A polar bear sits among the tundra grasses in summer in Churchill

Photo: BJ Kirschhoffer / Polar Bears International

How Do Polar Bears Spend Their Summers?

By Kieran Mulvaney, Guest Contributor



04 Jun 2024

Most North American bears are active in the summer and hibernate* in winter. Polar bears, however, are different. As creatures of the sea ice, they naturally are at peak activity when that ice is most plentiful and they can hunt their seal prey, which rules out a winter rest.

So, does that mean polar bears flip the script? If they’re out and about in winter when brown and black bears are in a deep rest, do they hibernate in summer?

In a word, no. Some polar bears do indeed spend their summers resting quietly in cool, dark dens (although they don’t enter a state of hibernation). Others turn their attention to nearshore or even onshore prey. Still others never have to leave the ice and can stay on the frozen surface of the ocean hunting seals all year.

Geographic differences

How a polar bear spends its summer depends largely on where it lives. Surprising as it may seem, not all regions of sea ice are the same.

Following work by Polar Bears International’s Chief Scientist Emeritus Steve Amstrup, scientists divide the Arctic into four sea ice “ecoregions,” differentiated from each other by the way in which sea ice stays with or drifts away from the shore, and by whether ice persists from one year to the next or melts each summer. The bears in each ecoregion adopt different strategies for summer – but even within each region there can be significant variance, too.

Map of four polar bear ecoregions defined by grouping recognized populations which share seasonal patterns of ice motion (dark blue lines) and distribution

Photo: Excerpted from Amstrup et al. 2008

Regions with year-round ice

Two of the ecoregions – the Convergent Ice Ecoregion and the Archipelago Ecoregion – are located primarily in the North American High Arctic: the former stretches east from the northern Beaufort Sea across the top of Canada and down along the eastern coast of Greenland, while the latter encompasses the islands and channels of the Canadian Arctic Archipelago. These two regions are similar in that they generally boast sea ice year-round, meaning that polar bears by and large don’t have to make many changes to their behavior from season to season.

However, there are differences even here: in 2022, scientists documented a new possible sub-population of polar bears in southeast Greenland, physically isolated and genetically distinct from its neighbors. Despite being in the Convergent Ice Ecoregion these bears have access to sea ice only from February to late May each year, and spend the rest of each year, including summers, hunting seals from freshwater ice deposited into fjords from constantly calving glaciers. 

Region with retreating ice

A third region, the Divergent Ice Ecoregion, encompasses the largest share of the Arctic, stretching from Svalbard and the Barents Sea across the top of Arctic Russia, to the Chukchi and Southern Beaufort seas and coastal Alaska. Here, ocean currents pull sea ice away from the shore as it forms, and while during the cooler months new ice forms to replace it, in summer that isn’t the case. The 1,000 or so bears in Svalbard, therefore, adopt one of two strategies: the majority travel with the ice, roaming vast distances in search of seals and other prey. Approximately 250, however, stay behind, focusing their efforts on ringed seals on “landfast” ice – ice that is fastened to the shore – or glacial ice in fjords.

Elsewhere in the Divergent Ice Ecoregion, the bears of Wrangel Island in the Russian Arctic tend to move back and forth from shore to ice much of the year. And, notes Geoff York, Polar Bears International’s senior director of research and policy, the bears on Wrangel that do stay ashore show varied approaches to the summer. "You have some that adopt a strategy of slowing things down and conserving energy, but then you also have bears that are routinely going back and forth between resting areas and feeding areas because they have access to walrus haulouts or because they are feeding on whales that have stranded on shore,” he explains.

Region with seasonal ice

The fourth region is the Seasonal Ice Ecoregion, where the sea ice completely melts during summer and all the polar bears must come ashore. This region encompasses much of the central and eastern Canadian Arctic, including Hudson Bay, Foxe Basin, Davis Strait, and Baffin Bay. Here, too, the response of bears to the arrival of summer varies.

In Western Hudson Bay, home of the famous Churchill bears, polar bears in summer come closest to replicating the winter strategies of their more southerly brown and black bear brethren. Although it is still possible to see polar bears in the region in the summer months, by and large bears hole up in earthen dens and wait out the warmer months until the temperature begins to drop again, then they rouse themselves to gather along the coast of Hudson Bay and wait for the formation of new sea ice. During the ice-free period, they lose roughly 1 kilogram of fat a day. (You can see the locations of some of these bears on our Polar Bear Tracker.)

In Foxe Basin, however, says York, the situation is “completely different.” There, he explains, “there are much higher levels of prey abundance and prey type,” so the bears there tend to remain active in summer, “crossing islands in search of a walrus haulout or a stranded whale that they can smell.”

Changes afoot

However, all the above comes with a caveat: what has historically been true may not be the case in the future. In Svalbard and the Southern Beaufort Sea, for example, summer ice is retreating ever farther away from the shore, so that it is now over deeper, less productive waters where hunting is less likely to be fruitful. In Western Hudson Bay, on average ice breaks up earlier in summer and forms later in fall, forcing bears to spend longer ashore without food, resulting in a declining population of bears that are literally physically smaller than they used to be.

So, the answer to “what do polar bears do in summer?” isn’t a straightforward one. And as the world warms, and the Arctic heats up faster than anywhere else on Earth, it is unlikely to become any less complicated.

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.

* Well, sort of. The body temperatures and metabolisms of true hibernators – smaller mammals such as Arctic ground squirrels – drop so low that it is almost impossible to rouse them. Black and brown bears do, however, have periods of wakefulness during winter, and although their heartbeats slow significantly, their temperatures do not. For that reason, technically, “hibernating” bears are considered to actually be in a state known as “carnivore lethargy.”