Spatial and temporal dynamics of wintering waterbird communities in South Korea along the East Asian–Australasian flyway

Wetlands underpin biodiversity and vital ecosystem services but are rapidly altered by climate and land-use change. We analyzed nationwide mid-winter counts from the Winter Waterbird Census of Korea (WWCK) to resolve spatial and temporal dynamics of wintering waterbird communities across South Korea from 2010 to 2020. Using a self-organizing map (SOM), we classified 208 sites into six ecologically interpretable assemblages spanning coastal, riverine, lacustrine, tidal-flat, and Jeju Island/southern mosaic. Indicator species were identified using the Indicator Value (IndVal) method, which quantifies species’ associations with specific assemblages, and assemblage-level trajectories were quantified with Multispecies Indices (MSIs; 2010 = 1.0). Trajectories diverged among assemblages. Coastal, seabird-dominated sites (cluster 1) declined steadily (−2.8% yr⁻¹; −41.3% overall), whereas large river–lake systems (cluster 4) and the Jeju/southern mosaic (cluster 6) increased (+5.0% yr⁻¹; +60.1% overall and +3.0% yr⁻¹; +30.4% overall, respectively). Tidal-flat communities (cluster 5) were broadly stable (+0.1% yr⁻¹; +3.6% overall). Generalized linear models related MSIs to human and environmental factors, revealing negative associations with aquaculture (cluster 1), salt pans (cluster 5), and streams & rivers (cluster 4), and a positive association with rice-field extent in inland systems (cluster 4). These results show that wintering community change is structured by habitat context and human use. We recommend habitat-tailored actions: bycatch mitigation and aquaculture management along coasts; protection and water-level management at reservoirs and rivers; wildlife-friendly rice-field practices; and maintenance of Yellow Sea tidal flats and roost–forage linkages. Implemented within East Asian–Australasian Flyway partnerships, such measures can help stabilize or reverse declines in migratory waterbirds.