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UBC Theses and Dissertations

Social and spatial organization of Vancouver Island cougar (Puma concolor vancouverensis, Nelson and… Hahn, Apryl M. 2001

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SOCIAL AND SPATIAL ORGANIZATION OF VANCOUVER ISLAND COUGAR (Puma concolor vancouverensis, Nelson and Goldman, 1943) B y Apryl M . Hahn B.Sc. , The University of British Columbia, 1993 A THESIS S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R OF S C I E N C E in T H E F A C U L T Y O F G R A D U A T E S T U D I E S (Department of Animal Science) We accept this thesis as conforming to required standard T H E 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 November 2001 © A p r y l M . Hahn, 2001 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date DE-6 (2/88) A B S T R A C T Vancouver Island is noted for having the highest concentration of cougar-human interaction in North America, yet prior to this study, little scientific data were available on the only subspecies of cougar to occur on Vancouver Island. I studied a cougar (Puma concolor vancouverensis) population in coastal temperate rainforests on southeastern Vancouver Island, British Columbia. Initiated in 1991 and conducted during 1993 - 1996, my study examined home range characteristics, dispersal, recruitment, population structure and density. Mean size (61 km) of annual home ranges of female cougar was as small or smaller than reported in other studies. Male home ranges were exclusive and overlapped several resident females, a social structure that is typical of most studied populations. Dispersal of young was male-biased in my study with all young males dispersing from the study area and included the first scientifically documented occurrence of a cougar swimming from Vancouver Island to adjacent G u l f Islands. In contrast, all known female offspring remained within the study area and provided the only identified source of recruitment into the resident female population. Subadult females displayed 100% philopatry establishing home ranges that overlapped or were immediately adjacent to their natal home range. Recruitment of female offspring continued irrespective of increasing density in the final 2 years of the study. Cougar densities (5.0 /100 km 2 ) , documented in the final year of the study, were among the highest recorded densities in North America. Observed densities were characterized by small home ranges with considerable home range overlap among resident female cougar. Indices of deer abundance were insufficient to explain the high density of cougar or small size of home ranges. Only 2 types of mortality were identified in this population. Animal control kil ls contributed most (58%) to cougar mortalities and was l ikely attributable to the close proximity o f the study to human populated areas. Intraspecific ki l l ing accounted for 80% of remaining mortality or 33% of total mortalities. The high density and level of intraspecific strife observed in this cougar population are characteristic of a population regulated by social interactions and may suggest that social interactions were a regulatory factor in my study population. in T A B L E O F C O N T E N T S Abstract i i Table of Contents iv List o f Tables v List o f Figures v i Acknowledgements v i i I N T R O D U C T I O N 1 S T U D Y A R E A 5 M A T E R I A L S A N D M E T H O D S 6 Capture 6 Relocation with Radio Telemetry 7 Home Range Analysis 8 Juvenile Dispersal 9 Subadult Home Range Establishment 10 Population Structure and Density 11 Mortality 12 R E S U L T S 13 Home Range Characteristics 13 Home Range Size 13 Home Range Shifts 15 Home Range Overlap 15 Juvenile Dispersal, Philopatry and Recruitment . 18 Mortality 22 Population Structure and Density 23 D I S C U S S I O N 24 Home Range Characteristics 24 Effect of Reproductive Status on Home Range Size 25 Home Range Overlap 27 Juvenile Dispersal and Philopatry 29 Population Structure and Density 32 Mortality and Intraspecific Behaviour 34 Population Regulation 36 L I T E R A T U R E C I T E D 38 iv LIST O F T A B L E S Table Page 1 Mean seasonal and annual home range sizes (100% M C P ) of resident male and female cougars in Northwest Bay on Vancouver Island, B C , 1 9 9 2 - 1996 13 2 The effect reproductive status on mean size of seasonal ranges (km 2) of female cougars in Northwest Bay on Vancouver Island, B C , 1992 - 1996. . . 15 3 Annual estimated population structure and minimum density of cougars in Northwest Bay study area, Vancouver Island, B C , 1993 - 1996 23 4 Mean size o f home ranges of cougars from studies that reported home ranges in a similar manner, presented in order of increasing size of female home range. Data were modified from Hemker et al. (1984) and expanded to incorporate recent studies 26 5 Estimated densities (residents, transients and juveniles) of cougars from studies that reported densities in a similar manner, presented in order of decreasing density 33 v LIST O F FIGURES Figure Page 1 Location o f Northwest Bay study area on Vancouver Island, British Columbia, Canada 4 2 Individual mean and standard deviation of annual home range sizes (km 2) of 13 resident cougars in Northwest Bay, Vancouver Island, B C , 1 9 9 2 - 1996 14 3 Examples of shifts in location and size of annual home ranges (100% M C P ) of 2 adult female cougars in Northwest Bay, Vancouver Island, B C 16 4 Overlap of annual home ranges among all radio-collared resident cougars in Northwest Bay, Vancouver Island, B C , 1995 - 1996 16 5 Overlap of annual home ranges among all radio-collared resident cougars in Northwest Bay, Vancouver Island, B C , 1993 - 1994 17 6 Onset of site fidelity marked the transition from subadult to adult home ranges for 4 non-dispersing female cougars, as determined by the mean squared distance versus time relationship 20 7 Philopatric home range relations within 1 family group o f cougars, Northwest Bay, Vancouver Island, B C a) Mother (F3) - daughter ( F l ) home range relations, over the years 1991 - 1992 21 b) Philopatric relations of F3 and her female offspring ( F l , F6 & F13) from 3 sequential litters, over the years 1995 - 1996 21 8 Causes of mortality for the different sex-age classes ( M = male, F = female) o f cougar in Northwest Bay, Vancouver Island, B C , 1992 -1996 22 vi A C K N O W L E D G E M E N T S This research was supported by Habitat Conservation Trust Fund (HCTF) , a G R E A T scholarship from Science Council of British Columbia, British Columbia Ministry of Environment, Lands, and Parks ( M E L P ) , MacMi l l an Bloedel Limited, TimberWest Limited, B C Hydro, and the Department of Animal Science of the University of British Columbia. For logistic support, I thank G . Brunham, D . Janz, M . M c A d i e , and T. Hamilton of M E L P , as well as J. Connors, J. Eden, and R. McLaughl in o f MacMi l l an Bloedel Limited in Nanaimo, R. Will ington and D . Lindsay of TimberWest Limited in Crofton, J. Maher of B C Hydro in Nanaimo, B C and Maureen Wayne of H C T F . M y thanks to all who helped me in the field: my incredibly capable field assistants, Joanne Leo, Denise Koshowski, Mandy Kellner, Aaron Gladders and Karen Goh; and volunteers, Benoit Roberge, Roger Ramcharita, G w y l l i m Blackburn, Gideon - for good fortune in finding kil ls , and Robin - for the hilarity. Thanks to my pilot, Don Brown o f Vi ta l Aviation. Many thanks to the houndsmen who gave their time and effort: Ted Barsby, Ted Chappell and the B team: Danny Judson, Dean Cook, and especially Clem Ingram - for keeping the pace reasonable. Special thanks to Gerry for his support and good companionship in the field and to David - for just everything. Both Shack and Dr. Al ton Harestad provided valuable editorial comments. Finally, thanks to my friends and family for endless moral support and encouragement. This thesis is dedicated to the memory of the late Knut Atkinson, who conceived and supported this project from its inception. INTRODUCTION The cougar (Puma concolor, Linnaeus 1758) is a large felid widely distributed but restricted to the New World (Hall 1981). It ranges from latitudes of 60° N in North America through Central America to 55° S at the tip of Tiera del Fuego in South America. Across this wide range, cougars occupy