Air pollution and greenness independently and interactively influence bird communities in an urban neighborhood

Given the accelerated pace of global biodiversity loss and 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 declines. One of the main drivers of these declines is habitat loss and degradation associated with urbanization. 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 was 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 volume density but negatively associated with NO₂ at 200 m. As ultrafine particle (UFP; <100 nm in diameter) concentration decreased, the strength of the positive relationship between NDVI and the relative abundance of native birds increased. We also observed a negative relationship between the abundance of native birds and NO₂ at 200 m. Unlike native birds, invasive birds were not sensitive to NO₂ or UFPs. Moreover, the average number of invasive birds was negatively correlated with canopy volume density at 50 m. Thus, our research suggests that reductions in air pollution, in combination with greening efforts that increase NDVI and canopy volume density 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.