How Birds Respire

Respiratory system in birds is the most efficient and elaborate. The birds are very active animals with high metabolic rate, and thus need large amount of oxygen. The respiratory system in the birds is so arranged that there is one way flow of the air through the lungs and the air is renewed after inspiration. In the lungs of birds, tiny thin walled ducts called parabronchi are present instead of alveoli. These parabronchi are open at both ends and the air is constantly ventilated. The walls of parabronchi are chief sites of gaseous exchange. The direction of the blood flow in the lungs is opposite to that of air flow through the parabronchi. The counter current exchange increases the amount of oxygen which enters blood. Lungs in birds are very efficient in this respect as well, because no stale of air remains in parabronchi.

The lungs have also developed several extensions known as air sacs which reach all parts of the body and even penetrate some of the bones. In some birds the air sacs are nine in number which become inflated by air at atmospheric pressure when the rib articulations are rotated forward and upward. The infated air sacs act as bellows and send air into the parabronchi for gaseous exchange.