Optimal foraging theory (OFT) and the energy maximization hypothesis (EMH) have long been essential when examining wildlife habitat selection. At high latitudes and altitudes, animals in winter face greater limitations in availability and accessibility of forage. Here we explore the foraging behavior of wood bison (Bison bison athabascae) during winter within the Ronald Lake bison herd in northeastern Alberta, Canada, and examine the trade-offs they face due to limitations in forage abundance and availability (snow conditions), as well as the need to minimize predation risk. We used Global Positioning System (GPS) location data collected from 70 female wood bison to identify winter foraging sites and craters selected by bison to access forage beneath the snow. Within wetlands used by bison we selected 190 pairs of used (foraged) and random available sites to test eight a priori hypotheses explaining how bison traded-off between forage availability, accessibility, and minimizing predation risk. We found with matched-paired logistic regression that Carex atherodes was 1.21-times more likely to be selected per unit increase in cover, compared to 1.17-times per unit cover for C. aquatilis and C. utriculata. However, all Carex species showed an increase in selection when cover was >50% cover within individual craters. While the importance of Carex was clear, forage site selection was still inversely related to snow depth. We suggest that bison maximized their energy return by avoiding areas with deep snow (>50 cm) that demanded intensive cratering, even when highly selected forage was accessible beneath. Specifically, there was a 1% decrease in selection of Carex per cm depth in snow when interacting with any Carex species. Avoidance of forage areas with deep snow demonstrates that wood bison employed a foraging strategy that considers both forage availability and environmental conditions, with snow depth being a limiting factor. We highlight the relationship between optimal foraging based on food availability and the trade-offs within an energy restrictive winter season, furthering the understanding of how large herbivores in forage strategically to maximize energy intake in northern environments.

We recorded environmental characteristics of bison selected foraging sites, and random paired avaliable sites during the winters of 2020 and 2021. This dataset holds the values for snow characteristics, forage characteristics, and distances to nearest cover recorded from these sites. It is organized in a way to support a matched-pair logistic regression.