Geographic Variation in the Diet of Red Knot ( Calidris canutus ) Chicks Reflects Local Prey Communities

ABSTRACT Aim To describe and compare the diets of an Arctic‐breeding shorebird, the Red Knot ( Calidris canutus ), across three geographically distinct breeding sites. We aimed to document the dietary patterns and identify key prey groups that characterise each population's foraging ecology. Location Northwest Alaska (Nome), Northeast Greenland (Zackenberg) and North‐Central Russia (Taimyr Peninsula). Taxon Red Knot (Aves: Calidris canutus ). Methods We characterised chick diet by applying COI DNA metabarcoding to faecal samples and quantified local prey availability using standardised arthropod pitfall trap sampling at the three Arctic breeding sites. We described and compared the dietary composition, diversity, and relative abundance of major prey taxa among locations. Results We found substantial geographical variation in the chick diet. Diptera was a major food source across all locations, but its constituent families and importance varied. In Taimyr, the diet was dominated by Tipulidae (crane flies), comprising nearly 50% of the relative read abundance (RRA). In contrast, chicks in Greenland consumed a diet dominated by Diptera (87.8%) that almost entirely lacked Tipulidae. The diet in Alaska was the most diverse, with balanced contributions from Diptera (28.5%), Coleoptera (22.3%), and Lepidoptera (23.2%), along with other invertebrate groups, including Agriolimacidae. Main Conclusions The diet of Red Knot chicks differed among the study sites and appeared to be shaped primarily by the local availability of arthropod prey. This foraging plasticity allows the species to breed successfully across a wide circumpolar range with a heterogeneous prey landscape. However, this distinct specialisation on local prey, particularly Tipulidae in Taimyr, may create a critical phenological vulnerability.