Disappearing polar bear dens on Svalbard

Svalbard, Norway - In what was historically a prime spot for polar bears to build dens and give birth, researchers are finding far fewer dens -- and changes in sea ice are responsible.

In research supported by WWF, scientists from the Norwegian Polar Institute (NPI) found that the number of dens on Kongsøya, a particularly important denning area in Norway's Svalbard islands, has fallen sharply in the past few years.

Three years ago, winter sea ice arrived at Kongsøya in mid-October, and researchers found 25 dens. But this year, the ice didn't come until early December -- and the dens numbered only five.

Female bears can travel vast distances across the ice from their hunting grounds to mountain slopes to find a perfect denning spot. When sea ice appears by early November, says NPI researcher Jon Aars, most bears will succeed.

"In years when sea ice appears late, bears may have trouble getting there in time."

A similar reduction in dens was found in a study on Hopen Island, to the south.

The full impact of later ice arrival on polar bear denning isn't yet clear, says Aars. Bears that can't reach Hopen or Kongsøya could be waiting a year to raise cubs, or just finding an alternative place to den. 

NPI is monitoring a number of Svalbard polar bears with radio collars. This data will help the researchers understand the potential cost of sea ice changes, from added energy expenditure to disruption of the bears' timing and success in raising cubs.

• Follow 4 of the bears being studied by NPI on the WWF Polar Bear Tracker.
• Norwegian Polar Institute (in Norwegian)