March 23, 2008 in Outdoors

Winter snoozing not always hibernation

The Spokesman-Review
 

Warmer weather and longer days create a wake-up call to the many critters with a gift for sleeping through the winter.

While many birds have the means to split to warmer climes during winter, some terrestrial creatures cope with the cold and lack of food sources by checking out for a long nap — and we’re not necessarily talking about hibernation.

A true hibernator, such as a chipmunk, can reduce its body temperature to nearly freezing during hibernation and change its heart rate from 350 beats a minute to as low as four beats a minute within hours of retiring to its den.

Bears, which are not true hibernators, slip into a winter lethargy. A bear’s heart rate drops, but not as rapidly and initially to only about 50 beats a minute. That’s plenty of blood pumping for a quick awakening to rebuff a bear researcher entering the den with a rectal thermometer. However, if the sleep is uninterrupted for several months, the rate could drop as low as eight beats a minute.

While pregnant female bears wake in midwinter to give birth and then go back to sleep while their newborn cubs nurse, most bears sleep through the winter.

Rodents that exercise true hibernation, by contrast, wake every few weeks to eat small amounts of stored food and pass wastes.

That means animals that truly hibernate don’t actually sleep all winter, while “winter lethargic” species often do.

The National Wildlife Federation gives this scientific explanation:

“The difference between these two winter survival strategies — true hibernation and winter lethargy — is related to the animal’s size. Bears are too large to dissipate the heat necessary to enter hibernation, whereas smaller mammals, with their high surface-to-volume ratio, can achieve this temperature drop quickly and evenly.”

Possibly the largest rodent that truly hibernates is the hoary marmot, and it’s a champion napper. In the Northwest, it has been known to enter its burrow in September and not emerge until April.

Sounds pretty far-fetched until you realize that some die-hard baseball fans pretty much fade out after the World Series and have no life until opening day.

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