Winter diets of reintroduced bison (Bison bison) in northwestern Canada

Abstract

I examined the winter diets of a reintroduced population of bison (Bison bison) in a mountainous region of northwestern Canada. The impetus of this study was to examine the winter diets of bison in this ecological region and to test for sexual and seasonal variation in the winter diet. Microhistological analyses of fecal samples from animals of known sex- and age-classes were examined to determine winter diets. I evaluated the hypothesis that sexual segregation in bison may be due to differences in diet. In addition, diet composition between early and late winter was examined to test for seasonal differences. Overall, bison winter diets were diverse, including at least 31 genera of vascular plants, but dominated by sedges (Carex). Nine species of Carex were identified in the winter diet. Diets of adult males in early winter differed in percentages of 7 forage classes used from those in late winter. The proportion of shrubs increased in late-winter diets, while that of sedges decreased. No evidence was found to support hypotheses of sexual segregation in bison based on differences in diet, at least for this population during late winter. This study shows that bison diets in winter are more diverse than previously thought based on studies in lowland boreal environments, where dietary niche breadth was comparatively narrow. Dietary flexibility is important within the context of choosing new sites for reintroducing bison, or predicting colonization of vacant habitats as existing populations grow.