- The respiratory system delivers oxygen from the air to the tissues and also removes carbon dioxide.
- In addition, the respiratory system plays an important role in thermoregulation (maintaining normal body temperature).
- The avian respiratory system is different from that of other vertebrates, with birds having relatively small lungs plus nine air sacs that play an important role in respiration (but are not directly involved in the exchange of gases).
- Lungs lie against the dorsal and lateral walls of the thorax. Using a complex series of air sacs and bronchi, oxygenated air is passed through tubular respiratory surfaces (parabronchi) during both inspiration and expiration.
- The lungs do not expand and contract while they are being ventilated. Respiration is facilitated by movements of the sternum that draw air in and force it out. The sternum pivots on the coracoid at the anterior end while hinged ribs flex allowing the bony plate to lower and raise like a bellows. See the diagram above.
- The efficiency of the system is such that (some) birds may fly above 20,000 feet where there is little available oxygen.