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Spacing behavior of snowshoe hares in relation to their population dynamics Boutin, Stanley A. 1979

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SPACING BEHAVIOR OF SNOBSHOE HARES IN RELATION TO THEIR POPULATION DYNAMICS by STANLEY A..BOUTIN B . S c . ( H o n s . ) , The U n i v e r s i t y o f A l b e r t a , 1977 A THESIS IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GSADUATE STUDIES (Department o f Z o o l o g y ) We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA December 1979 tanley A. Boutin, 1979 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date flg<. /( I V<7 ABSTRACT The importance of spacing behavior on snowshoe hare population dynamics was studied in the Kluane Lake, Yukon area from May 1978 to July 1979. Two study s i t e s , each consisting of a 9.29 ha live-trapping g r i d , were used to capture and tag animals. Numbers were increasing over the study with May breeding densities going from 8 in 1978 to 20 i n 1979. The increase was a re s u l t of higher than average (12.25 young caught per female) natality rates. Yearly juvenile and adult s u r v i v a l rates were equal at 20JL A t o t a l of 116 hares were equipped with radio-transmitters during the study. These were monitored to determine home range locations and i n d i v i d u a l movements. Home ranges overlapped by at leas t 30% between and within sexes throughout the year. Home ranges averaged larger for males (4-8 ha) than females (3-5 ha). During periods of b i r t h , females contracted the size of t h e i r home range but not s i g n i f i c a n t l y . 14 radio-tagged in d i v i d u a l s dispersed during the study. They moved an average of 1045 m and were from a l l age and sex classes with the exception of adult males. To determine the importance of spacing behavior on breeding females' home ranges and movements I removed a small group of ind i v i d u a l s from a much larger group of radio-tagged animals. The i n i t i a l removal was done 10 days before the. bi r t h of the f i r s t l i t t e r s and was then repeated 10 days before birth of the second l i t t e r s . Home ranges were monitored before and after each removal and compared to a control area. Females did not increase t h e i r use of the removal area nor was i t colonized by i n d i v i d u a l s from beyond the ring of radio-tagged animals.,This suggests that breeding female densities were not limited by spacing behavior. Females did s h i f t use of th e i r home range after the removal by spending up to 30% more time on the removal side of t h e i r range. This suggests that females use th e i r range in a manner that avoids interaction. Adult females were removed from one of the study areas during the la t e breeding season to assess t h e i r influence on juvenile movements and survival. There were no s i g n i f i c a n t differences in these aspects between the manipulated area and a control., However, telemetry showed that juvenile and adult female home ranges overlapped l i t t l e on the control area during September. The movements to create t h i s s i t u a t i o n were done by juveniles at a time before they could be trapped or radio-tagged. This suggests that some juveniles may leave th e i r parents' home ranges at a time prior to which i s detectable by conventional trapping and telemetry. The need f o r further inve s t i g a t i o n i n t h i s area i s stressed. iv TABLE OF CONTENTS ABSTRACT - - i i TABLE OF CONTENTS . . . . . . i v LIST OF FIGURES ............................................... v i LIST OF TABLES ix ACKNOWLEDGEMENTS , .X 1. INTRODUCTION ................................................ 1 2. STUDY AREA .....3 2.1 S i l v e r Creek Control .....6 2.2 Telemetry 7 3. MATERIALS AND METHODS 8 3.1. Trapping..........................................8 3.2. Telemetry., 9 4. DEMOGRAPHY 1 5 4.1. Results..........................................16 4.1-1. Trappability 16 4.1-2. Changes in Numbers....................... 18 4.1-3. I n i t i a t i o n of the Breeding Season........ 18 4.1-4. Number of Young 24 4.1-5. Survival. ................................ 27 4.1- 6. Juvenile Survival........................ 34 4.2 Discussion. ...............40 4.2- 1. Reproduction. ................44 4.2-2. Changes i n Numbers 45 4.2-3. Survival 47 5. HOME RANGE SIZE AND SPATIAL ARRANGEMENT 48 5.1. Methods. 48 V 5.2. Results ... 56 5.2-1. Home Range Size.......................... 56 5.2-2. Percentage Overlap....................... 61 5. 2-3. Dispersal 68 5.3. Discussion. ..7^ 6. FEMALE SPACING BEHAVIOR .................................... 83 6.1. Methods 85 6.2. Results 86 6.2-1. Removal One..............................86 6.2-1-1. Use of the Removal Area.... 86 6.2-1-2. Home Range Use..,,....., 93 6.2-1-3. Number of Immigrants............ 95 6.2-2. Results of the Second Removal............ 97 6.3. Discussion. .....103 7. EFFECT OF ADULT FEMALES ON JUVENILE MOVEMENTS AND SURVIVAL 111 7.1. Methods.. 112 7.2. Results 113 7 . 2 - 1 S u r v i v a l and Dispersal.................. 113 7.2-2. Changes i n Home Range................... 113 7.3. Discussion. ..............................127 8. SPACING BEHAVIOR AND SNOWSHOE HARE POPULATION DYNAMICS ...,130 LITERATURE CITED ...................135 LIST OF FIGORES Figure 1. Location of study areas............................... 4 Figure 2. Changes in error polygon length produced by the telemetry system. ............................11 Figure 3. Minimum number a l i v e (M.N.A.) estimates f o r S.C.C.and Telemetry during the study..................... 19 Figure 4. J o l l y population estimates for S.C.C. and Telemetry during the study....................... 21 Figure 5. Number of young trapped in 1978 on S.C.C. and Telemetry.............................................25 Figure 6. Monthly survival rates determined by trapping on 1050, a grid where no animals were radio-tagged, and S.C.C. and Telemetry, grids where a large portion of animals were radio-tagged................................. 30 Figure 7. Comparison of monthly survival rates as determined by trapping and telemetry (two methods)................... 32 Figure 8. Comparison of telemetry monthly survival rates on S.C.C. and Telemetry................................... 35 Figure 9..Comparison of monthly s u r v i v a l rates on S.C.C. and Telemetry as determined by trapping r e s u l t s . . . . . . . . . . . . . . . 37 Figure 10. Method used to determine the e f f e c t of telemetry system error on estimated home range s i z e . . . . . . . . . . . . . . . . . 50 Figure 11. Relationship between error polygon length and overestimation of home range s i z e . . . . . . . . . . . . . . . . . . . . . . . . . 53 Figure 12. Mean monthly home range sizes of radio-tagged hares in 1978....... 57 Figure 13. 1979 mean monthly home range sizes of radio-tagged v i i hares... 59 Figure 14. Mean heme range sizes of females showing smaller range sizes during b i r t h vs. i n t e r b i r t h periods........... 62 Figure 15. Female 90% home ranges on S.C.C. showing extensive overlap during the breeding season.............. 64 Figure 16. % overlap of female home ranges during b i r t h vs. i n t e r b i r t h periods... 66 Figure 17. 90% heme ranges of males on S.C.C. showing high overlap during the breeding season............ .......69 Figure 18. 90% home ranges of 3 males and 5 females on S.C.C. showing high overlap between and within sexes......71 Figure 19. 90% home ranges of males and females on the study areas during November 1978................ 73 Figure 20. Relative locations of female home ranges on Telemetry before the f i r s t removal........................ 87 Figure 21. Relative locations of female home ranges before and aft e r the f i r s t removal................. ........91 Figure 22. Relative locations of female home ranges on Telemetry prior to the second removal..................... 98 Figure 23. Relative locations of female home ranges before and after the secend removal............................. 101 Figure 24. Home ranges of juvenile snowshoe hares on Telemetry showing no change i n location before vs. after the removal of adult females........ .....116 Figure 25. Home ranges of juvenile hares on S.C.C, showing no change i n location before vs. after the removal of adult females en Telemetry ....................118 v i i i Figure 26. Relative locations of 5 adult and 5 juvenile home ranges on S.C.C. .............................121 Figure 27. Relative locations of 4 adult and 6 juvenile home ranges on Telemetry.................................... 123 Figure 28. Home ranges of 5 adult and 10 juvenile hares on S.C.C. showing low overlap throughout late August and September. 125 LIST OF TABLES Table 1. Trappability of animals on Telemetry and S.C.C-....... 17 Table 2. Survival rates of juveniles from f i r s t trapping to May 1..................... 39 Table 3. Causes of death of radio-tagged hares................. 41 Table 4. Status, g r i d , timing of movement, distance moved, and f i n a l fate of hares dispersing during the study...................................... 75 Table 5. Changes i n the proportion of locations found i n the removal area following the f i r s t removal....... 89 Table 6. Home range use by Telemetry females following the f i r s t removal 94 Table 7. Home range use by S.C.C. females after the f i r s t removal.........................................96 Table 8. Changes in the proportion of locations found i n the removal area after the second removal....... 100 Table 9. Home range use by Telemetry females following the second removal................................... 104 Table 10. Heme range use by S.C.C. females following the second removal.......... ...................105 Table 11. Fates of radio-tagged juveniles caught on S.C.C. and Telemetry at least once before removal of adult females.......... ............................. 114 Table 12. Number of untagged animals captured on each grid after removal of adult females on Telemetry.... 115 X ACKNOWLEDGEMENTS I would sincerely l i k e to thank my supervisor, Dr. A. B. E. S i n c l a i r * for his advice and help throughout the study.. His cr i t i c i s m s along with those of Dr. Charles J. Krebs helped to improve t h i s thesis. I would l i k e to thank Dr. Krebs and Dr. J . N. M. Smith for h e l p f u l suggestions throughout the fieldwork..In addition I would l i k e to thank a l l of the above for t h e i r continuous and generous f i n a n c i a l support. Thanks are due to Kathy Hanson, Vivian Haist, Steve M i l l a r , and es p e c i a l l y Scott Gilbert f o r c o l l e c t i n g portions of the data. Vivian Haist taught me the fundamentals of computer programming and Alton Harestad provided the home range programs used in the study. Scott G i l b e r t and Ron Graf provided h e l p f u l comments on the th e s i s . I would esp e c i a l l y l i k e to thank Andy Williams for l o g i s t i c a l support during the f i e l d work. I received support from a OBC teaching assistantship and an NSERC postgraduate scholarship. F i n a l l y , I wish to thank my wife, Louise, who contributed unselfishly to every aspect of the study. 1 Is. INTRODUCTION The snowshoe hare ( Lepus americanus ) i s known to exhibit regular 10 year population cycles throughout much of i t s range ( Keith 1963 ). Although t h i s phenomenon has attracted widespread i n t e r e s t , causal mechanisms are s t i l l unknown. Work to date has been primarily concerned with the r e l a t i o n of hare demographic changes to food supply and predation ( Keith 1974; Keith and Windberg 1978 ). Few studies have examined the behavior of snowshoe hares, which i s p a r t i c u l a r l y i n t e r e s t i n g because behavior i s rapidly being recognized as an important component of the population dynamics of a number of species ( Krebs and Myers 1974; Watson and Moss 1970 ).. There are two major hypotheses which attempt to explain the snowshoe hare cycle. The f i r s t , formulated by Chitty ( 1960 ), attempts to explain a l l small mammal cycles and contends that "... a l l species are capable of l i m i t i n g t h e i r own population densities without either destroying the food resources to which they are adapted, or depending on enemies or c l i m a t i c accidents to prevent them from doing so." In contrast, Keith ( 1974 ) states that snowshoe hares are "...incapable of s e l f -regulation below densities determined by available food supplies." Chitty f e e l s that aggressive spacing behavior acts to l i m i t numbers below that dictated by food supplies whereas Keith ( 1974 ) feels behavior i s unimportant and hare numbers are determined d i r e c t l y by a combination of food supply and predation. Examining the e f f e c t of spacing behavior on hare movements, s u r v i v a l , and reproduction then, should help to 2 decide between these two hypotheses. In t h i s study I have examined snowshoe hare movements and spacing behavior, p a r t i c u l a r l y that of juveniles and adult females. I chose juveniles because Keith and Windberg ( 1978 ) found that changes i n t h e i r s u r v i v a l rates were most i n f l u e n t i a l i n ov e r a l l changes in hare numbers. Females were chosen because I f e l t they would be most i n f l u e n t i a l i n determining o v e r a l l reproductive rates which were also found to change with the cycle ( Cary and Keith 1979 ). I was concerned with answering the following questions: 1. What i s the s p a t i a l arrangement of hare home ranges and what does t h i s arrangement suggest about snowshoe hare s o c i a l organization? 2 . Is the presence of adjacent females important i n determining the use and location of a female's home range? 3. Do adult females influence juvenile movements and survival? Answers to the f i r s t question w i l l give some.indication as to how hares divide up resources such as food and space. The second question i s aimed at determining whether female spacing behavior i s i n f l u e n t i a l enough to prevent some individuals from breeding. The f i n a l guestion i s an attempt to determine i f spacing behavior can affect juvenile s u r v i v a l and thus be important i n hare population dynamics. To answer these questions I monitored hare populations and carried out experiments from May 1978 to July 1979. The demography of these populations and res u l t s of the experiments w i l l be provided. F i n a l l y , answers to the above questions w i l l be discussed in the context of hare population dynamics. 3 2. STUDY AREA The two main study areas, S i l v e r Creek Control ( S.C.C..) and Telemetry, were located near Kluane Lake, 240 km northwest of Whitehorse, Yukon Te r r i t o r y ( Fig. 1) . The s i t e s were separated by 700 meters of continuous forest and S i l v e r Creek, a small stream that blocked hare movement between s i t e s from June to mid-September.. Another study area, Sil v e r Creek Removal was located between the two main s i t e s . I t was only i n d i r e c t l y involved with t h i s study. Animals were caught and removed from t h i s area, thus creating a block of unoccupied habitat. Topography i n the Kluane area i s highly variable. The study s i t e s were located on l e v e l ground with shallow, old creek beds providing the only r e l i e f . To the north of Telemetry and the south of S.C.C. the land becomes more rugged and gains i n elevation. The area surrounding each s i t e w i l l be described i n more d e t a i l l a t e r . The climate i s characterized by long winters with l i g h t but persistent snow cover from November to late A p r i l . Snow depths were never more than 40 cm during the study. Temperatures are variable throughout the year with lows of -50°C i n winter and highs of 25°C i n summer. The sun i s above the horizon for 4-6 hrs. during November-February and 18-21 hrs. in June and July. The f r o s t free period runs from early June to late August. New leaves and herbs begin to appear in spring from mid to l a t e Way, and the growing season ends in late August. This means hares have growing herbaceous and woody material available to them for roughly four months each year. 4 Figure 1. Location of study areas. S.C.C.