The great shearwater is a large shearwater in the seabird family Procellariidae. Ardenna was first used to refer to a seabird by Italian naturalist Ulisse Aldrovandi in 1603, and gravis is Latin for "heavy". The great shearwater's relationships are unclear. It belongs in the group of large species that have been separated as genus Ardenna; within these, it might be allied with the other black-billed, blunt-tailed species, the short-tailed shearwater and especially the sooty shearwater. Alternatively, it could be a monotypic subgenus, an Atlantic representative of the light-billed Hemipuffinus group. This species breeds on Nightingale Island, Inaccessible Island, Tristan da Cunha, and Gough Island. It is one of only a few bird species to migrate from breeding grounds in the Southern Hemisphere to the Northern Hemisphere, the normal pattern being the other way around. This shearwater nests in large colonies, laying one white egg in a small burrow or in the open grass. These nests are visited only at night to avoid predation by large gulls. This shearwater, like the sooty shearwater, follows a circular route, moving north up the eastern seaboard of first South and then North America, before crossing the Atlantic in August. It can be quite common off the southwestern coasts of Great Britain and Ireland before heading back south again, this time down the eastern littoral of the Atlantic. This bird has the typically "shearing" flight of the genus, dipping from side to side on stiff wings with few wingbeats, the wingtips almost touching the water. Its flight is powerful and direct, with wings held stiff and straight. This shearwater is 43–51 cm in length with a 105– to 122-cm wingspan. It is identifiable by its size, dark upper parts, and under parts white except for a brown belly patch and dark shoulder markings. It has a black cap, black bill, and a white "horseshoe" on the base of the tail. The stiff flight, like a large Manx shearwater, is also distinctive. The only other large shearwater in its range is the all-dark sooty shearwater. The great shearwater feeds on fish and squid, which it catches from the surface or by plunge-diving. It readily follows fishing boats, where it indulges in noisy squabbles. This is a gregarious species, which can be seen in large numbers from ships or appropriate headlands. They have a piercing eeyah cry usually given when resting in groups on the water.
