Some animals use winter to catch up on ZZZs

Look down almost any alley this month and trash cans are turned over.

Almost every house 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 consume 15,000 to 20,000 calories per day. Also during this time, bears must drink large amounts 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 in order to have a transition period where the metabolic processes change in preparation for hibernation. They voluntarily eat less, but continue to get rid of body wastes and get increasingly lethargic, resting 22 or more hours a day. Active heart rates fall from 80 to 100 per minute to 50 to 60 per minute, and sleeping heart rates fall from 66 to 80 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, where boulders are plenty, piques the imagination, as the abundance of rock caves is evident. A group of students in our snowshoe program at Haviland Lake stumbled upon a cave containing a hibernating bear last winter.

Hibernation is continuous dormancy with distinct decreases in heart rate and metabolic rate. Bears use up to 4,000 kilocalories 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 eight to 21 beats per minute, and blood flow to skeletal muscle, 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 give birth to 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, one I especially like is the one where Froggy wakes his friend, Turtle, to have Christmas with him. This gets kids thinking about hibernation. Gay Grossman, one of our educators at Durango Nature Studies, did research about other hibernators in our area. Here is a synopsis of what she found:

“One of the only birds in the world known to be a true hibernator can be found locally. The common poorwill, known by the Hopi as “Holchoko” (“Sleeping One”), spends the winter hibernating in a rock crevice or other shelter. Dormancy can last for months at a time. The poorwill can be picked up and handled while hibernating and not awaken.

“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 or seven months – hibernating in underground dens. Other hibernators in our area include the little brown bat (which can hibernate for 83 days straight without rousing itself), the ground squirrel, the white-tailed prairie dog and the Gunnison prairie dog.”

Remember, this feeding frenzy for bears will soon be over, but be respectful of our slumbering neighbors when you are out in the backcountry this winter.

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