Molecular analysis of amphipods in the diets of migrating shorebirds

Each spring great numbers of shorebirds gather in Delaware Bay, USA during the reproductive season of Horseshoe Crabs Limulus polyphemus to capitalize on crab eggs. Due to overharvesting, the abundance of both crabs and their eggs has significantly declined in the last two decades, and little is known about alternative food types. We examined potential consumption of amphipods by Dunlins Calidris alpina, Semipalmated Sandpipers C. pusilla, Least Sandpipers C. minutilla and Short-billed Dowitchers Limnodromus griseus during spring migration through Delaware Bay, by amplification of prey DNA fragments in feces with amphipod-specific primers. Our analysis shows that amphipods contributed to the diet of shorebirds and we found significant differences in utilization of these crustaceans among species. Over 80% of Least Sandpipers tested positive for amphipod DNA, implying that these birds may rely heavily on amphipods, and possibly other benthic invertebrates, rather than Horseshoe Crab eggs. A considerable proportion of Semipalmated Sandpipers and Short-billed Dowitchers consumed amphipods as well. Together with previously documented use of tidal mudflats and marshes by shorebirds in Delaware Bay, this may suggest new conservation strategies regarding these habitats.