How wild animals go about sleeping?

A lion sleeping.

Anyone who has ever seen a lion sleeping in the hot midday sun might well conclude that this fierce feline is as tame as a house cat.

Looks are deceiving, as the 17th-century writer Thomas Campion wrote: 

“Who a sleeping lion dares provoke?”

Yes, even the mighty lion needs sleep—about 20 hours a day—in order to carry out its demanding predatory life-style.

Consider, too, the Tuatara,a lethargic lizard like animal found in New Zealand.

A picture of a New Zealand Tuatara.

It spends about half the year in a state of light hibernation.

Why, the Tuatara is so sluggish that it even falls asleep while chewing its food!

But all that sleep evidently does it some good, for scientists estimate that some Tuataras can live about 100 years!

However, many of this wild animals sleep for long periods of time not out choice.

It is the way many of them survive cold winters.

In preparation, the animal builds large layers of fat that will keep it nourished during its long period of sleep.

What, though, prevents the slumbering animal from freezing to death?

As the book Inside the Animal World explains, the brain triggers chemical changes in the animal’s blood, creating a kind of natural antifreeze while it is sleeping.

As the animal’s body temperature drops to just above freezing, its heartbeat falls to a fraction of its normal pace; its breathing slows down.

A deep sleep then ensues, and it can last for many weeks.

Sleeping ‘on the wing’?

An image of a sooty tern bird flying.

Some animals sleep in very unusual ways.

Consider the sea bird called the sooty tern.

When a young sooty tern leaves its nest, it heads out to sea and stays in constant flight for the next few years!

Since it is not equipped with waterproof plumage and it does not have webbed feet such as those of other terns that can make a water landing, the sooty tern avoids being submerged in the sea.

It hunts by scooping small fish from the surface of the water.

So, when does it sleep?

The book Water, Prey, and Game Birds of North America suggests:

It seems unlikely that they sleep on the ocean since their feathers would get waterlogged. Some scientists suggest that these birds may sleep on the wing.”

Do fish sleep?

A picture of a fish in an aquarium.

According to The World Book Encyclopaedia, among vertebrates:

only reptiles, birds, and mammals experience true sleep, with changes in brain wave patterns.”

Even so, fish do enjoy sleep-like periods of rest—though most cannot close their eyes.

Some fish sleep on their sides; others, upside down or vertically.

Some flatfish, like the flounder, dwell on the bottom of the seabed while awake.

When asleep, they assume a floating position a few inches off the bottom.

The colourful Parrot fish has a unique bedtime routine: It dons a “nightgown.”

As its period of rest comes near, it secretes a mucus, or slime, that completely encloses its body.

The purpose?

“Presumably to keep predators from detecting [it],” says nature-writer Doug Stewart.

It breaks out of its slimy garment when it awakens.

Seals likewise have an interesting bedtime routine called bottling. They inflate their throats like a balloon, creating a sort of natural life jacket.

Buoyed up in this way, they can sleep as they float vertically in the water with their noses exposed at the surface for breathing.

Keeping one eye open

Picture of wildebeest resting from hot savanna heat.

Of course, going to sleep in the wild makes an animal more vulnerable to predators.

Many creatures thus sleep with one eye open, so to speak.

Their brains maintain a level of alertness during sleep, allowing them to respond to any sounds that spell danger.

Yet other animals survive by making regular safety checks.

For example, birds sleeping in a flock will periodically open an eye and peek, checking for danger.

Herds of Antelope or Zebras in Africa likewise look out for one another during rest periods.

Sometimes the entire herd will laze on the ground with their heads upright in a state of alertness.

Periodically, one animal will roll over on its side and lay limp on the ground in a deep sleep.

After a few minutes, another member of the flock takes its turn.

Elephants similarly sleep as a herd.

The adults, however, usually remain on their feet and sleep lightly, opening their eyes from time to time, lifting and spreading their huge ears to catch any sounds of danger.

Under the shadow of these huge watchmen, the smaller calves are free to lay flat on their sides and fall into a deep sleep.

In her book Elephant Memories, writer Cynthia Moss recalls seeing an entire herd go to sleep:

First the young calves, then the older ones, and finally the adult females all lay down and went to sleep. In the moonlight they looked like huge grey boulders, but their deep, peaceful snoring belied the image.”

We still have much to learn about the sleeping habits of wild animals.

However, the more we learn the more we are amazed at their ingenuity in making sleep a apart of their animal world.