Disentangling the diet composition of chicks of Arctic shorebirds provides a new perspective on trophic mismatches

With rapid climate change over the past decades, organisms living in seasonal environments are suggested to increasingly face trophic mismatches: the disruption of synchrony between different trophic levels due to a different phenological response to increasing temperatures. Strong effects of mismatches are especially expected in the Arctic region, where climatic changes are most pronounced. Nevertheless, relatively few studies have found strong evidence for trophic mismatches between the breeding period of Arctic-breeding shorebirds and the arthropod prey on which they rely. Here we argue that this is potentially caused by a generalization of trophic interactions. While many studies have measured the mismatch relative to the peak in abundance of all available arthropod species, we use metabarcoding of prey items in faeces to show that chicks of four different shorebird species (red knot, curlew sandpiper, little stint, and red phalarope) strongly differ in their arthropod diet. We found that two arthropod families, Tipulidae and Chironomidae, on average contributed >50% to the diet of chicks. While red knot chicks were relying mainly on Tipulidae (70% in 2018 and 39% in 2019), the chicks of the other three shorebird species were mainly preying on Chironomidae (43% for red phalarope, 37% for curlew sandpiper and 44% for little stint). We found that taking into account the species-specific diet changed our measure of trophic mismatch for two out of four shorebird species. We conclude that ignoring diet data may hamper our understanding of trophic mismatches.