Naturespeak A naturalist's view of the world

February 5, 2008

Stone Cold Chuck

Filed under: Uncategorized — wykes @ 8:53 pm

    A mid-winter woodchuck is basically dead to the world. When I say this, I don’t mean “dead” as in the midst of a deep sleep, I mean it as being as close to death as you can get without actually being actually so.  Despite the apparent ease with which Malverne Mel, Stanton Island Chuck, Pardon Me Pete, and Punxsutawney Phil rise out of their stupor to make their Ground Hog Day predictions they can do so only with the heavy assistance of their handlers. I believe that Phil has a heated burrow with a hot tub and tiki bar at his pad.  He is not one of the common ‘chucks, but instead one that is forced to deny his very woodchuckiness.  It is rumored that he even chucks wood – an activity totally against the species grain.

 Most wild woodchucks, this time of year, are curled up into a tight ball and engrossed in a self induced state of denial. Deep within their burrows they are hibernating and completely removed from the realities of the harsh world above (see here a picture of a hibernating woodchuck- click on the 6th picture down).  You could dig ‘em up and put them in front of the television cameras and they would say exactly nothing.  It’s not an antisocial thing, rather a physiological thing.

  There is a very select group of mammals that have the ability to hibernate.  Animals such as the Woodchuck, Thirteen-lined Ground Squirrel, Jumping Mice and all of our regional bat species choose this strategy.  Others such as Opossums, Raccoons, and Skunks retreat to their dens to sleep off bouts of severe weather, but they need to come back out to re-fuel throughout the winter. They sleep but don’t hibernate. Even Black Bears don’t truly hibernate – they go into a deep sleep. Winter bears can be roused relatively easily, so it’s a wonder why folks don’t go about waking them up on Groundhog Day to ask them for predictions. The answer to that question should be fairly obvious (an angry bear will not tolerate men in top hats and crowds of reporters with flashing cameras).

  The answer to the question asking why true hibernators do what they do is not so obvious. The impending seasonal lack of available greens certainly forces the decision out of the woodchuck, but this is not the entire answer. The cottontail rabbit, a mammal of similar size and food needs, chooses to scrape through the winter as an active creature.  For now let’s just gloss over the thing and simply say that the ‘chuck and his fellow members of the “Hiber Nation” do what they do because they can.

  Hibernation is controlled by body chemicals.  A substance, unimaginatively called H.I.T., or Hibernation Inducement Trigger, is produced at the request of a structure in the brain called the hypothalamus. This control center, located mid brain under the thalamus, east of Eden, and just ahead of the hippocampus, is prompted into action by the shortening days of autumn. Once this chemical is circulating in the bloodstream, all kinds of things begin to happen. Woodchucks become Ground Hogs, for instance. They begin to eat like, well, hogs and put on a rich layer of fat – including a special patch of fat called brown fat between the shoulder blades.

  Next, the corpulent creature vows abstention from further eating, makes one last visit to the bathroom, crawls down in his den and curls up.  The transformation into hibernation mode is gradual but dramatic. Blood composition changes, hormonal balances are re-figured, insulin levels are increased, and vessels dialate (constrict) in order to maintain blood pressure. Breath rate, heartbeat, and body temperature all take a plunge.  This isn’t napping!

  A woodchuck in full hibernation is cold to the touch and appears to be stone dead. From an active body temperature around 95 degrees F the critter has descended to around 46 degrees F. The heart only beats about 5 times a minute (as opposed to an average of 100 beats per minute) and the breath rate is reduced from 30-100 per minute to once every 5 minutes. Only the heart and brain are kept relatively warm and they are fed by the reserves of body fat.

  Researchers have conducted all kinds of experiments, some down right evil, in their attempts to understand the mysteries of hibernation, but two stick out in my mind. In one, a hibernating chuck was sealed up in an airtight jar filled only with Carbon Dioxide gas for one hour.  This treatment would have killed a summer chuck within minutes, but had no ill effect on the slow respiring winter chuck.  In another experiment, blue dye was injected into the leg vein of a hibernating ground hog. The dye didn’t circulate to the rest of the body until springtime when the critter woke up. That same experiment on an active animal resulted in the dye reaching all parts of the body within a few minutes -even tinting the eyeballs blue.

  Only warming ground/ air conditions or the internal ringing of a pre-set biological clock will awaken our sleeping beauty (while not exactly beautiful, chucks are kinda cute).  Quick metabolism of the brown fat is involved in this, but we’ll talk about the awakening procedure some other time. For now I’d like to let sleeping chucks lie about the weather.

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