According to scientists, small numbers of Grizzly Bears have moved into Polar Bear breeding areas and pose a danger to Polar Bear cubs which are typically born at around the same time of year Grizzlies wake up from hibernation.
From the BBC:
The researchers first spotted a grizzly bear (Ursus arctos ) in August 2008.
"The first time we saw a grizzly we were flying over the middle of Wapusk, counting fox dens," explained CUNY's Professor Robert Rockwell, who is also a research fellow at the American Museum of Natural History.
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."
Perhaps, in order to survive, the two kinds of bear will merge into one. There have been reports of Grizzly/Polar Bear hybrids. Normally found only in zoos, a "Prizzly" aka "Grolar Bear" was identified after it was shot in Banks Island.
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