Spatial and behavioral response of white-tailed deer to forage depletion

We tested predictions regarding the effects of forage depletion on patterns of foraging effort, diet selection and quality, and patch selection by white-tailed deer (Odocoileus virginianus). Two deer were allowed access to four 150-m2 enclosures (patches) for 8, 16, 24, and 32 days, resulting in the exposure of the patches to deer for 16, 32, 48, and 64 animal-days and different levels of forage depletion. When the deer were given simultaneous access to all four enclosures, feeding patch selection was markedly skewed toward heavily and lightly grazed environments, while moderately depleted patches were selected least. Deer primarily consumed woody browse in patches with low (16 days) and high (64 days) forage depletion, and forbs in patches that were moderately depleted (32 and 48 days). Deer responded to forage depletion by foraging less selectively, reducing movement rates, and increasing average bite size. During the last phase of the trial, biting rates on forbs declined but increased on woody browse in response to declining forage availability. Diel foraging times remained unaffected by changes in forage availability. The behavior of deer foraging in experimental patches appeared to be consistent with predictions based on the maximization of nutrient (protein) gain, although use of the most depleted patch was greater than expected. We conclude that vegetative biomass alone is a poor indicator of foraging rewards for highly selective herbivores.