A sanderling on a winter beach runs down the sand as a wave withdraws, probes rapidly with its short black bill, and turns to outrun the next one. The window matters. As the swash drains, small crustaceans and worms move within reach and the saturated sand offers little resistance to a probing bill, so a few seconds of retreating water is the most productive moment on the beach.
Sanderlings also lack a hind toe, which is uncommon in the sandpiper family and is generally associated with running on firm wet sand. In winter plumage the bird is strikingly pale, close to white below with a dark shoulder mark, so the summer bird, rufous-headed and mottled on Arctic tundra, is often not recognised as the same species.
The familiar beach bird is therefore a high Arctic breeder on holiday. The migration is long and the species winters on sandy coasts on almost every continent. What is not well understood is why sanderling numbers have declined on several flyways despite the species remaining globally widespread.