Great black-backed gull

The great black-backed gull was one of the many species originally described by Carl Linnaeus in his 1758 10th edition of Systema Naturae, and it still bears its original scientific name of Larus marinus. or when taken together, "sea gull". The name predates Linnean taxonomy, as it had been called Larus ingens marinus by Carolus Clusius. The species is sometimes referred to as the greater black-backed gull. ==Description==

This is the largest gull in the world, considerably larger than a herring gull (Larus argentatus); only two other gulls, glaucous gull (Larus hyperboreus) and Pallas's gull (Ichthyaetus ichthyaetus), come close to matching this species in size. It is long with a wingspan and a body weight of . In a sample of 2009 adults from the North Atlantic, males were on average and females were on average . Some adult gulls with access to fisheries in the North Sea can weigh up to roughly and averaged . An exceptionally large glaucous gull was found to outweigh any known great black-backed gull, although usually that species is slightly smaller. The great black-backed gull is bulky and imposing in appearance with a large, powerful bill. The standard measurements are: the bill is , the wing chord is and the tarsus is . The adult great black-backed gull is fairly distinctive, as no other very large gull with black on its upper-wings generally occurs in the North Atlantic. In other white-headed North Atlantic gulls, the mantle is generally a lighter grey and, in some species, it is a light powdery grey or even pinkish. It is greyish-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 tip of lower bill. The adult lesser black-backed gull (L. fuscus) is distinctly smaller, typically weighing about half as much as a great black-back. The lesser black-back has yellowish legs and a mantle that can range from slate-grey to brownish but it is never as dark as the larger species. A few superficially similar dark-backed, fairly large gulls occur in the Pacific Ocean or in the tropics, all generally far outside this species' range, such as the slaty-backed (L. schistisagus), the western (L. occidentalis) and the kelp gull (L. dominicanus). Juvenile birds of under a year old have scaly, checkered black-brown upper parts, the head and underparts streaked with grey 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 base and a broken blackish band near the tip. The bill of the juvenile is brownish-black with white tip and the legs dark bluish-grey with some pink tones. As the young gull ages, the grey-brown colour 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. The call is a deep "laughing" cry, kaa-ga-ga, with the first note sometimes drawn out in an almost bovid-like sound. The voice is distinctly deeper than most other gull species. Juvenile great black-backed gull (26635).jpg|First winter File:Great black-backed gull Larus marinus second-winter.jpg|Second winter File:Great black-backed gull Larus marinus third-winter.jpg|Third winter File:Great black-backed gull Larus marinus fourth-winter.jpg|Fourth winter ==Distribution and habitat==

This species can be found breeding in coastal areas 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. Though formerly mainly just a non-breeding visitor south of Canada in North America, the species has spread to include several colonies in the New England states and now breeds as far south as North Carolina. Individuals breeding in harsher environments will migrate south, wintering on 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. Exceptionally, the species can range as far south as the Caribbean and off the coast of northern South America. The great black-backed gull is 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 are generally found within striking distance of large bodies of water while ranging inland. Today, it is a common fixture at refuse dumps both along coasts and relatively far inland. The species also makes extensive use of dredge spoils, which, in the state of New Jersey, are their most prevalent nesting sites. It generally breeds in areas free of or largely inaccessible to terrestrial predators, such as vegetated islands, sand dunes, flat-topped stacks, building roofs and sometimes amongst bushes on salt marsh islands. During the winter, the great black-backed gull often travels far out to sea to feed. ==Diet==

Great black-backed gulls are opportunistic feeders, apex predators of the oceanic sky, and are very curious. They will investigate any small organism they encounter and will readily eat almost anything that they can swallow. They get much of their dietary energy from scavenging, with refuse, most provided directly by humans, locally constituting more than half of their diet. The proliferation of garbage or refuse dumps has become a major attractant to this and all other non-specialised gull species in its range. They will also catch flying passerines, which they typically target while the small birds are exhausted from migration and swallow them immediately. Most foods are swallowed whole, including most fish and even other gulls. When foods are too large to be swallowed at once, they will sometimes be shaken in the bill until they fall apart into pieces. 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. Alternative foods, including berries and insects, are also eaten when available, and they will readily exploit easy food sources, including chum lines made by boats at sea. They are skilled kleptoparasites who will readily pirate fish and other prey captured by other birds, and their size allows them to dominate over other gulls when encountering them. At tern colonies in coastal Maine, American herring gulls (L. smithsonianus) occasionally also attack nestling and fledgling terns but in a great majority of cases their catch were immediately pirated by great black-backs. In one observation, an adult great black-back was seen to rob a female peregrine falcon (Falco peregrinus) of a freshly caught gadwall (Anas strepera). In another case, a third-year great black-back was observed fighting an adult female northern goshawk (Accipiter gentilis) off its kill, although the goshawk attempted to strike the gull before leaving. Due to their method of using intimidation while encountering other water and raptorial birds, the species has been referred to as a "merciless tyrant". Naturally, these gulls are attracted to the surface activity of large marine animals, from Atlantic bluefin tuna (Thunnus thynnus) to humpback whales (Megaptera novaeangliae), to capture fish driven to the surface by such creatures. ==Breeding==

