Use of Arctic ground squirrels (Urocitellus parryii) by brown bears (Ursus arctos)

Abstract

Brown bears (Ursus arctos) in the Mackenzie Delta in the Northwest Territories of Canada are at the northern edge of their range and persist in a nutrient poor environment with limited available protein. Arctic ground squirrels (Urocitellus parryii) are widespread across northern Canada and are often cited as an important protein source for brown bears. We hypothesized that Arctic ground squirrels form an important part of brown bear diet in the Mackenzie Delta region, and that their importance varies seasonally, with peak use occurring during bears’ pre-dormancy hyperphagic period, as well as annually with fluctuating availability of other food. To investigate the seasonal use of Arctic ground squirrels by brown bears, we used resource selection function analysis to describe habitat use, stable isotope analysis to determine individual trophic level and examine its relationship with habitat use, and GPS satellite telemetry to facilitate site investigations. Arctic ground squirrel habitat was not a significant covariate in resource selection functions for pooled sexes, pooled females, and pooled males. However, at the individual level, bears displayed a range of behaviors from selection against, no selection, to selection for Arctic ground squirrel habitat. We found no significant interannual variation in use of Arctic ground squirrel habitat. Site investigations and stable isotopic values for individual bears also suggest a range of foraging behaviors for Arctic ground squirrels. Individual resource selection models combined with trophic level and site investigations provide support for limited use of Arctic ground squirrels that varied between individuals and provided additional evidence for the diversity of niches exploited by individuals.