Birds have air bags, air bags connected to the lungs to back up into the air while flying. When birds inhale Air bags expand into the air duct to the air bag back. And air from the lungs to blow into the front air bags. On the exhale Air bags, air intake from the back to the lungs. Air bags and air from the front to the exterior. Thus, each cycle of breathing air to stop the bird to breathe in and out 2 times.