The Sooty Shearwater (Puffinus griseus) is a medium-large shearwater in the seabird family Procellariidae. In New Zealand it is also known by its Maori name tltl and as "muttonbird", like its relatives the Wedge-tailed Shearwater (P. pacificus) and the Australian Short-tailed Shearwater (P. tenuirostris).
It appears to be particularly closely related to the Great ("P." gravis) and Short-tailed Shearwaters, all blunt-tailed, black-billed species, but its precise relationships are obscure. In any case, these three species are among the larger species of shearwater which might belong into a separate genus Ardenna.
Sooty Shearwaters are 40-51 cm in length with a 94-110 cm wingspan. It has the typically "shearing" flight of the genus, dipping from side to side on stiff wings with few wing beats, the wingtips almost touching the water. Its flight is powerful and direct, with wings held stiff and straight, giving the impression of a very small albatross. This shearwater is identifiable by its dark plumage which is responsible for its name. In poor viewing conditions it looks all black, but in good light it shows as dark chocolate-brown a silvery strip along the center of the underwing.
Usually loud, Sooty Shearwaters coo and croak while on the breeding grounds.
In the Atlantic, it is the only such bird, whereas in the Pacific part of its range, other all-dark large shearwaters are found. Particularly the Short-tailed Shearwater is almost impossible to tell apart from the present species at a distance.