Omnivorous diets of sympatric duck species in a subtropical East Asia wetland unveiled by multi-marker DNA metabarcoding

Abstract

The East Asian-Australasian Flyway (EAAF) is experiencing notable population decreases in its migratory waterbird species. Our understanding of the foraging ecology of these waterbird species, including ducks, is crucial for monitoring and safeguarding their food sources and wetland habitats. Here, we used a DNA metabarcoding approach to analyze the fecal DNA from duck species to elucidate their dietary composition during the wintering period in a subtropical East Asian wetland. By employing multiple markers (18S, COI, and trnL) targeting different taxonomic groups and levels, we offered a comprehensive dietary analysis for omnivores that consume both plants and animals. We revealed the dietary compositions of common migratory duck species and their intraspecific and interspecific variations. While ducks are generally known to be omnivorous, Anas crecca had a more specialized diet and was primarily herbivorous throughout winter. In contrast, the sympatric Mareca penelope and Spatula clypeata exhibited a more omnivorous foraging behavior. Moreover, A. crecca displayed less dietary variation among individuals, while individuals of M. penelope and S. clypeata were highly variable in their diets. Comparing our results with those of studies conducted in different regions, we found that the dietary compositions of these duck species varied to different degrees across geographic locations. This variation underscores the flexibility of these duck species in their diets and their adaptable foraging strategies. Our findings also indicate that grasslands rich in herbaceous plants and aquatic environments abundant in small aquatic invertebrates are vital foraging habitats for duck species during their winter stay.