The avian respiratory system is unique. It differs from mammals in that birds have no diaphragm, have a syrinx at the end of the trachea instead of vocal cords in the larynx, and have no epiglottis.
Birds also have air sacs, limited lung expansion, and air capillaries instead of alveoli.
It is important to understand how this system works in order to prevent, diagnose and treat disease. When a bird breathes, the mouth is closed and the glottis creates a seal with the choanal slit, allowing air to travel from the nasal cavity to the trachea. From the trachea the air travels through the syrinx into the bronchi, which connect the trachea to the lungs. The lungs, which are attached to the backbone, have air capillaries that are interwoven with blood capillaries for gas exchange. Most birds have four paired and one unpaired pulmonary air sacs that connect to the lungs to create a large respiratory capacity.