A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Do bears really sleep all winter? Plus: who was the first person to use a parachute?

January 21, 2000

Dear Cecil:

Do bears actually sleep straight through winter, and if so, how do they keep from dehydrating?

Easy.  They don't pee. You were expecting maybe Gatorade?

You may think hibernation is another bit of naturalist hype, like the millipede having a thousands legs or the century plant blooming every hundred years. Uh-uh. Although they can rouse themselves quickly if disturbed, bears really do sleep for three to seven months during winter — not because of the cold, but because of the scarcity of food. What's more, they do so without dehydration or other harm to themselves, although they shed more than a quarter of their body weight during their long nap — as much as 250 pounds. (They bulk up during the warm months.) Bear hibernation is of great interest to scientists, who hope it will teach us how to help people with kidney disease, anorexia, and other problems. And while we're at it, how to sleep off extra weight.

Bear hibernation is sometimes called winter sleep or denning to distinguish it from the deep hibernation of marmots, woodchucks, and certain squirrels, which basically go into suspended animation and are cold to the touch. In contrast, says bear expert Edgar Folk, the bears' body temperature drops only about ten degrees Fahrenheit. Still, they undergo some pretty dramatic physiological changes. Oxygen use drops 50 percent, and heart rate decreases from 40 to 50 beats a minute during summer sleep to 8 to 10 beats during hibernation. Eating, drinking, urination, and defecation cease. (One notable aspect of bear hibernation is formation of an anal plug, but I'd just as soon not get into that.) Despite all this, pregnant females give birth in midwinter and afterward nurse their cubs.

How do bears avoid going to the potty? First of all, they subsist entirely off their own body fat, which produces a minimum of waste, just water and carbon dioxide. Second, they recycle what urine they do produce. (What do you mean, "Eww"? Next time you're on a long car trip, you'll wish your kids could do it.) Bears are able to convert the toxic urea in urine into usable protein, a feat that offers hope to people with kidney failure. Bears do lose a certain amount of water through respiration, but they're able to replace that with water metabolized from fat.

Bears also recycle calcium, so they don't suffer loss of bone mass, a problem that bedevils astronauts on long space missions. This inspired hibernation expert Ralph Nelson to suggest in a 1973 paper that the space program could learn a lot from bears. Noting that body fat, which supplies approximately 3,500 calories per pound, is a much more efficient fuel source than conventional food, Nelson proposed (in all seriousness, he tells me) hiring obese astronauts, who could live off their own blubber rather than haul along a bulky food supply. Not a bad idea, especially since 20 percent of Americans are now considered obese anyway. "Off my case!" you can tell people as you scarf another Ho Ho. "I'm training for a mission to Mars."

Dear Cecil:

Parachuting out of airplanes is routine now, but who was the first person crazy enough to think he could do this and live?

Dear Landlubber:

The person credited with first demonstrating the principle of the parachute is Louis-Sebastien Lenormand of France. Some accounts say that, in a characteristic display of Gallic abandon, he jumped from a tower with two parasols in 1783. More likely, however, he dropped animals. Several other people are also reported to have jumped, but the question is whether we should count guys with cruddy makeshift parachutes who fell like pigs, breaking their legs. The first guy definitely known to have jumped successfully himself is Andre-Jacques Garnerin, who gave his first parachuting exhibition on October 22, 1797. He used a balloon to haul his rig, a canopy ten meters in diameter with a basket beneath, to a height of 600 meters (some say higher) before cutting loose.

Necessity has been the mother of many parachuting innovations. The first free-fall parachute jump has been credited (by some, anyway) to Tiny Broadwick of the U.S., who began doing parachute jumps as part of a carnival act at age 15. On September 13, 1914, she was demonstrating parachute jumping for the army when her static line, which automatically opens the chute, became entangled in the underside of the airplane. Cutting the line, she threw herself free of the plane, then pulled the end of the line. The chute opened, she reached the ground safely, and another extreme sport was born.

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