Local and landscape drivers of bird abundance, species richness, and trait composition in urban agroecosystems

Abstract

Urban gardens, or spaces that include vegetables, fruit trees, and ornamental plants, can support bird species and communities by providing food and nesting habitat within urban landscapes. Yet, variation in management of gardens (e.g., garden size, number of tree and shrub species, ground cover) and the landscape (e.g., urban cover, landscape diversity) that surrounds them may alter communities within gardens. We examined how garden management and landscape features influence bird abundance, richness, species composition, and traits in 19 urban community gardens in the central coast of California. We found that bird abundance was higher in larger gardens and in gardens with more grass, and species richness was higher in larger gardens. Bird abundance also differed with garden ecoregion. Urban cover influenced bird species composition while bird trait distributions were influenced by urban cover, ecoregion, and grass cover. Gardens with more urban cover supported fewer insectivores, ground-nesters, and forest-associated birds, higher nesting height and more urban-associated bird species. Gardens in the ecoregion closer to the coast had more cliff nesters and more marsh-associated birds. Although urban cover and ecoregion were important for the composition and trait distribution of birds, manipulation of garden management and size may promote bird species richness, or abundance of functionally important birds in gardens.