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Adapted for flight
A female hen harrier has a wing span of more than a metre
Gliders
Some animals are gliders. Flying squirrels, for instance, can glide over 100 metres between one tree and another by jumping off and stretching out special flaps of skin between their limbs. But gliding is not the same as flight, since there is no power behind it. It’s like throwing a paper aeroplane – which soon falls to the ground.
Other flyers
Only some animals can fly properly. Most winged insects can do it, such as flies, moths and dragonflies. Bats are the only true flying mammals – their wings are made of skin stretched out between special long finger bones.
Flying machines
Birds are the champion flying machines of the animal world. Their bodies are designed for it. Instead of arms, they have wings to power them along. Instead of heavy jaws and teeth, they have lightweight beaks. And instead of fur, they have feathers – which are light, streamlined and cleverly adjustable for flight control.
Egg weight
Laying eggs gives birds another advantage for flight. Unlike mammals, such as humans, a young bird develops outside its mother’s body – in the egg. So the mother has less weight to carry. This may be why the largest egg of any bird relative to its size is actually laid by the flightless kiwi. This huge egg takes up one third of the mother’s body before it is laid. There’s no way she could fly and carry the egg, even if her wings worked.
Last modified: 01 March 2005