What Do Polar Bears Do in Autumn?

For polar bears across the Arctic, the arrival of autumn historically presages a coming bounty, as waters begin to freeze, sea ice begins to form, ice seals establish winter ranges, and bears prepare themselves for a winter hunting on the ice. That said, the autumn months and early winter remain a time of mystery as increasing darkness and newly forming ice combine with early storms to limit research activity — at least for now.

In some parts of the Arctic, such as the islands of the Canadian Archipelago, ice persists through the summer. But elsewhere, autumn’s return prompts an uptick in activity as the bears anticipate the largely ice-free summer months with little to eat on land finally giving way to an icy smorgasbord. 

With 20 populations of polar bears across the Arctic, there are 20 different stories as the bears adjust to different ice and prey conditions. Following are some representative populations.

Svalbard archipelago, Norway

In the Barents Sea, the bulk of the population spends as much of the year as possible on drifting sea ice, while a smaller number of bears — roughly 250 — remain on the coastal ice or on land around Svalbard. During autumn, says Jon Aars, senior scientist with the Norwegian Polar Institute, "The coastal bears have no choice, they have to stay on land, as there is no sea ice in most places on Svalbard from September until late in the autumn.” Even when the ice does begin to form, these coastal bears remain close to shore at all times.

In the Svalbard region, sea ice is constantly being pushed away from shore by currents, and so, when summer arrives and new ice is no longer being formed, some of the so-called pelagic bears may find themselves trapped on or near land as the sea ice drifts away; come autumn, they will be waiting anxiously for the ice to re-form so they can once more set out far from shore. Others, however, never leave the ice at all if they can avoid it.

“You can have pelagic bears in Svalbard or the Barents Sea that are on the ice 12 months a year,” explains Aars.

Southern Beaufort Sea, U.S. and Canada

In the Southern Beaufort Sea, sea ice that traditionally stayed close to the northern coast of Alaska and Canada in summer now retreats hundreds of miles from shore. Bears in this region are forced to make a choice between following the ice over deep, less productive waters — where the hunting is less optimal — or remaining on land, where they are largely food-deprived. Among the land bears is a subset whose behavior is driven by a powerful food reward. They have discovered the Inupiat subsistence whale harvest in the community of Kaktovik, says Geoff York, senior director of conservation for Polar Bears International, with “regular and predictable access to bowhead whale remains.”

Autumn finds most of the bears in this population far out on the sea ice, where they seek to spend their entire year when possible. But as late autumn extends the ice closer to shore, over more productive seal-hunting grounds, they follow it. Meanwhile, the bears that chose to remain on land wait for the ice to return.

Chukchi Sea, Russia and U.S.

In the Chukchi Sea, a population shared by the U.S. and Russia, some bears are happy to spend at least part of their summers on Russia’s Wrangel Island, where walruses may gather in congregations 10,000 strong, giving those bears steady access to carcasses from natural mortalities. Additionally, says York, currents in the area are such that “Wrangel is a place where things tend to strand, be it wrecked boats that have blown off their moorings in Alaska or large marine mammal carcasses.” Pregnant females in the Chukchi Sea also uniquely choose Wrangel Island for denning and will remain through the winter.

Even so, here too, the return of autumn leaves most bears ready and anxious to return to the sea ice where hunting is ultimately more productive and reliable. Alaska bears in this population await the freezing of coastal waters so they can rejoin the ice as it forms over productive continental shelf waters; on Wrangel Island, the return of autumn historically sees the formation of an ice bridge from shore to the ice edge which grants bears relatively easy access to the riches of the frozen Arctic waters.

Hudson Bay, Canada

Nowhere in the polar bear’s range is autumn greeted with as much enthusiasm as in Canada’s Hudson Bay. There, sea ice melts completely in summer, forcing all the bears ashore during the warmer months. As soon as the temperatures begin to drop, the bears are on the move, keen to find food after weeks of fasting.

