Ivory gull
The ivory gull (Pagophila eburnea) 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.
The ivory gull is a medium-sized gull that is easy recognized by its pure white plumage, black legs and yellow bill with dark base. The eye is dark. Its round chest, short legs and rolling gait give it a pigeon-like appearance when on the ground, but in flight it is graceful and agile. Adults are 40-43 cm long and weigh 450-700 g. Males and females look alike. Immature birds are also white, but are sprinkled with fine, black spots on the back and upper side of the wings. Moreover, they have a dusky colour on the forehead, cheeks, throat and around the eyes. The amount of black in the plumage varies among individuals. Ivory gulls acquire adult plumage during their second winter. The legs are black in all age groups. The voice is a piercing, tern-like cry "krrea".
Distribution
The ivory gull has a patchy circumpolar breeding distribution across the high Arctic. Scattered colonies occur in arctic Canada, Greenland, Svalbard, Franz Josef Land (Russia), on islands in the Kara Sea and on Severnaya Zemlya (Russia). 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. Although few in numbers, 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. The migration pattern of the Svalbard population is insufficiently known. They are though to forage along the ice edge outside the breeding period. The first ivory gulls are usually observed in Svalbard around the settlements in March, and the birds disperse into the breeding areas in May. Ivory gulls probably leave the colonies soon after the young fledge in August-September.
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 more than 10-20 pairs. Altogether 44 colonies locations have been documented in the archipelago. However, ivory gull colonies are unstable through time, and hence the size or even existence of the colonies that have previously been registered are uncertain. Ivory gulls usually breed on steep cliffs, often on nunataks (rock outcropping at the top of mountains that poke through ice sheets) in remote areas. Colonies have also been found on flat ground, e.g. on Storøya, Kvitøya 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. At sea, it is a surface-feeder, foraging primarily on small fish, such as polar cod, and macro-zooplankton, such as amphipods and euphausiids. Ivory gulls are also scavengers of marine mammals killed by polar bears or other predators, and they sometimes also forge on marine mammal faeces and placentae. Arctic foxes and glaucous gulls are the most important predators on eggs and chicks. Polar bears and arctic foxes can destroy entire breeding colonies in flat areas in some years.
Life history and reproduction
Both sexes participate in building the nest from various types of plant materials and feathers. The amount of building material brought to the nest varies greatly. The nest is placed either on a narrow ledge or in a shallow depression on gravely ground. Unlike most gulls which regularly lay three eggs, the ivory gull usually lays only one or two. Egg-laying 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 24–26 days. The young leave the nest fully fledged at four to five 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. Ivory gulls are sexually mature two years of age. The oldest bird ringed in Svalbard was six years old.
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. There are no good estimates of the breeding population in Svalbard, but the population is probably between 200 and 750 breeding pairs. The current population trend in this area is not known. However, some colonies have disappeared or been reduced in size, and remarkably few new colonies have been discovered. Due to the species’ strong and year-round association with pack-ice and its scavenging habits, it is probably 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. The reason for this decline is not known.