In the winter, animals hibernate as a form of adaptation. It serves as a survival tactic in hostile environments where food is in short supply. Bears frequently hibernate, though not all animals do. The majority of bears hibernate during the winter, including the males. In this write-up, we will discuss why do bears hibernate, time period of hibernation and what happens during the period.
why do bears hibernate?
The reasons for the hibernation of bears are stated below-
1.Food Scarcity
During winter, bears’ food sources like plants, berries, nuts, and fish are scarce or inaccessible. With limited food around, bears enter hibernation to lower their metabolic rate and survive on stored body fat. Their need for calories is reduced by up to 75% during hibernation. This allows them to live off fat stores for months until food is plentiful again in spring.
2.Energy Conservation
So, why do bears hibernate? Hibernating conserves energy for bears at a time when they cannot regularly eat. Their body temperature drops by only 7-8 degrees Celsius from normal and heart rate slows from 40-50 beats per minute to 8-10. Breathing also slows dramatically. By reducing their activity levels and body functions, bears are able to conserve the energy.
3.Insulation in Dens
Bears hibernate in dens which provide insulation and protection from the outside elements. Their winter fur coat also grows thicker. In the den, bears curl up which allows them to retain body heat. The combined insulation means bears don’t have to waste energy keeping warm and can maintain a stable body temperature.
4.Giving Birth to Cubs
Female bears give birth during winter hibernation and nurse their cubs throughout. The warm, protected den provides an ideal place for birth and early cub development. Hibernating allows mother bears to conserve enough energy to carry out reproduction and lactation while expending minimal energy.
5.Safety from Predators
Safety from predators is one of the most important reasons to note if you want to know why do bears hibernate. Hibernating keeps bears safely protected from predators like wolves and cougars. Their winter dens provide a sheltered space away from danger. Without hibernating, bears would be more exposed to attacks during food foraging.
6.Avoiding Severe Weather
Entering hibernation allows bears to stay protected from freezing temperatures, storms, and bad weather which could be dangerous. In the sheltered dens, bears are insulated from wind, precipitation, and frigid conditions.
7.Healing from Injuries
The hibernation period gives injured bears time to rest and heal. With dramatically reduced activity, any wounds have time to recover before bears resume movement in spring. Hibernation promotes healing by diverting energy to recovery that would normally fuel foraging.
8.Preventing Muscle and Bone Loss
Many studies have found an important answer to the question why do bears hibernate and that is to prevent muscle and bone loss. Despite being inactive, hibernating bears can recycle nitrogen waste into protein which prevents muscle deterioration.
How long do bears hibernate?
The hibernation period for bears can last up to 7 months, typically from late fall through early spring. Bears hibernate for as long as they need to wait out the cold winter months when food is very scarce.
In colder climates, bears may hibernate for 5-7 months without waking up much. That is why many people wonder why do bears hibernate because bears can’t be seen during that period. Black bears in Alaska hibernate for up to 7 months from October or November through early May. Grizzly bears can hibernate for 6-7 months as well in northern areas.
In warmer climates with more moderate winters, bears may hibernate for only 2-5 months. American black bears in some southern states may hibernate for only 1-3 months.
Pregnant female bears tend to hibernate longer to allow time for birthing and raising newborn cubs in the safety of the den. Females with yearlings may also hibernate longer.
The exact hibernation duration depends on location, climate, food availability, the bear’s fat stores, and whether cubs are expected. But most bears hibernate for 4-6 months on average, allowing them to conserve energy through frigid winters until spring.
What happens during the hibernation period?
Now that you know why do bears hibernate, let’s have a look at what happens to them during the hibernation period.
1.Denning Up
In late fall, bears start looking for winter dens. Pregnant females den first, followed by males and non-pregnant females. Bears often use rock caves, hollow trees, and dug out holes as dens. Inside the den, they create a nest for sleeping using twigs, leaves, and branches.
2.Reduced Body Temperature
A bear’s normal body temperature is around 37-38°C. During hibernation, their temperature drops to only 30-34°C. This hypothermic state means less energy is needed to keep the body warm.
3.Slowed Heart and Breathing Rate
A hibernating bear’s heart rate slows from around 40-50 beats per minute to just 8-10 bpm. Their respiratory rate decreases from 6-10 breaths per minute to 1-2. This dramatic slowing of heart and breathing rate allows bears to conserve huge amounts of energy.
4.Nutrient Recycling
Because bears don’t eat, drink or defecate during hibernation, their bodies have special mechanisms to recycle nutrients and minerals and avoid deficiencies. Calcium and other bone minerals are reused as bone tissue is resorbed and formed again.
5.Fat Metabolism
Stored body fat is metabolised to provide energy for basic body functions during hibernation. Bears can lose up to 1 kg of fat per day. Up to two-thirds of their body weight can be lost by the end of winter.
6.No Urination or Defecation
Since bears don’t take in any food or water during hibernation, they also don’t urinate or defecate the whole time. Their urine is highly concentrated before hibernation starts. Faeces in the intestines are reabsorbed and reused.
7.Lighter Sleep Phases
Bears don’t sleep deeply the entire hibernation as their sleep follows a cycle. About once a week they will wake up for 12-24 hours before going back into a lighter sleep. This allows for any necessary urination, defecation or changing positions in the den.