Beyond habitat loss: Spatiotemporal heterogeneity in mediating the effects of urban heat islands on waterbird richness

Urbanization alters avian communities through habitat modification, yet the mechanisms by which urban-induced microclimatic changes influence bird diversity remain poorly understood. In particular, the role of the urban heat island effect in mediating the impacts of urbanization and landscape fragmentation on bird richness has rarely been tested. The Yangtze River Delta Urban Agglomeration, a critical bottleneck along the East Asian–Australasian Flyway and one of the fastest-growing urban regions globally, was selected as the study area. Here, we leverage an extensive dataset of over 10,000 waterbird records (2007–2021) and multi-source remote sensing data to deconstruct the urbanization–urban heat island–waterbird cascade using Structural Equation Modeling. Results suggest that the urban heat island effect acts as a critical mediator linking the adverse impacts of urbanization level and landscape fragmentation on waterbird richness. Moreover, this mediation exhibits distinct spatiotemporal heterogeneity. Seasonally, UHI functions as a primary physiological stressor during the breeding season. Spatially, the driving mechanisms diverge along the urban–rural gradient: in rural peripheries, the urban heat island mediates the impacts of landscape fragmentation, whereas within urban cores, it also mediates the impacts of urbanization level. These findings indicate that traditional strategies focusing solely on habitat area are insufficient. Therefore, we advocate for a paradigm shift in conservation planning that prioritizes habitat climatic suitability, ensuring the persistence of waterbirds in an increasingly warming Anthropocene.