The Ark Files - Life on the wing

Birds, bees and bats. They have different body shapes. They have different body coverings. But what they have in common is that they all fly.

Flying mammals

Australian Sugar Gliders have a large cloak of skin stretching from their little finger to their big toe. As they leap from a tree trunk this cloak becomes taut and, with their tail to steer them, they can glide 50 metres to another trunk. As they get close, they tilt upwards to slow themselves down and, once safely landed, gallop up the tree, their furry cloaks tucked away underneath.

Is this flying? Well, not really!

To get into the air you need wings. When a wing beats, it creates high pressure below it and low pressure above, and this produces lift.

Bats are the only mammals that flap their wings for powered flight. Their wings have developed from their arms. Four of the bat's fingers have become very long and have a thin, rubbery membrane of skin stretched between them. Bats roost by hanging upside down, so to take off they can First finger (thumb) . just let go and fall into the air. Ever wonder why there is such a mess below trees where bats are roosting? They are heavier than birds and, after feeding, they must digest their food very quickly, spitting out any undigested food and going to the toilet so they are a bit lighter when flying.

Hot air fliers

Vultures have broad, rectangular wings and circle at very slow speeds, supported by a pillar of rising warm air. Their wing shape allows them to make sharp turns as they twist up within this thermal. When they reach the top, they search for prey by wheeling around and around until they spot a dead or dying animal. Their downward glide is now steep and fast and, as they land on the carcass, they indulge in a noisy feeding frenzy until they are so full that flying is impossible. They just manage to reach a nearby thorn tree and perch there till their meal is digested. Only then will they be light enough to seek out a thermal and take to the skies again.

Humming Birds don't glide or soar; they hover. They fly almost upright and beat their wings so incredibly fast (80 beats per second) that they create enough high pressure below them to hover and fly backwards.

Lift-off

Taking-off can be a problem if you are a heavy bird. You need big wings and powerful wing muscles. A strong wind blowing over your wings can help create the pressure differences needed to produce lift.

The Wandering Albatross is the largest of all flying birds, with a wing span of over three metres. Flapping such huge wings is difficult. When they nest on steep cliffs, taking-off is easy - they just free-fall into the air. But when they nest on the ground in vast numbers, it's a lot more difficult.

No matter how crowded they are and how short of space for nest sites, albatrosses will leave a clear strip of ground beside or right through the middle of their colonies. This is their airstrip and the birds queue up at the end of the runway, facing into the wind, like jet planes at a busy airport. When it is their turn they run into the wind, building up speed by slapping the ground with their large, webbed feet, leaning forward and beating their vast wings as fast as they can. Finally they get the lift needed to soar into the air and across the sea, looking a whole lot more graceful than they did on the ground.

Record breakers

The swift is well named - an African Swift can fly at 170km per hour and as far as 900km a day to collect its insect food on the wing. Swifts have extremely long, curved wings and spend at least nine months of the year continuously in flight, so their rarely used feet have become tiny, grasping hooks. They even mate in mid-air.

The Sooty Tern beats this record. It can fly constantly for three or four years, not coming to land on earth or water until it is time to nest.

The Great Wandering Albatross patrols the Antarctic oceans for hours without a single beat of its wings. Amazingly, these large birds can fly around the globe year after year, swooping to the surface of the water to feed, until they reach seven years of age. Only then will they land on an island to mate and rear their young.

Insect aeronauts

Thrips are tiny insects that live on flowers. They have wings which are only thin rods fringed with hairs. To move from one plant to another a thrip flies. But it is so small, so light and has such weak muscles that it can't beat its wings very well and flying is like trying to swim through molasses. When it sweeps its feeble wings downward, the thrip is sucked upwards and takes off, like a fluff of dandelion.

A Bumble Bee is much heavier than a thrip so it needs stronger wings, and muscles to beat them. A Honey Bee can beat its wings 15,000 times per minute and a Dragonfly reaches speeds of over 30kmh.