Effects of domestic goats on deer wintering in Utah oakbrush

Abstract

Dietary composition and quality, activity budgets, and foraging behavior of tame mule deer (Odocoileus hemionus hemionus) were monitored in winter to ascertain the effects of prior summer use of oakbrush communities by domestic goats (Capra hircus). Reduction of deciduous browse by goats resulted in increased use of Wyoming big sagebrush (Artemisia Nutt. subsp. wyomingensis Beetle and Young) by deer when snow cover precluded use of understory species. As a result, the diets of deer confined to goat-browsed pastures contained less fiber and tannins, and were more digestible than those of deer in control pastures. Digestible protein in diets did not differ. No goat-related effects were observed in the absence of snow because deer grazed the herbaceous understory which had not been substantially altered. Quantity of cured herbage was low, and deer did not effectively select for fall regrowth. Consequently, diet quality under snow-free conditions was not substantially different from that observed under snow-covered conditions. Snow reduced foraging efficiency; deer travelled faster, and exhibited lower bite and intake rates when feeding under snow-covered conditions than under snow-free conditions. Goat-induced vegetal differences were not reflected in activity budgets or foraging behavior, regardless of snow condition. We conclude that goats may be used to periodically manipulate composition of oakbrush winter range, thereby enhancing quality of deer diets under snow-covered winter conditions. However, enhancement of deer diets under snow-free winter conditions probably requires annual manipulation of the understory.