Dynamics of coastal wetlands and their impacts on migratory bird habitats in China-Southeast Asia-South Asia

Coastal wetlands are vital for sustaining migratory bird populations, providing essential stopover and wintering (or breeding) habitats. However, the interactions between coastal wetland and migratory bird habitats remain understudied. Utilizing a long-term global wetland dataset, this study examines the spatiotemporal variations of coastal wetlands across the China–Southeast Asia–South Asia (CSESA) region and their impacts on migratory bird habitats. We identify a net gain of coastal wetlands in the studied area, which is dominated by mangroves, permanent water bodies, and tidal flats, from 2000 to 2022. However, gain and loss of coastal wetlands exhibits heterogeneity across regions, with concentrated occurrences in coastal Jiangsu and Bohai Bay in China, Borneo and Sumatra in Indonesia, the Ganges Delta, and the tidal estuary along the India-Pakistan border. Considering different wetland types, swamps, marshes, and salt marshes expanded throughout the study period, whereas tidal flats, flooded flats, and mangroves suffered substantial losses, with tidal flat losses surpassing gains 1.46 times. Non-breeding season and resident habitats are most significantly affected, particularly for Chlidonias leucopterus, Tringa nebularia, and Charadrius dubius. Passage and breeding season habitats are also influenced by net loss of coastal wetlands. Although over 70 % of the affected habitats belong to Least Concern species, significant impacts are also observed in those of Near Threatened, Vulnerable, and Endangered species. These findings highlight the ecological consequences of coastal wetland dynamics, providing a scientific basis for regional strategies of wetland conservation and habitat protection.