Stable isotopes show that across non-breeding sites migratory shorebirds rely on different primary producers

Coastal environments are amongst the most heavily impacted and threatened natural systems. One group of threatened species that are reliant on coastal ecosystems for survival are migratory shorebirds. These birds often consume invertebrates on mudflats, however, the nutritional sources for these invertebrates likely derive from other areas of the coastal system, such as saltmarsh and mangroves. It is critical that these nutrient provisioning habitats are identified, so they can be protected or restored to the benefit of shorebirds. The aim of this study was to identify the primary producers underpinning shorebird food chains. We quantified among- and within-species variation in basal nutrition in two threatened migratory shorebird species, the Bar-tailed Godwit Limosa lapponica and the Curlew Sandpiper Calidris ferruginea , at three sites of international significance – two sites on Australia’s west coast, and a third on the east coast. We measured the δ 15 N and δ 13 C isotopic composition of each shorebird species and the dominant primary producers at each location. In some sites, benthic organic matter from mudflats was the top contributor to the birds’ nutrition, highlighting the value of this poorly protected habitat type for provisioning shorebirds. Other highly contributing primary producers to shorebird nutrition include mangroves at one west coast site, and saltmarsh and mangroves at the east coast site. Our results suggest that shorebirds and their invertebrate prey likely show dietary plasticity at differing spatial scales, indicating that local-scale analyses are critical to revealing the dominant habitats that support shorebird food chains. • Migratory shorebirds are a threatened group of birds reliant on coastal habitats. • Stable isotopes were used to identify habitats provisioning shorebird food chains. • The top contributing primary producers to shorebird nutrition varied by location. • Shorebirds and their prey likely show dietary plasticity across spatial scales. • Local-scale analysis is needed to reveal habitats that support shorebird food chains.