a diversity of habitats from forests and mountainous desert to grassland communities. A s many as 27 subspecies are recognized throughout its broad geographic and ecological distribution (Anderson 1983). Historically in North America, cougar occurred from coast to coast, but its eastern distribution is now restricted to a threatened population in Florida. Today in North America, the cougar primarily inhabits western and south-central regions. Cougar have been studied over much of their range, but most studies have been located in western North America (Seidensticker et al. 1973, Ashman et al. 1983, Hemker et al. 1984, Ross and Jalkotzy 1992, Beier and Barrett 1993). The bulk of this research has examined population characteristics, particularly social organization and space use. Throughout the cougar's range, both males and females are solitary and only females support their offspring for between 9 and 21 months (Anderson et al. 1992, Ross and Jalkotzy 1992). Both sexes occupy home ranges and males typically overlap several females (Seidensticker et al. 1973, Logan and Irwin 1985, Laing 1988). However, it is uncertain whether or not cougars are territorial. Part of this confusion arises from reports of extensive home range overlap at least among resident females (Seidensticker et al. 1973, Neal et al. 1987, Ross and Jalkotzy 1992). Some authors (Hornocker 1969, Logan et al. 1986, Ross and Jalkotzy 1992), though they provide no quantitative evidence, suggest that animals still actively avoid each other despite spatial overlap. It has been further proposed that social interaction through this 1 "mutual avoidance reaction" (Hornocker 1969:462) acts to regulate resident population density at levels below that set by prey abundance alone (Seidensticker et al. 1973, Lindzey etal. 1994). Most studies of cougar have found that all young disperse when independent of their mothers. Seidensticker et al. (1973) and Logan et al. (1986) suggested that juvenile dispersal is independent of adult density, whereas Ross and Jalkotzy (1992) think the non-dispersal o f female offspring was unrelated to adult density, possibly because their population had not reached "carrying capacity". Just 2 studies (Ross and Jalkotzy 1992, Laing and Lindzey 1993) have reported evidence of philopatry where female offspring established ranges adjacent to their mothers'. In other studies where it has been investigated, subadults have dispersed beyond the study areas (Hemker et al. 1984, Beier 1995, Spreadbury et al. 1996). Reports on cougar population density have varied widely, partly because various methods are used to estimate density (Anderson 1983). Differences also l ikely reflect the diverse habitats, exploitation rates of the studied populations, and differences in prey type and abundance. Only 3 previous studies have been long enough to adequately describe population structure (Seidensticker et al. 1973, Ross and Jalkotzy 1992, Lindzey et al. 1994-) and the results have varied. Resident adult density is generally stable, particularly male density, whereas juvenile and transient (cougars that move through an area without returning) numbers fluctuate. Difficulty in detecting both these components of a population, as well as the normal annual variation in number of kittens (Lindzey et al. 1992) may contribute to this variability. Cougars are both widespread and numerous in British Columbia (BC) , with 3 subspecies recognized (Cowan and Guiguet 1965). British Columbia is also where most 2 cougar-human interactions have been reported in North America (Beier 1991). One subspecies occurs only in B C - the Vancouver Island cougar (P. c. Vancouverensis). Movement of cougars between Vancouver Island and the Mainland is unlikely because of the distance across channels and straits. Hence, it is the only subspecies of cougar restricted to a large island with little possibility of genetic interchange with the Mainland. Like the adjacent mainland subspecies, it inhabits dense coastal forests, where large mammal prey diversity is probably lower than anywhere else in the cougar's British Columbian range. Prior to my study, only 1 other study of cougars had been conducted on Vancouver Island. Initiated in 1972, it produced 2 brief progress reports, but detailed findings were not released. Despite a lack o f scientific data, it has always been assumed that cougar densities on Vancouver Island were among the highest in the species' range. The goal of my study was to f i l l gaps in our knowledge of this subspecies and to help provincial wildlife officials better manage and conserve cougars on Vancouver Island. One particular concern on Vancouver Island was a higher than usual proportion of females (50 %) in the hunter harvest (D. Janz, M E L P , pers. comm.). M y specific objectives were to study: social organization and space use; dispersal of young; and population structure and density. I concentrated my research on females for 2 reasons. First, as is typical of polygynous mammals, only females rear the young and hence are a key factor in population demographics. Second, the adult sex ratio is usually highly skewed with fewer males than females (Seidensticker et al. 1973, Hemker et al. 1984, Logan et al. 1986, Beier and Barrett 1993, Lindzey et al. 1994) and males usually have larger home ranges than females. Both of these considerations make it more difficult to study males with a limited budget and personnel. 3 STUDY A R E A The Northwest Bay Cougar Study ( N W B ) was located on eastern Vancouver Island and centred 25 km northwest of the City of Nanaimo. I defined the study area boundary based on the composite home ranges of the maximum number of radio-collared cougars. The 525 k m 2 area (Figure 1) encompassed the Englishman River watershed and extended into the adjacent Nanaimo and Cameron River drainages. The rural-urban Township of Errington and the coastal communities of Parksville and Nanoose bounded the eastern half of the study area to the north and northeast. Elevations range from sea level to 1817 m on M t . Arrowsmith, with the majority of mountainous terrain being under 1000 m a.s.l. Topography varies from flatlands to steep-sided slopes, although most are not deeply incised. The study area primarily falls in the rain shadow of the mountains on Vancouver Island. A t lower elevations, the climate is characterized by warm, dry summers and mild, moist winters. Snowfall is limited and rarely lingers for more than a few days at a time. A t higher elevations, snow accumulates and snowpacks persist throughout the winter (Meidinger and Pojar 1991). Three forested biogeoclimatic zones (Klinka et al. 1991) occur within the study area. Most of the area is comprised of the Coastal Western Hemlock ( C W H ) zone. The Coastal Douglas F i r (CDF) zone occupies a narrow strip bordering the coastal communities and extending inland to about 150 m a.s.l. The Mountain Hemlock ( M H ) zone is restricted to higher elevations on ridges and mountaintops, generally above 900 m a.s.l. Stands of Douglas fir (Pseudotsuga menziesii), in various secondgrowth stages, dominate the forest cover over most of the study area. Douglas fir is predominant in secondgrowth forests of the region because this species was used for reforestation of 5 clearcuts. Western hemlock (Tsuga heterophylla) and western redcedar (Thuja plicata) are typical secondary tree species in N W B ' s secondgrowth, although they are the dominant species in naturally regenerated and recently reforested areas of the C W H and M H zones. Salal (Gaultheria shallon) and Oregon grape (Mahonia nervosa) dominate the understory vegetation, except in receiving sites where swordfern (Polystichum munitum) and bracken (Pteridium aquilinum) prevail. Heavy shrub cover consisting primarily of red alder (Alnus rubra), oceanspray (Holodiscus discolor), and various Rubus species characterize highly disturbed sites, stream edges, and areas of poor conifer regeneration. Private lands within the study area have been extensively logged with some logging of secondgrowth already completed. Small amounts of active logging occurred throughout the study period. M A T E R I A L S AND M E T H O D S Capture Untagged cougar were detected by searching for tracks after fresh snowfalls. Usually two separate capture