Diet analysis reveals key prey of a Critically Endangered waterbird in aquatic farming habitat

Aquatic farming may provide compensation for the loss of wildlife habitat, however the dietary composition of endangered waterfowl within these modified environments remains poorly understood. The range of the Critically Endangered Baer's Pochard ( Aythya baeri ) has contracted from northeast China to central and northern China. From 2020 to 2023, we conducted bird surveys in 33 key wetlands of Wuhan, one of the southernmost breeding grounds for this species. We also assessed aquatic biodiversity and diet composition in the two areas with the most stable A. baeri populations. A total of 31 aquatic plant species and 78 benthic invertebrate species were identified in these habitats. Significant differences in aquatic plant communities were observed between sites and seasons, but no significant differences were found in the benthic invertebrate communities. Our results indicate that A. baeri has an omnivorous diet. Fecal DNA metabarcoding revealed consistent detection of Nymphaeaceae and Potamogetonaceae, with a high similarity in diet between two sites and seasons. However, the richness of the invertebrate taxa in the diet differed between sites. Stable isotope data further confirmed a higher proportion of hydrophytes in the diet during the breeding season, while crustaceans accounted for a relatively small proportion of the diet. These findings emphasize the ecological importance of submerged vegetation in supporting the foraging needs of A. baeri , and suggest that enhancing hydrophyte abundance may be a feasible conservation strategy. Additionally, aquatic farming may provide some compensatory benefits for the endangered bird conservation, but this depends on specific farming practices. • We give the first quantitative insights into the diet of the Critically Endangered Aythya baeri. • They have a strong reliance on hydrophytes in two different aquatic farming habitats. • Nymphaeaceae and submerged plants were preferred; crustaceans were not a primary choice. • Conservation of this duck requires enhancing submerged vegetation and sustainable aquaculture.