From the BBC News site:
Grizzly bears are being spotted in Manitoba, Canada, where biologists say only polar bears are usually found.
Scientists from City University of New York say sightings are increasing.
"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.