Bat Detector Bandwidth
That is because heterodyne or tuneable detectors like these can only scan a few frequencies above and below where you are tuned on the dial. This is called the detector bandwidth. Bandwidths are usually +/- 5kHz (check your detector instruction leaflet).
If for example you are tuned at 25kHz with a +/-5kHz bandwidth, you would pick up any sounds up to 30kHz and down to 20kHz.
Because you cannot listen in on all the frequencies at the same time with a tuneable detector, in order to survey for different species we ask you to change the frequency between the walks and spots and listen only for particular species.
When you are out listening for bats in general with a tuneable detector (not during this survey) you can gradually scan up and down through the frequencies to pick up different bat sounds.
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