Habitat Utilization by Four Species of Woodpeckers in a Central Illinois Woodland

Abstract

A sympatric guild consisting of the red-headed woodpecker (Melanerpes erythrocephalus), the downy woodpecker) (Dendrocopus pubescens), the red-bellied woodpecker (Centurus carolinus) and the yellow-bellied sapsucker (Sphyrapicus varius) segregated realized niches by: (1) differential foraging techniques; (2) exploiting different height classes; (3) selection of different tree species; (4) use of relative different amounts of alive and dead substrate; (5) differential selection of limb size. In downy woodpeckers, sexes separated the species' realized niche into subniches, which in the past may have caused evolution of different bill structures. Yellow-bellied sapsuckers exploited primarily a sap resource from hickory trees while in wigration. They foraged on larger limbs at lower levels. Red-headed woodpeckers had a more restricted woodland foraging pattern than did downies and red-bellied woodpeckers. Red-heads, however, spent more time out of the wooded area. Intersexual overlap values for the sexually dimorphic downies were greater than interspecific values. INTRODUCTION The principle of competitive exclusion (Hardin, 1960) implies that ecologically sirnilar, cohabiting species should exhibit various degrees of evolutionary divergence which reduce competition and thus increase fitness. The nature of divergence or niche differentiation of sympatric species of birds has been the subject of several ecological investigations, and differential foraging patterns have been found to be a major factor permitting coexistence (Dixson, 1961; Koplin, 1969; Lack, 1954; MacArthur, 1958; Root, 1966; Willson, 1970). Evolutionary divergence also occurs intersexually, presumably to reduce competition and thus allow strengthening of the pair bond. Davis (1965) and Selander and Giller (1959) have shown that sexual dimorphism in bill length exceeds that in other size characters in most species of woodpeckers. Selander (1966) discussed the role of bill dimorphism in reducing intraspecific competition and presented evidence that in Centurus striatus on Hispaniola, both bill sizes and feeding behavior of the sexes were different. Red-headed woodpeckers (Melanerpes erythrocephalus), downy woodpeckers (Dendrocopus pubescens), red-bellied woodpeckers (Centurus carolinus) and yellow-bellied sapsuckers (Sphyrapicus varius), all occur in central Illinois during the early spring. This study was initiated to quantify the behavioral and habitat use patterns which segregate these species and any intersexual differences in behavioral and habitat use patterns in the downy woodpecker. Specific questions to be answered were: (1) how does a sympatric guild of woodpeckers segregate its respective niches; (2) are the real-