Bird Community Structure on Early-growth Clearcuts in Western Oregon

Abstract

Total density of nesting birds ranged from 326-552 birds/40.5 ha on 12 early-growth clearcuts in western Oregon. The number of nesting species varied little among sites. Predominant species (ca. 50 birds/40.5 ha/site) on all sites were the whitecrowned sparrow (Zonotrz'chzi'a leucophrys), song sparrow (Melospzza melodia), rufous hummingbird (Selasphorus rufus) and Swainson's thrush (Catharus ustulatus). Nesting species with moderate density estimates (ca. 30 birds/40.5 ha) were the willow flycatcher (Empidonax trailliO), American goldfinch (Cardueli's tristis), rufous-sided towhee (Pzipilo erythrophthalmus) and orange-crowned warbler ( Vermivora celata) MacGillivray's warbler (Oporornis tolmzel) and Wilson's warbler (Wilsoni'a pusilla) were present on all sites, although their densities were low (ca. 20 birds/40.5 ha). Discriminant function analysis of habitat use by birds identified three functions with significant ability to separate bird communities. Increasing cover and height of deciduous trees (Factor I) accounted for the majority of variation (74.5 %). Placement of species on the first three discriminant axes was related primarily to varying combinations of shrubs and deciduous trees. Total density of nesting birds decreased with increasing height of conifers, but increased with increasing cover of deciduous trees. Densities of the bird communities increased where patches of deciduous trees formed breaks in plant communities dominated by shrubs and conifers.