Syrinx

A syrinx is a conically shaped vocal organ found in birds, located where the trachea bifurcates into the lungs. It is analogous to the larynx in mammals, though its structure and mechanism of sound production are quite different. Unlike the mammalian larynx, which is located in the throat, the syrinx is located much deeper within the bird's body.

The syrinx consists of cartilaginous rings, membranes, and associated muscles. The exact configuration varies between different bird species. Sound is produced by the vibration of the tympaniform membranes (internal and external), which are located on the lateral walls of the syrinx. These membranes are set into vibration by air flowing from the lungs.

The muscles surrounding the syrinx control the tension and position of the tympaniform membranes, allowing birds to produce a wide range of complex vocalizations, including songs, calls, and other sounds. Different muscles control each side of the syrinx independently, enabling some bird species to produce two distinct sounds simultaneously, creating complex and varied songs.

The complexity of the syrinx and the muscles controlling it are often correlated with the complexity of the bird's vocal repertoire. Songbirds (Passeri) generally possess the most complex syrinxes and the largest number of associated muscles, enabling them to produce the most intricate and melodious songs.

The syrinx is also a significant feature in the study of bird evolution and vocal communication. Comparative studies of syrinx morphology and muscle structure across different bird species provide insights into the evolution of vocal learning and the development of diverse avian vocal repertoires.