Echolocation signals of Heaviside's dolphins ( Cephalorhynchus heavisidii )

• Published in: The Journal of the Acoustical Society of America 2011, Vol.129 (1), p.449-457
• Main Authors: Morisaka, Tadamichi, Karczmarski, Leszek, Akamatsu, Tomonari, Sakai, Mai, Dawson, Steve, Thornton, Meredith
• Format: Article
• Language: English
• Subjects: Acoustic signal processing; Acoustics; Acoustics - instrumentation; Animals; Cephalorhynchus; Cephalorhynchus heavisidii; Cetacea; Dolphins - physiology; Echolocation; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Physics; Pressure; Signal Processing, Computer-Assisted; Sound; Sound Spectrography; Time Factors; Transducers; Underwater sound; Vocalization, Animal
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.3519401

Field recordings of echolocation signals produced by Heaviside's dolphins ( Cephalorhynchus heavisidii ) were made off the coast of South Africa using a hydrophone array system. The system consisted of three hydrophones and an A-tag (miniature stereo acoustic data-logger). The mean centroid frequency was 125 kHz, with a −3 dB bandwidth of 15 kHz and −10 dB duration of 74 μ s. The mean back-calculated apparent source level was 173 dB re 1 μ Pa p.-p. . These characteristics are very similar to those found in other Cephalorhynchus species, and such narrow-band high-frequency echolocation clicks appear to be a defining characteristic of the Cephalorhynchus genus. Click bursts with very short inter-click intervals (up to 2 ms) were also recorded, which produced the "cry" sound reported in other Cephalorhynchus species. Since inter-click intervals correlated positively to click duration and negatively to bandwidth, Heaviside's dolphins may adjust their click duration and bandwidth based on detection range. The bimodal distribution of the peak frequency and stable bimodal peaks in spectra of individual click suggest a slight asymmetry in the click production mechanism.