Earth Notes: Bats Around our Home aka 16WW (2021)

Updated 2021-04-08 13:13 GMT.
By Damon Hart-Davis.
Learn how my shiny new AudioMoth will help monitor these night-flying insect chompers!
20210408 MW TTPP KT2 t2021 03 13 PpPpy
I am hoping to continue bat observations at 16WW, including with some more elements of automation and direct ultrasound capture with an AudioMoth.

2021-01-19: AudioMoth

An AudioMoth v1.2.0 arrived today, with waterproof case, 64GB microSD card, and jack socket.

2021-04-02: AudioMoth Setup

initial configuration of AudioMoth, but with the time set

Finally, over this long weekend, I think that I have time for AudioMoth's Initial Setup and some test recordings!

I have installed 3 x AA NiMH cells from my desktop stash. I have also installed the 64GB SD microSD card. The switch is in the USB/OFF central position.

Flicking the switch to CUSTOM has both (red and green) LEDs flash.

I downloaded the AudioMoth Time app to my Mac and used it to set the time over the USB cable, which seemed to be retained when unplugging the cable. This app also tells me that the AudioMoth is running AudioMoth-Firmware-Basic 1.5.0, and that the battery is at 4.1V.

The AudioMoth Flash app similarly detects V1.5.0 on the AudioMoth.

The AudioMoth Configuration app likewise detects V1.5.0, 4.1V, the time, and offers me a selection of options.

I note that the default recording sample rate for the AudioMoth is 48ksps, as I use for non-ultrasonic field recordings. So a reasonable initial test is a recoding by each at that sample rate, ideally using mono on both devices. But getting the Zoom H1n to record mono seems a bot tricky, and I don't want to mess up later recordings, so I'm leaving it be, at 48ksps 16bit WAV.) The AudioMOth defaults to medium gain.

(I've configured the AudioMoth to know that it has NiMH cells in.)

I'm going to take the recording on the AudioMoth at my desk by flipping the switch to DEFAULT, and will manually start a Zoom recording too. Note that there is a disc rattling away taking a backup on the desk, and some noise outside!

The aim is to make sure that I can actually record at all, get at the files, load them in to Audacity, etc.

(The H1n's clock is currenlty about 4 minutes fast at this point. I fixed it after these desktop co-recordings.)

When I remove the microSD card from the AudioMoth and plug it into my MacBook Air's SD card slot using the supplied adaptor, it does not show up in Finder in the 'Locations' section, nor immediately in Disk Utility, so I wondered if it had a filesystem on it at all. It did show up in About This Mac --> System Report ... --> Storage as a 64GB ExFAT volume "Untitled 1" internal. It did seem to show up later in Disk Utility, maybe after fsck completed. But still not in Finder directly. It was available under the DHDMacBook device. I have renamed it AudioMoth.

I was then able to access the initial recording, the CONFIG.TXT configuration file, and the Zoom H1n recording at the same time, filed for posterity in folder img/audio/AudioMoth/20210402.

AudioMoth recording:

35s "20210402_122404" Uploaded . Download mono WAV clip 3264kB.

Zoom H1n recording:

22s "ZoomH1n 210402 122858" Uploaded . Download stereo WAV clip 4178kB.

The file utility reports both recordings to be 16-bit:

20210402_122404.WAV:       RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 48000 Hz
ZoomH1n-210402-122858.WAV: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 48000 Hz

The config file content is:

Device ID                       : 242A26045F772B95
Firmware                        : AudioMoth-Firmware-Basic (1.5.0)

Time zone                       : UTC

Sample rate (Hz)                : 48000
Gain                            : Medium

Sleep duration (s)              : 5
Recording duration (s)          : 55

Active recording periods        : 0

Earliest recording time         : ---------- --:--:--
Latest recording time           : ---------- --:--:--

Filter                          : -
Amplitude threshold             : -
Minimum threshold duration (s)  : -

Enable LED                      : Yes
Enable low-voltage cutoff       : Yes
Enable battery level indication : Yes (NiMH/LiPo voltage range)

Always require acoustic chime   : No

As a further test I set up the AudioMoth and H1n to record an entire 15 minute prewash cycle side-by-side in front of the Electra C1845W dishwasher.

AudioMoth raw sample from end of prewash:

56s "AudioMoth prewash end" Uploaded . Download mono MP3 clip 617kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 344kB, hi-fi mono lossless clip 3201kB.

