The Amazing Bodily Function Bears Still Perform Even During Hibernation

An apex predator, doting mother, and winning survivalist — bears are known for it all. Eight species of this animal exist throughout the world, all of which are found in North and South America, Asia, and Europe. Despite their distance, all of these bears have one thing in common: they hibernate.

While bears are busy consuming up to 20,000 daily calories to prepare for hibernation, humans eat a fraction of that and wish that we could sleep through the chilly winter months. If you’re wondering how a bear sleeps away eight months of the year, we’ve got the answers on all things hibernation — from how they prepare, what physiologically takes place, how long this state of dormancy lasts and so much more.

What is Hibernation, and Why Do Bears Do It?

Simply put, hibernation is the act of slowing down the metabolic state. During this process, a bear will slow down its heart and breathing rates, and lower its body temperature. According to World Animal Protection US, a bear will barely be conscious as it goes into this natural energy-saving state.

During hibernation, bears move very little if at all, reserving energy to help them survive the winter months. Leading up to hibernation, their daily caloric intake significantly increases in order to produce body fat, which helps sustain them during those months when they’re not actively hunting or foraging.

How Long Do Bears Hibernate?

Depending on the environment and geographic location, bears will hibernate for different lengths of time. The best example of this can be seen in Alaska, where bears hibernate different lengths of time based on climate and location. In warmer parts of the state, that hibernation period may only last two to five months, whereas it may last up to seven months where the weather is colder. The location of a bear’s den may also play a role in how long it hibernates, depending on whether the area is frequently disturbed or mostly remote.

Do All Bears Hibernate? Where Do They Go?

Hibernation is a natural part of being a bear though where they go and how long they hibernate can vary. For example, according to Yellowstone Bear World, Alaskan brown bears often hibernate the longest, whereas a grizzly bear may only hibernate for two to five months. Bears in warmer climates can hibernate for as long as several months or as little as several weeks, further showing how the environment plays such a large role.

Bears can pick some surprising locations to hibernate, while others are just as you’d expect. Anything from hollowed-out tree logs to a cave can become a safe space for a bear, but you can even find them high up in a tree if they live in warmer climates. Rock crevices and root masses at the base of thick trees will also do the trick — you’d be surprised at how many places such a large mammal can fit!

Preparing for Hibernation

In the fall, bears go into hyperphagia — a phase of increased caloric intake to bulk up in preparation for hibernation. The goal is to put on substantial weight to sustain themselves. This is one of the most active times of a bear’s life and is often when people see them the most, according to the National Park Service. During hyperphagia, they can travel further distances and may be more aggressive.

How Do Bears Survive Without Food and Water for Months?

Hyperphagia allows bears to hibernate without needing to eat or drink anything. In fact, according to the National Forest Foundation, bears can sleep more than 100 days without eating or drinking. As a bear goes through hibernation, any energy expended will come from their fat reserve, allowing them to avoid leaving their den. Their metabolic processes, such as those that convert waste to protein, help maintain their muscle mass through the winter. Essentially, they become fully self-sustained mammals for two to eight months out of the year.

Do Bears Defecate or Urinate While Hibernating?

Bears do not defecate or urinate during hibernation. In fact, they have the unique ability to turn their urine into protein. During this process, the bear’s kidneys shut down and the body recycles urea. As this major urine byproduct is recycled, it’s turned into protein that goes straight back to a bear’s muscles and organs.

Similar to recycling urea, the moisture from fecal matter will be absorbed back into a bear’s body during hibernation. What’s left is a dehydrated waste product that forms a plug in their intestines, keeping anything from exiting their body. This maintains the cleanliness of their den but also prevents the bear from needing to move as much while hibernating. Don’t worry — the fecal plug does eventually work its way out and is often found just outside of a bear’s den, according to TPL Kids.

