Effects of Urbanization on Breeding Bird Community Structure in Southwestern Desert Habitats

Breeding bird communities in Sonoran Desert habitats show strong correlations between total bird density and an index of vegetation volume. We have suggested that this empirical relationship is due to responses of breeding birds to critical resources, for which vegetation volume is an accurate estimator. In 1987, we conducted a study in Tucson, Arizona, to determine how this empirical relationship is affected by the presence of exotic species of plants and birds, and other factors associated with urbanization. We supported five predictions of our resource-based hypothesis by examining patterns of bird density and diversity in 34 neighborhoods. Densities of territorial native bird species, as well as native species richness and overall species diversity, were strongly correlated with the vegetation volume of native plant species, and uncorrelated with volume of exotic plant species. Densities of exotic and nonterritorial native birds correlated with exotic vegetation volume, the factor which best estimated the distribution of roosting and nesting sites preferred by these species. Vegetation factors explained more of the variance in breeding bird density than did measures of housing density. We interpret these results as confirming our hypothesis that densities of breeding birds correlate strongest with factors associated with critical resources. In addition, these patterns suggest that native bird populations may be better retained in areas of urban development by landscaping with native plants in such a way as to retain predevelopment distributions of vegetation volume.