Although birds have air sacs that work in the process of respiration, they also have lungs. What they don't have is a diaphragm to power inspiration and instead, rely on intercostal muscles (rib muscles) to raise their chests to breathe.
This should be considered when restraining birds and care taken not to constrict their chest area too tightly.
Air sacs are found in the thoracic area (chest), abdomen and bones. The number of air sacs present varies by species; loons have 10, song birds 7. I don't know how many chickens have.
Major bones are `pneumatic', either perforated with connections to the air sacs or filled with hollow cavities. Because birds lack sweat glands, the air sacs not only aid in respiration but also help to cool the bird. Air flows over the moist surfaces of the air sacs causing evaporation. Unlike mammals, birds must take two breaths to complete the cycle of respiration.
A basic explanation of a complete respiratory cycle for a bird is as follows:
1. First Inhalation. Air flows down the trachea into the lungs. The abdomen expands on inhalation and this pulls the inhaled breath from the lungs into the posterior abdominal air sacs.
2. First Exhalation. The bird's abdomen contracts forcing the air in the abdominal sacs back into the lungs. This is when the exchange of oxygen for carbon dioxide occurs and the air is oxygenated.
3. Second Inhalation. As the bird inhales again, the air in the lungs is driven out and the stale air full of carbon dioxide now passes into the anterior thoracic sacs.
4. Second exhalation. The anterior air sacs contract and this drives the stale air out of the thoracic sacs into the trachea where it passes out of the nostrils completing the respiratory cycle.
Kind of interesting, eh?
Sue
WLR
CHICKENS-101@yahoogroups.com
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