It’s a bear-eat-bear world as climate changes

Climate change and a resulting lack of food may be driving polar bears to eat each other, suggests a research paper recently published in Polar Biology.

The paper cites three instances of polar bears eating polar bears, which American and Canadian biologists noted along the Beaufort Sea coast of Alaska and the Yukon in 2004.

“During 24 years of research on polar bears in the southern Beaufort Sea region of northern Alaska and 34 years in northwestern Canada, we have not seen other incidents of polar bears stalking, killing, and eating other polar bears.”

The biologists admit that a single rogue polar bear, with a taste for his own kind, could have been responsible for the three incidents.

But they believe polar bears in the Beaufort Sea could be the first of their species to be affected by climate change because reductions in sea ice cover there may be cutting their food supply.

“It appears that climate is already well known to be affecting lots of things in Nunavut, of which polar bears are only one,” Ian Stirling, one of the paper’s authors, said in an email to Nunatsiaq News. “If starvation and hunger become severe for a polar bear, no matter what the reason, they are likely to look for alternate food sources, whether it is other bears or humans.”

The only other incident previously recorded of a polar bear eating another comes from Norway’s Svalbard Islands where starvation led one bear to pursue, eat and attack another.

Killing between related species, such as polar bears, brown bears and black bears, has been reported before, although the ecological factors causing cannibalism are “poorly understood,” says the paper.

But it says the killing sprees, involving only male polar bears, could have been motivated by hunger due to “nutritional stresses”: the manner in which the cannibalized polar bears were stalked and killed suggests they were preyed on by hungry, prowling polar bears.

Their hunger could be on the increase because longer ice-free seasons in the Beaufort Sea affect supplies of ringed seals and other foods, which polar bears prefer.

Hungry bears are increasingly affecting communities.

“We are already seeing increases in problem bears in western Hudson Bay, and there have been reports from other areas of more bears around villages and hunting camps. Most tend to be hungry, thin, sub-adult males because they are the ones that have the hardest time looking after themselves,” Stirling said.

One case outlined in the paper is of a female polar bear killed by a much stronger, large male bear. The bear was hunting in a denning area near the northern shore of Pingok Island, northwest of Alaska’s Prudhoe Bay, where it discovered the den by scent. The male bear apparently pounced on the den, killed the female and dragged her away and devoured a good part of the carcass.

“In the face of the den’s outer wall were deep impressions of where the predatory bear had pounded its forepaws to collapse the den roof, just as polar bears collapse the snow over ringed seal lairs,” the paper says.

The second case involved an adult female and cub, recently emerged from their den.

In April 2004, while following polar bear tracks on sea ice near Herschel Island, biologists discovered the partially-eaten carcass of the adult female. The dead female was a 15-year-old that had been captured and tattooed as a cub in Alaska. They determined from the track patterns that a much larger adult male had charged this female and her cub. The male did not follow the cub, showing it had killed for food instead of mating.

The fact that the male polar bear was even hunting near the den, which is about 25 kilometres away from normal hunting grounds, suggests it was hunting purposely there — that is, to catch and eat another polar bear.

The third case of cannibalism involved a yearling male, who was found by Canadian researchers about 100 kilometers northwest of Herschel Island. The yearling had been in a snow pit on a pressure ridge with a view of the surrounding area. A predatory bear stalked and killed the yearling.

Polar bears do sometimes kill and eat both walrus and belugas. They have been known to hunt reindeer and sometimes eat other foods including birds, bird eggs, kelp and beached whales.

On the Svalbard Islands, polar bears were once found feasting on a 350-year-old bowhead whale carcass that was uncovered by a retreating glacier, and, in recent years in Alaska, polar bears have also been seen gnawing on bowhead carcasses left by Inupiat whalers.

Polar bears can also develop an appetite for human beings. Last year, a group of starving polar bears reportedly terrorized local reindeer hunters and herders in Yakutia, Siberia.

Last February, Lydia Angyiou of Ivujivik tackled a male polar bear posied to attack her son. The polar bear was found later to be in poor condition, with an empty stomach.