Great black-backed gulls breed singly or in small colonies, sometimes in the middle of a European herring gull (Larus argentatus) colony. Young adult pair formation occurs in March or April. The following spring the same birds usually form a pair again, meeting at the previous year's nest. If one of the birds does not appear, the other bird begins looking for a new mate. Usually a single bird does not breed successfully in that season. 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 three eggs sometime between late April and late June. When only two eggs are found in a nest, the reason is almost always that one egg, for one reason or another, has been destroyed. It takes around one week for the female to produce the three eggs, and the incubation does not begin until all three eggs are laid, so all three chicks hatch on the same day. The birds are usually successful in bringing up all the three chicks. The eggs are greenish-brown with dark speckles and blotches. Both parents participate in the incubation stage, which lasts for approximately 28 days. 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. Young great black-backed gulls leave the nest area at 50 days of age and may remain with their parents for an overall period of around six months, though most fledglings choose to congregate with other immature gulls in the search for food by fall. These gulls reach breeding maturity when they obtain adult plumage at four years, though may not successfully breed until they are six years old. ==Longevity and mortality==

The great black-backed gull is a relatively long-lived bird. The maximum recorded age for a wild great black-backed gull is 27.1 years. In one study from Norway, great black-backed gulls were the fifth highest frequency prey item for white-tailed eagles and gulls are prone to mobbing these huge eagles. The great black-backed gull has also been observed engaging in aerial combat with bald eagles, attacking the eagles and chasing them away. A great skua (Stercorarius skua) was filmed in Scotland unsuccessfully attempting to kill a second or third year great black-backed gull. In Norway, great black-backed gulls have also been reported to fall prey to Eurasian eagle-owls (Bubo bubo). Killer whales (Orcinus orca) and sharks also reportedly prey upon adult and juvenile birds at sea. In some biomes, where large eagles are absent the great black-backed gull may be considered the apex predator. ==Status==

Historically, the great black-backed gull was shot as a hunting trophy ("after about 1850 ... smaller gulls were shot remorselessly for little more than target practice but the Great Black-backed Gull was a prize worth displaying") and harvested for its feathers, which were used in the hat-making trade; as a result the species became locally extinct from particularly southern parts of its range as a result of this exploitation. Today, however, its adaptability to human presence and the use of urban environments as artificial nesting sites has resulted in the great black-backed gull rapidly increasing in number and range. It is now a widespread and abundant species in its range and its numbers have increased to such high levels in some areas that it is often seen as a pest species, especially near airports where it risks collisions with airplanes, and in some coastal areas where it sometimes outcompetes or hunts rarer seabirds, such as Atlantic puffins, possibly resulting in conservationist intervention. The increase and expansion of great black-backed gulls has been attributed to increasing winter fishery activities in the North Sea. Although there are no known major threats to the great black-backed gull, 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. ==Gallery==

File:Larus marinus head 01.jpg|Great black-backed gull has a bulky, powerful beak File:LarusMarinus and LarusArgentatus.JPG|Larus marinus and Larus argentatus together, Øresund File:Svartbak.jpg File:Larus marinus EM1B0978 (34665035760).jpg File:Larus marinus 2.jpg|Great black-backed gulls displaying File:Great Black-backed Gull Juvenile.jpg|Juvenile, Cape May Point, New Jersey File:Larus marinus eggs.jpg|Great black-backed gull nest and eggs File:Larus marinus nestlings.jpg|Chicks File:Great Black-backed Gull flock.jpg|Flock taking off during southern migration through Ottawa, Ontario File:Greater Black-backed Gull from the Crossley ID Guide Britain and Ireland.jpg|ID composite File:Great Blacked Backed Gull (19244633653).jpg File:Great black-backed gull (Larus marinus) in flight.jpg File:Larus marinus MHNT.ZOO.2010.11.127.9.jpg|Larus marinus - MHNT File:Svartbaksungi (cropped).jpg|Great black-backed gull chick Great black-backed gull (26769).jpg|Adult in New York ==References==