Polar Bears, Black Bears and Grizzlies in Hibernation – The Long Sleep

Some interesting things you may not have known about hibernating…

Polar Bears:

  • With the exception of pregnant females, polar bears do not hibernate in the winter, but roam across the sea ice in search of food.
  • Polar bears go into a state of ‘walking hibernation’ during the summer months – they do not enter a den but their metabolic rate is reduced.
  • They can switch readily between their active state and walking hibernation based on the availability of food- an ability that is exclusive to the polar bear.

Grizzly Bear in the Snow

Black Bears and Grizzlies:

  • Contrary to popular belief, it is not the cold temperatures that drive black bears and grizzlies into hibernation, it’s the lack of food. Bears in the zoo will not go into hibernation during the winter if they continue to be fed.
  • Bear gall bladders are used in traditional Oriental medicine to treat jaundice, abdominal pain and distention, often caused by gallstones. Research has revealed that bear bile contains a substance called ursodeoxycholic acid (UDCA), which will dissolve certain kinds of gallstones without causing substantial side effects. Today UDCA is produced synthetically for use in hospitals and as a prescription drug.

A bedridden person will suffer from muscular atrophy within a short time – weightlessness in space causes the bones of astronauts to weaken – even other mammals show a continuous loss of body protein when fasting – how do bears manage to stay curled up in their dens for months, and yet experience little loss of muscle mass or bone strength?

“…How bears maintain bone density is unknown. It is hormonally related, but how the biochemical processes work has yet to be discovered. Maintenance of muscle mass is accomplished through an almost complete recycling of metabolic waste products into proteins. This also prevents metabolic waste from accumulating and reaching toxic concentrations. we need to drink and urinate to flush nitrogen compounds out of our system. Otherwise, altered pH levels in the cells would cause our metabolism to collapse. The kidneys are in charge of detoxifying the body, and people with kidney disease or kidney failure depend on frequent dialysis to stay alive. If we could understand how bears recycle their metabolic wastes, the lives of many could be improved.

Their physiological feats have made bears popular research subjects for human medicine. The results of this research my provide new medications and treatment for diseases such as osteoporosis and kidney failure. The discovery of the hibernation induction trigger (HIT) may prove to be a milestone in organ transplants. Tissue deterioration results in as many as 20 percent of donor organs to be discarded. However, if the donor organs are perfused with HIT, tissue deterioration is slowed down threefold. There are other possible applications for HIT as well. A monkey injected with HIT fell asleep for six hours, it’s heart rate and body temperature dropped, and its appetite was depressed for almost a week. This suggests that probably all mammals, including humans, are responsive to HIT. If so, the hormone might prove useful in treating various conditions such as obesity and insomnia.”

Playtime in the Snow

Bears: A Year in the Life Chapter 10 – The Long Sleep

Salmon Season for Brown Bears and Black Bears

Taking the Plunge…If push comes to shove, the brown bears are dominant but mostly a fragile truce prevails. [Referring to brown bears and black bears fishing for salmon in the waters of Anan Creek south of Wrangell, Alaska] In times of overabundance, strife over a copious resource is a waste of effort. Still, black bear females, in particular females with young, usually abandon their fishing spot and leave the river or seek shelter up high in a tree when the bruins appear on the scene. Some juvenile brown bears apparently regard it as good sport to chase their smaller cousins. Mature male black bears generally stand their ground against these hooligans.
Taking a Breather
At the peak of the salmon season, between mid-July and mid-August, as many as fifteen bears can be seen fishing along the stream at the same time. Individuals who are skinny at the start of the fish run are often plump by the end of it, adding as much as two pounds of fat to their stocky frame per day. Salmon lie piled up in dense rows in the pools below small waterfalls, waiting for their turn to leap the obstacles in the river. Bears line the river, staring at the water and the promised meal contained within. Fishing techniques vary between individual bears and also between the two bear species. Some hurl themselves into the midst of schools of fish, others dive below waterfalls, again others simply stand midstream hoping for a disoriented fish to get within their reach. Generally the brown bears take a more active role in the pursuit of their prey, leaping into the stream and chasing fish into shallows. Most black bears, possibly as they feel more vulnerable, wait on the water’s edge for the opportunity to quickly grab a fish and retreat back into little caves among the boulders piled up next to the river. Black Bears Fishing at Anan CreekCubs learn from their mothers. Fishing techniques get passed on to the next generation and favorite fishing spots get reused by daughters and sons. Brown bear cubs sit right on the bank of the river while their mother fishes. By comparison, the offspring of a black bear female are more cautious and watch her fishing from high in a tree or sit at the base of one, always ready to scramble up the trunk to safety. The river is a dangerous place for young bears. A lack of caution, a moment of inattentiveness, can have fatal consequences. For cubs, the salmon run is a stressful, scary time of the year, a time when they have to weigh boldness against caution. Sows only feed cubs that demand a meal. A cub that is too shy, won’t get much food; one that is too courageous may not live to see the fall.

From Matthias’s book on bears and Alaskan wildlife – Wild Alaska. View images from the book.


Black Bear Cubs – Who’s Your Daddy?

Black bear cub in tree

When a mama bear gives birth to two or more cubs, each cub can have a different father? Litters of bear cubs (2 cubs or more), are fraternal rather than identical multiple births.

Each ovulation in a female bear produces but one ovum, several copulations are required to stimulate the release of the eggs and fertilize them. Ovulation in mammals either occurs spontaneously (without any external trigger), as in humans, or is induced by the male, as in bears.

This information is from Breiter’s book on black bears, brown bears or grizzlies, and polar bears – Bears: A Year in the Life