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 latewinter 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.

Dietary overlap and potential competition in a dynamic ungulate community in Northwestern Canada

“…At low elevations, dietary overlap was high for bison and horses, the species most similar in body size, and lowest for bison and deer, which had the greatest difference in body size. Both bison and horses are primarily grazers (Hudson and Frank , McInnis and Vavra , Larter and Gates , Jung ); as such, they made extensive use of grasses and sedges and rushes during winter and summer. Both species commonly used similar genera of sedges and rushes ( Carex spp., Juncus spp., and Eriophorum spp.…”

Short‐term effect of helicopter‐based capture on movements of a social ungulate

“…At lower elevations, small open areas comprised of wet sedge meadows, wet shrub meadows, or remnant boreal grasslands on south‐facing slopes were interspersed throughout a forested matrix. These open patches were preferred winter foraging areas for bison (Jung , Jung et al ). Climate was cold and semi‐arid, with persistent snow cover extending from October to May Human development was low, with a small human footprint, and much of the study area was remote and subject only to natural disturbances such as fire and flooding.…”

Effects of linear features on resource selection and movement rates of wood bison (Bison bison athabascae)

“…The final stages of model selection considered the addition of interactions among LFs, land-cover type, and fire. For LF × land cover interactions, we focused on treed land covers (e.g., upland deciduous), hypothesizing that because bison diet is dominated by sedges, grasses, and shrubs (Larter and Gates 1991;Jung 2015), bison may show greater response to the early seral habitat created by LFs within forests. All interaction variables were coded directly as dummy variables (e.g., LF in upland deciduous); thus, each of these variables became an additional land-cover type.…”

“…Because of differences in life history strategies, the wood bison's response to LFs may fundamentally differ from those reported for caribou. For example, bison diets are composed largely of sedges and graminoids (Larter and Gates 1991;Jung 2015;Jung et al 2015) and they may select LFs because these disturbances have an increased abundance of grasses and sedges compared with the surrounding forest (Leverkus 2015;Finnegan et al 2018). Selection may occur despite the potentially increased predation risk associated with LFs because adult bison have a lower probability of death on wolf encounter compared with caribou (Mech et al 2015).…”