Energetics and Patch Use in the Fox Squirrel Sciurus niger: Responses to Variation in Prey Profitability and Patch Density

Abstract

We examined the response of free-ranging fox squirrels (Sciurus niger) to patches (individual trees) of longleaf pine cones (Pinuspalustris) that varied in both individual cone profitability and cone density (number of cones per tree). Cost-benefit analyses revealed that average cone profitability (net energy gain per unit handling time [e/h]) was an increasing, but decelerating, function of cone size. Thus, we predicted that to maximize feeding efficiency squirrels should select patches that contain the highest densities of the largest cones. At one site, in which cone density was positively correlated with median cone size per tree, squirrels exhibited the predicted pattern of selection. Preferred trees contained more cones, larger cones and more viable seeds per cone than those trees sampled once by a squirrel and subsequently avoided. At a second site, there was a significant negative correlation between cone density and cone size and, as a result, squirrels were faced with a trade-off. Interestingly, at this site there were no discernible differences in any univariate measure of cone or quality (e.g., the size, energy content or density of cones) between preferred and avoided trees. However, individual cone profitability and total seed mass of preferred trees were significantly higher, indicating that squirrels were not making choices on the basis of simple prey and characteristics, such as cone size and/or density. Moreover, these choices resulted in the highest shortand long-term rate of energy gain. We recommend that future field investigations on use consider interactions and possible trade-offs between diet and patch choices. Such an approach may lead to a better understanding of the mechanisms by which animals make choices.