Birds have air sacs that store inhaled air and push into the lungs like bellows. This process keeps the lungs filled constantly oxygenated air. Their lungs have millions of teeny-weeny passages that create a large surface area for gas exchange with the blood.
(P.S.) Bellows means, "A device with an air bag that emits a stream of air when squeezed together with two handles, used for blowing air into a fire." courtesy of Google's dictionary. ❤
