Robert B. Wielgus

SINK POPULATIONS IN CARNIVORE MANAGEMENT: COUGAR DEMOGRAPHY AND IMMIGRATION IN A HUNTED POPULATION

Carnivores are widely hunted for both sport and population control, especially where they conflict with human interests. It is widely believed that sport hunting is effective in reducing carnivore populations and related human-carnivore conflicts, while maintaining viable populations. However, the way in which carnivore populations respond to harvest can vary greatly depending on their social structure, reproductive strategies, and dispersal patterns. For example, hunted cougar (Puma concolor) populations have shown a great degree of resiliency. Although hunting cougars on a broad geographic scale (> 2000 km2) has reduced densities, hunting of smaller areas (i.e., game management units, < 1000 km2), could conceivably fail because of increased immigration from adjacent source areas. We monitored a heavily hunted population from 2001 to 2006 to test for the effects of hunting at a small scale (< 1000 km2) and to gauge whether population control was achieved (lambda < or = 1.0) or if hunting losses were negated by increased immigration allowing the population to remain stable or increase (lambda > or = 1.0). The observed growth rate of 1.00 was significantly higher than our predicted survival/fecundity growth rates (using a Leslie matrix) of 0.89 (deterministic) and 0.84 (stochastic), with the difference representing an 11-16% annual immigration rate. We observed no decline in density of the total population or the adult population, but a significant decrease in the average age of independent males. We found that the male component of the population was increasing (observed male population growth rate, lambda(OM) = 1.09), masking a decrease in the female component (lambda(OF) = 0.91). Our data support the compensatory immigration sink hypothesis; cougar removal in small game management areas (< 1000 km2) increased immigration and recruitment of younger animals from adjacent areas, resulting in little or no reduction in local cougar densities and a shift in population structure toward younger animals. Hunting in high-quality habitats may create an attractive sink, leading to misinterpretation of population trends and masking population declines in the sink and surrounding source areas.

Does hunting regulate cougar populations? A test of the compensatory mortality hypothesis

Many wildlife species are managed based on the compensatory mortality hypothesis, which predicts that harvest mortality (especially adult male mortality) will trigger density-dependent responses in reproduction, survival, and population growth caused via reduced competition for resources. We tested the compensatory mortality hypothesis on two cougar (Puma concolor) populations in Washington, USA (one heavily hunted and one lightly hunted). We estimated population growth, density, survival, and reproduction to determine the effects of hunting on cougar population demography based on data collected from 2002 to 2007. In the heavily hunted population, the total hunting mortality rate (mean +/- SD) was 0.24 +/- 0.05 (0.35 +/- 0.08 for males, 0.16 +/- 0.05 for females). In the lightly hunted population, the total hunting mortality rate was 0.11 +/- 0.04 (0.16 +/- 0.06 for males, 0.07 +/- 0.05 for females). The compensatory mortality hypothesis predicts that higher mortality will result in higher maternity, kitten survival, reproductive success, and lower natural mortality. We found no differences in rates of maternity or natural mortality between study areas, and kitten survival was lower in the heavily hunted population. We rejected the compensatory mortality hypothesis because vital rates did not compensate for hunting mortality. Heavy harvest corresponded with increased immigration, reduced kitten survival, reduced female population growth, and a younger overall age structure. Light harvest corresponded with increased emigration, higher kitten survival, increased female population growth, and an older overall age structure. Managers should not assume the existence of compensatory mortality when developing harvest prescriptions for cougars.

Cougar Population Dynamics and Viability in the Pacific Northwest

Abstract Increasing reports of human/cougar conflicts may suggest that cougars are increasing in the Pacific Northwest. We determined minimum relative densities and average fecundity, survival, and growth rate of an apparently increasing cougar population in northeastern Washington, USA; northern Idaho, USA; and southern British Columbia, Canada, from 1998 to 2003. Minimum relative densities declined from 1.47 cougars/100 km2 to 0.85 cougars/100 km2. We estimated average litter size at 2.53 kittens, interbirth interval at 18 months, proportion of reproductively successful females at 75%, and age at first parturition at 18 months for a maternity rate of 1.27 kittens/adult female/yr. Average survival rate for all radiocollared cougars was 59%: 77% for adult females, 33% for adult males, 34% for yearlings, and 57% for kittens. Hunting accounted for 92% of mortalities of radiocollared cougars. The annual stochastic growth rate of this population was λ = 0.80 (95% CI = 0.11). Contrary to accepted belief, our findings suggest that cougars in the Pacific Northwest are currently declining. Increased conflicts between cougars and humans in this area could be the result of the 1) very young age structure of the population caused by heavy hunting, 2) increased human intrusion into cougar habitat, 3) low level of social acceptance of cougars in the area, or 4) habituation of cougars to humans. To help preserve this population, we recommend reduced levels of exploitation, particularly for adult females, continuous monitoring, and collaborative efforts of managers from adjacent states and provinces.

