Great Shearwater

The great shearwater (Ardenna gravis) is a robust member of the seabird family Procellariidae. It is a large shearwater, with a body length ranging from 43 to 51 centimeters and a wingspan stretching between 105 and 122 centimeters. Its plumage is characterized by dark upper parts contrasted with white underparts, save for a distinctive brown belly patch and dark shoulder markings. A black cap and bill, along with a white "horseshoe" marking at the base of the tail, round out its notable features.

Identification Tips

When observing the great shearwater, look for its sizeable frame and the contrast between its dark upper body and the predominantly white underparts. The brown belly patch is a key identifier, as are the dark shoulder markings. In flight, its stiff-winged gliding, reminiscent of a large Manx shearwater, is distinctive. The black cap and bill are also prominent, as is the white tail base.

Habitat

The great shearwater is a pelagic bird, spending much of its life on the open ocean. It breeds on rocky islands in the south Atlantic.

Distribution

This species follows a remarkable circular migration route, traveling northward along the eastern coasts of the Americas before crossing the Atlantic in August. It is often seen off the southwestern coasts of Great Britain and Ireland, before making its way southward down the eastern Atlantic.

Behaviour

The great shearwater exhibits the genus-typical "shearing" flight, moving from side to side on stiff wings with minimal wingbeats, the wingtips nearly skimming the water's surface. Its flight is powerful and direct, with wings held rigidly straight.

Breeding

Breeding colonies of the great shearwater are found on Nightingale Island, Inaccessible Island, Tristan da Cunha, and Gough Island. Unique among many birds, it migrates from the Southern Hemisphere to the Northern Hemisphere for breeding. The shearwater nests in burrows or open grass, laying a single white egg, and visits these nests exclusively at night to evade predation by large gulls.

Food and Feeding

The diet of the great shearwater consists primarily of fish and squid, which it captures from the surface or by plunge-diving. It also feeds on crustaceans, fish offal, and refuse from fishing vessels. This species is known to follow fishing boats, engaging in noisy disputes over scraps. It is a sociable bird, often found in large groups at sea, where it can be heard emitting a piercing "eeyah" call.

Conservation status

The IUCN Red List currently classifies the great shearwater as Least Concern, indicating that it is not at immediate risk of widespread decline. However, it is important to note that great shearwaters are among the seabird species most affected by plastic ingestion, which poses a significant threat to their health and the broader marine ecosystem.