Scientists say shrinking Arctic sea ice may be forcing some polar bears into cannibalizing young cubs.
"When (bears) are very hungry, they go looking for something to eat," biologist Ian Stirling said Friday. "There's nothing much to eat along the Hudson Bay coast in the fall other than other bears."
So far this fall, tour operators and scientists have reported at least four and perhaps up to eight cases of mature males eating cubs and other bears in the population around Churchill, Man. Four cases were reported to Manitoba Conservation; four to Environment Canada.
"That's a very big number,"said Stirling, a retired Environment Canada scientist, who has studied the Churchill population for 35 years.
"I worked there well over 30 years and never saw a single case of cannibalism."
Bears lose up to 30 per cent of their body mass as they spend the summer and autumn on land waiting for the sea ice to refreeze so they can use it as a platform to hunt seals.
They used to be able to get out on the ice of Hudson Bay by early November, but freeze-up is now weeks later. This year, as December approaches, it still isn't solid enough for the bears.
Bill Watkins, a zoologist with Manitoba Conservation, reports he hears about one or two cases of cannibalism a year. He said it's possible more cases have been seen this year because more tourists are on the land, but he also suspects a climate change link.
"We would really need several years of data like this to confirm that something unusual's going on," he said. "While it's very suggestive of an impact of climate change, it's a little early to confirm that definitively."
Nick Lunn, another Environment Canada scientist who's spent decades studying the bears of Wapusk National Park near Churchill, said he saw polar bears eating other polar bear carcasses four times this fall. He couldn't confirm the bears killed their meal themselves, but he suggested the number of cases was startling.
"I've been working there since the early 1980s and I have never come across (four) cases of bears feeding on the remains of bears before. There's something going on."
The cases may be increasing.
Stirling said between 2004 and 2006, he and other researchers found evidence of cannibalism in the carcasses of three adult females and one yearling.
"Killed, simply to be eaten."
He added that there have also been four cases of such cannibalism in the past several years among the southern Beaufort population in Canada's northwest corner.
Adult males killing young of their species isn't unknown among animals, especially bears. But in most cases it happens in the spring so the male can then impregnate the sow he has left without cubs.
The timing of the recent killings suggests hunger may be the motivation, said Stirling, because "the females aren't going to be reproductively receptive until next spring."
Stirling's research has shown for years that the condition of the bears around Churchill is slowly deteriorating. Adult females are weighing less and less.
The Hudson Bay bears are considered Canada's most vulnerable bear population. Scientists point to them as an example of what may happen to other bears as Arctic sea ice continues to shrink.
A group of specialists recommended over the summer that, in light of sea ice trends, Canada should reconsider its decision not to include the mighty predators on its list of endangered species.
Canada has 13 of the world's 19 bear populations, which amounts to somewhere between 12,000 and 16,000 animals.
The International Union for the Conservation of Nature, one of the world's largest environmental science networks, considers eight bear populations to be in decline. Three populations are considered stable and one is increasing.
Information on seven populations is still too scarce for scientists to draw solid conclusions.