-Silver Creek Control S.C.H.-Silver Creek Removal Tel.-Telemetry 1-7 - Tower Locations 5 6 The winter of 1978-79 was unusually harsh with the coldest February on record occurring. Temperatures never rose above 30°C f o r the entire month. This was followed by a mild March and r e l a t i v e l y early spring. Vegetation i n the area i s northern boreal forest. I t i s sim i l a r to the closed spruce community as c l a s s i f i e d by Douglas (1974). White spruce (Picea qlauca) i s the dominant tree species with various amounts of willow j S a l i x spp. ) and buffaloberry (Shepherdia canadensis) making up the understory. Bearberry (ft rc t o s t ap h v 1 o s uva-ursi). Dryas drummpndii, Hedysarum boreale and Lupinus arc t i c u s provide much of the herbaceous ground cover. Potential competitors of the snowshoe hare are moose iA l e e s alces) and Ar c t i c ground squirrels (Spermpphilus undulatus). Mammalian predators present are lynx ijvynx canadensis) , coyote (Canis latrans) , wolf (Canis lupus),, weasel (Mustela rixpsa)_ and (Mustela frenata) and marten ^Marteo americana). Great horned owls (Bubo Virginianus ), goshawks (Accipiter g e n t i l i s ), red-t a i l e d hawks (Buteo jamaicensis ) and Swainson's hawks (Buteo swainsoni ) are the major avian predators*. The above gives a general description of the study area. I w i l l now describe the two s p e c i f i c s i t e s i n more d e t a i l . 2. 1. S i l v e r Creek Control S.C.C. was located on an old rocky stream outwash. The entire area i s covered by mature white spruce with a sparse 7 understory of willow and buffaloberry. The Alaska Highway runs along the southern edge of the area and creates an open space of 250 meters between the study area and suitable hare cover beyond. Very few animals are known to have crossed t h i s s t r i p . The remaining three sides of S.C.C.. have habitat s i m i l a r to the s i t e i t s e l f . S i l v e r Creek runs 300-350 meters north of the gr i d . However, the area up to 100 meters from the creek has a more open spruce canopy and a thicker understory of willow and buffaloberry than on the study area. 2-.2^ . Telemetry Telemetry i s bordered on the south by S i l v e r Creek and the north by a l i g h t l y used road. The road does not act as a barrier to movements and animals pass f r e e l y from one side to the other. The east and west sides of Telemetry are bordered by continuous f o r e s t . Vegetation on the actual study area i s more variable than on S.C.C. . The north half i s covered by mature spruce with a sparse understory while the southern half has a thick willow understory and open spruce canopy. 8 3. MATERIALS AND METHODS 3.1. Trapping Each study area consisted of a 300 x 300 meter (9.29 ha) trapping g r i d . One hundred stations were arranged in a 10 x 10 pattern with 30 meters tetween stations. F i f t y double door l i v e traps were placed at alternate stations on each gr i d . If runways were present nearby, traps were placed on them. Traps were baited with a l f a l f a cubes throughout the study. In late May and June of 1979 t h i s was supplemented with apples. During winter, most traps were set with a single door open and the bait well behind the treadle. Traps were set for two consecutive nights and checked each morning* During the summer they were also checked i n the evening of the f i r s t day. When not i n use traps were l e f t i n position and locked open. From May through September 1978 traps were set on both grids once a week. They were also set once i n mid-October, twice i n l a t e November, weekly i n March 1979, twice i n late A p r i l , and then weekly u n t i l the end of July., S.C.C. was also trapped once i n each of August, September, and October, 1977. The l o c a t i o n , tag number, sex, reproductive condition* and rig h t hind foot length was recorded for each animal captured. Newly captured animals were ear-tagged with a numbered metal tag. Reproductive condition of females was determined by the size and appearance of nipples. Medium or large nipples with matted fur indicated that the i n d i v i d u a l was nursing a l i t t e r * 9 Pregnant females close to term could be determined by palpation. Males with testes in s c r o t a l sacs were considered to be in breeding conditon. 3. 2. Telemetry In mid-May of 1978, hares on both study areas were equipped with radio transmitters (Wildlife Materials Inc.). Each transmitter produced a pulsing s i g n a l at a s p e c i f i c frequency within the range of 150.8 to 151.8 Mhz. Each unit weighed 30 g and was attached around the animal's neck with strapping. Radios were located with a receiver attached to a d i r e c t i o n a l yagi antenna.. Strongest s i g n a l reception occurred when the antenna was pointed d i r e c t l y at the transmitter. In the i n i t i a l stages, during late May and early June 1978, radio-tagged animals were located by means of a small portable handheld antenna. The direction of strongest s i g n a l strength was followed u n t i l I was certa i n of the animal's location. For the rest of the study, the majority of animals were located by use of permanent towers. Two or more of these were established near each grid and t h e i r r e l a t i v e locations are shown i n Fig . 1. Towers 1, 2, 4, and 5 were established i n mid-June 1978. Tower 3 was established i n l a t e August 1978 while 6 and 7 were erected i n May 1979. Towers 1 and 2 were 12 meters high while 6, 7, 3, and 4 were f i v e meters high. The l a t t e r two, however, were placed on high points of land to increase t h e i r range. Radios could be detected at a distance of up to two km with these permanent towers. 10 Each tower supported a d i r e c t i o n a l yagi antenna that could be rotated from ground l e v e l . The di r e c t i o n of the antenna was read off a protractor at the base. Positions of radio-tagged animals were determined by tri a n g u l a t i o n . The bearing of strongest si g n a l for each transmitter was determined from two towers. The point at which these two bearings crossed indicated the transmitter's location. The location of a radio by t h i s technigue i s not actually a point but a polygon shaped prob a b i l i t y area. The size and shape of the polygon i s dependent upon the location of the radio r e l a t i v e to the locating towers (Heezen and Tester 1967). This i s due to the fac t that some mechanical error e x i s t s i n determining the bearing of the strongest radio s i g n a l . To determine the size of t h i s error I placed radios at known locations and recorded the bearing to each a t o t a l of 20 times from each of the towers. The 95% confidence i n t e r v a l s around the means were determined and found to be near 3° each time. I took this to be the error of the system. In other words a 3° band centered around the recorded bearing would contain the true bearing 95% of the time. If a 3° band i s drawn from each of two towers as shown i n Fig. 2 the l i n e s meet to form an error polygon (Heezen and Tester 1967). This polygon changes i n size and shape depending on where the l i n e s meet r e l a t i v e to the towers. For example, compare the error polygons at points A and B. That at position A has a much shorter length r e l a t i v e to that at position B. During the study, radios were located from tower combinations that minimized the length of the error polygon. Radio locations f a l l i n g i n an area where the error polygon 11 Figure 2 . Changes i n error polygon length (EPL) produced by a telemetry system having a 3° error (3° confidence i n t e r v a l C.I.). Notice EPL changes with i t s position r e l a t i v e to the locating towers (A vs. B). . 3 ° C I - - - E P L \ 1 B A S E L I N E 2 13 length was greater than 150 meters were disregarded. When possible, each transmitter was located synchronously by two people, one at each of two towers. However, in most instances, a single person located a l l of the transmitters i n the area before moving to the next tower to repeat the process. This meant that a maximum of 15 minutes could occur between the taking of the f i r s t and second bearings on each animal. Rapid variations i n transmitter signal strength are produced when an animal changes i t s orientation r e l a t i v e to the receiving antenna. These changes were used to determine whether the animal was active or not. Individuals that showed no a c t i v i t y or changes i n location over 2-3 days were then located with a handheld antenna to see whether the animal was dead or i f the transmitter had f a l l e n o f f . This was also done for any animals making unusual movements. Transmitters found i n t h i s way were examined to determine what had happened to the owner. If a portion of the animal s t i l l remained the proximate cause of death could often be determined. If only the radio was found and the strapping was s t i l l i n t a c t I could be sure that the animal was dead. When the strapping was missing or broken the owner's status was recorded as unknown. Locations of radio-tagged animals were taken at various times and freguencies throughout the study. These w i l l be specified where pertinent.. In late July of 1978 the f i r s t juveniles were radio-tagged., No animals were tagged below a weight of 500 g. The above provides a description of general methods used during the study. More s p e c i f i c technigues w i l l be provided at the beginning of relevant sections. 15 ib. DEMOGRAPHY This section examines the demography of hare populations on Telemetry and S.C.C. . Trapping estimates of population density w i l l be provided along with s u r v i v a l rates from both trapping and telemetry techniques. The number of young produced in each area w i l l also be estimated. F i n a l l y , the values obtained w i l l be compared to those of previous studies. I used two mark-recapture techniques to estimate numbers. They were: complete enumeration ( Krebs 1966 ) and the J o l l y stochastic model ( J o l l y 1965 ). As the name suggests complete enumeration involves capturing a l l of the animals present during each trapping session. The J o l l y method i s based on multiple capture data which i s used to generate probability values of s u r v i v a l and population growth. These i n turn are incorporated into a model which produces population estimates.. Both estimation technigues are sensitive to the t r a p p a b i l i t y of the animals involved. The J o l l y method assumes that a l l indiv i d u a l s i n the population have egual p r o b a b i l i t y of capture while complete enumeration i s e f f e c t i v e only when the t r a p p a b i l i t y of animals i s greater than 50% ( Hilborn et a l . 1976 ). To determine whether these c r i t e r i a were met I measured the t r a p p a b i l i t y of the population at d i f f e r e n t times. Trappability for each animal was calculated by the formula: ( number of captures during time t ) -2 ( maximum potential number of captures during time ) - 2 16 An example would be as follows. Over six trapping sessions i n time t an animal was f i r s t caught in session numbers 1 and then again i n 3, 4, and 5. The t o t a l number of captures over time t was 4. The maximum potential number of captures was 6. Subtracting f i r s t and l a s t captures gives a t r a p p a b i l i t y value of 2/4 or 50%. Values for each animal were then averaged to give a mean for the population. Subtracting 2 from the numerator and denominator excludes animals that are captured only once or twice ( Hilborn et a l . 1976 ). 4.1. Results 4. 1-1. Trappabilit y Table 1 shows that mean t r a p p a b i l i t y was less than 50% i n Oct. 78 - Feb. 79 and May-June 1979 on Silver Creek Control* Values though, were never less than 40%. In three of f i v e time periods examined, animals were l e s s catchable on S.C.C. than on Telemetry..Trappability varied between sexes. Major differences were apparent i n March-June 1979 on Telemetry and Aug.-Sept. 1978 on S.C.C Males were highly trappable in March and A p r i l 1979 on both grids. Average t r a p p a b i l i t y over the entire study was 59% on Telemetry and 53% on S.C.C Hilborn et al.(1976) found that complete enumeration underestimated population size by at least 20% when t r a p p a b i l i t y dropped below 50%. Conseguently both J o l l y and complete enumeration estimates w i l l be provided for comparison. Any differences between estimates may indicate biases that can be 17 TABLE 1 Trappability of animals on Telemetry and S.C.C...All values are expressed as percentages. Sample sizes are i n brackets. NO. TRAPPING PERIOD SESSIONS M TELEMETRY S • C • C m MEAN MEAN May-July/78 67. 7 (7) 69.6(6) 68.6 74.0 (3) 40.0 (6) 51.0 Aug-Sept/78 55. 2 (16) 53.8(13) 54.6 40.2 (11) 66. 2(18) 56.3 Oct-Feb /79 62. 9 (18) 62.5(10) 62. 8 48.3 (11) 44.4(14) 46.1 Mar-Apr /79 86.5 (13) 53.0(11) 71.2 85.2 (9) 70.4 (9) 77.8 May-June/7 9 69. 2 (13) 41.7(14) 55.0 39.4 (11) 48.3(10) 43.7 May/78- 28 July/79 59.3 (36) 59.0 (38) 59.6 52.2(26) 54.2(26) 53.5 18 corrected for. 4.1-2. Changes i n Numbers Fig. 3 shows , that M.N.A. ( minimum number a l i v e ) estimates were si m i l a r for the two study areas. Numbers began to increase in 1978 with the recruitment of juveniles into the population. This occurred in early July on both grids but at a slower i n i t i a l rate on Si l v e r Creek Control..After numbers peaked i n September there was a moderate drop i n October and subsequent recovery i n November. In early March 1979 the population had dropped to ha l f that present i n September. Immigration, primarily by females, i n early May, caused an increase i n estimates. Estimates in June were 1.9 and 2.6 times those of one year e a r l i e r on S.C.C. and Telemetry respectively. The M.N.A. estimate for August 1977 on S.C.C. was 4. Fig.,4 shows that J o l l y population estimates followed a pattern s i m i l a r to M.N.A. but are up to 20 % higher. Hare numbers then, were increasing during 1977-1979. Both grids followed s i m i l a r patterns of density change. 4.1-3. I n i t i a t i o n of Breeding Season Trapping did not begin early enough i n 1978 to determine when males came int o breeding condition. A l l adult males captured between May 1 and August 7, 1978 were s c r o t a l . A l l were i n non-breeding condition after mid-August. 19 Figure 3. Minimum number al i v e (M.N.A.) estimates for S.C.C. and Tel. during the study. 20 21 Figure 4. J o l l y population estimates for S.C.C. and T e l . during the study. 22 1 0 0 7 0 j 2 1 1 M A Y J S N 1 9 7 8 F E B A J 1 9 7 9 23 In 1979, four of 15 males captured during March 6-8 were scrotal- Two weeks l a t e r 20 of 23 were classed as scrotal and the three abdominal animals continued to be so even i n l a t e June, suggesting that they did not breed. Thus half of the males were in breeding condition by March 15,1979. The f i r s t l i t t e r s of 1978 were born between May 25 and June 3, and four of six S.C.C. females caught on May 28 were la c t a t i n g while a f i f t h was four days l a t e r . The f i n a l female was l a c t a t i n g when i t was next captured on June 12. M l females on Telemetry were l a c t a t i n g by June 3. Thus a gestation period of 37 days ( Severaid 1942 ) would put f i r s t l i t t e r conception dates in 1978 around A p r i l 23. F i n a l l i t t e r s were born i n early August and females had ceased l a c t a t i n g permanently by September 23. In 1979 f i r s t l i t t e r s were born around May 19. Two females removed from Telemetry and placed in 3 x 9 m pens gave b i r t h at t h i s time. Twc pregnant females which died while being l i v e -trapped on May 17-18 had embryos weighing over 50 g i n d i c a t i n g that they were close to term. Four of eight females caught on S.C.C. during the week of May 21-27 were l a c t a t i n g . The remaining four were l a c t a t i n g the next week. On the Telemtry grid two females had given b i r t h during the week of May 14-20, 1979. Two weeks l a t e r a l l but two females captured were l a c t a t i n g . I t appeared, through l a t e r trapping, that these two animals did not produce a f i r s t l i t t e r . To summarize, f i r s t l i t t e r s i n 1979 were born between May 18 and June 3. This places f i r s t l i t t e r conception dates at A p r i l 11, almost two weeks e a r l i e r than i n 1978.. 