Small and fluttery. Dark blackish-brown overall with even-width white rump patch and conspicuous pale wing panels. Long legs extend past the tail in flight; difficult to spot unless close. Frequently hovers and patters feet on surface of water when feeding. Most often seen in small, loose groups; sometimes feeds or rests on the water in a dense flock. Eats plankton from the surface of the water. Vexed taxonomy might include several cryptic species. Breeds in Antarctica and islands in the southern oceans. Ranges across all oceans when not breeding, mainly from May to October, typically staying offshore but sometimes seen from land. Most common in North Atlantic.