ACOUSTIC-SIGNALS OF SOLITARY DUGONGS - PHYSICAL CHARACTERISTICS AND BEHAVIORAL-CORRELATES

We describe frequency and amplitude patterns of sounds produced by individually identifiable wild dugongs (Dugong dugon) in Shark Bay, Western Australia. Chirp-squeaks, barks, trills, and sounds transitional between chirp-squeaks and barks and trills (prebarks and pretrills) are defined. Chirp-squeaks are frequency-modulated signals in the 3 to 18-kHz range lasting ca. 60 ms. Trills last as long as 2,200 ms, are frequency-modulated over a bandwidth of 740 Hz within the 3-18-kHz band, and have two to four or more harmonics. Barks are broadband signals of 500 to 2,200 Hz lasting 30-120 ms with up to five harmonics. Dugongs may produce all of these sounds in the frontal region of the head rather than in the larynx. Chirp-squeaks, recorded from at least nine individuals, were emitted as dugongs rooted in the bottom or patrolled mutually exclusive activity zones, but not when dugongs were stationary or were investigating the research vessel. Frequency and amplitude modulation of chirp-squeaks suggests a ranging function. Variability among individuals in chirp-squeak characteristics may be adequate for a signature function. Barks have physical characteristics appropriate for aggressive behavior. They were recorded in circumstances suggesting territorial defense. Trills had characteristics more appropriate to affiliative functions and were associated with movements that appeared to be displays.