24 4. 1-4. Number of Young Meslow and Keith ( 1968 ) found that births of l i t t e r s were highly synchronized. This, along with immediate postpartum mating, served to produce d i s t i n c t l i t t e r groups distinguishable by weight. Three l i t t e r s were born on both Telemetry and S.C.C. in 1978. F i r s t trapping dates of individuals from respective l i t t e r s were June 22, July 19, and August 18 on Telemetry. Second and t h i r d l i t t e r young were captured 10 days l a t e r i n each case on S.C.C. Young started to enter traps around roughly 25 days of age and at a weight of 300-400 g. Adult females were not caught often enough to determine whether each i n d i v i d u a l produced three l i t t e r s * The number of young caught from each l i t t e r and each grid i s shown i n Fig.5. Numbers are determined from young caught before Sept. 30. After t h i s time trapping was not frequent enough to place newly tagged juveniles into t h e i r respective l i t t e r groups. Numbers of young caught per l i t t e r were s i m i l a r on each grid except f o r l i t t e r two where the number was 50% higher on Telemetry. The second l i t t e r produced as many young as the f i r s t and t h i r d l i t t e r s combined. The difference i n number caught between f i r s t and second l i t t e r s may be explained by larger l i t t e r sizes i n the l a t t e r as found by Cary and Keith ( 1979 ). This cannot explain the difference between l i t t e r s two and three however, as Cary and Keith ( 1979 ) found l i t t e r sizes and pregnancy rates s i m i l a r for the two. The t o t a l number of young trapped to September 30 was 49 on Telemetry and 37 on S*C.C. This produced a juvenile/female r a t i o of 12.25 on 25 Figure 5. Number of young trapped i n 1978 on S.C.C.. and Telemetry. Notice that over half of the animals were from the second l i t t e r . 4 OJ c/> 3 0_ LU < 2 0. 104 s . c . c . n T E L . L I T T E R NO. 27 on S.C.C. of the juveniles captured were from many juveniles were caught per as on S.C.C. 4.1-5 Survival Telemetry as compared to 6*3 To summarize, over half the second l i t t e r . Twice as female on the Telemetry grid Survival estimates were calculated i n three d i f f e r e n t ways. They were: 1. Trapping method - t h i s method uses recapture data to calculate the r a t i o of (number of animals released at time t and known to be a l i v e at t + 1) (number of animals released at time t) 2. Simple telemetry - This technique records the number of animals known to be a l i v e at time t, as determined by telemetry and then records how many of these are s t i l l a l i v e at time t+1. I t i s s i m i l a r to the trapping method except that a radio-tagged animal located and considered to be al i v e i s eguivalent to an animal being released af t e r trapping. 3. Trent and Eongstad ( 1974 ) - This technique uses telemetry to calculate a mean da i l y s u r v i v a l rate (Sd) by the formula: Sd = ( x-y )/x where: x = number of radio-hare days ( 1 radio-hare day i s equal to 1 radio-tagged hare i n the f i e l d for 1 day ) i n time 28 period t. y = number of mortalities in time period t. Survival over n days can be determined by ( Sd ) and confidence l i m i t s can be placed on the estimate by following the method of Trent and Hongstad ( 1974 ). Telemetry i s useful as a method of measuring survival only i f radio-tagged animals survive as well as untagged in d i v i d u a l s . Tew studies have attemped to determine i f t h i s i s true ( Herzog 1979; Boag et a l . 1973 ). Brand et a l . ( 1975 ) showed that overwinter weight loss of hares was similar i n c o l l a r e d vs. uncollared hares. However, sample sizes were small. As well, radio-tagged animals which die over the winter may s t i l l lose weight at a greater rate than untagged individuals and thus suffer higher mortality rates. This could not be detected by looking at weight losses of survivors. To test for equal survival I compared the trapping s u r v i v a l of radio-tagged animals with those that were not tagged. Because the majority of the animals were radio-tagged at some point during the study i t was d i f f i c u l t to obtain a large sample of untagged animals. I overcame t h i s by examining the survival of a l l i n d i v i d u a l s captured for the f i r s t time between July 1 and December 1. These were divided according to whether or not they had received radio c o l l a r s . F i n a l l y I calculated how many of these in d i v i d u a l s were s t i l l a l i v e May 1, 1979. Trapping s u r v i v a l of radio-tagged animals was higher than for untagged in d i v i d u a l s . None of 25 animals on S.C.C. without c o l l a r s survived to May 1. Five of 21 with c o l l a r s survived. On Telemetry 3 of 43 without c o l l a r s survived whereas 5 of 22 with 29 c o l l a r s survived. Although t h i s suggests that c o l l a r s did not increase mortality rates, i t i s not completely s a t i s f a c t o r y . Animals that received radios were most often those being captured regularly on the grid. As a res u l t most untagged animals i n the sample were captured only once or twice, thus biasing the sample toward i n d i v i d u a l s with high rates of early disappearance. To test further whether radio-tagged and untagged hares had s i m i l a r s u r v i v a l rates I examined survival of indiv i d u a l s on another trapping grid with no radio-tagged hares. This grid (1050) was located two km east of the main study areas. I t consisted of a trapping grid arranged s i m i l a r l y to S.C.C. and Telemetry* Animals were trapped every three weeks throughout the summer and most of the winter. F i g . 6 shows that survival of radio-tagged hares on S.C.C.. and Telemetry was always egual to or greater than those merely live-trapped on 1050. This too, suggests that radio-tagged hares had s u r v i v a l rates comparable to untagged animals. F i g . 7 compares survival rates as determined by the three methods previously described. Animals from both grids were combined. Juveniles and adults were pooled since there were no s i g n i f i c a n t differences in survival between the two groups. Trapping estimates were always lower than either of the methods using telemetry. The difference between the trapping and telemetry estimates was s i g n i f i c a n t i n Nov. - Feb. and May -June 1979 ( X2; P<.05 ). Survival estimates by the two telemetry methods were very s i m i l a r . Because of t h i s , for the sake of brevity, only the simple telemetry method w i l l be 30 Monthly su r v i v a l rates determined by trapping on 1050, a gri d where no animals were radio-tagged, and S.C.C. and Telemetry, grids where a large portion of animals were radio-tagged. Notice su r v i v a l rates on S.C.C. and Telemetry were egual to or higher than those on 1050. Sample sizes are placed above each column. 31 S U R VI V AL co H h RATE 03 (0 I > (0 -J 00 CO . I o CO z o < I n m 03 r o o o CO b b H m CO CO 2 i CO 32 Figure 7. Comparison of monthly s u r v i v a l rates as determined by trapping and telemetry (two methods). Grids have been combined. Notice that trapping rates are much lower than telemetry estimates i n Nov.-Feb. and May-June 1979. Sample sizes are found at the top of each column. Trent and Rongstad (1974) sample sizes represent radio-hare days. 34 discussed from now on. Fi g . 8 shows that monthly telemetry survival estimates were sim i l a r for the two grids throughout the study. Rates were lowest i n March - A p r i l 1979 and highest i n July -August 1978 but the differences were not s i g n i f i c a n t ( X 2; P>.05 ) . No losses were recorded u n t i l September at which time s u r v i v a l dropped by 10%. I t continued to remain near 90% per month for the duration of the study. In contrast to telemetry s u r v i v a l rates F i g . 9 shows that monthly trapping s u r v i v a l estimates averaged 15% lower on S.C.C. control than on Telemetry. The largest differences occurred i n May-June of each year. To summarize, monthly survival during the study was f a i r l y constant with l e v e l s s l i g h t l y lower i n March - April 1979. Survival estimates by trapping and telemetry d i f f e r e d in Nov. -Feb. 1978 and May - June 1979 by 17% and 24% respectively. The difference in May - June 1979 was due mainly to an unusually low trapping s u r v i v a l on S. C.C. at t h i s time. 4.1-6. Juvenile Survival A number of workers have concluded that juvenile s u r v i v a l may be important i n hare cycles ( Keith and Windberg 1978; Green and Evans 1940a ) and small mammal cycles in general ( Krebs and Myers 1974 ). Table 2 shows juvenile s u r v i v a l rates from f i r s t trapping to May 1. The animals are grouped according to the l i t t e r they were born i n . Survival of f i r s t l i t t e r young was twice that of the second. No t h i r d l i t t e r young survived. Overall juvenile survival from f i r s t trapping to spring was less 35 Figure 8. Comparison of telemetry monthly su r v i v a l rates on S.C.C. and Telemetry. Note t h e . s l i g h t l y lower rates during winter. Sample sizes are placed above each column.. SURVIVAL RATE 3 6 I I CO Ol 0) I I oo to o I > oo CO -J 00 CO I o t o o o < I T l m 03 CO —i CO m o r b urn C O CO -J CO 03 CO I 37 Figure 9. Comparison of monthly su r v i v a l rates on S.CC. and Telemetry as determined by trapping r e s u l t s . Notice the low rates during Novi-Feb. on both grids and on S.C.C. in May-June 1979. Sample sizes are placed above each column. SURVIVAL RATE 38> N> CO l I I I I I I 1.1. . . J I. I I 00 (O o CO 0 0 00 CO CO I O) (0 I - J > CO N> m CO O O z o < I m 03 CO ro -si • - 0 TABLE 2 Survival rates of juveniles from f i r s t trapping to Way 1. Individuals were divid-ed according to l i t t e r group by weight at f i r s t capture. Sample sizes are i n brackets* L i t t e r No. 1 2 3 Total S.C.C. 0.33 (9) 0.15 (20) 0*0 (8) 0. 16(37) Telemetry 0.33 (12) 0.17 (29) 0.0 (8) 0. 18(49) Combined 0.33(21) 0.16 (49) 0.0 (16) 0. 17 (86) no than 20%. This was the same as annual adult survival ( 2 of 10 ). Juvenile survival did not decrease throughout the winter as suggested by Keith and Windberg ( 1978 ). . Monthly telemetry survival rates were .92 ( n=23 ) from Sept. 1 - Dec._1..This compares with rates of .88 ( n=23 ) from Dec. 1 - May 15. Trapping s u r v i v a l rates showed s i m i l a r changes. . Table 3 shows the proximate causes of death of 38 radio-co l l a r e d animals. Predators were responsible for 24 of the 27 cases i n which the cause of death could be determined. This figure i s probably an overestimation of the e f f e c t of predation as i t was sometimes d i f f i c u l t to determine whether animals had been predated or scavenged aft e r they died. I t r i e d to reduce t h i s problem by placing finds where there was some doubt i n the unknown cause of death category. Only three animals were found dead with no signs of predation. A l l of these occurred in early March near the end of a long continuous cold s p e l l . The i n d i v i d u a l s were found i n forms completely undisturbed. I t appears that death was probably due to starvation triggered by the long period of cold temperatures ( Pease et al..1979 ). Four animals died because of poorly f i t t i n g c o l l a r s which became lodged between t h e i r upper and lower jaws. They were unable to eat and thus starved. 4.2. Discussion Since changes i n numbers and s u r v i v a l rates are i n t e g r a l parts of the snowshoe hare cycle i t i s important that the values obtained accurately r e f l e c t the events occurring. The fact that TABLE 3 Causes of death of radio-tagged hares. Predator Starvation C o l l a r Unknown Caused Terr. avian Unknown 10 9 5 3 4 7 42 the changes i n numbers determined by the J o l l y and complete enumeration technigues were sim i l a r throughout the study support the v a l i d i t y of the estimates as an index of density. Hilborn et a l . ( 1976 ) found that M.N.a. underestimated vole populations by 1 0 - 2 0 % . If t h i s amount i s added to the M.N.A., estimates i n t h i s study, f i n a l values are comparable to those obtained by the J o l l y technique. This too, suggests that the estimates are correct. Survival estimates determined by trapping were always lower (up to 35%) than those from telemetry. This was due to two factors. F i r s t l y , trapping cannot d i f f e r e n t i a t e between death and emigration. An animal leaving the grid e n t i r e l y or s h i f t i n g i t s home range so that i t s chances of capture are low w i l l appear to have died. Secondly, telemetry estimates are biased s l i g h t l y high. This i s because animals losing t h e i r radios and subsequently dying before being retrapped are not included in the determination of telemetry s u r v i v a l rates. Those that lose t h e i r c o l l a r but are retrapped before they die are included. As a resu l t the chances of missing an animal that dies are greater than missing one that survives. This bias was small however, as only 8 of 116 radio-tagged animals disappeared with no evidence as to t h e i r fate. Trapping s u r v i v a l rates were s i g n i f i c a n t l y lower than those determined by telemetry i n the Nov. 1978 to Feb. 1979 period. This was probably due to the following. A number of radio-tagged animals were found dead i n late Feb. - early March 1979. These animals died at a time three months after the l a s t trapping session i n November 1978 and one week before the f i r s t session 43 i n March 1979. Because November was the l a s t time of capture for many of these ind i v i d u a l s , trapping s u r v i v a l would concentrate a l l of the losses i n the Nov. - Feb. period. Telemetry estimates on the other hand, would spread them more evenly between the two periods. The end result i s an underestimation of su r v i v a l rates by the trapping technique i n the Nov, - Feb. period. Trapping s u r v i v a l rates were also s i g n i f i c a n t l y lower than telemetry estimates i n May - June 1979. This was the r e s u l t of low trapping survival estimates on S.C.C. which was caused by the following s i t u a t i o n . F i r s t l y , as revealed by telemetry, many animals on S.C.C. shifted t h e i r home ranges from on the grid i n May to s l i g h t l y off i t f o r the duration of the summer. This movement decreased the chances of capture as shown by the low t r a p p a b i l i t y of animals on S.C.C. i n May - June 1979. A s i m i l a r s i t u a t i o n occurred i n 1978 but high s u r v i v a l and a l a t e r return to the gr i d allowed most of the animals to be recaptured. With trapping being stopped in 1979 however, the animals were not recaptured and thus were recorded as having died. The o v e r a l l r e s u l t was to bias trapping s u r v i v a l downward i n May - June 1979. The above si t u a t i o n s exemplify the value of telemetry as a method of estimating s u r v i v a l rates. Because animals do not have to be regularly trapped to supply information, behavior af f e c t i n g t r a p p a b i l i t y has no influence on s u r v i v a l rates. Telemetry survival estimates then, are unaffected by home range s h i f t s or dispersal movements and thus present a clearer picture of s u r v i v a l than do trapping methods. 