Polar Bear Facts | Churchill Wildlife Guide
THE POLAR BEAR: A MARINE MAMMALA good place to start is with the name used by biologists, Ursus maritimus. Translated from Latin, this name means “marine bear,” and is particularly descriptive. While other bears such as brown and black bears may spend time on the coast, only the polar bear spends most of its time out on the frozen sea. In fact, the U.S. government has officially listed the polar bear as a marine mammal, and it enjoys all of the same protections as a whale or dolphin.
That the polar bear is so closely associated with the marine environment is in many ways surprising. However, the Arctic Ocean is an especially biologically productive place, and the polar bear has uniquely evolved to take advantage of a food source that would otherwise be neglected: seals.
It’s worth taking a minute to understand how that works. The most important idea for understanding the ecosystem of the Arctic Ocean is that it completely freezes in wintertime, including Hudson Bay where Churchill lies. In fact, much of the high Arctic basin is frozen even in summertime, year after year. It would be easy to think that the ice is a barrier to the ocean and that nothing exists on its snowy, windblown surface. However, frozen sea ice is subject to movements by ocean currents, wind and tides. This means that the ice is constantly being pushed around, creating cracks and sizable expanses of open water, allowing access to the bounties of the sea. It is in these areas, from atop the sea ice, that polar bears excel at hunting seals.
The reasons the seals are there are twofold. First, since they are mammals, seals need to breathe air, and so the open water within the frozen ocean is necessary. Second, the seals are taking advantage of the richly productive sea ice habitat.
On the underside of the ice, various algae and phytoplankton bloom as sunlight filters through. This vegetation acts as the base of the food chain. Microscopic critters graze that vegetation, which are in turn eaten by small and young fish, which are consumed by larger fish that then serve as a meal for seals. Without the sea ice “nursery,” the Arctic would be significantly less productive and far fewer animals would be found.
The ringed seal is especially equipped to fit into this sea ice paradigm. From a polar bear’s point of view, this is great because more ice equals more ringed seals, which is the ice bear’s favorite prey. This is particularly true in areas like Hudson Bay, which melts and refreezes each year. That young ice is preferable to seals, and the higher concentration of prey means more polar bears per capita than you’d find in some of the more northerly locations where thicker sea ice persists from year to year.
The Polar Bear at a Glance
Global Population: 22,000–31,000
Length: 6–9 feet long
Weight: Males 800–1500 pounds; females 400–900 pounds
Largest recorded: 2,200 pounds
Oldest recorded wild bear: 32, a female in James Bay, Canada
Countries with Polar Bears: 5
PHYSICAL CHARACTERISTICS & FEEDING HABITSWhile the marine bear is perfectly capable of swimming in the ocean for miles or even days on end, they can’t outcompete and kill a seal when swimming. Instead, polar bears capture seals by still-hunting or stalking from the sea ice, taking advantage of unsuspecting seals surfacing to breathe or rest. The Norwegians recognized that the polar bear not only depends on the sea but also specifically requires the frozen sea as a platform for hunting. And so, their name for the polar bear is isbjorn, the “ice bear.”
Polar bears are perfectly outfitted for life on the ice. One of the first things you’ll notice is the sheer size of the beast. Size is a great advantage in the cold Arctic, allowing for efficient conservation of heat. Their furred feet also act as insulation against the cold ground while allowing for exceptional traction even on smooth ice. Claws are short and stout, best for grip rather than digging. Their feet are also disproportionally large, acting as snowshoes or as paddles when swimming. And, of course, they are white, perfectly camouflaged within their snowy domain. These white hairs are also important for insulation, with two layers that maximize warmth and protection from the wind. Beneath this coat is a layer of fat several inches thick, again insulating against heat loss. In fact, polar bears are so well insulated that an adult bear can rest comfortably in temperatures down to about minus 34°C! It is only when the temperature goes below that threshold that a healthy adult bear must move to stay warm.
Picture yourself now as a polar bear. You’re up in the snowy Arctic, warm and fit, and it’s time for a meal. But there’s a problem. The sea ice you are on is constantly moving due to ocean and wind currents, which means the location of open water—seal hunting habitat—is constantly changing. You look left, right, and behind you but all you see is a great white expanse. How will you find the seals?
The good news for polar bears is that they are equipped with what is perhaps the most advanced seal detection technology available—their noses. While their sight and hearing are comparable to that of a human, their noses are exceptionally powerful. In fact, ship-based spotters have tracked polar bears moving across dozens of miles in a straight line, directly to a seal hauled out on the ice.
Take a look at the shape of a polar bear’s head, and you will get a sense of the capacity of its olfactory sense. The huge nose essentially begins on its forehead and extends down to the nostril. This is in stark contrast to the dish-shaped face of a brown bear that you may already be familiar with. Given the challenges presented by locating seals on a frozen ocean, it makes sense that the nose of a polar bear would be overdeveloped. And the large nasal passage also has a secondary duty; as the bear breathes in and out, the passage retains moisture, preventing dehydration, while at the same time preheating cold, fresh air as it enters the body.
