Finding The Peak Frequency

A useful skill to help you to identify bats with a tuneable detector is to find the ‘peak frequency’ of a sound.

To do this when a bat comes by, you wobble the dial to a slightly higher frequency and then to a slightly lower frequency. In one direction the tone or pitch of the sound will generally become noticeably lower and in the other direction it will become higher.

Continue to turn the dial in the direction of the DEEPENING note. The sound should also start to get louder.

When you get to the deepest note you can read the dial and that should give you the peak frequency the bat is using. It is usually just beyond the loudest frequency.

Many bat species use typical peak frequencies and finding this can help us to identify them.

Some typical peak frequencies:

• Noctule bat 21kHz or below
• Serotine bat 25 - 32kHz
• Common pipistrelle 44- 48kHz
• Soprano pipistrelle 52 - 63kHz
• Lesser horseshoe bats 110kHz
• Greater horseshoe bats 81kHz

The Myotis bats (whiskered, Brandt’s, Daubenton’s, Bechstein’s and Natterer’s bats) and also long-eared bats, usually use a very short call and the peak frequency is much less obvious heard through a heterodyne detector.