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

Updated 2022-09-17.
Learn how my shiny new AudioMoth will help monitor these night-flying insect chompers!
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 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 currently 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 . Downloads:

Zoom H1n recording:

22s "ZoomH1n 210402 122858" Uploaded . Downloads:

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 . Downloads:

Zoom H1n raw sample from end of prewash:

56s "ZoomH1n prewash end" Uploaded . Downloads:

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 . Downloads:

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 . Downloads:

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 . Downloads:

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 . Downloads:

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 . Downloads:

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 TTPP KT2 t2021 03 13 PpPpy MW
AudioMoth overnight recordings in KT2 (across Kingston from 16WW) displayed per Temporal Pass Plots: An intuitive method for visualising activity patterns of bats and other vocalising animals'.

2021-06-25: LOUD Wren

Not quite a bat, even when squinting...

This evening ~7pm, a wren making continuous loud staccato calls, likely contact calls, while munching the bugs on my apple tree. Also while sitting on top of my garden solar panels only feet from me, and clinging to the house wall.

The suggestion is that it has a very new brood, and I think that I have seen the other one from the pair, and heard a frenzy of even louder calls, possibly when a cat was nearby.

(Sitting in the garden looking up videos of wrens, and other candidates such as dunnock, I think playing the wren video generated some interest...)

I hope that I have captured some of this in photos, videos, and on my Zoom field recorder!

123s "20210625T1900Z wren loud contact calls in 16WW back garden" (captions) Uploaded . Downloads:

2021-08-03: Bats on the Hogsmill!

Walking back from Surbiton, I saw lots of bats near the Villiers Road bridge over the Hogsmill. I only saw one bat further down Hogsmill Lane.

2021-08-10: Bats on the Hogsmill!

Again, coming from Surbiton ~22:00Z (11pm BST), I saw at least one busy bat flitting back and forth over the water about road height near the Villiers Road bridge. I saw probably one bat further down Hogsmill Lane. I'm guessing from size and flight pattern (eg not low over the water) that they were pipistrelles.

2021-08-15: Bats at my Study Window

19:43Z: at study window Pettersson detector at 45kHz het on speaker. (Sunset 19:24Z, temperature ~18°C, partly cloudy.) 19:46Z heard bat! Likely a common pip. Another pass at 19:56Z. 20:05Z window closed.

2021-08-16: Birds at my Study Window

The Pyracantha hedge outside by window badly needs a trim. In the interim it is host to a host of sparrows by day. Not bats, no, but equally welcome. I suspect that the Pyracantha hosts some bat-approved insects too!

2021-08-17: Bats on the Hogsmill!

Coming from Surbiton ~21:15 BST (20:15Z) bats visible from the bridge. Also up to 2 or 3 in view at once at various places along Hogsmill Lane. All seemingly pips from the 'random walk' flight paths. No obvious water skimming bats at any point along the lane.

2021-08-31: Bats Beta AudioMoth

Conversation with prof Alex Rogers, started on Twitter, revealed the existence of a beta build of the firmware and config app for Linux that (eg with PyAudio) allows continuous real-time use of the AudioMoth as a USB-attached ultrasonic microphone for the Raspberry Pi. The AudioMoth draws power via the USB connection used for audio and does not even need batteries.

There is a small residual issue of getting USB in and keeping the mic waterproof, but at 1/4 the price of existing ultrasonic mics that seems OK.

MW has managed to make it all work and configured the mic as 192ksps. He says: Seems to work with real bats too ... on my evening stroll in the park ... The sample rate was 192k, filter was high pass above 15kHz.

2021-09-01: It Works!

MW wrote to me and said:

I went for a short walk last night with Raspberry Pi bat detector equipped with both AudioMoth (set to 192k, medium gain and high pass filter of 15kHz) and Ultramic (200k as spec, set to highest gain, and high pass filter of 15kHz implemented in recording process) USB microphones.