Sexual Segregation and Female Grizzly Bear Avoidance of Males

We examined seasonal use of habitat for 14 male and 5 female grizzly bears (Ursus arctos) in southwestern Alberta, 1981-84, to test 2 competing hypotheses regarding segregation of the sexes. The male avoidance hypothesis predicts increasing differences in use of habitat with increasing male use of female-occupied areas because of female avoidance of males. The no avoidance hypothesis predicts decreasing differences in use of habitat with increasing male use of female-occupied areas because of increasing similarity of available habitat. Differences in use of habitat were greatest during late summer, when many males concentrated in the female-occupied area, and they were less during other seasons when few males were in the female-occupied area

Tests of hypotheses for sexual segregation in grizzly bears

We studied 2 grizzly bear (Ursus arctos) populations to test 3 hypotheses of sexual segregation. The no avoidance hypothesis predicts that females do not avoid males and male-occupied habitats but simply have different habitats available to them within their home ranges. The food hypothesis predicts that subadult and adult females avoid males because of competition or cannibalism by males for food. The sex hypothesis predicts that only sexually mature adult females avoid males because of sexually motivated infanticide by nonsire males. Sexually mature females avoided (P < 0.05) food-rich, male-occupied habitats in Kananaskis, Alberta, but selected (P < 0.05) such habitats in the Selkirk Mountains of Idaho. Sexually immature females selected (P < 0.05) food-rich, male-occupied habitats in both areas. Unequal availability of habitat did not explain the pattern of segregation because food-rich habitats were available to all age-sex classes. Competition or cannibalism by males did not explain segregation because only sexually mature females avoided male-occupied habitats in Kananaskis and no females avoided males in the Selkirks. Adult female avoidance of potentially infanticidal, nonsire, immigrant males in Kananaskis appeared to explain the pattern of segregation. High mortality of older males in Kananaskis coincided with an influx of younger, potentially infanticidal, immigrant males, and adult females avoided those males and their favored habitats. No such segregation was observed in the Selkirks where mortality of older males was low and where there were few or no immigrant males. Results are inconsistent with the no avoidance and food hypotheses but consistent with the sex hypothesis of sexual segregation.

Estimating effects of adult male mortality on grizzly bear population growth and persistence using matrix models

We radio monitored a hunted, sexually segregated grizzly bear (Ursus arctos) population and an unhunted, unsegregated population for demographics and constructed a stage- and age-classified matrix model to test for the effects of adult male mortality and resulting sexual segregation on population growth and persistence. Population parameters in the model were adult female survival, subadult female survival, offspring survival, probability of litter sizes, and probability of unsuccessful pregnancy. The last three parameters were affected by adult male mortality and segregation, the others were not. We compared population growth with and without effects of hunting by holding adult female and subadult female survival constant and by using hunted and unhunted values for offspring survival, litter size, and pregnancy. Population growth (Lambda) showed the greatest elasticity for adult survival, subadult survival, offspring survival, litter size, and unsuccessful pregnancy, in that order. This corresponds with observed anti-infanticide tactics (sexual segregation) by adult females to maximize their fitness. The hunted population decreased at a rate of 0.99 whereas the simulated, unhunted population increased at a rate of 1.05. The hunted population was much more susceptible to population extinction. Under demographic stochasticity mean time to extinction was 32 years in the hunted population and 110 years in the unhunted population. Under environmental stochasicity mean time to extinction was 21 years in the hunted population and 43 years in the unhunted population. We suggest that sexual segregation caused by hunting resident adult males can result in population decline and can even contribute to rapid population extinctions when numbers are small.

