Ecological traits and landscape characteristics predicting bird sensitivity to urbanization in city parks

Habitat loss and fragmentation caused by urbanization often have negative impacts on wildlife in cities. There are considerable studies investigating the relationship between species traits and fragmentation vulnerability. However, so far, very few studies have examined the influence of species traits combined with landscape factors on vulnerability to urbanization in urbanized landscapes. In this study, we investigated how species traits and park characteristics influenced bird sensitivity to urbanization in the highly urbanized city of Nanjing, China. We used the line-transect method to survey birds in 37 urban parks. For each bird species, we collected data on nine life-history and ecological traits that are commonly assumed to influence urbanization vulnerability. For each park, we selected six landscape variables that are commonly considered to influence bird response to urbanization. After phylogenetic correction, the nine species traits were used separately and in combination to evaluate their associations with species abundance, an indicator of urbanization vulnerability. We then used the RLQ and fourth-corner analyses to test relationships between species traits and environmental variables. We found that the 75 species analyzed demonstrated considerable variation in vulnerability to urbanization. Using PGLS analyses and model averaging, we found that habitat specificity was the single best ecological predictor of urbanization vulnerability in birds in Nanjing city parks. The RLQ analysis showed that body size and habitat specificity were correlated with distance to city center and connectivity of the parks, reflecting strong effects of trait-mediated environmental filters that selectively benefit species with smaller body mass and lower habitat specificity in urbanized landscape. Therefore, conservation efforts giving priority to species with high habitat specificity and to parks with high connectivity and far away from the city center may prove effective for the preservation of bird diversity in our highly urbanized system. Meanwhile, preventing future habitat loss and destruction in existing city parks may also effectively conserve these vulnerable species.