The Sanderling is a small, light-colored sandpiper with a straight, black bill and black legs. The male and female look similar. In breeding plumage, it has a rufous head and neck and a rufous wash that extends onto its back. In non-breeding plumage, the adult is white underneath and very pale gray above while the juveniles are white underneath with a dark and light mottled top. Late-molters, Sanderlings don't reach their breeding plumage until late May. This is the only sandpiper that lacks a hind toe, which allows it to be a strong runner.
There was several large flocks along Copalis Beach.