Heterogeneous urban green areas are bird diversity hotspots: insights using continental-scale citizen science data

Abstract

Urbanization fragments and destroys natural landscapes, generally decreasing bird diversity. While in some cases bird diversity continuously decreases in response to urbanization, in others a non-linear response is evident, with peak bird diversity observed at intermediate levels of urbanization. But many studies previously investigating this pattern are spatially or temporally constrained. In this study, we analyzed the impacts of urbanization on bird diversity, stratified to native and exotic species. We specifically investigated the differences in bird diversity between natural and urban green areas. We used eBird citizen science data (> 4,000,000 bird-survey lists) and remotely-sensed landcover data, throughout the contiguous United States of America. We found a non-linear response to urbanization for both species richness and Shannon diversity. There was distinctly greater bird richness and Shannon diversity in urban green areas compared to natural green areas. Our observed response is likely explained by an increase in habitat heterogeneity of urban green areas compared with natural green areas. Our work highlights the importance of diverse urban green areas for supporting bird diversity in urban areas. We recommend that urban planning should focus on maintaining high habitat heterogeneity in urban green areas to promote greater bird diversity.