Polar Bear-Grizzly HybridA stuffed "grolar bear," or "pizzly"—grizzly-polar bear hybrid—looms over the living room of Jim Martell in Glenn Ferry, Idaho, in 2007. Martell shot the animal (picture), the first recorded grolar bear, in Canada's Northwest Territories in 2006. As the Arctic thaws as a result of global warming, polar bears will increasingly be forced to stay onshore, where they're likely to bump into their grizzly cousins—some of which are moving north as temperatures rise. Arctic Ocean sea ice, which polar bears rely on to hunt marine mammals, is predicted to disappear in summer before the end of the century, experts say. (See "Grizzly Bears Moving Into Canada's Polar Bear Capital.") The two bear species are among the 22 Arctic marine mammal species most likely to interbreed, or hybridize, in a new Arctic "melting pot," according to a commentary published this week in the journal N ature. For the paper, scientists combed through studies and museum collections to find evidence of hybridization already underway in some species, and concluded that as many as 34 hybrids may occur. What's more, of the 22 types of animals, 14 are listed or may be listed as endangered, threatened, or of special concern by one or more nations. The polar bear and grizzly are currently on the U.S. endangered species list. Hybridization "can be the final straw in loss of species," commentary lead author Brendan Kelly, a research biologist at the U.S. National Marine Mammal Laboratory in Juneau, Alaska, told National Geographic News. Species in healthy numbers can interbreed naturally without disappearing, Kelly noted. But "when humans alter habitat particularly abruptly, they can greatly accelerate and make more likely these hybridizations and extinctions," he added. As for the pizzly, a second-generation individual—with a grizzly bear father and a hybrid mother—was killed this year in Canada, according to the Nature paper. —Christine Dell'Amore

Photograph by Troy Maben, AP