High levels of mercury may be a factor in the drastic decline of the rare ivory gull, Environment Canada's Birgit Braune says.

The Arctic seabird was assessed as "endangered" last year by the national group that evaluates species at risk in Canada.

The bird's population has dropped about 80 per cent from 2,400 to 300, said Braune, who is with the department's National Wildlife Research Centre in Ottawa.

"It turned out that in fact they [gull eggs] are amongst the highest mercury concentrations that we've seen in seabird eggs from the Arctic marine environment anywhere," she told CBC News in an interview.

"The ivory gull mercury levels are close to and, in some cases, above toxic threshold levels for reproductive success."
 
The ivory gull has a higher metabolic rate than other gull species, which means it needs to eat more, which could explain the higher mercury levels, she said.

But it's too early to say whether the heavy metal is directly responsible for the ivory gull's decline, she said.

Climate change, contaminants and overhunting in Greenland could also be affecting the bird's population, she said.

The number of ivory gulls in Norway and Russia has also declined, she said.