Backyard bird feeders tend to attract aggressive, introduced bird species while discouraging native species that eat
insects and nectar, essentially restructuring urban bird communities and skewing them toward non-native species, a new study says. Data based on nearly 600 surveys of 18,000 birds from 33 species in New Zealand show that yards with bird feeders tended to attract non-native omnivores such as house sparrows, spotted doves, and blackbirds. Outdoor areas without bird feeders had significantly more native bird species such as the grey warbler, whose diet consists mainly of insects. Although the population trends reversed when feeders were removed, the researchers say that over time bird feeders in urban areas likely give non-native bird species a competitive and reproductive edge over native species.