EM172 lapel mic, Zoom H4n Pro audio recorder, Audiomoth and mini USB mic (photo: Simon Gillings)

Equipment Comparison February 2020

On one of the few calm nights in February 2020 I tried to make simultaneous recordings of the same flight calls using a variety of equipment. I tested:

  1. A cheap USB microphone connected to a desktop PC. Mic level set to 90/100.
  2. An AudioMoth in a plastic bag. Gain set to Medium
  3. An AudioMoth in a homemade waterproof case. Gain set to Medium.
  4. A lapel microphone (EM172) with a digital audio recorder (Zoom H4n Pro; record level set to 80/100).
  5. A Dodotronic parabolic microphone with a digital audio recorder (Sound Devices MixPre 3; gain set to 25dB)

There was very little bird movement but I got useful comparisons for a Redwing and a Moorhen pass. Below is a recording of each call and a side-by-side comparison of the spectrograms.

Redwing

A single Redwing call at 2010. The call is a bit atypical but still conveys the quality of the recording using the different equipment. Without adjusting the gain on the USB recording this call is inaudible. It is visible and audible on all the other equipment setups but is stronger and more clearly defined on the final two recordings. The bird was not directly overhead, which explains why the lapel mic and parabolic mic have similar performance. Had the bird been directly above the parabolic dish that recording would have been much louder.

Cheap USB mic and computer:

AudioMoth in bag:

AudioMoth in case:

Digital audio recorder and EM172 lapel mic:

Digital audio recorder and parabolic reflector:

Spectrogram comparison
Redwing comparison 2

 

Moorhen

The Moorhen call was picked up and visible on all recorders, though it was still faint on the USB. On the two AudioMoth recordings only the first kek-kek-kek series is clearly visible whereas on the Lapel mic and Parabolic mic recordings the subsequent kek-kek notes are also clearly visible.

Cheap USB mic and computer:

AudioMoth in bag:

AudioMoth in case:

Digital audio recorder and EM172 lapel mic:

Digital audio recorder and parabolic reflector:

Spectrogram comparison
Moorhen comparison 2

 

Conclusion

Based on this very limited comparison the USB mic would miss some birds, though I should note that the mic used here is quite old and newer models might be more sensitive. More distant calls, calls of quiet birds, or calls where fine detail is needed for identification (e.g. flycatchers) might be easily missed or hard to identify with the AudioMoth. I did not run the AudioMoths on the high gain setting which might partly explain the slightly poorer detections. Previously I have found high gain generated too much white noise (hiss) in the recordings. Next time there is a break in the wind I will try again…

Postscript

The wind dropped again briefly and I was able to make a comparison of two AudioMoths, one with gain set to Medium and another with gain set to High. Again not many birds moving so not many comparisons possible. Of three Redwings detected by parabola: i) one was not detectable via either AudioMoth; ii) one was missed on Medium gain and barely visible on High gain; iii) one was picked up by both with negligible difference in sound quality. Of two Song Thrush calls detected by the parabola: i) one was missed by the Medium gain AudioMoth and just visible on the High gain one; ii) the second call was visible on all as can be seen in the following comparison:

ST call cf

Note this bird was not directly overhead, as evident from differences between the left and right channels of the parabolic recording. Without knowing these calls were present from the parabolic recording I may well have missed some of them in the AudioMoth recordings.

The lack of birds prevented a more detailed comparison but this does suggest the high gain setting might be better for the AudioMoths for nocmig.

Standardised Nocturnal Flight Call Monitoring

Recording nocturnal flight calls is seeing a big surge in interest in Europe and all this effort scrutinising hours of audio has the potential to generate invaluable data on a large scale for understanding movement patterns of birds. Witness the amazing nocturnal movements of Common Scoters through inland England recorded in April-May 2018, the tantalising records of nocturnal Ortolan Buntings in southern England and continental Europe, and the amazing breadth and magnitude of nocturnal movements through Besh Barmag, Azerbaijan. There’s much to learn if the data can be collected and collated in a consistent manner.

protocol_coverBTO, Sound Approach and Sovon have teamed up to produce a Protocol for Standardised Nocturnal Flight Call Monitoring (available here), and in parallel, significant improvements have been made to Trektellen for the submission and sharing of nocmig data. The protocol aims to highlight simple ways that recordings and the data extracted from them can be standardised whilst still allowing flexibility for local circumstances. It details aspects such as where and when to record, times of night to cover and which species to log. For example, we recommend that call logging starts no earlier than civil dusk and continues no later than civil dawn to exclude diurnal migrants. Ideally counts should be submitted in hourly blocks to allow future analyses of timing and weather, and all birds flying over should be logged whether they are considered to be migrants or local birds. These suggestions will be familiar to many seasoned recorders and should act as a guide for those just starting out.

Trektellen has been collecting nocturnal flight call data for several years and with the latest modifications it is now possible to submit numbers of individuals and numbers of calls, which will be invaluable for species where estimating bird numbers is problematic. It is now easier to indicate which records relate to flying versus stationary birds and sound files uploaded to xeno-canto can now be embedded within Trektellen lists, which will be especially useful for sharing recordings of unusual or unverified records.

trektellen_dayview
Alongside the advances being made by the Sound Approach and others in species identification, we hope this protocol promotes further interest in recording and submission of data from nocturnal flight call monitoring.

Nocmig recording in Cambridge

I started nocmig recording in March 2017 from my garden in Chesterton, one of the eastern suburbs of Cambridge. My garden is about 250 m from the River Cam but separated by a moderately noisy road and housing. In a birding sense it’s an uninspiring bit of the city and not somewhere you’d expect to have significant bird passage.

2017-03-28 08.07.36

My first recording gear was a very cheap USB microphone, the kind designed for Skype calls. For under £15 this gave me my first Moorhen and Water Rail for my nocmig garden list. In a bid to improve the quality of my recordings I upgraded to a Yeti USB mic but stubbornly stuck to using my computer to capture the audio. Spring 2017 was amazing for inland wader passage and I soon added Spotted Redshank and Grey Plover to a growing list of waders.

20170903 OBEarly September 2017 was a turning point – I was away with my family for the weekend and had taken the Yeti mic with me but on a whim decided to leave the mini USB running from Friday evening to Sunday. On my return I discovered that I had recorded not only a Sandwich Tern and a Tree Pipit but also an apparent plik call of an Ortolan Bunting – a potential first for Cambridgeshire. With hindsight, claiming an unseen county first based on a single call, when I was not even present, was asking for trouble. But it made me rethink my recording setup and invest in a proper microphone so that I’d be better prepared next time…

2017-10-17 21.11.41

Since October 2017 I’ve been using a Dodotronic Stereo parabolic microphone connected via a 10 m cable to a Zoom H4n Pro recorder. I recorded in Chesterton whenever I can and have so far recorded over 10,000 nocturnal flight calls of over 60 species, including highlights such as multiple Ring OuzelsCommon Scoter, Stone-curlew, Pied Flycatcher and Bittern.  I’ve just started putting these records onto Trektellen to add to the picture it is building of nocturnal migration in Europe.

This website came about when Nick Moran and I found we wanted to collate the answers to many of the questions we had as we were starting out. We’re keen to promote nocmig recording and especially interested to see useful counts generated and submitted to Trektellen for wider research uses.