Description
Giant petrels earn their name. The Southern Giant Petrel is slightly larger than the Northern Giant Petrel, at 3–8 kg (6.6–17.6 lb), 180–210 cm (71–83 in) across the wings and 86–100 cm (34–39 in). The Northern Giant Petrel is 3–5 kg (6.6–11.0 lb), 150–210 cm (59–83 in) across the wings and 80–95 cm (31–37 in). They superficially resemble the albatross, and are the only procellarids who can equal them in size. They can be separated from the albatrosses by their bill; the two tube nostrils are joined together on the top of the bill, unlike on albatross where they are separated and on the side of the bill. They are also the only members of the Procellariidae family to have strong enough legs to walk effectively on land. They are also much darker and more mottled brown (except for the white morph Southern, which are whiter than any albatross) and have a more hunch-backed look. The bills of Procellariiformes are also unique in that they are split into between 7 and 9 horny plates. The Petrels have a hooked bill called the maxillary unguis which can hold slippery food. They produce a stomach oil made up of wax esters and triglycerides that is stored in the proventriculus. This is used against predators as well as an energy rich food source for chicks and for the adults during their long flights. Finally, they have a salt gland that is situated above the nasal passage and helps desalinate their bodies, due to the high amount of ocean water that they imbibe. It excretes a high saline solution from their nose.
They are harder to tell from each other, possessing similar long pale orange bills and uniform mottled grey plumage (except for 15% of Southern Petrels, which are almost completely white). The billtip of halli is reddish-pink and that of giganteus is pale green, appearing slightly darker and lighter than the rest of the bill, respectively. The underside of older halli is paler and more uniform than giganteus, the latter showing a contrast between paler head and neck and darker belly. Additionally, adult halli typically appear pale-eyed, while adult giganteus of the normal morph typically appear dark-eyed (occasionally flecked paler). Classic examples of Northern Giant are identifiable at some range. Unfortunately 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 and thus this species is harder to confirm.
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