Possible negative effects of adult male mortality on female grizzly bear reproduction

We studied 2 grizzly bear (Ursus arctos) populations to test 3 hypotheses on the effects of adult male mortality on female reproduction. The “no effect” hypothesis predicts that reproduction should be higher in the population with superior overall diet quality, regardless of mortality of adult males. The “increased reproduction” hypothesis predicts that reproduction should be higher in the hunted population because of lowered numbers of competitive or cannibalistic adult males. The “decreased reproduction” hypothesis predicts that reproduction should be lower in the hunted population because of increased immigration by potentially infanticidal, nonsire males with subsequent reduced survival of cubs, and/or increased sexual segregation resulting in reduced production of cubs. Reproduction rates were 0.46 in a hunted population in Kananaskis, Alberta and 0.74 in non-hunted populations in the Selkirk Mountains of Idaho and British Columbia. Mean litter size was smaller in Kananaskis than in the Selkirks (1.40 vs 2.22) but age at first parturition was earlier in Kananaskis (5.50 vs 7.30 years). Mean birth intervals were not different between populations. Age of mothers, overall diet quality, and total population density were not associated with differences in litter size and age at first reproduction, but adult female avoidance (sexual segregation) of nonsire immigrant males and associated food-rich habitats were. Our results are inconsistent with the “no effect” and “increased reproduction” hypotheses but consistent with the “decreased reproduction” hypothesis. Higher hunting mortality of older males coincided with higher numbers of potentially infanticidal, immigrant males in Kananaskis. Adult females avoided those males and their food-rich habitats in Kananaskis and female reproduction appeared to suffer as a result.

Minimum viable population and reserve sizes for naturally regulated grizzly bears in British Columbia

Abstract Estimating minimum viable population and reserve size is a fundamental cornerstone of conservation biology—but these estimates require representative demographic parameters. For example, “Benchmark” Grizzly Bear (Ursus arctos) Management Units in British Columbia (BC) are defined as unhunted and naturally regulated populations that can serve as population sources to surrounding hunted areas and provide information on natural population processes. Such benchmarks should have a very small probability of becoming threatened (N 1 2 K, 3 4 K, and K. Results indicated that 200–250 bears were required for a sufficiently small probability (P 20 years. Reserve sizes varied from 8556 km2 to 17,843 km2 depending on population density in each benchmark. These minimum viable populations and reserve sizes would protect approximately 12% of the estimated provincial grizzly bear population and would cover approximately 5% of the landmass of BC.

Population dynamics of Selkirk Mountains Grizzly bears

We investigated population dynamics of grizzly bears (Ursus arctos) in the Selkirk Mountains Grizzly Bear Ecosystem (SMGBE) of Idaho, Washington, and British Columbia to assist grizzly bear recovery from threatened status. We captured and radiomonitored 28 bears from 1985 to 1990. Estimated densities were 1.41 ± 0.14 (95 % CL) and 2.33 ± 0.36 bears/100 km 2 for the U.S. and Canadian portions of the SMGBE, respectively. Litter size (cubs ≤ 1.5 yr) was 2.22 ± 0.26 and mean birth interval was 3.0 ± 0.5 years for an estimated reproductive rate of 0.74 ± 0.10 cubs/adult female per year. Age at first parturition was 7.3 ± 0.38 years. Estimated annual survival rates were 0.96 ± 0.05 for adult females, 0.81 ± 0.20 for adult males, 0.78 ± 0.22 for subadult females, 0.90 ± 0.17 for subadult males, and 0.84 ± 0.16 for cubs

Cougar Prey Selection in a White-Tailed Deer and Mule Deer Community

Abstract Widespread mule deer (Odocoilus hemionous) declines coupled with white-tailed deer (O. virginianus) increases prompted us to investigate the role of cougar (Puma concolor) predation in a white-tailed deer, mule deer, and cougar community in northeast Washington, USA. We hypothesized that cougars select for and disproportionately prey on mule deer in such multiple-prey communities. We estimated relative annual and seasonal prey abundance (prey availability) and documented 60 cougar kills (prey usage) from 2002 to 2004. White-tailed deer and mule deer comprised 72% and 28% of the total large prey population and 60% and 40% of the total large prey killed, respectively. Cougars selected for mule deer on an annual basis (αmd = 0.63 vs. αwt = 0.37; P = 0.066). We also detected strong seasonal selection for mule deer with cougars killing more mule deer in summer (αmd = 0.64) but not in winter (αmd = 0.53). Cougars showed no seasonal selection for white-tailed deer despite their higher relative abundance. The mean annual kill interval of 6.68 days between kills varied little by season (winter = 7.0 days/kill, summer = 6.6 days/kill; P = 0.78) or prey species (white-tailed deer = 7.0 days/kill, mule deer = 6.1 days/kill; P = 0.58). Kill locations for both prey species occurred at higher elevations during summer months (summer = 1,090 m, winter = 908 m; P = 0.066). We suspect that cougars are primarily subsisting on abundant white-tailed deer during winter but following these deer to higher elevations as they migrate to their summer ranges, resulting in a greater spatial overlap between cougars and mule deer and disproportionate predation on mule deer.