Climate Change Forcing Polar Bears to Stay on Land

A new study has found that climate change has forced polar bears to spend a lot of time on land. Since the polar bears require drifting sea ice to travel, hunt and mate, less ice means they have to survive on their fat reserves. Researchers add that the change in the migration pattern has also affected the reproduction of these bears.

The study was conducted on polar bears living in western Hudson Bay. In this region, sea ice melts completely each summer and then starts re-freezing from autumn (late November to early December). Each summer, polar bears stay on the land. But here they can't hunt seals, and so must survive on their fat reserves.

"This poses an interesting challenge for a species that has evolved as a highly efficient predator of ice-associated seals. Because although polar bears are excellent swimmers compared with other bear species, they use the sea ice to travel, hunt, mate and rest," said Dr. Seth Cherry of the University of Alberta, lead author of the study.

The researchers wanted to understand how change in global temperatures was affecting the melting and freezing of ice and how this change in turn was affecting the survival of polar bears.

"Defining precisely what aspects of sea ice break-up and freeze-up affect polar bear migration, and when these conditions occur, is a vital part of monitoring how potential climate-induced changes to sea ice freeze-thaw cycles may affect the bears," Cherry said.

The study was based on the data obtained from 109 female polar bears. These bears were fitted with a collar and were tracked between 1991-97 and 2004-09. Researchers also monitored the movement of sea ice using satellite images, according to a press release from British Ecological Society.

"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," Cherry concluded.

According to estimates, there might be about 20,000 to 25,000 polar bears in the wild. In the western Hudson Bay, the number of polar bears is estimated to be around 900. The number of cubs making it to adulthood along with the bears' body composition has declined drastically over the past two decades.

The study is published in the Journal of Animal Ecology.