The Curlew Sandpiper (Calidris ferruginea) is a small wader that breeds on the tundra of Arctic Siberia. It is strongly migratory, wintering mainly in Africa, but also in south and southeast Asia and in Australasia. It is a vagrant to North America.
These birds are small waders, only slightly larger than Dunlin at 19.5–21 cm in length, but differ from Dunlin in having a longer down-curved bill, longer neck and legs and a white rump. The breeding adult has patterned dark grey upperparts and brick-red underparts. In winter, this bird is pale grey above and white below, and shows an obvious white supercilium. Juveniles have a grey and brown back, a white belly and a peach-coloured breast.
The male Curlew Sandpiper performs an aerial display during courtship. The clutch of 3–4 eggs are laid in ground scrape in the tundra.
This wader is highly gregarious, and will form flocks with other calidrid waders, particularly Dunlin. Despite its easterly breeding range, this species is regular on passage in western Europe, presumably because of the southwesterly migration route.
It forages in soft mud on marshes and the coast, mainly picking up food by sight. It mostly eats insects and other small invertebrates.
The numbers of this species (and of Little Stint) depend on the population of lemmings. In poor lemming years, predatory species such as skuas and Snowy Owls will take Arctic-breeding waders instead.
This species occasionally hybridizes with the Sharp-tailed Sandpiper and the Pectoral Sandpiper, producing the presumed "species" called "Cooper's Sandpiper"