We gathered presence/absence and abundance data from published studies and reports for 319 well-characterized assemblages spanning 50 cities from Africa, Australia, Europe, North America and South America. We focused on cities with comparable survey data within urban habitats and in nearby natural habitat. The final dataset contains almost 10,000 records for 1507bird species, 66 of which are introduced (non-native) in at least one study region. Species abundance per unit area or unit time were available for 269 assemblages from 42 cities, comprising 1353 species. Following Newbold et al. (2015), we used published habitat descriptions to classify the intensity of human use in urban habitats for each assemblage: (1) highly urbanised environments mainly contain densely packed buildings with vegetation scarce or absent; (2) moderately urbanised environments are residential areas with single-family houses and associated gardens; and (3) little-urbanised environments have few buildings and abundant vegetation (e.g. urban parks). The habitats outside the city were assigned to either natural vegetation or rural habitat based on the description of the habitat given in the source paper. Standardised survey methods were used across habitats within each region.

We gathered presence/absence and abundance data from published studies and reports to characterize avian assemblages. The survey method varied across studies, but the same method was used for each habitat within a particular region, making data comparable using appropriate models.