Study of the relationship between sound signals and behaviors of a sperm whale during the hunting process

Abstract

In order to study the relationship between the vocal law and the hunting demand of a sperm whale in the process of approaching and capturing prey, time domain characteristics such as waveform amplitude and inter click interval (ICI) and frequency domain characteristics such as centroid frequency and rms bandwidth of the sperm whale pulses are calculated firstly. Secondly, the sonar waveform parameters such as range resolution, speed resolution and Doppler tolerance are calculated using the wideband ambiguity function (WAF). Finally, variation of the above seven parameters is analyzed. The results show that the seven parameters change continuously during the hunting process. When switching from the approaching stage to the capture stage, the values of waveform amplitude, inter click interval, centroid frequency and range resolution will decrease, the values of speed resolution and rms bandwidth will increase, and the values of Doppler tolerance remain relatively unchanged. By analyzing variation of the seven parameters of the pulses and the hunting demand of the sperm whale in different hunting stages, we can better understand the relationship between the vocal law of the sperm whale and its hunting demand. We prove that the click pulses of the sperm whale transmitted during the stage of approaching and capturing prey are Doppler tolerant signals. The sperm whale constantly changes the ICI and signal forms of the transmitted signals during the approach and capture stages to adapt to different hunting demands at different hunting stages. Unlike the sonar signals of bats, the sperm whale does not change the length of the signals when switching from approach stage to capture stage, and instead it will reduce the peak pressure of the clicks significantly. The click pulses of the sperm whale in the process of approaching and capturing prey are more likely specially designed to accurately distinguish the position rather than the speed between targets, which is similar to the results of the previous research on dolphins.