teams were employed, each with a biologist and up to 3 experienced houndsmen. Trained hounds would typically pursue a cougar until it sought refuge in a tree. Treed cougar were immobilized with a mixture of medetomidine hydrochloride ( M H C L ) and ketamine hydrochloride ( K H C L ) administered by remote dart injection. Intended doses were 0.08 mg M H C L /kg and 2.75 mg K H C L /kg of estimated body weight with a 10 mg M H C L / m L and 100 mg K H C L / m L mixture. A standard 2 m L injection of long-lasting penicillin was given intramuscularly to reduce the possibility of infection in the dart wound. Atipamezole hydrochloride was administered to reverse the effects of the 6 medetomidine at a dosage of 0.15 mg/kg body weight. I observed animals were until they were able to walk away. Recovery times varied from 4-35 minutes. Longer recovery times occurred when external stimuli were minimal. Captured cougar were sexed, weighed and ear-tagged, had body measurements taken and blood sampling attempted. Eruption, wear and colouration of teeth were used to estimate ages (Ashman et al. 1983). Cougar were fitted with radio-collars (Telonics Inc., Meza, A Z ) . A l l radio-collars were equipped with mortality sensors that caused the pulse rate o f the transmitters to double after 4 hours of inactivity. Beginning with the 1994-95 capture season, female cougar were fitted with colour-coded radio-collars refurbished to include an activity sensor. Relocation with Radio Telemetry Ground telemetry provided 80% of relocation data. I attempted to relocate each cougar every 1-4 days during all daylight hours and occasionally at night; however, there were 32 occasions when consecutive relocations for individual cougars were separated by >15 days. Ground monitoring was conducted with a receiver or scanner-receiver and a single, hand-held " H " antenna (Telonics Inc. and Lotek Engineering Inc.). Relocation points were determined by triangulating >3 compass bearings. Locations were recorded on 1:20 000 T R I M maps and assigned Universal Transverse Mercator ( U T M ) co-ordinates. The U T M system is a rectangular co-ordinate system used to place a point on the earth's surface between 80° S latitude and 84° N latitude (White and Garrott, 1990). Aerial telemetry supplemented ground relocations throughout the study, but prior to October 1995, it was used only to locate missing animals. Additional funding in the final year of fieldwork permitted aerial reconnaissance of radio-tagged cougar about twice per 7 month. Aer ia l telemetry was conducted from a 172 Cessna equipped with a Geographic Positioning System (GPS) and two outfacing Lotek H-antennas. A scanner-receiver was used for signal reception (Telonics Inc. and Lotek Engineering Inc.). I used aerial photographs together with the U T M co-ordinates provided by the GPS unit to place each cougar's aerial location onto T R I M maps (Terrain Resonance Imaging Maps). I assessed telemetry error by searching for concealed transmitters and comparing known and estimated (triangulation) locations of activity sites (e.g., feeding site). Accuracy of aerial locations was within 100 m. Estimated ground locations were within 50 m of the known site when fixes were obtained at close range (<200 m) and within 100 m at distances <500 m. Home Range Analysis Where applicable, terminology of cougar social organization follows Seidensticker et al. (1973). Resident cougars were breeding members of the adult population that limited their movements to predictable areas of use. I divided dependent young into 2 age categories: kittens (0-6 mo) and juveniles (from 7 mo to when they became independent of their mothers). Subadults were newly independent cougars that did not restrict their activities to any particular area. I considered subadult cougars to be residents when they began to exhibit site fidelity (see Subadult Home Range Establishment below). I used the minimum 100% convex polygon method ( M C P : Mohr 1947) to define home range boundaries. I chose this method because it has been used consistently in previous cougar work (Seidensticker et al. 1973, Hemker et al. 1984, Logan et al. 1986, Ross and Jalkotzy 1992, Beier and Barrett 1993). I believe M C P provides an adequate interpretation of the data given the small sample sizes obtained, which precluded using more complex and possibly more meaningful methods of home range analysis. 8 I estimated annual home ranges, and 2 seasonal ranges - summer and winter. Analysis of annual home ranges was based on a biological 12-month period (April-March) rather than a calendar year. I defined the summer (April-October) and winter (November-March) seasons to correspond with those recognized for deer habitat use on Vancouver Island (Nyberg and Janz 1990). Home range areas were calculated using the program C A L H O M E (Kie et al. 1994). I examined the variability in home range sizes for cougars radio-collared >1 year by comparing a cougar's first estimate of annual home range size to each subsequent year. Home range overlap was defined as the percentage of 1 cougar's home range area that was included within another's (Ross and Jalkotzy 1992), and total range overlap as the non-additive percentage o f a female cougar's home range that was overlapped by other resident female neighbours. I included 2 females ( F l and F14) recaptured in January 1996 in the final year of home range analysis. Female N o . l was supporting 2 large male juveniles when she was recaptured 22 months after her radio transmitter failed. I think her reproductive status and fidelity to previously calculated home ranges are sufficient to infer her continuous presence in the study population. Female No. 14 was similarly recaptured in association with young following 2 captures in 1994, first as a juvenile and later as an independent subadult. Juvenile Dispersal Most dispersal data were collected incidentally. I attempted to remove radio-collars as soon as juvenile males demonstrated signs of dispersing, so dispersal was largely documented through hunter returns and animal control complaints. I estimated dispersal distances by measuring the straight-line distance between the centre (x,y) o f a dispersing cougar's natal home range and its reported recapture or k i l l site. I defined 9 direction of dispersal as the angle created by the trajectory of the straight-line distance from the central point o f the natal range. Subadult Home Range Establishment A n animal's home range is defined as the area traversed by the individual in its normal activities of food gathering, mating and caring for young (Burt 1943). I was interested in studying when subadults left their mothers and established their own home ranges. Subadult cougars typically travel over large areas when first independent (Seidensticker et al. 1973), so to classify a subadult cougar as a resident, I needed to determine when a subadult shifted from patterns of exploration to the predictable movements exhibited by adult females. I regarded a subadult cougar to have established a resident home range when it began to exhibit site fidelity. Following Weir (1995), I quantified site fidelity using the mean squared distance ( M S D ) of successive sets of locations (Calhoun and Casby 1958), with each set comprised of 6 consecutive locations. M S D is calculated by averaging the squared distances of a set of x-y points from each set's arithmetic centre. In 2 dimensions, it is a measure of the dispersion of points (in this case, locations) from the calculated centre (Weir 1995). A s the distance between consecutive locations decreases, the squared distance of each location from the central point w i l l also decrease. The M S D of successive locations w i l l , therefore, be high for a subadult cougar exhibiting little site fidelity, and w i l l decrease as the animal restricts its movements to a particular area. Comparing the M S D from successive sets of locations provided a quantifiable measure of the site fidelity exhibited by each subadult female cougar. A subadult's first 6 locations, when it no longer associated with its mother, comprised the initial set. I generated 10 each successive set by including the next location in time and dropping the first. In this way, each set shared 5 locations with the previous set. I