Optimal diet selection by white-tailed deer: Balancing reproduction with starvation risk

Summary Energy intake rates of wintering deer vary over time because of variation in the abundance and quality of their natural foods. Accordingly, there is a chance that energy requirements will not be satisfied in a feeding period. This is especially critical because deer are reproductive during winter; hence selecting diets to minimize the risk of starvation may not maximize fitnss. I examined diet selection by white-tailed deer (Odocoileus virginianus) using a risk-sensitive foraging model which predicts the optimal diet when foragers face starvation risks during a reproductive period. Optimal diets were estimated by quantifying the mean and variance in energy intake rate deer could obtain when selecting different potential diets and substituting these values into functions for estimating offspring production and starvation risk. I conducted a field experiment to ask whether deer selected deciduous and coniferous twigs according to model predictions. Starvation risk was manipulated by providing deer supplemental feed. When faced with starvation risks, deer appeared to select diets that balanced offspring production with starvation risk. When starvation risk was climinated, deer tended to select diets that simply maximized their mean energy intake rates.