Polar Bears Survive Disappearance Of Sea Ice By Moving To Land


Polar bears live an incredibly specialized existence in the Arctic. Though born on land, they prefer to live on sea ice, from which they can hunt the seals that make up the majority of their diet. But with sea ice disappearing, there’s been well-founded worry about what will happen to the polar bear (Ursus maritimus).

It might be easy to assume that the bears will give up their icy lives and move to land. And a study of the polar bears of the Western Hudson Bay, published by theĀ Journal of Animal Ecology, has found that the bears do just that — moving onto shore when the sea ice retreats and returning to the ice when it grows again later in the year. By tracking more than 100 female polar bears for over a decade, the researchers found that the bears’ migration could be timed to the movements of the sea ice.

But that time between the sea ice retreat and return has been getting longer and longer as the Arctic warms, with the result that the bears are spending more and more time on land.

“The data suggest that in recent years, polar bears are arriving on shore earlier in the summer and leaving later in the autumn. These are precisely the kind of changes one would expect to see as a result of a warming climate and may help explain some other studies that are showing declines in body condition and cub production,” the study’s lead author, Seth Cherry of the University of Alberta in Canada, said in a statement.

The problem is that on land the bears don’t hunt, or at least not enough to matter; they live off their stores of fat. Subadult bears, like the one above, are particularly vulnerable because, due to their smaller size, they have less fat to rely on. And their survival rate has been dropping. This might also explain the trend in decreasing litter size. Females don’t have enough fat to both survive the long summer and give birth to, and maintain, multiple cubs.

Which all makes me wonder: What happens when the summer gets too long for even the fattest bears to survive?

Image copyright Andrew Derocher, Univeristy of Alberta, via EurekAlert