4.2-1. Reproduction The e a r l i e r dates of f i r s t l i t t e r conceptions i n 1979 compared to 1978 seemed to be linked primarily with the onset of spring. Snow disappeared and new growth began two weeks e a r l i e r i n 1979 than i n 1978. In both years f i r s t l i t t e r s were born just as t h i s new growth became readi l y available to the females. The linkage between onset of spring and breeding seems to be common among leporids ( Meslow and Keith 1971; Cary and Keith 1979; Wight and Conaway 1961 ). Results showed that during 1978 twice as many young per female were caught on the Telemetry as on S.C.C..One possible explanation i s that females on Telemetry actually produced twice as many young as those on S.C.C. I do not think t h i s was the case. The discrepancy was probably due to the r e l a t i v e s p a t i a l arrangements of animals on each g r i d . Radio-telemetry locations showed that females on Telemetry spent most of t h e i r time on the actual gr i d while those on S.C.C spent considerably more time off in peripheral areas. As as r e s u l t , there was a greater chance that juveniles on S.C.C. were born o f f the gri d . Consequently, they had to move greater distances than t h e i r Telemetry counterparts before there was any chance of capturing them. Juveniles seem to remain f a i r l y close to t h e i r place of b i r t h at l e a s t u n t i l weaning ( Rongstad and Tester 1971 ). This means there was less chance of capturing juveniles, at le a s t i n i t i a l l y , on S.C.C. This explains why f i r s t captures for the respective l i t t e r s always occurred 10 days la t e r on S.C.C. than on Telemetry. 45 Another complicating factor may have been the presence of the removal grid ( Fig. 1 ). This area was a block of vacant habitat r e l a t i v e l y close to S.C.C. and Telemetry and was created by live- t r a p p i n g and removal of hares. This unoccupied habitat may have influenced animals to move into t h i s area rather than onto S.C.C. Over 40 juveniles were caught i n the removal area. This was more than enought to compensate for the differences observed between S.C.C. and Telemetry. The above factors may have caused the differences i n number of young caught per adult female on each of the two study areas. I f 12.25, the number of young caught per adult female on Telemetry, i s taken as an estimate of average n a t a l i t y rates i n the area, the value i s r e l a t i v e l y high. Cary and Keith ( 1979 ) provide r e a l i z e d n a t a l i t y rates of 11.3 to 16.3 young per female during increase years while Green and Evans ( 1940a ) provide values of 6.6. Ernest ( 1974 ) found values as high as 11.7 young per female during a hare peak i n Central Alaska. These figures were not computed from the number of young entering traps but from mean values of l i t t e r s i z e s , pregnancy rates, and adult s u r v i v a l . The number of young actually being caught would undoubtedly be somewhat le s s . 4.2-2. Changes i n Numbers Numbers doubled on S.C.C. and Telemetry from spring 1978 to spring 1979. This rate of change seems c h a r a c t e r i s t i c of increasing hare populations ( Green and Evans 1940b; Keith and 46 Windberg 1978 ). M.N.A. and J o l l y estimates remained high throughout the f a l l and then declined over winter. The sharp temporary decline in October was not completely due to lower s u r v i v a l although rates did drop from summer to Sept. - Oct.. Up to October any losses were compensated for by new individuals showing up i n traps. The same was true for November. In October though, no -new individuals were captured. This could have been caused by poor weather conditions during the trapping session. Freezing rain made most of the traps inoperable and decreased the catch..Because of t h i s , the drop in October appeared larger than i t actually was. The increase in numbers i n early A p r i l was also due to high numbers of untagged indiv i d u a l s showing up i n traps. These ind i v i d u a l s may have been present on the grid during winter or more l i k e l y , existed on the edge of the g r i d , and with the onset of breeding, became more mobile ( Hewson 1976 )._This, coupled with a possible expansion of home range, may have increased the chances of capture as suggested by the high t r a p p a b i l i t y of males at t h i s time. The decrease i n numbers i n May - June 1979 can, again, be only partly explained by mortality losses. The rest i s due to a trapping a r t i f a c t . Although many of the animals previously trapped were s t i l l a l i v e at the end of June, as shown by telemetry survival estimates, they were not captured during the f i n a l trapping session. The population estimation techniques would then record them as dying and thus reduce population size accordingly. This re s u l t s i n numbers being underestimated at the end of the study. 47 4,2-3. Survival An annual adult s u r v i v a l of 20% i s r e l a t i v e l y low for increasing hare populations. Keith and Windberg ( 1978 ) found values greater than 30% in Alberta populations. Juveniles never suffered s u r v i v a l rates s i g n i f i c a n t l y lower than adults and rates were comparable to those of other studies ( Keith and Windberg 1978; Dolbeer and Clark 1975 ). Proximate causes of losses throughout the study appeared to be due to predation. Losses seemed to increase s l i g h t l y from summer to winter, which may have been related to changes i n cover and subsequent s u s c e p t i b i l i t y to predation..There was very l i t t l e evidence of starvation or disease. To conclude, numbers doubled over the study even though adult s u r v i v a l was lower than that found i n other studies. This seemed to be compensated for by higher than average n a t a l i t y rates. Juveniles survived as well as adults at a l l times. Survival rates were s l i g h t l y lower in winter months and most losses had predation as t h e i r proximate cause. 48 5. HOME RANGE SIZE AND SPATIAL ARRANGEMENT Home range was defined by Burt ( 1943 ) as "... that area traversed by the ind i v i d u a l i n i t s normal a c t i v i t i e s of food gathering, mating, and caring f o r young." The way these a c t i v i t i e s are performed i n turn, determines the type of s o c i a l organization experienced by that i n d i v i d u a l * . Consequently, knowing such things as the s i z e , location, and s p a t i a l arrangement of the home ranges of a group of ind i v i d u a l s should provide some information as to th e i r s o c i a l organization. This concept i s p a r t i c u l a r l y important i n species l i k e the snowshoe hare where i t i s d i f f i c u l t to observe behavioral interactions d i r e c t l y . With the development of radio-telemetry i t i s r e l a t i v e l y easy to obtain an accurate measure of the position of a number of hares' heme ranges. This section presents data on the s p a t i a l arrangement of snowshoe hares monitored during the study and discusses i t s relevance to the animals' s o c i a l organization. 5.1. Methods Home ranges were determined by the convex polygon method ( Mohr 1947 ) which joins the outermost locations where an animal i s found to form a convex polygon. I modified t h i s technique to include only 9058 of the t o t a l number of points. Locations which were furthest from a l l others were discarded. This was done to exclude locations representing brief long 49 distance forays outside an animal's normal area of use ( Burt 1943 ) . animal locations were determined by radio-telemetry. As explained previously, a radio-location has associated with i t , an error polygon whose length provides some index of the accuracy of the location. This length i s a function of the telemetry system error and the transmitters' location r e l a t i v e to the locating towers. Heezen and Tester ( 1967 ) have shown that the s i z e of a home range i s affected by the accuracy of the points involved. To see how the error of my telemetry system affected home range size I performed the following analysis. Points were placed at various position on a map. These were used as centres of hypothetical sguare home ranges having an area equal to 3 ha. One of these ranges can be seen i n Fig. 10. When using the convex polygon method the size of a home range i s affected most by the outer locations which form the actual boundary. In turn, the error involved in estimating these outer points w i l l be most i n f l u e n t i a l i n o v e r a l l home range size error. To obtain an estimate of t h i s effect I determined the bearings of each corner from two locating towers ( Fig. 10 ). Five bearings for each corner were generated by computer from a normal d i s t r i b u t i o n with a mean equal to the actual corner bearing and a 95% confidence i n t e r v a l of 3 (telemetry system error = 3° ). Bearings from each tower were combined to give f i v e locations for each corner. They are represented by the black dots i n Fig. 10 and in e f f e c t , mimic the range of locations a telemetry system with a 3° error would produce when locating an animal on the boundary of i t s home range. When 50 Figure 10. Method used to determine the e f f e c t of telemetry system error (3°) on estimated home range si z e . 51 52 combined to produce a 90% home range these points w i l l give an estimate of the actual range. The error i n estimating home range area ( i . e . radio location estimate - actual area ) i s a function of where the home range i s situated r e l a t i v e to the baseline of the two towers ( F i g . 10 ). An index of t h i s location i s the length of the error polygon of the radio locations which i s represented by AB i n Fig..10. The error polygon i s smallest when the home range i s at 45° from each of the towers and increases in length when the range deviates from t h i s position. To predict and therefore correct the error i n home range area, I plotted a home range error factor: ( Estimated area - Actual area ) ( Estimated area ) against AB, the error polygon length ( F i g . 11 ) . AB i s the independent variable since i t can be calculated for any position r e l a t i v e to the towers from the known 3° bearing error. Estimated area was always greater than actual area and as error polygon length increased so did the overestimation or error f a c t o r . To correct home range sizes of animals monitored during the study I determined the error polygon length associated with the home range location and used the regression equation in F i g . 11 to calculate the appropriate error factor. Estimated home range size was then multiplied by (1-error factor) to obtain the corrected size. Error polygon lengths below 75 m were not used i n the ca l c u l a t i o n of the regression. When lengths below t h i s l e v e l 53 Figure 11. Relationship between error polygon length and overestimation of home range si z e . E = estimated range size A = actual range s i z e . 5 4 ERROR P O L Y G O N L E N G T H (m) 55 were included i t was found that the relationship between error polygon length and the error factor was much poorer ( r 2=. 65 ). This may be due to the following s i t u a t i o n . Heezen and Tester ( 1967 ) found that estimated home range areas remained equal to actual range size u n t i l error polygon length reached a certain s i z e . After t h i s , estimated ranges showed increasing over estimations i n a fashion s i m i l a r to t h i s study..There appears to be an i n f l e c t i o n point then,75 m i n t h i s study, below which error polygon length i s not related to home range size error* Consequently, I used the regression equation shown i n Fig..11 to correct the siz e of animals' home ranges which f e l l i n regions with error polygon lengths greater than 75 m and less than 150 m. Those i n areas with greater error were discarded because i t was f e l t that the error involved was too great to estimate even the centre of the home range with any accuracy..Home range sizes of animals i n areas where the error polygon length was less than 75 m were l e f t unchanged. A l l animals on Telemetry were in t h i s category as well as over. 50% of those on S.C.C, The percentage overlap between animals' home ranges were determined in the following manner. The estimated 90% home ranges f o r a l l animals i n an area were drawn on a map. The proportion of radio-locations f o r animal ( x ) found inside the area defined by a l l other animals' home ranges was taken as the percentage overlap for animal ( x ). Values were determined for each animal i n t h i s manner and averaged* Overlap by a single i n d i v i d u a l was considered the same as overlap by two or three animals. 56 5. 2. Results 5.2-1. Home Range Size Fig. 12 shows the 1978 monthly home range sizes of male and female hares radio-tagged on the two study areas. Home ranges were s l i g h t l y smaller on Telemetry as compared to S.C.C.. but the two grids were combined to increase sample s i z e . Wale home ranges averaged 25% larger than females. Fig* 13 shows monthly home ranges of radio-tagged animals i n 1979. Grids have been separated because range size d i f f e r e d on the two areas. In a l l cases except July animals on Telemetry had smaller ranges. The differences were signfic a n t for males in Nay and June ( P<.01 ) and for females i n June ( P<.001 ). Males had s i g n i f i c a n t l y (P < .01) larger home ranges than females in a l l cases except on the Telemetry area in May. Home range size appeared similar i n breeding and non-breeding seasons. Female home ranges averaged 25% smaller in 1979 as compared to 1978. . Average female home range size varied from 3-5 ha while that of males varied from 4-8 ha. These figures are s i m i l a r to those found i n other studies ( Bider 1961; Adams 1959, O'Farrell 1965 ). Rongstad and Tester ( 1971 ) found that female hares contracted t h e i r home range size just prior to p a r t u r i t i o n . To see i f t h i s occurred i n my study I compared home range size for the two week period centred around each b i r t h with the two week period midway between births in 1978, while i n 1979 I reduced t h i s to weekly i n t e r v a l s . In each case the number of locations used to determine home ranges f o r b i r t h and i n t e r b i r t h periods 57 Figure 12. Mean monthly home range sizes of radio-tagged hares i n 1978 showing that males have s l i g h t l y larger ranges than females. Narrow bars represent 95% confidence l i m i t s . Sample sizes are placed above each column. 5 8 1 2 11 10 9 8 I .7 6 X < x 5 4 . ~ 3 . . 2 . . 1 . . 1 0 F E M A L E S M A L E S O 1 7 11 1 8 JUNE JULY AUG S E P T NOV 59 Figure 13. 1979 mean monthly home range sizes of radio-tagged hares. Females had s i g n i f i c a n t l y smaller ( t - t e s t , P < .01) home ranges than males i n a l l cases except on Telemetry i n Way and July. Narrow bars represent 95% confidence i n t e r v a l s . Sample sizes are paced above each column. o U 3 01 9. 8. 7. X 6 1 4. . 3. . 2. . 1. . M A Y J U N E S . C . C . J U L Y F E M A L E S M A L E S • 15 15 M A Y J U N E T E L . 13 J U L Y 61 were equal. This was done to avoid biases due to sample sizes as pointed out by Jennrich and Turner ( 1969 ). Results are shown in F i q . 14. Home ranges were very small during the f i r s t two sampling periods of 1978* This i s probably due to the fact that locations during t h i s time were determined by using a handheld antenna to get very near the animal. As a re s u l t animals were located during daylight hours only, which may have resulted i n an underestimation of home range size. After these two i n i t i a l periods average home range size was 35% lower during b i r t h vs. i n t e r b i r t h periods. The only s i g n i f i c a n t diference between b i r t h and i n t e r b i r t h periods was that of l i t t e r 1 on Telemetry i n 1979 ( P<.01 ) when b i r t h ranges were 40% smaller than those of i n t e r b i r t h periods. 