The syrinx is the name given to the vocal organ of birds. The syrinx has a similar function to the vocal cords in the larynx (voicebox) in humans, and is the organ that enables songbirds to sing and talking birds (such as parrots and budgerigars) to mimic human speech.
The syrinx is a bony organ surrounded by an air sac and located at the base of the bird's trachea (windpipe), at the point where it forks into the lungs (making it much lower down than the human larynx). Birds have a larynx, but it contains no vocal cords and its only function is to prevent food and water from entering the lungs.
Sound is generated by vibration in the syrinx walls and by tympanic membranes, which vibrate when air passes through the syrinx. The bird changes the sound by changing the tension in the muscles around the syrinx and the entrance to the lungs. This changes the tension of the tympanic membrane, and changes the pitch or tone of the sound (a bit like tightening the skin of a drum).
The bird can change the volume and pitch of sound by adjusting the pressure of air passing from the lungs through the syrinx.
The position at the base of the trachea means the syrinx has two sources of air: one from each lung. The two sides of the syrinx are controlled separately, and these two features enable some songbirds to make more than one sound at a time. The song repertoire seems to be dependent on the size of the song-control area of the brain of the bird. The structure of the syrinx enables birds to make a much greater variety of sound than humans can.
In talking birds, such as the parrot, parakeet or budgerigar, the bird combines an extraordinary control of the syrinx with excellent hearing and a habit of trying to mimic sounds around them. As well as imitating human speech, they convincingly mimic other sounds, such as a creaking door, a telephone ringing, a doorbell, or whistling.
The syrinx is very similar in all birds, and the songs appear to differ because of differences in learning rather than physiological differences. Interestingly, some birds, such as vultures, storks and ostriches have no syrinx, which is why they do not sing, and can only hiss or grunt.
Syrinx comes from the Greek word syrinx meaning pipe or pipe-like object. In classical mythology syrinx was a nymph in Arcadia who was chased by Pan, and who saved her chastity by transforming herself into the reed which Pan then used to make his famous pipes of Pan, the pan pipe.