A Quantitative Study of the Foraging Ecology of Downy Woodpeckers

Abstract

Studies of the foraging ecology of Downy Woodpeckers (Dendrocopos pubescens) at the University of Kansas Natural History Reservation indicate that there is intersexual partitioning of the foraging niche, seasonal variation in the relative frequency of the modes of foraging, variation in the mode of foraging on live versus dead trees, and seasonal variation in the use of live and dead trees. Partitioning of the foraging niches by the sexes is accomplished behaviorally by a differential use of the available substratum according to limb height and diameter. The degree to which these unisexual subniches are expressed varies on live versus dead trees. Males tend to forage on small branches, generally 5 cm in diameter or less; females tend to forage on the trunk and larger limbs. The mean foraging height of males in live trees (6.0 m) is significantly different from that of males in dead trees (8.9 m); the mean foraging height of females in dead trees (8.4 m) is not significantly different from that of females in live trees (8.1 m) or of males in dead trees. The mean foraging height of males in live trees is significantly different from that of females in live trees. A similar relationship exists among the heights of the trees in which Downy Woodpeckers forage. Both male and female Downy Woodpeckers use sub—surface foraging techniques to a greater extent during the winter and superficial techniques during the warmer months. Greater use of dead trees during winter is also indicated. Dead American elms (Ulmus americana) are used as foraging sites by both sexes to a greater extent than expected by chance. Some other tree species seem to be favored and some avoided by one or both sexes.