But even as the bears gather on the tundra along the shore of the bay, and even as the bay begins to freeze in November, they must still wait for the temperature to drop low enough and the ice to grow thick enough for them to head out and hunt. While a handful will get lucky in nearshore seal hunting, most need a good shelf of shorefast ice to gain sustained access to better hunting opportunities.

“I imagine this time of year as if polar bears were starting to line up at a restaurant, waiting for the doors to open,” explains Alysa McCall, director of conservation outreach and staff scientist for PBI. “The ice starting to freeze is the equivalent of the restaurant’s doors opening. But the restaurant isn’t really prepared for the rush, and so the food doesn't all come out right away. So basically, freeze-up is great. The bears are stoked to get out on the ice, and they're going to find some food. But it can be slim pickings at first. Autumn really isn't the best hunting time. So, it's not like they're immediately bouncing back to their original weight or getting all the food they need.”

As a result, early in the autumn on Hudson Bay, bears can often be seen tentatively testing the first of the ice to see if it is thick enough to support their weight. And even when the ice forms near to shore, it can still take several weeks before it is thick and extensive enough to allow the bears to head out and focus on food.

“They really have to navigate carefully as the ice is freezing up,” explains McCall. "Plus, even as the ice is freezing, as long as there is still open water in the bay conditions can be quite stormy. So, it’s an exciting time for them, but it's still difficult.”

Autumn sparring

For subadult and adult males in Hudson Bay and other regions with seasonal ice, autumn is time for sparring. As they await the ice, these male bears will tussle with each other on the tundra, behavior that exercises the muscles they need for hunting and also may help to establish both social bonding and hierarchy, as the bears determine which among them are the strongest. 

 “While sparring behavior has been documented across polar bear range, it is most easily seen in coastal Manitoba due to the predictable concentration of polar bears on land and the ease of access for people. Because the ice melts completely across Hudson Bay and then re-forms in the autumn, we see these large on shore gatherings of bears here,” explains McCall. She adds, because so many researchers and tourists visit this area “there are just more eyes on the bears here, so there are more people to see bears sparring". There is anecdotal evidence that females may also engage in sparring occasionally, although that hasn’t been clearly documented yet.

Autumn maternity dens

For one group of bears, however, autumn does not present an opportunity to head back out immediately onto the ice. Autumn is when pregnant bears separate themselves from the others and fashion maternity dens in the snow to give birth.

Across much of polar bear range, pregnant females come ashore to preferred denning areas where deep snow drifts are likely to form- steep coastal bluffs, river and lake banks, and in areas with more topography, steep slopes of hills or mountains. In some areas females can move inland quite a ways to access quiet areas with good snow depth to hollow out their snowy birthing lair. In Western Hudson Bay, bears curl up in peat dens that may be 200 years old and wait for snow cover to seal them in and shelter them.

Climate changes are affecting where polar bears den

Other regions are seeing more recent adaptive changes driven by both sea ice dynamics and snowfall. In the Southern Beaufort Sea north of Alaska, about half of all pregnant females used to den on the stable pack ice, but by the mid 2000’s, they had all shifted to land based denning as that sea ice became less predictable and more active throughout the winter. In the Barents Sea, the southern islands of Svalbard that were historically primary denning areas are no longer accessible due to a lack of sea ice. As a result, says Jpn Aars of NPI, it seems that more and more pregnant bears in that population travel on the sea ice to den either on the main Island of Spitsbergen, the northern Island of Nordaustlandet, or travel all the way to the archipelago of Frans Josef Land in Russia, “because they often don’t have sea ice around the traditional denning areas anymore.”

As other bears head out onto the ice and begin to gorge on seals, those females rest in the warm, dark dens, where they give birth in the winter and emerge with their cubs in the spring. They eat as much as they can in the spring — the best hunting time — so they can survive the summer shortfall and wait for sea ice to form anew the following autumn, as the cycle begins again.

Kieran Mulvaney is a freelance writer who has written extensively about polar bears and the Arctic for publications including National Geographic, The Guardian, and The Washington Post. A native of Bristol, England, he lives in Bristol, Vermont.