5.2-2. Percentage Overlap Home range overlap of males and females during the breeding season was analyzed to determine how ind i v i d u a l s arranged themselves s p a t i a l l y at t h i s time. F i g . 15 shows that female 90% home ranges overlapped extensively. Actual percentages are shown in F ig. 16. The breeding season was again broken down into periods centered around and between the bi r t h of l i t t e r s . Average overlap was never less than 30% and was 20% lower during b i r t h ( 40% ) vs. i n t e r b i r t h ( 60% ) periods. Female home range overlap was further analyzed to determine i f i ntensively used areas of an indiv i d u a l ' s range were overlapped by others. 50% home ranges were taken as representing these more inte n s i v e l y used areas as suggested by Michener 62 Figure 14. Mean home range sizes of females showing smaller range sizes during b i r t h versus i n t e r b i r t h periods. Grids have been combined except during the b i r t h of l i t t e r 1 in 1979 when home ranges i n the two areas were s i g n i f i c a n t l y d i f f e r e n t . Narrow bars represent 95% confidence i n t e r v a l s . Sample sizes are placed above each column. < X 9. 8_ 7_ 6. . 5. . 4. . 3. 2. 1J: 8 BIRTH INTERBIRTH Q SCC. 20 TEL. 18 25 21 L I T T E R NO. 19 78 19 7 9 64 Figure 1 5. . Female 90% home ranges on S.C.C. showing extensive overlap during the breeding season. MAY 1 5 - 30 1979 150 m 66 Figure 16. % overlap of female home ranges during b i r t h vs.. i n t e r b i r t h periods. Home ranges were determined over two week i n t e r v a l s i n 1978 and weekly in t e r v a l s i n 1979. A l l percentages have been transformed by arc sine square root function. 95% confidence i n t e r v a l s are shown by narrow bars and sample sizes are placed above each column. Notice the lower amount of overlap during b i r t h periods. 10 0.. 9 0- . 8 0. . 7a . 6 0- -5 a -4 0. 3 0. 2 o r 10. JULY 3 JULY 21 AUG 8 19 78 B I R T H I N T E R B I R T H Q 8 11 AUG 26 MAY MAY 16 26 JUNE JUNE JUNE 5 13 2 5 LITTER NO. 1 2 1979 68 ( 1979 ). The 50% home range of an i n d i v i d u a l female was plotted on a map and the 90% ranges of a l l other individuals were superimposed on i t . Percentage overlap was determined and found to be as high in these 50% areas as i t was when 90% home ranges were considered. There was no suggestion that females avoided areas used extensively by another female. Male 90% home ranges also overlapped extensively during the breeding season as shown i n F i g . 17. As with females, mean values were never l e s s than 35%. Fig. 18 shows that males overlapped females and did not exclude other males from females within t h e i r range. An i n d i v i d u a l male could come into contact with as many as seven females but the average was just over three. Animals did not change t h e i r s p a t i a l arrangements outside of the breeding season. F i g . 19 shows that i n November 1978, ranges continued to overlap between and within sexes, and a si m i l a r arrangement occurred i n early March 1979. I t seems that hares never exclude individuals of the same or opposite sex from part or a l l of their home range at any time of the year. 5 X2-3. Dispersal The majority of animals radio-tagged during the study occupied the same home range throughout the year. However, 14 of 116 tagged individuals did undergo di s p e r s a l movements. Dispersal was considered to be any movement i n which an animal l e f t i t s home range and did not return. Table 4 l i s t s the 14 dispersers along with t h e i r age, sex, time and distance of 69 Figure 17. 90% heme ranges of males on S.C.C. during the breeding season. showing high overlap M A Y 15 - 30 1979 / N 150 m 71 Figure 18. . 90% home ranges of 3 males ( ) and 5 females (- - -) on S.C.C. showing high overlap between and within sexes. M A Y 15-30 1979 ,Hrc \ 100 m 73 Figure 19. 90% home ranges of males ( ) and females (- - -) on the study areas during November 1978. Notice the overlap between and within sexes. 1U S . C . C . 75 TABLE 4 S t a t u s # g r i d # t i m i n g of movement,distance moved,and f i n a l fate of hares dispersing during the study. GRID LITTER STATUS SEX AGE AT DISPERSAL TIME OF DISPERSAL DIST. . MOVED (M) FATE s e c 1 m juv. July 2 8 / 7 8 850 mortality s e e 1 m juv. July 2 9 / 7 8 860 dispersed Sept. 3/78 1524 mortality s e c f ad. Nov. 12/78 2670 mortality s e c 2 f juv. Dec-Fab 460 mortality s e c 2 f juv. Dec-Feb 500 mortality s e c 2 f juv. Dec-Feb 460 removed s e c f ad. May 2 0 / 7 9 2290 unknown Tel. . 1 f juv. July 2 9 / 7 8 760 unknown Tel. , f ad. July 3 0 / 7 8 1200 mortality Tel. . 2 m juv. Sept.,2 5 / 7 8 890 mortality Tel. 2 m juv. Sept. 26/78 840 unknown Tel. 1 f juv. Oct. 3 0 / 7 8 615 dispersed ** A p r i l / 7 9 615 removed Tel. 2 f ylng Nov-Mar 1000 a l i v e Tel. f ad. May 5/79 915 a l i v e * f ad. June 2 0 / 7 9 1370 removed •caught i n peripheral traps near Telemetry Grid ••animal returned to i t s o r i g i n a l home range 76 movement, and t h e i r f i n a l fate. Included i n the table i s a female which l e f t i t s home range in late October to occupy an area 700 meters away. I t remained in t h i s location u n t i l mid-March 1979 at which time i t returned to i t s old home range. This was the only animal which showed t h i s migratory type of movement. Dispersal was primarily by juveniles but did occur i n a l l age and sex classes with the exception of adult males. This was probably due to the fact that few adult males were radio-tagged. Animals dispersed at a l l times throughout the study and moved a mean distance of 1045 meters. Of the 10 animals which dispersed prior t o May 1979 and whose fate was known, three survived to breed in 1979. Only two animals dispersed after May 1, 1979 and both survived to breed in their new range. 5.3. Discussion A wide variety of techniques have been used to define the home ranqe of an animal ( S t i c k e l 1954; Jennrich and Turner 1969 ). Each has i t s favorable and unfavorable points. I chose to use the convex polygon method because of i t s s i m p l i c i t y and h i s t o r i c a l prominence. I t s major shortcoming i s that as sample size increases so does home range si z e . To see how thi s bias affected estimates i n t h i s study I plotted home range size against the number of radio-locations used. Home range size increased with additional locations u n t i l a t o t a l of 20 were reached, at which time an increase i n locations caused l i t t l e or no increase in range s i z e . As a r e s u l t I t r i e d to use at lea s t 77 20 points for a l l home range estimates. As a futher precaution against sample size bias, a l l comparisons of home range size were made with values estimated from equal numbers of locations. The r e l a t i v e size and s p a t i a l arrangement of members of a population w i l l depend to some extent on the s o c i a l organization of that group. Knowing the s o c i a l organization of a population then, should allow one to predict the type of s p a t i a l organization of home ranges of i t s members. In turn, knowing t h i s arrangement for a species whose s o c i a l organization i s unknown should allow one to make inferences about i t s s o c i a l system* I w i l l now t r y to do t h i s for snowshoe hares. If the breeding season i s considered f i r s t , there are two basic types of s o c i a l organization shown by mammals ( Crook 1977; Jewell 1976 ). These are based on the mating systems involved and can be defined as monogamy and polygyny. In monogamous systems males mate with a single female and usually p a r t i c i p a t e in the rearing of young. One would expect home range sizes to be si m i l a r between sexes and the ranges of pairs to overlap extensively. Neither of these occurred i n t h i s study. Male home ranges were larger than females' which agrees with the findings of Bider ( 1961 ). Also, there was no association of one male with one female.. Severaid ( 1942 ) found that male hares mated with more than one female. It seems unlikely therefore, that hares have a monogamous mating system. Polygynous mating systems are those i n which males mate with more than one female. The way i n which they obtain access to additional females determines how the i r home ranges are s p a t i a l l y arranged. The various methods can be grouped i n the 78 following manner: ( 1 ) home range abandonment - Smith ( 1968 ) found that male red s q u i r r e l s abandon the i r regular home ranges during the breeding season to roam over r e l a t i v e l y large areas i n search of receptive females. In t h i s system male ranges would be extremely large during the breeding season and probably bear no relationship to the i r i n i t i a l position prior to breeding. ( 2 ) t e r r i t o r i a l polygyny - This mating system i s characterized by breeding males obtaining exclusive r i g h t s to females either d i r e c t l y by defending females against other males or i n d i r e c t l y by defending a resource required by females ( Emlen and Oring 1977 ). In either case males would show larger home ranges than females and would overlap more than one female home range. More importantly, male-male home range overlap would be minimal as a r e s u l t of males a c t i v e l y preventing other male access to females in t h e i r home ranges. A variation of t h i s type of t e r r i t o r i a l system i s one i n which males defend very small t e r r i t o r i e s through which females move i n search of mates. This i s found i n a number of ungulate species ( Jarman 1974 ). Home ranges of males i n t h i s s i t u a t i o n would be smaller than those of females. ( 3 ) dominance heirarchy polygyny - In t h i s system males gain access to females by being behaviorally dominant to other males i n the area. A dominant male would then have access to any females within i t s home range. Home ranges of males would again be larger than those of females. The 79 major difference from a t e r r i t o r i a l polygynous system would be that male home ranges would overlap both female and male ranges. Males would not exhibit exclusive areas.. ( ) promiscuous polygyny - This system would possess the same s p a t i a l organization of home ranges as the previous system. In t h i s case however, any male overlapping a female's home range would have an egual chance of mating with that female. There would be no d i f f e r e n t i a l access according to aggressive interactions between males. The s p a t i a l arrangement of snowshoe hare home ranges i s most s i m i l a r to that predicted by the dominance hierarchy or promiscuous polygyny system. Males show larger home ranges than females and there i s high male-male overlap. The f a c t that males did not maintain exclusive areas rules out the p o s s i b i l i t y of a t e r r i t o r i a l polygynous system existing. As well, the fact that males remain in th e i r pre-breeding home ranges throughout the breeding season makes the home range abandonment system unlikel y . I t i s impossible to d i f f e r e n t i a t e between dominance hierarchy and promiscuous polygyny systems on the basis of home range s p a t i a l arrangements alone.. Doing so would require behavioral or genetic data. Observations in the wild or i n large enclosures would suggest whether c e r t a i n males were dominant to others. Genetic markers could be used to determine how many females a male mates with. In a promiscuous system th i s should be r e l a t i v e l y even among males while i n a dominance hierarchy some males should do the majority of mating. The various s p a t i a l systems discussed so f a r have been related to how the male attempts to obtain mates. Unlike males, 80 female home range location should be dependent on the welfare of the offspring as well as mate selection. Females should arrange themselves then, i n a manner that allows the requirements or rearing young to be met. One of these might be a suitable p a r t u r i t i o n s i t e . Bider ( 1961 ) f e l t that female snowshoe hares were t e r r i t o r i a l just prior to p a r t u r i t i o n and Eongstad and Tester ( 1971 ) found that females contracted t h e i r home range at t h i s time. I f females were t e r r i t o r i a l during t h i s period t h e i r home ranges should show l i t t l e or no overlap. This was not the case. Percentage overlap did decrease during periods of par t u r i t i o n but s t i l l remained greater than 35%. The decrease was most l i k e l y due to the fac t that home range size decreased and consequently, the amount of overlap would be expected to decrease by chance alone. The decrease in home range size by females may have been due to decreased a c t i v i t y at t h i s time and not an attempt to avoid other i n d i v i d u a l s . However, Michener ( 1979 ) found that female Richardson's ground s g u i r r e l s did not defend t e r r i t o r i e s but contracted there range during pregnancy and were much more l i k e l y to be dominant to other animals in th e i r core area. The degree and outcome. of aggressive interactions was dependent on location then, even though exclusive areas were not maintained* Hares might behave in a si m i l a r manner. There i s a p o s s i b i l i t y that females may maintain exclusive areas during p a r t u r i t i o n but do so for only a short period of time. The weekly and biweekly periods of analysis used i n t h i s study may have been too long to detect t h i s type.of short term spacing. Determining whether or not t h i s was true would require 81 intense radio monitoring during the time each female was to give b i r t h . Enough locations could then be obtained to produce accurate estimates of heme range over shorter time periods. The s p a t i a l arrangement of home ranges remained unchanged throughout the breeding season. There was no indicati o n that either sex attempted to defend resources by maintaining exclusive home ranges. This lack of t e r r i t o r i a l spacing suggests that hares gain p r e f e r e n t i a l access to resources i n some other manner. One p o s s i b i l i t y i s the formation of a dominance heirarchy as observed by L i n d l o f ( 1978 ) i n European hares. Another explanation could be that resources are not i n short supply during periods of increasing hare numbers such as i n t h i s study. As a r e s u l t , aggressive spacing would not necessarily be apparent. Hares may i n fact, s h i f t t h e i r s p a t i a l arrangement as densities increase but only further monitoring during peak and decline years would indicate whether t h i s i s so. . Dispersal was primarily by juveniles and occurred throughout the study. There did not appear to be a s p e c i f i c time in which the majority of animals dispersed. This was sim i l a r to the findings of Windberg and Keith ( 1976 ) and suggests that factors t r i g g e r i n g dispersal do not act or change at a s p e c i f i c time. Possible factors causing juvenile dispersal w i l l be discussed in a la t e r section. Lidicker ( 1975 ) pointed out that two types of dispersal can occur i n natural populations. The f i r s t , termed saturation dispersal, occurs when populations are at carrying capacity, and emigrants of t h i s type are usually subordinate animals i n poor physical condition with l i t t l e chance of surviving* The second 82 type, pre-saturation dispersal, occurs when populations are below carrying capacity, usually during increase, and include i n d i v i d u a l s such as pregnant females which have high reproductive potential. The problem with t h i s method of describing dispersal types i s in deciding whether or not the population i s at carrying capacity. I have no data concerning t h i s question. However, hare populations on S.C.C., and Telemetry were increasing, and a number of pregnant females did show dispersal movements suggesting that some pre-saturation dispersal was occurring. I t seems that the key to deciding between these two types of dispersal i s knowing whether dispersers were forced to leave t h e i r home area or l e f t on t h e i r own accord. Data on the s o c i a l status of dispersers and non-dispersers would help to answer t h i s guestion. To summarize, high male and female home range overlap during the breeding season suggests that snowshoe hares have a promiscuous or dominance hierarchy mating system. There was no evidence to suggest that females defend p a r t u r i t i o n s i t e s as suggested by Bider ( 1961 ). Hares did not attempt to maintain exclusive areas during the non-breeding season, suggesting that resources were divided among in d i v i d u a l s by some other means. 