Are Grizzly Bears and Polar Bears Hybridizing in Alaska?

In June 2019, Peter Flynn was on a 19-day trek through the Arctic National Wildlife Refuge (ANWR) when, 400 meters away, he and his companions saw a bear pounce like a fox on squirrels. terrestrial. At first, Peter thought it was a grizzly bear. When he examined it with binoculars, he wasn’t so sure. One of his classmates took a photo of the bear with her iPhone. The far photo shows what looks like a light-colored grizzly bear with an abnormally long neck. Peter and his companions wonder if the bear was a hybrid, the result of a cross between a polar bear and a grizzly bear.

“His coloration was white as a mountain goat’s butt with a bit of brown mixed in. It had a really big rump and a long neck and a streamlined shape. We didn’t want to mess with it, so we kept our distance. Now, I wish we had gotten closer,” Peter said.

Pizzly Bear in Alaska
The bear that Peter Flynn and his companions encountered during their long journey through the Brooks Range. Jill Weitz

Biologists have never documented polar bears and grizzlies crossing in Alaska, but, with the Arctic rapidly warming, that could change soon. Kerry Nicholson directs the North Slope Grizzly Project, which focuses on grizzlies that live in Alaska’s Arctic oil fields. She points out that grizzlies in the Arctic can be exceptionally light in color.

“It’s not that (hybridization) hasn’t happened in Alaska,” he wrote in an email, “it’s just that we haven’t had any confirmed documentation of it, and we don’t have anyone specifically looking for it.”

The first documented pizzly

Biologists have only documented polar and grizzly bear interbreeding in the wild in Canada’s western Arctic. The resulting viable offspring are often called “pizzly” or “grizlar”. The pizzly blew up news headlines in 2006, when Idaho resident Jim Martell shot what he assumed was a polar bear on a hunt near Banks Island. As Martell approached the dead bear, his Inuit guide noticed the animal’s long claws, slight hump and brown spots on its fur and realized it was something unique. An analysis of the bear’s DNA revealed that it was the offspring of a male and a female polar bear.

The hunt for Martell took place 90 miles north of mainland Canada. Inuit living in Sachs Harbour, the only town on the southern tip of Banks Island, recently noted grizzly bears on the island. Further north, on Canada’s Melville Island, a research team sighted brown bears in 2003 and 2004, even photographing one fleeing from a helicopter near ground level.

Grizzlies have been documented appearing on Canada’s western Arctic islands for the last 70 years, but there has been an uptick. They have all been males, most of which are believed to have traveled from the mainland over the ice to the islands during the spring mating season. Some are likely hibernating on desolate islands.

Since 2006, eight hybrids have been verified after being killed or captured. They have all been to Canada’s western arctic islands. A 2017 research paper shows that all eight of these hybrids were descended from a female polar bear that mated with two different male brown bears. Four hybrids were 50 percent grizzly and 50 percent polar bears. The other four were 75 percent grizzly and 25 percent polar bear, the result of the two original grizzly parents mating with one of the first-generation hybrid offspring. Several other bears that appear to be hybrids have been sighted, but without a DNA sample there is no way to verify this for sure.

Béarjà vu

arctic grizzlies
Arctic grizzlies approaching the author. Bjorn Dihle

Brown bears, despite being smaller than polar bears, are more aggressive and dominant. When it comes to mating, male grizzlies have an advantage over polar bears. This leads some biologists to believe that grizzly bears could take over polar bear populations through one-way gene flow. What happened around Banks Island could be a preview of what is to come. During one of the last periods of rapid climate warming, scientists think that’s exactly what happened in southeastern Alaska.

The southeastern ABC Island archipelago (Admiralty, Baranof, and Chichagof) is inhabited by a dense population of genetically unique brown bears. They look and act like grizzlies, but their mitochondrial DNA is closer to polar bears than other grizzlies, even those found just a few miles away on the mainland of southeast Alaska. For a time, biologists were puzzled by this genetic conundrum, even wondering if bears on ABC Island gave rise to polar bears. A team of researchers hypothesized in 2013 that the ABC Island bears are the result of mating male brown bears with female polar bears that are believed to have been marooned on the islands during the late Pleistocene when glaciers and ice marine quickly disappeared from southeastern Alaska. His theory is that polar bears inhabited the ABC islands until about 12,000 years ago, when the climate began to warm rapidly. Male brown bears traveled across the ice, or even swam, to the islands, then mated with female polar bears and subsequent generations of hybrids until all notable polar bear traits were eliminated.

