 300 y = 47.7x + 126.8 R = 0.72 p<0.001  200  2  100 0  10 (C)  1994 third litter  900 800 700 600 500 400 300 200 100 0  y = 37.2x + 258.2 R = 0.86 p<0.001 2  10  Litter size  43  15  Table 8. Number of female hares born in maternity cages on Jacquot Island and mainland study sites in 1993 and 1994 (total number of newborn hares in parentheses).  Number of females  1993 Litter  1994  Jacquot Island Mainland  Jacquot Island North South  Mainland  1  3 (4)  2  16 (29)  51 (91)  21 (48)  3  20 (41)  54 (103)  24* (64)  28* (36)  * significantly different than 1:1 (G-test, df=1)  44  22 (44)  15 (34)  because only one  estimate i s made per year, but i n  Jacquot I s l a n d had a higher reproductive the mainland: 15.2  16.8  juveniles/female  juveniles/female  1994  output compared to  on Jacquot I s l a n d  on the mainland. T o t a l  and  reproductive  output of Jacquot Island, the mainland and another c y c l i c population of hares i s shown i n Figure  Evidence of  a Fourth  10.  Litter  There i s evidence that a f o u r t h l i t t e r was 1994.  On the i s l a n d 75%  produced i n  (n = 16) of adult males had  scrotal  t e s t e s i n the l a s t two weeks of J u l y when breeding f o r a f o u r t h l i t t e r would be o c c u r r i n g .  I t i s doubtful that  females with l a t e r t h i r d l i t t e r s would have a f o u r t h but some of those with e a r l y l i t t e r s may mainland i n 1994,  a j u v e n i l e hare was  t h a t , due t o i t s small s i z e , was leveret.  Unfortunately  have.  On  caught i n September  Jacquot I s l a n d was  litter  not trapped  September t o determine i f a f o u r t h l i t t e r occurred; during the f i n a l t r a p p i n g s e s s i o n of August, two There was  Jacquot  no s i g n from on  the  Island  l e v e r e t s were radio-tagged  on the south g r i d during radio-tagged  however,  however the p o s s i b i l i t y cannot be r u l e d out.  J u v e n i l e S u r v i v a l on Only two  during  adult  the August t r a p p i n g t h a t a f o u r t h l i t t e r occurred i s l a n d i n 1993,  litter,  the  probably a f o u r t h  females were judged t o be pregnant.  the  1993.  Ten and  from the f i r s t  litter  13 l e v e r e t s were  on both g r i d s during second and t h i r d  litters  r e s p e c t i v e l y . Because sample s i z e s were small the data from both g r i d s were pooled.  None of the 25 l e v e r e t s t h a t were  45  F i g u r e 10. T o t a l reproductive output (number o f l e v e r e t s produced per a d u l t female s u r v i v i n g the breeding season) i n r e l a t i o n t o population peaks and lows f o r an A l b e r t a population of snowshoe hares from 1962 t o 1976 (Carey and K e i t h 1979), a Yukon population of snowshoe hares from 1989 to 1990 (O'Donoghue 1991) and 1994, and the Jacquot I s l a n d population of snowshoe hares from 1991 t o 1992 (Zimmerling 1993) and 1993 t o 1994.  46  47  radio-tagged were known t o have d i e d . transmitters  F i v e of the r a d i o -  disappeared before 30 days of age. I t i s not  p o s s i b l e t o know whether the r a d i o s malfunctioned o r whether the l e v e r e t s were preyed upon and the radios destroyed. Because the f a t e of these f i v e l e v e r e t s i s unknown they were t r e a t e d as censored i n d i v i d u a l s i n the s u r v i v a l c a l c u l a t i o n s . J u v e n i l e s u r v i v a l data f o r Jacquot I s l a n d i n 1994 were c o l l e c t e d from 94 radio-tagged l e v e r e t s .  Of the 94 l e v e r e t s  that were radio-tagged, there were 16 known deaths. radio transmitters recovered.  Thirteen  disappeared before 30 days and were not  Because the f a t e o f these 13 l e v e r e t s i s unknown,  they were t r e a t e d as censored i n d i v i d u a l s i n the s u r v i v a l calculations. 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 the s u r v i v a l r a t e s of j u v e n i l e hares on the two i s l a n d g r i d s f o r l i t t e r one o r two ( l i t t e r one, log-rank t e s t s t a t i s t i c = 0 . 2 5 , p=0.803; l i t t e r two, log-rank t e s t s t a t i s t i c = l . 6 0 , p=0.110) so I pooled the data t o increase the sample s i z e .  For the  t h i r d l i t t e r , there were only 4 r a d i o tagged l e v e r e t s on the north g r i d so I pooled the data from both g r i d s .  Juvenile Survival  on the  Mainland  No s u r v i v a l data were c o l l e c t e d i n 1993.  During 1994, 123  l e v e r e t s were radio-tagged and there were 47 known deaths. F i f t e e n of the 123 r a d i o t r a n s m i t t e r s disappeared before 30 days and were not recovered.  Because the f a t e o f these 15  l e v e r e t s i s unknown they were t r e a t e d as censored i n d i v i d u a l s for  the s u r v i v a l c a l c u l a t i o n s .  48  Comparison the  of Juvenile  Mainland  Survival  on J a c q u o t  Island  and  i n 1994  For the f i r s t l i t t e r , e a r l y j u v e n i l e s u r v i v a l on Jacquot Island was not s t a t i s t i c a l l y d i f f e r e n t from the mainland (Figure 11; log-rank t e s t s t a t i s t i c = 0 . 9 4 , p=0.35).  However  s u r v i v a l was higher on Jacquot I s l a n d f o r second and t h i r d litters  (Figure 12 and Figure  13; l i t t e r 2, log-rank t e s t  s t a t i s t i c = 3 . 9 0 , p<0.001; l i t t e r three, log-rank t e s t s t a t i s t i c = 2 . 1 8 , p=0.03). three l i t t e r s  The average s u r v i v a l r a t e over a l l  was 0.79 on Jacquot Island and 0.52 on the  mainland. Comparison Groups  of Juvenile  Survival  Over D i f f e r e n t  Litter  i n 1994  E a r l y j u v e n i l e s u r v i v a l of the f i r s t l i t t e r group on Jacquot I s l a n d was lower than second l i t t e r and s i g n i f i c a n t l y lower than t h i r d l i t t e r  (Figure 14; f i r s t and t h i r d  litters  log-rank t e s t s t a t i s t i c = 2 . 3 9 , p=0.02; f i r s t and second litters  log-rank t e s t s t a t i s t i c = l . 7 6 , p=0.08).  On the  mainland second l i t t e r  s u r v i v a l was s i g n i f i c a n t l y lower than  f i r s t and t h i r d l i t t e r s  ( f i r s t and second l i t t e r , log-rank  t e s t s t a t i s t i c = 3 . 0 6 , p=0.002; f i r s t and t h i r d l i t t e r , l o g rank t e s t s t a t i s t i c = 2 . 7 3 , p=0.006; Figure 14). Overwinter  Survival  of Juvenile  Hares  on  Jacquot  Island Overwinter j u v e n i l e s u r v i v a l on Jacquot I s l a n d from August 1993 t o s p r i n g 1994, based on t r a p p i n g was 48%.  Only  three  r a d i o - c o l l a r e d j u v e n i l e hares were monitored overwinter.  