Urban bird community composition influenced by size of urban green spaces, presence of native forest, and urbanization

Understanding what determines wildlife species richness and community composition in urban green spaces is important for wildlife management and urban planning. Numerous studies have assessed the relationships between attributes of urban green spaces (size, vegetation, isolation, urbanization) and bird species richness, but little is known about how these factors influence community composition. I censused breeding land birds in 93 urban green spaces in Oslo, Norway, and species were grouped according to ecology (habitat preference, nest site, migration, diet, and red-list status). I analysed how species richness and, in particular, how community composition (relative proportion of different ecological groups) was influenced by size of urban green spaces, presence of native forest, isolation (i.e. distance from the periphery of the city) and urban zone (i.e. centre or periphery of city). Species richness increased with size of green spaces and presence of native forest, but did not decrease towards the city centre. Community composition was affected most strongly by presence of native forest, but site size and urbanization affected some ecological groups. Specifically, sensitive ecological groups of birds (in particular forest species, ground-nesters, migratory species, and species with a specialist diet) depended in particular on the presence of native forest in urban green spaces, with additional positive effects of increasing size of urban green spaces and location close to the periphery of the city.