Saturday, 11 August 2007

Mercury may be killing Ivory Gulls

Latest research has highlighted mercury poisoning as a possible cause for Ivory Gull declines. Surveys in the Canadian Arctic during the early 1980s counted about 2,400 birds, while a survey done from 2002 to 2006 by the Canadian Wildlife Service only found several hundred birds - a drop of 80 per cent.

Evidence is building to link mercury levels with these huge declines. Birgit Braune, a research scientist with Environment Canada who studies toxic chemicals in Arctic wildlife, has examined Ivory Gull eggs from Seymour Island, a tiny island just north of Bathurst Island, in 1976, 1987, and 2004. She ran tests for persistent pollutants, such as PCBs and DDT, and also for mercury.

She found that some gull eggs contained high levels of mercury, enough to prevent some other bird species from reproducing normally. Just how these high mercury levels may affect Ivory Gulls is unknown, as are the origins of mercury in the high Arctic. But as Ivory Gulls are scavengers, and are high on the food chain, chemicals such as mercury, regardless of the source, will tend to accumulate in their tissues.

Ivory Gulls are also threatened by the retreat of ocean pack ice. They depend entirely on edges of sea ice to find food and the ice also acts as a natural barrier, keeping the Ivory Gulls safe at their inland breeding sites. Their safely isolated outcrops of barren rock, if no longer surrounded by ice and snow, are unable to keep predators such as Arctic foxes away.

In 2006, the World Conservation Union (IUCN) designated the Ivory Gull as near threatened, and Canada listed the bird as a species of special concern under its Species at Risk Act (SARA).

Photo: Ivory Gull by Steve Young (