For years, as the world has warmed, the territories of polar bears and grizzly bears have started to overlap. Grizzlies now venture into the Arctic more often. In doing so, they occasionally cross paths with their white cousins. Very rarely, they mate. A new study confirms the existence of at least eight “grolar” bears.
There are two forms of the polar-grizzly hybrid. The grolar is the offspring of a male grizzly and a female polar bear. A pizzly comes from the mating of a male polar bear and a female grizzly.
Usually, pizzlies only occur in captivity, while grolar bears do exist in the wild. Although the ranges of the two bear species overlap, “the overlap typically happens in the summer when polar bears are on the mainland coast waiting for the sea ice to form again,” Ruth Rivkin, co-author of a new study, explained to IFL Science.
“Mating season for polar bears occurs in the winter while the bears are out on the sea ice hunting seals.”
Polar bears mate on the sea ice, not on land, so the opportunities to meet grizzlies are rare. Photo: Jerry Kobalenko
Why pizzlies are even rarer than grolars
Mating typically happens when male grizzlies also venture out onto the sea ice to hunt. If they cross paths with a female polar bear, they occasionally mate. But female grizzlies rarely go far onto the sea ice, so they encounter male polar bears far less frequently.
This is the first large-scale study of the bears. Using a genetic sequencing chip, the team analyzed samples from 371 polar bears and 440 grizzly bears from Canada, Alaska, and Greenland. The chip can track over 8,000 polar bear genetic markers from a small blood or tissue sample.
The team photographed the sequences through a microscope and then compared them to the two bears’ known genetic sequences. They found only eight hybrids, and all these individuals were previously known.
“[This] suggests that while hybridization does happen, it is so far restricted to a small portion of the western Arctic,” said Rivkin.
Interestingly, all eight hybrids come from the same female polar bear. They are either her direct offspring or her hybrid offspring that have since mated.
Researchers suspect that the number of hybrids will increase with climate change. Though these are the only ones confirmed through genetics, Indigenous communities have reported the existence of these grizzly-polar bear creatures for many years. However, it’s not always easy to confirm that the bears are actually hybrids. By sight, a dirty polar bear can seem like a hybrid.
