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Unraveling the mystery of grolars -- grizzlies that mate with polar bears

Ned Rozell
Courtesy Canadian Wildlife Service

When he heard the news of a grizzly-polar bear hybrid shot in Canada’s Arctic, Tom Seaton thought back to an unusual polar bear hide he’d once seen at Nelson Walker’s home in Kotzebue.

“He had two polar bear rugs in his house — one was a huge one, and the other was special. It had lots of brown in it,” Seaton said. “It looked like a regular polar bear, but for every square inch of hide, 5 to 20 percent of the hairs were brown instead of white.”

Walker, who has since passed on, was a polar bear hunting guide in the village. Seaton was then a teenage hunter who loved to listen to Walker’s stories. He’s now a biologist with the Alaska Department of Fish and Game in Fairbanks. Because he had heard that polar bears and brown bears had bred successfully in a zoo, Seaton was pretty sure Walker’s white-and-brown hide was from the mating of a polar bear and a brown bear.

Confirmation from DNA tests 

That combination of large bears is so rare that DNA testing of the hybrid bear shot in 2006 off Banks Island in Canada’s high Arctic proved for the first time that a wild bear had a polar bear as its mother and a grizzly as its father. An Associated Press reporter wrote that the bear had brown patches on its white coat, long claws, and the humped back of a grizzly.

Biologists say the merger is unlikely because the two species don’t interact much -- barren-ground grizzlies of the Arctic hibernate during much of the time polar bears have access to land. Polar bears are often far out on the sea ice when they’re ready to breed, but people sometimes see them on land in summer, as was the case in 1990 when oil exploration workers saw a polar bear 50 miles inland from the Beaufort Sea coast.

UAF scientists doing genetic testing about a decade ago found that grizzly bears may be the ancestral fathers of polar bears, which over many thousands of years perhaps evolved to life on sea ice by developing all-white coats, furry feet, and teeth designed to rip seal flesh. People sometimes see the two bears together at whale carcasses, such as a bowhead whale boneyard outside the village of Kaktovik on the shore of the Beaufort Sea. Both polar and grizzly bears feast on the remains of whales harvested by villagers there. Those who have seen the bears there say that the grizzlies, often smaller than the polar bears, dominate the encounter.

Brown bears chase off polar bears 

“They are two very different animals as far as behavior goes,” said Geoff York, a polar bear researcher at the USGS Science Center in Anchorage. “When a brown bear comes in at the bone pile, it chases off all the polar bears.”

Dick Shideler, a biologist at the Alaska Department of Fish and Game in Fairbanks who studies the farthest-north grizzly, has documented grizzly bears on the sea ice north off Alaska’s coast.

“We’ve radio collared a grizzly bear who hunts seals in the spring,” Shideler said. “Our pilot has tracked him on the ice, going from hole to hole. He’s figured it out.”

Shideler also said biologists from the Northwest Territories have in the past shared reports of what could have been hybrid bears.

“There was a grizzly up there towards Banks Island that killed a bunch of seals, and (a pilot) tracked it and saw its tracks intersecting with those of a polar bear,” he said. The carpet of tracks on the snow looked like the bears could have mated, Shideler said.

“The next year a helicopter pilot saw a female with darker cubs,” he said. “And (hybrids) have been reported quite a few times by Natives (of Canada’s Arctic).”

Biologists don’t think “grolar bears” could outcompete either species; a hybrid probably wouldn’t forage on land as well as a grizzly bear, and a mottled brown coat wouldn’t be the best camouflage on sea ice.

Ned Rozell is a science writer with the University of Alaska Fairbanks' Geophysical Institute. Reach him at nrozell@gi.alaska.edu. Used with permission. This column first appeared in 2006.