Mechanism of sound production and air recycling in delphinids: Cineradiographic evidence

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Abstract
Soft tissue silicone-casting techniques, spot-film radiography and cineradiography were combined to examine the in situ anatomy and movement of the upper airway structures in live-phonating and dead delphinid porpoises. Three species, Tursiops truncatus, T. gilli and Stenella longirostris were studied under high-speed X-ray motion picture cameras to observe the movements in the laryngeal and nasal regions associated with sound production. Accurate reconstructions of the nasal sac anatomy were made by associating castings of silicone rubber, with various X-ray photographs using radiocontrast materials. Sounds produced during the video recordings were simultaneously recorded through a contact piezoelectric hydrophone and stored on magnetic tape. Movement of the left nasal plug was precisely associated with internal whistle production, and the right nasal plug was speculated to be the source of internal click production. Externally produced sounds were generated at the blowhole and the air supply control mechanism was the same for all 3 types of phonation. The nasopharyngeal air space in the anteroventral portions of the skull and in the bony nares controlled the outward movement of air into the upper passages. The nasopharyngeal muscular pump functioned in withdrawing spent air back down from the upper passages.

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