Remote and local threats are associated with population change in Taiwanese migratory waterbirds

Although several countries along the East Asian-Australasian Flyway have recently begun reporting population trends and identifying threats to migratory waterbirds, there remains rather sparse geographical coverage of systematic waterbird monitoring, impeding our understanding of the flyway-wide status of waterbird populations. To fill this gap, we used the data from a nationwide citizen science project, the “Taiwan New Year Bird Count'' to examine recent population trends of 31 migratory waterbird species across Taiwan, and within three of its waterbird hotspot regions, between 2014 and 2021. Island-wide, the abundance of two species declined significantly while five species increased. However, there was substantial heterogeneity in population trends among regions, with nine species declining significantly in Yi-Lan, four species in Chang-Hua and one species in Chia-Nan. Conversely, 11 species increased significantly in Chia-Nan, one species in Chang-Hua, but no species increased in Yi-Lan. This suggests that a combination of local and remote factors is driving population change in Taiwanese migratory waterbirds. Moreover, species that use local rice paddies or are dependent on tidal flats around the Yellow Sea were more likely to show population declines, and those able to use aquacultural wetlands showed growth. These results suggest that recent rice paddy loss and habitat loss in the Yellow Sea have been contributing to migratory waterbird declines in Taiwanese wetlands. Our findings suggest that local land use planning policies within Taiwan as well as mitigation of Yellow Sea tidal flat loss are likely to be complementary in safeguarding the future of migratory waterbirds in Taiwan.