Foraging theory predicts that animals should feed more selectively in response to an increased abundance of high-quality foods. We tested these predictions by examining changes in patterns of diet selection by white-tailed deer (Odocoileus virginianus) and Angora goats (Capri hircus) in response to habitat enrichment. When a high-quality supplement was provided ad libitum, both species responded by increasing foraging effort and by feeding more selectively on natural forages. Supplemented animals consumed a greater proportion of plants containing high concentrations of crude protein (CP) and digestible energy (DE), which resulted in an increase in average diet quality. Responses of individual deer and goats varied and appeared to be related to differences in habitat heterogeneity between trial enclosures. Our results suggest that supplementation may be disruptive to normal behavioral processes affecting the distribution of free-ranging herbivores on the landscape. These processes may be important in reducing the probability of excessive utilization of palatable forage species, and to the competitive relationships between range plants.

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