Data from: Trade-offs between forage availability, accessibility, and predation risk on winter foraging strategies of wood bison (Bison bison athabascae)

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.