Global patterns and drivers of urban bird diversity

The rapid urbanization of the world has profound effects on global biodiversity, and urbanization has been counted among the processes contributing to the homogenization of the world's biota. However, there are few generalities of the patterns and drivers of urban birds and even fewer global comparative studies. Comparable methodologies and datasets are needed to understand, preserve, and monitor biodiversity in cities. We explore the current state of the science in terms of basic patterns of urban birds in the world's cities and lay out a research agenda to improve basic understanding of patterns and processes and to better inform conservation efforts. Urban avifaunas are often portrayed as being species poor and dominated by omnivorous and granivorous species that tend to be nonnative. Common families in cities include Accipitridae, Anatidae, and Scolopacidae, all of which have more species than expected in cities compared to the global distribution of species in these families. Recent research shows that cities support an avifauna dominated by native species and that cities are not homogenized at the global level. However, cities have lost substantial biodiversity compared to predicted peri-urban diversity, and 31 of the world's most invasive bird species are found in cities. Future research is needed to better characterize the anthropogenic, environmental, and ecological drivers of birds in cities. Such mechanistic understanding is the underpinning of effective conservation strategies in a human dominated world.