83 6s_ FEMALE SPACING BEHAVIOR Keith ( 1974 ) stated that lagomorphs, including snowshoe hares, are "... incapable of s e l f - r e g u l a t i o n below densities determined by available food supplies." Much of the work by Keith and his associates has been aimed at elucidating the relationship between changes i n hare numbers and food supply ( Pease et a l . 1979; Keith and Windberg 1978 ).,No work has been directed toward examining the importance of behavior on these changes i n numbers. Chitty ( 1960 ) postulated that "... a l l species are capable of l i m i t i n g t h e i r own population densities without either destroying the food resources to which they are adapted, or depending on enemies or climatic accidents to prevent them from doing so." He l a t e r pointed out that t h i s l i m i t a t i o n was brought about by aggressive spacing behavior passed from one generation to the next by genetic mechanisms ( Chitty 1967 ). Further work by others has shown that both food and behavior can be linked i n complicated ways that l i m i t population numbers ( M i l l e r and Watson 1978; Watson and M i l l e r 1971; Gibb et a l . 1978 ). I t seems important then, to examine snowshoe hare behavior, p a r t i c u l a r l y aggressive spacing behavior, and i t s r e l a t i o n to population dynamics.. When the behavior of animals cannot be observed f i r s t hand, in d i r e c t methods must be employed to obtain some understanding of this factor. A number of studies have shown that removal of various types of individuals i s one such i n d i r e c t method that has proven p a r t i c u l a r l y useful ( Jenkins et al..1963; Redfield et a l . 1976 ). I used t h i s approach to answer the question: How 84 are the movements of in d i v i d u a l female hares influenced by the presence of other females? In other words does use of an area by one hare aff e c t use of that area by another? I chose females because there i s some suggestion that t h i s sex i s p a r t i c u l a r l y sensitive to other individuals just prior to p a r t u r i t i o n ( Grange 1932 ). This may be sim i l a r to t e r r i t o r i a l nest defence i n female voles as suggested by Krebs ( 1978a ).,As hare numbers increase, spacing at t h i s time may become, more and more important. To examine the influence of hares on each other's movements I removed a group of females from the Telemetry area and monitored subseguent movements of the remaining individuals. The basic design of the experiment was to: ( 1 ) radio-tag a number of adjacent females and determine t h e i r home ranges* ( 2 ) create a vacant area surrounded by radio-tagged in d i v i d u a l s by removing the innermost members of the group. ( 3 ) monitor subsequent movements of the remaining females by telemetry and compare these movements to females on a control area. One would predict no difference between the types of movement shown by control and experimental females aft e r the removal i f females had l i t t l e or no influence on each other's movements. Conversely, differences would suggest some e f f e c t . More s p e c i f i c a l l y , i f females were prevented from using areas occupied by other females one would predict that: 1. females surrounding the removal area would increase t h e i r use of that area by s h i f t i n g the boundaries of t h e i r 85 home range. 2. females may immigrate from somewhere beyond the ring of radio-tagged females and come to occupy the removal area. If females influence the movements of other females within t h e i r home ranges and do so i n a manner that causes minimal in t e r a c t i o n one would predict that females surrounding the removal area should increase use of the portion of t h e i r home range nearest the removal. 6.1. Methods In March 1979 a l l females on S.C.C. and Telemetry were radio-tagged. To increase sample size on Telemetry I began to trap the area surrounding the grid on a weekly basis. Traps were i n i t i a l l y placed on a l l sides of the grid at distances up to 350 meters away. However, after a number of days i t became clear that no animals were present on the western edge of the grid. Consequently, traps i n t h i s area were moved to places of greater hare a c t i v i t y . Any females caught i n peripheral traps or on the actual grids were radio-tagged and monitored. Each was located up to four times d a i l y ; prior to 1000 h, 1100-1700 h, 1800-2100 h, and after 2200 h. In most cases animals were active during three of these four periods. Every week traps were set on S.C.C. and Telemetry f c r two days. During t h i s time individuals were radio located only once each afternoon* This system produced roughly 20 locations per animal between trapping sessions and was followed throughout the experiment. Four females were removed from Telemetry on May 12, 1979. 86 Movements of the remaining animals were compared to females on 5. C.C. which served as an experimental control. Prior to the removal, the home ranges of 19 females on the Telemetry area and 11 females on S.C.C. were known from up to 18 days of radio locating and as many as 35 actual locations per animal. The r e l a t i v e locations of the four indiv i d u a l s that were removed can be seen in F i g . 20. These s p e c i f i c animals were chosen for the following reasons. F i r s t l y , they were located on the actual g r i d , the area i n which 1 was most confident that a l l females had been captured and radio-tagged. As well, trapping i n t e n s i t y was greatest in thi s area and thus afforded the best chances of catching any new animals immigrating. Secondly, t h i s area had supported four adult breeding females in 1978. I t seemed l i k e l y then, that i t was capable of doing so i n 1979. The animals were removed 10 days before the f i r s t l i t t e r s were born. Remaining indivi d u a l s were monitored u n t i l June 20, at which time the experiment was repeated* Results of the f i r s t removal w i l l be given before d e t a i l s of the second are outlined. 6. 2. Results 6.2-1. Removal Number One 6.2-1-1. Use of the Removal Area To test i f females increased t h e i r use of the removal area I compared the proportion of radio locations found i n the vacated area before the removal with that afterwards. Table 5 87 Figure 20. Relative locations of female home ranges on Telemetry before the removal. The dark polygon represents the area occupied by the four females (R1, R2, R3, R4) which were removed. CO oO PRE - REMOVAL TABLE 5 Changes in the proportion of locations found i n the removal area following the f i r s t removal. HARE NO. MAY 12-21 MAY 22-31 JONE 1-8 JUNE 9-20 T1 +0.45 -0.30 -0.01 +0.05 T2 + 0.10 + 0.03 -0.23 -0.14 T3 -0.0 2 -0.07 -0.07 -0.07 T4 PREDATOR KILL T5 -0. 10 -0.04 -0. 10 -0. 10 T6 + 0.15 +0.06 0.0 -0.02 T7 + 0.37 +0. 13 + 0.23 + 0.27 T8 + 0.09 +0.09 -0. 15 -0.01 T9 + 0.08 0.0 -0.06 -0.06 T10 -0.06 -0.06 -0.06 -0.06 T1 1 i l +0. 29 + 0.50 T12 0.0 0.0 0.0 0.0 T13 0.0 0.0 0.0 0.0 *T14 0.0 0.06 0.09 0.04 *T15 0.66 0.60 0.39 0. 86 *T16 0.0 0.11 0.05 0. 13 no. animals showing increase 6/11 4/11 2/12 3/12 •Proportions for these animals represent the actual proportion of locations found i n the removal area. No locations were obtained before the removal. 1 - Lost Radio Contact 90 shows the changes occurring in four successive periods following the removal. I f a l l females are considered together, use of the vacated area was never s i g n i f i c a n t l y greater after the removal ( Wilcoxon's signed-ranks t e s t , P>.05 ). However, three in d i v i d u a l s ( Hares T7,T11, and T15 ) did show substantial increases i n th e i r use of the area. A fourth, hare T1, did so for one week. Hare T15 spent the majority of i t s time a f t e r the removal in the vacated area. Unfortunately, i t s home range was not known before the manipulation. However, i t was never captured i n the removal area p r i o r to the removal.. A l l other radio-tagged females that had greater than 25% of the i r radio-locations i n the vacated area were captured at least once prior to the removal. This would indicate that hare T15 spent l i t t l e time i n t h i s zone before the removal. Hare T11 was found to have increased i t s use of the vacated area after the removal* I t may have done so sooner but i t s home range could not be determined immediately after the removal because of a malfunctioning radio. F i g . 21 shows that no noticable s h i f t in home ranges occurred after the removal. Any increase i n use was r e s t r i c t e d to the outer edges of the vacated area while the bulk remained unused. . No animal shifted i t s home range to occupy the removal area exclusively. To summarize, although a few animals showed major increases in use of the area vacated by the removal, the o v e r a l l change was not s i g n i f i c a n t and the majority of the removal area remained unoccupied. 91 Figure 21. Relative locations of female home ranges before and after the f i r s t removal. Dotted l i n e s indicate home ranges of animals newly tagged after the removal. Notice that the removal area remained unoccupied. PRE-REMOVAL T9 T8 T6 T5 T3 -K75m POST-REMOVAL -EL >T5 T12 ,4-75m 93 6.2-1-2. Home Range age Females did not s h i f t t h e i r home ranges after the removal but they may have responded by a l t e r i n g movements within t h e i r home range. If females avoid each other one would expect them to use t h e i r home ranges i n a manner that minimized i n t e r a c t i o n . I f so and some ind i v i d u a l s were removed, females would be expected to increase t h e i r use of the portion of the i r home range nearest the removal area. To test i f t h i s occurred I performed the following analysis. The 90% pre-removal home ranges of a l l females surrounding the removal area were determined. I then located the centre of the removal area and drew a l i n e from i t through the arithmetic centre of each female's home range. Perpendicular to each of these l i n e s another l i n e was drawn through the median point of each home range. This bisector served to divide the radio locations of each female's home range into halves, leaving 50% of the locations on the side of the bisector nearest the removal area. F i n a l l y , these bisectors were superimposed on each appropriate female's home range during four consecutive nine day time periods following the removal., The proportion of radio-locations on the removal side of the l i n e s were determined in each case. Table 6 shows the changes i n the proportion of radio locations found on the removal side of the bisecting l i n e . Females spent s i g n i f i c a n t l y more time on the removal side of th e i r home range i n a l l time periods except May 22-31 ( Wilcoxon matched pairs test P<.005 ), and the response increased with TABLE 6 Home range use by Telemetry females following the f i r s t removal. Values represent the proportion of locations for each animal i n the half of i t s home range nearest the removal area* Pre-removal values were equal to 0.50. HARE NO. MAY 12-21* MAY 22-31(NS) JUNE 1-8** JUNE 9-20** T1 0.92 0.05 0.43 0.42 T2 0.63 0.55 0.64 0.81 T3 1.00 0.87 1.00 1.00 T5 0.60 0.84 0.88 0.78 T6 0.89 1.00 1.00 1.00 T7 0.76 0.25 0.78 0,88 T8 0.83 0.81 0.69 0.95 T9 0.50 0.67 0.82 0.89 T10 0.14 0.?4 0.78 I T1 1 l l 1.00 1.00 T12 0.50 0.67 0.69 0.60 T13 0.81 0.42 1.00 0.83 no. animals showing 8/11 8/11 11/12 10/11 increase NS - not si g n i f i c a n t * P < . 025 ** P < . 005 l -• l o s t radio contact 95 time. One week af t e r the removal, animals were spending an average of 2055 more time on the removal side of t h e i r home range and 8 of 11 animals showed positive increases..By June 1-8 t h i s had increased to 30% and 11 of 12 animals. To test i f si m i l a r d i r e c t i o n a l changes i n home range use occurred for S.C.C. females I performed the.same analysis on these i n d i v i d u a l s . The same r e l a t i v e grid location was used as a midpoint and l i n e s were drawn to the centres of each female's home range. Table 7 shows the changes in home range use aft e r the removal on Telemetry. Use was never s i g n i f i c a n t l y d i f f e r e n t from the pre-removal period ( Wilcoxon's matched pairs test, P>.05 ). I t should be noted however, that animals on S.C.C. did show large s h i f t s i n use of t h e i r home range, but never i n any consistent d i r e c t i o n . To summarize, females did not respond to the manipulation by increasing t h e i r use of the vacated area. However, they did spend a s i g n i f i c a n t l y greater amount of time on the half of t h e i r range nearest the removal area. S.C.C. females did not show s i m i l a r changes. 6.2-1-3. Number of Immigrants Another possible response by females to the removal might be long range immigration. In other words, females other than those immediately surrounding the removal area might s e t t l e i n the vacated space. I tested t h i s by measuring the number of new adult females being caught on S.C.C. and Telemetry after the removal. The number of immigrants were si m i l a r on both grids: 96 TABLE 7 Home range use by S.C.C. females a f t e r the f i r s t removal.. Values represent the proportion of locations for each animal i n the half of i t s home range nearest the removal area. Pre-removal values were equal to 0.50. HARE NO. MAY 12-21 (NS) MAY 22-31 (NS) JONE 1-8(NS) JUNE 9~20(NS) S1 l 0. 11 0.00 i S2 0.93 1 .00 0.94 0;84 S3 0. 08 0.00 0.00 0.00 S4 1.00 1.00 0.95 0.55 S5 0. 53 0.89 0.00 0.00 S6 0. 25 0.50 0.00 0.07 S7 0. 21 0.17 0. 23 0.00 no. animals showinq 3/6 3/7 2/7 2/6 increase NS - not s i g n i f i c a n t P > .05 1 - l o s t radio contact 97 four females and four males on Telemetry and three females and two males on S.C.C. This suggests that the removal area had no influence on the number of animals immigrating. Fig. 21 shows that the new animals caught on Telemetry did not occupy the centre of the removal area but existed along i t s edges. I t i s possible that these animals were not immigrants but rather residents occupying the edge of the grid. Because they spent l i t t l e time on the g r i d , they avoided being trapped previously. 6.2-2. Results of the Second Removal On June 20, 1979, six more females were removed from the Telemetry area. As shown i n F i g . 22, the removal of these animals served to enlarge the area vacated by removal one. The remaining animals were followed u n t i l Aug..1 i n a fashion si m i l a r to the f i r s t experiment. The only differences were that s l i g h t l y fewer locations were taken each week and traps were set bi-weekly rather than weekly. Pre-removal home ranges of the remaining indiv i d u a l s were determined from radio locations taken during the 20 days prior to the second removal. Table 8 shows the changes in the proportion of time spent on the removal area following the manipulation. Changes were not s i g n i f i c a n t l y d i f f e r e n t i n any of the periods following the removal ( Wilcoxon's matched pairs test P>.05 ). Hare T20 was the only animal that showed a noticeable increase i n the use of the area. As well, no new adult females were captured i n the removal zone following the manipulation..Fig. 23 shows that the vacated area remained unused, a r e s u l t i n agreement with that of 98 F i g u r e 22. R e l a t i v e l o c a t i o n s of female home ranges on Telemetry p r i o r to the second removal. The removal area c r e a t e d by removal of animals (T1, T6, T7, T10, T11, T15) i s o u t l i n e d with heavy l i n e s . TABLE 8 Changes in the proportion of locations found i n the removal area after the second removal. HAEE NO. JUNE 20-31 JULY 1-15 JULY 16-31 T2 + 0. 