International importance of tidal flats in the Republic of Korea as shorebird stopover sites in the East Asian–Australasian flyway

Tidal flats along the southwestern coast of the Republic of Korea are known as internationally important habitats for migratory shorebirds in the East Asian–Australasian Flyway (EAAF). Recent habitat destruction at stopover sites has caused declines in migratory shorebird populations, but the population sizes and habitat use patterns of these species remain poorly understood. We investigated the status of migratory shorebirds using tidal flats in the Republic of Korea. Using population sizes and species diversity, we identified internationally important stopover sites for shorebirds and compared the results of shorebird surveys conducted during the 2014–2015 and 2019–2020 migration period. On Korean tidal flats, 230,000–270,000 shorebirds were counted on their northward migration, and approximately 120,000 individuals were counted on their southward migration. All surveyed areas met internationally important stopover site criteria because they contained more than 0.25% of the shorebird population of one or more species (as opposed to 1% to allow for turnover). We estimated that approximately 20% of the EAAF populations of the Eurasian Curlew (Numenius arquata), Far Eastern Curlew (Numenius madagascariensis), Kentish Plover (Charadrius alexandrinus), and Eurasian Oystercatcher (Haematopus ostralegus) used tidal flats in the Republic of Korea. Importantly, we also confirmed that the critically endangered Spoon-billed Sandpiper (Calidris pygmaea) continued to migrate to the Republic of Korea. These results imply that Korean tidal flats still have great international importance as shorebird stopover sites. Thus, expanding the protection of internationally important stopover sites is necessary to ensure the conservation of migratory shorebirds in the EAAF.