From traits to services: How urban avian communities support ecosystem services in Nanjing, China

Balancing biodiversity conservation with the provision of ecosystem services remains a critical challenge in high-density urban environments. Focusing on the main urban area of Nanjing, we integrated four years of citizen science observation records and species functional trait data to investigate how avian functional traits respond to urbanization factors and drive the supply of cultural and regulating ecosystem services. We employed a combination of the fourth-corner model, redundancy analysis, and hierarchical partitioning to analyze these relationships. Additionally, we used spatial prediction techniques and local indicators of spatial association to characterize the spatial distribution patterns of multiple ecosystem services and their coupling with urbanization gradients. The results indicate that environmental variables such as normalized difference vegetation index (NDVI), population density, and slope exhibit significant interactions with avian response traits. At the community level, response traits were significantly correlated with effect traits associated with the provision of regulating and cultural services. NDVI generally had a positive effect on most community-scaled effect traits, whereas building density and impervious surfaces broadly constrained the formation of functional traits within avian communities. The environmental drivers of different types of avian-mediated ecosystem services varied. Regulating services were consistently negatively associated with building height, while cultural services tended to be positively associated with natural conditions such as slope and the largest patch index. Hotspots of ecosystem service were typically concentrated along land—water ecotones, areas with high green space connectivity, and regions characterized by high habitat structural complexity. By coupling trait perspectives with spatial service mapping, this study elucidates how urban form shapes community assembly and service delivery. Our results underscore two actionable levers—enhancing vegetative structural complexity and reducing green space fragmentation—to integrate biodiversity conservation with urban sustainability.