Avian community composition, but not richness, differs between urban and exurban parks

Abstract

Urban development alters landscape structure and available resources, potentially threatening avian diversity worldwide. However, it is unclear how bird communities respond in areas currently undergoing urban development, particularly in the non-breeding season. We examined avian communities at 8 parks in urban (within established urban matrix; >50% built cover) and 9 parks in exurban (within adjacent grassland; 5–20% built cover) areas in Sacramento County, CA. We measured bird species and abundance, conducting five line-transect surveys per park (85 total). We investigated factors influencing avian assemblage, including local habitat features (land cover, number of trees, fruiting trees and tree species, tree height and diameter at breast height, park size, park age), and landscape features (land cover within 500 m and distance to riparian habitat). Fifty bird species, including 15 migrants, were observed. Total species richness and abundance at urban and exurban parks was not significantly different, but community assemblages differed significantly. Park area positively predicted species richness. Abundance was negatively associated with inpark percent built cover, average number of fruiting trees and landscape-scale percent water cover. Species composition changes were associated with distance to riparian habitat and landscape percent grass cover for all but one exurban park; and with tree height, DBH and park and landscape percent tree cover for urban parks. The expansion of exurban areas in many parts of the world poses a significant risk for natural habitat loss. Parks in such areas should be planned to harbor some of the displaced biodiversity.