49  One  50  o CO  LO (NJ  T3  O  c o o  (NJ  CO XT  CD O CD L_  14— ,  CO  CO  ±L  T3  i  CO LD  TJ CU CD <  (J  (0  5  E  TJ CU Ci= -C c ^ O TJ O c (0  LO  Y  CD jo - C CO 4-»  £  o  "> 3. 0  9-  c 0  !c LO  CO CO _0)  .> cu  M  00 -o cu (_NJ CD 2 ^  (O  JJ V 3  O )  CD  CO  d  d  CO  d  d  d  vT  CO  d d fiujAjAjns uoi+jodojd  51  (NJ  d  T —  d  O  °  TJ  iZ 2  52  land  uot 1  TJ C ro (/>  HJa  cr _c o 'ca  E  ay  10  X i X5  L—  nd  C o CO re 4-1 c < )' r e i _/ VI— E OJ <D -C -C 4-< 4-" o LO ro  V*—  o  D) L—  CM  +J X !  an  3  jUlj  CL  o 4J c o a> 3 T3 VI—  CT O  c -ro o > o c  an  o LO CO CT) TJ -C 4-"  CM"  to a) 1— 4-1  O reC Q.  1  3  rvi  O> iO) L_ 3 <D *->  1 1  to 4J  •t  1  ure  *r  1  1 CT1  d  1 oo  d  1 d ajEJ  1 CD  1  1  1  CM  d d |BAiAjns A"ep-rj£  d  1  d  d  53  1  «-  d  L_  o VI—  0)  VI—  CD CT)M— CT)  o  LL. o  «—  of these d i e d due t o coyote predation and the other two s u r v i v e d t o the f o l l o w i n g s p r i n g . E i g h t r a d i o c o l l a r e d j u v e n i l e s were monitored on the mainland over the w i n t e r .  S u r v i v a l was 11.3% (95% confidence  i n t e r v a l 0-32%) from August 1993 t o A p r i l 1994.  Proximate Causes of M o r t a l i t y of  J u v e n i l e Hares  On the mainland red s q u i r r e l s , unknown predators and weasels were the main proximate causes of m o r t a l i t y .  The  main proximate causes of m o r t a l i t y on Jacquot I s l a n d were non-predator/abandoned and unknown predator. P r e d a t i o n accounted f o r 62.5% of deaths on Jacquot I s l a n d w h i l e on the mainland i t accounted f o r 97.9% of deaths (Table 9 ) . Abandonment accounted f o r 6 out of the 16 m o r t a l i t i e s  (2 of  the 49 l i t t e r s ) on Jacquot I s l a n d whereas on the mainland no deaths were a t t r i b u t e d t o abandonment.  P r e d a t o r Numbers Fewer predators were seen on Jacquot I s l a n d than on the mainland i n 1993 and 1994; however, i n 1993 the s i g h t i n g index f o r coyotes (Canis  latrans)  s i m i l a r t o t h a t on the mainland.  on Jacquot I s l a n d was In 1994 t h e r e were no  coyote s i g h t i n g s on Jacquot I s l a n d while those on the mainland had increased from 1993 (Table 10). The other main mammalian predator, the lynx (Lynx canadensis),  was not seen  at a l l on Jacquot Island i n e i t h e r year and was seen only during 1993 on the mainland. Fewer avian predators were s i g h t e d on Jacquot I s l a n d than on the mainland i n both y e a r s .  54  S i g h t i n g s of i n d i v i d u a l  Table 9. Proximate causes of mortality of radio-tagged, juvenile snowshoe hares on Jacquot Island (J I) and the mainland in 1994.  Percentage of mortalities  Litter 1 Mortality factor unknown predator red squirrel small mammal weasel great-horned owl boreal owl red-tailed hawk unknown avian abandoned/non-predator  total mortalities total radio-tagged  Litter 2  Litter 3  Jl  Mainland  Jl  Mainland  Jl  44.4 33.3 0.0 0.0 0.0 0.0 0.0 0.0 22.2  60.0 20.0 0.0 0.0 20.0 0.0 0.0 0.0 0.0  20.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 80.0  15.4 38.5 7.7 7.7 0.0 11.5 0.0 15.4 3.8  50.5 0.0 0.0 0.0 0.0 0.0 50.5 0.0 0.0  25.0 12.5 6.2 50.0 0.0 0.0 6.2 0.0 0.0  9 30  5 27  5 34  26 46  2 30  16 50  55  Mainland  Table 10. Sighting index of hare predators on Jacquot Island and mainland grids during the summers of 1993 and 1 994.  Sightings/100 hrs  1993 Predator type  Predator  Mammalian  Avian  1994  Jacquot *  Mainland  coyote lynx weasel Total mammalian  0.14 0.00 0,00 0.14  0.13 0.14 0.05 0.32  0.00 0.00 0.00 0.00  0.23 0.00 0.04 0.27  great horned owl hawk owl red-tailed hawk goshawk marsh hawk unidentified raptor Total avian  0.00 0.00 0.00 0.00 0.00 0,70 0.70  0.07 0.47 2.52 0.91 1.02 0.52 5.51  0.00 0.00 0.50 0.00 0.06 0.26 0.82  0.02 0.00 2.01 0.42 0.96 0.46 3.87  *August not included  56  Jacquot  Mainland  r a p t o r species were a l s o higher on the mainland than on Jacquot I s l a n d d u r i n g both years; however, i n 1993 t h e r e was a higher i n c i d e n c e of u n i d e n t i f i e d r a p t o r s i g h t i n g s on Jacquot  Is1and.  S l i g h t l y more r a p t o r s were seen on Jacquot I s l a n d i n 1994 than i n 1993.  During the summer of 1994 a great-horned owl  was heard hooting on the i s l a n d i n August which i s not r e f l e c t e d i n the s i g h t i n g index o b s e r v a t i o n s . unexpected  T h i s i s not  s i n c e the owls are n o c t u r n a l and most of the f i e l d  work occurred during the day. The mainland had fewer mammalian and r a p t o r s i g h t i n g s i n 1994 compared t o 1993.  The s i g h t i n g i n d i c e s of a l l  i n d i v i d u a l s p e c i e s , except the coyote, were lower i n 1994 than 1993 (Table 10). Red s q u i r r e l d e n s i t i e s were estimated at 0.2/ha f o r both Jacquot I s l a n d north and south g r i d s .  D e n s i t i e s of red  s q u i r r e l s d i d not vary between y e a r s .  On the mainland red  s q u i r r e l d e n s i t i e s ranged between 1.75/ha and 3.83/ha Boreal Ecosystem P r o j e c t , unpublished).  (Kluane  Ground s q u i r r e l s  were not observed on Jacquot I s l a n d d u r i n g t h i s study nor i n previous s t u d i e s on Jacquot I s l a n d .  A d u l t Male S p r i n g Body Weights and C o n d i t i o n  Indices  There was no s i g n i f i c a n t d i f f e r e n c e i n male s p r i n g body weights or c o n d i t i o n i n d i c e s i n 1993 or 1994 between north and south Jacquot Island g r i d s (1993, weights, t=0.87, p=0.21, c o n d i t i o n index t=0.61, p=0.28; 1994, weights, t=0.77, p=0.23, c o n d i t i o n index, t=0.68, p=0.26).  57  Therefore  I pooled Jacquot north and south g r i d s i n both years t o i n c r e a s e sample s i z e . The body weights and c o n d i t i o n i n d i c e s of snowshoe hares on Jacquot I s l a n d and the mainland c o u l d not be compared i n 1993 because only two hares were caught on c o n t r o l areas on the mainland i n A p r i l and May of 1993.  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 the body weights and the c o n d i t i o n i n d i c e s of hares on Jacquot I s l a n d and the mainland i n 1994 (weights, t=1.27, p=0.11; c o n d i t i o n index, t=1.52, p=0.07) and there were no d i f f e r e n c e s between years on Jacquot I s l a n d (weight, t=1.29, p=0.11; c o n d i t i o n index, t=1.25, p=0.11; Tables 11 and 12).  DISCUSSION During a previous study by Zimmerling  (1993) both Jacquot  I s l a n d and the mainland underwent p o p u l a t i o n d e c l i n e s reaching low l e v e l s by the f a l l of 1992.  