Summit Outside: Bears: When do they go slumbering?
November 24, 2012
Some Summit County residents want to know whether or not the bears are hibernating yet and if it is safe to put bird feeders out. Apparently bear prints have been found in the snow recently, so the answer is some are out still lumbering about and not slumbering.
Certain animals sleep through the winter; they bed down in the fall, and don’t arise again until the spring. Raccoons and skunks, woodchucks and chipmunks, hamsters and hedgehogs, bats and bears sleep throughout the winter.
The question is what triggers bears to go into hibernation? Sometime in late fall, black bears receive a signal that it’s time to bed down for the winter. It is not known exactly what that signal is, but one possibility is food availability which is probably linked to ambient temperature. When the available food runs out, then it might be time to hibernate. They need to gain as much body fat as possible before hibernating, as much as 30 lbs/week. Perhaps the unusually warm fall (November has been the fourth warmest in history) has provided more available food and they are still out eating.
If a female bear has not accumulated enough fat by the time she settles into her den to hibernate, the fetus will spontaneously abort.
Bears are amazing. During hibernation, they can go for as long as 100 days without eating, drinking, urinating, defecating or exercising.
A lot of research has been done on bear hibernation. Can we create just such a state of hibernation in humans? In the areas of medical care or space travel this might be very advantageous. One example might be that rapidly the reducing metabolic demand in victims of stroke, heart attack or trauma so they would be put in a stabilized, protected state which would provide more time to arrange advanced medical care. Could you induce this state for space travel to save on resources?
During hibernation, the black bears’ metabolism slows by 75 percent, but their core body temperature is decreased only five to six degrees. Hibernating bears only breathe one to two times per minute and their heart slows between breaths: sometimes even 20 seconds between beats.
Bears live off of a layer of fat built up during the summer and fall months. Waste products are produced, but bears recycle it. The urea produced from fat metabolism is broken down and the resulting nitrogen is used by the bear to build protein, which allows them to maintain muscle mass and organ tissues.
Bears lose fat, but actually increase lean-body mass while hibernating due to this nitrogen recycling. Bears may lose 15-30 percent of their fall body weight during hibernation.
The saying: “Let sleeping bears lie” means even when hibernating, they can wake to fend off a sudden attack.
When they emerge from their dens it takes some time for their metabolism to reach normal rates. Scientists found that it took the bears two to three full weeks to stabilize at their summer metabolic levels. So if you encounter a bear in the spring they may be a little sluggish.
The American black bear is a shy and retiring creature that will generally turn and amble away when approached. According to data from the National Center for Health Statistics, for every person killed by a black bear in North America, 60 are killed by domestic dogs, 180 by bees and 350 by lightning. Of course there are a lot more dog and bee encounters than bear encounters.
A friend of mine had an almost too close encounter with a black bear. She called to tell me she has been mountain biking down an incline with a sharp blind turn when right across the trail was a bear. How she managed to brake and turn around without colliding with the bear she didn’t know, but when she turned to look the bear was still right in the middle of the trail.
Another friend posted a picture of a bear cub in front of her garage on Facebook. My first reaction was “I want one!” How much cuter can a creature get?
Bears are closely related to our culture. We bring our children up with bear stories and with stuffed bears. We have Cub Scouts. Of course there is Smokey the Bear of the Forest Service who warns people about forest fires and how to prevent them. There is the age-old story of Goldilocks and the Three Bears. My son had all of the Berenstein Bear stories. Who could not have been enchanted with Winnie the Poo? There are people who have extensive stuffed bear collections. All over the West the chain saw bears decorate our doorways and hearths. We are sad to see that the store with all the cute whimsical chain saw bears along Highway 9 as we enter Breckenridge is leaving. The story of Theodore (Teddy) Roosevelt refusing to shoot a bear which had been purposefully injured and bound to a tree for sport hunting somehow sparked the name “Teddy Bears.” As a child I remember having a large stuffed bear that started out as big as I was and as I out grew it, it got more thread bear! Teddy bears are plush counterparts to what bears are in the wild; something ferocious turned into a fluffy protector.
Bears are powerful creatures and we admire power. We try emulating the sense of them in our sports teams like the Bears and the Bruins. There is a brand of cross country skis, sporting goods and beer named “Karhu,” the Finnish word for bear. You can find bears in our myths; in the constellations, like Ursa Major. The polar bear is often called the ‘spirit of the north.’
Joanne Stolen is retired from teaching microbiology at Rutgers University.