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Polar bears turn cannibal


June 14, 2006

Two polar bears have starved to death and two others were found dead this year in the region where scientists previously discovered unprecedented cannibalism within the population.

Scientists were stunned to discover that two mother polar bears had been stalked, killed and eaten near their Beaufort Sea dens, and that much larger male bears cannibalized a young male during the spring of 2004.

Now, four more dead polar bears have been found in the Alaskan and Canadian regions of the Beaufort Sea, and researchers are getting very worried.




What was initially thought to be a curious event could indicate a radical shift in the behavior of polar bears as they battle dangerous drops in nutrition levels, said the lead author of a report into the 2004 deaths.

Dr. Steven Amstrup, polar bear project leader for the U.S. Geological Survey, Alaska Science Center, said cannibalism is not unheard of in bear populations, but it usually happens after an has animal died for other reasons, such as during a fight over territory.

What sets the 2004 deaths apart is the calculated manner in which the bears appear to have been sniffed out, stalked and killed by large males bears hunting for food.

"These are very rare events. The fact that we observed three in a row is very profound," Amstrup said.

This year, researchers found two females with radio-tags were found dead from starvation in Alaska and the remains of a third.

Canadian researchers found one dead polar bear in their study region.

"We've never seen anything like that before," Amstrup said. "Two of the dead bears were extremely emaciated and appeared to have starved. We don't know what the cause of the starvation was. We're concerned these could be another symptom of changes in the habitat, but we don't know enough yet to know."

The radio-collared bears had not exhibited any unusual roaming habits before their deaths, he said.

While the 2004 deaths could be due to a rogue bear, or could be a regular occurrence not witnessed before, Amstrup said the trigger was more likely nutritional stress caused by dwindling food sources.

"Four of the last five years have been record ice retreats in the polar basin. That gives polar bears the option of staying on land, which isn't too common here, or staying on the sea ice further off shore," he said.

Both options appear to cut access to food, he said. The report states that adult males in the southern Beaufort Sea region were in poorer condition than bears to the north and west. Males concentrate on breeding during spring, as opposed to feeding, and are the first to show adverse effects to large ice retreats.

"Most wildlife respond to changes in the environment in a series of steps with rapid transitions. We can see a gradual change over time in the condition of sea ice. We might not see a gradual change for polar bears. They might reach a threshold and have to respond in a different way. There might be a very major change in the distribution of polar bears," Amstrup said.


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