What is the primary function of air sacs in birds?

The primary function of air sacs in birds is to allow fresh air to flow through the lungs even during exhalation. This is a key component of the avian respiratory system, which is highly efficient compared to that of mammals. Birds possess a unique system of air sacs that are interconnected with their lungs; during inhalation, fresh air enters the air sacs while stale air is expelled from the lungs. When the bird exhales, the air sacs contract, pushing the fresh air that was stored in them into the lungs for gas exchange.

This continuous flow of air ensures that birds have a high level of oxygen available for metabolism, which is especially important during flight when their energy demands are significantly elevated. The unidirectional airflow provided by the air sacs means that oxygen-rich and carbon dioxide-rich air do not mix, maximizing the efficiency of gas exchange.

The other options do not accurately describe the function of air sacs. Storing food during flight does not occur in air sacs; instead, birds have other mechanisms for storing food. While birds do regulate body temperature through various means, air sacs specifically are not the primary method for thermoregulation. The filtering of impurities from the air is also performed by structures such as the nasal passages and the respiratory system but