Diet and habitat selection of wood bison in relation to seasonal changes in forage quantity and quality

Abstract

Diet and habitat selection of wood bison (Bison bison athabascae) were studied in the Mackenzie Bison Sanctuary, Northwest Territories, between February 1986 and April 1988. Wood bison showed pronounced seasonal changes in diet. Sedges constituted 96.1–98.8% of the winter diet. During summer, the diet became a more diverse mix of sedge (Carex spp.), grass (Graminae), and willow (Salix spp.). Lichen (Cladina mitis) became a major dietary component in fall. Summer browsing on willows increased when sedge standing crops were reduced. Forage availability was the main factor determining habitat selection. Wet sedge meadows provided the most available crude protein in winter and were the preferred winter habitat. Willow savannas provided the most available crude protein in summer and were the preferred summer habitat. Between June and October, all forages except lichen decreased in nitrogen content and increased in fibre content. The lack of distinct habitat preference in fall corresponded to dispersion of animals into forested habitats, increased use of lichen as forage, and more homogeneous availability of crude protein among habitats. Snow conditions were harsher in 1987–1988 than in 1986–1987, which affected forage availability and caused a noticeable shift in habitat use.