Climate crisis pushing polar bears to mate with grizzlies, producing hybrid ‘pizzly’ bears

Back in 2006, a strange polar bear was seen in the Northwest Territories of the Canadian Arctic. It had patches of brown on its otherwise white fur and an unusual face shape.

Hunters shot the bear dead and DNA tests confirmed what had been suspected: it was the hybrid offspring of a polar bear and a grizzly bear.

In 2010, another hybrid bear was shot by a hunter in the western Canadian Arctic. Tests revealed this animal was a second-generation cross born of a hybrid mother and grizzly father.

These were the first recorded instances of so-called “pizzly” or “grolar” bears. But over the last decade researchers have noted an increase in sightings of the hybrid creatures, and believe the climate crisis is behind the rise.

As the world has warmed, temperatures in the Arctic have risen about twice as fast as they have elsewhere in a phenomenon known as Arctic amplification.

Larissa DeSantis, a paleontologist and associate professor of biological sciences at Vanderbilt University in Tennessee, told The Independent the climate crisis “was definitely playing a role” in the hybridisation of bears.

The rapid changes to the Arctic environment have resulted in declining sea ice, which the polar bears depend on to hunt, but scientists also believe it is allowing grizzly bears to expand their territories further north.

The result is that grizzly bear ranges are now within polar bear ranges and the two species are coming into contact with each other with greater regularity.

Dr DeSantis’s recent research has been into the dietary habits of bears and how the climate crisis is impacting them, with polar bears increasingly forced to scavenge from human waste as they look for alternative food sources.

“Polar bears are so specialised on hunting seals that they may have a harder time adapting to the warming Arctic,” she said.

“The shift to eating hard foods in a handful of bears in the 21st century is also concerning. Polar bears may be reaching a tipping point and may now be forced to consume less-preferred foods.”

Unlike polar bears, Dr DeSantis said, grizzlies are well adapted to eating hard foods such as plant tubers or to scavenge carcasses when resources are limited. The changing terrain brought about by the warming climate also means that grizzly bears can venture further north and compete with polar bears for whatever food is available.

Some scientists have warned that greater instances of hybridisation could threaten biodiversity, if the process results in the loss or replacement of existing species.

But it is not the first time hybrid species have been recorded in the Arctic. According to the journal Nature, in the late 1980s, a whale found in west Greenland was believed to be a narwhal–beluga mix dubbed the narluga.

In 2009, a whale appearing to be a hybrid of a bowhead whale and right whale was photographed in the Bering Sea, between Alaska and Russia.

Meanwhile Dall’s porpoises have been recorded mating with harbour porpoises off the coast of British Columbia, and numerous seal hybrids have been identified in museum specimens and in the wild.

‘Pizzly bears’ Q&A with Dr Larissa DeSantis

Is it known how many hybrid polar-grizzly bears are in existence?

This is not known and remains a big question. But, we do know that this has happened numerous times, including in the past based on genetic data. There is evidence of admixture in bears, times when polar bear DNA has become integrated with grizzly bear DNA. We also know that they only diverged about 500-600 thousand years ago.

Why has this happened, and what is the role of the climate crisis in this?

Climate change and in particular arctic warming is definitely playing a role. The warming arctic is resulting in grizzly bears moving north due to warming conditions, while at the same time polar bears are having difficulty hunting from sea ice and [finding] bowhead whale carcasses where these bears engage in opportunistic mating.

Are there clear benefits for the hybrid bears?

We need to study the effects of hybridisation 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. These hybrids might be better suited for a broader range of food sources, like the grizzly bear, and in contrast to polar bears which are hyper-specialised.

Can hybrid bears mate and produce offspring with either polar bears, grizzly bears or other hybrid bears?

This is difficult to assess, but overall there is clear evidence of hybridisation. There is also evidence that these hybrids are fertile and there are second generation hybrids, where hybrids have mated with grizzly, for example. Additionally, hybridisation has been observed in captivity.

Do the hybrid bears stand a better chance of long-term survival than polar bears?

Unfortunately, what we are learning about the polar bear and what we know about hyper-specialised apex predators in the past, such as sabertooth cats, does give us reason to be concerned with the ability, or rather inability, of polar bears to adapt to a warming Arctic, especially when climate change is occurring at an unprecedented rate.

The hybrids do have certain features like intermediate skull forms that may make them better suited for eating mechanically challenging food, but this comes with trade offs: they are not as strong swimmers as polar bears.

If the warming Arctic makes seal hunting from sea ice untenable, then perhaps the hybrid pizzly or grolar bears can give hope for the survival of these types of bears. That being said, more research and monitoring is needed.