ANCHORAGE - Four big polar bears - including three 1,000-pound males with bloody muzzles and yellow-stained fur - were dining together on whale carcasses at a sand spit about a mile outside the northeastern Alaska village of Kaktovik.

Despite the odor from rotting bowhead and the sound of chomping jaws, the midnight scene at the bone dump along the Arctic Ocean was remarkably peaceful. Recorded as part of a three-year study of polar bear feeding behavior, it showed that these predators were willing to share discarded remains with each other, said federal biologist Susi Miller.

But then the majestic rulers of Beaufort Sea ice met their match: a scrappy tundra grizzly.

As Miller and a colleague watched from the cab of a pickup, a small brown bear sow emerged from the darkness and ambled up the spit, trailed by two yearling cubs.

Without hesitation, the grizzly lunged at the first polar bear, huffing and snarling, driving it into the lagoon. Soon the second, third and fourth polar bears had joined it, leaving the food to a gnarly little bruin about one-third their size.

"She just went in there and cleared them out, one after another," Miller said. "She just would not tolerate any bears being there with her cubs.

"It really goes to show that size is not everything. Attitude counts for a lot."

Between 2002 and 2004, scientists from the U.S. Fish and Wildlife Service have documented large, unusual congregations of bears on two barrier islands in Alaska's Beaufort Sea, feeding on whale remains left over from subsistence harvests by Native crews in Nuiqsut and Kaktovik. The observations come as polar bears appear to be increasing along that coast during fall, possibly due in part to sea ice remaining offshore for longer periods as winter approaches. Study will continue this year.

"There are more bears on the shore for longer periods of time in the fall," Miller said. "It looks like the use of the coastal habitat is increasing, and it may be linked to climate change. But it may also be related to the fact that the population has increased."

Whatever the cause, the setting was extraordinary, said Scott Schliebe, polar bear team leader for the U.S. Fish and Wildlife Service. Imagine the overpowering smell, Kaktovik residents arriving by car to view the activity from a few hundred yards away, half-ton animals passing in the night.

"You'll see these bears sitting on top of a rotten carcass with their head down in the carcass, burrowed down into the carcass up to their shoulders, not even coming up for air and just feeding," Schliebe said.

"You hear all the noise that goes with it," he added. "It sounds like something out of Jurassic Park in the dark."

But the biggest surprise may be the growing number of brown bears crashing the party on Barter Island. And guess who is dominating?

"Out of the interactions that we saw, the brown bears tended to be a lot more aggressive," Miller said. "These brown bears ruled the roost.

"They're just not very tolerant of other bears around them, whereas the polar bears were amazingly tolerant," she said.

"It's unusual," added Kaktovik Mayor Lon Sonsalla. "In the last four or five years, (brown bears) are getting to be regular visitors in the fall."

An estimated 2,300 polar bears roam Alaska and Canadian areas of the southern Beaufort Sea in a distinct population thought to be stable since the 1990s. But the iconic Arctic predator faces an unknown future.

The development of offshore drilling on gravel islands near Prudhoe Bay has raised the possibility that the animals' habitat may be fouled by an oil spill. Climate may also change how these animals live.

During the past few years, shifting wind patterns and warmer temperatures have shrunk ice coverage near Alaska during late summer and fall, sometimes stranding bears on shore. If the Arctic climate continues to warm as projected, sea ice could retreat even farther or disappear during summer, threatening the existence of an animal that hunts seals from ice floes.

The Center for Biological Diversity, a conservation watchdog group based in the Lower 48, has petitioned the Environmental Protection Agency to protect the bears under the Endangered Species Act.

With more polar bears using coastal areas and scores of them gathering at these carcass sites, scientists say the possibility of human-bear conflicts has also increased.

Cross Island, about 12 miles offshore, is used by people from Nuiqsut only during whaling season. But Kaktovik whalers dispose whale remains at a northeastern spit of Barter Island, a few miles from the village itself.

Schliebe said he's suggested that the community dump the carcasses elsewhere as a way to head off problems. But Sonsalla said that the island community doesn't have a better alternative and that the site works best.

"The people are OK with it," he said.

The picture is complicated by brown bears, which began showing up in larger numbers in 2003, wandering out from the mainland portion of the Arctic National Wildlife Refuge.

"I think we have a unique situation," Schliebe said. At one peak moment, six to seven brown bears were feeding on whale meat near 15 to 20 polar bears, something never reported before, he said.

Brown bears and polar bears have probably always overlapped during certain seasons, according to several biologists. Brown bears inhabit Alaska's Arctic mainland and on rare occasions venture to barrier islands, said biologist Dick Shideler, who studies brown bears in Prudhoe Bay for the Alaska Department of Fish and Game.

Likewise, polar bears regularly come ashore, especially when ice retreats after drifting close. One animal even wandered 100 miles up the Dalton Highway toward the Brooks Range in 2002.

With both species occasionally in the same territory, it follows that they would sometimes target the same food, Shideler said.

"We've had reports from some other biologists of grizzly bears and polar bears feeding on walrus carcasses and gray whale carcasses at Cape Lisburne (on the Chukchi Sea)," he said. "We know it's happened before, and it makes sense that it's happened."

Federal wildlife biologist Patricia Reynolds, who studies brown bears in the Arctic National Wildlife Refuge, called grizzlies "ultimate omnivores" that are one of nature's premier opportunists.

With funding from the Minerals Management Service and support from the Alaska Nanuuq Commission, the North Slope Borough and the villages of Nuiqsut and Kaktovik, Schliebe, Miller and several other biologists spent 1,231 total hours at Cross and Barter islands, according to a preliminary report of their work.

They found an average of 25 polar bears roamed the vicinity of the Barter Island site, with an average of about five actively feeding bears. Cross Island saw fewer polar bears, averaging four or five on the island and about two at the carcasses.

More sows and cubs appeared on Barter, while adults dominated at Cross. The bears were most active at night, resting much of the day. The polar bears frequently swam, played, traveled and even ate in the sea.

"I actually saw a bear lying on its back like a sea otter," Miller said. "They were very comfortable in the water."

With some heart-pounding exceptions, the bears shared the meat and blubber without a lot of commotion.

"We never saw them draw any blood," Miller said. "They just don't spend a lot of time fighting. Their aggressive interactions tend to be short, and they tend to work out their social issues quickly. We have a lot to learn from them."