Q1. How far away can a bat be detected using the Anabat bat detectors?
Detection distances vary with frequency and loudness (amplitude) of the bat calls, atmospheric attenuation, the directional characteristics and sensitivity of the bat detector. It is also affected by the amount of structural clutter (obstacles such as vegetation) which can block the path of the signal.
The frequency and amplitude of the bat call has a major influence on how far away the call can be detected. This makes some species easier to detect from afar than others. Quiet (low amplitude) bat calls are more difficult to detect than loud (high amplitude) calls. Call amplitude can vary within an individual (as many bats will reduce the amplitude of their calls as they approach prey or clutter) and also vary between species. Species which always produce low amplitude calls ("whispering bats") will be more difficult to detect from a distance than other species. In addition, bat calls of higher frequencies cannot be detected from as far as those of lower frequencies. Higher frequencies are often absorbed by the atmosphere (attenuate) faster than lower frequencies.
How quickly sounds attenuate in the atmosphere depend upon weather conditions such as temperature, humidity and air pressure. This relationship is complex, but in general, cool dry conditions will allow the detection of bat calls over greater distances.
The sensitivity of the detector also has a major influence on detection distance. While there is always some variability in sensitivity among units, the biggest influence is the setting of the sensitivity control.
Given all the above, it is obvious that detection distances will vary enormously. Many bats are easily detected over 30m under typical conditions, while some species which call at low frequencies may be detectable from as far as 100m. However, some species will be hard to detect from even 1m away. This is why only relative rather than direct statistical comparisons of bat activity are made between species.
Further information on detection distances and the calculation of detection fields and distances can be obtained from Chris Corben’s AnaVolumes software and the associated manual (http://users.lmi.net/corben/Beta/).
Q2. Does Titley Scientific still make radio-tracking equipment?
We no longer make Australis receivers, radio tags, collars or yagi antennas. We do still supply radio-tracking accessories including chargers, car chargers, battery packs, leather Australis cases, canvas yagi antenna cases and coaxial cables for yagi antennas. We also still service Australis receivers and yagi antennas.
Q3. Does Anabat Insight identify bat calls?
Anabat Insight does not identify bat calls to species. It does have a plug-in for BatClassify UK, which will perform automated identification of UK woodland bats. Outside of this region, automated identification is not currently provided.
Anabat Insight does have filters, search and decision tree tools that you can use to build your own automated identification system. If you are not confident with species identification in your region, you can still use Anabat Insight to separate noise files, so that you can reduce the volume of files being sent to an expert for analysis. This will likely save you money on your analysis costs as it will save the expert time.
Q4. What is the difference between a directional and omnidirectional microphone?
Each microphone has an area of detection, the shape of this area relates to the directionality of the microphone. An omnidirectional microphone has a, more or less, spherical area of detection, whilst a directional microphone has a lobed (Christmas tree-shaped) area of detection in front of the microphone (see below).
Typically, a directional microphone will detect a bat from further away, but only directly in front of the detector. An omnidirectional microphone will detect a great volume around the microphone.
Which microphone is best depends upon your recording requirements. For example, a directional microphone may be best if you are recording a reference call and only want to record that particular individual in flight, or if you are conducting an active transect with spotlighting where you can follow the bat with your detector. An omnidirectional microphone with a cone may be best where you are performing a walking transect and you do not want footfall noise. An omnidirectional microphone may be best where you are performing a passive survey where there is no clear flyway. Speak to your local distributor about which microphone may suit your needs best.
Q5. What is the difference between full spectrum and zero crossing?
There are two main recording formats for bat files, zero crossing analysis (.zc, .zca, & .xx#) and full spectrum (.wav). Full spectrum records the full spectral information within a sound file, just like a music file. Whereas zero crossing analysis renders the spectral information down into a series of time vs. frequency dots.
|Full Spectrum||Zero Crossing|
The advantages of full spectrum include the ability to see intensity, harmonics, multiple bats calling at the same time, and faint bat pulses during high ambient noise. The disadvantages of full spectrum are that they are much larger files (typically 6 times the size of a zero crossing file), they require more processing power to record, and are slower to render on a computer for post-recording analysis. The advantages of zero crossing analysis is the small file size, so memory space is not an issue, and many published guides to bat calls are based on zero crossing analysis. The disadvantages of zero crossing are that spectral information is lost (which may be helpful to species identification), and that in cases of high frequency ambient noise (eg. insects), bat calls may not be recorded fully.
