Pattern analyses on the vocal structure of calls and geographic variations among three areas

Abstract

Dugongs (Dugong dugon) vocalize several calls in a row. Previous reports showed that dugongs have two kinds of calls: long duration calls (trills) and short duration calls (chirp-squeaks hereinafter called chirps). Vocalization pattern of the dugong were classified and the differences and the similarities in the phonetic structure among different dugong populations are discussed in this paper. We recorded the dugong calls from the southern part of Talibong Island, Thailand (2222 calls in total), Toba aquarium, Japan (694 calls), and Underwater World, Singapore (203 calls). Short duration calls with less than 300 milliseconds were defined as chirps and trills ware defined as a call lasting over 300 milliseconds. The end of a call sequence was defined by a silence over 1 second. Within a call sequence, chirp-to-chirp transition was the most frequent among the 3 groups. Trills appeared at the end of a call sequence. The position of the trill did not differ among the 3 groups. The average of the dominant frequency component of dugong calls collected in Thai waters was 4179.8 + 1630.6 Hz (S.D.), 2567.2 + 1371.3 Hz (S.D.) in Toba aquarium, and 7362 + 1745.6 Hz (S.D.) in Underwater world. This study provided detailed information on the vocalization pattern of the dugong, although the functional use of the calls in the context of acoustic communication is yet to be clarified.