While the human voicebox can produce only one sound at a time, a bird’s syrinx is a paired structure that allows birds to sing complex, fast-paced songs. Located where the bronchial tubes from each lung come together, both sides are equally capable of producing sound. They can be used in concert to sing two different notes simultaneously and to complete broad sweeps in pitch quickly. In the Northern Cardinal, the left side of the syrinx produces the lower pitch portion of the sweeping notes, while the right side produces the higher pitch portion. Studies of a number of songbird species have shown that potential mates listen closely to song quality and cue in to small variations when distinguishing desirable mates from those who don’t quite have the chops.