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Winter is a potentially stressful time for bears, especially new mothers. Photo by the National Park Service.

After my article about bear hibernation a couple weeks ago, several readers wrote to share their amazement at bears’ incredible adaptations for hibernation. I’ve been looking for an avenue to write about bears for some time, which may be part of the reason I overlooked some additional very important information about bear hibernation, and may in fact have stressed out the very creature who I’m so enthralled by. I was grateful for a very thoughtful letter from Ken Jonas, a recently retired DNR wildlife biologist, who offered some cautions, and some additional important information about bear hibernation. I want to share it with you all, too, because I think my previously casual attitude about disturbing a challenging time in a bear’s life is common among people in the Northwoods.
One of the key aspects of hibernation is a decrease in bodily functions like metabolism, heart rate, breathing rate, and body temperature. While bears have a unique ability to stay warmer and wake up faster than some other, smaller hibernators, that does not mean that waking up has no consequences for them. As a bear’s fight-or-flight mechanism revs up in response to some disturbance, all of those body functions increase and a portion of their limited energy stores are used up.
While this may not be a significant problem if it only happens once, repeated disturbances can cause a bear to deplete its energy stores to a dangerous level. During one study of hibernating bears, researchers discovered that the bears’ heart rates increased as soon as a human approached and remained elevated for several days after even minimally invasive visits. Who knows how much stress a barking dog causes (Hunter has been kept away from the area since he first found the den), or even a few humans with a flashlight and cameras?
Although many who visit the Northwoods in the summer are concerned about having a bear encounter in the woods, it is actually the bears who are deathly afraid of humans – especially at close quarters – according to Ken. He wrote: Although hibernating bears “usually have the response to just stay put and hope for the best…They’re still scared as heck, with all of the measurable physiological responses that go along with that condition.”
Ken also informed me that excavated and underground dens, similar to the one I visited, are typical of pregnant female bears. While it is exciting to think that my friend might have cubs near his house in the spring, it is also worrisome. The consequences of disturbance are even more serious for a mother bear. This is the time of year when cubs are being born. Not only are the mother’s fat stores especially important because of her need to feed the cubs as well as herself, disturbance can sometimes lead to den abandonment. Ken wrote, “Relocating to a new den in the midst of winter has a huge energy cost for any bear. If it is a sow with newborns she may not come back for them, in which case they definitely will not survive.”
Now, while we three naturalists who visited the den did so only out of our affection for and fascination of bears, according to the information provided by Ken, this may have been a pretty selfish act. In the field of outdoor education, we often discuss the cost/benefit ratio of various activities that might cause some harm to a single organism or section of a forest but result in significant teachable moments or an increase in affection for nature in the next generation. Sometimes the benefits outweigh the costs and we allow kids to participant in mildly destructive hands-on learning. In hindsight, I’m not so sure that the potential costs of our den visit were justified.
Hopefully, by sharing my newfound knowledge with you, we can all use this as a learning experience. While no one I’ve talked to up here has advocated for repeatedly bothering a hibernating bear, I’ve gotten the impression that most people don’t think twice about a single visit. And while Wisconsin law says that no person may harass protected wild animals (which includes bears), the consequences of even small disturbances to a hibernating bear are not prominent in the DNR’s web resources. Now that we know, we can respectfully keep our distance and let the sleeping bears lie.

 “I think that is the story people need to hear – leave winter wildlife alone, it is the most difficult time of the year for them in terms of survival. We should not be adding to their stress for our own selfish purposes.” – Ken Jonas

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