As global temperatures rise, ecosystems and the species they harbor are adjusting in response. Many habitats are either shifting their boundaries polewards—or disappearing altogether—sending wildlife into new regions, where they interact with resident creatures in surprising and often unprecedented ways.
When this geographic collision is between two closely related species, they sometimes cross-breed, leading to the emergence of an entirely new species. Perhaps one of the most fascinating examples of this is the grizzly-polar bear hybrid: the “pizzly” or “grolar” bear.
Brown bears (Ursus arctos)—of which grizzlies are a subspecies—and polar bears (Ursus maritimus) are different species with different adaptations to their respective ecosystems, but they are closely related. Polar bears diverged from brown bears less than 500,000 years ago—not long at all on an evolutionary timescale—and the two animals retain enough genetic similarity that they can interbreed and produce fertile offspring.
When the hybrid offspring come from a polar bear father and a grizzly bear mother, the hybrid is typically called a “pizzly” bear, a portmanteau of “polar” and “grizzly.” When the parentage is reversed? A “grolar” bear.
Much of what we know about “pizzlies” and “grolar bears” comes from hybridization in captive conditions, specifically in zoos. In these situations, the hybrids are often the result of the two bear species cohabitating in the same enclosures. Around seventeen of these hybrid bears are known to exist, mostly in European zoos.
The hybrids present as an amalgamation of the key characteristics of their parents. Their fur isn’t white or brown, but a dingy, creamy blond. They have long necks like polar bears, but hunched shoulders like grizzlies. Their feet are partly covered in fur, intermediate between the bare paws of grizzlies and the fuzzy feet of polar bears. Their heads blend together the sleek features of polar bear heads and the thick, rounded features of grizzly heads.
In regards to behavior, though, the hybrids more resemble their polar bear parents, hurling large toys and stamping on objects in a similar fashion. They also lie down with their hind limbs splay-legged—a distinctive polar bear pose.
Pizzlies and grolar bears are undoubtedly striking curiosities, but how regularly do they show up in the wild? Not that often. Many purported hybrids end up being purebreds of one of the two bear species. In 2016, a bear shot in Nunavut, Canada was thought to be a hybrid based on its cream-colored coat, but genetic testing later determined that it was just a grizzly with a rare, blond coat.
However, true hybrids have definitely turned up in the wild in recent years. One of the most famous cases also comes from Nunavut, but a decade earlier. In 2006, an American hunter shot what was thought to be a polar bear (for which he had a hunting permit), albeit with strange features. After much drama and the possibility of incurring fines and jail time for targeting a species for which he had no permit, the hunter was let off the hook by genetic testing results, which confirmed that this was a special case: a wild grizzly-polar bear hybrid, thought to be the first ever recorded. In 2010, another bear—this time from the Northwest Territories—was confirmed by genetic testing as a three-quarters grizzly hybrid.
These hybrid bears come from areas in northern Canada where grizzlies and polar bears are crossing paths with increasing frequency as grizzlies encroach on polar bear habitat. A large part of this upswing in grizzly and polar bear encounters is likely due to climate change.
Grizzlies don’t typically stray north of the treeline in the Arctic, and permafrost is too frigid for them. But as permafrost rapidly melts and prey moves poleward into polar bear-inhabited coastlines, grizzlies are bumping into polar bears and mating with them. Likewise, as sea ice wanes, polar bears will likely find themselves stuck in terrestrial locations filling with a slow creep of grizzly invaders.
Rather than “grolar bears” taking over the Arctic, the real risk is that what we know as polar bears will simply be absorbed into a tide of grizzly DNA through successive crossbreeding events. While research suggests that the possibility of climate change-induced hybridization is still low for most species, it is already threatening animals like cutthroat trout, and could someday pose a similar extinction threat to polar bears if it continues unabated.