It’s In Your Nature: Black bears, and a bit about hibernation
During the ’70s when I was an undergrad and graduate student at East Stroudsburg State College (now East Stroudsburg University), I took nearly every biology course, and especially biology field courses that I could.
Not one of my professors, who did any lecturing on hibernation, ever referred to bears as hibernators. Their reference point was that bears while denning for the winter, see very little body temperature drop. True hibernators, as they pointed out, will see their body temperatures drop to nearly 40 degrees Fahrenheit.
A woodchuck, for example, is a true hibernator. Somewhere since those college course days, biologists now classify a black bear as a hibernator. (Although, in my research for this column, some biologists still classify bears as not true hibernators). I’ll explain some of this.
“True hibernators” like a woodchuck have some differences with hibernating bears. A woodchuck will enter its burrow in October, whether it is relatively warm or not. Once in the den, a woodchuck’s heart rate slows to 4 to 10 beats/minute and they slow their breathing to as little as one breath every 4 or 5 minutes. Meanwhile their body temperature eventually drops. Their stored fat is their energy source.
Our eastern chipmunk is a bit different. It goes into hibernation mode but somehow will rouse every week or so and eat some of its food stored in its underground burrow. Then back to hibernation. I’m surmising that the chipmunk’s body is so much smaller and they can’t “fatten” enough to sustain them throughout the winter. This is why you might see a chipmunk eating some of your bird seed in January.
Black bears are genetically cued to when they den. Black bears in northern areas, like Canada, will probably be denned by October. They will remain in hibernation for sometimes 7 months.
Black bears here in the Times News region will den later, especially if they are near excellent food sources. While in hibernation, bears still use about 4,000 calories a day and reduce their oxygen need. They may only breathe once every 15 seconds.
In fall, before hibernation, a bear will commonly consume 10,000 to 15,000 calories of food a day. Their heart rate slows to 8 to 10 beats per minute. From a normal summer body temperature in the 100s a denning male bear’s temperature drops considerably. However, a female bear will give birth while denning, and her body temperature remains in the high 90s - she needs to keep her helpless cubs warm. A mother bear in the den (this is gross) will eat the cub’s feces and urine. I’m assuming otherwise the den would be a dirty, smelly cavity. A female bear will lose considerable weight throughout the winter keeping her body warm and producing milk to feed her cubs. She may not regain much of that weight until midsummer. Both males and females use up much of their stored body fat to survive the denning time.
Male bears usually den later than females. I have game camera photos of a bear on Dec. 31, and a few years ago, surprisingly, one was still active on Jan. 20. Cubs born in January will probably den with the mother the following winter and stay with her to the end of May. The female will breed again that following June or early July.
Den sites vary, males are less particular and could den next to a fallen tree trunk on top of some grasses or leaves it pulls beneath him. Females usually find more protected spots in rock ledges, or even under a porch of a Poconos’ summer home. The Pennsylvania Game Commission currently has a live camera of a denning bear in the Poconos. Look for Live Black Bear Cam/HDOntap.com.
Even though it’s still winter, find time to get out there. Begin looking for the first blackbirds to arrive shortly.
Test Your Outdoor Knowledge: A Pennsylvania black bear, on average, has a litter of ____cubs. A. 2 B. 3 C. 4 D. 5
Last Week’s Trivia Answer: Of our three local squirrel species, the flying squirrel is the smallest.
Email Barry Reed at firstname.lastname@example.org