Impacts of urbanization on multiple dimensions of bird diversity in Atlantic forest landscapes

Urbanization is resulting in habitat loss and fragmentation around the world, but its effects on biodiversity remain poorly understood. We investigated how the increase of urban cover surrounding nine Brazilian Atlantic forest reserves (14 ha - 1058 ha) affects the taxonomic, functional and phylogenetic diversity of bird communities, considering forest and non-forest species separately. Using a multi-scale local landscape approach, we estimated the percentage of urban cover in circular buffers of varying radii (200–1000 m). We calculated 10 complementary metrics of bird diversity and modelled them against the percentage of urban cover using generalized additive models. Urbanization had a negative, non-linear impact on the taxonomic diversity of bird communities, with a sharp decrease of up to 50 % in the effective number of rare, typical and dominant species in landscapes with 20–40 % of urbanization. This decrease was not restricted to forest species (urban avoiders), but also affected non-forest ones (urban utilizers and dwellers). The impact of urbanization on functional and phylogenetic diversity were less evident, suggesting that the vulnerability to urbanization has a weak phylogenetic and phenotypic signal. We conclude that urbanization impacts a broad spectrum of bird clades and traits and drastically reduce the taxonomic diversity of bird communities.