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

 

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

 

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:

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.