Selection of Nuts by Gray Squirrels and Optimal Foraging Theory

The choice of food by free-living gray squirrels (Sciurus carolinensis Gmelin) was determined by recording the selection of nuts from the natural nutfall of four species of nut-bearing trees, where abundance of nuts of each species was determined by sampling. The rate of energy intake the squirrels achieved while consuming nuts of the four species was measured separately. The ranking of the three species of acorns by use-availability ratios was the same as the ranking of the acorns by the rate of energy intake. However, hickory nuts were consumed disproportionately even though they gave a low rate of energy intake. Foraging models based on maximizing the rate of energy intake do not predict the preference for hickory nuts. The incorporation of nutrient constraints or risk minimization may be necessary to accommodate the models to observation when the foods available to the consumer differ in composition.