Foraging Behavior of Bark-Foraging Birds in the Sierra Nevada

Abstract

Data on foraging behavior are often used for examining use of habitat and describing community structure among co-occurring species of birds using the same resource base (e.g., Johnson 1966, Eckhardt 1979, Rusterholz 1981). Differences in tree species, foliage morphology, and bark structure may influence the types of prey taken and the species of bird using the substrate (e.g., Jackson 1979, Holmes and Robinson 1981, Robinson and Holmes 1984). Elucidation of foraging behaviors and tree species preferences is important if we are to determine the role of birds in forest ecosystems, and make informed decisions regarding management of these forests. In this study we describe the use of tree species, foraging modes, and foraging substrates by a group (or guild, sensu Root 1967) of bark-foraging birds breeding in the western Sierra Nevada. A similar study on foliage insectivores was conducted previously near our study area (see Airola and Barrett 1985). The species analyzed, in order of decreasing abundance, were: Red-breasted Nuthatch (Sitta canadensis), Brown Creeper (Certhia americana), Red-breasted Sapsucker (Sphyrapicus ruber), White-headed Woodpecker (Picoides albolarvatus), Hairy Woodpecker (P. villosus), and Pileated Woodpecker (Dryocopus pileatus) (see Morrison et al. 1986). All are typical inhabitants of coniferous forests in the Sierra Nevada (Grinnell and Miller 1944). The Downy Woodpecker (Picoides pubescens) and Northern Flicker (Colaptes auratus) occurred rarely in our study area and are not analyzed herein. STUDY AREA