Auditory sensitivity of northern fur seals ( Callorhinus ursinus ) and a California sea lion ( Zalophus californianus ) to airborne sound

Aerial audiograms were obtained in a specially constructed acoustic chamber from three otariid pinnipeds—two yearling female Callorhinus and one 2-yr-old female Zalophus. A “go/no-go” response procedure was used and threshold estimates were obtained by a tracking method. Behavioral measurements at 1, 2, 4, 8, 16, 24, and 32 kHz resulted in average thresholds for the two Callorhinus, in the order of frequencies given above, of 29, 9, 22, 13, 7, 22, and 34 dB re0.0002 dyn/cm2, and for the one Zalophus they were, respectively, 41, 19, 26, 16, 28, 37, and 61 dB re 0.0002 dyn/cm2. The thresholds for Callorhinus, although inferior in air compared to in water, show good accommodation for hearing airborne sounds. The present results from Zalophus indicate that a previous study [R. J. Schusterman, J. Acoust. Soc. Am. 56, 1248–1251 (1974)] was noise limited in threshold determinations below 24 kHz. Although only a limited number of species have been looked at, the otariid pinnipeds appear to be more sensitive to airborne sounds than do the phocid pinnipeds. [Work supported by ONR.]