In response to sudden shifts in their habitats’ climate, many species cannot adapt so they are forced to change the location of their migration or foraging habitats. In some situations, this can result in some unexpected consequences.
Pushed by warming temperatures, grizzly bears are increasingly migrating north where temperatures are colder, while polar bears are moving south pushed by melting ice in the Arctic Circle. Inevitably, the two species crossed paths and interbred, producing hybrids known as “pizzly bears” or “grolar bears”, depending on how you look at it. Some of these hybrids may be fertile, which raises interesting questions about what bears in the Arctic may look like in the future.
The first pizzly was identified in 2006. Although there were reports of strange-looking bears prior to this date, it was only after Roger Kuptana, an Inuvialuit guide from Sachs Harbour, North West Territories, drew attention to a bear shot by an American sports hunter that polar bear and grizzly bear hybrids were taken seriously. DNA tests confirmed that the shot bear was indeed a hybrid — the first documented one in the wild. Previously, in 2004, two pizzly bear cubs were born in captivity after polar bears and grizzly bears were allowed to mate at Osnabrück Zoo in Germany.
Since then, at least eight more pizzly bear hybrids have been identified in the wild. In a 2017 study, researchers showed through a combination of field observations and genetic analysis that all eight hybrids sprung from a single female polar bear who mated with two grizzly bears.
“Grizzly bears have recently become more common on the Arctic Islands in the Inuvialuit Settlement Region, concurrently with a period of environmental change. Over the last decade, grizzly bear – polar bear hybrids have been confirmed within this region, triggering extensive discussion and speculation regarding the impact of hybridization on the parent species,” the researchers at the University of Alberta and the University of Calgary in Canada wrote.
Historically, grizzly bears ranged from Alaska to Mexico and from the Pacific Ocean to the Mississippi River. However, hunters and trappers have reported increasingly frequent sightings of grizzlies in Canada’s High Arctic, and scientists say climate change and human encroachment on their habitat is to blame for this northward migration.
The Inuvialuit Settlement Region, for instance, has seen its seasonal freeze pushed back from August to the end of September or even early October in the last 30 years. This means there are now more grasslands and other vegetation that are attractive to grizzly bears.
Meanwhile, polar bears are migrating from north to south due to loss of sea ice. Polar bears now stay longer on land and have to use more body fat to sustain their energy than decades ago. As a result, polar bears have experienced a drop in population, reduced survival rates, and a decrease in food.
In the middle, grizzly and polar bears met, and nature took its course. The two species only diverged about 500,000-600,000 years ago, so they are able to mate. However, the pizzly bear hybridization could be a threat to biodiversity, leading in time to the loss or replacement of existing species.
Polar bears are hyper-specialized animals that hunt seals and are less adapted than grizzlies to eating hard foods such as plant tubers or at scavenging carcasses. There are many unknowns at this stage, such as whether or not the hybrids are fertile, but it wouldn’t be preposterous to see polar bears replaced by grizzlies or even pizzly hybrids as the 21st century unfolds.
“We need to study the effects of hybridization on these bears. Most of the time hybrids are not more vigorous than either of the two species, as grizzlies and brown bears have unique adaptations for their particular environments. However, there are a few examples where hybrids can be more vigorous and better able to adapt to a particular environment, particularly if the environment is deviating from what it once was. This requires further study and careful monitoring. Time will tell if these hybrids are better able to withstand a warming Arctic,” Larissa DeSantis, a paleontologist and associate professor at Vanderbilt University in Tennessee, told The Independent.