Below: picture shows the flapping motion of a common bird.

The ability to fly is surely the most remarkable feature of birds. Other creatures such as insects and bats can fly, but it is birds that have made the sky their own. Nevertheless, for all the work that has been done on aerodynamics, we still know remarkably little about some aspects of bird flight. Aircraft engineers have tended to study the fixed wings of aeroplanes. But the bird's wing is flexible; birds can alter not only the size of the wing, but also its shape. An aeroplane flies because its wings generate enough lift by the plane's forward movement threw the air to overcome its weight.