The hare p o p u l a t i o n  d e c l i n e on Jacquot I s l a n d was l e s s dramatic and of s h o r t e r d u r a t i o n than t h a t of the mainland p o p u l a t i o n .  The Jacquot  Island p o p u l a t i o n reached peak s p r i n g d e n s i t i e s i n 1991 and d e c l i n e d 71% over the next 2 years, reaching low d e n s i t i e s i n the s p r i n g of 1993, whereas, the mainland p o p u l a t i o n d e c l i n e d 94% over 4 years, from the s p r i n g of 1990 t o the s p r i n g of 1994.  The Jacquot I s l a n d hare p o p u l a t i o n d e c l i n e d one year  l a t e r than the mainland p o p u l a t i o n and never reached the low l e v e l s seen on the mainland.  U n l i k e the c y c l i c p o p u l a t i o n on  the mainland, which showed no change i n p o p u l a t i o n d e n s i t y from the s p r i n g of 1993 t o the s p r i n g of 1994, the Jacquot  58  Table 11. Mean body weights ± S.D. of male snowshoe hares in spring on study areas (sample size in parentheses). No significant differences were found between years on Jacquot Island or between areas in 1994.  Male body weights  Jacquot Island  Mainland  Spring 1993  Spring 1994  1217 + 121 (9)  1271 + 109 (33)  -  1 2 3 0 + 140 (26)  59  Table 12. Mean condition indices ± S.D. of male snowshoe hares in spring on study areas (sample size in parentheses). No significant differences were found between years on Jacquot Island or between areas in 1994.  Condition Indices  Jacquot Island  Mainland  Spring 1993  Spring 1994  0.937 + 0.08 (9)  0.976+0.08 (33)  -  0.941 +0.09 (26)  60  Island hare population  increased  rebound i n the population  3.5 f o l d .  This  a f t e r a d e c l i n e i s not  c h a r a c t e r i s t i c of c y c l i c populations  which have a d e c l i n e and  low p e r i o d which can l a s t 4 years (Keith 1990). e i t h e r reproduction  immediate  Consequently  or s u r v i v a l were higher on Jacquot I s l a n d  than the mainland from the s p r i n g of 1993 t o the s p r i n g of 1994.  Survival In t h i s s e c t i o n I d i s c u s s how overwinter a d u l t s u r v i v a l , overwinter j u v e n i l e s u r v i v a l , e a r l y j u v e n i l e s u r v i v a l ( b i r t h to 30 days), and summer adult s u r v i v a l d i f f e r between Jacquot Island and the mainland.  I a l s o discuss p o s s i b l e causes of  these d i f f e r e n c e s .  Adult S u r v i v a l Following a Population  Decline  There was no d i f f e r e n c e i n a d u l t s u r v i v a l between the mainland and Jacquot Island i n the summer of 1993. Therefore,  poorer adult s u r v i v a l during the summer on the  mainland compared t o Jacquot Island does not appear t o be responsible  f o r keeping the mainland hare population  a t low  s p r i n g d e n s i t i e s from 1993 t o 1994. Overwinter s u r v i v a l of hares on Jacquot I s l a n d was higher than on the mainland i n t h e 1993-1994 winter.  Overwinter  s u r v i v a l on Jacquot based oh trapping data was 83% (equivalent t o 98% per 30 days) and based on 7 r a d i o - c o l l a r e d hares was 71% (equivalent t o 96% per 30 days).  This i s  higher than the 12.6% (equivalent t o 77.2% per 30 days) s u r v i v a l seen on t h e mainland during t h i s p e r i o d  61  (based on  radio-collared hares). may  Therefore higher overwinter s u r v i v a l  be an important f a c t o r that allowed Jacquot I s l a n d t o  increase so d r a m a t i c a l l y . Factors  Influencing  Adult  Survival  Predation has been found t o be the main proximate cause o f death f o r both c y c l i c and n o n - c y c l i c snowshoe hare populations K e i t h 1985).  (Keith 1990, Boutin e t al.  1986, S i e v e r t and  S i m i l a r r e s u l t s were found i n t h i s study with  60% o f the m o r t a l i t i e s being a t t r i b u t e d t o p r e d a t i o n (Table 3). Food shortage, poor weather and d i s e a s e may i n c r e a s e t h e r i s k o f p r e d a t i o n f o r hares because these f a c t o r s tend t o cause hares t o become malnourished which reduces body c o n d i t i o n (Keith 1990).  L i t t l e e m p i r i c a l evidence i s  a v a i l a b l e , but S i e v e r t and K e i t h (1985) found t h a t hares with below average body c o n d i t i o n i n d i c e s s u f f e r e d higher predation r a t e s than hares i n good c o n d i t i o n .  In 1994  Jacquot I s l a n d hares had higher summer s u r v i v a l than the mainland and than Jacquot I s l a n d i n 1993.  In both these  cases t h e r e were no d i f f e r e n c e s i n the c o n d i t i o n i n d i c e s o f male snowshoe hares i n the s p r i n g i n d i c a t i n g t h a t these f a c t o r s do not provide a l i k e l y e x p l a n a t i o n f o r the lower s u r v i v a l rates seen. D i f f e r e n c e s i n predator numbers seem a more l i k e l y e x p l a n a t i o n o f the patterns o f adult s u r v i v a l , as there were d i f f e r e n c e s i n predator numbers between areas.  Adult  s u r v i v a l on Jacquot I s l a n d was higher i n 1994 than 1993 and,  62  although s l i g h t l y more avian predators than i n 1993, mammalian predator  were s i g h t e d i n 1994  s i g h t i n g s dropped t o zero.  There was no s i g n i f i c a n t d i f f e r e n c e i n a d u l t s u r v i v a l on Jacquot i s l a n d and the mainland i n 1993. predators  In general,  fewer  were sighted on Jacquot I s l a n d compared t o the  mainland during the summer of 1993, however the s i g h t i n g index f o r coyotes was s i m i l a r .  In the summer of 1994 a d u l t  s u r v i v a l was higher on Jacquot I s l a n d than the mainland and the s i g h t i n g index f o r a l l predators Island.  was lower on Jacquot  The main d i f f e r e n c e between 1993 and 1994 on Jacquot  I s l a n d was t h a t s i g h t i n g s of mammalian predators zero and s u r v i v a l increased.  dropped t o  Higher summer s u r v i v a l of hares  on Jacquot I s l a n d i n 1994 compared t o 1993, and on Jacquot I s l a n d compared t o the mainland i n 1994, was not a s s o c i a t e d with fewer predator  numbers i n general, but with the presence  of fewer mammalian  predators.  If mammalian predators  have the l a r g e s t impact on s u r v i v a l  rates of a d u l t hares, the majority of k i l l s i n 1993 should be due  t o coyotes.  In f a c t , the major m o r t a l i t y f a c t o r i n the  summer of 1993 was unknown predators l e f t a t k i l l s s i t e s i n summer.  due t o the l a c k of signs  R a d i o - c o l l a r i n g more hares i n  future s t u d i e s may help i n c r e a s e the number o f k i l l s f o r which the cause of death i s known. Other s t u d i e s have a l s o suggested t h a t mammalian  predators  have the most impact on hare population d e n s i t i e s and a d u l t survival.  