Calidris

Calidris is a genus of small to medium-sized wading birds in the family Scolopacidae, known in English variously as sandpipers, stints, dunlin, knot, sanderling, and surfbird, that breed across the Arctic and undertake long-distance migrations, forming large mixed flocks on coasts and estuaries during winter. Most species share a broadly similar colour pattern, brownish above and paler, usually white or buff, below, often with a pale supercilium above darker cheeks, though close similarity between species and variable breeding, non-breeding, juvenile, and moulting plumages can make field identification difficult; in North America the smaller species are colloquially known as peeps. Their bills are notably flexible, able to flex at the tip through a mechanism called rhynchokinesis, and carry sensitive nerve endings that let the birds locate buried invertebrate prey by touch while probing wet sand and mud.