The ivory gull is globally rare and probably does not number more than 12,000 breeding pairs. The majority – some 85% – nest in Russia, where numbers appear to be stable. There is limited information on the species in Greenland though numbers have been estimated at around 1500 pairs and are thought to be stable. The ivory gull’s rarity and penchant for extremely remote breeding and wintering grounds makes it one of the least understood seabirds in the world. It is classified as ‘endangered’ in Norway and Canada, ‘rare’ in Russia, and is ‘fully protected’ from hunting in Greenland.
The ivory gull (Pagophila eburnea) is a medium-sized gull particularly noted for its striking pure white adult plumage. The species survives year-round in the High Arctic where it breeds in small, often inland, colonies scattered across barren regions of the eastern Canadian Arctic, Greenland, Svalbard (Norway), and the islands and archipelagoes of the Barents and Kara seas (Russia). Wintering generally occurs along the southern edge of pack ice of the Arctic, North Atlantic and Pacific oceans or at polynyas (open water areas surrounded by ice). Ivory gulls are opportunistic feeders and forage for small fish and zooplankton, marine mammal carcasses and placentae, and perhaps small mammals.
All evidence suggests that the ivory gull is in steep decline in Canada and Norway. Numbers in Canada are estimated at about 800 individuals, a drop of approximately 80% since the late 1980s. Surveys conducted in Norway at Svalbard during 2006-2007 show a population numbering between 350 to 500 breeding pairs; while some new colonies were found, most previously know colonies had disappeared and those remaining supported fewer birds. However, the magnitude of longterm declines in Svalbard are difficult to assess because of the lack of historical data.
The cause for such declines are unknown and particularly worrisome as they are occurring in some of the most remote regions of the world and where human impact is expected to be minimal.
Very high levels of PCBs and DDT have been reported in ivory gull eggs from Russia and northern Norway.
The species’ great dependency on sea ice leaves it highly vulnerable to an environment that is being rapidly altered by climate change. There is increasing concern that the sensitivity of the Arctic to greenhouse gas loading is much greater than originally anticipated. Indeed, a study published in early 2007 concluded that the shrinking of summertime ice is about 30 years ahead of the recent Intergovernmental Panel on Climate Change (IPCC) projections.
Little is known about the reason for the decline of the ivory gull in Norway though illegal hunting, contaminants and declines in sea ice are considered to be the primary suspects by the Norwegian Ministry of the Environment.
The cause of the steep decline in Canada is also unknown though researchers suspect that the species is likely to be affected by various factors:
• Habitat change
A retreat of sea ice away from nesting sites or changes in its seasonal extent or thickness would be expected to exert considerable stress on a species which forages for ice-associated invertebrates, fish, and carrion. Patterns of ice formation are changing in the species wintering habitat in the Northwest Atlantic with likely effects on the timing and extent of marine primary production; any nutritional stress during over-wintering can affect survival, reproduction and chick-rearing.
• Environmental contaminants
Mercury concentrations in ivory gull eggs from Canada appear to have slightly increased over the past three decades and are at levels in which reproductive success may be impaired. Levels found have been among the highest reported for seabird eggs in the Arctic. Concentrations of organochlorines (e.g., PCBs, DDT, chlordane) have either decreased or have remained constant over the same time period and are below thresholds where toxicological effects in wild birds would be expected (though synergistic or additive effects cannot be excluded). Concentrations of the brominated diphenyl ethers, while still relatively low, are increasing. Their toxicological effects in birds, however, are poorly understood.
• Illegal hunting
Ivory gulls breeding in Canada have in the past been killed illegally in northwest Greenland during spring and fall migration. The current extent of the problem is unknown. The species is rarely hunted by the Inuit in Canada.
• Oil pollution
Gulls are highly vulnerable to oil pollution and the ivory gull may be more so due to its extensive time spent at sea. There have been no reports of oiled ivory gulls though recovery of carcasses would not be expected given the offshore range of the species. The threat of oiling will increase in tandem with increased shipping as northern waters become progressively more ice-free during summer.
Most ivory gull colonies in Arctic Canada rarely have human contact and any visitation disturbance in these cases (e.g., by researchers) is expected to be minimal. However, extensive diamond exploration occurs in other areas supporting ivory gull colonies and the associated disturbance (e.g., air traffic, drilling) may be enough to be detrimental to breeding success. Areas of industrial activities in the Arctic have, in the past, attracted such species as arctic foxes, polar bears, ravens and large gulls; an influx of these predators into ivory gull breeding habitat could have severe consequences.
Numbers in a range of arctic wildlife species have declined over the past decades. A variety of factors may be involved – e.g., over-hunting, natural climatic cycles and human-induced climate change, commercial fisheries, contaminants, oil spills, habitat loss, introduced species and disturbance – depending on the species and location. In many cases, as with the ivory gull, the causes are poorly understood. Marine species declines in Alaska have been particularly noticeable and include, for example, beluga whales in Cook Inlet, northern fur seals, Steller sea lions, northern sea otters, eider sea ducks (Steller’s, common, king and spectacled), Kittlitz’s and marbled murrelets, short-tailed albatross, red-legged kittiwakes, and polar bears in the Beaufort Sea.
The Arctic is currently exposed to the largest temperature increases – nearly twice the global average – as a result of climate change. The region, as well, is projected to experience the greatest warming in the future, with rapid and dramatic responses by fauna and flora as greenhouse gases from human activity continue to accumulate in the atmosphere. Profound changes have recently been documented in even the High Arctic where such spring events as plant flowering or egg-laying in birds have advanced, in some cases, by over 30 days since 1996.
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