A r c t i c hares (Lepus  arcticus)  t h a t were  introduced  onto i s l a n d s reached high d e n s i t i e s on 2 i s l a n d s where no  63  mammalian predators were present (Mercer e t al.  1981).  Angerbjorn (1986) found that a d u l t s u r v i v a l of a p o p u l a t i o n of mountain hares decreased on an i s l a n d i n Sweden when a fox remained on an i s l a n d i n the summer.  When a lynx remained on  Jacquot I s l a n d d u r i n g the summer of 1992 there was a s i g n i f i c a n t drop i n s u r v i v a l r a t e s on the p a r t of the i s l a n d where the animal concentrated i t s hunting e f f o r t s  (Zimmerling  1993).  J u v e n i l e S u r v i v a l on Jacquot  Island  Comparisons of e a r l y j u v e n i l e s u r v i v a l between years are important f o r determining i f the r e s u l t s seen are p a r t of a consistent pattern.  In 1991 Zimmerling  (1993) found t h a t  hares on t h e Jacquot I s l a n d south g r i d had s i g n i f i c a n t l y higher s u r v i v a l than those on the north g r i d f o r f i r s t and second l i t t e r s .  The main cause of m o r t a l i t y on the north  g r i d was coyote p r e d a t i o n while no deaths on the south g r i d were a t t r i b u t e d t o coyote p r e d a t i o n .  I f there had been no  coyote p r e d a t i o n on the north g r i d and a l l those j u v e n i l e s survived, s u r v i v a l on both g r i d s would have been s i m i l a r . This suggests t h a t coyote p r e d a t i o n was r e s p o n s i b l e f o r the d i f f e r e n c e s i n s u r v i v a l on the two g r i d s . Zimmerling  (1993) hypothesized t h a t higher s u r v i v a l on the  south g r i d was r e l a t e d t o dense cover a t 10 cm above the ground.  When coyotes are present, s u r v i v a l may d i f f e r  between g r i d s on Jacquot I s l a n d because cover d e n s i t y d i f f e r s between the two g r i d s .  An a l t e r n a t i v e t o the cover  hypothesis i s t h a t the coyote concentrated i t s hunting on the  64  north g r i d during 1991,  and t h a t d i f f e r e n c e s i n predator  pressure caused the d i f f e r e n c e s i n s u r v i v a l . hypotheses island.  These two  can be examined when coyotes are present on the  R a d i o - c o l l a r i n g the coyote(s) would allow us t o  determine where they concentrate t h e i r hunting e f f o r t s . examination of cover at s i t e s where hares were k i l l e d allow us t o determine predation r a t e s .  An  would  i f poor cover i s a s s o c i a t e d with higher  During 1994  no j u v e n i l e deaths were  a t t r i b u t e d t o coyote p r e d a t i o n and there was  no d i f f e r e n c e i n  e a r l y j u v e n i l e s u r v i v a l between the Jacquot I s l a n d g r i d s . Exposure was i n Zimmerling's  an important m o r t a l i t y f a c t o r f o r j u v e n i l e s (1993) study, but not i n t h i s study  i n d i c a t i n g t h a t i t i s not a r e g u l a r occurrence.  There were,  however, i n my study two instances of l i t t e r s being abandoned i n an open area where they may exposure and p r e d a t i o n .  have been more v u l n e r a b l e t o  I t i s p o s s i b l e t h a t l i t t e r s were  abandoned i n other s t u d i e s and t h a t the deaths were a t t r i b u t e d t o other f a c t o r s .  More i n t e n s i v e s t u d i e s  (monitoring the l e v e r e t s twice d a i l y f o r example) of e a r l y juvenile survival w i l l  help us t o determine  i f abandonment i s  a r e g u l a r occurrence.  J u v e n i l e S u r v i v a l on  Jacquot I s l a n d Compared w i t h  the  Mainland The p a t t e r n of s u r v i v a l of l i t t e r s d i f f e r s between Jacquot Island and the mainland.  On the mainland the second  litter  had lower s u r v i v a l than f i r s t and t h i r d l i t t e r s during the peak and the low phase ( t h i s study, O'Donoghue 1994) while on  65  Jacquot I s l a n d the f i r s t l i t t e r has had the lowest s u r v i v a l ( t h i s study and Zimmerling  1993).  O'Donoghue (1994)  hypothesized t h a t small mammal predators a c t i v e l y foraged f o r the newborn hares and t h a t the number of p o t e n t i a l predators of  l e v e r e t s during the second l i t t e r was g r e a t e r than f o r  f i r s t l i t t e r on the mainland because  independence  of j u v e n i l e  s q u i r r e l s corresponds t o the second l i t t e r of hares.  One  hypothesis f o r the d i f f e r e n t patterns o f s u r v i v a l seen on Jacquot I s l a n d and the mainland i s that lower d e n s i t i e s of small mammal predators and b e t t e r cover on Jacquot I s l a n d during second and t h i r d l i t t e r s r e s u l t i n higher s u r v i v a l f o r those l i t t e r s .  F i r s t l i t t e r s are u s u a l l y born j u s t as the  v e g e t a t i o n i s emerging  and cover may be reduced making them  more s u s c e p t i b l e t o p r e d a t i o n than are second and t h i r d litters. Trostel  (1986) examined recruitment, which encompasses  e a r l y j u v e n i l e s u r v i v a l , r e p r o d u c t i o n , and d i s p e r s a l ,  through  l i v e - t r a p p i n g , and found no d i f f e r e n c e s between Jacquot I s l a n d and the mainland from 1977-1984.  However, Zimmerling  (1993) d i r e c t l y examined e a r l y j u v e n i l e s u r v i v a l  (using  radio-telemetry) on Jacquot I s l a n d over one year and found that s u r v i v a l on t h e i s l a n d was higher than t h e mainland during the f i r s t year o f the d e c l i n e phase on the mainland. E a r l y j u v e n i l e s u r v i v a l during both my and Zimmerling's (1993) s t u d i e s was higher than that measured f o r t h e mainland population during the peak (O'Donoghue 1994).  During t h i s  study j u v e n i l e s u r v i v a l was s i m i l a r on Jacquot I s l a n d and the  66  mainland f o r f i r s t l i t t e r s of 1994.  However, s u r v i v a l was  higher f o r second and t h i r d l i t t e r s on Jacquot I s l a n d r e s u l t i n g i n o v e r a l l higher s u r v i v a l on Jacquot I s l a n d . Jacquot I s l a n d appears t o have c o n s i s t e n t l y higher e a r l y juvenile survival mainland  (during the f i r s t 30-days of l i f e ) than the  (Zimmerling 1993, t h i s s t u d y ) .  Although  mainland  data are l a c k i n g f o r 1993 i t appears that high e a r l y  juvenile  s u r v i v a l allowed Jacquot I s l a n d t o recover q u i c k l y a f t e r the population d e c l i n e .  