L. A. D. Williams, Michael Stat, Andrea S. Griffin
ABSTRACT Estuarine habitats are amongst the most threatened globally. Fortunately, the ecosystem services of estuaries have been recognised in recent decades resulting in a shift to preserving and restoring estuaries. One group of threatened species that rely heavily on estuaries for their food provisioning qualities are migratory shorebirds. These birds largely consume macroinvertebrate prey taken from the intertidal flats of estuaries and other coastal areas. It is critical to know the invertebrate species eaten by these birds so areas of coastal estuaries hosting these invertebrates can be protected, and so that restoration activities can create habitat that encourages the inhabitation of these dietary invertebrates to the benefit of shorebirds. The aim of this study was to identify the dietary organisms consumed by migratory shorebirds at a southern hemisphere non-breeding site. We used environmental DNA (eDNA) metabarcoding of shorebird scats to characterise and compare the dietary richness and taxa composition of two threatened migratory shorebird species, the Bar-tailed Godwit Limosa lapponica and the Far Eastern Curlew Numenius madagascariensis at an internationally significant shorebird site on Australia’s east coast. Both shorebird species had diets of similar taxa richness but differed in their taxa composition and hence showed niche differentiation. Crustaceans, mainly crabs, dominated the diet of both shorebirds; however, Bar-tailed Godwit diet was also characterised by a gastropod and fish. Several terrestrial invertebrates were also detected in scat samples of both shorebird species. Our results suggest that protected and restored estuarine tidal flats should contain a high level of macroinvertebrate richness, particularly of crustaceans, to support shorebirds. Associated terrestrial habitats should also be protected and restored for their role in providing supplemental dietary items for shorebirds.