Two Canadian biologists have reported sighting a handful of grizzly bears and hybrid grizzly/polar bears at unusually high latitudes in the Arctic, indicating that the interbreeding of the two bear species is becoming more common as the climate warms and grizzlies venture farther north. The sightings of three grizzly bears and two hybrid bears, made in late April and May, represent an unprecedented cluster of these animals at such high latitudes. The biologists even took DNA samples from a grizzly bear at 74 degrees North latitude.
The report of the sightings comes on the heels of a recently published analysis of newly sequenced polar bear genomes, suggesting that climate change and genetic exchange with brown bears helped create the polar bear as we know it today. The genetic mixing that the Pennsylvania State and University of Buffalo analysis identified happening in the past — in which polar bears would interbreed with grizzly bears as the polar bears’ sea ice habitat shrunk — is now happening again, according to bear biologists.
A hybrid polar/grizzly bear in the Canadian Arctic. Photo courtesy of Jodie Pongracz
The sightings this spring represent the fourth and fifth confirmed hybrid bear sightings in recent years. Scientists say that it is evident from reports from Inuit hunters that many other animals are adapting their lifestyles to changes in climate, just as grizzlies did when they split from polar bears four to five million years ago.
When University of Alberta biologists Jodie Pongracz and Evan Richardson flew up to Viscount Melville Sound in the High Arctic of Canada this spring to capture and satellite-collar polar bears, they were astonished to see a grizzly bear travellng with what they initially thought was a polar bear hundreds of miles north of where brown bears are normally found. That sighting occurred on April 23 in Wynniatt Bay at 73 degrees North latitude. Upon closer examination, the polar bear turned out to be a hybrid cross between a polar bear and grizzly.
Two days later, the scientists saw another grizzly bear 15 miles offshore on sea ice in Viscount Melville Sound, closer to 74 degrees North. This bear was so fat and healthy that it was almost certainly hunting seals, something that grizzlies on the mainland don’t normally do, except along one small spot on the central Arctic coast in an area known as the Smoking Hills. Also on April 25, the scientists saw what they thought was another grizzly until photographic analysis suggested that it was a hybrid bear. On May 31, the scientists sighted and took DNA samples from a grizzly bear off the northwest coast of Banks Island, at about 74 degrees North.
Polar bear experts said it is possible that the grizzly bears are leaving from the Arctic mainland and traveling roughly 400 miles north, crossing the sea ice as they pursue a caribou herd that annually migrates over the sea ice to Victoria Island. Unable to get back because of rapidly melting ice, some of these grizzly bears have evidently managed to adapt to life in the polar bear’s world, eating seals, hibernating, and mating with polar bears.
Up until about 20 years ago, sightings of grizzlies in the High Arctic were relatively rare. But that began to change as a succession of brown bears started showing up on the Arctic islands, following caribou perhaps that routinely cross over from the mainland. No one had seriously thought that these grizzlies would eventually mate with polar bears until Roger Kuptana, an Inuit guide from Sachs Harbour on Banks Island, led an American hunter to one in the spring of 2006. The killing of that animal made headlines around the world.
Will this result in a new and improved Arctic bear in the future?
But will this result in a new and improved Arctic bear in the future, as might be inferred by the recent Penn State/University of Buffalo study? University of Alberta scientist Andrew Derocher doubts it for a variety of reasons. He is a veteran polar bear scientist and an academic advisor to both Pongracz and Richardson, who work in his lab.
“As I see it, the latest hybridizations are just more in a long history of such events,” he says. “The key is that the genetic mass of both grizzlies and polar bears are far away from the hybridization area, as we know it just now. This means that the few genes moving from grizzlies to polar bears aren’t that significant. The bulk of the polar bear population doesn’t interact with grizzlies, so it will take a long time for the few genes that move between the species to have any effect.”
The other thing to consider, says Derocher, is that polar bears and grizzly bears are two very different animals from an ecological point of view. While they may closely resemble each other physically and genetically, they have evolved in very different ways. Grizzlies, for example, have learned to live off a variety of foods such as caribou, berries, roots, and even seals. The polar bear, on the other hand, is almost exclusively a hunter of seals.
“In general, hybrids don’t tend to do as well as the source species because they’re not well adapted to the conditions of either parent species,” he says “Could this change? Sure. Why not? However, predicting evolution is a fool’s game and how this plays out is anyone’s guess.”
As the polar bears’ sea ice habitat continues to shrink as the world warms, the bears may be forced increasingly onto land, where interbreeding with northward-migrating grizzlies could occur. Should rapid warming continue, the only polar bears left in the Arctic by the mid- to late-21st century could be somewhere in the Ellesmere Island/northern Greenland region, which is about as far from grizzly bear country as one can get in the Arctic.
Derocher noted that there are currently no regulations in place restricting the hunting of a hybrid polar/grizzly bear, which most bear hunters would pay dearly for the chance to shoot. That could mean that hybrids — not subject to the strict hunting quotas governing the threatened polar bear — could face heavy hunting pressure.
Derocher said the bear sightings made by his two protégés this spring were an important contribution to understanding the increasingly frequent interactions between polar and grizzly bears.
“We know that grizzlies are in the area, and that local Inuit had seen hybrids, and recently shot two,” he said. “So perhaps it isn’t that surprising. Nonetheless, given the size of the area involved, and the small number of hybrids that exist, I’d say they were extremely fortunate to make such sightings. I’d do back-flips to see what they saw.”
