Calidris

Calidris is a genus of Arctic-breeding, strongly migratory wading birds in the family Scolopacidae. These birds form huge mixed flocks on coasts and estuaries in winter. They are small to medium-sized sandpipers, long-winged and relatively short-billed; some are difficult to identify because of the similarity between species, and various breeding, non-breeding, juvenile, and moulting plumages. With a few exceptions, they have a fairly stereotypical colour pattern, being brownish above and lighter, usually white or buffy coloured, on much of the underside. They often have a lighter supercilium above brownish cheeks. The species are variously known in English as sandpipers or (particularly the smaller species) stints; some have their own unique names, with dunlin (a mediaeval name meaning "[small] brown bird"), knot (imitative of its call), ruff (named after its male display plumage), and sanderling and surfbird (named after their habitat and behaviour). In North America, the smaller species are often known colloquially as peeps. Their bills are flexible, able to exhibit rhynchokinesis, and have sensitive tips which contain numerous corpuscles of Herbst. This enables the birds to locate buried prey items, which they typically seek with restless running and probing. Migratory shorebirds are shown to have declined in reproductive traits because of temporal changes of their breeding seasons.