In-air and underwater hearing sensitivity of a northern elephant seal (Mirounga angustirostris)

In-air and underwater sound detection thresholds were obtained for a female northern elephant seal (Mirounga angustirostris). Hearing sensitivity in air was generally poor, but was best for frequencies between 3.2 and 15 kHz, and showed greatest sensitivity at 6.3 kHz (43 dB re: 20 µPa). The upper frequency limit in air was approximately 20 kHz. The underwater audiogram is similar to those obtained from other phocids in that sensitivity was best between 3.2 and 45 kHz, with greatest sensitivity at 6.4 kHz (58 dB re: 1 µPa) and an upper frequency cutoff of approximately 55 kHz. The elephant seal was more sensitive to low frequencies (<1 kHz) than other pinnipeds tested. Thresholds obtained in water were lower than those obtained in air (19 dB in terms of sound pressure, 52 dB in terms of sound intensity), indicating that the elephant seal is adapted for underwater hearing. The outer and middle ears of the elephant seal are modified relative to those of other phocids. These modifications are probably needed to cope with extreme static pressures related to deep diving, and are likely to confer relatively good auditory sensitivity under water.