Winters in the arctic regularly get down to -40 degrees Fahrenheit (which is also -40C). To keep themselves warm, polar bears rely on their metabolism to generate heat.
They also have two thick layers of fur layers of fat, and black reflective skin, that combined help to trap heat into the bear’s body. When it’s extremely cold, the polar bear’s blood vessels on their skin close automatically, allowing the bear to keep their blood warm.
Summary: How Polar Bears Stay Warm
|1.||They Use Non-Shivering Thermogenesis||Polar bears generate heat internally through their metabolism. Their cells generate heat directly, whereas most mammals need to generate energy first.|
|2.||They Have Thick Layers of Fat||They have a layer of blubber around their body that is 4cm thick.|
|3.||They Have Thick Layers of Fur||They have two layers of fur which are about 15cm thick.|
|4.||They Have Black Skin||Their black skin absorbs UV rays and traps heat in the body.|
Are Polar Bears Cold-Blooded?
Polar bears are warm-blooded mammals and maintain their own body temperature even in the coldest conditions. Today, scientists use the term ‘endotherms’ to refer to warm-blooded animals like polar bears.
An ectotherm (cold-blooded animal) relies on their environment to keep warm. Ectotherms need to constantly manage their body temperature by remaining in warmer climates and basking in the sun. When they can’t maintain warmth, their metabolisms will slow down significantly, allowing them to conserve energy until they warm up again.
An endotherm (warm-blooded animal) uses the energy produced through the metabolic process to stay warm. The sun’s rays, fur, and body fat are secondary mechanism that endotherms can use to maintain body temperature.
Because polar bears regulate their temperature through metabolic processes, we consider them to be endothermic (or in the old language: warm-blooded).
How do Polar Bears Stay Warm in the Arctic?
Polar Bears live in some of the most inhospitably cold climates in the world. Even their cousins, the black bear and grizzly bear could not live in these cold climates.
To stay warm throughout the winter (and even stay active – they don’t hibernate!), polar bears:
- Use Non-Shivering Thermogenesis
- Have Thick Layers of Fat
- Have Thick Layers of Fur
- Have Black Skin
These four elements combined help the polar bear to stay nice and warm, even in the middle of an arctic winter! (Even their little tails stay warm under all that fat and fur!)
Furthermore, this combination of heat retention means that the bear loses very little body heat. In fact, they’re almost invisible to night-vision goggles, which capture on the infra-red heat rays animals emit from their bodies. Because polar bears retain so much heat, you can often only faintly see them through infra-red goggle.
Method 1: Non-Shivering Thermogenesis
Polar bears’ bodies use a process called “non-shivering thermogenesis” which involves the production of heat instead of energy.
The cells in most mammals, including humans and other types of bears, will usually convert their food into energy, which they can then use to move their muscles.
When humans really cold, we shiver. That’s because our cells have gone into hyperdrive to turn our food into energy, then our shivering turns that energy into heat.
Polar bears don’t have to do that.
Instead of turning food into energy, polar bears turn it straight into heat! They don’t have to shiver to create heat … their body is naturally good at heat generation.
Method 2: Thick Layers of Fat
Like humans, polar bears also use fat to maintain their body temperature. Your average polar bear will have about 4 Inches (11 centimeters) of fat around their body to keep in the heat.
They’re one of the fattest land mammals on earth and have developed this fat to help them keep in the heat their body produces.
Method 3: Thick Fur
A polar bear’s fur is about 15cm thick. It actually has two layers of fur. The first is the ‘guard layer’, which is fluffier but not as thick. The undercoat is shorter but denser.
The bear’s fur is actually transparent, but sun particles that hit the fur are scattered, causing an effect called luminescence, which appears white to the human eye.
The scattering of light particles within the fur causes them to bounce around, giving a small greenhouse effect that helps to contain as much of the sun’s heat as possible.
Method 4: Black Skin
Below the transparent fur is the bear’s black skin. Of course, due to luminescence, we can’t see the skin.
But, we believe the skin is black so that it absorbs more heat than light skin, absorbs invisible infrared rays, and keeps in body heat. It works in the same way as wearing a black t-shirt on a hot day can make you feel hotter than wearing a white t-shirt.
How do Polar Bears Stay Cool?
With all of their layers of warmth, the true problem for polar bears is actually staying cool! They can’t transpire to cool down and can’t exercise too much or they will overheat.
Polar bears choose not to chase their prey, because running will rapidly increase their core temperature. Rather, they wait patiently for unassuming seals at the water’s edge.
If a bear does chase a seal, it will reach a speed of only about 7 kilometers per hour. After its chase, it will jump in the water to cool down.
They also cannot transpire through pores in the skin. Sweat would, of course, quickly turn to ice, so it’s probably useless anyway.
So, when a polar bear wants to cool down, it will stick out its tongue and pant like a dog.
What About Other Bears?
There are eight species of bears, Asiatic, brown, black, panda, polar, sloth, ant-eating bear, sun bear, and Andean bear. All bear species are warm-blooded.
Are Black Bears Cold-Blooded?
Just like polar bears, black bears are not cold-blooded. They are warm-blooded mammals.
Polar bears can’t handle cold weather conditions like polar bears can, though. Their fur is thinner and their bodies don’t go through non-shivering thermogenesis.
While black bears are endothermic (can control their body temperature), when it gets too cold, they will go into hibernation to get through the cold winter.
During hibernation, they will also lower their body temperature a little (down to about 30 to 36 degrees Celsius), which helps them conserve energy.
Are Grizzly Bears Cold-Blooded?
Like polar bears, grizzly bears are not cold-blooded. They are warm-blooded mammals.
Grizzly bears are more like black bears than polar bears. They do not have the special ability to efficiently produce heat instead of energy, and they do not have extremely thick coats of fur.
Grizzly bears will hibernate during winter to slow their metabolism and lower their body temperature, but because they continue to internally regulate their temperature during hibernation, they remain endothermic mammals.
Polar bears, like other mammals, are warm-blooded and not cold-blooded animals. They can regulate their own temperature extremely effectively through a combination of non-shivering thermogenesis, thick fat, thick fur, and black skin. This allows them to stay warm year-round, meaning they don’t even hibernate like their black and grizzly cousins.