Sparrows and a brushpile: Foraging responses to different combinations of predation risk and energy cost

Our observations of wintering house sparrows (Passer domesticus) feeding on cracked corn at feeders placed at different distances from a brushpile and in positions differentially exposed to the wind supported the hypothesis that where food patches are equal in net energy return, foragers use the one furnishing the most protection from predation. Results reinforced the hypothesis that when food sources furnish equal protection from predators, homeotherms below their lower critical temperature use the one providing the largest net energy return. When the sparrows had available both a colder, safer feeding site and a warmer, riskier one, they frequented both over the course of the winter and, as predicted, their use of the colder, safer site was negatively correlated with wind velocity and positively related to temperature and solar radiation. In this last case, it appeared the birds decided where to feed on the basis of some threshold difference between metabolic rates at the colder, safer site and the warmer, riskier location.