Passive Sound-recording

A sample from an impressive morning of VISMIG at Tarifa. Here the parabola and recorder were left to record on the southern limit of Spanish soil, as birds flew south to the northern limits of Morocco, visible in the background. Listen as several groups of Tawny Pipit (Anthus campestris) , Yellow Wagtails (Motacilla flava) & Tree Pipits (Anthus trivialis) depart Europe for the impending winter season. Photo: Seán Ronayne.

1. WHAT AND WHY?

Passive sound-recording (PSR) is viewed upon by some as “cheating”, in that it is achieved without the operator present. NocMig is one of the more famed members of the PSR family, but can also be carried out during the day. Another example of PSR can be achieved with the use of “drop-rigs”. Drop-rigs are typically water-proofed, compact recording devices which, as the name suggests, dropped off at a location of choice, usually, but not always, with a particular target in mind. The device is set or programmed to record of its own accord, without the need for a physical presence. Whatever the view on the authenticity of the technique, there is no doubt that it is very effective and can produce show-stopping results. Read on for a list of some of the numerous positives associate with PSR:

  • Animals (birds, mammals or otherwise) can be sound-recorded in more natural circumstances, as they are not influenced by the operator’s presence.
  • It is possible to obtain extremely close recordings of your target, with some careful planning.
  • Because drop-rigs can be placed right at the point where an animal is expected to vocalise, a high-quality audio can be obtained with even the cheapest of equipment.
  • Shy or nocturnal species can readily be recorded using this technique.
  • One can amass a very large volume of data (up to several months or more) without having to put in the man-hours, in the field (it will still require man-hours to process and edit).
  • It means you can never be too busy to record!
  • It’s exciting! When it comes to retrieving the device, the mystery of what may or may not have been captured can be thrilling, although it can be equally nerve-wracking, wondering whether or not your device has been stolen or damaged.

2. WHAT DO I NEED?

An audiomoth ready for deployment in the territory of an extremely mimetic Red-backed Shrike (Lanius collurio) , in the Catalan Pyrenees – Summer 2020. Photo: Seán Ronayne.

Passive-recording can be achieved with all manner of devices. Because the unit can be placed right at the point where you expect your target to vocalise, you can obtain extremely nice results with even the cheapest of equipment. To keep things simple, and to demonstrate this point, we will talk you through the three pieces of kit we currently use to passively record, with a very impressive bonus setup used by Cork-based birder Thomas Wallenda.

An audiomoth in deployment in Catalunya, mid-summer 2020, at a site which held high densities of both European & Red-necked Nightjars (Caprimulgus europaeus & Caprimulgus ruficollis) . With a little bit of creativity, these devices can be concealed extremely well. Photo: Seán Ronayne.
The elusive (sometimes!), nocturnal nature of Red-necked Nightjar (Caprimulgus ruficollis) makes this a subject well-suited to the PSR style. Listen below for a sample recorded by the audiomoth photographed above. Photo: Seán Ronayne.

Let’s start with the deservedly popular, and amazingly versatile Audiomoth. Despite being the size of a matchbox, this little device packs a powerful punch. It takes three AA batteries and can last weeks in the field. It is highly programmable and gives you to power to tell it when and for how long to record. It is easily water-proofed, using a ziplock bag, or a small junction-box with a small opening, sealed with light plastic. To demonstrate what this gem is capable of, let’s take a look at some of our favourite passively-recorded tracks using the device.

This old Catalan farmhouse, seemingly quiet at first glance, was a hive of Rock Sparrow (Petronia petronia) activity, as revealed by an Audiomoth deployment. Photo: Seán Ronayne
Rock Sparrow (Petronia petronia) – Summer 2020 – Catalunya. Seán was having great difficulty recording this species so he deployed an audiomoth on the stone ruins of an abandoned farmhouse. Seán knew it held a colony of Rock Sparrows, as his survey route passed by, and every time he came even remotely close, they would disappear. The device was left in place for an evening and when he collected it, it was packed full of beautiful Rock Sparrow vocalisations.
Red-billed Chough (Pyrrhocorax pyrrhocorax), Ballynamona Strand, East Cork, Ireland. Photo: Seán Ronayne.
Red-billed Chough (Pyrrhocorax pyrrhocorax) – Summer 2020 – Catalunya. This recording was simply the result of exploratory passive-recording. An audiomoth was again placed in a stone-ruin and collected several days later. The chough were never seen in person, so this recording came as quite a surprise!
A bit of detective-work helps to place a passive-recording device in the right location. In this case, the above Otter (Lutra lutra) spraint was a sure sign that the specie was using the site. Photo: Seán Ronayne.
Eurasian Otter (Lutra lutra)- Jan’ 2021 – Cork. This recording was planned. The audiomoth was placed in an area with several otter signs (spraint and tracks) for three nights. As luck would have it, an individual apparently sat right below the device, on the very first night of deployment. If only it was always this easy!

