Which Bat Detector?

We are often asked by new bat group members for advice on which bat detector they should buy. A search on the internet will find lots of different models at all price ranges so it’s not surprising that people get confused. Hopefully the information below will help you to decide.

What do you want to use it for?

A stupid question you may be thinking but read on. If you want a detector to take on batwalks then a simple heterodyne type will be all that you need. If however you want to be able to record calls for later computer analysis then you will need a frequency division or a time expansion model plus an extra device to record the calls onto (tape recorder, minidisk or digital recorder).

Heterodyne Bat Detectors

These are perhaps the most useful type of detector out in the field. You tune the detector to a chosen frequency and it will pick up bats that are calling close to that frequency. Depending on the frequency tuned to, the tone of the call will give an indication of the species of bat. Heterodyne detectors have a bandwidth of about 8khz either side of the tuned frequency so if you are tuned to 40 kHz you will pick up calls from 32 to 48kHz. Therefore you risk missing bats that are not calling within that bandwidth e.g. noctule and horseshoe bats. The secret is to keep the frequency dial moving. Most models have a recording output but the only analysis you can make would be of pulse rate as no frequency information is included.

Look for a model with a digital display for accurate frequency readout like the Batbox IIID (approx£150) or the Magenta Bat5 (approx £95). If you think you will use the frequency division feature then the Batbox Duet (approx £250) would be my first choice.

Frequency Division Bat Detectors

This type of detector detects all frequencies at the same time so there is no need to tune and you won’t risk missing any species. Recordings made using frequency division can be recorded for later analysis on computer. Sonograms are not as good as those produced by time expansion but OK for species identification. Now the bad news – frequency division is not a pleasant noise to listen to for any length of time and you get none of the tonal variation of a heterodyne detector.

The Batbox Duet has both systems but only the heterodyne signal is fed to the speaker/headphones leaving the frequency division part for recording only. The Batbox Baton (approx £70) has just frequency division and produces sonograms as good as the Duet. It also comes with Batscan software. The popular Anabat system uses frequency division but is very expensive (£1400). If you want to record calls you will also need to budget for a recording device (a future article perhaps)

Time Expansion Bat Detectors

Time expansion detectors work by storing the call in their internal memory and then replaying it back 10 x slower thus lowering the frequency. The advantage of this system is that all frequency information is retained for later analysis. A major disadvantage is that when it is playing back a call it can’t listen for other bats. The other disadvantage is cost – typically over £1000.