The syrinx.

Birds contribute prominently to the terrestrial soundscapes on Earth. The sounds can arise from different sources, such as drumming by woodpeckers, bill clapping by storks or feather vibrations in the courtship flights of snipes and hummingbirds. However, most avian sounds are generated in the avian vocal organ, the syrinx. Vocal behavior is used in many different contexts and features prominently in mate choice and reproduction. It is therefore thought to have played an important role in the remarkable diversification of birds.