Earth Notes: Bats Around our Home aka 16WW

Updated 2020-10-31 17:20 GMT.
Our house in a bat hotspot - pipistrelles rather than vampires! #bat #Chiroptera #dataset
20201003T18:25Z 16WW front window Batbox Duet 20kHz het spectrogram

Cheat podcast episode! Bats on the Hogmill River a few minutes' walk away:

2275s "20201007T18:10Z Hogsmill Lane Hogsmill River multiple bats FD10 bandpass 1500 to 7500Hz resampled 48ksps to 16ksps" Uploaded . Download mono MP3 clip 10861kB, hi-fi mono FLAC clip 48851kB.

Notes on Bats at 16WW

I am happy to say that there are lots of bats around our home. Mainly common pipistrelles (Pipistrellus pipistrellus) it seems, maybe a soprano pipistrelle or three. They can be seen flying at about bedroom window height against the dusk and detected by their feeding and social calls. Feasting on mosquitoes and other insects.

A few minutes' walk away at the Hogsmill River is a veritable bat party feast, with other species such as Natterer's and Daubenton's in the mix.

The cemetery just over the road from 16WW also seems to host at the very least a crowd of pipistrelles (common and soprano).

It's all go round here!

Here are some 16WW Chiroptera notes, sounds and images, and anecdata, with some exposed slightly more formally as a dataset.

Local bat survey October 2018, c/o Alison Fure
October 2018 survey of bats in the 'hood, c/o Alison Fure.

2020-09-12: Just Outside

Some bat chat with Alison Fure and a couple of bat detectors just outside the far corner of our garden in the alleyway, then up the alley and round the front:

308s "20200912T19:00Z bat chat around 16WW with AF at dusk" Uploaded . Download stereo MP3 clip 7522kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 1782kB, hi-fi stereo FLAC clip 31157kB.
Soundwalk 2020-09-12 near 16WW
September 2020 snapshot of activity on CRE near 16WW at end of Soundwalk, c/o Alison Fure.

Also, spectrograms (aka sonograms) and log files mainly from the night of 2020-09-17, captured by a static bat detector in the tree in 16WW's back garden (west side) close to where the loudest signals were heard a few days before:

Alison says:

It shows really what we know that there is a common pipistrelle but it appears to have set up a mating roost (possible interpretation) and is song flighting. This means it is fairly constant activity all through the night. There was one soprano pipistrelle also.

There is some interference which is CF around 25 kHz that begins around 3.20, there is a bat that can do that but it would be exceptional to find it there.

2020-09-21: Low Passes at Dusk

I tried a few times to catch them, and at just before 8pm BST they appeared.

One or two (presumably common pipistrelles, Pipistrellus pipistrellus), at 45kHz on the detector), flying back and forth along the terrace over the back gardens, close to the houses.

They were obliging me with low passes only 1m or 2m directly above the detector on the garden table in front of me!

I have rarely seen a bat so close up, framed against the nearly-dark sky!

I captured four samples on the field recorder, the first quite faint.

31s "20200921T18:39Z 16WW back garden common pipistrelle 45kHz" Uploaded . Download stereo MP3 clip 596kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 165kB, hi-fi stereo FLAC clip 2742kB.
81s "20200921T18:40Z 16WW back garden common pipistrelle 45kHz" Uploaded . Download stereo MP3 clip 1693kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 479kB, hi-fi stereo FLAC clip 7493kB.
28s "20200921T18:45Z 16WW back garden common pipistrelle 45kHz" Uploaded . Download stereo MP3 clip 579kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 149kB, hi-fi stereo FLAC clip 2497kB.
47s "20200921T18:47Z 16WW back garden common pipistrelle 45kHz" Uploaded . Download stereo MP3 clip 992kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 250kB, hi-fi stereo FLAC clip 4177kB.

2020-09-22: Out Front

2020-09-22 ~9pm BST common pipistrelle distribution c/o Alison Fure

While participating in a webinar 7pm to 8pm BST, I also had the bat detector at my open front east-facing window (at 45kHz), and detected feeding activity.

19s "20200922T18:31Z 16WW front window common pipistrelle 45kHz" Uploaded . Download stereo MP3 clip 411kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 100kB, hi-fi stereo FLAC clip 1666kB.

Out the back for a few minutes a little after 8pm I didn't detect anything.

A little before 9pm, on the grass at the entrance to Willingham Way with Alison, I heard a few more bat passes for feeding. Alison said that there were no social calls.

As the weather is likely to take a turn for the colder and wetter now, this may almost be the end of bat detection for this calendar year here.

2020-09-23: Nathusius?

bat detector het/heterodyne

I opened my front window just before 7:43pm BST and I quickly detected feeding! Two or three passes in as many minutes. Common pipistrelle I think.

About 8:15pm I stepped out the back door and almost immediately heard a new bat, clearest and babbling on ~39kHz, which may just be a Nathusius’ pipistrelle (P. nathusii). Difficult to be sure with current heterodyne device, and given that I know nothing about this topic!

12s "20200923T19:13Z 16WW back garden possible Nathusius pipistrelle 39kHz" Uploaded . Download stereo MP3 clip 286kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 64kB, hi-fi stereo FLAC clip 1098kB.

2020-09-24: Not Torpid Yet

bat detector handheld Batbox Duet heterodyne and frequency division 4 DHD

I opened my front window at ~7:23pm BST and quickly detected feeding again! Likely a solo common pipistrelle making multiple passes, one quite close...

