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.
Great black-backed gulls breed from the extreme northwest portion of Russia, through much of coastal Scandinavia, on the Baltic Sea coasts, to the coasts of northwestern France, the United Kingdom, and Ireland. Across the northern portion of the Atlantic, this gull is distributed in Iceland, the Faroe Islands, southern Greenland, and on the Atlantic coasts of Canada and the United States. Populations breeding in harsher environments migrate south, wintering on the northern coasts of Europe from the Baltic Sea to southern Portugal, and regularly down to coastal Florida in North America. During the winter in the Baltic Sea, the bird usually stays close to the ice boundary. North of the Åland islands, the sea often freezes all the way from Sweden to Finland, and then the bird migrates to open waters. Great black-backed gulls are found in a variety of coastal habitats, including rocky and sandy coasts and estuaries, as well as inland wetland habitats, such as lakes, ponds, rivers, wet fields, and moorland. They generally breed in vegetated islands, sand dunes, flat-topped stacks, building roofs, and sometimes amongst bushes on salt marsh islands. During the winter, they often travel far out to sea to feed.
These social birds are active during the day. They are very curious and during forage will investigate any small organism they encounter and will readily eat almost anything that they can swallow. They are highly predatory and frequently hunt and kill any prey smaller than themselves, behaving more like a raptor than a typical larid gull. Lacking the razor-sharp talons and curved, tearing beak of a raptor, Great black-backed gulls rely on aggression, physical strength and endurance when hunting. When attacking other flying birds, they often pursue them on the wing and attack them by jabbing with their bill, hoping to bring down the other bird either by creating an open wound or simply via exhaustion. Like some other gulls, when capturing molluscs or other hard-surfaced foods such as eggs, they will fly into the air with it and drop it on rocks or hard earth to crack it open. Great black-backed gulls are skilled kleptoparasites who will readily pirate fish and other prey captured by other birds and dominate over other gulls when they encounter them. The voice of Great black-backed gulls is distinctly deeper than most other gull species. Their call is a deep "laughing" cry, kaa-ga-ga, with the first note sometimes drawn out in an almost bovid-like sound.
Great black-backed gulls are opportunistic feeders and apex predators. They get much of their dietary energy from scavenging, with refuse, most provided directly by humans, locally constituting more than half of their diet. They also eat various fish, squid, Jonah crabs, rock crabs, sea urchins, green crabs, starfish, and other echinoderms, crustaceans, and mollusks when they come across the opportunity. They also attack seabirds and their eggs, nestlings or fledglings at the nest, land animals, including rats at garbage dumps, rabbits, and even sickly lambs. Alternate foods, including berries and insects, are eaten when available.
Great black-backed gulls are serially monogamous; they form pairs only for one breeding season and following spring the same birds usually form a pair again, meeting at the previous year's nest. If one of the birds doesn't appear, the other bird begins looking for a new mate. Usually, a single bird does not breed in that season. Great black-backed gulls breed singly or in small colonies and pair formation occurs in March or April. They make a lined nest on the ground often on top of a rocky stack, fallen log, or other obstructing object which can protect the eggs from the elements. Usually, several nest scrapes are made before the one deemed best by the parents is selected and then lined with grass, seaweed or moss, or objects such as rope or plastic. When nesting on roofs in urban environments, previous year's nests are often reused over and over again. The female lays usually 3 eggs sometime between late April and late June. The incubation lasts for approximately 28 days and is done by both parents. During this time, the birds attempt to avoid being noticed and stay silent. The breeding pair are devoted parents who both take shifts brooding the young, defending the nest, and gathering food. The chicks leave the nest area at 50 days of age and may remain with their parents for an overall period of around 6 months, though most fledglings choose to congregate with other immature gulls in the search for food by fall. Young birds become reproductively mature when they obtain adult plumage at 4 years, though may not successfully breed until they are 6 years old.
Historically, the Great black-backed gull was harvested for its feathers, which were used in the hat-making trade, and this species was extirpated from large parts of its range as a result of this exploitation. Although there are no known major threats to the Great black-backed gull at present, high levels of toxic pollutants, which are ingested with contaminated prey, are often found in individuals and eggs, reducing reproductive success. Breeding is also interrupted by human disturbance, which can lead to eggs being abandoned, leaving them vulnerable to exposure and predation.
According to IUCN Red List, the total population size of the Great black-backed gull is 500,000-999,999 individuals. The European population consists of 118,000-133,000 pairs, which equates to 237,000-266,000 mature individuals or 360,000-400,000 individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.