The higher s u r v i v a l seen on Jacquot  I s l a n d may be due t o fewer small mammal predators and b e t t e r cover on Jacquot I s l a n d .  Long term monitoring of e a r l y  j u v e n i l e s u r v i v a l on Jacquot I s l a n d and t h e mainland should be done t o determine i f e a r l y j u v e n i l e s u r v i v a l i s c o n s i s t e n t l y higher than the mainland. of e a r l y j u v e n i l e s u r v i v a l w i l l  Experimental s t u d i e s  allow us t o determine i f  b e t t e r cover and fewer small mammal predators are r e s p o n s i b l e for  the higher s u r v i v a l seen on Jacquot I s l a n d . S u r v i v a l o f j u v e n i l e s from September 1993 t o May 1994  based on t r a p p i n g was 48% on Jacquot I s l a n d while on the mainland s u r v i v a l of j u v e n i l e s over the same p e r i o d was 11.3% based on t e l e m e t r y .  Trapping u s u a l l y underestimates  survival  because animals t h a t have d i s p e r s e d are counted as mortalities  (Boutin and Krebs 1986) so Jacquot I s l a n d may  have had even higher overwinter s u r v i v a l .  High overwinter  j u v e n i l e s u r v i v a l appears t o have c o n t r i b u t e d t o the 1993 population recovery on Jacquot I s l a n d ; however, overwinter s u r v i v a l o f j u v e n i l e s does not appear t o be c o n s i s t e n t l y high  67  on Jacquot I s l a n d .  Zimmerling  (1993) found overwinter  s u r v i v a l o f j u v e n i l e s (based on 11 r a d i o - c o l l a r e d  juveniles)  to be 36% during the winter of 1991-1992 when the p o p u l a t i o n was undergoing a d e c l i n e .  Overwinter s u r v i v a l should be  s t u d i e d on Jacquot I s l a n d u s i n g r a d i o - t e l e m e t r y t o determine how overwinter j u v e n i l e s u r v i v a l v a r i e s from year t o year. Using r a d i o - t e l e m e t r y t o study s u r v i v a l allows us t o d i f f e r e n t i a t e between m o r t a l i t y , emigration, and immigration and would a l l o w us t o determine i f d i s p e r s a l was an important f a c t o r i n f l u e n c i n g the p o p u l a t i o n dynamics o f Jacquot I s l a n d . Reproduction In t h i s s e c t i o n I d i s c u s s the impact of the l e n g t h of time a female was caged p r i o r t o p a r t u r i t i o n on r e p r o d u c t i v e data c o l l e c t e d on Jacquot I s l a n d .  I a l s o d i s c u s s how r e p r o d u c t i o n  d i f f e r e d between Jacquot I s l a n d and a c y c l i c p o p u l a t i o n and suggest reasons f o r the d i f f e r e n c e s found. The  Effect  o f M a t e r n i t y C a g e s on R e p r o d u c t i v e  Data  Females were kept i n maternity cages and s u p p l i e d with food p r i o r t o p a r t u r i t i o n .  I t i s possible that t h i s could  e i t h e r n e g a t i v e l y (increased s t r e s s ) o r p o s i t i v e l y ( a d d i t i o n a l food) a f f e c t the female and the young. to  I tried  l i m i t the impact of the cages by keeping the females i n  them f o r as short a p e r i o d as p o s s i b l e and by l i m i t i n g my contact with them t o once d a i l y .  For l i t t e r groups one and  two of 1994 the time a female spent i n a maternity cage p r i o r to p a r t u r i t i o n was s i g n i f i c a n t l y r e l a t e d t o l i t t e r  size;  however, l i t t e r s i z e c o u l d not i n c r e a s e d u r i n g the l a s t week  68  of  pregnancy.  I t h i n k the p o s i t i v e " e f f e c t " of the maternity  cages on l i t t e r s i z e was  a consequence  of  p u t t i n g the  females i n maternity cages at s i m i l a r weights, but d i f f e r e n t stages of pregnancy. Because l a r g e r l i t t e r s have a h e a v i e r t o t a l weight  (Figure 9a-c) i t would f o l l o w t h a t females with  l a r g e r l i t t e r s would themselves weigh more at the time of b i r t h than females with s m a l l e r l i t t e r s .  Since a l l females  were put i n maternity cages at s i m i l a r weights, the females with l a r g e r l i t t e r s would be put i n the cages at an e a r l i e r stage of pregnancy than the females with small l i t t e r s  and  would t h e r e f o r e remain i n maternity cages longer than females with small l i t t e r s . r a b b i t chow, was  E x t r a food, i n the form of  commercial  added t o hare g r i d s i n the Yukon and  O'Donoghue (1992) d i d not f i n d any d i f f e r e n c e i n the  litter  s i z e s of hares on these g r i d s compared t o c o n t r o l areas. For  the f i r s t l i t t e r group i n my study a s i g n i f i c a n t  e f f e c t of days caged on average l e v e r e t weight per l i t t e r  was  found. I t i s c o n c e i v a b l e that newborn weights were n e g a t i v e l y a f f e c t e d by the time spent i n the maternity cage; however, t h i s can more e a s i l y be explained by the r e l a t i o n s h i p between l i t t e r s i z e and newborn weights f o r the f i r s t l i t t e r 8a).  In the second l i t t e r where there was no  (Figure  significant  r e l a t i o n s h i p between l i t t e r s i z e and weight, the l e n g t h of time spent i n maternity cages was r e l a t e d t o l i t t e r only.  size  I t h i n k t h a t the apparent e f f e c t of maternity cages on  average l e v e r e t weight per l i t t e r i s a consequence  69  of the  negative r e l a t i o n s h i p between average l e v e r e t weight l i t t e r s i z e found i n the f i r s t  and  litter.  I do not b e l i e v e that the time a female spent i n the cage p r i o r t o p a r t u r i t i o n a f f e c t e d reproduction on Jacquot I s l a n d . The r e s u l t s t h a t were obtained can more e a s i l y be e x p l a i n e d by the f a c t t h a t females with l a r g e r l i t t e r s were put i n cages at an e a r l i e r stage of pregnancy.  The  apparent  negative e f f e c t of time spent i n a cage p r i o r t o p a r t u r i t i o n on the average l e v e r e t weight per l i t t e r seen i n the l i t t e r group of 1994 was  first  most l i k e l y a r e s u l t of the negative  r e l a t i o n s h i p between l i t t e r s i z e and l i t t e r weights.  A  s i g n i f i c a n t e f f e c t of time spent i n maternity cage on  litter  s i z e and l i t t e r weight has not been found i n other s t u d i e s using t h i s same technique (O'Donoghue 1991,  Reproduction Following a Population  Zimmerling  1993).  Decline  U n f o r t u n a t e l y no r e p r o d u c t i v e data were c o l l e c t e d on the mainland d u r i n g 1993  so i t i s impossible t o d i r e c t l y  determine i f d i f f e r e n c e s i n reproduction or s u r v i v a l are r e s p o n s i b l e f o r the d i f f e r e n t dynamics seen on Jacquot I s l a n d and the mainland.  