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The ivory gull is a high arctic species that frequents ice-filled waters throughout the year, and is a medium-sized gull that is easy recognized by its pure white plumage, black legs and yellow bill with dark base. Scattered colonies occur in Arctic Canada, Greenland, Svalbard, Franz Josef Land, on islands in the Kara Sea and on Severnaya Zemlya. In Svalbard the ivory gull breeds in small numbers on Spitsbergen, Kong Karls Land and Nordaustlandet, with the largest numbers occurring in the northern and eastern areas.
Contents
Description
The ivory gull is a medium-sized gull with striking pure white plumage that is highlighted by their ebony black legs. Adults have a length of about 44 cm and weigh 400–500 g; males and females look alike.
Immature birds have a dusky face and black spots on the breast and flanks, as well as at the tips of the primaries, and tail and outer wing coverts, although the extent of speckling is highly variable among individuals. The eye is dark.
Ivory gulls acquire adult plumage during their second winter. In adults, the bill is generally slate blue at the base, becoming pale yellow and tipped with red, but it is darker in juveniles. The ivory gull’s legs are black in all age groups. Its round chest, short legs and rolling gait give it a pigeon-like appearance when on the ground. However, although it is a stocky bird, in the air it has a graceful and agile flight.
The voice is a piercing, tern-like cry ‘kree-kree’.
Distribution
The ivory gull has a patch circumpolar breeding distribution across the high arctic. Scattered colonies occur in arctic Canada, Greenland, Svalbard, Franz Josef Land, on islands in the Kara Sea and on Severnaya Zemlya. The species is monotypic.
In Svalbard the ivory gull breeds in scattered colonies in the eastern part of Spitsbergen (as far south as Hornsund), Barentsøya, Kong Karls Land and Nordaustlandet, with the highest colony densities occurring in the east og north. The ivory gull is a common species in ice-filled waters around the archipelago at all times of the year. It often follows ships within the pack-ice zone, and also appears regularly in small numbers in the settlements on Spitsbergen, often at rubbish dumps or at sewage outlets.
Ivory gulls leave the colonies soon after the young have fledged in late August and beginning of September, and move up to the sea ice edge between Svalbard and Severnaya Zemlya (Russia). They stay in this area until mid-October when they start migrating along the sea ice edge to the wintering areas along the ice edge in the Labrador Sea between Canada and Greenland. Some birds may winter in the Bering Sea, in the north Pacific.
The spring migration starts in April, and the birds disperse into the breeding areas in May.
General ecology
The ivory gull is a high arctic species that frequents ice-filled waters throughout the year. The species breeds as single pairs or in colonies of up to more than a hundred pairs.
In Svalbard most colonies are small, rarely containing more than 10–50 pairs. The largest colony recorded in Svalbard in recent years contained 150 pairs. Altogether 80 colony locations have been documented in the archipelago.
Ivory gulls usually breed on steep cliffs, often on nunataks (rock outcropping at the top of mountains that peek through ice sheets) in remote areas. It has previously also been found nesting on flat ground, e.g. on Storøya and Abeløya. Some ivory gulls breed in mixed colonies with black-legged kittiwake or other seabirds. Nests can be found from just above sea level to about 800 m.
Like most gulls, the ivory gull is an opportunistic feeder. They forage mostly within drift ice areas and at glacier fronts. At sea, it is a surface-feeder, foraging primarily on small fish, such as arctic cod Boreogadus saida, and macro-zooplankton, such as amphipods and euphausiids.
Ivory gulls are also scavengers of marine mammals killed by large predators, and they sometimes also forge on marine mammal faeces and placentae. Arctic foxes are well-known nest predators, and can destroy entire breeding colonies in flat areas in some years. Polar bears will take eggs and young on occasion. Avian predators such as glaucous gulls are known to prey on eggs and young.
Life history and reproduction
The ivory gull is thought to breed for the first time in their second year of life. The nest is made from various types of plant materials and feathers. The nest is placed either on a narrow ledge like that of the black-legged kittiwake or in a shallow depression directly on gravely ground.
Unlike most gulls, which regularly lay three eggs, the ivory gull usually lays only one or two eggs. Egg-laying probably take place in late June or early July. The eggs are grey-brown or greenish with dark brown speckles. They are incubated by both parents for about 25 days.
The young leave the nest fully fledged at about seven weeks of age. The birds probably leave their colonies immediately after breeding and disperse to offshore foraging areas. The reproductive rate of ivory gulls is thought to be relatively low and to vary considerably from year to year.
The highest age recorded in Norway (including Svalbard) is ten years.
Management status and monitoring
The ivory gull is a rare species in a global context, and it remains one of the most poorly known seabird species in the world. The current global population estimate is 14,000 pairs, of which 80% breed in the Russian Arctic. The breeding population in Svalbard is estimated to be between 1000 and 2000 pairs. Monitoring initiated in 2006 suggests that numbers are declining, but there is considerable inter-annual variation in the number of breeding pairs and also in which colonies they occupy.
Due to the species’ strong and year-round association with pack ice and its scavenging habits, it might be vulnerable to changes in sea ice cover and the accumulation of high levels of organic contaminants. An 80% reduction (from the 1980s) in the Canadian breeding population has recently been documented. A decline has also been documented in south Greenland. The reasons for these declines are not known.