If you’re feeling a little bit braver, you can also leave a handheld recorder or even a parabola out in the field. Why risk it? Well, the sound quality, or in the case of the parabola, the quality and range will be greatly increased. Of course it is only advisable to do this if you feel confident enough that your expensive equipment won’t be stolen or damaged. Let us talk you through some of our past scenarios with samples.

First up is the handheld recorder. We love our Olympus LS-12 and because of this, wouldn’t leave it anywhere too risky. It wasn’t the most expensive piece of kit but they cost quite a bit more than an audiomoth and are discontinued. As we are often in the field surveying, this little device is often sealed in a ziploc bag and left out to capture some of the natural sounds of the environs. It’s usually close enough to keep an eye on and because we aren’t targeting flying birds, it works just fine as is. Of course, it could be used to target a specific bird or mammal too.

Olympus LS-12 handheld recorder in a simple ziploc bag. Ziploc bags are sound-transparent, and protect devices from wind noise and rain. Photo: Seán Ronayne.
Passively-recorded stream sounds in the uplands of North Cork, Jan’ 2021. As it was too windy to record birds, the Olympus LS-12 was wrapped in a ziplock bag and left to record the sounds of this trickling waterway.
Dodotronic Hi-Sound Parabola (right), passively-recording as it points to a busy garden bird-feeder. Photo: Seán Ronayne.

We often use our parabola to passively record, with amazing results. Setting up a parabola to point towards a bird-feeder or area which hosts a hive of bird activity is a great way to cheat yourself some nice bird audio. You can be working from home, whilst recording at the same time, with your equipment in a safe place. Don’t have a garden? Don’t worry – just find an area out in the countryside that has a lot of bird activity, setup your device to record, and retreat to a safe distance. Whilst surveying in nice conditions we often run our parabola alongside. But of course, it’s not essential to do this with a parabola. Just work with what you have. As we’ve said before: good quality recordings are possible with even the cheapest of devices.

Male Eurasian Bullfinch (Pyrrhula pyrrhula) . Photo: Caroline Legg – Flickr.
Eurasian Bullfinch (Pyrrhula pyrrhula) calls and subsong – passively recorded at a feeding station in Cobh, with a Dodotronic Hi-Sound Parabola.
Eurasian Magpie (Pica pica) calls – passively recorded at a feeding station in Cobh, with a Dodotronic Hi-Sound Parabola. Photo: Seán Ronayne
Red-rumped Swallow (Cecropis daurica) , Catalunya – June 2020. The parabola was set to point at a territory when the adults were out foraging. Seán waited in the car with bated breath for the birds to perch over the parabola and hopefully sing. And sing they did! Photo: Seán Ronayne.

Now for something a little bit different: Cork-based birder Thomas Wallenda uses a highly inventive Raspberry-Pi setup to passively record in his garden with great success. The sound quality is very nice and to our surprise everything was very cheap. Thomas tells us that he has had this setup in a bush for over a year now, with no rain-based or any other form of damage incurred.

Thomas’ homemade setup is still going strong after over a year in his garden. Photo: Thomas Wallenda

Here are some more technical details, kindly provided to us by Thomas:

“This is the hardware that you need: the basic bits cost about 50 euro plus the power bank(s). All the software is free. And obviously my parabola needs an upgrade 🙂

A closer look at Thomas’ setup, with details below. Photo Thomas Wallenda.

What about the sound quality then? Check it out for yourself below. It’s really quite good

European Starling (Sturnus vulgaris) song, passively-recorded by Thomas’ setup, in his garden.
Redwing (Turdus iliacus) NFC, recorded by the same device.

So there you have it. It’s possible to record with all manner of devices, cheap and small, large and expensive, and everything in-between. There’s a recording option to suit everyone’s budget s and needs, so why not start?

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