I t i s p o s s i b l e , however, t o compare the  reproductive output found on Jacquot I s l a n d with the p a t t e r n that has been seen i n other c y c l i c p o p u l a t i o n s .  The  reproductive output of a c y c l i c p o p u l a t i o n i n A l b e r t a  was  monitored over 15 years and encompassed two p o p u l a t i o n lows (Carey and K e i t h 1979; reproductive output was to  F i g u r e 10). During t h i s study at i t s lowest l e v e l two summers p r i o r  the lowest p o p u l a t i o n d e n s i t y .  70  The year before the  population low reproductive output i t s lowest  increased 1.5 f o l d from  l e v e l s but the population continued  to decline.  This one year delay before the p o p u l a t i o n began t o recover was not evident on Jacquot I s l a n d .  Reproductive  output on  Jacquot I s l a n d increased 2.3 f o l d the summer a f t e r reproduction was a t the lowest density increased.  l e v e l and the p o p u l a t i o n  Higher reproductive output may have  played a p a r t i n a l l o w i n g the Jacquot I s l a n d hare p o p u l a t i o n t o i n c r e a s e while the mainland remained a t low d e n s i t i e s over the summer of 1993; however, i t i s not the only Carey and Keith's  factor.  (1979) population had s u f f i c i e n t l y  high  reproduction t o i n c r e a s e i n the year p r i o r t o the p o p u l a t i o n low.  I estimated  the expected f a l l p o p u l a t i o n d e n s i t y (EFPD)  f o r the years p r i o r t o the population lows of the A l b e r t a p o p u l a t i o n , t a k i n g only reproduction and a d u l t s u r v i v a l  into  account. EFPD=(RN *SPD/2)+(SPD*SAS) Where RN i s r e a l i z e d n a t a l i t y (number of l e v e r e t s produced per female a l i v e a t the s t a r t of the breeding  season),  SPD i s  s p r i n g p o p u l a t i o n d e n s i t y and SAS i s summer a d u l t s u r v i v a l . Based on t h i s c a l c u l a t i o n I p r e d i c t e d a 3 t o 4 f o l d increase i n p o p u l a t i o n d e n s i t y over the summer. j u v e n i l e s u r v i v a l o r overwinter important 1  Therefore  a d u l t s u r v i v a l must be  f a c t o r s i n causing the c y c l i c p o p u l a t i o n t o remain  low because r e p r o d u c t i v e output population t o i n c r e a s e .  71  i s high enough t o allow the  The  reproductive output of c y c l i c populations  appears t o  be s u f f i c i e n t l y high t o allow the p o p u l a t i o n t o i n c r e a s e the summer before the population low;  however, the  population  does not i n c r e a s e , i n d i c a t i n g t h a t other f a c t o r s , l i k e a d u l t or j u v e n i l e s u r v i v a l , must be keeping the p o p u l a t i o n at numbers.  Nonetheless, the reproductive output  I s l a n d was  at l e a s t 1.5  times higher than the  low  on Jacquot reproductive  output of a c y c l i c population i n A l b e r t a the year before  the  low i n d i c a t i n g t h a t reproduction of c y c l i c populations may some way Timing  in  be r e s t r i c t e d during t h i s p e r i o d . of  Breeding  The t i m i n g of breeding of the i s l a n d p o p u l a t i o n i n and of both the i s l a n d and mainland populations  i n 1994  advanced by almost two weeks compared t o a 1991  study on  mainland and a 1992 Zimmerling 1993).  1993  study on Jacquot Island (O'Donoghue This allowed  was the 1992,  f o r the production of a  f o u r t h l i t t e r on the mainland which has not been recorded during previous s t u d i e s i n the Kluane area. evidence  t h a t there was  There i s a l s o  a f o u r t h l i t t e r on the  however, no d e t a i l e d study of f o u r t h l i t t e r was  island, completed i n  either location. Total  Reproductive  Output  The t o t a l reproductive output  (number of l e v e r e t s produced  per a d u l t female s u r v i v i n g the breeding  season) on Jacquot  Island v a r i e d 2.5  (Zimmerling  16.8  i n 1994.  f o l d from 6.8  i n 1992  This i s s i m i l a r to the 2.4  reproductive output  1993)  fold variation in  seen i n a c y c l i c p o p u l a t i o n i n A l b e r t a  72  to  (Carey and K e i t h 1979).  I t i s important  t o note t h a t  although n o n - c y c l i c populations do not show p r e d i c t a b l e population f l u c t u a t i o n s they do go through periods of increase and d e c l i n e .  The  2.5  fold variation i n total  r e p r o d u c t i v e output of hares on Jacquot I s l a n d was during a p o p u l a t i o n i n c r e a s e .  recorded  No other s t u d i e s of n o n - c y c l i c  populations have recorded t o t a l reproductive output during a population i n c r e a s e and the t o t a l reproductive output always been constant K e i t h 1983).  (Dolbeer and C l a r k 1975,  has  Kuvlesky  and  More long term s t u d i e s of reproduction of  non-  c y c l i c populations w i l l allow us t o determine i f reproduction on Jacquot I s l a n d i s s i m i l a r t o other n o n - c y c l i c p o p u l a t i o n s . Litter  Size  and  Neonate Weights  Through l i v e t r a p p i n g , T r o s t e l (1986) found t h a t j u v e n i l e recruitment, which encompasses reproduction, emigration,  and e a r l y j u v e n i l e s u r v i v a l , was  immigration, s i m i l a r between  the n o n - c y c l i c Jacquot Island hare p o p u l a t i o n and the mainland p o p u l a t i o n between 1977  and  1984.  cyclic  In a more  d e t a i l e d study Zimmerling (1993) compared r e p r o d u c t i o n i n one year on Jacquot I s l a n d with the mainland and differences.  found no  During t h i s study, however, both l i t t e r s i z e s  and newborn weights were l a r g e r on Jacquot I s l a n d than on mainland i n 1994,  i n d i c a t i n g t h a t females were able t o  produce more o f f s p r i n g . Large l i t t e r s and heavier neonate weights have been recorded  f o r other species l i v i n g on i s l a n d s .  Ebenhard  (1990) found t h a t an i n s u l a r p o p u l a t i o n of f i e l d v o l e s  73  the  (Microtus  agrestis)  had l a r g e r l i t t e r and neonate masses than  mainland populations,  however the body masses of the a d u l t  i s l a n d v o l e s were a l s o g r e a t e r .  