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20,000 calories a day: Get ready to hibernate

For bears, hibernation is not a time of total inactivity. While in their dens, they birth and nurse their cubs.

Cooler weather has always been a stimulus for eating warm food.

Quite the opposite of summer’s heat causing a drop in calories, a chill in the air often makes me think about the comfort and coziness of food. While humans are not hibernators, it’s easy to pretend that it’s necessary to start stocking up in September. Other animals certainly share my instincts.

Look down almost any alley this month and trash cans are turned over. Houses near forested areas have piles of bear scat littering the lawns in the morning. And, if you have windows open at night, expect to be awakened by dogs barking incessantly.

Yes, folks, bears have entered their pre-hibernation feeding frenzy, called hyperphagia. During this period of excessive eating and drinking, a black bear can eat 15,000 to 20,000 calories a day. Also during this time, bears must drink large quantities of water to process this amount of food and rid the body of nitrogen. Therefore, bears are also urinating 1 to 2 gallons a day.

Even though bears don’t actually enter their dens until closer to snowfall, they begin hyperphagia early in the fall to have a transition period where the metabolic processes change in preparation for hibernation. During this transition phase, they voluntarily eat less but continue to get rid of body wastes and get increasingly lethargic, resting 22 or more hours a day, often near water. Active heart rates fall from 80 to 100 beats per minute to 50 to 60 beats per minute, and sleeping heart rates fall from 66 to 80 beats per minute to less than 22 per minute.

The hibernation period of a bear’s life cycle takes place during winter months, usually in a cave. Walking around the Dalla Mountain Park area, with its abundance of rock caves, can stir the imagination. Last winter, a group of students in our snowshoe program at Haviland Lake stumbled upon a cave containing a hibernating bear.

Hibernation is continuous dormancy with distinct decreases in heart rate and metabolic rate. Bears use as much as 4,000 calories per day, mainly body fat, but do not eat, drink, urinate or defecate. They can reduce oxygen consumption and metabolic rate by half and breathe only once every 45 seconds. Heart rate can drop periodically to 8 to 21 beats per minute, and blood flow to skeletal muscles, particularly the legs, can be reduced by 45 percent or more, making some bears slow to arouse and run away in winter. Even though many people think of hibernation as a time where animals don’t wake, hibernation can be interrupted by normal periods of activity lasting 12 to 24 hours. Bears even birth and nurse their cubs while in the den.

Even though bears are the most well-known hibernators, other species hibernate as well. If any parents out there have read the “Froggy” books by Jonathan London, I especially like the one in which Froggy wakes his friend, Turtle, to celebrate Christmas. This gets kids thinking about hibernation.

Mammals in our area known to go into deep winter slumbers include yellow-bellied marmots. These “whistle pigs” can spend longer than many other mammals – six to seven months – hibernating in underground dens. Other hibernators in our area include the little brown bat (which can hibernate for 83 consecutive days without rousing itself), the ground squirrel, the white-tailed prairie dog and the Gunnison prairie dog.

So, remember, this feeding frenzy for most hibernators will soon be coming to a close. Lucky for us, we can continue eating through the winter.

sally@durangonaturestudies.org or 382-9244. Sally Shuffield is executive director of Durango Nature Studies.

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