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The Great black-backed gull (Larus marinus ) is the largest member of the gull family. Described by the Cornell Lab of Ornithology as "the king of the Atlantic waterfront", it is a very aggressive hunter, pirate, and scavenger.
The Great black-backed gull is 64–79 cm (25–31 in) long with a 1.5–1.7 m (4 ft 11 in – 5 ft 7 in) wingspan and a body weight of 0.75–2.3 kg (1 lb 10 oz – 5 lb 1 oz).
The adult Great black-backed gull is fairly distinctive, as no other very large gull with blackish coloration on its upper wings generally occurs in the North Atlantic. In other white-headed North Atlantic gulls, the mantle is generally a lighter gray color and, in some species, it is a light powdery color or even pinkish. It is grayish-black on the wings and back, with conspicuous, contrasting white "mirrors" at the wing tips. The legs are pinkish, and the bill is yellow or yellow-pink with some orange or red near the tip of the lower bill.
Juvenile birds under a year old have scaly, checkered black-brown upper parts, the head and underparts streaked with gray-brown, and a neat wing pattern. The face and nape are paler and the wing flight feathers are blackish-brown. The juvenile's tail is white with zigzag bars and spots at the base and a broken blackish band near the tip. The bill of the juvenile is brownish-black with a white tip and the legs are dark bluish-gray with some pink tones. As the young gull ages, the gray-brown coloration gradually fades to more contrasting plumage and the bill darkens to black before growing paler. By the third year, the young gulls resemble a streakier, dirtier-looking version of the adult. They take at least four years to reach maturity, development in this species being somewhat slower than that of other large gulls.
