The vocal tract is that cavity in animals an humans, where sound that is produced at the sound source (larynx in mammals; syrinx in birds) is filtered. In birds it consists of the trachea, the syrinx, the oral cavity, the upper part of the esophagus, and the beak. In mammals it consists of the laryngeal cavity, the pharynx, the oral cavity, and the nasal cavity, and in some nonhuman mammals maybe also the airsacs.