Polar Bears and Cannibalism Revisited

//

Photo Credit: Corbis

In December 2009, we published the blog below about a case of polar bear cannibalism that had been witnessed on the shores of Hudson Bay, near Churchill, Manitoba, the "polar bear capital of the world." As we mentioned at the time, while not without precedent, such cases are believed to be extremely rare, although researchers have suggested that they may become more common as sea ice disappears and bears become more nutritionally stressed.

The journal Arctic has just published an account of another case, witnessed by photojournalist Jenny Ross of the Svalbard archipelago last year. She was in a boat approaching an adult bear on an ice floe, when she noticed it had some prey in its jaws. It took her a while before she realized the prey was a juvenile polar bear.

"As soon as the adult male became aware that a boat was approaching him, he basically stood to attention; he straddled the young bear's body, asserting control over it and conveying 'this is my food,'" Ross told the BBC.

The bear then picked up its young prey in its jaws and carried it some distance away, before setting it down and feasting on it.

"Predating another bear is a way to get food; it's probably a relatively easy way for a big adult male," Ross, who also presented images of the incident at this week's American Geophysical Union conference, said to the BBC. "And it seems that because of the circumstances of the loss of sea ice, that kind of behavior may be becoming more common."

From Dec. 17, 2009 …

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 the San Diego Zoo:

"On Nov. 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, 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.

"What makes this so unique is it is the first time ever seen in the Churchill area during fall," said JoAnne in an email.  "As you can imagine, with all the eyes out there for so many years, if this were 'normal,' it would have easily been seen.  What made this year abnormal was the ice was so very late in forming.  In my nine years [studying polar bears in Churchill], I have never seen it so late and I have also never seen so many bears in such a small area waiting to get on the ice."

Observation of this behavior was made possible through the work of Polar Bears International and Frontiers North Adventures.

Bottom two photos: J. Simerson