Sound Production: Vertebrates

Abstract

This article compares the mechanisms of sound production in frogs, toads, birds, and mammals. The production of sounds for acoustic communication generally involves two steps. Sound is first generated in the vocal organ and then modified as it passes through the vocal tract. In terrestrial mammals and anura, sound is generated by the oscillation of vocal folds in the larynx. The acoustic variety of vertebrate vocalizations reflects in part the morphological diversity of their vocal organ, particularly the vocal cords. Birds have a unique vocal organ, the syrinx, which is located at or near the caudal end of the trachea. Oscine songbirds have increased the spectral and temporal diversity of their songs by exploiting their ability to independently control the sound produced on each side of their syrinx. Resonance filters in the vocal tracts of all these animals can produce formants that may be important information-bearing elements in a vocalization. Sac-like out-pouchings of the vocal tract or vocal organ may act as Helmholtz resonators or may provide a low-impedance pathway for sound to pass from the vocal tract into the external environment. In response to the special demands of a marine environment, toothed whales have evolved a sound source in their nasal passages. The sound from this source is channeled through acoustic fats that focus it into a forward directed beam.