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.

Taxonomy

The genus Calidris was introduced in 1804 by the German naturalist Blasius Merrem with the red knot as the type species. The genus name is from Ancient Greek kalidris or skalidris, a term used by Aristotle for an unidentified grey-coloured waterside bird.

Many of the species have been treated under other generic names at various times in the past, but these treatments leave Calidris polyphyletic; synonyms are in brackets in the list below.

The genus contain 24 species:

Red knot Calidris canutus
Great knot Calidris tenuirostris
Surfbird Calidris virgata (syn. Aphriza virgata)
Ruff Calidris pugnax (syn. Philomachus pugnax)
Sharp-tailed sandpiper Calidris acuminata
Broad-billed sandpiper Calidris falcinellus (syn. Limicola falcinellus)
Curlew sandpiper Calidris ferruginea (syn. Erolia ferruginea)
Stilt sandpiper Calidris himantopus (syn. Micropalama himantopus)
Spoon-billed sandpiper Calidris pygmaea (syn. Eurynorhynchus pygmaeus)
Red-necked stint Calidris ruficollis
Temminck's stint Calidris temminckii
Long-toed stint Calidris subminuta
Buff-breasted sandpiper Calidris subruficollis (syn. Tryngites subruficollis)
Sanderling Calidris alba (syn. Crocethia alba)
Dunlin Calidris alpina
Purple sandpiper Calidris maritima
Rock sandpiper Calidris ptilocnemis
Baird's sandpiper Calidris bairdii
Pectoral sandpiper Calidris melanotos
Semipalmated sandpiper Calidris pusilla (syn. Ereunetes pusillus)
Western sandpiper Calidris mauri
Little stint Calidris minuta
Least sandpiper Calidris minutilla
White-rumped sandpiper Calidris fuscicollis

The following species-level cladogram is based on a molecular phylogenetic study by David Černý and Rossy Natale that was published in 2022. Some of the nodes are only weakly supported by the sequence data.

Calidris	Red knot – Calidris canutus Great knot – Calidris tenuirostris Surfbird – Calidris virgata Ruff – Calidris pugnax Sharp-tailed sandpiper – Calidris acuminata Broad-billed sandpiper – Calidris falcinellus Curlew sandpiper – Calidris ferruginea Stilt sandpiper – Calidris himantopus Spoon-billed sandpiper – Calidris pygmaea Red-necked stint – Calidris ruficollis Long-toed stint – Calidris subminuta Temminck's stint – Calidris temminckii Buff-breasted sandpiper – Calidris subruficollis Sanderling – Calidris alba Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis Baird's sandpiper – Calidris bairdii Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Red knot – Calidris canutus Great knot – Calidris tenuirostris Surfbird – Calidris virgata
	Red knot – Calidris canutus

	Great knot – Calidris tenuirostris Surfbird – Calidris virgata
	Great knot – Calidris tenuirostris

	Surfbird – Calidris virgata



	Ruff – Calidris pugnax Sharp-tailed sandpiper – Calidris acuminata Broad-billed sandpiper – Calidris falcinellus Curlew sandpiper – Calidris ferruginea Stilt sandpiper – Calidris himantopus Spoon-billed sandpiper – Calidris pygmaea Red-necked stint – Calidris ruficollis Long-toed stint – Calidris subminuta Temminck's stint – Calidris temminckii Buff-breasted sandpiper – Calidris subruficollis Sanderling – Calidris alba Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis Baird's sandpiper – Calidris bairdii Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Ruff – Calidris pugnax

	Sharp-tailed sandpiper – Calidris acuminata Broad-billed sandpiper – Calidris falcinellus Curlew sandpiper – Calidris ferruginea Stilt sandpiper – Calidris himantopus Spoon-billed sandpiper – Calidris pygmaea Red-necked stint – Calidris ruficollis Long-toed stint – Calidris subminuta Temminck's stint – Calidris temminckii Buff-breasted sandpiper – Calidris subruficollis Sanderling – Calidris alba Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis Baird's sandpiper – Calidris bairdii Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Sharp-tailed sandpiper – Calidris acuminata Broad-billed sandpiper – Calidris falcinellus
	Sharp-tailed sandpiper – Calidris acuminata

	Broad-billed sandpiper – Calidris falcinellus


	Curlew sandpiper – Calidris ferruginea Stilt sandpiper – Calidris himantopus Spoon-billed sandpiper – Calidris pygmaea Red-necked stint – Calidris ruficollis Long-toed stint – Calidris subminuta Temminck's stint – Calidris temminckii Buff-breasted sandpiper – Calidris subruficollis Sanderling – Calidris alba Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis Baird's sandpiper – Calidris bairdii Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Curlew sandpiper – Calidris ferruginea Stilt sandpiper – Calidris himantopus Spoon-billed sandpiper – Calidris pygmaea Red-necked stint – Calidris ruficollis Long-toed stint – Calidris subminuta Temminck's stint – Calidris temminckii
	Curlew sandpiper – Calidris ferruginea Stilt sandpiper – Calidris himantopus
	Curlew sandpiper – Calidris ferruginea

	Stilt sandpiper – Calidris himantopus


	Spoon-billed sandpiper – Calidris pygmaea Red-necked stint – Calidris ruficollis Long-toed stint – Calidris subminuta Temminck's stint – Calidris temminckii
	Spoon-billed sandpiper – Calidris pygmaea Red-necked stint – Calidris ruficollis
	Spoon-billed sandpiper – Calidris pygmaea

	Red-necked stint – Calidris ruficollis


	Long-toed stint – Calidris subminuta Temminck's stint – Calidris temminckii
	Long-toed stint – Calidris subminuta

	Temminck's stint – Calidris temminckii




	Buff-breasted sandpiper – Calidris subruficollis Sanderling – Calidris alba Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis Baird's sandpiper – Calidris bairdii Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Buff-breasted sandpiper – Calidris subruficollis

	Sanderling – Calidris alba Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis Baird's sandpiper – Calidris bairdii Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Sanderling – Calidris alba Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis
	Sanderling – Calidris alba

	Dunlin – Calidris alpina Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis
	Dunlin – Calidris alpina

	Purple sandpiper – Calidris maritima Rock sandpiper – Calidris ptilocnemis
	Purple sandpiper – Calidris maritima

	Rock sandpiper – Calidris ptilocnemis




	Baird's sandpiper – Calidris bairdii Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Baird's sandpiper – Calidris bairdii

	Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Little stint – Calidris minuta White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla
	Little stint – Calidris minuta

	White-rumped sandpiper – Calidris fuscicollis Least sandpiper – Calidris minutilla
	White-rumped sandpiper – Calidris fuscicollis

	Least sandpiper – Calidris minutilla



	Pectoral sandpiper – Calidris melanotos Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Pectoral sandpiper – Calidris melanotos

	Western sandpiper – Calidris mauri Semipalmated sandpiper – Calidris pusilla
	Western sandpiper – Calidris mauri

	Semipalmated sandpiper – Calidris pusilla

Hybrids

Several hybrids have been discovered between different species in the genus. See Hybridisation in shorebirds for further details.