Do Black Bears Hibernate?
By Sam Nunes, Environmental Educator, Photo By Jana Hogan, Woodcock Nature Center Board President
What do animals do in winter? They hibernate! At least, many species do. If you ask anyone what animals hibernate, the first one they mention is usually the bear. But do bears really hibernate? What exactly is hibernation? The facts about hibernation might just blow your mind.
Hibernation is a process certain species perform during the cold winter months to lower their metabolic demands during a time when resources are scarce. Put simply, their bodies down so they use less energy and can rely on energy stores built up during the warmer months were there was more food.
The characteristics of hibernation are:
Duration of sleep: Hibernation goes on for as long as months without the animal waking up.
Body temperature, heart rate, and breathing rate all drop significantly: Ground squirrels can lower their body temperatures below freezing and bats can lower their heart rates from 400 beats per minute to 11 beats per minute.
So do black bears hibernate? Even though they have many of the traits of hibernation, they actually don’t sleep for the full time during the winter months. Bears do something called torpor or denning, which means they sleep for a little and wake up for a little. Think of it as a mini hibernation lasting from a night to a few days. Bats and hummingbirds also have torpor behavior. The benefit of torpor is that the animals can safely exit and reenter this state without much problem throughout the season. If true hibernation is interrupted, though, it could be fatal to the animal.
In addition, black bears don’t drop their body temperatures more than 12oF below normal (100-101oF), which was previously considered a requirement for true hibernation. They do reduce their metabolic rate to around 50% of their usual rate, and they can bring their breathing rate down to one breath every 45 seconds. What’s also really cool is they can reuse the nitrogen in their waste to produce protein and maintain their body tissue.
Torpor and hibernation serve similar purposes. The non-scientific community can get away with blending the two terms together, but it’s always interesting to find the little complexities in nature that make each species unique and different!
Research on animals that reduce their heart rate and blood flow dramatically is being used to help humans reduce the risk of stroke due to low blood circulation. Also, research on animals maintaining muscle tissue during torpor and hibernation is being used to help humans stuck in bed rest for long periods of time.
Holland, Mary. Naturally Curious. North Pomfret: Trafalgar Square Books, 2010.