It is important to note that post-recording full spectrum files can be converted to zero crossing, but zero crossing files cannot be converted to full spectrum. Deciding which recording format is best will depend on the aims of your survey, the recording environment, and your budget.
Q6. What file types do Titley Scientific detectors record?
There are a number of file types used by Titley Scientific detectors. The Anabat Swift and Anabat Walkabout can record in either full spectrum (.wav) or zero crossing (.zc), you can select your recording format on the detector. The Anabat Walkabout additionally allows you to record both formats at the same time. The Anabat Express will record zero crossing analysis files in .zca format, which records one file per night. The .zca can be split into individual .zc files using Anabat Insight.
Q7. What metadata format is recorded on Titley Scientific detectors?
All Titley Scientific detectors now save metadata in the GUANO (Grand Unified Acoustic Notation Ontology) format. This format is now the standard across bat acoustic fields. GUANO is also supported by the Anabat Insight software package.
Q8. How does Night-Only Mode work?
On the Anabat Express and Anabat Swift, there is a Night-Only mode. This mode uses the built-in GPS to determine your location, it then calculates the sunset and sunrise times, and will automatically record from 30 minutes before sunset, until 30 minutes after sunrise. It will continue to record in this mode until the batteries run flat, the card/s become full, or you turn the detector off. This mode requires a GPS fix when first deployed, so be sure to make sure the Check LED on the front of the detector has stopped flashing to indicate the detector is ready to deploy. You can also use schedule mode to manually specify a location, for situations where GPS is not available.
Q9. What is the difference between Continuous and Constant Recording Mode?
On the Anabat Swift & Anabat Express, you can choose from Night-Only Mode, Continuous Mode, and Schedule Mode. These modes refer to when the detector is active and ‘listening’ for audio triggers. You choose between Night-Only, Schedule and Continuous Mode using the button on the control panel. Continuous Mode will keep the detector awake (day & night) and ready to record whenever a trigger event occurs.
Constant Recording is a different feature available only on the Anabat Swift, which can be used in conjunction with any of the operating modes listed above. This feature can only be turned on using the Settings Menu on the touchscreen. Constant Recording will constantly save files to the card instead of waiting for triggered events. For example, if the Swift has been configured to record Night-Only from 6pm to 6am, with Constant Recording on, each night will result in a full 12 hours of files being recorded. The Swift will automatically create a new file as soon as the maximum file length has been reached, so as soon as one file ends, another will begin. This can be used to record soundscapes, or to record everything where there is a particularly quiet species of interest.
Q10. What is the best way to mount the microphone?
This will depend on your survey aims, however there a few general pieces of advice:
Mount the microphone pointing horizontally to prevent water droplets hitting the microphone element. Such water droplets generate large amounts of noise and can block ultrasound signals from reaching the microphone until they dry out. This needs to be considered when you are analyzing your data. Sensitivity can be reduced by inclement weather. Do not let heavy rain land directly onto the microphone element. The impact force of the raindrops can permanently damage the sensitive element, reducing its sensitivity.
Mount the microphone at a ‘flyway’ if possible (and if not contradictory to survey requirements). A flyway is a corridor where bats will fly through or beside vegetation, such as a track or open gully. Do not point the microphone across the flyway, but instead pointed along the flyway, this will increase your chances of recording a longer, high-quality pass.
