In Canada, Grizzlies Invade Polar-Bear Turf

If you want to see polar bears up close, the place to go is Churchill, Man., on the western shore of Hudson Bay. When the ice breaks up in the summer, the bears come ashore by the hundreds to wait for the autumn refreeze. So it's where tourists and scientists go, to gawk at and study the huge white predators. Just south of Churchill, the Canadian government recently created Wapusk National Park (wapusk means "white bear" in the indigenous Cree language) to protect the area where pregnant females dig their dens. (See the top 10 invasive species.)

But in recent years, another large predator, not quite as big as the polar bear but equally fierce, has been spotted in Wapusk. Although hunters eradicated them from Manitoba more than a 100 years ago, grizzly bears are trickling back and setting the stage for what could be a fascinating natural ecological experiment. (See pictures of Germany's polar bear celebrity.)

If a reshuffling of the grizzly- and polar-bear populations is nigh, it's not clear where the new lines will be drawn, says Robert Rockwell, a biologist with the American Museum of Natural History in New York City and co-author of a new paper documenting a spate of recent grizzly sightings in the journal The Canadian Field-Naturalist. Before 1996, there had been no evidence of grizzlies in the national park, but between 1996 and 2009, Rockwell says, there were nine confirmed sightings, plus three more in 2009.

Some experts have suggested that the grizzlies might not stick around long enough to face off with the polar bears, says Rockwell, but he isn't buying that. The 4,000-plus-sq.-mi. park where hunting is banned is what Rockwell calls a "food mecca" for grizzlies. Wapusk is home to some 7,000 caribou, an equal number of moose and untold numbers of rabbits, fish, geese and other creatures. When Rockwell and his team ask the real experts — the Cree elders whose ancestors have lived there for generations — they say, "Why would a bear that's found a huge food source go someplace else?" according to Rockwell. (See pictures: "Bye-Bye, Panda Tai Shan.")

Paradoxically, the intrusion of another top predator could in some ways make life easier for the white bears, says Rockwell. "Polar bears will eat anything they can get their grubby little mouths around," he says. "They'll take flightless geese, seals silly enough to get caught on shore when the tide goes out and caribou and moose calves. But they can't run fast enough to bring down adult moose or caribou." Grizzlies can and do — but the catch is, as soon as a grizzly knocks one down, the polar bears will smell it. "An adult male grizzly might weigh 600 lb. An adult polar bear is more like 1,500 lb. Grizzlies aren't stupid," says Rockwell. (See the top 10 animal attacks on humans.)

That same instinct for self-preservation will probably mean there won't be many outright fights between the two species. "If they hadn't evolved behavioral mechanisms to reduce unnecessary aggression, they would be extinct," Rockwell says, adding, "In 41 years in the field, where I sometimes see 200 bears in a day, I've seen exactly one aggressive encounter."

A more likely scenario is that the grizzlies will snatch polar-bear cubs as they emerge from their winter dens or vice versa, says Rockwell. Most intriguing of all is the possibility that the two species might interbreed. "These guys only split off evolutionarily about 150,000 years ago, so hybrids are viable," he says. That's no speculation: DNA analysis has proven that a bear shot in 2006 in Canada's Northwest Territories was part-grizzly, part–polar bear; the names "grolar bear" and "pizzly" have been floated in reference to it. (The hunter who killed the animal was spared a fine because the local laws against hunting bear apply only to grizzlies.) "I think it will be a rare event," says Rockwell. (See "Will the Polar Bear Survive?")

The reason for the potential habitat overlap is twofold: grizzlies seem to be expanding their range east and south from the Rockies, mostly as a result of their growing population, says Rockwell. Polar bears, meanwhile, are spending more time on land, as global warming causes ice to break up earlier and refreeze later in the year. And that means that while encounters between these huge bears might be rare today, they could become increasingly common.

See a story about a threat to the Yellowstone grizzlies.

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