What is a primary benefit of air sacs in birds?

Air sacs play a critical role in the respiratory system of birds, primarily by facilitating a highly efficient and continuous flow of air through the lungs. This enables birds to maintain an optimal level of oxygen exchange even during flight, which is essential given their high metabolic demands. The presence of these air sacs allows for a unique respiratory cycle that includes both inhalation and exhalation phases, which enhances the efficiency of oxygen uptake.

In addition to aiding respiration, air sacs also contribute to thermoregulation. Birds can use them to help dissipate heat while flying or during periods of high activity, which is beneficial for maintaining their body temperature. This function is particularly important in environments where they may experience varying temperatures or need to regulate their body heat quickly during intense physical exertion.

In contrast, options such as storing food during flight or increasing lung capacity do not accurately reflect the functions of air sacs in avian anatomy. Similarly, while buoyancy is important for birds that are aquatic or spend time in water, air sacs are not primarily designed for this purpose; instead, they serve a more crucial role in respiration and temperature regulation.