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The respiratory system of birds is uniquely adapted to meet their high oxygen requirements, which are essential for flight. Birds have a highly efficient system for gas exchange that is distinct from that of mammals. One of the primary adaptations is the presence of air sacs, which are absent in mammals. Birds possess a set of anterior and posterior air sacs that function as reservoirs, facilitating a continuous flow of air through the lungs during both inhalation and exhalation. This arrangement allows for a more efficient exchange of gases, ensuring that oxygen is delivered to the bloodstream more effectively. The lungs of birds are relatively small and rigid compared to those of mammals. Instead of the spongy, expandable lungs seen in mammals, bird lungs are structured ____ ______ _____ _________ ____ _________ _____ ______ ________.
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