Foraging Ecology of Bison in Aspen Boreal Habitats

Abstract

Studies on several wild and domestic ungulates suggest that large grazers attain higher maximum forage intake rates but require relatively higher forage biomass to do so. In this study, forage intake rates and feeding times of North America's largest wild grazer, the bison (Bison bison), were related to forage biomass during summer and autumn in aspen boreal forest habitats. Irrespective of season, maximum feeding rates of 68 g/min declined by 50% as forage biomass was reduced to 780 kg/ha. This reduction was due primarily to smaller bite sizes. However, bison compensated by increasing cropping bite rates to more than 60 bites/min on heavily grazed swards. Grazing times increased from 9 h/day in summer to 11 h/day in autumn, offsetting slight decreases in average foraging efficiency. During summer, a greater proportion of grazing occurred at night. Upland meadows were preferred habitats for grazing despite relatively low pasture biomass and potential dry matter intake rates.