Effects of Urbanization on Avian Community Organization

-The avian community of a mature residential area was studied and compared with an undisturbed climax beech-maple forest. Urbanization was presumed to be responsible for decreasing species richness and diversity, increasing biomass and density, and favoring dominance by a few species. Foraging guilds shifted from forest insectivores that were canopy foliage gleaners or bark drillers to urban ground gleaners. Analyses of habitat structure showed that although urban foliage height diversity was like that of the forest, the urban area contained only one-third of the total percent vegetative cover. As compared to the forest, urban vegetative cover was: (1) significantly less in all but the middle layer; (2) replaced by man-made structures, ground cover and ornamental vegetation in the low and middle layers but dominated the high layer; and (3) highly discontinuous, existing as isolated strata. Differences in avian community organization between the forest and urban area are discussed in relation to urban habitat manipulation and population-suppressing factors. Bird communities of residential and urban areas contain higher bird densities than outlying natural areas (Graber and Graber 1963, Emlen 1974), with only forest edge communities supporting greater densities in temperate zones. In addition to the factors controlling natural communities (Lancaster and Rees 1979), the diversity of birds in urban areas is affected by the age of the neighborhood (Lucid 1974), type of housing (Geis 1974), and degree of urbanization (Batten 1972). Few studies have compared the avifauna of cities with that of outlying natural areas and have measured habitat structure in both communities. The difficulties arise in selecting comparable study areas and quantifying the synthetic urban habitat in relation to natural parameters. In this study, we determined how urbanization affected avian community organization by comparing the ecological characteristics of the birds of a mature residential area with those of the regional vegetative climax, an outlying forest.