Polar and grizzly bears intermixed in Alaska

Pizzly bear in Alaska.
The bear that Luke and Kiah Dihle encountered during their journey through the Brooks Range kiah dihle

In 2022, my brother Luke and his 18-year-old daughter Kiah were at the start of a two-week hike in the middle of the Brooks Range when they saw what they thought was a strange, light-colored rock. As she started to move, Kiah pulled the camera on her with a 600mm super telephoto lens and was shocked to see that she was a bear. Luke remembered that she had a whitish color similar to that of a mountain goat. We had been warned by the people of the village they had flown to at the beginning of their journey about how curious and aggressive Arctic brown bears can be, so they decided to give the bear enough space.

“Now, I wish we hadn’t been such a coward and gotten closer,” says Luke.

Biologist Richard Shideler, who ran the Alaska North Slope Grizzly Project for three decades until recently, when Kerry Nicholson took over, has seen five or six grizzlies that were as light as or even lighter than the bear seen by Luke and Kiah. He reminded a biologist that he was pretty sure he was looking at a hybrid. They radioed for him to be shot and tested. The results showed that it was 100 percent grizzly. Shideler’s studies revealed that male North Slope grizzly bears have a home range, if you can call it that, of more than 1,000 square miles. Most of the bears’ movement was east and west, but one collared male was followed to the sea ice, where he was hunting seals like a polar bear. Shideler also noted instances of polar bears roaming inland. Some people have thought that these outliers were hybrids, when, in fact, they were just bears exhibiting seemingly strange behavior.

Mixing of the two species in Alaska during the breeding season is very rare. Polar bears, which, except for pregnant females, do not hibernate, are known to breed on sea ice in March and April. Male grizzlies begin to emerge from their dens in April, but one is unlikely to come into contact with a female polar bear in heat unless she ventures far out on the sea ice. Unlike western Canada, there are no large offshore islands in Alaska. Numerous pregnant polar bears hibernate on the North Slope, so there is a small chance that another adult bear will kill a polar bear’s cubs and put her into heat. However, the odds are exceptionally low, considering the polar bear would try to get out onto the sea ice to hunt seals as soon as she could.

Polar bears spend time on land on the Alaskan mainland in Kaktovik, the only village in the Arctic Alaska National Wildlife Refuge, about 40 miles from where Peter saw the rare bear in 2019. They also spend time on land in Cross Island, a dozen miles north of Prudhoe Bay. Bears also come to feast on the remains of bowhead whales captured by Inupiaq hunters. Most of the time, polar bears show up in August and stay until October, when sea ice forms and gives them a platform to hunt seals. Grizzlies periodically use both locations. Observation data does not show that the two species intermingle, aside from grizzlies fleeing from much larger polar bears. Todd Atwood, a biologist with the US Geological Survey who studies these bears, notes that Alaska has “a genetic database of over 2,000 individuals that have been sampled over decades and we have never found a hybrid.”

Wapusk Park in southern Canada’s Hudson Bay is another hotspot for potential hybridization. In 2018, Doug Clark of the University of Saskatchewan was part of a research team that documented all three species of North American bears in the same area with trail cameras. A camera trap showed a polar bear and a black bear passing by within three hours of each other. Grizzly bears, attracted by fast-moving vegetation to feed, are arriving recently.

The End is Near… Or is it the Beginning?

grizzly bear in alaska
A male brown bear from ABC Island. Bjorn Dihle

I shared the photos of the bears that Luke and Kiah, and Peter, found with a handful of biologists. There’s no way of knowing for sure, but they haven’t completely ruled out that either bear is a hybrid. It’s hard to say anything for sure, with how rapidly the Arctic ecosystem is transforming and with sea ice shrinking.

“I’m not going to say never. Things are changing very fast,” says Shideler.

A recent study shows that the Arctic is warming four times faster than the global average. This is leading to a variety of consequences and changes. Some are “bad”, like winter rain in snow events that are terrible for ungulates like caribou and Dall sheep. Some are “good,” like the streams of salmon that colonize rivers and streams flowing from the North Slope into the Arctic Ocean. What all this means for the possible hybridization of polar bears and grizzlies remains to be seen.

Todd Atwood summed it up well: “We know that hybridization can and has occurred, albeit infrequently to date. Will its frequency increase as polar bears spend more time on land? Maybe. Time will tell.”