| How Does Your Bird Breathe? |
| A bird�s respiratory system is unique, and very different from humans and other mammals. Birds have no diaphragm � they have a syrinx at the end of the trachea instead of vocal cords in the larynx. Birds have air sacs and limited lung expansion. Their lungs have air capillaries instead of alveoli. If we understand how a bird breathes, it will help us to prevent and treat disease. Air is inhaled through the nares, and travels through the nasal cavity, being moistened and warmed along the way. The air exits the nasal cavity via the choanal slit. A bird breathes with a closed mouth and �the glottis creates a seal with the choanal slit, allowing air to travel from the nasal cavity to the trachea.� From there, the air goes through the syrinx to the bronchi (the bronchi connect the trachea to the lungs). The lungs have air capillaries interwoven with blood capillaries, which enables gas exchange. Most birds have 4 paired and 1 unpaired pulmonary air sacs connecting to the lungs. These create a large respiratory cavity. Six inspiratory muscles expand the chest by moving the ribs outward and cause air to flow into the respiratory tract (inhale). Nine expiratory muscles cause the ribs and sternum to move inward. This creates an increase in pressure inside the air sacs and causes expiration (exhale). This is why a bird will suffocate if it cannot move its ribs. On each inhalation, half the fresh air goes into the lungs and the other half goes into the caudal air sacs. At the same time, the air already in the lungs moves to the cranial air sacs. When exhaling, a bird moves the air out of its air sacs, and air from the caudal air sacs moves into the lungs. Then the air from the lungs, by way of the trachea, moves out of the body, as does the air from the cranial air sacs. In other words, picture all this happening during an inhalation: fresh air goes into the lungs and into the caudal air sacs AND the air that was already in the lungs goes into the cranial air sacs. Then on the exhalation, the fresh air that was inhaled into the caudal air sacs is moved into the lungs, and the stale air from the lungs and the cranial air sacs is removed from the body. Therefore, in birds, with every inhalation AND every expiration, the lungs are filled with fresh air. The air sacs fill with inhalation and empty with exhalation. This breathing method is much more efficient than ours. �Birds have fresh air (high in oxygen) in the lungs on both inspiration (from the trachea) and on expiration (from the caudal air sacs),� says Dr. Frederickson. And since the air capillaries in birds are smaller and thinner than the alveoli in human lungs, the �blood gas barrier is more efficient.� Diseases of a bird�s respiratory system can have many causes, including nutritional deficiencies, infection, toxins or blockages. Carefully observe the condition of your bird�s nares for any crustiness or discharge. Also watch the bird�s posture � tail bobbing with each breath can indicate a breathing problem. Your vet can visually check the condition of the choanal slit and trachea, listen to the bird�s breathing, take an x-ray, and collect samples for lab tests, if you suspect a respiratory problem. |