11 + 0. 04 • 0.05 T3 -0.06 + 0. 03 -0 .06 T5 + 0. 04 + 0. 33 I T8 + 0.43 -0. 03 + 0.06 T9 + 0.04 + 0. 08 +0. 13 T13 -0. 03 + 0. 14 -0.03 T12 + 0.05 + 0. 09 + 0.05 T16 -0.09 1 i T14 -0.06 0. 0 -0.0 1 T1 8 +0.02 " 0. 0 + 0.03 T20 + 0.04 + 0, 19 + 0.39 *T21 0.24 0. 17 0. 17 *T19 0.0 0. 11 0.04 no. animals 7/11 7/10 6/9 showing +ve increase •Figures for these animals represent the actual proportion of locations found i n the removal area. No locations were obtained before the removal. * - l o s t radio contact 101 Figure 23. Relative locations of female home ranges before and aft e r the second removal. Notice that the majority of the removal area remained unoccupied. P O S T - R E M O V A L 103 the f i r s t removal. Table 9 shows changes in home range use after the second removal. As with the f i r s t removal, individuals showed an increase i n use of the portion of t h e i r home range nearest the removal area and, i n addition, the change increased with time. However, the o v e r a l l difference was less pronounced in t h i s instance and was s i g n i f i c a n t only during the l a s t two weeks of July ( Wilcoxon's matched pairs t e s t , P<.05 ). Table 10 shows that S.C.C. females showed no sim i l a r s h i f t s in home range during the period after the second removal on Telemtry* Females then, s h i f t e d use of the i r home range in a simlar fashion after each of the the two removals, although the response was les s pronounced following the second removal. 6.3. Discussicn In t h i s experiment I t r i e d to assess the influence of spacing behavior on female movements by removing females and monitoring subseguent movements of the surrounding animals. The u t i l i t y of t h i s design i s dependent on a number of assumptions. The f i r s t of these assumptions i s that the. vacated areas created i n each manipulation were completely free of adult females. Animals missed may have prevented other females from moving into the area. To reduce the chances of t h i s happening the removals were done i n areas of highest trapping i n t e n s i t y . No new animals were ever captured i n the middle of these areas. A l l were caught on the outer edge and subsequent monitoring by telemetry showed that they spent l i t t l e time i n the actual TABLE 9 Home range use by Telemetry females following the second removal. Values represent the proportion of locations for each animal i n the half of i t s home range nearest the removal area. Pre-removal values were equal to 0.50. HARE NO. JUNE 20-31 (NS) JULY 1-15(NS) JULY 16-AUG 1* T2 0. 75 1. 00 0.87 T3 0.36 0.90 1.00 T5 0. 42 0. 50 i T8 0.71 0. 70 0.69 T9 0.39 0. 46 0.39 T12 0.75 0. 54 0.53 T13 0. 08 0. 50 0.43 T1 4 0.29 0.27 0. 50 T16 0. 50 t I T18 0.33 0. 60 0. 50 T2 0 0. 87 0.57 0. 65 T22 0.00 0. 22 0.70 T23 l 0.83 1.00 no. animals 4/12 7/12 7/11 showing increase NS - not s i g n i f i c a n t P > .05 * P < .025 * - l o s t radio contact 105 TABLE JO Home range use by S.C.C. females following the second removal. Values represent the proportion of locations for each animal in the half of i t s home range nearest the removal area. Pre-removal values were equal to 0.50. HARE NO. JUNE 20-31 (NS) JULY 1-15(NS) JULY 10-AUG 1 (NS) S2 0.46 0. 50 0.37 S3 0.77 0. 82 0.89 S4 0.78 0.93 0. 38 S5 0.8 3 0. 42 0.63 S6 0.11 0. 00 0.75 S7 0.73 0.70 i S8 0.50 1. 00 1.00 S9 0.20 0. 50 0.45 no. animals showinq 4/8 4/8 4/7 increase NS - not s i q n i f i c a n t P > .05 i - l o s t radio contact 106 removal area. I t seems unlikely then, that trappable females at least, were missed on the removal areas. However, there i s s t i l l the p o s s i b i l i t y that trap-shy animals remained. To determine i f t h i s was true a hare drive s i m i l a r to that described by Keith et a l . ( 1968 ) was conducted prior to the f i r s t removal. People moved through the removal area attempting to drive hares into a net. The drive was conducted twice and no animals were captured. Further support f o r the contention that no trap-shy hares were present i n the area ccmes from observations made while se t t i n g and checking the trapping grids. No unradio-tagged animals were ever sighted on S.CC. where a l l animals received radio-c o l l a r s . Unfortunately, some males on Telemetry were not tagged and so one could not be sure that any animals without c o l l a r s sighted there were females. The fact that none were sighted on S.C.C. would suggest that a l l animals present on the trapping gri d f o r any length of time were captured. The second assumption i s that the removal was done at the appropriate time. The e f f e c t of spacing behavior on movement may be more important at certain times of the year. I chose the time period just p r i o r to b i r t h of the f i r s t l i t t e r because females appear to be most aggressive at t h i s time. Grange ( 1932 ) observed that females would not allow males near them prior to p a r t u r i t i o n . Rongstad and Tester ( 1971 ) suggested that female snowshoe hares contract the size of t h e i r home range prior to giving b i r t h . This may be an attempt to avoid other i n d i v i d u a l s . Haugen ( 1942 ) f e l t that c o t t o n t a i l ( Sylyilagus floridanus ) females were t e r r i t o r i a l during the breeding season and Harsden and Holler ( 1964 ) obvserved some defence of nest s i t e s . Hence 107 the time prior to par t u r i t i o n appeared appropriate for t h i s experiment. Spacing may also be important at other times of year and further experiments w i l l be necessary to examine these periods. The t h i r d assumption i s that the individuals removed were representative, in terms of s o c i a l status, of the entire population. I f for example, females were organized into a dominance hierarchy ( Lindlof 1978 ) and only subordinate animals were removed, res u l t s could be very d i f f e r e n t from those obtained i f dominant animals were removed. There i s no e f f e c t i v e way of determining i f t h i s did actually occur. However, a l l of the females removed were pregnant and showed no noticable differences i n body weight, condition, or home range size from other females i n the area. I f s o c i a l differences did exist, they were not indicated by these factors. The f i n a l assumption i s that telemetry locations give a reasonable estimate of home range location and use. The accuracy of the locations has already been discussed. The da i l y schedule of l o c a t i o n times was designed to locate animals during periods of a c t i v i t y and resti n g , thus eliminating any biases due to d i f f e r e n t i a l use of home range during each behavior. Since the locating schedule was not changed during the study any unknown biases would be similar before and after the. removal and conseguently would not have affected the re s u l t s . Females could have responded to the removal by: 1 . Increasing t h e i r use of the vacated area by s h i f t i n g the boundaries of t h e i r home range. 2 . Immigrating to the removal area from long distances 108 (beyond the group of radio-tagged females) 3. S h i f t i n g use of t h e i r home range but not changing the actual boundaries. 4. Showing no change i n t h e i r movements af t e r the removal. Females as a whole, did not increase t h e i r use of the removal area following each of the two removals. Some individ u a l s did spend more time i n the area but none showed a major s h i f t from t h e i r old home range to the area l e f t vacant by the removal. As well, no long distance immigrants came to occupy the removal area. Females appear unwilling to s h i f t t h e i r home range during the breeding season, a finding s i m i l a r to that of Windberg and Keith ( 1976 ). These authors reduced female density at the beginning of the breeding season in two successive years. In the f i r s t , a year of increase, there was no replacement during the breeding season. During the second, a peak year, females were replaced by in d i v i d u a l s from adjacent habitats. This suggests that females may be more mobile during high numbers, possibly because of increased s o c i a l interaction. It appears though, that the normal interactions between breeding females during increase years at l e a s t , are not s u f f i c i e n t to force animals to s h i f t t h e i r home range to unoccupied areas. This r e s u l t i s important i n terms of answering the question of whether behavior can l i m i t hare breeding densities. Watson and Moss ( 1970 ) outline four c r i t e r i a that must be s a t i s f i e d for t h i s to be true. The most pertinent to t h i s study i s that a substantial portion of the population does not breed.. This c r i t e r i o n i s usually considered to be true i f vacant areas created by experimental removal of breeding animals are f i l l e d 109 by other i n d i v i d u a l s which i n turn breed. This i s the case in red grouse ( Jenkins et a l . 1963 ) and i n Microtus townsendii ( Krebs et a l . 1976 ). Hares did not r e f i l l vacated areas created by experimental removal of females. This suggests that there were no i n d i v i d u a l s around that could increase t h e i r f i t n e s s by moving into those areas. In other words, there were no individuals present but not breeding because they did not have space to do so. However, t h i s i s negative evidence and as such i s open to a variety of other possible explanations. The most obvious of these i s that the removal of breeding females was done at the wrong time. Behavioral interactions may have sorted out which animals were going to breed at an e a r l i e r time. Losers may have died soon after and so were not available to colonize the removal area. I f t h i s were true though, one would expect to see an abrupt drop i n sur v i v a l when t h i s behavioral organization occurred. This study detected no such drop. Further removal experiments at other times w i l l be the only method of determining i f there i s a non-breeding surplus of animals at some time during the year or the cycle. The fact that Windberg and Keith ( 1976 ) did get animals moving into vacated areas i n a peak year suggests that such a surplus may exi s t at t h i s time. Although females did not respond to the removal by s h i f t i n g the location of t h e i r heme range they did a l t e r t h e i r actual use of of that range. I f females avoid conspecifics, they would be expected to spend more time in the portion of t h e i r home range nearest the removal area and away from other females* This i s what actually occurred. The fact that S.C.C. females showed no 110 simi l a r s h i f t s suggests that Telemetry females were responding to the removal and not to some other unknown fac t o r . The s h i f t i n home range use by Telemetry females was less pronounced after the second removal. Many of these had already shifted a large portion of th e i r a c t i v i t y to the removal side of t h e i r home ranges after the f i r s t removal. I t would be d i f f i c u l t then, for the animals to s h i f t a c t i v i t y even more without actually moving the boundaries of t h e i r home ranges. As previously pointed out, females were unwilling to do t h i s . To conclude, female spacing behavior during the breeding season does not influence the actual location of an animal's home range. This seems to be set prior to the breeding season and subseguent changes i n density have no e f f e c t . However, females responded to the removal experiment i n a manner which suggests they u t i l i z e t h e i r home range i n a way that avoids int e r a c t i o n . 111 Is. EFFECT OF ft DOLT FEMALES ON JUVENILE MOVEMENTS AND SURVIVAL One of the few common agreements among people working on small mammal population dynamics i s the important influence of juvenile s u r v i v a l on changes in population numbers (Krebs and Myers 1974; Keith and Windberg 1978 ). However, the factors c o n t r o l l i n g juvenile survival are largely unknown. Keith and Windberg (1978 ) point to the influence of juvenile s u r v i v a l , p a r t i c u l a r l y from summer to midwinter, on changes in snowshoe hare numbers. Survival they f e e l , i s determined by the a v a i l a b i l i t y of woody browse i n winter. However, the e f f e c t of the s o c i a l milieu i n which juveniles exist has not been examined. As a f i r s t step i n t h i s d i r e c t i o n I examined the influence of adult females on juvenile movements and s u r v i v a l during f a l l and winter. Females have been shown to influence dispersal of juveniles i n a number of species including pikas (Smith 1974 ), ground s q u i r r e l s (Sherman 1977 ) and voles (Redfield et a l . 1978 ). I removed adult females from an area durinq the l a t e breeding season and monitored juveniles on t h i s area as well as on a control. This experiment allows a number of predictions from s p e c i f i c hypotheses to be tested. They include: 1. Females force juveniles to disperse into areas free of adults. If so t h i s would be r e f l e c t e d by the removal area having: (a ) fewer juveniles dispersing (b ) greater rates of ingress 2 . Females aff e c t juvenile survival rates. Rates then, 112 should d i f f e r between control and manipulation areas. 3. Females influence use of an area by juveniles.. This would be reflected by juveniles on the removal area s h i f t i n g t h e i r home ranges after the manipulation. No differences between the removal and control areas would indicate either that females were unimportant i n determining juvenile survival and movements or that changes were not detected by my methods. 7. 1. Methods Juveniles were trapped on the two study areas, Telemetry and S.C.C. Animals having a weight greater than 500 g were radio-tagged and located twice d a i l y . Monitoring continued u n t i l Oct.. 1st, 1978 a f t e r which animals were followed intermittently with intensive locating periods i n l a t e November 1978 and l a t e February-March 1979. Grids were trapped weekly from May 1, 1978 to Oct. 1, 1978. Traps were also set once i n October, twice in l a t e November and weekly i n March. On August 14, 1978 the four adult females present on Telemetry were removed by trapping or shooting. The s u r v i v a l rates and movements of a l l juveniles caught at least once on either g r i d before the removal were monitored by trapping and telemetry. S.C.C. was used as an experimental control. 113 7.2. Results 7,2-1. Survival and Dispersl A t o t a l of 32 juveniles were equipped with r a d i o - c o l l a r s . The fates of these animals a f t e r the removal can be seen i n Table 11. Sexes were combined to increase sample size. There were no s i g n i f i c a n t differences between the two grids i n number s t i l l a l i v e , number dying on the g r i d , or number dispersing. Also survival rates of a l l animals live-trapped at least once before the removal were not d i f f e r e n t between grids either ( X2,P > .05 ). There was some suggestion that the number of animals leaving Telemetry was higher (6 vs 3 ) but small sample sizes prevented meaningful comparisons. The number of new animals caught on the grids after the removal was used as a measure of ingress. Results i n Table 12 show that the number of ingressors was never s i g n i f i c a n t l y d i f f e r e n t on the two grids ( X 2,P > .05 ). Results i n Tables 11 and 12 then, provide no evidence that adult females influence the s u r v i v a l rate or long distance movements of juveniles during early f a l l to spring. 