20 Unbelievable Bear Hibernation Facts

Bear Hibernation Facts: Historically it was unclear whether or not bears truly hibernate, since they experience only a modest decline in body temperature (3–5 °C) compared with the much larger decreases (often 32 °C or more) seen in other hibernators. Many researchers thought that their deep sleep was not comparable with true, deep hibernation, but this theory was refuted by research in 2011 on captive black bears and again in 2016 in a study on brown bears.

20 Unbelievable Bear Hibernation Facts

Hibernating bears are able to recycle their proteins and urine, allowing them to stop urinating for months and to avoid muscle atrophy. They stay hydrated with the metabolic fat that is produced in sufficient quantities to satisfy the water needs of the bear. They also do not eat or drink while hibernating, but live off their stored fat. Despite long-term inactivity and lack of food intake, hibernating bears are believed to maintain their bone mass and do not suffer from osteoporosis.

They also increase the availability of certain essential amino acids in the muscle, as well as regulate the transcription of a suite of genes that limit muscle wasting. A study by G. Edgar Folk, Jill M. Hunt and Mary A. Folk compared EKG of typical hibernators to three different bear species with respect to season, activity and dormancy, and found that the reduced relaxation (QT) interval of small hibernators was the same for the three bear species. They also found the QT interval changed for both typical hibernators and the bears from summer to winter. This 1977 study was one of the first evidences used to show that bears are hibernators.

In a 2016 study, wildlife veterinarian and associate professor at Inland Norway University of Applied Sciences, Alina L. Evans, researched 14 brown bears over three winters. Their movement, heart rate, heart rate variability, body temperature, physical activity, ambient temperature, and snow depth were measured to identify the drivers of the start and end of hibernation for bears. This study built the first chronology of both ecological and physiological events from before the start to the end of hibernation in the field.

This research found that bears would enter their den when snow arrived and ambient temperature dropped to 0 °C. However, physical activity, heart rate, and body temperature started to drop slowly even several weeks before this. Once in their dens, the bears' heart rate variability dropped dramatically, indirectly suggesting metabolic suppression is related to their hibernation. Two months before the end of hibernation, the bears' body temperature starts to rise, unrelated to heart rate variability but rather driven by the ambient temperature.

The heart rate variability only increases around three weeks before arousal and the bears only leave their den once outside temperatures are at their lower critical temperature. These findings suggest that bears are thermoconforming and bear hibernation is driven by environmental cues, but arousal is driven by physiological cues.

Unexpected Bear Hibernation Facts

  • Bears hibernate without eating, drinking, urinating or defecating.
  • They don't just not eat during hibernation. They don't wee or poo either!
  • During hibernation a bear's heart rate drops to as slow as 8 beats per minute.
  • Baby bears are born in winter during hibernation and are nursed in the den until they emerge in spring.
  • Once a bear has foud a good spot, they're often come back to it every winter for several years. That's just sensible!
  • Bears sleep in dens they dig out in hollowed-out tree cavities, under logs or rocks, caves, banks and shallow depressions.
  • Once they're in hibernation, bears slow their bodies right down. It's quite normal for their hearts to beat only 8 times a minute! A healthy human hearts beats 60-100 times a minute!
  • When they emerge, they are in a state called walking hibernation for 2-3 weeks while their metabolic processes adjust to normal levels and they do not eat or drink much during this time.
  • Mother bears grow their bear cubs in their wombs over the winter months and typically give birth in February. They then nurse their young for a few months before they all leave the den in the spring!
  • Bears will often dig themselves a cozy den to sleep in, but sometimes they'll just curl up in the roots of a tree or even just in a pile of leaves! It all depends on their situation and how cold it is, and every bear is different!

Funny Facts About Bear Hibernation

  • Bears need to put away a LOT of food to get themselves ready for hibernation. They can eat up to 20,000 calories a day - that's 10 times what a human should eat! If they are in a situation with loads of food, they won't hibernate at all - but most of the time they have to.
  • Yellowstone bears typically dig their dens on slopes at high elevation. The den entrance is just large enough for the bear to squeeze through so it will cover quickly with insulating snow. The chamber is dug only slightly larger than the bear’s body to allow for maximum heat retention.
  • Scientists have been studying animals that hibernate for a long time, because they hope that we can learn something from their amazing abilities. Bears basically switch their kidneys on and off when they hibernate, and learning how they do that could be very handy for fixing kidney problems in humans!
  • Giant pandas live in some of the coldest habitats of any bear. So they must hibernate too, right? Wrong! Pandas only eat bamboo, which is almost totally fat free. So pandas could never build up the fat reserves that other bears need for hibernation. Instead, pandas look for a sheltered spot and just stay there eating bamboo all winter!
  • Bears hibernate to save food during the difficult winter months. But did you know they don't sleep all the way through the winter? Bears will sometimes wake up, and are always ready to defend themselves if they're attacked or if their den gets flooded. Animals that are "true" hibernators include hedgehogs - and they really do sleep all winter!
  • During the summer mating season, fertilized eggs will remain in a female bear’s womb but will not implant until weeks or months later. This helps Mama Bear to conserve energy until hibernation, and may be a way to control the population if food is scarce. If she has not accumulated enough fat by the time she settles into her den, the egg will spontaneously abort.
  • Rapidly gaining weight and then lying still for several months is not generally considered a recipe for fitness, yet most bears remain healthy during hibernation. Biologists are studying hibernation in the hopes of preventing osteoporosis and Type II diabetes, helping those suffering from kidney failure, and prolonging the viability of human organs for transplant.
  • We have heard since childhood that bears “sleep” through the winter, but in fact they are awake and in a reduced metabolic state. Yellowstone bears go months without performing the usual bodily functions, and their breathing and heart rates slow significantly. This has inspired scientists to explore putting astronauts into “hibernation” for long space voyages to Mars or beyond!
  • In the autumn, Yellowstone bears enter a period of excessive eating called hyperphagia, sort of like humans at Thanksgiving, but lasting several weeks. During this fall feeding frenzy, grizzlies can eat up to 20,000 calories—and put on up to three pounds of weight—each day. Bears need to put on a lot of weight fast, as they’ll survive entirely off their fat stores during hibernation.
  • So these strange microscopic animals aren't REALLY bears (at all) but they are nicknamed water bears. Officially called tardigrades, they live in puddles of water and when it comes to hibernating they're much more impressive than regular bears! Water bears go into a really extreme form of hibernation when their puddles dry up. Their bodies totally shut down until they get wet again - which could be years. Hibernating water bears can even survive in space!

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