According to research by American and Canadian scientists, polar bears in the Beaufort Sea are turning to cannibalism - due to a lack of ice, stopping them from reaching their normal food.

The study reviewed three examples of polar bears preying on each other from January to April 2004 north of Alaska and western Canada, including the first-ever reported killing of a female in a den shortly after it gave birth.

Polar bears feed primarily on ringed seals and use sea ice for feeding, mating and giving birth.

Polar bears kill each other for population regulation, dominance, and reproductive advantage, the study said. Killing for food seems to be less common, said the study's principal author, Steven Amstrup of the U.S. Geological Survey Alaska Science Center.

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