Impact of disturbance characteristics and age on grizzly bear habitat selection

Abstract

Grizzly bears (Ursus arctos) have complex reactions to forest disturbances due to their use of forest clearings for foraging, their large home ranges, and the continued human expansion into undisturbed grizzly bear habitat. The goal of this paper is to quantify how grizzly bears interact with forest disturbances over time in west-central Alberta in order to inform habitat management decisions. This is accomplished using a four-decade remotely sensed disturbance history and detailed grizzly bear movement and habitat use information. Global positioning systems (GPS) collars were used to collect telemetry data for 22 adult grizzly bears (8 females, 14 males) from 2005 to 2009 in the eastern slopes of the Canadian Rockies. The resultant telemetry data were partitioned based on known biological variation in habitat selection into sex and seasonal groups. Density of grizzly bear telemetry locations was calculated for each forest disturbance and compared to expected density via a randomization conditioned on observed trends in overall habitat use. The comparison of observed and expected density of grizzly bear telemetry locations allowed disturbances to be labelled as selected or avoided. Each disturbance was attributed with characteristics (area, elevation, average tasselled cap transformation (TCT) greenness, and distance to nearest populated place), which were compared between selected and avoided disturbances using a Mann–Whitney U-test. Male bears selected for 30–40-year-old disturbances more frequently than younger disturbances; females demonstrated equal selection of all ages of disturbances except those less than 10 years old. Females selected for disturbances more in the summer and fall than the spring. Disturbances selected by female bears were larger, with lower TCT greenness, and a consistent elevation (1250–1300 m) across seasons and disturbance age. Male bears showed lower selection of disturbances in the fall than in other seasons, and lower selection than females in the summer and fall. Compared to females, disturbances selected by males were larger, and more likely to show seasonal variation in greenness and elevation. Both sexes selected for larger disturbances of all ages, although disturbance size has generally decreased through time. Limiting human access to disturbances with characteristics attractive to grizzly bears will reduce grizzly bear and human interactions, and reduce mortality.