It is very possible to watch bats without any equipment, especially where they emerge from roosts, or shortly after dusk along well used bat flight paths. However as bats echolocation is mostly beyond the range of human hearing, a bat detector is essential if you want to hear bats to locate them, learn more about them, and be able to understand the differences between species.
Recent advances in bat detector technology mean that some advice on the internet is now out of date. So the summary of our current advice for 2020 is:
- For a naturalist, or interested amateur, wanting to listen to bats echolocation then a basic Heterodyne detector like the Magenta 5 is ideal (£87)
- For a committed amateur, or Ecologist, wanting to automatically identify species, or record the echo-location calls for later desk analysis an Echo Meter Touch 2 (£200-£360), used with phone or tablet is a great tool
- Don’t forget a good head torch for hands free illumination – The LED Lenser MH6 (£45) is a favourite
(Prices from Jan 2020)
Details of each type of detector below:
Heterodyne Bat Detectors
Heterodyne bat detectors are tuneable, you select the frequency range to listen to, and bat calls near that frequency are converted to sounds which you can hear.
The bat calls are picked up by an ultrasonic microphone and compared against the frequency you set. A sound is then produced that is the difference between the set frequency, and the part of the bats call close to that frequency.
They produce sounds that are quite melodic and easy to listen to, and you will hear descriptions such as “wet slaps, dry clicks, whipcracks…”. With experience it is possible to identify some species with heterodyne detectors.
There are many detectors available, the following are tried and tested:
- Magenta 5 (£87) – this is a good quality basic detector. Simple digital backlit tuning, inbuilt torch, and fairly loud volume. The group has three sets of a dozen of these for loan on Bat walks, and has had great after sales service from the manufacturer.
- The BatBox III D (£157) in various versions has been the “go-to” bat detector for group members. Still a solid choice.
- The new kid on the block is the Elekon Batscanner (£219), this has the huge advantage of scanning all frequencies simultaneously, and then automatically tuning to, and displaying, the strongest ultrasound frequency. There is also a unique Stereo version (£265), that when used with headphones reportedly indicates which direction a bat is coming from.
There are other cheaper options for those on a budget:
- The Magenta 4 (£60) is as good as the Magenta 5 for listening to bat calls, but has a simpler analog tuning dial and no backlight.
- For those with good soldering skills there is the Magenta 2 kit (£46), which when assembled (approx 2 hours) produces a device very similar to the Magenta 4.
- The budget option is the Haynes Do-It-Yourself Bat Detector Kit (£20), this is easy to plug together and works fine. The major drawback are, there is no calibration of the frequency tuning, and it assembles into the cardboard box it comes in.
Full Spectrum Bat Detectors
These detectors record sounds at their original frequencies, i.e. ultrasonic sounds are not converted to a lower frequency in order to make them audible. They offer the ‘best of both worlds’ able to capture sound in the same high level of detail as Time Expansion, but they record in real time continuous monitoring as with Frequency Division. Hence they have become “the standard” with professional ecologists, either handheld, or as “static” devices left out in the field recording for many nights at a time. The recordings made are then downloaded, and analysed later.
The resulting sound files are very large so these detectors tend to use a triggering system so that recordings are made only when sounds are above certain frequency and amplitude thresholds.
Until very recently these detectors were in the highest price range for detectors and hence quite rare in amateur hands. However recent advances in mobile technologies mean there are now affordable options:
Echo Meter Touch 2 EMT2 (£200-£360)
This is a combination of a Ultrasonic microphone that plugs into your phone or tablet, and software that you install. With this you can listen to, record and view ultrasonic echolocation calls on a colorful, interactive spectrogram. The software can even suggest the most likely species detected.
There are currently three versions of the EMT:
- Echo Meter Touch 2 Pro (£360) – The industry standard, lower noise, a few more settings, and more sensitive at higher frequencies.
- Echo Meter Touch 2 (£200) – “Good enough” for most none pros. For most bats it is similar to the Pro, but is poorer at highest frequencies, and hence it will miss some of the quieter Lesser horseshoe calls.
- The original black Echo Meter Touch, is no longer made, but fell between the two above in price and performance.
In practice results do vary, in general:
- The software works better on faster, more expensive devices, and the application is more stable and reliable on iOS (iPhone) devices, than on Android (6.0+)
- Its important to check your device is compatible.
- Depending on speed of device, there is some lag as the software analyses the sound from the microphone, hence its difficult to match echolocation with bat behavior (feeding buzzes etc..)
- The software can mimic Heterodyne or Time Expansion output to the speaker, but again this can be laggy or broken up sound, and is worse on slow devices.
However having said this, the combination of near real time graphs of frequency detected over time, and auto ID, of species mean that a novice with a EMT2 will usually detect more bats, than a seasoned bat worker of 25+ year experience with their trusty Heterodyne detector. The book by John Russ, British Bat Calls, is very useful in understanding the displayed sonograms.
So complete has been the revolution, that there are young bat ecologists starting their careers, that only talk about “hockey stick” , or “staple shaped” calls, and have never heard a bat call via a heterodyne detector.
However many ecologists use both devices in tandem:
- A EMT with sound off, to detect bats onscreen, and check peak frequencies.
- Then a Hetrodyne detector to tune to the specific frequency identified on the EMT, to enable watching of bat behavior and hear echolocation in real time.
As stated above, static full spectrum devices like the Song Meter SM4Bat (£1230) are often deployed by professionals in the field for weeks at a time. But the cost prohibits amateur use, the group does however have an Anabat available for loan to members.
However a partnership between Oxford and Southampton Universities has produced the AudioMoth (£60), a tiny, low cost, static ultrasound recorder. While the AudioMoth is more noisy, and not as sensitive as professional equipment, its low cost means it can be deployed in many different situations without worry.
The device has been trialed by the BCT over the past couple of years as part of their British Bat Survey, but it is still at early stages of development. Hence some DIY skills are needed to produce housings, and software skills are needed to configure for use. A couple of our group members have Audiomoths and are working with them, so you can expect to hear more about them over the coming year.
Where to buy a Bat Detector?
Bat detectors are mostly sold online. A web search of “bat detector” will bring up links to the major retailers. The Bat group has used the following suppliers over the years, with good service:
Other older types of Bat Detector
There are older technologies of bat detectors that have now largely been replaced in the professional field by full spectrum devices.
Frequency Division Bat Detectors
These detect all frequencies at the same time so there is no need to tune and you don’t risk missing any species. Recordings are made by the device dividing the frequency by a known factor (usual 10x) so the calls can he heard and be recorded for later analysis on computer (usually by a separate recorder). Sonograms are not as good as those produced by other types, but OK for species identification. The big downside is that frequency division is not a pleasant noise to listen to for any length of time and you do not get the pleasing tones of a heterodyne detector.
Common Frequency Division devices are:
- The Batbox Duet (£255) has been a standard of the bat group members for many, many years. It has both systems but only the heterodyne signal is fed to the speaker, with the frequency division and heterodyne signals being feed to separate channels of the line out socket. A separate recording device is used to make recordings for later analysis with free software.
- The Batbox Baton (£78) has just frequency division and produces sonograms as good as the Duet. It also comes with Batscan software.
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, so it misses some bat calls. The other disadvantage is cost – typically over £1000.
The group has one Petterson D240x available for loan to members