Authors: Batary, Peter; Kurucz, Kornelia;Suarez-Rubio, Marcela;Chamberlain, Dan;

Urbanization is one of the most extreme forms of environmental alteration, posing a major threat to biodiversity. We studied the effects of urbanization on avian communities via a systematic review using hierarchical meta-analyses. We found that urbanization had an overall strong negative effect on bird species richness, whereas abundance increased marginally with urbanization. Effects of urbanization on species richness were more negative for studies including public green spaces in the sampled landscapes. In contrast, studies performed solely in the urban matrix revealed a strong positive effect on bird abundance. When performing subset analyses on urban–suburban, suburban–rural and suburban–natural comparisons, species richness decreased from natural to urban areas, but with a stronger decrease at the urban–suburban interface, whereas bird abundance showed a clear intermediate peak along the urban–rural gradient although abundance in natural areas was comparable to that in suburban areas. This suggests that species loss happens especially at the urban–suburban interface, and that the highest abundances occur in suburban areas compared to urban or rural areas. Thus, our study shows the importance of suburban areas, where the majority of birds occur with fairly high species richness.