Great black-backed gull (Larus marinus)

The great black-backed gull is a large gull similar in size to the glaucous gull. The great black-backed gull breeds across the North-Atlantic and adjacent seas; from Baffin Island in the west, through Greenland, Iceland and the Norwegian coast to Novaya Zemlya and Vaygach Island in the east. In Europe, its breeding range extends south to northern France and north to Svalbard. The species is an opportunistic predator, scavenger and pirate – obtaining its food at sea, in the intertidal zone, behind fishing boats or at rubbish tips. It was found breeding on Bjørnøya for the first time in 1921 and on Spitsbergen in 1930. Since then it has increased in number and range, particularly after 1960.

Great black-backed gullThe great black-backed gull. Photo: tromsofoto.net

The great black-backed gull is a large gull similar in size to the glaucous gull. The sexes have a similar appearance. Adult birds are approximately 64-78 cm long and weigh 1.2-2.2 kg. The adult birds have a black back and the upper sides of the wings have well-defined white wing-tips. The rest of the plumage is white. Their powerful bill is yellow with a red spot and their legs are pale flesh-coloured. This species can be confused with the lesser black-backed gull, but the latter species is smaller and slimmer in appearance, has yellow legs and a less stout bill. In winter the plumage of the head is finely streaked. The plumage of the juvenile is an evenly variegated dark brown. The head is whiter than that of young herring gulls. The adult plumage is attained at four years of age. The great black-backed gull’s call is a hoarse "ack-ack".

Distribution

The great black-backed gull breeds across the North-Atlantic and adjacent seas; from Baffin Island in the west, through Greenland, Iceland and the Norwegian coast to Novaya Zemlya and Vaygach Island in the east. In Europe, its breeding range extends south to northern France and north to Svalbard. The species is considered monotypic. In Svalbard, the great black-backed gull breeds in small numbers on Bjørnøya and along the western coast of Spitsbergen. This species can also be found in the eastern part of Svalbard but in low numbers. During the summer, great black-backed gulls can be encountered over most of Svalbard. Northern populations of this species are more migratory than populations at the southern end of the range. Birds from the western part of the Barents Sea (including Svalbard) probably winter along the coast of Western Europe and at sea in the North Atlantic. They return to Svalbard in April-May and leave in September.

Ecology

The great black-backed gull is usually associated with the coast, inhabiting skerries and small islands during the breeding season. It usually nests as single pairs or in small colonies, and it often mixes with glaucous gulls. The species is an opportunistic predator, scavenger and pirate – obtaining its food at sea, in the intertidal zone, behind fishing boats or at rubbish tips. It feeds on a wide selection of fish species, molluscs, crustacea, echinoderms, polychaetes, insects, berries, eggs, nestlings and adult birds of various species, and human garbage. The proportions of these food items vary between years, seasons and regions, but fish probably always dominate the diet. The arctic fox and the glaucous gull are predators of eggs and chicks of the great black-backed gull.

Life history and reproduction

The breeding biology of the great black-backed gull population in Svalbard is insufficiently known. It usually places its nest on a rocky crag or on a platform on islets. The nest consists of dried grass, seaweed and feathers. The two or three are olive-green with dark brown speckles. Both sexes take part in incubation of the eggs, which lasts 27-28 days. The nest is protected and defended against intruders. The young usually leave the nest within a few days of hatching, but they remain nearby and are fed by the parents until they fledge after seven or eight weeks. The young birds reach maturity at four or five years of age. The highest age recorded in Norway (including Svalbard) is 27 years.

Management status and monitoring

The great black-backed gull is a relatively new species in Svalbard. It was found breeding on Bjørnøya for the first time in 1921 and on Spitsbergen in 1930. Since then it has increased in number and range, particularly after 1960. The great black-backed gull’s expansion in Svalbard is a result of a broader expansion of the species’ breeding range and numbers on both sides of the Atlantic in the 20th century. The breeding population in Svalbard is probably 100-300 breeding pairs, whereas the Barents Sea population is estimated to be 33,000 pairs. The European breeding population is estimated to be approximately 110,000 pairs, and is regarded as stable. The great black-backed gull, like the glaucous gull, likely accumulates high levels of organic contaminants. Studies conducted on mainland Norway suggest negative effects of contaminant burdens on reproductive performance.

MOSJ indicators (Environmental Monitoring of Svalbard and Jan Mayen):

Awaiting results from MOSJ…