Peak Frequency of a Pipistrelle

In this video clip the detector is being used to tune into the peak frequency of a pipistrelle.

You can hear how the pitch of the sound changes from a higher note at 45kHz to the deepest pitch at around 48kHz. The type of sound and the richness also changes.

The call changes from quite a high and thin clicking or rattling sound, to a deeper, richer popping as the peak frequency is approached. This is characteristic of the pipistrelles.