Mortality Causes and Survival Estimates for Adult Female Columbian Black-Tailed Deer

Abstract

Declines in black-tailed deer (Odocoileus hemionus columbianus) populations and in hunter harvests of deer on Vancouver Island have been contrary to management objectives since the late 1970s. Because predators were presumed the major cause of declines, arguments for retention of winter habitat were difficult to support and managers were asked to reduce deer mortality before addressing habitat concerns. Changes in population management were instigated even though estimates of deer survival rates were lacking and little was known about mortality causes. We documented mortality causes and estimated average monthly survival (S) for 105 radio-collared black-tailed deer at 4 sites on Vancouver Island, British Columbia, from February 1982 through june 1991. Predation accounted for 61% of all deaths (n = 54) and occurred mostly during February-june. Average annual survival was 74% (S = 97.5%, SE = 0.3%). We used logistic regression to model monthly cause-specific mortality (M j ) and S using 5 independent variables: study area, seasonal movement behavior of deer, monthly elevation used by deer, month of year, and mean monthly snow depth. The model that best (Akaike's Information Criterion [AIC] = 624.02; Chatfield 1992) explained M j and S was based on seasonal movement behavior. Resident deer remaining at low elevations were more (P = 0.024) prone to predation. We recommend that retention of old, intact forests at low elevations is basic to rebuilding deer populations on Vancouver Island