Sexual Differences in Foraging Behavior in Two Species of Dendrocopos Woodpeckers

Abstract

The red-cockaded (Dendrocopos borealis) and Arizona (D. arizonae) woodpeckers demonstrate sexual differences in foraging behavior. The former shows little morphological correlation with the behavioral differences, whereas the latter has pronounced sexual difference in bill length. Males of D. borealis forage largely on the branches and twigs of pines, the females almost exclusively on the trunk. The 2 sexes of D. arizonae also forage in different parts of the trees but overlap much more than in D. borealis. In D. arizonae the differences in beak size are correlated with differences in foraging techniques, thus the sexes utilize the same portions of the trees in somewhat different ways. Two possible mechanisms for the evolution of sexual foraging differences are discussed. A secondary result of selection for increased compatibility is a more efficient utilization of the habitat. Possible reasons that some trunk foragers appear to demonstrate sexual differences more conspicuously than do birds that do not forage on trunks include: (1) the long-term nature of the pair bond in some spp. requiring compatibility between members of the pair; and (2) a reduced accessibility or quantity of foods on tree trunks as compared with other foraging sites.