Giant petrel

Genus of birds
Automatic taxobox
| name = Giant petrel
| fossil range = Geological range|Pliocene|Holocene|<small>Pliocene

The genus Macronectes was introduced in 1905 by the American ornithologist Charles Wallace Richmond to accommodate what is now the southern giant petrel. It replaced the previous genus Ossifraga which was found to have been earlier applied to a different group of birds. The name Macronectes combines the Ancient Greek makros meaning "great" and nēktēs meaning "swimmer". The present day giant petrels are two large seabirds from the genus Macronectes. Long considered to be conspecific (they were not established as separate species until 1966), the two species, the southern giant petrel, M. giganteus, and northern giant petrel, M. halli, are considered with the two fulmars, Fulmarus, to form a distinct subgroup within the Procellariidae, and including the Antarctic petrel, Cape petrel, and snow petrel, they form a separate group from the rest of the family. A fossil giant petrel, Macronectes tinae is known from the Pliocene epoch of New Zealand.

The southern giant petrel is slightly larger than the northern giant petrel, at , across the wings, and of body length. The northern giant petrel is , across the wings and of body length. They superficially resemble the albatross, and are the only procellarids that can equal them in size. They can be separated from the albatrosses by their bill; the two tube nostrils are joined on the top of the bill, unlike on albatross, where they are separated and on the side of the bill. Giant petrels are also the only members of the family Procellariidae to have strong legs to walk on land. Petrels have a salt gland situated above the nasal passage that helps to desalinate their bodies by excreting a high saline solution from their noses. The two species are difficult to tell from each other, possessing similar long, pale, orange bills and uniform, mottled grey plumage (except for around 15% of southern petrels, which are almost completely white). The billtip of M. halli is reddish pink and that of M. giganteus is pale green, appearing slightly darker and lighter than the rest of the bill, respectively. The underside of older M. halli birds is paler and more uniform than M. giganteus, the latter showing a contrast between paler head and neck and darker belly. Additionally, adults of M. halli typically appear pale eyed, while adults of M. giganteus of the normal morph typically appear dark eyed (occasionally flecked paler). Classic examples of northern giant are identifiable at some range. Young birds of both species are all dark and very hard to distinguish unless bill tip colour can be seen. Some relatively young northern giant petrels can appear to be paler on the head, suggesting southern giant, thus this species is harder to confirm. The extinct Macronectes tinae is characterized by having smaller bodies than their living relatives.