Foraging Behavior of Dendrocopos villosus and D. pubescens in Eastern New York State

Abstract

Studies on differential foraging behavior have usually pertained to the interspecific level (Lack 1947; MacArthur 1958; Dixon 1961; Brewer 1963; Koplin 1969; Koplin and Baldwin 1970). Some recent emphasis, however, has been placed on intraspecific differences (Kilham 1965, 1970; Storer 1966; Selander 1966; Koplin 1967; Ligon 1968; Jackson 1970; Willson 1970). Kilham (1965) noted that female Hairy Woodpeckers (Dendrocopos villosus) feed on elms dying of the Dutch elm disease more frequently than males, and he stated that this differential feeding is adaptive by making more effective use of the environment. Concurrent studies by Jackson (1970), Kilham (1970), and Willson (1970) have shown intersexual partitioning of the foraging niche in the Downy Woodpecker (D. pubescens). Selander and Giller (1963) found that the degree of sexual dimorphism in culmen length of Centurus woodpeckers is greater than any other morphological measurement compared. Their proposal that this disproportionate degree of sexual dimorphism in trophic structure is adaptive and serves to alleviate intersexual competition for food was later confirmed by Selander (1966). In support of this postulate, Koplin (1967) found that the intersexual difference in culmen length of the Northern Three-toed Woodpecker (Picoides tridactylus) correlated with spatial, temporal, and dietary differences in the feeding ecology of the sexes. However, he found no significant differences in foraging behavior of either the Hairy or Downy Woodpeckers, probably because the spruce-fir forest is a marginal habitat for both species. As both the Hairy and Downy Woodpeckers are common residents of the maple-beechhemlock forests of New York, I undertook this study to determine whether there are spatial or temporal differences in their foraging behavior in this location, which correlate with interspecific and intersexual differences in culmen length. METHODS