What is the relationship between the external and internal structure of the bird with the mode of movement?

The external structure of the bird has the following features: the forelimbs are modified into wings, the streamlined shape of the Y-shaped body of the chest (keel) reduces resistance to air flow during flight, hollow and light feathers smooth out irregularities in the body, warm and light down protects from hypothermia at high altitudes … The internal structure of the bird has the following features: strong pectoral muscles that ensure the duration of the flight, a hardy heart, the presence of air sacs in the chest, thin and hollow bones.