Cumulative Duration and Habitat Selection Across the Annual-Cycle Stages: Links to Human Modification in Two...

Although tracking studies have identified shorebird migration routes along the East Asian-Australasian Flyway, how cumulative duration and habitat selection vary across annual-cycle stages and relate to human modification of habitats remains poorly understood. We integrated GPS tracking data (2017-2025), high-resolution land-use data, and human modification mapping to identify breeding, stopover, and wintering regions for two declining shorebirds: the Black-tailed Godwit (Limosa limosa; 18 individuals) and Eurasian Curlew (Numenius arquata; 25 individuals). We identified 93 regions for godwits and 67 for curlews. Godwits exhibited the longest mean cumulative duration at the Vilyuy River (breeding), Binzhou coast (southward migration), Gulf of Thailand (wintering), and Tianjin coast (northward migration). Curlews spent the longest duration at the Horqin Right Wing Middle Banner farm (breeding), Tianjin coast (southward migration and wintering), and Ingoda River (northward migration). Across stages, godwits exhibited broader habitat selection than curlews, though both preferred marsh, tidal flat, and flooded flat habitats. Cumulative duration increased significantly with human modification for curlews during migration, whereas no significant relationship was detected for godwits. Notably, both species repeatedly used highly modified coastal regions for extended periods, particularly basins draining into the Gulf of Thailand between the Mekong and Kolok rivers, the Chao Phraya River Basin, the Tianjin coast, and the Putian coast. These findings improve our understanding of the full annual-cycle habitat use and highlight the critical need to conserve key coastal regions while mitigating anthropogenic pressures across the flyway.