Bodily Changes That Take Place During Hibernation

You might expect a bear to emerge from a den looking radically different from when it entered, but most of the changes happening to its body are internal. During hibernation, a bear’s body will undergo the following:

• Decreased Body Temperature: A bear will drop its body temperature anywhere from eight to 12 degrees but will keep their overall body temperature fairly high.
• Slower Heart Rate: A bear’s heart rate will drop as it enters a slower metabolic stage, usually remaining at 40 to 50 beats per minute, but it can drop as low as eight to 12 beats per minute.
• Decreased Breathing Rate: A bear’s breathing rate will also drop, resulting in about one breath for every 45 seconds.

While bears pack on the pounds in preparation for hibernation, they typically emerge afterward having lost roughly 20 to 40 percent of their overall body mass.

Do Bears Wake Up During Hibernation?

It’s not uncommon for bears to wake up during hibernation. They may wake up if they sense danger or need to leave the den for another urgent reason like a damp or wet hibernation space. Bears may also wake up to get into a more comfortable position, avoid dangers that arise or to give birth.

Yes, Bears Can Actually Give Birth While Hibernating

Bears typically mate in the summer, but the embryo does not become implanted until a female bear has denned. It’s only when her fat reserves have reached enough to enter hibernation that the embryo will begin growing in her uterus, which means she will give birth at some point six to eight weeks into hibernation. Bears are one of the only species to give birth during the harshest time of year weather-wise.

Bear cubs are heavily dependent on their mothers from an early age, and are significantly smaller compared to a full-grown adult bear. From the day they’re born, they need to be sheltered and kept warm by their mother, who provides warmth through body heat and protection from the elements and enemies. A mother bear will also provide nourishment for her cubs, who will survive on milk while nursing in hibernation.

What Triggers a Bear to Enter and Exit Hibernation?

There are actually several things that trigger hibernation for a bear, and it’s not as simple as sensing winter is on its way. The main triggers for hibernation are:

• Shorter Daylight Hours: The fall transition is the final stage before hibernation for a bear, and it can be triggered as days get shorter. With fewer hours of daylight, a bear will get lethargic and move toward hibernation.
• Lack Of High-Calorie Intake: As bears move through the fall months, it becomes evident that sources of high-calorie foods are scarce. In Alaska, this is what’s believed to trigger bears into hibernation as early as October.
• Hormones: A bear’s hormones may also play a role in hibernation. As thyroid hormone levels decrease and glucocorticoids increase, this can also cause a lethargic state before entering full hibernation.

How Climate Change Affects Hibernation

Climate change increasingly affects bear hibernation. With rising temperatures worldwide, bears enter hibernation later in the fall and end hibernation earlier in the spring. Sometimes bears skip hibernation altogether. Additionally, if warmer temperatures do wake a bear from a shorter hibernation period, they risk using up all their fat reserves before finding more food to replenish it. This has led to starvation and even malnutrition.

How Scientists Study Bear Hibernation

It’s accurate to call the study of bear hibernation a hands-off process. Rather than tracking and observing bears themselves, scientists use tools such as sensors, cameras, and tracking devices. Bears are outfitted with certain tools prior to hibernating, and scientists can then monitor the process remotely so as not to disturb the bears. These tools monitor things such as:

• Heart rate
• Body temperature
• Movement
• Snoring
• Oxygen consumption

Dangers During Hibernation

Bears can face a number of dangers while in hibernation, and surprisingly, humans are one of them. If a human wakes a bear from hibernation, it’s possible the bear will burn through more energy than it has stored. Additionally, humans may unintentionally wake a slumbering bear who is trying to take care of her cubs, causing further disruption to the hibernation process.

Predatory threats to bears include mountain lions and wolves, both of which prey on bears. However, according to Bear With Us, it’s estimated that fewer than one percent of black bears die in their dens during hibernation. While predators are a concern, they don’t significantly impact the rate of slumbering bears. Humans are a bigger concern, according to the American History Museum.