Foraging theory predicts that animals should feed more selectively in
response to an increased abundance of high-quality foods. We tested th
ese predictions by examining changes in patterns of diet selection by
white-tailed deer (Odocoileus virginianus) and Angora goats (Capri hir
cus) in response to habitat enrichment. When a high-quality supplement
was provided ad libitum, both species responded by increasing foragin
g effort and by feeding more selectively on natural forages. Supplemen
ted animals consumed a greater proportion of plants containing high co
ncentrations of crude protein (CP) and digestible energy (DE), which r
esulted in an increase in average diet quality. Responses of individua
l deer and goats varied and appeared to be related to differences in h
abitat heterogeneity between trial enclosures. Our results suggest tha
t supplementation may be disruptive to normal behavioral processes aff
ecting the distribution of free-ranging herbivores on the landscape. T
hese processes may be important in reducing the probability of excessi
ve utilization of palatable forage species, and to the competitive rel
ationships between range plants.