The Ark Files - Sleeping on the job

Sleeping under water

Aquatic animals, surprisingly enough, sleep as normal.

Hippos sleep under the water and then 'wake up' and go to the surface for a breath. Manatees sleep upside down under water but also need to surface for air.

Sea Otters float on their backs in the middle of patches of seaweed, wrapping themselves in the strands to keep from drifting away, their babies going to sleep on the mothers' stomachs.

Dolphins have the strangest method of sleeping. They keep one half of their brain awake so they are always only half asleep and can keep on swimming. The Bottle-nosed Dolphin sleeps one to two hours with one side of the brain at rest and then swaps over to the other side for another few hours. They also keep one eye open and will swim in circles in a group so that the open eye faces the other dolphins in the circle. This circle of sleeping dolphins is tight and because it is a large group of large animals, no predator is going to make an attack!

Some sharks have to move in order to breathe as they need the water passing over their gills to get oxygen. They don't sleep as we do but have a state of lowered brain function where they just shut down for awhile.

Parrot fish find a neat little ledge to nestle under and then spit vast amounts of mucous, wrapping themselves in this sticky cocoon as if in a sleeping bag. Octopuses seek out underwater caves in which to sleep, and the beaches in Queensland are probably safe after sunset since it has recently been discovered that the deadly Box Jellyfish goes to sleep at night spread out on the ocean floor.

Sleeping on high

Animals that sleep in trees have special features to keep them from falling. Birds that sleep perched on branches have an intricate arrangement of muscles and tendons in their feet that are the opposite to most animals. When they are sleeping and their muscles are relaxed, the claws are closed. In order to open their claws and release their grip on a branch they must wake up and flex these muscles. Birds are also able to stay semi conscious whilst still resting to keep an 'eye open' for predators. Amazingly, migratory birds can sleep whilst flying across the ocean.

Orang-utans make a bed high in a treetop each night. They will spend up to half an hour gathering leaves, twigs and branches to build their nest. Orang-utans will only settle to sleep after they have wrapped their fingers and toes around the branches to secure themselves.

Nap times

Brown Bats are the champion sleepers needing almost 20 hours a day, while giraffes get by on only two. Cheetahs need about 12, chimps and gorillas about ten, humans eight, Asiatic Elephants about four and horses about three. And it's not just mammals that need to snooze. Alligators, lizards, frogs, fish, insects and scorpions also have a time when they go into a rest mode and 'shut down'. The Bullfrog is reportedly the only animal that never sleeps or profoundly rests.

Sleeping on the hoof

Sleeping standing up is easier for larger animals which might have difficulty getting up from a prone position. It is also much quicker to run from a standing start if you are being chased. Animals that travel in herds will sleep in groups for warmth and safety, often posting a guard to keep watch. Horses can lock their knees in the standing position so they don't fall over while they sleep. Elephants and rhinos cannot sleep lying on their sides for too long as they would drown from the fluid entering their lungs due to the pressure of their bulky bodies.

Dreaming

Dogs are fascinating to watch as they dream. They yap, whimper and even move their legs as if in a chase. Kangaroos twitch, make running movements and smack their lips whilst stretched out with eyes closed, sound asleep. Roos also have a light-sleep mode where the eyes are open, but unseeing, and the slightest noise or disturbance will rouse them.

Clever lizards

Chameleons are cautious sleepers. They will change colour to match their surroundings even while they are sleeping. This is temperature regulated so if they go to sleep in the shade and the sun comes out, they are able to stay hidden.

The Basilisk lizard is even more crafty. It chooses to sleep at the far end of small branches hanging out over a pond or lake in a rainforest. If a snake tries to slither up the branch to eat it, the snake makes the branch move which shakes the lizard off. The Basilisk then falls safely into the water.