Wild dugongs’ vocal responses to conspecific calls

• Published in: The Journal of the Acoustical Society of America 2006-11, Vol.120 (5_Supplement), p.3152-3152
• Main Authors: Ichikawa, Kotaro, Arai, Nobuaki, Akamatsu, Tomonari, Shinke, Tomio, Adulyanukosol, Kanjana
• Format: Article
• Language: English
• Subjects: Dugong; Marine
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4787822

Wild dugongs were found to call back more to conspecific calls than to artificially synthesized sounds. The population was exposed to four different playback stimulii a wild dugong chirp, a synthesized down-sweep sound similar to the dugong chirp, a synthesized constant-frequency sound, and no sound as a control. Vocalizing dugongs were localized using an array of stereo-underwater-recording systems. Wild dugongs vocalized more frequently after the playback of dugong chirps (2.8 calls/min) than those of constant-frequency (0.55 calls/min) and control (0.2 calls/min), (p>0.01, Kruskal-Wallis test). Dominant frequencies of response calls were 4810 Hz to dugong chirps and 4470 Hz to down-sweep sounds. These were higher than those to other stimuli (3794 and 4044 Hz). Distances of calling-back dugongs from the playback speaker were significantly shorter for dugong chirps (10.19 m) and down-sweep (19.02 m) than that for constant frequency (105.84 m) (p>0.001). The observed dominant frequencies of response calls (4510 Hz) were above the cutoff frequency of Lloyd’s mirror effect in shallow waters of the present study. Frequency-modulated narrow-band sounds like chirps travel longer and enable accurate measurements of source directions by binaural receivers. These suggest that chirps could be used for conspecific recognition in noisy acoustic scenes in tropical shallow waters.