When we look at a bird, we see its chest rise and fall just as a human chest does when we breathe, but what’s going on inside the bird’s lungs is quite different from what’s happening in a human’s.
When a human breaths in, the oxygen-rich air goes into the lungs, oxygen is exchanged for carbon dioxide in structures called alveoli, and carbon dioxide is breathed out. We don’t constantly have air in our lungs: a bird does.
Structure of a Bird’s Lungs and Respiratory System
In a bird’s lungs, air passes through tiny tubes called air capillaries, where oxygen is absorbed into the blood stream and carbon dioxide is expelled. But a bird's lungs don’t expand and contact as air flows through them; instead, muscles in the bird’s chest push air through a series of air sacs arranged around the lungs, and through the lungs themselves.
Some birds have seven air sacs and some have nine, mostly in pairs (there is only one “interclavicular” air sac), all with specific names, but it is easier to understand how a bird breathes if we think of them as posterior air sacs—the ones nearest the tail—and anterior air sacs—the ones nearest the head.
How a Bird Breathes
When a bird breathes in, the muscles in its chest force its breastbone out and draws air in through its nostrils. It will take two breaths before that air is expelled:
- The inhaled air goes into the posterior air sacs.
- Chest muscles force the breastbone in, putting pressure on the posterior air sacs and pushing the air into the lungs, where it passes through the air capillaries.
- Chest muscles force the breastbone out, pulling the air into the anterior air sacs, and pulling a new breath into the posterior air sacs.
- Again the breastbone comes in, forcing the first breath out through the nostrils, and the second breath into the lungs.
- Thus, oxygenated air is constantly moving through a bird’s lungs, allowing it to maintain a high oxygen level in body tissues. This provides for the high energy levels that birds need to fly.
Because the movement of the breastbone is what draws air into a bird’s respiratory system and moves it through, anything that constricts this movement, such as being held too tightly, will kill a bird quickly—something for pet owners and bird handlers to keep in mind.
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Sources:
“Airflow in Birds.” William K. Purves, David Sadava, Gordon H. Orians, and H. Craig Heller. The Life Wire: Student Website for Life: The Science of Biology, Seventh Ed.
Firefly Encyclopedia of Birds. Perrins, Christopher ed. Buffalo: Firefly Books, 2003
"Respiratory System of Birds: Anatomy and Function.” Doctors Foster and Smith. peteducation.com
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