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This section gives you some general tips on using a detector. If you are familiar with detectors or have done the survey before you may want to skip this part.

If you have never used a detector before, you may need to come back to this section again before you go out to do the survey.

For this survey you will be using a bat detector that you can ‘tune’ to pick up different frequencies. This is called a tuneable or heterodyne detector.

Bats find their way around in the dark by echolocating. They make high frequency sounds and listen for the echoes that bounce back to give them information about the world around them.

The sounds that bats make are usually high above our hearing. Human hearing generally can take in sounds up to about 20kHz. Most bat calls are between 20 and over 100kHz, far above our range. The detector brings the frequencies down to around 0.1 – 10kHz so that we can hear them.




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How far away a detector can pick up a bat will depend on how loud the bat is calling and how sensitive the detector is. Some bats like noctules make very loud echolocation calls and can be heard 50-100m away while others like brown long-eared bats may make very quiet calls that can only be heard less than 10 metres away.

In order to get the best out of the detector make sure you hold it towards the bats, keep the batteries fresh and avoid moisture on the microphone.


The Bat Conservation Trust retains intellectual copyright of the material contained in this tutorial.
Any unauthorised use will be considered a breach of that copyright.