Grizzlies Moving Into Polar Bear Habitat in Manitoba

iologists affiliated with the American Museum of Natural History and City College of the City University of New York have found that grizzly bears are roaming into what was traditionally thought of as polar bear habitat—and into the Canadian province of Manitoba, where they are officially listed as extirpated. The preliminary data was recently published in Canadian Field Naturalist and shows that sightings of Ursus arctos horribilis in Canada's Wapusk National Park are recent and appear to be increasing in frequency.

"Grizzly bears are a new guy on the scene, competition and a potential predator for the polar bears that live in this area," says Robert F. Rockwell, a research associate at the Museum and a professor of Biology at CUNY. "The first time we saw a grizzly we were flying over the middle of Wapusk, counting fox dens, when all of the sudden Linda Gormezano, a graduate student working with Rockwell and a co-author of the paper, shouted 'Over there, over there—a grizzly bear.' And it wasn't a dirty polar bear or a moose—we saw the hump."

That sighting in August 2008 spurred Rockwell and Gormezano to look through records to get a better picture of the bear population in the park. There was no evidence of grizzly bears before 1996, not even in the trapping data from centuries of Hudson Bay Company operation. But between 1996 and 2008 the team found nine confirmed sightings of grizzly bears, and in the summer of 2009 there were three additional observations.

"The opportunistic sightings seem to be increasing," says Gormezano. "This is worrying for the polar bears because grizzly bears would likely hibernate in polar bear maternity denning habitat. They would come out of hibernation at the same time and can kill polar cubs."

Before this study, researchers thought that the barren landscape north of the Hudson Bay was an impassable gap in resources for potentially migrating grizzly bears. But some U. arctos horribilis have managed to move from their historic ranges in the Rockies, the Yukon, and Nunavut, probably because of their flexible, mixed diet of berries and meat. The potential gap was navigable, and now some grizzly bears have reached the abundant caribou, moose, fish, and berries found to the south in Canada's Wapusk National Park.

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