7.2-2. Changes in Home Range The home ranges, as determined by telemetry, of f i v e juveniles on S.C.C. and four juveniles on Telemetry were known before and after the removal. Figs. 24 and 25 show that there TABLE 11 Fates of radio-tagged juveniles caught on S.C.C. and Telemetry at l e a s t once before removal of adult females. Figures cover time period from Aug 14-Mar 31 1979. S.C.C.. TELEMETRY NO. ALIVE ON GRID 6 5 NO. DISPERSING 3 6 NO. DYING ON GRID 7 5 TOTAL 16 16 TABLE 1 2 Number of untagged animals captured on each grid after removal of adult females on Telemetry. AUG14-OCT1/78 0CT1-DEC1/78 DEC1/78-MAR31/79 M F M F W F _ _ _ _ _ _ _ _ _ _ _ _ _ _ — _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ S.C.C. 12 11 4 4 4 0 TEL. 15 10 9 5 1 1 116 Figure 24. Home ranges of juvenile snowshoe hares on Telemetry showing no change i n location before ( ) versus a f t e r (- - -) the removal of adult females. Home ranges of ind i v i d u a l animals are not in r e l a t i o n to each other. 117 o5m 118 Figure 25. Home ranges of juvenile hares on S.C.C. showing no change in location before ( ) versus after (- - -) the removal of adult females on Telemetry. Home ranges of i n d i v i d u a l animals are not i n re l a t i o n to each other. 119 85m 120 were no s h i f t s i n any of these ranges following the manipulation. Additionally, some knowledge of the whereabouts of juveniles caught before the removal but not radio-tagged could be determined by trapping r e s u l t s . These animals were l a t e r radio-tagged and subsequent monitoring showed that t h e i r pre-removal points of capture were never outside t h e i r post-removal home ranges. The above suggests that removal of adult females on Telemetry had no e f f e c t on movements of juveniles i n that area. However, changes i n the amount of overlap between juveniles and adult home ranges on S.C.C. suggests that some interaction may have been occurring. Figs. 26 and 27 show the r e l a t i v e locations of the trapping grids and juvenile and adult female home ranges in both study areas prior to the removal. Juveniles overlapped adults considerably in each case. There were major differences in the location of adult females' home ranges r e l a t i v e to the trapping grids. Females on Telemetry were located d i r e c t l y on the grid while those on S.C.C. spent much more time in the surrounding area. This s i t u a t i o n was consistent throughout the e n t i r e breeding season. Fig.. 28 shows that juvenile-adult overlap on S.C.C. decreased st e a d i l y throughout late August and September* As more and more juveniles were radio-tagged on the grid i t appeared as though they were avoiding areas occupied by adult females. Again, telemetry showed no s h i f t i n home ranges to cause the decreased overlap. Juveniles had already chosen the unoccupied areas by the time they were f i r s t radio-tagged. To summarize, there were no detectable differences i n survival rates or movements between juveniles on S.C.C. and 121 Figure 26. Relative locations of 5 adult female ( ) and 5 juvenile ( - - - ) heme ranges on S.C.C.. The trapping grid i s represented by the dark l i n e s . Notice the small proportion of adult ranges en the g r i d . 1 0 0 m 123 Figure 27..Relative locations of adult female ( ) and juvenile ( - - - j home ranges on Telemetry. The trapping grid i s represented cy the dark l i n e s . Notice the c e n t r a l location of adult ranges r e l a t i v e to the trapping grid. 125 Figure 28. Home ranges of 5 adult females ( ) and 10 (- - -) juvenile hares on S.C.C. showing low overlap throughout la t e August and September. The trapping grid i s represented by the dark l i n e s . 1 2 6 AUG 15-31 197o SEPT. 1 5 - 0 C T . 1 1978 100 m 127 Telemetry after the removal of adult females on Telemetry. This suggests that adult females had l i t t l e influence on these parameters. The small amount of overlap between juveniles and adults on S.C.C. however, indicates that the location of juveniles might be determined by females at a time prior to radio-tagging. ,7» 3. . Discussion Results of the above experiment indicate that females had no detectable effect on the sur v i v a l and movements of juveniles during the l a t e breeding season. The possible reasons for t h i s outcome w i l l now be discussed. The f i r s t of course, i s that the above conclusion i n correct. Other factors such as food (Keith and Windberg 1978 ) or adult male behavior (Healey 1967 ) may be more important at thi s time. It i s also possible that female e f f e c t s may become more important during peak and decline portions of the cycle. Removal experiments at t h i s time would indicate whether t h i s i s so. Females may influence juvenile movements each year but at times other than the l a t e breeding season. In many mammals weaning i s often a time when juveniles are forced to leave t h e i r parents' home range (Smith 1974 ). In t h i s study the above i s suggested by the fact that juveniles and adult home ranges on S.C.C.. overlapped very l i t t l e . Movements to reduce overlap, which i n i t i a l l y must have been 100%, were done by juveniles since radio-telemetry revealed that adults did not s h i f t t h e i r home range. As well, these movements had to occur before 128 juveniles were radio-tagged as no tagged animals showed s h i f t s . The peculiar arrangement of adult females r e l a t i v e to the S.C.C. trapping grid created a si t u a t i o n where juveniles had to leave t h e i r mothers' home range before they could be captured. Later monitoring by telemetry then, merely revealed that they did not return once they had l e f t . The f a c t that home ranges of the two groups remained d i s t i n c t suggests that some int e r a c t i o n was occurring even i n lat e f a l l . Why then, did the experimental r e s u l t s show that adult females did not influence juvenile movements? The answer may be related to one of the underlying assumptions involved i n the experiment. I t was assumed that prior to the removal, juveniles and adults had overlapping ranges on both the experimental and control areas.. Removal of adult females on Telemetry then, would create a s i t u a t i o n where Telemetry juveniles were free frcm adult female interaction but S.C.C, juveniles were not. However, as shown i n Fig. 26, S.C.C. juveniles occupied areas free of adult females. After the removal, juveniles on both grids existed i n areas free of adults. Therefore neither group was experiencing pressure from females i n the same area. As a r e s u l t , even i f adult females were important, the prediction of differences i n juvenile movements between the two grids would not be born out. It appears then, that the question of the importance of adult females on juvenile s u r v i v a l and movement durinq the f a l l and winter remains unresolved. Some juveniles leave t h e i r mother's home ranqe at weiqhts less than 500 g and come to occupy areas free of adult females.,These two groups continue to 129 exi s t in d i s t i n c t areas throughout the f a l l . Experiments involving removal of adult females e a r l i e r i n the breeding season would provide answers as to whether juveniles are forced by females into these vacant areas or move on t h e i r own accord. Si m i l a r l y , r e p l i c a t i o n of the experiment in t h i s study, but with a control area where the juveniles overlapped adult females, would provide more conclusive evidence as to the importance of adult females on juvenile survival and movement. 130 8.. SPACING BEHAVIOR AND SNOWSHOE HARE POPULATION DYNAMICS This study was designed to examine snowshoe hare spacing behavior, an aspect of the animal's ecology which has received l i t t l e attention and could be important i n understanding hare population dynamics..Three guestions were posed at the outset of the study. They were: 1. What i s the s p a t i a l arrangement of snowshoe hare home ranges? Home ranges overlapped extensively between and within sexes throughout the year. Neither sex showed any type of t e r r i t o r i a l organization. I t i s possible that a dominance heirarchy i s involved i n mate selection and resource a l l o c a t i o n . 2. Is female spacing behavior during the breeding season important i n determining the location and use of neighboring animal's home ranges? Changes in density did not a f f e c t the home range location of adult females. Animals were unwilling to s h i f t t h e i r home range from areas of high overlap to areas vacated by removal of breeding females. However, females did use t h e i r home range i n a manner that seemed to reduce interaction with neighbors. 3. Do adult females influence the movement and survival of juveniles? The answer to t h i s question i s not clear. Experimental removal res u l t s suggested that adult females' had no influence on 131 juveniles. However, the lack of overlap between juvenile and adult female home ranges during the f a l l suggests that some juveniles leave t h e i r parent's home range to occupy areas free of adults. This movement may occur p r i o r to the time animals can be radio-tagged. How do the above results r e l a t e to snowshoe hare population dynamics? This question i s best examined i n l i g h t of theories that attempt to explain the snowshoe hare cycle..The f i r s t and most prominent of these i s that proposed by Keith ( 1974 ). He hypothesized that snowshoe hare cycles are caused by two in t e r r e l a t e d predator-prey interactions. F i r s t l y , as hares near peak numbers they begin to overbrowse t h e i r winter food supply. This overbrowsing causes damage to the plants and results i n reduced plant growth. Food shortage for the hares re s u l t s i n lower rates of reproduction, adult, and juvenile s u r v i v a l . These combine to i n i t i a t e the hare decline. Predator populations, which have b u i l t up with r i s i n g hare densities, act at t h i s point to speed up and extend the decline phase. This allows the vegetation to recover but predator numbers, which decrease with lower hare numbers soon reach a point at which hare densities are allowed to increase once more. The key to Keith's hypothesis i s the hare-vegetation i n t e r a c t i o n . Spacing behavior i s considered unimportant, possibly having a minor role in terms of i n t r a s p e c i f i c competition f o r food. I f food supplies were abundant ( eg. during increasing numbers ) Keith's hypothesis would predict that spacing behavior should have l i t t l e influence on home range location. In other words, i f i n d i v i d u a l s were removed, as in 132 th i s study, there should be no replacement by surrounding in d i v i d u a l s . Results from this study are i n accordance with t h i s prediction. An alternative hypothesis to that of Keith would be one which incorporates behavior as an important component i n snowshoe hare population dynamics. Watson and Moss ( 1970 ) outline a hypothesis whereby spacing behavior l i m i t s breeding densities by preventing seme individ u a l s from breeding. This hypothesis would predict that removal of breeding females should be followed by replacement with animals that otherwise would not have bred. Results of t h i s study do not support the Watson and Moss ( 1970 ) hypothesis. However, the p o s s i b i l i t y s t i l l e x i s t s that numbers were limited at a time other than the one considered in t h i s study. Perhaps t h i s occurs during a season other than that studied here or possibly only during peak or decline phases of the cycle. Another behavior hypothesis i s that proposed by Chitty ( 1967 ) which also contends that numbers are li m i t e d by spacing behavior. Chitty goes on to point out that t h i s behavior i s under genetic control and subject to rapid selection. This means that during increasing numbers l e s s aggressive genotypes are favored while i n decline phases aggressive indivduals gain an advantage. One of the predictions of the Chitty hypothesis i s that spacing behavior w i l l be l e s s intense during increasing as compared to declining populations ( Krebs 1978b ). This could possibly explain why females were not forced i n t o the area created by the experimental removals i n t h i s study. Similar removals during peak and decline phases of the cycle are needed. 133 Work has shown that juvenile s u r v i v a l and movements are important to the population dynamics of snowshoe hares. The Keith hypothesis contends that changes i n these factors are brought about by changes i n food a v a i l a b i l i t y . The influence of spacing behavior remains unresolved. Results i n t h i s study suggest that seme juveniles leave t h e i r parent's home range to occupy areas free of adults. Questions s t i l l remain as to the mechanism that causes these movements and whether dispersers experience s u r v i v a l rates similar to those i n d i v i d u a l s which remain i n t h e i r parent's home range..Windberg and Keith ( 1976 ) postulated that juveniles dispersing during peak and decline years were forced to leave th e i r i n i t i a l home range because of i n t r a s p e c i f i c competition for food. However, i t i s d i f f i c u l t to believe that t h i s occurs during periods of increase when food supplies are adeguate. As pointed out by Lidicker ( 1975 ) dispersal might be a matter of choice rather than necessity during increase years. A l t e r n a t i v e l y , juvenile dispersal might be a function of adult aggressiveness which changes with phases of the cycle in a manner proposed by Chitty ( 1967 ). Deciding between these alternative explanations requires a thorough knowledge of an ind i v i d u a l ' s movements throughout i t s l i f e t i m e . Studies of dispersal to date have been hindered by the fact that the whereabouts of an i n d i v i d u a l are unknown for large portions of i t s l i f e t i m e . In the case of snowshoe hares nothing i s known about i n d i v i d u a l movements between b i r t h and the time of f i r s t trapping. As suggested by t h i s study, important movements may occur during t h i s time and because of present technigues, go unnoticed. These, as well as l a t e r long distance 134 movements must be taken into account i f the relationship of dispersal to population dynamics i s to be understood. To conclude, t h i s study serves as an i n i t i a l investigation of snowshoe hare spacing behavior and i t s r e l a t i o n to the animal's population dynamics. As such, i t has provided a better understanding of the s p a t i a l organization of hares and points to the need for continued work, especially i n terms of the relationship of behavior to juvenile movements and s u r v i v a l . Results of experiments during the study f i t the predictions of the Keith ( 1974 ) hypothesis more closely than they do alternate hypotheses incorporating behavior as a mechanism which l i m i t s numbers ( Watson and Moss 1970 ). However, i t must be stressed that t h i s work examined behavior during only one phase (increase) of the snowshoe hare cycle. The p o s s i b i l i t y e x i s t s that spacing behavior could be very different during peak and decline years and suggests the need for continued examination of spacing behavior during these periods. 135 LITERATURE CITED Adams, L. 1959. An analysis of a population of snowshoe hares i n Northwestern Montana. Ecol. Monogr. 29: 141-170. Bider, J.B. 1961.. An ecological study of the hare Lep_us americanus. Can. J. Zool. 39: 81-103. Boag, D.A., A. Watson, and B. Parr. 1973. Radio-marking versus back-tabbing red grouse. J. Wildl. Manage. 37: 410-412. . Brand, C. J . , R. H. Vowles, and L. B. Keith. 1975. 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Weather influences on the onset of breeding in Missouri c o t t o n t a i l s . J. Wildl. Manage. 25: 87-89. Windberg, L.A. and L.B. Keith. 1976. Experimental analysis of dispersal i n snowshoe hare populations. Can. J . Zool. 54: 2061-2081. 

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