Polar Bears on East Bay Island

Even a single polar bear can devastate all the eggs on a single island where birds such as common eiders nest. This unfortunate colony was visited by three bears at once. (Courtesy Steve Marson)

Shrinking Arctic sea ice has left polar bears scrambling to find food, and they've taken to eggs in a big way, unfortunately for the birds.

While some athletes may impress us by downing a mere dozen eggs for breakfast, a polar bear in the Northern Hudson Bay region can eat hundreds of seabird eggs in a sitting, report researchers from Carleton University and Environment Canada.

"A bear can essentially devastate all the eggs on an island," said Samuel Iverson, lead author of the report, in an interview with CBC's Quirks & Quarks Saturday.

Iverson, a Ph.D. candidate in the Department of Biology at Carleton University, recalled one rampage he witnessed in which a polar bear ate its way through an eider duck nesting colony with 300 nests, each containing about four or five eggs. The eggs were nearly "completely consumed within about a 48-hour period."

It's not just ground-nesting birds such as common eiders that are being targeted, the researchers report in a paper published this week in the journal Proceedings of the Royal Society B.

Cliff-climbing bears

Sam Iverson and Inuit assistant on an island

Researcher Samuel Iverson, led by an Inuit guide, visited islands where seabirds nest in Northern Hudson Bay to study the impact of polar bears. (Courtesy Samuel Iverson)

Cliff-nesting birds such as thick-billed murres are also losing their eggs to polar bears.

"They'll just walk right down the cliffs and work their way along the ledges and go from one egg to the next," Iverson said.

Polar bears normally prefer red meat, and spend much of their time prowling the sea ice for seals, which are high in fat and protein. But before and after the ice freezes, the polar bears must remain on land, where they can't reach the seals.

Iverson said the warming of the Arctic has reduced the sea ice season by 60 days in the Northern Hudson Bay – the thaw happens 30 days earlier in the spring, and the freezing is delayed 30 days in the fall – forcing bears to find other sources of food.

While these bears may have occasionally eaten bird eggs in the past, the researchers believe they are now targeting the nesting colonies. In fact, their data shows that polar bear incursions into seabird nesting colonies has increased more than seven fold since the 1980s, and bears show up more frequently as the sea ice season shortens.

Iverson said warming temperatures in the Arctic haven't directly affected seabirds, but the study suggests it may still have a negative impact in the end.

"I think that it shows that the effects of climate change are much more far reaching than we anticipate."