Climate-induced decline of habitat and connectivity imperils the Endangered Black-bellied Tern (Sterna acuticauda) in the Ganges-Brahmaputra-Mahanadi River Basin

Rivers and wetlands are one of the most biologically diverse ecosystems facilitating vital habitats for a wide range of species. However, the species within these ecosystems are increasingly threatened by climate change and anthropogenic pressures. The Black-bellied Tern ( Sterna acuticauda ), an endangered riverine bird endemic to the Indian subcontinent, is highly reliant on wetland environments. Once widespread in South and Southeast Asia, the species is now locally extinct in much of Southeast Asia. This study evaluates the potential impacts of climate change on habitat suitability and corridor connectivity of S. acuticauda across the Ganges–Brahmaputra–Mahanadi (GBM) River Basin, which remains a key refuge, harboring over 90% of the global population. Current estimates suggest that only 6.10% (143,273 km²) of the GBM Basin provides suitable habitat for this species. In projected future climate scenarios, this suitable area is expected to decline drastically by 88.765% to 93.068%. Moreover, these declines are expected to lead to severe fragmentation of suitable habitats in the future. These spatial transformations diminish both structural and functional landscape connectivity. Circuit-based modeling identified five key ecological corridors, all of which are projected to experience connectivity loss. These findings emphasize the acute vulnerability of water-dependent species under climate change and highlight the urgency of targeted conservation interventions. Therefore, preserving critical riparian habitats, strengthening ecological corridor connectivity, and integrating climate resilience into basin-wide management strategies are vital for safeguarding the future of this imperiled indicator species and ensuring the ecological integrity of riverine wetland systems in Asia.