What is the main function of air sacs in birds?

The main function of air sacs in birds is to facilitate respiration. Birds have a unique respiratory system that includes air sacs, which play a crucial role in improving the efficiency of gas exchange. Unlike mammals, which have a simple inhalation and exhalation cycle, birds have a continuous flow of air through their lungs.

When a bird inhales, oxygen-rich air enters the lungs and fills the air sacs. As the bird exhales, the air that initially filled the air sacs is pushed into the lungs, where oxygen is transferred to the bloodstream, and carbon dioxide is removed. This one-way airflow means that a bird can extract oxygen from the air even when exhaling, allowing for a much more efficient respiratory process, especially beneficial during activities like flying.

The other options related to digestion, energy storage, and hormone production do not align with the primary physiological role of air sacs in birds. They are not involved in these functions, which solidifies the importance of the respiratory role of air sacs in avian biology.