It seems an odd question, but do bears hibernate? We are taught from an early age that bears do hibernate, but scientists are still not sure if bears fully hibernate through the winter. I wanted to find out why scientists do not agree on this issue to bring you the correct answer.
Bears enter a state of torpor. Torpor is different from hibernation as they do not lower their body temperature to match the outside temperatures. This allows them to wake up quicker in the event of danger.
Whether or not bears hibernate is a complicated question, so I wanted to find out the correct answer for you. I also wanted to let you know which bears hibernate and why some species may not.
What Is Hibernation?
The definition in the Merriam-Webster dictionary has two definitions:
- To pass the winter in a torpid or resting state
- To be or become inactive or dormant
The dictionary gives an example for the first answer as “bears hibernating in their dens.”
Hibernation means taking a long sleep throughout winter. Hibernate is a word used to describe any dormant or inactive state. Hibernation is when an animal is inactive throughout the winter.
Some species that hibernate do not sleep throughout the winter. Hibernation is a longer form of torpor. Hibernation does not simply mean sleeping, although hibernation does include a long, deep sleep. The animal can reduce their heart rate, lower their metabolic rate, slow their breathing, and lower their body temperature.
Hibernation is a voluntary state that an animal can enter. Animals will prepare for hibernation by storing enough fat to survive off throughout 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 do happen, and the bear may wake up to do these. However, in hibernation, the animal is likely to 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.
Torpor is defined in the Merriam-Webster dictionary as:
- A state of mental and motor inactivity with partial or total insensibility
- A state of lowered physiological activity typically characterized by reduced metabolism, heart rate, respiration, and body temperature that occurs in varying degrees, especially in hibernating and estivating animals
Some animals that enter a state of torpor can reduce certain body functions to survive throughout the winter. However, some animals enter torpor 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, with an article by the National Forest Foundation stating 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 the state of torpor. Whereas hibernation lasts for long periods, torpor can be as short as a day or a night.
The article from the NFF also states, “Whether an animal hibernates or enter torpor has a lot to do with the size of the animal, smaller animals tend to hibernate, and larger animals tend toward torpor.
Why Do Animals Enter Torpor Or Hibernation?
Animals enter torpor or hibernation to get through difficult weather conditions. Hibernation is generally through the winter season, whereas aestivation is the act of a hot hibernation.
Animals drop their heart rate, body temperature, and respiration rate in torpor and hibernation. This allows them to save energy that they would normally use on these functions, allowing them to rely on their fat reserves to carry them through the winter.
If an animal did not enter hibernation in the winter when food is scarce, they might use up more energy to look for food than they get when they find it.
Do Bears Enter Torpor Or Do They Hibernate?
Scientists cannot fully agree whether bears enter a torpor or if they hibernate through the winter. It is known that bears can wake up quickly, a sign of torpor, rather than hibernation. Bears do not lower their body temperatures to the surrounding conditions, and they do not lower their metabolism significantly.
Bears go into a deep sleep throughout the winter, and they do prepare for this state by eating a lot of food in the preceding months to fatten themselves up, giving them enough reserves to live off whilst asleep.
Bears do not eat, drink, urinate or defecate whilst asleep but can wake up for any of these functions. Bears will wake up on warmer days to venture out for food and water.
Bears are not true hibernators; however, scientists can not agree on this. Frank Van Breukelen, from the University of Nevada-Las Vegas, researches hibernation and biochemical adaptations, said in an interview, “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.
For this article, we will call it hibernation, although technically it is torpor.
Do Black Bears Hibernate?
Black bears do hibernate in the United States, although the state is technically a torpor. It should be noted that the black bears in the warmer, southern states also enter torpor. The black bears in colder, northern states also enter the same state.
According to an article in Physiology magazine, July 2015, black bear hibernation consists of a continuous torpor for months. Oxygen consumption, while in the state, can be reduced to 25% of their normal values. The temperature of a black bear reduces slightly while in torpor, and their heart rate decreases.
Black bears prepare for hibernation by eating huge amounts to increase the amount of fat on their bodies. This fat is used as energy by their bodies while in hibernation. This allows them not to lose any body muscle whilst sleeping.
Black bears hibernate as a way to adapt to the cold weather outside. Black bears will wake up to eat every so often during the winter. Black bears do not urinate or defecate during hibernation.
Where Do Black Bears Hibernate?
Black bears hibernate in many different places. Black bears will use caves or previously occupied dens as their base. They can also excavate their dens under trees that have been felled by the wind and make their dens in hollow trees.
Black bears prefer to excavate or find dens on slopes that are on 20º-40º slopes. They prefer the dens to face north. The snow, which usually comes from the southwest, insulates the opening of the den. Black bears prefer their dens to be at heights between 5,800 – 8,599 ft.
Do Brown Bears Hibernate?
Brown bears do not technically hibernate, but they do enter a state of torpor for the winter. Brown bears prepare for their hibernation by eating a lot of food. As with the black bears, this allows them to live off their fat reserves during the long sleep.
Brown bears can reach incredible weights in the run-up to hibernation. Brown bears have been seen to eat 15 salmon in one meal to pack on the weight before they hibernate. 15 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 their winter dens at the base of large trees on north-facing slopes. North facing slopes are again insulated by snow that generally blows in from the southwest.
Brown bears usually dig new dens every year, although occasionally they will re-use a previous one, especially if this is a cave or other natural cavity. Most dens from the previous year will have collapsed by the time the bear wants to use it again.
It takes a grizzly bear between 3-7 days to excavate a den. Some bears start this well in advance of 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 and are unlike black bears and grizzly bears. Pregnant female polar bears will dig a den to give birth in but do not enter a state of hibernation or torpor. They will use the den to give birth, nurse them, clean them, and protect them until they are old enough to survive outside. Approximately three months later, 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 out of snow. Adult males and non-pregnant females do not dig a den at all. They will keep wandering, trying 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 get away from the cold weather by migrating.
The panda bears in China migrate to warmer climates further down the mountains, where there is also plenty of bamboos for them to eat.