considered a subadult to be exhibiting site fidelity when the value of the M S D , from consecutive sets of locations, declined and stabilized. I subjectively determined the change from subadult to resident status by visually assessing the M S D versus time relationship for each subadult female. I defined the establishment of a resident home range as beginning with the onset of site fidelity and the date of home range establishment to be the first date from the set of locations when site fidelity became apparent. I used all locations ensuing from the date of range establishment to estimate their resident home range. Population Structure and Density I estimated population structure and density following each capture season for the years 1993 to 1996. Estimates were based on captures, radio-tagged cougars and confirmed dependents. Two cougars were conditionally included in the population estimate on the basis of tracks alone, and in each case, I presented only the higher estimate of density. I classified independent female subadults as adult residents when they produced young (i.e., the following year). Resident females with failed radio transmitters were included in the estimate when they were subsequently recaptured and reproductive evidence supported their continuous presence in the study area. Capture opportunities and, therefore, captures were consistently limited by low snowfall, especially in the easternmost region of the study area. I do not think all cougars within the study area boundaries were accounted for. However, I think the recapture of 6 resident cougars on 10 separate occasions following radio transmitter failure suggests a considerable proportion of the population were identified. Climatic conditions, particularly 11 lack of snow, also prevented an estimation of the unmarked portion of the population. Hence, I have used the term "minimum density" because assumptions for population estimates (Krebs, 1989) could not be met in my study area. I calculated density by dividing the total estimated number of cougars by the size of the study area. Because study area was based on composite home ranges, I used home ranges calculated for the subsequent year when adult females accompanied by young were captured for the first time. In 1994, F10 was captured in the eastern part of the study. Inclusion of her home range expanded the study area boundaries almost to the Strait o f Georgia. Part of the decline in cougar density that year was due to this change in boundary because she resided in an area where little home range overlap was observed. Mortality We attempted to necropsy all cougars found dead with the exception of those kil led by hunters or by Conservation Officers ( M E L P ) responding to animal control complaints. I observed while a qualified veterinarian performed the necropsies on 3 of the 5 cougars found dead to determine cause of mortality. I think intraspecific strife was the probable cause of death for 1 of the remaining 2 dead cougars because wound patterns were similar to those on the necropsies I assisted with. The body of the last was too decayed for cause of death to be identified. 12 R E S U L T S Home Range Characteristics A total of 25 cougars, 14 female (F) and 11 male (M), were radio-collared and monitored for periods ranging from 1-42 months between 1991 and 1996. Approximately 1200 locations were recorded. I estimated annual home ranges for 13 different cougars (11 F, 2 M ) over 1-4 years of monitoring and 18 seasonal ranges for 9 female cougars (Table 1). The mean number o f radio locations used to calculate annual, winter, and summer home range sizes was 32 (range = 20-69), 23 (range = 20-25), and 28 (range = 20-44), respectively. Table 1. Mean seasonal and annual home range sizes (km 2) of resident female and male cougars in Northwest Bay on Vancouver Island, B C , 1992 - 1996. Winter Summer Annual Female Female Male 41 61 186 14.3 13.9 67.4 9 11 2 22 -60 4 0 - 94 139 -234 Female SE 15-7 n 5 Range 3 1 - 6 6 Home Range Size Annual home ranges of adult females varied from 40 - 94 k m 2 (Table 1). This variability declined when I was able to estimate home range size over multiple years. In this case, mean annual home ranges varied from 40 to 69 k m 2 (Figure 2). Annual home ranges were larger for resident males (x - 186 ± 67 k m 2 , n = 2) than for resident females (x =61 ± 14 k m 2 , n - 11) (Mann Whitney U = 22, P = 0.05). 13 Figure 2. Individual mean annual home range sizes (km 2) o f 13 resident cougars in Northwest Bay on Vancouver Island, B C , 1992 - 1996. 270 F11 F2 F1 F4 F7 F14 F3 F8 F6 F10 F13 M1 M7 Increasing size of mean home ranges by sex I found no differences in size of seasonal home ranges. Winter home ranges (Table 1) varied from 31 - 66 k m 2 and did not differ from summer home ranges of 22 to 60 k m 2 (Wilcoxon Signed Rank T = 7, P > 0.50, n = 5). However, both summer and winter ranges were smaller than the mean annual range (T = 1, P = 0.01). There were insufficient locations to estimate male seasonal home ranges. A female's reproductive status influenced her home range size. Females accompanied by kittens (Table 2) had smaller seasonal ranges than lone females (U = 19, P = 0.05). The seasonal home ranges of females with juvenile dependants were neither larger than those of females with kittens (U = 18, P = 0.10) nor smaller than lone female home ranges ( U = 14, P > 0.20). 14 Table 2. The effect of reproductive status on mean size of seasonal ranges (km 2) of female cougars in Northwest Bay, Vancouver Island, B C , 1992 - 1996. Size of home range (km 2) With kittens With juveniles Lone x 29 47 52 S E 7.8 14.4 9.2 n 5 4 4 Range 2 2 - 4 2 25 - 79 40 - 60 Home Range Shifts The perimeter outline of all home ranges shifted from one year to the next for both females (Figure 3) and males. However, variation in size of home ranges showed no consistent pattern or direction of change. Seven of 13 female home ranges were 17 - 49% smaller in size than the first year that a home range was calculated, with 5 of 7 reductions in home range size occurring in the year kittens were born. Otherwise, 5 home ranges increased by 3 - 59% and 1 home range did not change in size. Home Range Overlap I found extensive home range overlap amongst females and for males with females, but no overlap between males. A single female's range characteristically overlapped between 2 - 6 other resident females each year (Figure 4). Spatial overlap between individual pairs of female neighbours ranged from 1 - 78% of a female's annual home range (3 - 78% in 1993-94 and 1 - 60% in 1995-96). In total, females tolerated 13 to 90% of their home range being used by other female neighbours (x = 59%). Although spatial overlap was considerable, temporal overlap was not apparent (Wilson et al., submitted). I did not observe any pair of neighbours within 200 m of one another at the same time. 15 Figure 3. Examples of shifts in location and size of annual home ranges (100% M C P ) of 2 adult female cougars in Northwest Bay, Vancouver Island, B C . F7's Annual Home Ranges, 1993 -1996 F4's Annual Home Ranges, 1992-1995 • - - 1 9 9 2 - 9 3 • - 1 9 9 3 - 9 4 * - 1 9 9 4 - 9 5 400 402 404 406 408 410 412 414 416 U T M * (km) 386388390392394396398400402 UTM (km) * The U T M or Universal Transverse Mercator system is a rectangular co-ordinate system with units in meters, which places a point on the earth's surface (White and Garrott, 1990). Figure 4. Overlap of home ranges among all radio-collared resident cougars in Northwest Bay, Vancouver Island, B C , 1995-1996. 