Acoustic signals and acoustic behaviour of Chinese river dolphin (Lipotes vexillifer).

Chinese river dolphin's (Lipotes vexillifer) underwater acoustic signals can be divided into two classes, short-duration signal (pulse train or single pulses) and long-duration signal (whistle). In this paper, time waveforms of these signals are presented and the characteristics of the signals are discussed. The experimental results on this dolphin's acoustic behaviour are given. A sinusoidal pulse with duration of about 300 ms is used as the calling signal. In a certain frequency range, as soon as a calling signal is transmitted the dolphin answers with 2 or 3 whistles. The frequency range of sensitive response is from 4 to 7 KHz, in which the answering rate reaches 100%. When the dolphin's acoustic signals recorded on the tape are transmitted into the water it swims directly toward the transducer. When noise and music are transmitted the dolphin does not respond at all.