Birds Spring Morning

Sing the sweet song of a cool, crisp spring morning with nature's chosen trumpeters. A bird's voice box is called the syrinx; it is a bony structure at the bottom of the trachea. The syrinx and sometimes a surrounding air sac resonate to vibrations that are made when the bird forces air past special membranes. The bird controls the pitch by changing the tension on the membranes and controls both pitch and volume by changing the amount of exhalation. It can control the two sides of the trachea independently, which is how some species can produce two notes at once.