Listen to the following sequence of dugong squeaks and barks. It is in the common MP3 format.
to save with right mouse button, and for playback in Non-Microsoft-Browsers: Dugong's Voice
Dugongs make chirp and bark like sounds, in mother-calf communication and during mating. It is believed that infrasound, which is sound below the human hearing limits, is also used.
This is a spectrogram, the graphic representation of a high pitch squeak.
It shows four (two more unclear) harmonic bands below 10 kHz.
This is a hoarse, bark like call, there are no harmonic bands, frequency below 4 kHz.
(Sound of the Toba Aquarium male grabbed from TV, hence some background noise. Spectrograms made with Avisoft-SASLab Light)
Compare this with the voice of a Manatee. Not unexpectedly it is composed similarly to that of the Dugong, however, it has a greater frequency range, 20 kHz and more.
(the green bottom is caused by background noise)