When polar bears attack... other polar bears

The town of Churchill, Manitoba is the undisputed polar bear capital of the world. Every year from mid-October to late November, the town's 800 permanent residents are joined by a total of 12,000 visitors and seasonal workers, who take advantage of a unique opportunity to watch the world's largest bear species up close and personal.

The sea ice on Hudson Bay, on the coast of which Churchill is situated, melts completely every summer, forcing the bay's polar bears ashore en masse. There, they wait out the warm months in cool, earthen dens, and then, come the fall, they head back to the shores of the bay, waiting for the water to freeze again. As they journey to the coast and as they anticipate freeze-up, some wander through or past Churchill, or onto nearby tundra, in plain view of excited, camera-toting tourists.

The bears' easy accessibility also makes them an ideal population for scientists to study; nearby Cape Churchill has yielded an especially rich catalog of bear behaviors.

But no tourist or researcher at Churchill or environs during fall bear season has previously recorded the scene described here by JoAnne Simerson of San Diego Zoo:

"On November 20 here in Churchill, just east of Gordon Point, we saw the tragic loss of a 11-month-old cub and the grieving of the loss by its mother. We did not witness the actual death but the aftermath: a young adult female with her cub was attacked by an adult male polar bear. The female lost the battle as the large male overpowered her and killed her cub. Valiantly she charged him and tried to get her cub back, but it was too late.

Soon other bears arrived in the area, but the large male prevailed and began to consume the small body in a hill of willow bushes. Still the mother continued to wander the area with every hope of saving her cub. The male eventually moved the small body out to the coast where the mother had less opportunity to charge him, but he left much of the pelt behind.

The mother continued to circle the male, risking even more harm from the other bears gathering if not from the male. Eventually she moved back to the willows, desperately searching for her cub. What she found was the pelt. She picked the pelt up in her mouth, carrying it and swinging her head side to side, a behavior that bears do in extreme stress. The mother charged at the other bears, never dropping her precious possession. She wandered in this manner for a long time. We left her at dark still very unsettled, but she had finally placed her cub’s remains near a willow bush, protected from the wind."

Cases of polar bear cannibalism are not without precedent. However, there are very few documented cases in which one polar bear has killed and then consumed another; this paper describes three cases that took place within a very short period of each other on the north coast of Alaska a few years ago, but, as far as is known, much of the cannibalism that has been seen may just as likely have been of bears that had already died. Even then, known instances are very rare.

Part of the reason for that is that, when it comes to others of their kind, polar bears are quite risk-averse; as if aware of the damage they could do to each other, they seemingly never fight outside of the breeding season, when clashes can be quite severe. A polar bear would have to be extremely hungry indeed - particularly given the relatively low nutritional benefit involved - to tempt fate and a protective mother by making a move for a cub. It seems likely that it would be something of greater occurrence during times of food stress, when their true prey - ringed and bearded seals - are unavailable.

This year, according to the National Snow and Ice Data Center, fall sea ice levels on Hudson Bay are far lower than normal; with sea ice forming much later than usual, some of the Churchill bears, having already fasted over the summer, may have been more desperate for sustenance. Although the incident described by JoAnne was the only one in which the kill (or its immediate aftermath) was documented, researchers have reported as many as eight cases of cannibalism near Hudson Bay this fall.

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