No evidence of d i f f e r e n c e s  i n the s i z e of hares on Jacquot I s l a n d and the mainland were found so i t appears that Jacquot I s l a n d hares were able t o a l l o c a t e more resources  f o r reproduction  than mainland hares  i n 1994. A p o s s i b l e explanation  f o r the l a r g e r l i t t e r s i z e and  newborn weights found on Jacquot I s l a n d was t h a t hares on the I s l a n d were i n b e t t e r p h y s i c a l c o n d i t i o n than mainland hares. Boonstra and S i n g l e t o n  (1993) concluded, by examining the  s t r e s s response of male snowshoe hares, t h a t c o n t r o l hares i n a d e c l i n i n g population were i n poor c o n d i t i o n compared t o w e l l - f e d hares.  However, a comparison of c o n d i t i o n i n d i c e s  of male snowshoe hares trapped i n the s p r i n g on the i s l a n d and the mainland i n d i c a t e d that there was 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 t h e i r c o n d i t i o n (Table 12). Another p o s s i b l e explanation predators  c o u l d be the l a c k of  on Jacquot I s l a n d compared with the mainland.  Ylonen (1989) showed that reproduction (Clethrionomys  glareolus)  exposed t o weasel scent.  i n bank v o l e s  could be suppressed when they were A s i g h t i n g index of predator  numbers i n d i c a t e d that there were fewer predators  on the  i s l a n d and adult s u r v i v a l rates on the i s l a n d were a l s o higher.  I t i s p o s s i b l e that reproduction  on the mainland was  lower than the i s l a n d because there were more predators  74  on  the mainland.  The p o s s i b l e impact of predators on snowshoe  hare reproduction  should be examined  experimentally.  CONCLUSION Jacquot I s l a n d and the mainland both underwent d e c l i n e s reaching  population  s i m i l a r low l e v e l s i n the f a l l of  (Zimmerling 1993).  During my study the mainland  1992  population  remained at low d e n s i t i e s from the s p r i n g of 1993 t o the s p r i n g of 1994 while Jacquot Island increased  3.5  f o l d over  the same p e r i o d . Three main hypotheses were put forward t o e x p l a i n the d i f f e r e n t population Hypothesis  1.  trends seen during t h i s Differences  period.  i n reproduction  d i f f e r e n c e s seen i n the population  e x p l a i n the  dynamics of snowshoe  hares on Jacquot Island and the mainland. Hypothesis  2.  Differences  i n m o r t a l i t y e x p l a i n the  d i f f e r e n c e s seen i n the population  dynamics of snowshoe  hares on Jacquot Island and the mainland Hypothesis 2a.  Only j u v e n i l e m o r t a l i t y d i f f e r s between  the i s l a n d and the mainland. Hypothesis 2b.  Only a d u l t m o r t a l i t y d i f f e r s between  the i s l a n d and the mainland. Hypothesis 2c.  Both a d u l t and j u v e n i l e m o r t a l i t y  d i f f e r between the i s l a n d and the mainland. Hypothesis  3.  Differences  i n both reproduction  and  m o r t a l i t y e x p l a i n the d i f f e r e n c e s seen i n the population  dynamics of snowshoe hares on Jacquot  and the mainland. 75  Island  My r e s u l t s support hypothesis 3 and Table 13 o u t l i n e s the p r e d i c t i o n s f o r each hypothesis and the r e s u l t s obtained i n t h i s study. Proximate Population  Factors Influencing  the Jacquot  Island  Increase  During the summer of 1993  28-day s u r v i v a l r a t e s f o r a d u l t  hares on Jacquot I s l a n d and the mainland were s i m i l a r . However, overwinter s u r v i v a l of a d u l t s , from September t o May,  was  s i x times higher on Jacquot I s l a n d than the  mainland.  J u v e n i l e s u r v i v a l u n t i l weaning was  on the mainland i n 1993 Jacquot I s l a n d .  not monitored  and only 25 l e v e r e t s were marked on  None of these 25 l e v e r e t s were known t o have  died, which suggests that e a r l y j u v e n i l e s u r v i v a l was high on Jacquot I s l a n d i n 1993.  Overwinter s u r v i v a l of  j u v e n i l e s , from September 1993 t o May Jacquot I s l a n d than the mainland. hypotheses  very  1994, was  higher on  These r e s u l t s e l i m i n a t e  2a and 2b s i n c e both adult and j u v e n i l e m o r t a l i t y  were lower on Jacquot I s l a n d than the mainland  (see Table  13). Reproduction was 1993.  not monitored on the mainland d u r i n g  Comparisons with r e p r o d u c t i v e data from a d i f f e r e n t  c y c l i c p o p u l a t i o n of hares (Carey and K e i t h 1979) that r e p r o d u c t i v e output was  indicate  higher f o r Jacquot I s l a n d than  f o r a c y c l i c p o p u l a t i o n d u r i n g the low phase of the hare cycle.  Reproduction, t h e r e f o r e , may  be an important f a c t o r  i n a l l o w i n g Jacquot I s l a n d t o i n c r e a s e while c y c l i c populations remain at low d e n s i t i e s .  76  Since r e p r o d u c t i o n on  CO  0>  ZD CO  or  CD  CD  O  O  CD  <D  O  O  CD  CD  o  O  TJ C  co c o  4->  o  TJ  O CD  ro|  o E  O)  TJ  ±i 75  21 -Q  C  _ 0) CM .2,  CD  E CO CO  c o CD C\J  E  CD  E ro CO  E ro 00  CD  E ro  CD  o  E ro to  CD  E ro  CD  CD  O  M o  ro t CD o >3 CM  CO LU CO  hO  4^  i=  CO  •r t -c? g CM  E  CD  co  CD  g o  •4-" 3 TJ  O  k — Q. CD  D)  D_ >-  co  CD >  CC  o ho <  •3 2  s  Q.  Q^  2  O  ro t o E c: CD > 3  77  E ro co  CO  t o E  3 TJ CO  Jacquot I s l a n d was higher than f o r a c y c l i c p o p u l a t i o n during the low phase of the p o p u l a t i o n c y c l e , hypotheses 2a-c, t h a t lower m o r t a l i t y on i t s own allowed Jacquot I s l a n d t o i n c r e a s e while the mainland was a t low d e n s i t i e s , were t e n t a t i v e l y rejected  (see Table 13).  Reproductive  data should be  c o l l e c t e d on both Jacquot I s l a n d and the mainland during the population low t o be able t o t e s t these hypotheses. These r e s u l t s i n d i c a t e t h a t both higher output  reproductive  and lower m o r t a l i t y played a r o l e i n a l l o w i n g the  Jacquot I s l a n d hare population t o i n c r e a s e while t h e mainland remained a t low d e n s i t i e s (hypotheses 3 ) . While reproduction on Jacquot I s l a n d appears t o be higher than i n c y c l i c populations during the low, the reproductive output of c y c l i c populations  i s s u f f i c i e n t l y high t h a t t h e p o p u l a t i o n c o u l d  increase d u r i n g t h i s p e r i o d .  Despite t h i s , mainland  populations, remained a t low d e n s i t i e s suggesting t h a t poor s u r v i v a l must a l s o be a f a c t o r keeping the mainland population a t low d e n s i t i e s during 1994. Four components of s u r v i v a l were considered: e a r l y juvenile survival  (to 30 days), summer a d u l t s u r v i v a l , and  overwinter  a d u l t and j u v e n i l e s u r v i v a l .  