Behavioral assessment of in-air hearing range for the Pacific walrus (Odobenus rosmarus divergens)

Abstract

The conservation status of wild walruses (Odobenus rosmarus) is influenced by rapid warming of the Arctic, loss of seasonal sea ice, and increasing pressures related to anthropogenic activities and associated noise. Few data are available regarding acoustic sensitivity in walruses, although the species is known to be vulnerable to human disturbance. Here, we provide new information to describe the range of sound frequencies that are audible to walruses. These data were obtained through partnership with the Walrus Conservation Consortium and two zoological facilities. Two adult female walruses were trained to cooperate in an auditory detection task by responding to relatively high-amplitude airborne tones of approximately 80 dB re 20 μPa. Once performance was reliable, behavioral responses were generalized to a range of frequencies spanning more than six octaves. The upper- and lower-frequency limits of hearing were determined during audiometric testing with fully calibrated sounds. Results confirmed an audible range of hearing extending from 60 Hz to 23 kHz in air. Hearing range in water is expected to be similar or broader at high frequencies. This study provides evidence that hearing in walruses is different from that of other marine carnivores, including seals, sea lions, and sea otters, and better than suggested by early reports for the species.