Respiratory channels are highly developed, enabling the pigeon to fly continuously from 12 to 15 hours. Air circulates through the bronchial tubes and lungs and also through nine air sacs, from which other small, irregular cavities extend under the skin between the muscles, and even into the inside of the bones. These small air sacs contain a reserve of warm air which feeds the lungs during flight when the muscular apparatus consumes a large amount of oxygen. They inflate and collapse alternately, acting as a lift and force pump which renews air in the lungs.
13. Digestive Organs
Digestive organs of the pigeon are shown in figure 3 (for functions see [par. 50b]).
Figure 3. Digestive organs of homing pigeon.
14. Bloom or Milt
This white, chalky powder is one of the means provided by nature to protect feathers against moisture during flight. When the pigeon bathes, the bloom is deposited in the form of a white scum on the top of the water. If a bird is caught and held closely, the bloom rubs off, leaving a white substance on the clothes. Absence of bloom is a symptom of poor health.
Figure 4. A flight.