Fight of a Bird

A very neat explanation of how birds fly and different types of wings

http://en.wikipedia.org/wiki/Bird_flight

So from this article I understood what is required to fly.

Also, it is seen that different types of birds have different wing shapes, heavy birds (like eagle) might have short wing size for easy take off.

One conclusion that I can draw from this article is that no matter the weight, one can fly given type of wing and more important amount of energy expended during flight.