5465000 5460000 5455000 UT M (m) 5450000 5445000 5440000 5435000 —* -M7 Study area 380000 385000 390000 395000 400000 405000 410000 415000 420000 425000 UTM (m) 16 Male home ranges appeared to be exclusive throughout the duration of the study. Only 2 resident males were monitored during a single year (1994-95). M l , captured in 1992, gradually shifted his home range south over a 3-year period. B y March 1995, he no longer travelled within the study area. M 7 was captured late in 1994. He travelled primarily in the eastern half of the study area with occasional forays to the northwest (see Figure 4). In the winter of 1995, tracks indicated the presence of a second male west of M 7 ' s range, but we were unable to capture him and thus confirm continued residency. Both adult males' home ranges overlapped a number of resident females. In 1993-94, M l overlapped 6 of 7 females known to occur within the study area and occupied 0.2 - 98% of the females' home ranges (Figure 5). He was located with each female of reproductive age (n = 5) at least once, including one whose home range he overlapped by <1% (the 6th female did not have her first litter until the following year). In 1995-96, M 7 ' s home range overlapped 1 - 100% of the home ranges of 7 of 8 resident females (Figure 4), and his home range extended into areas of no capture effort where he may have overlapped more females. Figure 5. Overlap of home ranges among all radio-collared resident cougars in Northwest Bay, Vancouver Island, B C , 1993 - 1994. 384000 386000 388000 390000 392000 394000 396000 398000 400000 402000 404000 406000 408000 410000 412000 UTM (m) 17 Juvenile Dispersal, Philopatry and Recruitment Fourteen radio-collared females produced 18 litters with a total of 35 kittens identified (17 M , 11 F, 7 Unknown). Sixteen of the kittens survived to independence (9 M , 7 F); 9 (6 M , 3 F) were kil led as juveniles (0.6 -1.5 years) while still with their mothers. Six young were still dependent at the study's end (2 M , 4 Unknown). The fates of 4 of the kittens are unknown. A l l o f the 9 young males captured in the study area and surviving to independence dispersed from the study area. Radio-collars were removed from 2 young males that left N W B . Three others were kil led within 1 year of dispersal (1 by a hunter and 2 by animal control). We monitored the movements of 1 male for 5 months following his dispersal from the study area. A l l radio-collared subadults dispersed between the months of March and June. Direction dispersed showed no bias for 5 out of 9 dispersing males. Chronologically, subadult males dispersed N W (320°), S W (230°), SSE (160 °), N N W (330°) and E S E (105°). Dispersal distances for subadult males were 17 km, 102 km, 98 km, 63 km and 53 km, respectively ( x = 67 km). Information is lacking for the other 4 males. I identified 11 female young born to resident cougars during the study and most showed a high degree of philopatry when they established their own home ranges. A l l subadult females known to have survived (n = 5) remained in the study area and established home ranges that were either adjacent to, or included part of, their natal range. In the first year of independence, they used from 42 - 88% of their mother's home range. Three juvenile females were kil led before reaching independence; 1 by another cougar, 1 by a hunter (occurred during the hunting season immediately following the study's end), and 1 by animal control shortly after her mother met the same fate. O f the 3 remaining females, 2 were 18 establishing independence as the study ended and I was unable to monitor their subsequent movements or possible recruitment into the study population. The fate of the third was undetermined, however, it is possible she died because her mother was located and believed to be mating with the resident male prior to the juvenile's expected age of independence. I defined a subadult home range as the total area bounded by a subadult female's outermost locations following her last known association with the mother until the onset of site fidelity. Site fidelity was determined from the M S D versus time relationship (Figure 6), which indicated when a female began to restrict her movements. Philopatry, quantified by degree of home range overlap between mother-daughter pairs, refers to a daughter's resident home range, not her subadult range. Each of the subadult females that established residency within the study area associated intimately with their natal home range when first independent. Female No . 1 used 88% of her natal home range as a subadult. Females No . 6 and 13 similarly occupied 78% and 53% of the maternal home range, respectively. Female No. 11 used 42% of her natal range and inhabited a relatively small home range as a subadult. I was unable to calculate a subadult range for F14, however, as an adult she occupied 60% of F7's home range. Female No. 3 had 3 separate litters during the study period and provided the strongest evidence o f philopatry. A female from every litter was recruited into the resident study population. Each of the female offspring in turn established a home range that initially overlapped part of their mother's home range. Female N o . l , from F3's first documented litter, established residence east of her natal home range (Figure 7a). Home range overlap continued between these two cougars even when they both produced subsequent litters. Over the years, however, F l gradually eliminated all natal range use by shifting her home range 19 Figure 6. Onset of site fidelity marked the transition from subadult to adult home ranges for 4 non-dispersing female cougars, as determined by the mean squared distance ( M S D ) versus time relationship. A subadult female's last known association with her mother determined when M S D was first calculated. 20 Figure 7. Philopatric home range relations within 1 family group, Northwest Bay, Vancouver Island, B C . a) Mother (F3) - daughter (FI) home range relations, over the year 1991 - 1992. 5456000 5454000 5452000 5450000 E. S 5448000 5446000 5444000 5442000 5440000 -392 V - * ' F3 (Maternal) — - F I (Subadult) X 000 394000 396000 398000 400000 402000 404000 406000 408000 410000 UTM ( m ) b) Philopatric relations of F3 and her female offspring (FI , F6 & F13) from 3 sequential litters, over the year 1995 - 1996. 5458000 5456000 5454000 5452000 5450000 ? E 5448000 l-5446000 5444000 5442000 5440000 5438000 / * s / t > \ I t i 4 - . s \ \ * % # t 1 1 "AX ^ * * \ * * * * \ * K -v * 1 \ S * V 1 ^ * \ \ v * V - » \ \ 1 F3 Mother —«- - FI 1st litter —*- - F6 2nd Utter . . . . . F13 3rd litter i i i X * * • 388000 390000 392000 394000 396000 398000 400000 402000 404000 406000 408000 410000 412000 414000 4160001 UTWI(m) _ further east and north. Female No . 6 established her home range in the southeast of her natal area squeezing between F l and F3. Female No . 13 established a home range to the northwest that included 38% of her natal area. Altogether, the home ranges of F3's female offspring almost encircled the maternal home range (Figure 7b). Mortality I documented 12 deaths of cougars during the study period (Figure 8). Juveniles sustained the highest losses with 5 males and 2 females dying. Adult females accounted for the remaining deaths. Depredation of livestock led to 58% of the mortalities through animal control by Conservation Officers. Dependent juveniles from 2 family groups were kil led by animal control for similar depredations on livestock within days of their mothers' deaths. Intraspecific strife caused the deaths of 3 juveniles (2M, IF) and 1 adult female accounting for 33%> of the known mortality. One adult female died of unknown causes. Figure 8. Causes of mortality for the different sex-age classes ( M = male, F = female) of cougar in Northwest Bay, Vancouver Island, B C , 1992 - 1996. c •> "° 3 (0 o> 3 u 2 o z Adults Juveniles 1 M M I I Intraspecific strife • Animal Control • Unknown 22 Population Structure and Density The total number of known cougars in the study population ranged from 14 to 25 (Table 3). O f the annual totals, each year 6 to 10 (40 - 47%) of the known cougars were classed as resident adults, 7 to 14 (45 - 56%) as dependent offspring, and only 0 to 2 (0 -10%>) as independent subadults (Table 3). Min imum density estimates remained relatively constant over the 4 years, ranging from 3.4 to 5.0 animals/100 k m 2 for all cougar and from 1.6 to 2.2 cougars/100 k m 2 for adult residents (Table 3). The similarity in density of adult cougars during 1993 and 1996, despite an increase in total known population, was due to calculating the size of the study area based on composite home ranges. Using a fixed study area boundary (see Figure 1 or 4), total cougar density ranged from 2.9 - 5.0 cougars/100 k m 2 and adult density varied from 1.3-2.1 cougars/100 k m 2 . Table 3. Annual estimated population structure and minimum density of cougars in Northwest Bay study area, Vancouver Island, B C , 1993 - 1996. ( M = Male, F = Female, U = Unknown). Resident