"The opportunistic sightings seem to be increasing," says co-author Linda 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."

The grizzlies appear to be migrating south from Nunavut. Some believe that warming northern temperatures may be drawing the grizzlies into areas formerly dominated by polar bears.

"It's possible we have a first warning sign of what happens when our large mammals start shifting habitat due to climate change," said Gaile Whelan Enns, director of Manitoba Wildlands.

Robert F. Rockwell, research associate at American Museum of Natural History and co-author of the report said. "The Cree elders we talked to feel that now that grizzly bears have found this food source they will be staying."