Abstract: Acoustic communication range estimates for four northern elephant seal (Mirounga angustirostris) vocalization types are presented for this species. Maximum signal detection ranges are determined using an integrated approach involving: field measurements of vocalization source levels and spectral characteristics, signal directivity patterns, natural ambient noise measurements, and previously collected laboratory audiometric data. Signals and masking noise were analyzed using two filter bandwidths believed to approximate the upper and lower limit of auditory filter widths for the northern elephant seal auditory system. Signal detection ranges are estimated for representative pup 'female attraction calls' (FAC), adult female 'pup attraction calls' (PAC), adult female 'threat calls' (AFT), and adult male 'clap threat calls' (AMCT) in each of three intensity categories for biotic noise, wave noise, and wind noise. Signal detection ranges in these nine natural masking noise conditions vary from 5-70 m for FAC, 10-105 m for PAC, 41- 479 m for AFT, and 59-507 m for AMCT. The results demonstrate the extent to which communication ranges in the field can vary depending on call type, signal directivity, ambient noise conditions, and receiver capabilities. These data are also useful in considering natural constraints on acoustic communication in northern elephant seals, selective pressures on signal production and reception systems, and potential negative effects of anthropogenic noise.
Key Words: PINNIPEDS; ELEPHANT SEALS; ACOUSTICS; COMMUNICATION; ACTIVE SPACE; SIGNAL DETECTION; AMBIENT NOISE; MASKING.
Document Type: Research article