Abstract
A behavioral response paradigm was used to measure pure-tone audiograms for two white whales (Delphinapterus leucas). Tests were conducted over a 20 month period at the Point Defiance Zoo and Aquarium, in Tacoma, Washington. Subjects consisted of two males, aged 8–10 and 9–11 during the course of the study. Subjects were born in an oceanarium and had been housed together for all of their lives. Hearing thresholds were measured using a modified up/down staircase procedure and acoustic response paradigm where subjects were trained to whistle in response to hearing test tones and to remain quiet otherwise. Test frequencies ranged from approximately 2 to 130 kHz. Best sensitivities ranged from 40 to 50 dB re: 1 Pa. Both subjects had traditional U-shaped mammalian audiograms; however, one subject exhibited significant high-frequency hearing loss, above approximately 37 kHz. The experimental setup and procedure will be presented and the measured hearing thresholds compared to those previously measured in white whales. The potential role of ototoxic antibiotics in the observed hearing loss will be discussed. [Work supported by ONR Marine Mammal S&T Program and the U.S. Navy CNO(N45).]
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