Drivers of Bird Communities in an Urban Neighborhood Vary by Scale

Given the accelerated pace of global biodiversity loss and rapid urbanization, it is becoming increasingly urgent to identify ways to minimize the costs and maximize the benefits of urban environments for wild flora and fauna. For instance, it has been estimated that 48% of all bird species are experiencing population declines. One of the main drivers of these declines is habitat loss and degradation associated with urbanization. Increased urbanization necessitates a better understanding of how to conserve birds in urban areas. Although relationships between urbanization and bird communities have been explored extensively, few studies have been conducted in residential neighborhoods, and the influence of urban environmental conditions, particularly air pollution, on bird communities remains unclear. In this study, we examined relationships between bird community metrics and environmental measures related to vegetation and air pollution within a residential neighborhood at multiple spatial scales. We found that bird species richness and the average number of native species were positively related to greenness (as measured by the normalized difference vegetation index; NDVI) within 50 m, and negatively associated with ambient levels of NO2 at 200 m. Similarly, we found the Hill-Shannon diversity index was positively associated with canopy cover, but negatively associated with NO2 at 200 m. The average number of invasive bird species, however, was negatively correlated with canopy cover at 50 m. The average number of native birds was negatively related to ultrafine particle (<100 nm in diameter) concentration. Unlike native bird abundances, invasive bird abundances were not sensitive to NO2 or ultrafine particles. Thus, our research suggests that reductions in air pollution, in combination with greening efforts that increase NDVI and canopy cover via the restoration of vegetation within urban neighborhoods, are likely to increase bird diversity and the abundances of native birds while reducing the abundance of invasive birds.