Yearly and seasonal variation in the food of red knot chicks in Alaska

Studying animal diets using DNA-metabarcoding of faecal samples provides a non-invasive, high-resolution approach to identify prey. For long-distance migratory shorebirds, such as red knots (Calidris canutus), chick growth depends on the availability of surface-dwelling arthropods during the short Arctic summer, yet the exact diet of the Alaskan-breeding subspecies (C. c. roselaari) remains largely unknown. Using metabarcoding, we characterized the diet of red knot chicks in western-Alaska across four summers (2019, 2022, 2023 and 2024). We identified key arthropod prey taxa and described how diet composition varied among years and throughout the chick period. Diet composition was broadly similar between years, but shifted over the chick-growing period, reflecting temporal changes in prey availability. Weevils (Curculionidae) were the most abundant family in the diet (35.8%), especially early in the season, whereas owlet moths (Noctuidae, 11.1%), ichneumoid wasps (Ichneumonidae, 8.3%), slugs (Agriolimacidae, 6.5%), house flies (Muscidae, 4.8%), and crane flies (Tipulidae, 4.4%) became more prominent later in the season. These patterns suggest that red knot chicks forage opportunistically, with diet composition varying over the season in response to prey emergence and local environmental conditions. The limited representation of many prey families in pitfall traps highlights the need for improved sampling designs to fully capture prey availability. Together, these findings provide a foundation for future work on chick growth, survival, and responses to climate-driven changes in Arctic ecosystems by tundra-breeding shorebirds.