Black Bears
Featured Animal: January 2016
By Dr. Nicki Frey
Bears and Hibernation
We've heard the phrase before, " Ah, I slept like a bear (in winter)!", meaning that the well-refreshed person slept well all night. And most of us have heard about bears needing to eat and store fat for the winter hibernation. But did you know that bears are not truly hibernating? In fact, no large mammal actually hibernates. While we commonly refer to a bear's winter repose as hibernation, it is actually a process called torpor.
Hibernation is a response to a shortage of food, decreasing temperatures and snow on the ground. It can last a few weeks in warmer parts of North America to 6 months for bears in Alaska (NPS 2015). Hibernating bears enter a shallow torpor with a decrease in body temperature of only 10 degrees. It's metabolism and hear rate slows down. But it doesn't need to eat, drink or pass waste. In order to survive, fat in the bear’s body breaks down into water and calories for the body to use. Muscle and organ tissues break down to supply the body with protein. This is actually quite unusual. Muscle and organ tissue is rebuilt by using the nitrogen in urea (the basis of urine).
In contrast true hibernators, such as squirrels, reduce their body temperature to near freezing and greatly reduce their metabolism, to conserve energy when food is low. But they need to wake up once a week or so to eat some food and pass waste.
Waking from Hibernation
Important to most humans, is how a bear wakes from torpor. Because of the need to increase blood temperature and metabolism to normal body temperature, true hibernators awake slowly and are lethargic until fully awake. In contrast, bears can awake from torpor quite suddenly if danger is sensed. This behavior is also beneficial to females bears - bear cubs are usually born in winter. The cubs do not hibernate or go into torpor. While their mother is sleeping, they nurse and sleep too. However, the mother awakes every now and again to care for her cubs and ensure they are safe and warm. This would not be possible if she were truly hibernating.
Because of their unusual torpor behavior - higher body temps, but no "awakening" (return to normal body temps) - recently scientists have begun calling them "super-hibernators", although this new term is not universally accepted. (nps.gov)
I wouldn't mind sleeping like a bear, as long as it were a male bear
In the intermountain west, denning begins in October (for females) and November (for males) and lasts until April (for males) and May (for females). When the bears wake up, they are HUNGRY. This is a time when there are many bear encounters within the suburban-wildland interface, because bears will venture into suburban landscapes to find food. Utah Division of Wildlife Resources’ Wild Aware program provides these tips for safety in bear country.
Maintain a bear-safe campsite
Merritt, J. F. 2010. The biology of small mammals. Johns Hopkins University Press, Baltimore, Maryland
National Park Service. 2015. Denning and hibernation behavior. Accessed at: http://www.nps.gov/yell/learn/nature/denning.ht
Utah Division of Wildlife Resources. 2015. Safety in black bear country.
Utah Division of Wildlife Resources. 2011. Utah black bear management plan.
Featured Animal: January 2016
By Dr. Nicki Frey
Bears and Hibernation
We've heard the phrase before, " Ah, I slept like a bear (in winter)!", meaning that the well-refreshed person slept well all night. And most of us have heard about bears needing to eat and store fat for the winter hibernation. But did you know that bears are not truly hibernating? In fact, no large mammal actually hibernates. While we commonly refer to a bear's winter repose as hibernation, it is actually a process called torpor.
Hibernation is a response to a shortage of food, decreasing temperatures and snow on the ground. It can last a few weeks in warmer parts of North America to 6 months for bears in Alaska (NPS 2015). Hibernating bears enter a shallow torpor with a decrease in body temperature of only 10 degrees. It's metabolism and hear rate slows down. But it doesn't need to eat, drink or pass waste. In order to survive, fat in the bear’s body breaks down into water and calories for the body to use. Muscle and organ tissues break down to supply the body with protein. This is actually quite unusual. Muscle and organ tissue is rebuilt by using the nitrogen in urea (the basis of urine).
In contrast true hibernators, such as squirrels, reduce their body temperature to near freezing and greatly reduce their metabolism, to conserve energy when food is low. But they need to wake up once a week or so to eat some food and pass waste.
Waking from Hibernation
Important to most humans, is how a bear wakes from torpor. Because of the need to increase blood temperature and metabolism to normal body temperature, true hibernators awake slowly and are lethargic until fully awake. In contrast, bears can awake from torpor quite suddenly if danger is sensed. This behavior is also beneficial to females bears - bear cubs are usually born in winter. The cubs do not hibernate or go into torpor. While their mother is sleeping, they nurse and sleep too. However, the mother awakes every now and again to care for her cubs and ensure they are safe and warm. This would not be possible if she were truly hibernating.
Because of their unusual torpor behavior - higher body temps, but no "awakening" (return to normal body temps) - recently scientists have begun calling them "super-hibernators", although this new term is not universally accepted. (nps.gov)
I wouldn't mind sleeping like a bear, as long as it were a male bear
In the intermountain west, denning begins in October (for females) and November (for males) and lasts until April (for males) and May (for females). When the bears wake up, they are HUNGRY. This is a time when there are many bear encounters within the suburban-wildland interface, because bears will venture into suburban landscapes to find food. Utah Division of Wildlife Resources’ Wild Aware program provides these tips for safety in bear country.
Maintain a bear-safe campsite
- Store food, drinks and scented items securely (in your vehicle, a bear-safe container or a tree — never in your tent)
- Dispose of trash in bear-proof dumpsters, if available
- Wipe down picnic tables
- Burn food off stoves or grills
- Pitch tents away from trails in the backcountry
- Always sleep inside your tent
- Never approach or feed a bear
- Report bear sightings to your campground host
- Stay alert at dawn and dusk, when bears are more active
- Go with a group, if possible
- Make noise as you travel through dense cover
- Stay away from animal carcasses
- Store food, trash and scented items (such as sunscreen) in airtight plastic bags
- Keep kids in the center of the group
Merritt, J. F. 2010. The biology of small mammals. Johns Hopkins University Press, Baltimore, Maryland
National Park Service. 2015. Denning and hibernation behavior. Accessed at: http://www.nps.gov/yell/learn/nature/denning.ht
Utah Division of Wildlife Resources. 2015. Safety in black bear country.
Utah Division of Wildlife Resources. 2011. Utah black bear management plan.
