Composition and Quality of Mule Deer Diets on Pinyon-Juniper Winter Range, Colorado

Estimates of botanical composition and nutritional quality of mule deer diets on pinyon-juniper winter range in Piceance Basin, Colorado, were based on forage selections of 8 tame animals. Diets contained nearly all browse in early winter, but browse content decreased and forbs increased as winter progressed until April when consumption of new grass growth increased sharply. Dietary crude protein levels were marginally adequate for body maintenance during much of the winter. Levels of dietary in vitro digestible dry matter were inadequate. Browse was considered critical to winter survival of deer in Piceance Basin because it was the most available forage in deep snow. Also, its nutritional value was comparable or better than that of forbs and grasses selected by deer except in April when new plant growth was available. In spite of large variation in diet compositions, deer apparently selected forage mixes to maintain a consistent, although inadequate, diet quality through the critical wintering period.