How do birds aid there selves in flying?

If I'm understanding the question correctly, then birds have a number of ways that their bodies have adapted to allow for flight. Some of these would include hollow bones, an enlarged breast bone, rigid skeleton, beaks instead of jaws (less heavy than jaws), and feathers (allows for a more streamlined body).

Flying takes a great deal of energy, which means that birds have a very high metabolism. This leads to a great deal of their time not flying spent eating in an attempt to get enough energy to allow for more flight.