Urbanization impacts on habitat and bird communities in a sonoran desert ecosystem

Urbanization produces fundamental changes in ecosystem structure and populations. To study urbanization impacts on habitat and avian populations we chose 21 upland sites and 21 riparian sites in metropolitan Phoenix, Arizona, USA. Habitat structure and species composition were measured at each sample point and a variety of landscape-habitat metrics were measured from aerial photographs and recorded as to location using a geographic information system (GIS). Spearman's rank correlations of habitat and avian community descriptor variables tested the strength and significance of the relationship between variables. Full stepwise regression procedures assessed the response to independent variables of landscape-habitat to five bird guilds. Guilds varied in the strength and nature of the relationship between community parameters and several gradients of habitat structure, vegetation, area and site configuration. Significant negative correlations of species richness of permanent resident, winter resident, and neotropical guilds with housing density, road density and volume of exotic woody species were found. These same guilds were positively correlated to riparian area, channel density, and total volume of woody species. Linear and quadratic regression equations explained between 40 and 81% of the observed variation in avian guild richness and abundance. Total volume of woody species was the single most important predictor included in regression equations for four of seven community guilds. The impacts of urbanization on native bird diversity may be reduced if emphasis is placed on maintenance of native vegetation and native riparian channels and banks in urbanized riparian areas.