Nasal Pressure and Sound Production in an Echolocating White Whale, Delphinapterus leucas

Abstract

At the Jersey conference on Animal Sonar Systems in 1979 we gave strong evidence that dolphins produce sound in the nasal system rather than in the larynx as most mammals do (Ridgway et al. 1980). With electromyography (EMG), we studied the activity of laryngeal muscles and nasal muscles, making comparisons between the two groups of muscles during sound production. Certain muscles of the nasal system were active during all dolphin whistles and click trains while muscles of the larynx were active during respiration but not during sound production. Perhaps more importantly, we measured pressure in the nasal cavities and in the trachea adjacent to the larynx. During sound production, intranasal pressure increased markedly but intratracheal pressure remained unchanged. Subsequently, Amundin and Andersen (1983) replicated the EMG and pressure monitoring aspects of our study in Tursiops and Phocoena. Finally, we put a catheter or tube in the nasal cavity and sealed the opening of the tube with a thumb, the dolphin could produce sound with this sealed tube in place, but if the thumb was lifted, releasing pressure in the nasal cavity, the animal could not phonate. In none of the previous studies was the dolphin making an echolocation discrimination during the tests, so we could not be certain that we were studying the actual echolocation generating system. Therefore, we decided to study the Arctic white whale Delphinapterus leucas in a more sophisticated experiment.