The adaptability of the skeleton of birds to flight

1) To facilitate the skeleton, the bones are hollow, filled with air (air sacs).
2) To facilitate the skeleton, the number of bones is reduced, especially in the wings and legs.
3) There is a keel for attaching powerful flying muscles.
4) The forelimbs turned into wings, so you have to walk on two legs. To reach the ground, large birds have a long flexible neck.
5) The lumbar vertebrae, to create good support, are fused with each other, with the sacral and caudal vertebrae, as well as with the ilium.