I recorded with sox about 80 @ 3-second files over 4 minutes with both microphones simultaneously. The high gain of the AudioMoth microphone is evident in the [below] sonograms. I also processed the files with bat detect — — which also showed higher numbers for the AudioMoth.

MicrophoneFiles with bat callsTotal number of bat calls

I have also run BatClassify on the two sets of files which appears to show the Audimoth getting higher scores for the bat species but I might be able to quantify that somehow.

So thumbs up for AudioMoth.

20210831 AudioMoth MW
AudioMoth sonogram from evening of 2021-08-31.
20210831 Ultramic200K MW
Ultramic200K sonogram from evening of 2021-08-31.

2021-09-12: Wasp Spiders

Also not bats! This evening I saw two wasp spiders in their webs in long grass close to 16WW at Kingsmeadow. Quite large (like a garden orb spider) and with yellow and black stripes the dorsal side of the abdomen. A zigzag silk stabilimentum cross-hatching patch was visible clearly in one web. I have never seen wasp spiders before.

2021-09-19: Bats at my Study Window

18:19Z: at study window Pettersson detector at 45kHz het on speaker. (Sunset 18:07Z, temperature ~16°C, fairly overcast, has rained hard.) Seem to be lots of insects around. 18:27Z heard bat! Maybe a solo common pip. A close/prolonged pass at 18:35Z. A short pass at 18:36Z. Another pass at 18:38Z (I think I saw the critter!). More at 18:39Z (x2), 18:42Z (x2), 18:43Z (x2), 18::46Z (x2), 18:47Z, 18:48Z (x2, saw it!), 18:50Z, 18:51Z, 18:52Z (close pass and saw it, x2!), 18:54Z (x2), 18:55Z (x2), 18:56Z, 18:57Z (x3), 18:59Z. 19:00Z window closed.

2021-09-26: Experiment

17:55Z: at study window Pettersson detector at ~30kHz het on speaker. (Sunset 17:51Z, temperature ~19°C, has been a sunny afternoon.)

Experiment with 30kHz on het to try to hear social calls as well as feeding calls. May yield nothing!

18:15Z: heard faint bat call? (Can hear my own typing via the detector!)

18:24Z: maybe hearing some social calls?

18:25Z: pushed het frequency up to ~40kHz.

18:27Z: feeding call and maybe social call. 18:34Z: louder pass with feeding buzz. 18:39Z: pass. 18:46Z: pass with possible feeding/social buzzes. 18:50Z: window closed.

2021-10-03: Back To The Old Ways

17:35Z: at study window Pettersson detector at ~45kHz het on speaker. (Sunset 17:35Z, temperature ~13°C, has been a fairly sunny afternoon.)

I'm not repeating the experiment of 2021-09-26!

For the record, I'm not picking the nights I listen out for bats in any way to skew the results, eg make there seem to be more or fewer bats. I sample when I remember, and can be bothered! It's sort of random... Also, I don't want to get my room (and the house) too cold.

Nothing heard by 18:05Z ... short snack break until 18:08Z! 18:10Z: first (loud) pass, likely pip. 18:11Z: loud pass. 18:17Z: loud pass x2. 18:26Z: pass. 18:27Z: loud but brief pass. 18:35Z: window closed. (Getting cold!)

2021-10-18: Batless

A venture down to the Hogsmill River/Lane a little after 6pm BST did not generate any convincing bat indications.

A few things from the bat detector that may have been from cars, though were possibly pipistrelles.

Even though air temperature was ~16°C, it was raining quite hard at points.

2021-10-27: Bats on the Hogsmill!

Walking to and from Surbiton (~6:30 BST and ~9:15 BST) at least one bat (likely pip) visible from the Villiers Road bridge.

2021-11-11: Many Bats on the Hogsmill!

Alison F reports (~8pm): Lots of bats along Hogsmill tonight flying really low.