The great black-backed gull (Larus marinus) is the largest member of the gull and tern family Laridae. It is a very aggressive hunter, pirate and scavenger which breeds on the North Atlantic coasts and islands of northern Europe and northeastern North America. Southern populations are generally sedentary, while those breeding in the far north (northern Norway, northwest Russia) migrate farther south in winter. A few also move inland to large lakes and reservoirs. The adult has a white head, neck and underparts, dark blackish-grey wings and back, pink legs and the bill yellow with a red spot.
Taxonomy 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. Larus appears to have referred to a gull or other large seabird. The specific name marinus means "marine", or when taken together, "sea gull". The name predates Linnean taxonomy, as it had been called Larus ingens marinus by Carolus Clusius.
The terms swaabie (from ), baagie and baigie (, from ) are local names from the Shetland Islands. Francis Willughby called it the great black and white gull in the 17th century, noting that it was called the swarth-back in the Faroe Islands. 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.
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. A study to investigate how much time they spend foraging at refuse dumps in Massachusetts found great black-backed gulls were only observed actively foraging 19% of their time there, eating less garbage than other common gulls, and spent most of their time roosting or loafing.
Like most gulls, great black-backed gulls regularly capture fish, and any fish smaller than themselves found close to the surface of the water are potential prey. Stomach contents of great black-backed gulls usually show fish to be the primary food. On Sable Island in Nova Scotia, 25% of the stomach contents consisted of fish, but 96% of the regurgitations given to young consisted of fish. Similarly, on Great Island in Newfoundland, 25% of the stomach contents were fish but 68% of regurgitants were fish. The most regularly reported fish eaten in Nova Scotia and Newfoundland were capelin (Mallotus villosus), Atlantic cod (Gadus morhua), Atlantic tomcod (Microgadus tomcod), Atlantic mackerel (Scomber scombrus), Atlantic herring (Clupea harengus) and sand lance (Ammodytes hexapterus). Other prey often includes various squid and mollusks, Jonah crabs (Cancer borealis), rock crabs (Cancer irroratus), green crabs (Carcinus maenas) and other crustaceans, and sea urchins, starfish (Asterias forbesi and Asterias rubens) and other echinoderms when they come across the opportunity. From observations in northern New England, 23% of observed prey was echinoderms and 63% was crustaceans.
Unlike most other Larus gulls, great black-backed gulls are highly predatory and frequently hunt and kill any prey smaller than themselves, behaving more like a raptor than a typical gull. Lacking the razor-sharp talons and curved, tearing beak of a raptor, the great black-backed gull relies on aggression, physical strength and endurance when hunting. When attacking other animals, they usually attack seabird eggs, nestlings or fledglings at the nest, perhaps most numerously terns, but also including smaller gull species as well as eiders, gannets and various alcids. In Newfoundland and Nova Scotia, 10% of the stomach contents of great black-backed gulls was made up of birds, while a further 17% of stomach contents was made up of tern eggs alone. Adult or fledged juveniles of various bird species have also been predaceously attacked. Some fully-fledged or adult birds observed to be hunted in flight or on the ground by great black-backed gulls have included Anas ducks, ruddy ducks (Oxyura jamaicensis), buffleheads (Bucephala albeola), Manx shearwaters (Puffinus puffinus), pied-billed grebes (Podilymbus podiceps), common moorhens (Gallinula chloropus), terns, Atlantic puffins (Fratercula arctica), Little auks (Alle alle), coots (Fulica ssp.), glossy ibises (Plegadis falcinellus), rock doves (Columba livia) and even predatory birds such as hen harriers (Circus cyaneus). When attacking other flying birds, the great black-backed gulls 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. They may kill healthy adult birds weighing up to at least but take exclusively the small young of larger birds such as common eider (Somateria mollissima) and cormorants.Russell, J., & Montevecchi, W. A. (1996). Predation on adult Puffins Fratercula arctica by Great Black‐backed Gulls Larus marinus at a Newfoundland colony. Ibis, 138(4), 791–794.Munro, J., & Bédard, J. (1977). Gull predation and creching behaviour in the common eider. The Journal of Animal Ecology, 799–810.Kury, C. R., & Gochfeld, M. (1975). Human interference and gull predation in cormorant colonies. Biological Conservation, 8(1), 23–34. They will also catch flying passerines, which they typically target while the small birds are exhausted from migration and swallow them immediately. Great black-backed gull also feed on land animals, including rats (Rattus ssp.) at garbage dumps, rabbits (Oryctolagus cuniculus) and even sickly lambs (Ovis aries).