Influence of phenology on site selection by female American black bears in coastal British Columbia

Abstract

We examined factors that affect site selection by female American black bears (Ursus americanus) in coastal British Columbia, Canada, 1992-95. We monitored 9 radiocollared females and compared sites that were selected within their home ranges to those that were not selected using 1-1 matched logistic regression procedures. We used information-theoretic inference to assess the effect of 19 habitat, temporal, and spatial variables in 27 candidate models to explain selection of sites within home ranges. The model that best explained site selection was 50 times more likely to be the best model, given the data, than the second-best model. The best model suggested that the probability that a site would be used by female black bears increased with increasing values of phenologically adjusted berry value interacting with light levels, phenologically adjusted succulent forage value, and forest harvesting. Probability of use decreased with increasing distance from streams dependent upon salmon (Oncorhynchus spp.) availability and increasing distance from low-traffic roads. Although the best model included horizontal visibility and distance to high-traffic roads as variables, these factors had undetermined effects on the probability of use (95% confidence interval of odds ratio encompassed 1). Including phenological adjustments for abundance of berries and succulent foods greatly increased the support for the models by the data, compared to models based on cover of food plants alone. These results confirm that bears are cognizant of both temporal and spatial differences in food availability and that they modify their selection of sites based on these differences. Our results imply that site selection by female black bears involved a complex set of decisions about not only food availability, but also disturbance by humans. To increase the compatibility of timber production with conservation of black bear habitat, managers need to consider the spatial and temporal effects of the creation of food-rich openings and different types of roads on the suitability and effectiveness of habitats to support black bears.