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5 Stages of Activity and Hibernation

bear_in_burrow_den_.jpg The annual cycle of black bear activity and hibernation has five stages:

  1.  hibernation
  2.  walking hibernation
  3.  normal activity
  4.  hyperphagia
  5.  fall transition

The stages differ in biochemistry, physiology, appetite, and level of activity. The onset and duration of the stages are genetically programmed to fit regional norms of food availability, which differ across America.

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Do black bears hibernate?

bear_curled_up_in_den.jpg Short answer: yes.

When people defined hibernation simply in terms of temperature reduction, bears were not considered hibernators. However, when biologists discovered the many metabolic changes that let black and grizzly bears hibernate up to 7 ½ months without eating, drinking, urinating, or defecating, they realized that body temperature was only a small part of hibernation.

They redefined mammalian hibernation as a specialized, seasonal reduction in metabolism concurrent with scarce food and cold weather (Watts et al. 1981).

Black bears are now considered highly efficient hibernators.

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Digging a Den

June_den_digBefore researchers from the Wildlife Research Institute videotaped 3-year-old June digging this den in Eagles Nest Township, Minnesota, they had no idea some bears made dens so early—July 19, 2004.  It was the first time researchers watched a bear dig a den.  The most interesting part happened when she encountered a 68-pound rock.  She did not make futile attempts to roll it up the steep incline of the entryway.  

(see video below) 

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Heat Loss in Dens

BBC_Thermal_ImagingIn 2003, the BBC phoned researchers for help with a documentary using new thermal imaging technology. The telephone conversation sounded something like:

BBC: “We’re looking for someone dumb enough to try putting tiny cameras under a mother black bear with cubs in a den. Do you have such a person?”

Researcher: “Will it have educational value that we can use at the Bear Center someday?

BBC: “Yes. One of the cameras will make the very first thermal images of heat loss patterns in dens.”

Researcher: “We have just the person.”