What structural features have allowed typical flying birds to spread widely across the globe?

Typical flying birds have the following structural features: the front limbs are modified into wings, with the help of which long distances are covered; elongated, tear-shaped body shape, which reduces air resistance; the presence of feathers smooths out irregularities in the body, for example, birds hide their legs in them during flight, and the fluff prevents hypothermia; the bones of the skeleton are hollow, with thin walls – they are light and filled with air; The Y-shaped structure of the chest (keel) in flight cuts the air with a sharp edge, strong pectoral muscles are attached to it.