Polar bears and ice go together. These animals usually spend most of their time out on the pack ice, hunting for seals.

Polar bears living along the Beaufort Sea seem to like ice even more than most, as this is the only region in the world where bears are known to den out on the ice. Every year about half of the pregnant females dig their dens in snowdrifts out on the pack ice rather than along the coast.

But in recent years some of the Beaufort bears seem to have turned into a bunch of landlubbers as dozens of them have been spotted along the Alaskan coast.

Steve Amstrup, a polar bear researcher working at the Alaska Biological Science Center, says this sort of behaviour is a big change for these bears.

"This past year (2000) we probably had 80 bears on the coast in summer. That just did not happen a decade ago," says Amstrup.

Amstrup can only speculate on why the bears are now combing the beaches. One possibility is that there are just more bears around in general. Their numbers have increased steadily over the last 25 years, perhaps to historic highs, and it is thought that about 2,000 polar bears may now live in the Beaufort Sea area.

Another possibility is that the bears have found a new source of food. "The remains of bowhead whales captured by Inupiat hunters are potentially an enormous food supply. Up to 30 bowheads may be taken by Beaufort Sea hunters in any one year. So some bears may have developed a strategy of hanging around on shore even though there are no seals nearby," he says.

This change in behaviour could lead to problems for polar bears in the future if industrial activities along the Beaufort coast increase. It is likely that there will be more encounters between bears and humans if the bears continue spending more time on the coast.

In the last decade, more of the Beaufort bears have started to den on land, as well as hunt there. About 40 percent of radio-collared pregnant females that denned on land from 1981-2000 built their dens in the Arctic National Wildlife Refuge, where controversy over energy development is heating up once again.

Amstrup is now working with a new technology to locate polar bear dens. An infrared device is mounted underneath a helicopter, and used to detect differences in temperature underneath the snow. He is still working out the kinks in this system, but if perfected it could help biologists locate where polar bears are hibernating beneath the snow. Then construction of infrastructure such as ice roads could be steered away from the den sites.

Since polar bears can hunt seals year-round, they do not have to hibernate to avoid starvation, as do black and grizzly bears. The pregnant females head into dens to protect their young, which can weigh less than a kilogram when they are born and are not prepared to face Arctic conditions for several months.

Until 1983, it was assumed that the female bears all denned on land because it was safer there than out on the sifting pack ice, where dens could be crushed or overturned. "Ice is a less stable platform, and if the cubs had to leave before they were ready, they would not survive," says Amstrup.

Although there had been a few shreds of evidence that Beaufort bears might den at sea, most biologists were skeptical about this idea. But no one knew for sure until Amstrup figured out a way to radio-collar a number of pregnant female bears.

"Lots of money had been spent trying to locate dens with aerial surveys, but it never worked. With telemetry, we were able to follow the pregnant females to their dens, and 'lo and behold,' many denned at sea," he says.

Bears that den on the pack ice can also cover a lot of territory while they are holed up in their snowdrifts. One radio-collared bear entered her den near the Yukon-Alaska border, and emerged near Wrangel Island in Russia, a distance of more than 900 kilometres. Then, within a few weeks of emerging from her den, the bear had returned to the central Beaufort area.

Amstrup has found that bears like to den in the same general area time after time. Individual bears also have preferences for denning in either snowdrifts on the ice or on land.

Polar bears also den along the Yukon's north coast and on Herschel Island, but sightings of the bears in summer have not increased in these areas. During their regular patrols along the coast, wardens in Ivvavik National Park often see grizzly bears, but not polar bears.

Then again, only one bowhead whale carcass has washed ashore along the Ivvavik coast in recent memory, and the Inuvialuit have not had a bowhead hunt in Canadian waters in a number of years, though they do hunt beluga whales.

Amstrup speculates that back in the days when polar bears were being heavily hunted, the ones denning on the ice might have had a better rate of survival than the bears that denned on land. The increase in the number of bears now denning on land probably reflects the general increase in population, but recent controls on hunting in denning areas have probably also played a part.

It remains to be seen what the polar bears newfound interest in the coast means for their long-term future. Amstrup points out that polar bears in the Beaufort Sea area have flourished over the past 30 years, and thinks that humans and polar bears can coexist, if the right management steps are taken.

Steve Amstrup can be reached at Steven_Amstrup@usgs.gov.