adults Independent subadults Dependent young Total known Total Adult density density (cougars/ (cougars/ Year M F Total M F U Total M F U Total pop'n 100km2) 100km2) 1993 1 7 8 0 0 o - i a 0-1 4 2 2-3 a 8-9 17 4.5 2.1 1994 1 5 6 0 1 0 1 4 3 0 7 14 3.4 1.6 1995 2 7 9 0 2 0 2 6 3 0 9 20 4.2 1.9 1996 l - 2 b 9 10-11 0 0 0 0 8 4 2 14 25 5.0 2.2 3 Refers to tracks of one cougar associating with F3's family b One independent male known to be present 23 DISCUSSION Home Range Characteristics A s reported by others (Ross and Jalkotzy 1992, Beier and Barrett 1993), I found that female home ranges (100% M C P ) were significantly smaller than those of males. Average male home ranges in my study area were 3 times larger than those of females. This was similar to the 2-4.5 times difference observed by others (Seidensticker et al. 1973, Logan et al. 1986, Ross and Jalkotzy 1992, Spreadbury et al. 1996). Although not usually reported, I also observed annual variation in the boundaries of home ranges. This probably reflects, at least in part, the methods we used to define boundaries and estimate spatio-temporal movements of animals. The annual home ranges of adult females in my study area were as small or smaller than those in other studies presenting data for more than 1-year's fieldwork (Table 4). The only study reporting home ranges markedly smaller than what I observed was from southeastern British Columbia, and most ranges were only for a 1-year period (Spreadbury et al. 1996). Southeastern B C is known for its high diversity and number of ungulates (Shackleton 1999) so it is possible that prey availability was higher than in my study area where there are only 2 species of ungulates, Columbian black-tailed deer (Odocoileus hemionus columbianus) and Roosevelt elk (Cervus elaphus roosevelti). A more likely explanation is that Spreadbury et al. (1996) used a different method to calculate annual home ranges, which could account for the unusually small ranges they reported. They removed large areas of concentrated human activity from the cougars' home ranges. They considered cougars did not use these areas, but presented no evidence that cougars avoided these areas. Contrary to this finding, data from my study and from Beier and Barrett (1993) suggest that 24 cougars w i l l frequently use areas with high levels of human activity, which includes entering large urban areas. Interestingly, Spreadbury et al. (1996) is 1 of only 2 studies to report no home range overlap among female cougars, although they state this could also be an artefact of their methodology for estimating home range size. The other study to report exclusive female home ranges was located in northern California. Hopkins et al. (1986) suggest their unusual result was due to their small sample size of just 2 females. A pregnant female, kil led in the middle of 1 of their female's ranges, supports this interpretation because cougars do not generally reproduce until they have secured a stable home range (Anderson 1983). Effect of Reproductive Status on Home Range Size I found that females accompanied by kittens (0-6 months o f age) occupied significantly smaller home ranges than did lone females, and slightly smaller home ranges than females with juveniles. Only Ross and Jalkotzy (1992) reported similar changes in home range size with reproductive status, but they found home ranges used by females with kittens were significantly smaller than females with or without juveniles. Females, on average, give birth to young every 2 years (Anderson 1983). N o alternating trend in home range sizes mirrored this reproductive pattern, so changing reproductive status alone cannot explain variations in female home range size. Beier and Barrett (1993) reported that females moved kittens to refuges such as canyons or draws that were not used by other conspecifics. I found no evidence of this behaviour. Perhaps the main reason for the smaller home ranges is that very small kittens are less mobile than older dependents, so female movements are restricted by their youngs' low mobility. 25 Table 4. Mean size of home ranges of cougars from studies that reported home ranges in a similar manner, presented in order of increasing size of female home range. Data were modified from Hemker et al. (1984) and expanded to incorporate recent studies. Male home range (km 2) Female home range (km 2) Location Size SE Size S E Reference Southeastern B C 1 3 0 - 1 7 2 55 25 Spreadbury et al. (1996) Northwest Bay, Vancouver Is., B C 186 67 61 14 This study California 82 - 328 6 6 - 7 1 Hopkins et al. (1986) Wyoming 269 - 370 5 4 - 9 1 Logan et al. (1986) Western Alberta 334 37.1 140 13.7 Ross and Jalkotzy (1992) Nevada 616 161 Ashman (1981) Adam and Eve Rivers., Vancouver Is., B C — 258 36 Goh (2000) Idaho 453 268 45 Seidensticker et al. (1973) Utah 826 685 257 Hemker et al. (1984), Lindzey et al. (1994) 26 Home Range Overlap My findings, like those of most others (Seidensticker et al. 1973, Logan et al. 1986, Ross and Jalkotzy 1992, Spreadbury et al. 1996), show that 1 male overlaps the home ranges of several females. The ratio in NWB of 1 male overlapping 6 or more females was similar to populations on northern Vancouver Island (Goh 2000) and in Alberta (Ross and Jalkotzy 1992) but higher than the more common reports of 1 M : 2-4 F (Hemker et al. 1984, Logan et al. 1986, Spreadbury et al. 1996). Only in California was the reverse found, that is, exclusive female ranges overlapping those of several males (Hopkins et al. 1986). Most studies report overlap among both male and female home ranges. Degree of overlap among males varies from "minimal" (Hornocker 1969, Logan et al. 1986, Laing 1988) to "extensive" (Sitton 1977, Hopkins et al. 1986). Only Ross and Jalkotzy (1992) quantified overlap, reporting 12 and 20% as the respective overlap between 2 males. Most researchers have adopted Seidensticker et a/.'s (1973) theory that the spacing and density of resident cougars operates through a non-aggressive land tenure system. However, Seidensticker et al. (1973) did observe resident males entering other males' home ranges. They suggested these movements were either exploratory, or in response to receptive females. Male home ranges in NWB were exclusive and I found no evidence that a resident male moved into another male's area. I found considerable home range overlap among females each year. Overlap reported in other studies ranges from >40% (Ross and Jalkotzy 1992) up to 100% (Neal et al. 1987). Others merely report that overlap was "extensive" (Seidensticker et al. 1973, Logan et al. 1986). Spatial overlap would suggest female cougars are not territorial, however, they could still be avoiding each other temporally. Most researchers suggest cougar exhibit a "mutual 27 avoidance reaction" described by Hornocker (1969:462). However, analysis of data from my study and another on Vancouver Island (Wilson et al. submitted), showed that despite considerable spatial overlap there was neither avoidance nor attraction between neighbours. So why do adult female cougars seem to have such a high degree of conspecific tolerance? Based on my observations of home range establishment by subadult females, I suggest that the high degree of overlap could be because many neighbours are related. I found that all surviving female subadults established home ranges that either overlapped with or were immediately adjacent to those of their mothers (see next section). Only 2 previous studies mention philopatry (Ross and Jalkotzy 1992, Laing and Lindzey 1993), while others do not even suggest it may be occurring because they report that all subadult offspring dispersed out of the study areas (Seidensticker et al. 1973, Hemker et al. 1984, Logan et al. 1986). Unlike female cougars, males seem to be less tolerant of each other. As discussed earlier, male home ranges usually show little or no overlap, and in my study, although I know neither the identity nor sex of the individuals responsible, I found 2 cases where other cougars killed young males. Other researchers (Lindzey et al. 1988, Ross and Jalkotzy 1992, Spreadbury et al. 1996) have reported similar findings. I suggest that, because female cougars are induced ovulators (Kitchener 1991), it should pay males to guard females. Given the absolute