Unless specifically required, do not mount a detector directly at a dam/lake. Bats will often change their search phase calls when approaching water to drink, so species analysis may be more difficult. If water is rare in the area, many individuals of multiple species are likely to drink at the water source each night, these datasets will likely contain confounding social calls, and individuals shifting frequency in the presence of conspecifics. Additionally, the water if flat will create a lot of echoes, if turbulent will create ultrasonic noise, and will likely be home to a multitude of noisy insects. Instead place the detector (if possible) along the flyway approaching the water source, or further back from the water’s edge.
Mount the microphone on an extension cable away from flat surfaces. This is especially important if using the omnidirectional microphone. The omnidirectional microphone will record echoes from the surface of the detector if mounted directly to the detector, the same will occur if the microphone is placed next to a large flat surface. If possible, mount on a pole or small post/tree.
Windy, dry conditions can result in electrostatic build-up which may damage the microphone. Also, be aware that mounting your microphone or detector on a tall mast may attract lightning. To minimise the chance of electrostatic damage isolate the detector from ground, i.e. operate it from internal batteries or make sure the external power supply doesn’t have a path to ground. In dry conditions avoid mounting microphones on tall non-conductive masts (inc. fibreglass and nylon), wood or metal masts are preferable. Ground the microphone, either by making sure it is clamped to a properly grounded metal surface directly (metal to metal contact), or by attaching an earth wire to the body of the microphone (e.g. with a hose clamp) and then connect that wire to a grounded surface (e.g. metal mast or ground stake).
For more information on mounting, placement and weatherproofing considerations, see your detector user manual.
Q11. How does Anabat decide when to save a file?
Unless you are using constant recording mode (available only on Anabat Swift & Walkabout), your detector will not be constantly saving files. It will rely upon triggers to decide when to save a file. These triggers can be adjusted by the user to optimize the detection of bats based on local conditions/species. Trigger settings include sensitivity, minimum trigger frequency, maximum trigger frequency, minimum event time, and trigger window. The Anabat Swift allow you to set all the trigger settings on the device, the Anabat Express allows you to change the sensitivity using Anabat Toolbox, and the Anabat Walkabout allows you to change all trigger settings on the go, in addition to manual saving.
Please see individual user manuals for explanations on trigger settings and how to adjust them.
Q12. What is the maximum frequency a microphone can record, and what is a "roll-off"?
Microphones exhibit a ‘frequency response’, which basically means they have differing sensitivities at different frequencies. A microphone may be very sensitive at 40kHz, then lower sensitivity at 60kHz, then be very sensitive again around 80kHz. Microphone sensitivity doesn’t just flat-line at a specific frequency, but has a tendency to ‘roll-off’ around a certain frequency. We refer to this as the ‘maximum frequency’, however the microphone can still detect higher frequency sounds (they just need to be louder or closer to the microphone).
Q13. What is the difference between mono, stereo, dual and simultaneous recordings?
When you have a multi-channel detector (a detector that can have multiple microphones), there is a lot of new terminology to understand what you can and can’t record.
Mono – Mono recording is recording one file from one microphone. This is how our Anabat range of bat detectors work.
Stereo – Stereo recording is recording one file from two microphones. The recording will have multiple ‘channels’, which are slightly different depending on the microphone placement (one microphone will be closer to the sound).
Dual – Dual recording is recording multiple files from two microphones, but not simultaneously. For example, you can record ‘file X’ from the acoustic microphone at 5pm, then record ‘file Y’ from the ultrasonic microphone at 6pm.
Simultaneous – Simultaneous recording is the ability to record multiple files, from two (or more) microphones at the same time. For example, you can record ‘file X’ from the acoustic microphone AND ‘file Y’ from the ultrasonic microphone at exactly the same time.
Q14. What is the difference between acoustic and ultrasonic?
Acoustic and ultrasonic refer to generally accepted frequency ranges. Acoustic is recording audible sounds (eg. bird calls), whilst ultrasonic is recording high frequency sounds (eg. bat echolocation). There is some overlap between acoustic and ultrasonic frequencies. Acoustic generally means between 20Hz and 20kHz, whilst ultrasonic generally starts at 10kHz, extending beyond 250kHz. Microphones are designed to either record acoustic or ultrasonic.