Wildlife
Honouring one of Canada’s most beloved bears with stories about how polar bears hunt, how they are adapting to life on land, how they may have evolved and more!
As the world’s largest bear and the Arctic’s top predator, polar bears are an iconic symbol of strength and perseverance, loved by many across the planet. However, with global warming, toxic pollution and human development, polar bear populations are declining, and we must work together to ensure their survival.
During the first full week of November, Polar Bear Week is celebrated through live events, challenges, the sharing of educational resources and more. Every year the week coincides with the fall migration of polar bears to Churchill, Manitoba. During the winter, the bears gather here to await Hudson Bay freezing up so they can return to seal hunting. Unfortunately, this is becoming more and more challenging for the bears as the freeze over becomes more unpredictable with climate change. The main goal of Polar Bear Week is to focus on the importance of sea ice to polar bears and the need to reduce our environmental impact to protect them.
This year, Polar Bear Week runs from Oct. 30 to Nov 5. To celebrate this event, we have collected some of our previous Canadian Geographic articles into a quick read, kicking off the week by teaching you all about these magnificent bears.
One question, two contrasting answers. Two studies examining the remains of polar bears that lived hundreds of thousands of years ago have found evidence of mating and substantial genetic mixing between ancient polar bear and brown bear populations. Interestingly, they disagree on the direction in which the gene flow occurred.
The first study, published in Nature Ecology & Evolution and co-authored by Canadian polar bear expert Ian Stirling, looked at DNA taken from the tooth of a polar bear that lived over 100,000 years ago on the Beaufort Sea near Point McLeod in Arctic Alaska. Their analysis showed massive amounts of prehistoric mixing between the two species took place during this time, around 400,000 years after the two species diverged, when climate change caused their ranges to overlap. Evidence of this today, according to their research, can be found in all brown bear genomes, but not in those of living polar bears. They also found the direction of gene flow to have been one way — from polar bear to grizzly.
The second study, published in Proceedings of the National Academy of Sciences, also examined DNA taken from an ancient polar bear tooth — this one taken from the skull of an approximately 100,000-year-old polar bear found in Norway’s Svalbard archipelago. The researchers, however, concluded that gene flow between the two species was far more complex and intertwined than the Nature study suggests, similar to that seen in human evolutionary history. And, strikingly, that gene flow ran primarily from brown bears to polar bears.
It’s well known that these two sister species of bear have historically mated. As climate change once more causes their ranges to overlap, their future may become as intertwined as their past. Although the new findings are somewhat contradictory, scientists will now be in a better position to understand the history between the polar bear and the brown bear as well as anticipate what might happen in the future.
Loss of sea-ice habitat due to climate warming has been highlighted as the single most important threat to the long-term survival of polar bears, and could see the animal’s population decline by more than 30 per cent over the next 35 to 40 years, says the International Union for Conservation of Nature.
The prediction headlined the IUCN’s release of its updated Red List of Threatened Species, which includes 79,837 assessed species, 23,250 of which are threatened with extinction.
“Based on the latest, most robust science, this assessment provides evidence that climate change will continue to seriously threaten polar bear survival in the future,” said Inger Andersen, IUCN director general. “Climate change impacts go far beyond this iconic species, and present a threat our planet has never faced before.”
The IUCN update said that recent studies show that the loss of Arctic sea ice has progressed faster than most climate models had predicted, with September sea ice extent declining at a linear rate of 14 per cent per decade from 1979 through 2011.
“As polar bears rely on sea ice to access their prey, an annual ice-free period of five months or more will cause extended fasting for the species, which is likely to lead to increased reproductive failure and starvation in some areas,” the IUCN update said. “According to recent sea ice projections, large regions of the Canadian Arctic Archipelago will be ice free for more than five months by the late 21st century; and in other parts of the Arctic, the five-month ice-free threshold may be reached by the middle of the 21st centur
As the changing climate melts the Arctic ice, the animals that are part of these ecosystems will have to shift their lifestyles to survive in the terrestrial habitats they find themselves in.
A recent review article published in a climate change special issue of the Journal of Experimental Biology discussed how Arctic animals would be impacted, especially as they are forced onto land.
For the iconic polar bear, which relies on sea ice to provide access to high-calorie seals, they will have to change their diets in order to provide them with the energy they need to hunt, reproduce and survive in a challenging thermal environment. Polar bears, the most recently evolved marine mammals, have specialized — both behaviourally and physiologically — to hunt seals, which are rich in blubber.
Already, polar bears have already been observed to spend more time on land — and to consume more terrestrial food resources. But the food they are able to eat on land is less rich in digestible energy than the seals they are able to hunt on the ice. This infographic illustrates the alternative terrestrial food sources that would approximately make up for the energy from one ringed seal.
It’s an idea that seems as plain as the nose on a polar bear’s face. But researchers at the University of Alberta have proven that the animal uses its sense of smell to track prey, marking the first time that crosswinds have been shown to play a role in how a mammal hunts.
Researchers Ron Togunov and Andrew Derocher recently published the results of an 11-year study that merged polar bear movements with wind patterns on Hudson Bay.
Ringed seals, the bears’ preferred meal, give birth out of sight, hidden under layers of snow. Researchers knew that polar bears used their sense of smell to find the hidden seals, but Togunov says, “how they use that sense of smell had only been theoretical.”
Togunov and Derocher used satellite telemetry for their study, which allowed them to track both the movements of the wind and 123 polar bears simultaneously.
“Predators search for prey using odours in the air, and their success depends on how they move relative to the wind,” explains Togunov. “Traveling crosswind gives the bears a steady supply of new air streams and maximizes the area they can sense through smell.”
Now Togunov is looking at how wind speed affects the way polar bears hunt. As the Earth warms, the speed of Arctic winds is projected to rise and researchers predict this could make it harder for polar bears to find food. “Fast winds are associated with a decrease in foraging,” he says. “They make it more difficult for the bears to find the source of the smell they detect, but I don’t know at which wind speed it’s actually unfavourable.”
“We can’t conclusively say what effect it’s going to have on the bears,” he added, because “we don’t know how big of a role wind is playing. But we can say it’s definitely not going to be good.”
A new, genetically distinct population of polar bears has been discovered in Southeast Greenland. They are isolated, thriving and — unlike any other polar bear population — inhabit an area totally devoid of sea ice.
The newly discovered Southeast Greenland polar bears exist in a world that closely resembles the High Arctic of tomorrow — or the late 21st century, to be exact. With no sea ice in sight, they hunt year-round on the freshwater ice at the foot of marine terminating glaciers, also called glacial mélange. The discovery, published in the journal Science, provides a ray of hope for the future of an iconic species that mostly relies on rapidly disappearing sea ice to hunt.
Hunting from freshwater ice at marine terminals is a previously unreported behaviour, and an important one too, as doing this allows polar bears to feast on seals, their prey of choice, year-round. Whereas other bear populations must traverse over land or follow receding sea ice into less productive polar areas during the ice-free season, this adaptation allows the Southeast Greenland bears to succeed in an otherwise inhospitable place.
While these habitats are uncommon in most of the Arctic, they exist in places like Greenland and Svalbard. Could such glacial mélange habitats one day serve as climate refuges for the polar bear populations of the future?
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