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Exclusive Video: Polar Bear Cannibalizes Cub

A National Geographic expedition filmed the rarely seen behavior, which climate change may be making much more common.

EXCLUSIVE: Male Polar Bear Chases and Eats Cub

Polar bear cannibalism likely isn't a rare event, but it's rarely witnessed by people. This may be the first time it's been captured so well on video.

A new video has captured a gruesome and little seen side to polar bears: When times are tough, males cannibalize cubs.

The phenomenon, long known to the Arctic’s native peoples, has been studied since the 1980s. Scientists believe that polar bears eat cubs in the late summer and autumn, when seals, their typical prey, are at sea and less available.

“One of the only things that’s left to eat is, in fact, cubs of various ages,” says Ian Stirling, a biologist at the University of Alberta and Environment Canada. “The footage itself is quite rare, but the event probably isn’t.” (See "Flesh-Eaters: 5 Cannibalistic Animals.")

The raw video, shot in the summer of 2015 off Canada's Baffin Island (map) during a Lindblad Expeditions trip on the National Geographic Explorermirrors other scientists’ accounts of polar bear cannibalism. 

The slow-moving cub and the smaller female are no match for the large, fast male, which swiftly goes in for the kill, repeatedly biting the cub around the head and neck.

After briefly trying to rescue her doomed cub, the female hastily retreats, wary of becoming the male’s next meal.

Polar Bear Mom and Cubs When they're not playing, polar bear cubs learn under the watchful eye of their mother.

“It was really hard to look away,” says naturalist Jennifer Kingsley, who witnessed the event from aboard the National Geographic Explorer ship. 

“Sure, you understand that this is life in the Arctic, and this is something we know about polar bear biology. But to see it is really dramatic.”

Driven to Desperation

Cannibalism is common in nature, occurring in hippopotamuses, tiger salamanders, sloth bears, and various other species. (Related: "Rare Picture: Hippo Seen Eating Hippo—and More Cannibals.") 

The male polar bear's cannibalistic turn is par for the course. Males are twice the size of females and are generally more aggressive, making it "a much smaller step [for males] to turn cannibalistic when hungry," says Stirling. 

Females, on the other hand, tend to avoid fights, despite the fact that nursing cubs means they're more starved than males.

But climate change may be making the behavior more prevalent, Stirling says. 

Arctic sea ice has been continually shrinking over time; in 2015, scientists measured the lowest maximum extent of sea ice in three decades

As the ice disappears, so do the crucial platforms that polar bears use to hunt seals, Stirling says. (Also see "4 Ways Polar Bears Are Dealing With Climate Change.")

Without the ability to hunt seals, polar bears may be driven to ever more extreme cannibalism, if they’re not already.

In 2004, for instance, biologists working in Alaska’s Beaufort Sea (map) witnessed an adult male track a pregnant female to her den and eat her—a never-before-seen act perhaps motivated by climate-driven desperation.

Follow Michael Greshko on Twitter.