Shuteye: Animals and Sleep
Dog-tired.Cat nap. Let sleeping dogs lie. It’s idiomatic, and axiomatic: Our pets are sleep experts.
What else are they going to do all day? 1 in 1.49 (67%) pet cats is allowed to sleep in its owner’s bed, and they sure put those beds to good use: felines sleep around 12 hours a day. Dogs love their Z’s too, and may sleep anywhere from the floor (1 in 8.37) to a dog house (1 in 7.29) to the top of its owner’s bed (1 in 6.24) to its own doggy bed (1 in 8.6). Can any other creatures in creation sleep as much as our pets do?
They sure can, and then some. Maybe armadillo-tired and bat-napping simply don’t have the same cachet—they don’t trip off the tongue too well, either. But those animals sure can snooze.
In the animal kingdom, the bat and the armadillo are sleep’s ultimate virtuosos. Both sleep between 18 and 20 hours a day. The bat is well known for its sleep habits—bats sleep upside-down, after all, and only emerge at night—but the armadillo? What makes it so sleepy? Animal researchers don’t quite know, though it may be a defensive behavior: Armadillos tend to be solitary, and without the benefit of a protective herd, the next best thing seems to be crawling into a burrow and sleeping... and sleeping... and sleeping....
Another benefit of being conscious a mere four hours a day is a strong immune system. Scientists have found that the animals that sleep the most per day have up to six times as many immune cells, and 24 times fewer parasites, than those who sleep the least. Sleep also allows for the conservation of energy, and gives the body the best chance to repair itself.
So do all creatures sleep? It’s a simple question—and remarkably difficult to answer. Not only can it be difficult to tell (e.g., when is a cockroach asleep?), but sometimes even defining what constitutes sleep can be tricky. An animal may be at rest, but fully conscious. Conversely, some animals hibernate for months at a time, which, believe it or not, is not the same as sleeping. Some fish are thought to never fully fall asleep, if only because of the need to move forward to bathe their gills with fresh oxygen—although no one knows for sure.
Many aquatic mammals and birds have evolved a peculiar adaptation which the average college student would kill for come exam time. They sleep only half a brain at a time. The scientific term for this is unihemispheric slow-wave sleep, and it means that at any one time the animals are always at least half awake. They literally sleep with one eye open. Dolphins, whales, and some seals likely evolved this ability in order to be able to sleep without drowning. Ducks, on the other hand, seem to have developed it in order to evade predators.
Even animals that completely fall asleep seem be able to get by on very little shuteye. Cows don’t need more than four hours a day. Horses need even less: They get about three hours, much of it on their feet. (They lie down only for REM sleep, the phase when muscles go limp.) The gold star for staying awake goes to the giraffe. Among Earth’s mammals, the tallest also requires the least sleep, between ten minutes and two hours a day.
For most creatures, total sleeplessness is fatal; in laboratory tests, rats do not survive more than a few weeks without sleep. The longest sleepless stretch ever survived by a human, under medical supervision, is 11 days: Randy Gardner, a 17-year-old Californian, spent 264 hours awake with no stimulants of any kind. By day four, he’d begun hallucinating that he was a running back for the San Diego Chargers.
While there is no ideal amount of sack time—virtually all authorities on sleep simply recommend getting enough not to be sleepy—few adults, only 1 in 12.82, sleep less than six hours on most nights. We need our slumber, and our pets—from puppies to parrots to pot-bellied pigs—need it too.
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