Landscape evaluation of grizzly bear habitat in western Montana

We present a method for evaluating the cumulative effects of human activity on grizzly bear (Ursus arctos) habitat in the Northern Continental Divide Ecosystem of western Montana. Using logistic regression, we modeled the relative probabilities of female grizzly bear resource selection from telemetry data, TM satellite imagery (greenness), elevation, human activity points, roads, and trails. During spring, adult female grizzly bears were positively associated with low- and mid-elevation habitats. Logistic regression coefficients were negative for all road and human activity variables. Summer and fall coefficients were also negative for road, human activity, and trail variables. During summer and fall, females were positively associated with mid to high elevations. Coefficients were positive for greenness during all seasons. Extrapolations of seasonal potential and realized habitat models were made to other areas on the western side of the region where no telemetry data existed. During spring, much of the Bob Marshall Wilderness exhibited a relatively low probability of use by female grizzly bears, but the converse was observed during summer and fall. The mapping and extrapolation process highlighted areas where habitat restoration would have the greatest benefit. These areas were typically low-elevation spring habitats with high road densities and private lands where urbanization occurred. We recommend that habitat management agencies implement reductions in road densities in seasonal habitat and implement methods to maintain habitat function on private lands.