I was raised in a tradition that warned against the “Seven Deadly Sins.” I can’t endorse envy, greed, wrath, or gluttony, but sloth can be a virtue. Many critters would die if they couldn’t sleep for half their lives, a fact which I tried in vain to conceal from my teenage kids. The survival of bats, woodchucks, ground squirrels, and other animals is contingent on long bouts of sloth. Ironically, actual sloths do not hibernate.
Broadly defined, hibernation is a state of inactivity and lowered metabolism in warm-blooded animals (endotherms) during winter. Given that this describes me and a lot of my northern friends from January through March, hibernation must involve other factors as well. However, biologists are still debating what exactly counts as hibernation.
The label was once used only for species which entered profound dormancy, for example certain Arctic rodents whose internal temperatures fall below freezing in their winter dens. But eventually, that club was deemed too restrictive. These days, hibernation applies to any animal having the means to actively lower their metabolism and body temperature. I’d say actively lowering one’s metabolism sounds like an oxymoron, but I’ll refrain from name-calling.
Cold-blooded animals (ectotherms) like frogs and snakes also become dormant in winter. Although it’s the same as hibernation, biologists call it brumation. With ectotherms, one might say hibernation just happens; it’s not something that they “do.” Even though they don’t have to work hard at sleeping the way mammals do, their torpor is impressive in its own way. Some frogs, turtles, and fish can overwinter in mud that is devoid of oxygen, and as far as we know, they’re no worse for the wear come spring.
Most hibernators tailor their schedules based on the weather: if it’s a mild autumn, black bears and chipmunks will den-up later than usual. But some animals, known as obligate hibernators, doze off according to their Google calendars. If for some bizarre reason you were to send a European hedgehog to Aruba for a winter vacation, it would go narcoleptic at the same time as its mates back in the Scottish Highlands fell asleep.
Bears are among those creatures which in the old days didn’t qualify as hibernators, but which are now lumped in with Arctic popsi-squirrels and other high-latitude rodents in the frozen-mammals section. Bears in the far north may not freeze, but they don’t eat or drink for up to eight months, using stored fat for hydration and energy. If we were inert that long, our muscles would atrophy. Luckily for bears, they manage proteins in such a way that preserves muscle tissue.
As long as temperatures don’t plummet sharply, many insects survive winter by making glycols, antifreeze compounds which keep ice from forming inside their cells. Unlike honeybees, all members of wild bee and wasp colonies die in autumn except a few mated queens. Some of these overwinter alone, but others gather in large numbers in sheltered hibernacula,
In hot climates, a few animals find summers unbearable, and sit them out by hibernating. Actually, the proper term for hot-weather snoozing is estivation. Some desert-dwelling frogs surround themselves with a mucus “water balloon” to wait out dry spells. African lungfish have a similar trick for when their ponds temporarily dry up. More surprising is that at least one estivator is a primate: the fat-tailed Madagascar dwarf lemur sleeps in a hollow tree for half the year until the heat’s off.
If one of our primate relatives can go dormant for long periods, then maybe we can, too. Plenty of sci-fi movies depict astronauts waking after years of space travel. This may become yet another case where fiction becomes reality.
In 2014, NASA announced that they were looking for a way to place the crews of multi-year space missions into suspended animation for three to six months at a time. Presumably this is so Mission Control won’t have to listen to the incessant “Are we there yet?” whining from the back of the spaceship.
Though stories of human hibernation abound, documented cases are rare. Occasionally a person falls through the ice and is revived hours later with no evident brain damage or other long-term effects. This can occur when body temperature drops very fast, as it would if submerged in ice water or buried in a snowbank.
If the body cools slowly, hypothermia usually sets in, resulting in death if it continues. There are exceptions, apparently, like in 2006 when an injured hiker spent three frigid weeks on Mount Rokko in western Japan with no food or water. His temperature had fallen to about 73.4 degrees Fahrenheit (23 Celsius), but he made a full recovery.
Scientists will continue to study hibernation for its medical applications. But if you’re not a fan of winter, don’t pretend to hibernate by being slothful, just grin and bear it.
Paul Hetzler is a former Cornell Extension educator who sleeps a lot during the winter.
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