THE ARCTIC REALM OF THE GREAT WHITE BEAR: HOME RANGE & POPULATIONSo, the polar bear is a great traveler, smelling its way from seal to seal, place to place, and keeping up with the changeable frozen ocean in search of its next meal. Inuit in the Churchill region recognized this behavior, and so named the white bear nanuq, “the wanderer.” During its lifetime, an individual polar bear may travel an area equal to twice the size of California, and almost all of that is out on the sea ice. There is some evidence that bears in more northerly populations travel even more; some individuals have been found to patrol an astonishingly large area, equal to the size of Alaska. Adult females, on the other hand, will typically have cubs. Naturally, they will travel together and tend to range far less than their adult male counterparts.
You may wonder how a polar bear defends an area that is so large. Well, the answer is that it doesn’t. Given that the frozen ocean is always in flux, today’s open water and plentiful seals can easily be iced over tomorrow. It just doesn’t pay off for a polar bear to fight and risk harming itself for a hunting location that is ephemeral. So, an individual polar bear doesn’t have a territory—an area which it defends—but instead has a home range—an area within which it resides. The home ranges of individual bears overlap quite a bit, with each bear constantly on the move in search of food.
Nanuq does have its limits. Though their home ranges are generally quite large, they aren’t unbounded. In fact, bears within a certain region are very loyal to that area and typically won’t wander elsewhere. In this way they know where the most likely hunting spots might be at certain times of the year, they know where good denning habitat is, and they know where they can rest on land when the sea ice melts if they reside in an area where that happens.
Given the advantages of local knowledge, polar bears have instinctively divided themselves into 19 sub-populations scattered throughout the Arctic basin. Each of these populations contains bears that are mostly reluctant to travel out of their region, though there is genetic flow that occurs from mating interactions near the boundaries between sub-populations.
Biologists estimate there are between 22,000 and 31,000 polar bears wandering the Arctic. Mostly, these polar bears lead a solitary life. There are times, however, when they do come together. One is, of course, bear season in Churchill in anticipation of the returning ice. Another time would be during the springtime seal pupping season when food is plentiful and consolidated into more discrete locales. This event occurs annually throughout all bear populations, and so it has extra importance as the mating season for polar bears. Polar bears will also tolerate each other in closer quarters in areas with abundant, yet transient food sources such as a whale washed ashore, or a trash midden associated with a northern hunting community.
In the Churchill area, there are approximately 900 bears that comprise the Western Hudson Bay sub-population. These are the bears you’ll be meeting on your trip, and you’ll encounter them on land along the coast of the bay. They come to land only because the sea ice within Hudson Bay melts during the summer months. They will stay on land until the ice refreezes, eager to begin hunting seals again. Normally, this hiatus lasts from sometime in July until late November for a typical bear.
POLAR BEAR BEHAVIOR IN SUMMER & AUTUMNThe Churchill region contains several areas where bears reside during the summertime in the highest densities. In large part, the Wapusk National Park was created to protect these denning areas, and it is generally inaccessible to people. The word wapusk is the Cree name for the polar bear, which translates to “white bear.” What a sight it is to encounter these enormous white bears on land and away from their preferred icy habitat. It’s almost comical to see them lumbering in the heat and dealing with mosquitoes, sprawled out among the purple wildflowers. Their white coats make it clear that they are born of the ice and snow, and not the terrestrial environment like their bear cousins.
But polar bears still have some tricks up their proverbial sleeves. During these summer off-ice months, polar bears enter a physiological state similar to hibernation where their waste is recycled to prevent muscle loss while fasting. This allows them to live off their stored fat and conserve energy. They may also dig down into the frozen ground to stay cool, or even splash around in one of the countless shallow lakes along the coast. Some may even wander along the coast. On these long summer days, they also commit themselves seriously to the task of napping.
By the time polar bear season rolls around in October and November, the bears congregate along the coast, instinctively knowing that the ice—and the seals—will reappear soon. It is for this reason that Churchill is the “Polar Bear Capital of the World”—the particular shape of the coastline, combined with persistent northerly winds and ocean currents, means that the ice forms here first, year after year.
A common question that comes up at this point is: “Why don’t the polar bears just eat other stuff?” Certainly, the other seven bear species found around the world are perfectly capable of procuring terrestrial foods. As it turns out, polar bears aren’t generally able to take advantage of alternate food sources since they are so precisely tuned-up for a carnivorous life on the ice. Sure, some polar bears will eat goose eggs or the occasional whale that washes ashore. But those sources aren’t reliable and certainly cannot feed and sustain a population of hundreds of 1,000-pound polar bears. Polar bears just aren’t fast enough to catch land-based prey like caribou, and they would likely overheat if they tried. So instead, they sit and wait for the ice, patiently conserving their energy.
