By Doreen Walton, Science reporter, BBC News
Grizzly bears are being spotted in Manitoba, Canada, where biologists say only polar bears are usually found.
"Grizzlies would likely hibernate in polar bear maternity denning habitat," says CUNY's Linda Gormezano. They would come out of hibernation at the same time and can kill polar cubs," warned Ms Gormezano, who has seen the grizzlies from the air.
The researchers first spotted a grizzly bear (Ursus arctos ) in August 2008. Since then they have examined the records and found no evidence of grizzly bears before 1996. Between 1996 and 2008 they found nine confirmed sightings. In the summer of 2009, three more were spotted.
The scientists say that the barren landscape north of the Hudson Bay had been thought to be impassable for migrating grizzlies. But now some have reached Canada's Wapusk National Park to be rewarded with abundant caribou, moose, fish and berries.
"We don't yet know if they are wandering or staying - the proof will come from an observed den or cubs - these animals will eventually be residents of this national park," said Professor Rockwell.
"The Cree elders we talked to feel that now grizzly bears have found this food source, they will be staying.
"A big question is how to deal with these new residents... In Canada, both the polar and grizzly bear are federally listed as species of special concern," he added.
As grizzly bears move into areas usually populated only by polar bears, hybrids between the two become more likely. Also known as pizzly, prizzly or grolar bears, these have been bred in zoos. Their presence in the wild was confirmed by DNA tests after one was shot in Banks Island, in the Canadian arctic.
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