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The glaucous gull is a large gull, which is similar in size to the great black-backed gull. The glaucous gull has a circumpolar, high arctic, breeding distribution. In the north-east Atlantic it occurs in Greenland, Iceland, Jan Mayen, Svalbard, Franz Josef Land and Novaya Zemlya. Most glaucous gulls leave Svalbard in September–October and spend winter dispersed through the North Atlantic both along the coasts and in the open sea and as far south as Iceland, the Faroes and southern Greenland. However, many glaucous gulls also stay in the ice-free parts of the Barents Sea during winter.
Contents
Description
The glaucous gull is a large gull, which is similar in size to the great black-backed gull. Males and females are very similar in their external appearance. Adults are 65–78 cm long and weigh 1.2–2. 7 kg.
The adult bird has a very pale plumage, which is pale grey on the upper sides of the wings (paler than the herring gull) and has white (not black) wing tips. It has light flesh-coloured legs and a yellow eye-ring (in contrast to red in the Iceland gull which is also somewhat smaller).
The plumage of the juvenile is mottled grey and buff. The plumage becomes paler as the bird gets older, achieving adult colouration at about age five.
The glaucous gull’s call is similar to that of the herring gull but is somewhat lighter in tone.
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Distribution
The glaucous gull has a circumpolar, high arctic, breeding distribution. In the north-east Atlantic it occurs in Greenland, Iceland, Jan Mayen, Svalbard, Franz Josef Land and Novaya Zemlya. Four sub-species are generally recognized. The Svalbard population belongs to the nominate race L. h. gunnerus.
The glaucous gull breeds throughout most of Svalbard, either as single pairs or in small colonies. Their breeding areas are most often situated close to colonies of other seabirds. Glaucous gulls can also breed on small islets together with colonies of common eiders and geese.
Most glaucous gulls leave Svalbard in September-October and spend winter dispersed through the North Atlantic from the Barents Sea to Iceland. The birds return gradually to their breeding colonies in March and April.
General ecology
The glaucous gull is one of the largest gulls breeding in the Arctic and the only numerous avian predator in Svalbard. This species has the same ecological role as the birds of prey in more southern latitudes. Glaucous gulls usually nest in single pairs but some colonies can consist of more than hundred pairs. However, most colonies are small (5–15 pairs).
The glaucous gull is a generalist predator that feeds on a wide variety of fish, molluscs, crustaceans, eggs, chicks and adults of other seabirds, insects, carrion, refuse and offal. Birds breeding in or close to bird colonies are often specialized in preying upon eggs, chicks, and adult birds of certain seabird species. Undigested food parts are discarded as pellets and can be found close to the nest.
The arctic fox is an important predator of eggs and chicks of glaucous gull through most of its breeding range.
Life history and reproduction
Glaucous gulls usually nest close to seabird colonies, often on an elevated point at the top of the cliff, on a small pinnacle in the cliff wall or on rocks beneath the colony. The nest is built by both parents and consists of grass, moss and seaweed.
The two or three eggs are a pale olive-brown with darker speckles and blotches. They are incubated by both sexes for 27–28 days. The chicks remain for some time at the nest after hatching, but roam around the nest site area as they get older. They are fed by both parents and are fledged after approximately seven weeks after hatching. Breeding pairs are highly philopatric to previous nest sites if they have been successful at rearing young.
Birds that survive their first few years usually return to their natal colonies when they are three or four years old and will attempt to establish a territory in the area.
Management status and monitoring
The total breeding population in Svalbard has been crudely estimated to number in the 1000’s of pairs. At least 1,000 pairs breed on Bjørnøya, the largest glaucous gull colony in Svalbard (and the Barents Sea region).
Little is known about the trend in the total Svalbard population, but the population on Bjørnøya and Hopen has declined since 1986.
Glaucous gulls on Bjørnøya accumulate high levels of organic contaminants, especially in birds that specialized in preying on eggs and chicks of other seabirds. Effects on hormone production and the immune system as well as lower levels of reproduction and adult survival have been documented. Furthermore, changes in food availability and predation from a growing population of arctic foxes may be important factors in the declines observed in glaucous gull numbers on Bjørnøya.
