If an animal is lucky enough to be a house pet, it has been promoted to the top of the food chain. (Representational Image)
For most kids, the biggest concern about sleep is being told to go to bed before you want to. Things are different for animals.
Unless animals are at the top of their food chain, most can't afford to get a good night's sleep. (Or a good day's sleep, if they're nocturnal.) Why? Because they have to worry about whether someone will try to eat them while they're snoozing!
Animals have evolved different means to balance sleep needs with the need to stay alive. Because sleep can be measured only with a brain-wave test called an EEG, some "facts" about the sleep habits of animals are based on observation. After all, would you try to get a brain-wave test on a shark?
Dolphins have something called unihemispheric sleep. This means one side of the brain sleeps while the other is awake.
(The higher brain functions of most complex animals are divided into left and right hemispheres.) When this takes place, one eye is open and the other is closed. It's presumed dolphins do this so it's easier to swim to the surface for air and to watch for predators.
Giraffes spend a lot of time foraging for food, and their only defense against predators is speed. (They can run up to 35 miles per hour.) It's estimated that giraffes get about two hours of sleep in the form of short "naps." Giraffe moms can go weeks without sleep after giving birth. Because giraffes are vulnerable during the time it would take to get up from lying down, they usually sleep standing up.
Bats sleep upside down hanging from branches, the tops of caves and other structures. It's thought that a bat's wings aren't strong enough to lift them off the ground. By sleeping from a high perch, they get extra momentum as they drop into flight.
Mallard ducks can control whether to use regular or unihemispheric sleep depending on the risk. Ducks on the outside of a group will sleep with one eye open, watching for predators, while those in the middle sleep with both eyes closed.
Like people, rats go through multiple stages of sleep, including REM (rapid eye movement) sleep, which is associated with dreaming. Scientists have recently proved that rats dream. If you have nightmares about rats getting into your attic, just think that they may have nightmares about humans trying to kill them.
Sea otters wrap themselves in kelp and float on their backs when they sleep at night. The kelp provides some camouflage and prevents them from drifting too far because of ocean currents.
If an animal is lucky enough to be a house pet, it has been promoted to the top of the food chain. That's why dogs and cats can be found sleeping in the most vulnerable but adorable position - on their backs, paws outstretched with their soft tummies begging to be rubbed.
© 2016 The Washington Post
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