Two key questions for ecologists, throughout their careers, are:
Am I using the best tools for the job in hand?
Do I know what the best tools are for this job?
Take bird surveys, for example. If you want to carry out a bird survey of a woodland area, which tools and techniques would you use? Perhaps you would take binoculars, a camera, and possibly also a telescope and tripod (as well as a recording form, map and so on). But what are the options for listening to and recording acoustic information i.e. bird sounds?
Recognising bird calls and songs is a key skill when undertaking bird surveys. As with bat surveys, sound recordings can not only provide evidence for use in reports, but playing them back can be a very useful training technique for improving your species recognition.
There are a lot of different options for recording bird sounds and they fall into two general categories; techniques for listening in real time, and techniques for unmanned recording. Remote, unmanned detectors are an excellent tool for gathering data over specific, extended periods of time. But if you want to develop your ID skills, whilst experiencing real time bird activity and behaviour, being in the habitat at the same time as the birds is the best option. So … maybe the best approach is a mixture of both?
The pictures below show examples of these two approaches – a parabolic reflector being used for listening to greenfinches in a garden, and a recorder left overnight by a pool with breeding little grebes and foraging little egrets.
We have been carrying out acoustic surveys for birds for several years – most of this work has made use of sound recording equipment such as parabolic reflectors, a range of cardioid and omni microphones, and recorders such as models from Tascam, Sony and Nagra. I will come back to real-time recording in other blog posts.
We have also started testing some new tools for long-term deployment, sometimes referred to as PAM (passive acoustic monitoring); this has included Audiomoth and Zoom H3 VR recorders. When the Song Meter Mini was released a little while ago, this provided an opportunity to compare our recording setups, and in time we will have thoughts and observations to share on this blog. Deployment sites so far have included woodland, wetland, reedbed and marshy grassland habitats, with a focus on owls, warblers, flycatchers and waders – some example of recording sites are shown below.
Just for now, here are some initial observations about the Song Meter Mini. The unit has a number of benefits – it is waterproof (so far, anyway) and is capable of long deployment times using only AA batteries. Setting up the recorder is quite straightforward, and subsequent deployments are very efficient, although there are some issues with attaching to a substrate (see below for details). The idea of linking the recorder to a phone for set-up is an excellent approach and works well in all light conditions. The Song Meter Mini is small and lightweight – it will easily fit into a coat pocket, with no worries about knocking any of the controls, although the microphone cover is exposed and needs a bit of care to avoid damage to the foam. The microphone is omnidirectional (usually referred to by the shorthand term omni – see footnotes below for an explanation).
The principal benefit of an omni microphone when recording birds is that it enables a wide spatial area to be surveyed; this technique is of particular value when surveying both closed habitats such as woodlands, as well as open habitats such as heathland or grassland sites.
One other excellent feature is that length of recordings can be pre-set, and that recordings can be therefore viewed in manageable chunks. This is not to be sniffed at, and is a huge bonus when ploughing through hours of data.
As with all tools that we use as ecologists, there are limitations to the Song Meter that are worth bearing in mind. Most of these are a result of the very small size of the unit, and the need to accommodate so much technology in a tiny space.
The limitation that I find most frustrating is the lack of a tripod mount on the unit. Although the Song Meter does have a limited variety of holes along its sides, for ties, straps and screws, the lack of a ¼ inch thread means that this standard type of attachment is not possible with the unit as supplied. Use of a tripod (or ground spike, which we often rely on in soft ground) allows very quick deployment and flexibility in the siting of recording devices; this is particularly important in habitats with limited or non-existent attachment possibilities (coastal habitats, marshes and mires come to mind). Linked to this point is that fact that attaching the unit to a tree or fence post can create a limit to the recording, by way of an ‘acoustic shield’ effect, as the tree or post may block part of the sound from reaching the microphone. To overcome this for the time being, we are using a clamp to hold the Song Meter onto a tripod or ground spike.
Other limitations include the tiny switches and writing inside the machine – poor eyesight (a bugbear since my 40s), poor light and the need to wear gloves in cold weather make these quite frustrating at times. Also, there does not appear to be a way of checking that the recorder is working correctly once deployed (e.g. via a flashing light, visible on the outside of the chassis). Checking of recording levels (to ensure that the recording is within acceptable levels and avoids clipping – see footnote) also cannot be checked.
The use of a single omni microphone is a limitation, in that an additional purchase is required to enable stereo recording. However, the quality of the supplied microphone, in terms of its sensitivity and the data recorded is (so far) impressive.
So … what next?
We will continue to test the Song Meter Mini, along with other equipment, as we carry out surveys for birds and other species around the country in 2020; this includes nightjars, ravens, peregrine falcons and deer, as well as barn owls, herons and cuckoos more locally.
An omnidirectional microphone will, in principle, pick up sound equally from all directions. This means that given sufficient sound, recording conditions and microphone sensitivity, whether sounds come from the front, back, left or right side, above and, to an extent below, the microphone will receive the signals.
Clipping of audio is when an audio signal is amplified past the maximum allowed/required limit. This leads to distortion and a lowering of audio quality. You may have experienced this with your bat detector, when it becomes overloaded by a close-flying pipistrelle or noctule, affecting the appearance of the sonograms and the sound quality on playback.