size of even the smallest females' home ranges, it would be difficult for a male to effectively guard several females with other males in the vicinity. Males may therefore resort to exclusive territories that they defend aggressively. Adult weight is attained between the ages of 2 and 4 years (Currier 1983). At the time they disperse, subadult males on average weigh 30% less than adult males (Maehr and Moore 1992), so adults are likely, able 28 to dominate younger males. Based on facial scarring and mutual avoidance, Ross and Jalkotzy (1992) suggested male cougars in Alberta exhibited territorial behaviour. In California, where space is extremely limited by encroaching human development, Beier and Barrett (1993) suggested that exclusive home ranges among adult males provided evidence of territoriality. Beier (1995) also interpreted erratic behaviour by dispersing juveniles as attempts to avoid conflict with territorial adult males. In my study, male home ranges appeared to be exclusive, scars suggested fighting among males, and a substantial percentage of mortality was caused by injuries inflicted by other cougars. Despite this circumstantial evidence, there were too few resident males to infer that males in N W B are territorial. Juvenile Dispersal and Philopatry A l l known subadult males left the study area i f they were not kil led while still in it. This is consistent with all other reports of dispersal by male cougars. In my study, most males moved either generally north or south. I did not detect males dispersing west and the Strait o f Georgia effectively bounded the study area to the east. Dispersal distances are, in part, determined by body mass and diet type (Sutherland et al. 2000). The mean dispersal distance for subadult males in my study (67 km) was less than the average o f 85 k m reported in most previous studies (Anderson et al. 1992:61, 66), but comparable to studies where cougar habitat was fragmented or limited. In California, males dispersed a similar mean distance of 63 km (Beier 1995). In Florida, where viable habitat was limited, mean dispersal distance for males was 59 km (Maehr et al. 1991). The longest recorded distance (102 km) dispersed by a subadult male from my study area approached or extended beyond Vancouver Island's coastline in all compass directions except northwards. 29 Subadult male No. 9 was monitored for 5 months following his dispersal from the study area. He initially travelled southeast following the Nanaimo River valley, then moved generally east until he reached Northumberland Channel. Within 2 days, he swam to Gabriola Island, a minimum distance of 1000 - 1600 m. He remained there for about 1 month before crossing the short (250 m) but turbulent passage to Valdes Island, where prey were abundant and humans scarce. Unfortunately his appetite for domestic sheep led to him being killed by a Conservation Officer. Despite previous anecdotal reports, this is the first documented occurrence of cougars swimming to BC's Gulf Islands. The pattern of female dispersal was in marked contrast to that of males. I found 100% philopatry; all known subadult females (n = 5) remained in the study area after becoming independent. A l l subadult females established their own home ranges and initially occupied part of their mothers' home range. When shared use of the maternal home range continued, overlap was between 38 - 60%. Although dispersal of both male and female juveniles is most commonly reported (Seidensticker et al. 1973, Hemker et al. 1984, Logan et al. 1986, Beier 1995, Spreadbury 1996), recent reports document some female juveniles failing to disperse. In Alberta, 7 of 19 subadult females established home ranges adjacent to, or in some cases overlapping, the home range of the maternal female (Ross and Jalkotzy 1992), however, degree of overlap was not quantified. The replacement of resident females by daughters, or by daughters of adjacent neighbours in Utah, resulted in "clusters of related females with overlapping home ranges" (Laing and Lindzey 1993:1057). In Colorado, Anderson et al. (1992) reported 2 non-dispersing females. The overlap that I observed between the home ranges of mothers and daughters continued when the mothers had new litters, and when the independent offspring had litters 30 of their own. In one case, the boundary shifted, but remained immediately adjacent to its mother. This shift occurred when a younger sibling from a subsequent litter left the mother and established its home range between the maternal home range and its older sibling. A daughter from a 3 r d litter of this same mother established a home range that occupied part of a deceased neighbour's home range. Her home range overlapped the maternal home range by almost 40% and, to a lesser degree, her older sibling's. Philopatry has been shown to increase reproductive fitness in bushy-tailed woodrats by increasing survival of a daughter's first litter (Moses and Millar 1994). I think philopatry could enhance fitness of female cougars in 2 ways. First, it allows females to reproduce at a younger age. Hornocker (1971 in Anderson, 1983) believed "a female will not breed until she is established on a territory". Home range establishment is likely most rapid when independent-aged offspring are recruited into a population. Lindzey et al. (1993) found that vacancies were filled faster by daughters of residents than by immigrants. Second, establishing a home range in a familiar area likely increases survival of female progeny by allowing them to avoid the risks associated with dispersing and establishing a home range in unknown areas. Beier (1995) and Anderson et al. (1992) found that few dispersers survived to establish stable home ranges. The introduction of an unknown female into the study population coincided with 2 daughters (FI 1 and F14) establishing home ranges. Subsequent evidence of intraspecific strife may indicate resident females in NWB rarely tolerate unfamiliar cougars and that offspring are preferentially recruited into cougar populations. I suggest that relatedness increases tolerance among female cougars. 3 1 Population Structure and Density All 31 independent cougars captured and radio-collared on the study area remained in the study area except the 1 adult male that, over a 5-year period, gradually shifted his home range south. Based on these observations, I have no evidence of transients in the NWB population. This may reflect my difficulty in detecting cougars during periods of inconsistent snowfall at lower elevations, or simply that capture of cougars occurred prior to immigration of transients. Movements by dispersing subadult males typically peak during spring (Gerry Brunham, MELP, pers. comm.) while few dispersers (ca. 20%) survive to establish stable home ranges (Anderson et al. 1992, Beier 1995). Consequently, transient cougars would not likely be present during the following winter capture season. The adult sex ratio in NWB varied from 1 male to 3.5-7 females, which is high compared to other populations (1:2 - Seidensticker et al. 1973 and Lindzey et al. 1994; 1:2 to 1:3- Logan et al. 1986, Ross and Jalkotzy 1992). The NWB population was largest in 1996, due to an increase (real and apparent) in resident females. Successful reproduction by the 2 female offspring newly recruited into the population, and more complete enumeration of dependent young, accounted for most of this increase. Adult density was slightly higher in 1996 than levels documented in 1993. Recruitment of female offspring continued throughout the study's duration, irrespective of increasing density during the last 2 years. Similar to findings by Ross and Jalkotzy (1992), I suggest non-dispersal of females may be independent of density. Cougar densities in NWB were higher than in most study areas (Table 5). However, these are minimum estimates; I probably missed one or two cats (both tracks and sightings support this assertion), so cougar densities in my study area may be the highest so far 32 recorded. Why my study area supports such high densities is uncertain. There was no apparent correlation between deer abundance and the observed differences in cougar density on Vancouver Island (Wilson et al, submitted). However, available prey data are poor and indices may be unreliable in areas