THE VOCALIZATION MECHANISM OF THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

The mechanism by which Florida manatees produce vocalizations is unknown. Anatomically, the laryngeal region in manatees lacks clearly defined vocal folds. Initially we developed a method to visualize the entire manatee upper respiratory system. We then forced air through fresh necropsied manatee larynxes and generated artificial vocalizations which closely duplicated the normal vocalizations produced by live manatees, both in fundamental frequency and structure of harmonics. Here we report that sound is generated in the larynx when air vibrates bilateral strips of tissue embedded in the lateral laryngeal walls which are in close approximation anteriorly but which diverge posteriorly. We propose that these strips of tissue are the modified vocal folds containing ligaments and we support this through histological stained sections and because they are connected anteriorly to the posterior side of the thyroid cartilage and posteriorly with the arytenoidal cartilages. We also suggest that these vocalizations are then modified within the resonance cavities in the frontal area of the head and the air used to generate these vocalizations also causes a transient deformation of this region before being conserved and returned to the lungs.