The wedge-tailed shearwater (Ardenna pacifica) is a medium-large shearwater in the seabird family Procellariidae. It is one of the shearwater species that is sometimes referred to as a muttonbird, like the sooty shearwater of New Zealand and the short-tailed shearwater of Australia. It ranges throughout the tropical Pacific and Indian Oceans, roughly between latitudes 35°N and 35°S. It breeds on islands off Japan, on the Islas Revillagigedo, the Hawaiian Islands, the Seychelles, the Northern Mariana Islands, and off Eastern and Western Australia. Taxonomy The wedge-tailed shearwater was formally described in 1789 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it with the petrels in the genus Procellaria and coined the binomial name Procellaria pacifica. Gmelin based his description on the "Pacific petrel" that had been described in 1785 by the English ornithologist John Latham in his book A General Synopsis of Birds. The type locality was designated as the Kermadec Islands by Gregory Mathews in 1912. The wedge-tailed shearwater is now one of seven species placed in the genus Ardenna that introduced in 1853 by Ludwig Reichenbach. The species is monotypic: no subspecies are recognised. A molecular phylogenetic study published in 2022 found that the wedge-tailed shearwater was sister to Buller's shearwater. Description The wedge-tailed shearwater is the largest of the tropical shearwaters. The two colour morphs of the species are dark and pale; the pale morphs predominate in the North Pacific, the dark morph elsewhere. However, both morphs exist in all populations, and bear no relation to sex or breeding condition. The pale morph has grey-brown plumage on the back, head, and upper wing, and whiter plumage below. The darker morph has the same dark grey-brown plumage over the whole body. The species' common name is derived from the large, wedge-shaped tail, which may help the species glide. The bill is dark and legs are salmon pink, with the legs set far back on the body (in common with the other shearwaters) as an adaptation for swimming. This species is related to the pan-Pacific Buller's shearwater, which differs much in colour pattern, but also has a wedge tail and a thin, black bill. They make up the Thyellodroma group, a superspecies of the large shearwaters that were for a long time included in the genus Puffinus. Behaviour and ecology Food and feeding Wedge-tailed shearwaters feed pelagically on