THE DISTRIBUTION OF AN AVIAN GUILD ALONG A TEMPERATE ELEVATIONAL GRADIENT: THE IMPORTANCE AND EXPRESSION OF COMPETITION'

摘要: A guild of ground-foraging, insectivorous birds which seasonally occupy montane tem- perate forests was investigated. By examining the roles interspecific competition and specific habitat selection, I have dissected factors controlling distribution patterns members along extensive elevational gradients. The composed Hylocichla mustelina (Wood Thrush), Catharus fuscescens (Veery), C. guttatus (Hermit ustulatus (Swainson's minimus (Gray-cheeked Thrush). five thrush species are sympatric on high mountains in northeastern United States, but as one proceeds southward down Appalachian Mountain chain, drop out at a time. Anecdotal information indicated that showed amplitude expansion dropped with decreasing latitude. As consequence opportunity for ecological release southern latitudes, ideally suited testing role determining distributional limits when sympatric. studied behavioral interactions selection sympatry States. distinct distributions these gradients, large spatial overlaps between adjacent were observed. To test significant differences breeding territories quantified by measuring 55 structural variables. Using stepwise discriminant function analysis, detected statistically species' habitats. employing subset 9 initial variables, over 77% Northeastern quantifications assigned to correct group. Additional extracted from niche analysis breadth each degree overlap species, provided insight into limiting similarity allowed coexisting species. Song playback used contribution observed distri- bution patterns. All greater response conspecific song. results overt contributed little or nothing mountains, five-member Southeastern mountains. In Smoky range only H. breed. identical quantification techniques, tested two types not occupied other three Evidence obtained, implying strong Thus, my further implicate an integral force contributing organization temperate bird communities.