Polar bears are mating with grizzlies more and more often

Their fur shimmers between white and brown.

“Pizzlys” are the offspring of polar bears and grizzlies in Alaska and Canada. Researchers are concerned about the spread of these hybrid bears.

Their mothers are polar bears, their fathers grizzlies. In parts of Alaska and western Canada, bears with white-and-brown mottled fur are spreading, called Pizzlys or Grolars by locals: a blend of polar bears and grizzlies.

Such hybrid forms have occurred sporadically in zoos, but also in the wild. Now, however, their numbers are increasing. According to researchers, the reason is warmer temperatures brought about by climate change.

Overlapping habitats

“The habitats of polar bears and grizzlies are overlapping more and more,” explains Andrew Derocher. The biology professor at the University of Alberta (Canada) has been researching Arctic bears for 30 years. “We don’t know exactly how many hybrids exist at present. We have only genetically confirmed eight so far. But I estimate that several thousand polar bears live in regions of Alaska and Canada where they can encounter grizzlies.” Overlaps could also occur in Russia.

The DNA profiles examined show that it is always grizzly males that mate with female polar bears — never the other way around. This is because the females of both species tend to remain loyal to their home regions, while grizzly males in particular are inclined to expand their territory. Derocher and his team found not only 50:50 hybrids in Arctic latitudes, but also individuals with three-quarters grizzly DNA. This suggests that Pizzlys are capable of reproducing.

“We don’t know exactly how the hybrids live, but grizzlies and polar bears are dramatically different species,” Derocher emphasises. Polar bears need the ice, where they find walruses and seals as food; they do not hibernate and do not venture southward into the tundra. According to the WWF, there are currently an estimated 20,000 to 25,000 polar bears remaining worldwide.

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Grizzlies, on the other hand, do not normally roam north of the tree line, because the permafrost is too cold and hunting land animals on the ice is too difficult. But as temperatures rise, the tree line is also shifting northward. “Hybrids probably live more like grizzlies,” estimates Derocher. This is suggested by the first documented case from 2006, in which a pizzly hunted land animals. “That was all the more surprising given that it had spent two and a half years with its polar bear mother.”

The scientific director of the organization “Polar Bears International,” Steven Amstrup, emphasizes that hybrids like pizzlies are by no means genetic anomalies, but rather occur quite naturally among closely related species. There is the coywolf — a mix of coyote, dog, and wolf — as well as the mix of bobcat and lynx.

The Beginning of the End

In the case of bears, however, the question is who will spread further and possibly prevail. “Recreational hunting is not the main risk for polar bears,” says Derocher. “We do worry about hunting quotas, toxic chemicals, oil pollution, and shipping, but these are minor compared to the loss of habitat due to climate change.”

The grizzly’s advance northward is part of this. When the first female grizzlies mate with male polar bears, this may well mark the beginning of the end for the great white bears, estimates Derocher.

By the middle of this century, experts predict, two-thirds of today’s polar bear populations will have disappeared. In southern Alaska, there will no longer be enough ice.

Only at the highest points of the Canadian Archipelago and in northern Greenland will polar bears still be found. The decisive question, according to Derocher, will then be: “Is there enough space there for sufficient animals to preserve the species until the planet cools again?”

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