Zoom H1n raw sample from end of prewash:

56s "ZoomH1n prewash end" Uploaded . Download stereo MP3 clip 1218kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 294kB, hi-fi stereo lossless clip 4599kB.

I expect to use the AudioMoth in the field at 192ksps for bat detection, but here is a max-speed 384ksps ambient (evening, at desk, by window) sample because I can...

48s "20210402T1827Z desk ambient AudioMoth 384ksps" Uploaded . Download mono FLAC clip 17942kB.

And... The AudioMoth has been deployed outside at 192ksps after dark. I flipped the switch to DEFAULT, put it in its case, and strapped it to a bush. I'll check it in the morning, though it's unlikely to yield anything.

2021-04-05: Slack

I have been somewhat slack and only just looked at the AudioMoth recording of overnight on the 2nd. I turned off the AudioMoth and brought it in .

Rather than one huge recording there seem to be multiple separate WAVs, presumably up to the 4GB limit for 32-bit WAV files. Each recording seems to be about 3 hours long.

4294656488  2 Apr 22:49 20210402_194330.WAV
4294656488  3 Apr 01:56 20210402_224956.WAV
4294656488  3 Apr 05:02 20210403_015622.WAV
4294656488  3 Apr 08:09 20210403_050248.WAV
4294656488  3 Apr 11:15 20210403_080914.WAV
1650524160  3 Apr 12:27 20210403_111540.WAV

Trying to load everything into Audacity at once seems to have been an error, including filling my disc!

20210402T1943Z AudioMoth 16WW garden spectrogram
Spectrogram of first AudioMoth 16WW garden capture from 19:43Z on the 2nd.

Listening to the (non-ultrasonic bits of the) first one, the content seems to be mainly wind noise ie a breeze through the trees. There is the odd siren, and maybe signs of a small animal.

Here is a small sample (note the the FLAC is broadband ultrasonic):

19s "20210402T1953Z AudioMoth 16WW back garden sample ultrasound original 192ksps" Uploaded . Download mono MP3 clip 221kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 104kB, hi-fi mono lossless clip 4228kB.

FLAC encoding the first one does not quite halve its size at 2360541581 bytes out.

20210403T04Z 16WW garden ambient pre dawn birdsong breezes bells spectrogram
A pre-dawn chorus of birdsong with breezes and church bells faintly chiming 5am (04:00Z) in the background. The birdsong is visible as the chirps between about 3kHz and 10kHz, with the wind noise right up to about 40kHz.

A sample before dawn with birdsong, breezes and distant church bells (note the the FLAC is broadband ultrasonic):

378s "20210403T04Z 16WW garden ambient pre dawn birdsong breezes bells" Uploaded . Download mono MP3 clip 4424kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 1953kB, hi-fi mono lossless clip 79013kB.

A sample after sunrise mainly pigeons and parakeets, with some ultrasonics eg from wing flaps (note the the FLAC is broadband ultrasonic):

130s "20210403T06Z 16WW garden ambient sunrise pigeons and parakeets" Uploaded . Download mono MP3 clip 1540kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 696kB, hi-fi mono lossless clip 27438kB.

At solar noon (1pm local) birds on the metal feeder(s) (note the the FLAC is broadband ultrasonic):

39s "20210403T12Z 16WW garden ambient noon birds on metal feeder" Uploaded . Download mono MP3 clip 484kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 214kB, hi-fi mono lossless clip 8188kB.

2021-04-08: TPP Visualisation

Mark W tells me that he has been putting out an Audiomoth most nights this year in the garden. The WAV files recorded by the Audiomoth have a file header which includes the temperature, so even if there are no bats you still have a record of what the temperature was.

Hot off the press he tells me:

Just processed last night's Audiomoth files, the temperature was a bit higher than the night before so got some bats. I think the batteries ran out before sunrise as missing some data. The last bat recorded was at voltage of 3.0 Volts and there were 6 red flashes when I switched from Custom to USB/Off, I either have some old LiMH batteries, the battery usage is greater than the Configuration app suggests or the capacity is not as great when the temperatures are low.
20210408 MW TTPP KT2 t2021 03 13 PpPpy
AudioMoth overnight recordings in KT2 (across Kingston from 16WW) displayed per https://doi.org/10.1016/j.ecolind.2020.106202: Temporal Pass Plots: An intuitive method for visualising activity patterns of bats and other vocalising animals'.
~1171 words.