Ever feel like yawning to impress a date? Or falling asleep while balancing on your heels? What about sleeping with one eye open? All animals sleep, but not always in the ways you'd imagine.

Dolphins, Ducks and unilateral eye closure Dolphins and ducks both keep one eye open and one half of the brain awake at all times. This is called unilateral eye closure (UEC) and most birds as well as some other large sea mammals can do it. This unusual sleeping technique allows these animals to stay alert to predators. Dolphins are particularly unusual in their lack of need for sleep; a calf and its mother will have ZERO sleep for the first few months of the baby's life.

Migratory Thrush Nappers While migrating, Swainson's thrushes take hundreds of naps during the day, each of just a few seconds. Migratory birds tend to function well on 'micro-naps' and there is strong evidence to suggest that some species can sleep while flying. The albatross is probably the strongest contender for this impressive feat. They spend all of their time at sea and would be very open to attack if they slept while floating on water, so there's little other way they could grab a bit of shut eye. Birds that roost in groups will usually have a ring of 'sentries' that keep one eye open while the rest of the group sleeps soundly. Mallards observed sleeping in a line will often post sentries on either end of the group, allowing those in the middle to sleep more soundly. I wonder if his other eye is actually wide open...

Talon-ted Sleepers Bats sleep upside down. Sounds daft, right? Well, have a look at some of the reasons why they do it and an inverted snooze might begin to sound a lot more attractive: - bats' wings aren't really strong enough to launch them into the air from the ground; hanging from the roof means they can just drop into flight. - because of the unique design of their talons, bats use very little energy while hanging. The talons lock into place and the force of gravity does the rest. - there is no other competition for roosting spots. - gravity is a fast accelerator, so bats can simply 'drop' out of trouble should the need arise.

Frogs Frozen Hibernation Lots of animals hibernate. This is different from sleep and a hibernating animal can often take days to wake up properly. In hibernation, an animal's heartbeat will slow down dramatically and its temperature will drop close to whatever the outside temperature is. Hibernation is sleeping through cold and estivation is sleeping through heat. Frogs are some of the best hibernators around. Some species can survive being frozen solid with no heart beat or breathing for weeks at a time!

It's Not Yawning, It's An Ecstatic Display Most animals yawn, but it's probably not because they're bored or sleepy. Scientists are still on the case as to why, but there are lots of different theories. Baboons have been observed yawning to threaten their enemies. Similarly, Siamese Fighting Fish yawn only when they see another fighting fish (or their own mirror-image) and will often attack aggressively. Penguins yawn while courting- it's known as an 'ecstatic display'. Snakes meanwhile, usually yawn to realign their jaws after a meal.

The Deep-Sleeping But Deeply Stupid Duck-Billed Platypus If you feel shortchanged in the sleep department, thank goodness you're not a giraffe- they only sleep for about 2 hours out of every 24. The brown bat is at the other end of the spectrum and usually sleeps for 19 hours a day. Scientists seem to be in agreement that the larger you are, the less sleep you need. However, a more disputed theory argues that long periods of REM increase intelligence. This is mostly true in mammals, but for the exception of the deep-sleeping but deeply stupid duck-billed platypus. Another theory that makes more sense is that the amount of REM sleep an animal gets is related to its safety in its environment....

Ninja Style Sleeping Defenses The more dangerous life an animal leads, the less likely it is to sleep deeply. According to the Sleep Foundation, a particular kind of baboon sleeps on its heels on top of a tree. This helps it stay alert while asleep. Similarly, the golden dormouse can spend a lot of time sleeping by carefully balancing itself on the branch of a tree safe in the knowledge that any quiver of the twig will wake it up immediately.

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Check out lots more dozy animals at CUTE THINGS FALLING ASLEEP