How Do Bears Hibernate?

Most species of bears spend the harsh winter months in hibernation.
They retreat to dens, caves, or sheltered burrows, enter a near-dormant state, and remain there for months—
without eating, drinking, urinating, or moving—until the arrival of spring, when warmth and new vegetation return.

This extraordinary phenomenon has fascinated scientists for decades:
How can bears survive for so long without food and water and without suffering fatal health problems from inactivity?

The Key Discovery: A Special Protein

A research team from Washington State University (WSU) has provided important insight into this mystery.
By using echocardiography and analyzing cardiac tissue from hibernating bears, they discovered a remarkable adaptation at the molecular level.

• The contractions of the heart muscle are largely controlled by a protein called myosin.

• Myosin occurs in two main forms:

• Alpha-myosin (α-myosin): enables faster but weaker heartbeats.

• Beta-myosin (β-myosin): produces slower but stronger contractions.

• During hibernation, the left atrial muscle of bears produces more α-myosin, which allows the heart to beat more gently and at a slower rhythm, reducing strain and preventing cardiac damage during the long dormant period.

This discovery not only explains a key aspect of bear hibernation but also offers hope for human medicine.
Understanding how bears protect their hearts during months of slowed activity could inspire new approaches for treating heart failure and other cardiovascular diseases.

How a Bear’s Heart Adapts During Hibernation

A study published in the journal Physiological and Biochemical Zoology examined the grizzly bear (Ursus arctos horribilis), revealing dramatic seasonal changes in heart function.

• Grizzly bears typically hibernate for 5–6 months each year.

• While active in spring and summer, their heart rate averages around 84 beats per minute.

• During hibernation, their heart rate plummets to just 19 beats per minute.

For most animals—including humans—such a drastic slowdown would be life-threatening:

• Extremely slow heartbeats disrupt normal blood circulation, leading to fluid pooling in the atria and ventricles.

• This can cause the heart’s chambers to enlarge, weaken the heart muscle, and eventually result in heart failure.

Remarkably, bears not only survive such low heart rates but actually depend on them to endure the long winter fast.
The shift in myosin composition and other physiological adaptations protect the bear’s heart and ensure efficient energy use during months of near-complete inactivity.

The Ecological Significance of Hibernation

Hibernation is more than a survival strategy for individual bears; it plays a key role in broader ecological processes.

1. Energy Conservation

• By lowering body temperature, heart rate, breathing rate, and overall metabolism, bears can rely on stored body fat to survive when food is scarce.

2. Reduced Ecological Pressure

• Bears’ limited activity in winter eases predation pressure on other animals and helps maintain ecosystem balance.

3. Reproductive Advantage

• In many species, such as the brown bear, females give birth during hibernation in the safety of their dens.

• This sheltered environment improves the survival chances of cubs during the harsh winter months.

Lessons and Future Implications

The study of bear hibernation showcases nature’s remarkable evolutionary solutions:
by altering heart muscle proteins and slowing metabolic activity, bears endure months of fasting and inactivity without harm.

For humans, these findings open up exciting possibilities:

• Cardiac medicine: Insights from bear hibernation could inform therapies for heart failure or help protect patients during prolonged bed rest.

• Space exploration: The ability to safely lower metabolism for extended periods may one day aid astronauts on long-duration missions.

Conclusion: Nature’s Winter Survival Strategy

Bears’ ability to hibernate is a striking example of adaptive physiology in the animal kingdom.
It demonstrates how species evolve to thrive in extreme environments and how studying wildlife can lead to innovations that benefit both conservation and human health.

By protecting wild bear populations and their habitats, we not only safeguard an iconic species but also preserve an invaluable source of knowledge about life’s resilience and ingenuity.

animal tags： bears