February 27 is International Polar Bear Day! Nat Hab is celebrating the Queen of the North by taking a deep dive into her Arctic realm and unearthing the truth behind her mysterious habits. You won’t want to sleep on what we’ve discovered!
Habitat and History
Polar bears (Ursus maritimus) have a circumpolar distribution limited to four distinct sea ice habitats—or ecoregions—of the northern hemisphere. Sea ice is vast and transient, thus polar bears have aggregated into what scientists within the IUCN Polar Bear Specialist Group (PBSG) have identified as 19 subpopulations across the Arctic.
In central and eastern Canada, much of the polar bear habitat lies within the Seasonal Ice Ecoregion, where the sea ice melts entirely in the summer. The Divergent Ice Ecoregion extends around the Arctic from coastal Alaska to Svalbard and is characterized by ice that diverges from the shoreline as it forms and is pushed by ocean currents. In the Convergent Ice Ecoregion, locally formed sea ice, along with ice transported from the Divergent Ice Ecoregion, collects along the shore or moves parallel to shorelines.
The Archipelago Ecoregion, in addition to the northernmost portions of the Convergent Ice Ecoregion, is likely to provide a final refuge for polar bears as the ocean channels separating the islands of the far north Canadian Arctic have historically been covered by sea ice year-round.
While the polar bear’s Latin name means ‘sea bear’, this mammal’s venerable place in northern culture is reflected in the many titles it’s been given. In Eastern Greenland, Tornassuk means ‘the master of helping spirits’. In Norway & Denmark, Isbjorn means ‘the ice bear’, and in medieval Scandinavia, Norse poets wrote of the White Sea Deer; The Seal’s Dread; The Rider of Icebergs; The Whale’s Bane; and The Sailor of the Floe.
The Sami (or Lapp) Indigenous peoples from northern Europe say God’s Dog and The Old Man in the Fur Cloak in fear of offending the majestic creature. The Ket (Siberian tribe) uses the term Gyp, or ‘grandfather’, which is considered a sign of respect and awe.
Nanuk is used by the Inuit to signify ‘Animal Worthy of Great Respect’. Pihoqahiakis—also used by the Inuit—means ‘The Ever-Wandering One’.
Photographed by © Megan Brief on Nat Hab’s Tundra Lodge and Town Adventure
The polar bear’s earliest denomination originates with Ursus arctos, more commonly known as the brown bear. Brown bears and polar bears diverged between 150-500,000 years ago. Despite this relatively recent split, the polar bear has rapidly evolved unique morphological, physiological and behavioral traits to adapt to the Arctic’s climate and ecology.
In 2006, genetic testing confirmed the existence of polar bear-grizzly bear hybrids, known as ‘grolar bears’ or ‘pizzly bears’. Wild hybrids retain physical features from both species but often adopt polar bear behavior as a result of being birthed and raised by polar bear mothers.
This genetic history underpins the polar bear’s unique adaptations, such as the lack of fur pigmentation, which aids in camouflage. The most fascinating characteristic, however, is the polar bear’s sleep patterns—especially in juxtaposition to the other seven species of Ursus.
Hibernating vs. Denning
Throughout most of the world, bears hibernate during the winter months or perform annual denning behaviors in response to seasonal food shortages and cold weather. Hibernating helps the process of thermoregulation in the American black bear (Ursus americanus) and North American brown—or its subspecies grizzly bear (U. arctos horribilis)—in particular.
The duration of denning is contingent on latitude and pregnancy status, in addition to more unpredictable environmental factors like climate change. For instance, denning varies from a few days or weeks in Mexico to six months or more in Alaska. Pregnant females generally den earlier and longer than other bears, and in the Greater Yellowstone Ecosystem, grizzly bear females without cubs den on average for about five months.
The body temperature of a hibernating bear remains within 12°F of its natural range, allowing it to quickly react to impending threats. Bears sometimes awaken and leave their dens during the winter, but they generally do not eat, drink, defecate or urinate during hibernation.
Respiration—normally 6-10 breaths per minute—decreases to one breath every 45 seconds, and their heart rate drops from 40-50 beats per minute to 8-19 beats per minute. Their well-insulated pelts and lower surface area-to-mass ratio enable bears to reduce their metabolic rate by 50–60%. The urea produced from fat metabolism is broken down, and the resulting nitrogen builds protein that maintains muscle mass and tissue reserves.
Unlike brown and black bears, polar bears do not hibernate…not in the traditional sense, anyway. Polar bears contend with extreme environmental conditions and face laborious tasks that result in high energetic demands.
In the winter, males and non-pregnant females must maintain a constant body temperature to combat external temperatures that regularly fall as low as −50 °F. These regulation challenges are exacerbated by the Arctic’s biting winds, which can contribute to losses of greater than 75% of the metabolic heat the bears produce.
The winter months also prove to be challenging for polar bear scientists, as unpredictable conditions thwart research and tracking activities. Fortunately, there is enough data from radio-collared bears to unveil behavior known as “shelter denning.”
While most polar bears struggle to eke out a living in the winter, pregnant females enter a state of “light hibernation” in the safety of their icy lairs. The expectant mother will dig a maternity den—usually into a snowbank—in October or November and give birth to one to three cubs in December or January.
Inside the den, temperatures are approximately 40 degrees warmer. In addition to 2 layers of fur, a polar bear’s body fat can measure up to 4.49 inches. The mother relies on her fat storage to go without food, water, defecation and urination for as long as eight months.
During this time, her body recycles wastes biochemically (without kidneys) to prevent dehydration. However, she loses as much as 30% of her body mass, which translates to 43% of her body weight.
Pregnant or lactating females and their dependent offspring are most vulnerable to climate change. The melting of sea ice increases the length of summer-fall fasting—a period when polar bears lose access to their primary source of food—seals.
Usually, a female gives birth to a litter every two to four years, but due to decreasing ice floe quantity and quality, some mothers may only give birth to one or two litters during their lifetime.
Though the loss of habitat is the biggest threat to the survival of polar bears, other concerns include lethal response to human-polar bear conflict, toxic pollution in the environment and direct impacts from industrial development, such as disturbance of maternal dens or contact with an oil spill.
See the ‘The Ever-Wandering-One’ with Nat Hab & WWF
Arctic and subarctic Canada are home to two-thirds of the world’s polar bears, and Churchill is considered to be “The Polar Bear Capital of the World.” By mid-October, between 600 and 1,000 bears mass along a 100-mile stretch of coast between the Churchill and Nelson rivers. This spectacular gathering is the largest concentration of polar bears on the planet!
Join Natural Habitat Adventures & World Wildlife Fund on an Arctic adventure to the Great White North to see these great white bears! Our Expedition Leaders are consummate naturalists and outdoor explorers, eager to share their knowledge of this regal apex predator that is a bellwether species for tracking the impacts of climate change.
Search for polar bears, Arctic foxes, Arctic hares and other tundra dwellers on our custom Polar Rover, and gain a new perspective on mothers and cubs from a scenic helicopter flight over the vast frozen landscape.
We’ll also visit the Polar Bears International headquarters and Churchill Northern Studies Center to learn about the work being done to secure a future for polar bears across the Arctic.
Photographed by Nat Hab Expedition Leader © Garrett Fache
