Birds are most striking for the variety of adaptations that optimize flight ability: hollow, lightweight bones; a specialized air-sac breathing system; a large breastbone which affords anchoring large, strong flight muscles; and a rib structure which succors superior body support. Nonetheless, for the most part, birds are pedestrians. Only birds of prey earn their living in the air, and only migratory birds spend a great deal of time in flight.
Most birds forage by walking about, either on ground or in the trees. Birds that feed in the water have long legs for wading. Flight simply serves for an express getaway or a quick commute.