We are taught from an early age that bears hibernate, but scientists now agree that bears do not fully hibernate through the winter.
Bears enter a state of torpor in winter. Torpor is different from hibernation as bears do not lower their body temperature to match the temperatures outside. This allows bears to wake up quicker in the event of danger.
In this article, we look at how bears spend their winters.
Do Bears Enter Torpor, Or Do They Hibernate?
Scientists do not fully agree on whether bears enter a torpor or if they hibernate. It is known that bears can wake up quickly, which is characteristic of torpor. However, bears do not lower their body temperatures to the surrounding conditions, and they do not reduce their metabolism significantly.
Bears go into a deep sleep throughout the winter, preparing for this by eating a lot of food in the preceding months to fatten themselves up. This gives them enough reserves to live off while asleep.
Bears do not eat, drink, urinate or defecate while sleeping but will wake up if needed. Bears will wake up on warmer days to find food and water.
Bears are not true hibernators, but scientists disagree on this. From the University of Nevada-Las Vegas, Frank Van Breukelen researches hibernation and biochemical adaptations. In an interview, he said, “Now, we’re so much more aware of what happens and that we have a lot of different types of hibernations. Now, I’d tell you that bears really do hibernate.”
Marcella Kelly, an ecologist from Virginia Tech who researches at the University’s Black Bear Research Center, said, “It’s still a little controversial.” People have called bear hibernation, torpor, winter sleep, dormancy, and carnivoran lethargy. Most scientists now call it hibernation, even if this is not accurate.
Do Black Bears Hibernate?
Black bears do hibernate, although the state is technically torpor. Both the black bears in the warmer, southern states and the bears in the colder, northern states enter torpor.
According to an article in Physiology magazine, black bear hibernation consists of a continuous torpor for several months. Torpor can reduce oxygen consumption to 25% of its typical values. A black bear’s temperature reduces slightly while inactive, and its heart rate decreases.
Black bears prepare for hibernation by eating considerable amounts to increase the amount of fat on their bodies. This fat is used as energy by their bodies while asleep. This allows them not to lose any muscle while sleeping.
Black bears hibernate as a way to adapt to the cold weather outside. Black bears will wake up to eat when needed during the winter. Black bears do not urinate or defecate during hibernation.
Where Do Black Bears Hibernate?
Black bears will use caves or previously occupied dens as their base. They can also excavate their dens under trees that have fallen and in hollow trees.
Black bears prefer to excavate or find dens on north-facing slopes. The snow, which usually comes from the southwest, insulates the shelter’s opening. Black bears prefer their dens to be at heights between 5,500-9,000ft.
Do Brown Bears Hibernate?
Brown bears enter torpor for the winter. Brown bears prepare for their long sleep by eating a lot of food. As with the black bears, it allows them to live off their fat reserves during the winter.
Brown bears can reach incredible weights in the run-up to hibernation. Brown bears have been seen eating fifteen salmon in one meal to increase their fat reserves before hibernating. Fifteen salmon is approximately 67,000 calories, giving the bear an incredible amount of fat from one sitting.
Female brown bears wake up to give birth to their cubs during the winter. Pregnant females make their dens for the winter at higher elevations than males or other females.
Where Do Brown Bears Hibernate?
Brown bears usually make winter dens at the base of large trees on north-facing slopes. North-facing slopes are insulated by snow that generally blows in from the southwest.
Brown bears usually dig new dens yearly, although occasionally, they will re-use a previous one, especially if this is a cave or other natural cavity. Other shelters from the previous year will have collapsed when the bear is ready to use them again.
It takes a grizzly bear between three to seven days to excavate a den. Some bears start this well before the oncoming winter, whereas others will leave it until almost the last minute.
Do Polar Bears Hibernate?
Polar bears live in cold conditions for most of the year, unlike black bears and grizzly bears. Pregnant female polar bears will dig a den to give birth but do not enter a state of hibernation or torpor. They use the shelter to give birth, nurse, clean their cubs, and protect them until they are old enough to survive outside. After about three months, the female will appear with her cubs in the outside world.
Polar bears do not hibernate, and only pregnant female polar bears will dig a den. Adult males and non-pregnant females do not dig a den but will keep wandering to find the next meal.
Do Panda Bears Hibernate?
Although not found in North America, panda bears can be found in three zoos in the United States. I wanted to include them here because you do have a chance to see them. If you want to see them, you can see them at Zoo Atlanta, the Memphis Zoo, and the National Zoo in D.C.
In the wild, panda bears can only be found in the mountains of Central China. Pandas do not hibernate in China, but they try to escape the cold weather by migrating.
Panda bears in China migrate to warmer climates further down the mountains, where there is also plenty of bamboo for them to eat.
What Is Hibernation?
Hibernation means taking a long sleep throughout winter. Hibernation is a dormant or inactive state and is used to describe when an animal is inactive throughout winter. Whereas torpor includes physiological changes, including body temperature, metabolism, and water balance.
Some species that hibernate do not sleep through the whole winter. Hibernation does not simply mean sleeping, but it does a long, deep sleep. The animal can reduce their heart and metabolic rates by slowing their breathing and lowering their body temperature.
Hibernation is a voluntary state that animals enter. Animals prepare for hibernation in autumn. They will store enough fat to allow them to survive the winter.
Hibernation is different from torpor, as it can take several hours or even a day to wake up from hibernation. Eating, drinking, and going to the toilet still happen, and the bear may wake up to do these. However, in hibernation, the animal will likely stay asleep for as long as possible.
What Is Torpor?
Torpor is entered when an animal reduces several of its body functions to survive throughout a season.
Some animals that enter a state of torpor can reduce certain body functions to survive the winter. Not all torpor happens in winter as some animals use it to get through a long, hot period.
Entering a state of torpor is dependent on weather conditions. Waking up from torpor can be very stressful for the animals. An article by the National Forest Foundation states that “Waking expends energy and involves violent shaking and muscle contractions, such as shivering.”
What Is The Difference Between Hibernation and Torpor?
Torpor is different from hibernation, as the animal does not voluntarily enter torpor. Hibernation lasts for long periods; torpor can be as short as a day or a night.
The article from the National Forest Foundation also states, “Whether an animal hibernates or enters torpor has a lot to do with the size of the animal, smaller animals tend to hibernate, and larger animals tend toward torpor. This is one of the reasons that we know that bears enter torpor.
Why Do Animals Enter Torpor Or Hibernation?
Animals enter torpor or hibernation to get through challenging weather conditions. Hibernation is generally through the winter season, whereas aestivation is used to survive particularly hot periods.
Animals drop their heart rate, body temperature, and respiration rate in torpor and hibernation. This allows them to save energy that they would typically use on these functions and rely on their fat reserves to carry them through the winter.
An animal that does not enter hibernation when food is scarce would probably use up more energy looking for food than they receive from eating it.
Bryan Harding is a member of the American Society of Mammalogists and a member of the American Birding Association. Bryan is especially fond of mammals and has studied and worked with them around the world. Bryan serves as owner, writer, and publisher of North American Nature.