Sanderlings are medium-sized “peep” sandpipers recognizable by their pale non-breeding plumage, black legs and bill, and obsessive wave-chasing habits where they run back and forth on the beach, picking or probing for tiny prey in the wet sand left by receding waves.
You’ll most often see Sanderlings in non-breeding plumage, when they are very pale overall: light gray above and white below, with a blackish mark at the shoulder.
In spring and summer, Sanderlings are spangled black, white, and rich rufous on the head, neck, and back.
At all times, their legs and bills are black.
In flight, white wingstripes contrast with their dark wings.
These extreme long-distance migrants breed only on High Arctic tundra, but during the winter they live on most of the sandy beaches of the world.

Cascais, Lissabon, Portugal, 29 September 2021