The Wild Side: Bears in the winter
Last week I received reports of a small black bear roaming the woods north of Rhinelander. It turns out that this yearling bear had been treated by Wild Instincts Rehabilitation, and released in the State Forest near Stone Lake. It apparently found its way to a road, where well-meaning passers-by were attempting to feed it, which does the bear more harm than good.
If the bear follows its instincts, it will find a cozy den to settle in and rest the next couple of months. If it becomes accustomed to, or dependent on humans feeding it, this will only lead to trouble. As my warden friend would say, “a fed bear is a dead bear.” Ultimately, these bears will associate humans with food, and start searching vehicles, cabins, campsites and trash bins. These become nuisance bears, and unfortunately they usually end up being captured and euthanized by wildlife officials.
The people that contacted me or stopped at the DNR Service Center did the right thing, leaving the animal where they found it and reporting it to us. Humans have a built-in desire to tend animals, especially the young and the injured; it is natural to want to step in and try to nurse animals back to health. However, in most cases it is illegal to do so, primarily because someone who is not trained, qualified, or equipped to handle animals can do harm to the animals and themselves. Wisconsin sets high standards for their wildlife rehabilitation facilities, and our licensed rehabilitators (such as Wild Instincts here in Rhinelander) meet and usually exceed those minimum standards. To see a directory of licensed rehabilitators by county, see the DNR web page. But, if you see a bear out this time of year, it is not necessarily a death sentence. They do not sleep as soundly as you might expect through the winter.
Normally, black bears enter their dens in early winter. They drop into a deep sleep, which slows their metabolism and allows them to live off their body fat stored through the summer and fall months. True hibernation by mammals like groundhogs and chipmunks includes lowering body temperature to near freezing. Bears do not enter true hibernation, but more of a winter sleep, or torpor. Torpor allows them to rouse more easily than true hibernation, so they reposition, groom themselves, give birth, and if necessary, escape danger readily. However, as researchers discovered that bears can lower their heart rate down to eight beats per minute, and breathe once every 45 seconds, they have decided hibernation is still an accurate description of their overwinter condition.
During hibernation, bears form what is referred to as a fecal plug at the far lower end of their intestines, which was long thought to serve the purpose of “stopping up” the digestive system to cause the bear to stop eating. As research science has improved, though, we have learned that the fecal plug is simply a product of bears sleeping while their digestive system very slowly operates normally. Consequently, bears nearing the end of their sleep may get up and defecate, then return to their sleep.
Right now, bear cubs are being born-they weigh about a pound, and fit into the palm of your hand. They nurse from their mother through the winter, and emerge from their dens weighing about six pounds. While it was once considered a fact that a female bears have two cubs, we now know that three to five cubs are common. Success of the pregnancy depends heavily on how much fat the sow (female bear) puts on during her foraging before hibernating.
Visit the North American Bear Center website, bear.org, for more information, articles, and live bear den cameras they have posted there. They have changed what we thought we knew about the life science of black bears.
Jeremy Holtz is a wildlife biologist with the Wisconsin DNR in Rhinelander, and writes a weekly column in the Star Journal. To contact him, call (715) 365-8999.