Population Dynamics and Movements of Black Bears in East Central Alberta

Abstract

Demographic and spatial parameters of a high-density black bear (Ursus americanus) population were studied with radiotelemetry and live-capture techniques in 1974 and 1975 at Cold Lake, Alberta. During previous studies, the population on a 218-km2 study area closed to sport hunting of bears had doubled from a mean of 80 bears in 1968-71, to 175 in 1973 following the removal of 23 adult males in 1971 and 1972. The increase was attributed to increased subadult survival and ingress. By 1975 the population decreased to 137 and the adult male cohort was numerically restored. The subadult cohort remained large, however. Average weights of bears of the same age did not decrease when the population increased, suggesting that food was not in short supply at the higher densities. Size estimates for annual home ranges of males and females averaged 119 and 19.6 km2, respectively. Size of male home ranges was not affected by the density increase but size of female home ranges may have decreased. Areas occupied by 24 male bears of different ages overlapped extensively. Adult females appeared to be territorial toward one another, but tolerated bears of other sexes and ages. Mobility of male bears decreased from spring through fall and was likely influenced by seasonal food availability and breeding behavior. More subadult males moved off the study area than adult males. Male bears selected aspen and garbage dump areas but avoided muskeg habitat. Subadult males were located at garbage dumps twice as often as adult males. J. WILDL. MANAGE. 46(4):845-860 The Boreal Forest in Canada comprises the largest continuous area of occupied black bear habitat in North America. However, most studies of black bear demography and behavior have been conducted in mountain areas (Jonkel and Cowan 1971, Poelker and Hartwell 1973) or in the Boreal Forest at lower latitudes (Erickson et al. 1964, Rogers 1976). Also, most populations studied have been hunted. This paper examines demographic and spatial parameters of a black bear population near Cold Lake, Alberta in a section of the Boreal Forest closed to sport hunting. The study is part of a long-term project consisting of 2 phases. The first phase spanned the period 1968-73 and was conducted by personnel of the Alberta Department of Energy and Natural Resources (Fish and Wildlife Division). An intensive live-trapping program was used each year to provide estimates of population size and structure. Bear numbers were relatively stationary for the first 4 years (1968-71) suggesting that some regulatory mechanism may have been operating in the population. Incidents of snared yearling bears being killed by adult males, plus high rates of subadult disappearance during this same period, prompted the hypothesis that the population was being regulated by adult males. To test this hypothesis, 23 adult males were trapped and killed in 1971 and 1972. The population more than doubled by 1973. Kemp (1976) attributed the popul tion increase to greater subadult survival and ingress by subadult males. It should be noted that Kemp (1976) previously reported the removal of 26 adult males from the Cold Lake population. However, he lacked a reliable field aging criterion and age estimates were based solely on weight, i.e., if greater than 90 kg, the bear was considered adult. ' Senior author was killed in a plane crash on 27 February 1978 at Edson, Alberta, while employed by the Alberta Department of Energy and Natural Resources (Fish and Wildlife Division). J. Wildl. Manage. 46(4):1982 845 This content downloaded from 207.46.13.149 on Mon, 03 Oct 2016 05:45:08 UTC All use subject to http://about.jstor.org/terms 846 BLACK BEAR POPULATION DYNAMICS* Young and Ruff Subsequent aging by tooth sectioning revealed 2 such males were subadults. Another male was killed too distant from the study area to be considered a resident animal for purposes of this study. The main objective of the 2nd phase of the project, which began in 1974, was to investigate further the intrinsic and environmental mechanisms regulating the distribution and abundance of bears in this unhunted population. Specifically, it was hypothesized that if adult males prevented population growth prior to their removal, then the post-removal population would eventually decline toward preremoval levels as maturing subadults replaced the adult male cohort and began to assert their dominance. In this paper we document population changes during the 2 years following the peak year of 1973, and describe the spatial relationships of 38 radio-collared bears in a high-density population. Movements and habitat use of subadult and adult male bears are examined for possible relation to population regula-