Dietary diversity of multiple shorebird species in an Asian subtropical wetland unveiled by DNA metabarcoding

Global declines in shorebird populations resulting from foraging habitat loss have been recently reported, and the situation within the East Asian-Australasian Flyway (EAAF) is particularly concerning. Despite previous studies that analyzed the foraging niches of shorebirds worldwide, the dietary niche dynamics of shorebirds coexisting in Asia are very poorly understood. This study is therefore among the early few that aim to unveil the trophic organization of shorebirds in a subtropical wetland within the EAAF which is vital for species conservation. Our study first determined the dietary spectra of more than 10 shorebird species, such as Calidris ferruginea (near threatened), Charadrius leschenaultii, and Pluvialis squatarola, by applying DNA metabarcoding with 18S and COI markers to fecal DNA. The diet of Tringa stagnatilis was also characterized, which was previously undescribed. Shorebirds that occurred in the wetland consumed a variety of food items, primarily a high abundance of malacostracans, mollusks, annelids, insects, and some arachnids. Different proportions of plant materials were also detected in many shorebird species. Using the data, we then revealed clear patterns of inter- and intraspecific variations between these shorebirds. Importantly, we specifically compared the similarities of the spring diets among seven sympatric shorebird species. We found that the dietary compositions of the seven species have segregated from each other to varying levels, but the many similar taxa we identified in the diets among these shorebirds imply that these populations of shorebirds could be competing at different levels. Thus, any reductions in the abundance and diversity of these important food resources would likely intensify their inter- and intraspecific competition, and simultaneously threaten the survival of multiple species. With these findings, conservation measures must be taken to protect and monitor the vital food resources for these energy-deprived shorebirds during migration.