of mature secondgrowth forests. I would still expect prey to be the main reason for the high density I observed and discuss this further in the next section. Table 5. Estimated densities (residents, transients, and juveniles) of cougars in order of decreasing density from studies that reported densities in a similar manner. Location Density Reference (cougars/100 km2) Idaho 2.1 -7.4 Seidensticker et al. (1973) Northwest Bay, Vancouver Is., BC 3.4 -5.0 This study Wyoming 3.4 -4.5 Logan etal. (1986) California 3.5 -4.4 Sitton(1977) Southeastern BC 3.5 -3 .7 Spreadbury et al. (1996) Arizona 3.2 -3.5 Shaw (1977, 1979) Alberta 2.7 -3.3 Ross and Jalkotzy (1992) Colorado 1.7 -3.3 Currier et al. (1977) California 1.5 -3.3 Hopkins etal. (1986) Adam and Eve R., Vancouver Is., BC 1.4 -2.0 Goh2000 Nevada 1.4 -1.6 Ashman (1981) Utah 0.3 -0.5 Hemker et al. (1984), Lindzey etal. (1994) 33 Mortality and Intraspecific Behaviour Mortalities claimed between 6 and 21% of the known population each year. Annual mortality in NWB was comparable to reports from both hunted (0-27% - Logan et al. 1986, 3-14% -Ross and Jalkotzy 1992) and unhunted (5-15% - Spreadbury et al. 1996) populations, but less than that reported by Lindzey et al. (1988), where annual mortality of resident adults averaged 28% in an unharvested population. Sport hunting is the greatest source of mortality in harvested populations (Anderson 1983) and could limit cougar populations (Ross and Jalkotzy 1992). High hunting and animal control mortality for 2 years prior to the study on northern Vancouver Island might have contributed to the lower density of cougar observed there (Wilson et al. submitted). Although hunters refrained from killing radio-collared cougars during my study, sport hunting undoubtedly contributes to mortality under normal conditions. Two adult females and 2 older juveniles from the study population were all harvested late in 1996 after my study ended. Lindzey et al. (1992) found that losses due to hunting may be additive to other natural mortality. However, cumulative effects of hunting in NWB are likely mitigated by years with low snowfall when hunting success is reduced. I documented only 2 types of mortality during the study - animal control and intraspecific. The high proportion (58%) of animal control kills was due to the complete removal of 2 family groups each with 3 members. Intraspecific killing caused 80% of natural mortalities, resulting in the deaths of 3 juvenile cougars and 1 adult female. Two of these were cannibalised. Unfortunately, I could not identify the surviving combatants. Spreadbury et al. (1996) believed a relatively non-aggressive land tenure system facilitated spacing of residents but noted that transient males were aggressive, actively following each other and 34 also preying on kittens. Cannibalism on young by mature males is not uncommon in the literature (Hornocker 1970, Sitton 1977, Hemker et al. 1986). I suggest that a newly-established male or transient cougar, rather than resident, may have been responsible, because cannibalism of one's own progeny would reduce the fitness of a resident male. A male was also implicated in a fight that killed an adult female cougar. I identified the sex of the attacking cougar by comparing puncture wounds with morphological dental records (Thompson 1996), which suggested a male was responsible. The female did not have young at the time nor had she been in estrus for at least 3 months (as revealed by the necropsy). A nearby kill was a possible source of the conflict. I documented one other case of intraspecific aggression involving females. An adult female, translocated into the study population in January of 1995, was recaptured when she returned to her original area of capture. She had several new wounds, assessed by a veterinarian, that were apparently received from fighting and the radio-collar was extensively damaged. Given the high proportion of females in this population and concurrent recruitment of 2 subadult females, it is possible that resident female(s) were involved. One other possibility is that a bear inflicted the injuries. However, the likelihood of this is extremely low (<5%) because male bears rarely emerge from their dens at this time of year (H. Davis, R.P.Bio., pers. comm.). Altogether, the number of aggressive interactions documented in my study suggests some level of social intolerance among female cougars. 35 Population Regulation Both Hornocker (1970) and Seidensticker et al. (1973) postulated that the land tenure system exhibited by cougar populations, and maintained through social interactions, acted to regulate adult cougar densities at levels below that set by density o f prey. Lindzey et al. (1994) found evidence to support their thesis but cautioned that the observed increase in deer numbers in the Utah study area may have been "insufficient to provide an adequate test o f their hypothesis". N W B may have the highest density o f cougars yet recorded. The high density observed here was characterized by small home ranges wi th considerable overlap, particularly among related females. In general, smaller home ranges may be expected where prey is more abundant (Davies and Houston 1984). Black-tailed deer were the primary large prey o f cougars in this study, but annual deer indices did not support this explanation for the small size o f home ranges observed. Deer counts in open cutover habitats on Vancouver Island provide relative population estimates intended to detect changes in deer abundance (Harestad and Jones, 1981). However, prey indices may be unreliable in areas dominated by ageing secondgrowth forests, because observability o f deer is low in dense secondgrowth forests. The few man-made openings in my study area were not uniformly distributed in the landscape and road access was often limited to areas o f active logging, o f which there was little. Consequently, the deer indices obtained from the visually dense habitats that prevailed in my study area were insufficient to relate the density o f cougars in N W B wi th their principal prey. Other incidental evidence suggests deer were not abundant. The number o f animal control kil ls could infer that a shortage o f deer was driving adult females to prey on domestic animals. Ackerman et al. (1986) suggested that adult females wi th dependants would require 7-8 jackrabbits each day to support a family o f 4, yet females wi th young in 36 my study repeatedly entered risky areas for small and less efficient prey. Smaller prey are typically consumed whole and are, therefore, lower in energy content (kcal/kg wet weight) and digestibility because of the large proportion of hair and bones (Davison et al. 1978). Ackerman et al. (1986) also suggested that a greater abundance of deer might result in incomplete consumption of prey. All deer carcasses found in this study were completely consumed except when cougars were chased from a kill. High density and small home ranges may have contributed to higher levels of intraspecific aggression than in other studied populations. Rarely has aggressive behaviour among females been reported. The conflict, following the introduction of an unfamiliar female, suggests a social intolerance among females not evident in other studies. Rather, cougar populations that follow migratory prey (Pierce et al. 1999), or with detectable numbers of transients (Hornocker 1970, Seidensticker et al. 1973, Logan et al. 1986, Lindzey et al. 1994, Spreadbury et al. 1996) demonstrate a social flexibility that is in marked contrast to the findings in my study. I suggest that when space and prey are limited, social interactions become more aggressive. If the high densities and level of intraspecific killing can be interpreted as density-dependent mortality, then I suggest social interactions were a regulatory factor in my study population. 37 L I T E R A T U R E CITED Ackerman, B. B., F. G. Lindzey, and T. P. Hemker. 1986. Predictive energetics model for cougars. Pages 333-252 in S. D. Miller and D. D. Everett, eds. Cats of the World: Biology, Conservation and Management. Natl. Wildl. Fed., Washington, D.C. Anderson, A. E. 1983. A critical review of literature on puma (Felis concolor). Colorado. Div. Wildl. Spec. 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