Birds

Hi, This particular motion is called gliding. These birds spread their wings to increase the overall area of their body. Now the net upward thrust increases as the area increases. This force is called buoyant force. It is because of this increased upward force these bird can glide without even moving their wings. But they can't do it for long. Why can't some birds do the same thing? Its because even if they spread their wings wide apart, the area is not sufficient enough to provide the force that may let them float like that. The heavy ships made with iron also floats on water with the same principle. Thanks God bless you

As far as humming birds are concerned this page might help: http://www.humming-birds.com/facts.html The are very fascinating they can even fly upside down.