Recording common dolphin whistles aboard the Anna M

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Figure 1. Spectrograms

Spectrograms are used by scientists as a way of visualising animal sounds. This spectrogram shows two common dolphin whistles recorded in the Irish Sea. The frequency ranges from very low pitch sounds, below 0.5 kHz, to very high pitch sounds above 20 kHz (the upper limit of human hearing). The time of the first whistle shown is quite long - about 1.5 seconds. The red colour indicates that it is also quite loud (the yellow colour showing quiet background noise). If it were slowed down this whistle would sound rather like the three note high-low-high whistle people commonly use to attract one another's attention.

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