Let’s sum up what we’ve learned about the polar bear so far. As the marine bear, it relies on the frozen sea as its hunting grounds. As the ice bear, it has special adaptations that allow it to thrive out on the ice, even in the dead of winter. As the wandering bear, it requires a sizeable chunk of Arctic wilderness, yet stays within the boundaries of its sub-population. And as the white bear, we are reminded that it is seasonally forced from its icy realm yet has special traits that allow it to endure on land for periods of time. Collectively, these names paint a vivid picture of an individual bear’s life. However, there is one other name, originating from northern Europe, that speaks to the current challenges faced by the worldwide population of polar bears.
HOW CLIMATE CHANGE IS AFFECTING THE ARCTICThe Sami people know the polar bear as “the old man in the fur coat.” You’ll recall that throughout the North polar bears are viewed as being remarkably similar to people. In the context of this mythology, it is easy to envision a polar bear returning from a day of hunting out on the ice, taking off its fur coat and coming into its warm abode for the evening. In the natural world, however, this quick adaptation to a warmer environment isn’t possible. Here we have a simple metaphor for the biggest challenge faced by polar bears: a changing climate.
You now appreciate that polar bears depend on sea ice. The frozen sea is where they hunt, where they rest, and where they raise their young. The funny thing about that Arctic ice, though, is that much of it melts each summer, only to refreeze again in the autumn. Polar bears have evolved to work with this natural phenomenon, fasting on land for up to several months at a time. There, they cope with the relative heat and live off their fat stores. But this is becoming more challenging for the polar bear.
In today’s Arctic both summer and winter temperatures are rising, and this has a huge effect on the sea ice in two important ways. First, the total area of sea ice is diminishing over time. Modern satellite technology has given us the ability to study Arctic ice since 1981, and a continuous daily record has been established through the present. What this immense collection of visual data has revealed is that the extent of summer Arctic sea ice has declined by about 13% per decade during that time. Think about what shrinking habitat may mean for polar bears. If their habitat is diminishing, the threat is that bear populations will be obliged to follow suit.
Secondly, the timing of the ice is changing too. Compared to just a few decades ago, the sea ice in many areas of the Arctic is melting off weeks earlier in the summer and freezing weeks later in the autumn. So not only do polar bears have less time on the ice for hunting, but they also have more time on land where they are forced to fast. This all comes at an enormous energetic cost for the bears. One study showed that for every week earlier the ice breaks up, bears come ashore roughly 22 pounds lighter. Naturally, the longer they are required to stay ashore and fast, the less fit they become.
As one example of what this means to polar bears, we can look at reproduction. Past research has demonstrated that female polar bears will produce cubs based on their own fitness. That is, fat and healthy sows will typically birth and rear more cubs than those within their sub-population that are less fit. The early summer hunting time is especially important for these bears, with plenty of young naïve seals to prey upon. Consequently, a problem with decreased time hunting on the sea ice is that recruitment rates fall because females haven’t had as much time to fatten up. And if fewer cubs are being born, the population is in danger of decline.
To keep proper context within our example, know that the presence and timing of sea ice are not the only factors that affect polar bear reproduction rates. Genetics and experience, for instance, play an important role, and even in “bad” ice years there are plenty of sows successfully rearing multiple cubs. This complexity necessitates ongoing research to elucidate the longer-term population trends that are vital for policy making and polar bear management.
Currently, the worldwide population of polar bears is estimated to be 22,000—31,000 individuals. If sea ice loss trends continue, combined with lowered recruitment rates, global polar bear populations are projected by the World Wildlife Fund to decline by 30% by 2050. For this reason, polar bears are listed as “vulnerable” by the International Union for the Conservation of Nature (IUCN). It’s no surprise that a highly specialized predator at the top of the food chain would be especially vulnerable to changes in the quality of its habitat. Because of this, the charismatic polar bear has become the poster child for raising awareness of how climate change is affecting the Arctic.
A few sentences will never give merit to the intricacies needed to understand the complex concepts and processes involving climate change. Meteorology, oceanography, biology, glaciology, and numerous other disciplines all converge on the topic, ensuring that most of us will never fully appreciate it. However, the impacts of a changing climate are readily apparent to those who visit or live in the Arctic. Just a few years ago, for example, and for the first time in history, commercial shipping vessels were able to navigate the Northwest Passage in the absence of summer ice. And today you can join a cruise ship tour to see it for yourself. On that same line, governments are now sanctioning and funding oil and gas explorations into areas that were historically inaccessible due to the presence of multi-year sea ice.
In communities like Churchill, on the edge of the Arctic, building foundations are collapsing due to the thawing of historically frozen soils. Likewise, new forests are developing as soils thaw and trees move northward, now able to extend their woody roots deeper into the rich soils. And as the landscape changes, so does the wildlife. With thawing soils and boreal forest marching northward, terrestrial Arctic animals such as the Arctic fox are beginning to lose habitat too.
These are just a few examples of the changes that have impacted the Arctic and our polar bears. Ultimately, these changes are symptomatic of larger issues surrounding climate change that affect us all in myriad ways. If you are curious to learn more, you are encouraged to visit the website of our partner, World Wildlife Fund and be sure to read the “About World Wildlife Fund” section of this briefing.
Photo Credit: Henry Holdsworth