On Jacquot I s l a n d  overwinter  s u r v i v a l of j u v e n i l e s and adults and e a r l y  j u v e n i l e s u r v i v a l was higher than the mainland.  In t h i s  study a d u l t s u r v i v a l over the summer was not d i f f e r e n t between Jacquot I s l a n d and the mainland i n d i c a t i n g t h a t i t was not a f a c t o r i n the Jacquot I s l a n d p o p u l a t i o n  78  increase  between 1993 and 1994 and that i t was not i n v o l v e d i n keeping mainland d e n s i t i e s low. Higher r e p r o d u c t i v e output, higher e a r l y  juvenile  s u r v i v a l , and higher overwinter a d u l t and j u v e n i l e s u r v i v a l on Jacquot I s l a n d are the proximate f a c t o r s t h a t allowed the Jacquot I s l a n d p o p u l a t i o n t o i n c r e a s e while t h e mainland remained a t low d e n s i t i e s from 1993 t o 1994.  The u l t i m a t e  causes o f t h e d i f f e r e n c e s observed i n the two areas are harder t o determine.  Various hypotheses  have been proposed  to e x p l a i n the observed d i f f e r e n c e s i n s u r v i v a l and reproduction between the mainland and Jacquot I s l a n d . Ultimate  Causes o f Higher  Zimmerling  Survival  on J a c q u o t  Island  (1993) hypothesized that fewer s m a l l mammal  predators and more dense cover a t 10 cm above the ground were r e s p o n s i b l e f o r the higher e a r l y j u v e n i l e s u r v i v a l found on Jacquot I s l a n d i n 1991.  The only other year i n which  mainland and Jacquot I s l a n d data were c o l l e c t e d c o n c u r r e n t l y was  1994 and s u r v i v a l on Jacquot I s l a n d was higher i n t h i s  year a l s o .  During t h i s study, as i n Zimmerling's  (1993)  study, higher j u v e n i l e s u r v i v a l on Jacquot I s l a n d c o i n c i d e d with lower numbers of small mammal predators ( s q u i r r e l s ) . The importance of cover as p r o t e c t i o n a g a i n s t p r e d a t i o n c o u l d not be assessed i n 1994 s i n c e only 10 l e v e r e t s were depredated.  J u v e n i l e s u r v i v a l may be c o n s i s t e n t l y higher on  Jacquot I s l a n d than the mainland; however, we need t o o b t a i n a d d i t i o n a l data where j u v e n i l e s u r v i v a l i s c o l l e c t e d on Jacquot I s l a n d and the mainland d u r i n g the same y e a r s .  79  Experimental and o b s e r v a t i o n a l studies w i l l allow us t o determine i f d i f f e r e n c e s i n predator numbers and cover c o u l d account f o r the d i f f e r e n t s u r v i v a l r a t e s and  different  p a t t e r n of s u r v i v a l of the l i t t e r groups seen on Jacquot I s l a n d and the mainland. Overwinter s u r v i v a l of both j u v e n i l e and a d u l t hares  was  higher on Jacquot I s l a n d than on the mainland i n 1993-1994. There have been no d e t a i l e d s t u d i e s comparing overwinter s u r v i v a l on the two areas so i t i s not known i f overwinter s u r v i v a l of a d u l t and j u v e n i l e s i s c o n s i s t e n t l y higher on Jacquot I s l a n d .  In the s p r i n g of 1994 t h e r e were no  d i f f e r e n c e s i n c o n d i t i o n between hares i n the two areas i n d i c a t i n g t h a t i t i s not poor c o n d i t i o n of mainland that caused them t o have higher m o r t a l i t y r a t e s .  hares  One  hypothesis t h a t c o u l d e x p l a i n the d i f f e r e n t s u r v i v a l r a t e s i s d i f f e r e n c e s i n predator numbers a f f e c t i n g the populations.  two  A d e t a i l e d r a d i o - t e l e m e t r y study of overwinter  s u r v i v a l on Jacquot I s l a n d and the mainland would allow us t o determine i f s u r v i v a l i s c o n s i s t e n t l y higher on Jacquot I s l a n d and comparisons numbers may  of food a v a i l a b i l i t y and predator  allow f o r the determination of the u l t i m a t e  causes of any d i f f e r e n c e s found. Summer a d u l t s u r v i v a l d i d not d i f f e r between Jacquot Island and the mainland i n 1993, the mainland i n 1994.  Zimmerling  on Jacquot I s l a n d south g r i d was i n 1992.  however, i t was  (1993) found t h a t s u r v i v a l lower than on the mainland  T h i s study concurs with Zimmerling's  80  higher than  hypothesis  that summer a d u l t s u r v i v a l v a r i e s i n a s t o c h a s t i c manner depending on predator numbers.  On the mainland p r e d a t i o n  follows a p r e d i c t a b l e delayed d e n s i t y dependent p a t t e r n (Trostel Ultimate  1987). Causes o f Higher  Reproduction  on J a c q u o t  Island Reproduction was s t u d i e d c o n c u r r e n t l y on Jacquot I s l a n d and the mainland i n 1991 (Zimmerling 1993) and no s i g n i f i c a n t d i f f e r e n c e s were found.  However, i n 1994 Jacquot I s l a n d  hares had higher r e p r o d u c t i v e output than the mainland. C o n d i t i o n i n d i c e s were not d i f f e r e n t between Jacquot I s l a n d and the mainland, and as a r e s u l t lower r e p r o d u c t i o n on the mainland does not appear t o be a r e s u l t of poor c o n d i t i o n . There were, however, l a r g e d i f f e r e n c e s i n predator numbers and the i n f l u e n c e of predators on snowshoe hare r e p r o d u c t i o n should be examined e x p e r i m e n t a l l y . Summary Higher r e p r o d u c t i o n , higher e a r l y j u v e n i l e s u r v i v a l , and higher overwinter adult and j u v e n i l e s u r v i v a l were a l l key proximate f a c t o r s a l l o w i n g the Jacquot I s l a n d hare p o p u l a t i o n t o i n c r e a s e while the mainland p o p u l a t i o n remained a t low d e n s i t i e s from the s p r i n g of 1993 t o the s p r i n g o f 1994. These r e s u l t s support hypothesis 3, t h a t a combination of higher r e p r o d u c t i v e output and lower m o r t a l i t y accounted f o r the d i f f e r e n t dynamics seen on Jacquot I s l a n d compared t o the mainland.  More r e s e a r c h i s r e q u i r e d t o determine the  u l t i m a t e causes o f these d i f f e r e n c e s .  81  This study and e a r l i e r  s t u d i e s (Zimmerling 1993, T r o s t e l 1986)  have found some  evidence t o suggest t h a t d i f f e r e n c e s i n predator numbers and h a b i t a t are important areas r e q u i r i n g f u t u r e work. One of the l i m i t a t i o n s of t h i s study i s the l a c k of replication.  Only one set of c y c l i c and n o n - c y c l i c  populations was  compared i n t h i s study and consequently the  conclusions are l i m i t e d t o Jacquot I s l a n d and the mainland. 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