I have briefly tried out the new fancier frequency-division (FD) detector (Batbox Duet) that I have been lent.

With the Duet I picked up what sounds like a solo common pipistrelle out the back too.

I think that recording directly from the "tape" output into my MacBook (FLAC stereo at 48ksps) may be good. The left channel is input frequency/10, the right is heterodyne with whatever frequency I select with the dial. The input frequency range is 17kHz to 125kHz. At the very least I may get some pretty spectrograms/sonograms!

Recording directly to the MBA is nixed by it not having an analogue mic input! So I have ordered a 3.5mm stereo jack-to-jack cable from Duet to Olympus field recorder. (Thanks again Deniz for the recorder loan!)

Amazingingly, even though the cable order only went in after 9pm, it arrived next morning with an earlier order of PP3s (9V alkaline batteries) for the detectors.

2020-09-27: Common Pip Spectrum

I opened my front window just before 7 BST and heard a faint suggestion of a solo common pipistrelle.

I went out the back for 5 minutes and heard nothing.

Out of my window at ~7:10pm a faint signal again, a pass or two... The Duet and LS-P4 field recorder combo has captured about 5 seconds:

5s "20200927T18:14Z 16WW front window common pipistrelle 45kHz Batbox Duet" Uploaded . Download stereo MP3 clip 115kB, hi-fi stereo FLAC clip 695kB.

The left channel is the original frequency / 10, so the pipistrelle should appear somewhere around 4.5kHz. The right channel is 45kHz heterodyne.

Just the frequency division (FD) channel (looking plausible for a common pip):

5s "20200927T18:14Z 16WW front window common pipistrelle 45kHz Batbox Duet L only freq div" Uploaded . Download mono MP3 clip 63kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 27kB, hi-fi stereo FLAC clip 410kB.
20200927T18:14Z 16WW front window common pipistrelle FD spectrogram
Frequency division output of Batbox Duet, suspected common pipistrelle.
20200927T18:14Z 16WW front window common pipistrelle FD spectrogram

There may be stuff going on above 80kHz (8kHz in the above figure), as the Duet detects up to 125kHz (12.5kHz in the second spectrogram image). But it looks to me as if it could mostly be noise or aliasing. In any case, I should probably set the spectrogram default to better match the Duet, at 12.5kHz!

There was another teaser brief pass at ~7:50pm BST, while typing this up, not captured.

MW's Analysis

MW kindly analysed tonight's (second) recording. His manual analysis suggests presence of common pipistrelle peak 4877Hz after frequency division by 10.

FileAudioSpeciesPeak frequency after FD10
200927_0122015
15s "200927_0122015" Uploaded . Download mono MP3 clip 61kB, hi-fi mono FLAC clip 522kB.
Com pip4877Hz

File 200927_0122015 started recording at 7:11pm BST (18:11Z) and the above segment is the 15th 15s segment from it, so ~7:14.

2020-09-28: Social Calls

At just after 7pm BST I opened my front window and ~7:05pm heard a pass.

Just about the moment that by MacBook automatically switches to dark mode, which may be a big visual clue to break out the bat detector! I think that I get clipping in the right (heterodyne) channel whenever there's a bat pass, which may make searching for them quicker!

Had the Duet set up recording shortly after, and another faint pass ~7:08pm.

The field record is occasionally flashing the "peak" light, which suggests that maybe I should turn the (manual) sensitivity down to low. Done by 7:15pm, missing a faint pass or two.

There are plenty of insects around, some coming in my open window...

Before I finished listening a little before 8pm, I had heard many passes.

Here are the two recordings in their entirety, just the FD channel, as low-fi mono for compactness. Listen out in the first for passes in minutes 2 and 4, and in the second one for louder passes in minutes 7, 13, 19, 25, 28, 30, 34.

407s "20200928T18:05Z 16WW front window Batbox Duet FD10" Uploaded . Download mono MP3 clip 2299kB.
2488s "20200928T18:14Z 16WW front window Batbox Duet FD10" Uploaded . Download mono MP3 clip 14558kB.

About the clearest pass from the first (just before 5 minutes, with a little raspberry blown about 2s in as something is caught) is:

4s "20200928T18:09Z 16WW front window Batbox Duet loud pass FD" Uploaded . Download mono MP3 clip 54kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 26kB.

Manual analysis of the first recording by MW suggests presence of common pipistrelle peak 4682Hz and soprano pipistrelle 5300Hz after FD. See more below.

A segment from 34:17 to 34:22 (eg see segment 200928_0125138 below) in the second recording appears to show some social calls ~30kHz and in bursts of about 3:

20200928T18:49Z 16WW front window Batbox Duet FD10 feeding and social calls spectrogram
Mix of feeding (45kHz+ and social ~30kHz)?
6s "20200928T18:49Z 16WW front window Batbox Duet FD10 feeding and social calls" Uploaded . Download mono MP3 clip 78kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 36kB, hi-fi mono FLAC clip 418kB.

At some times (eg at minute 7 in the second recording) there seems to be more than one bat present.

One way to reduce the somewhat painful background hiss is to split out out the left (FD/10) channel as mono, then apply a Filter Curve with a band pass of 1kHz to 6kHz (10kHz to 60kHz original, maybe the latter should be higher), with fairly steep cut-off.

(For manual analysis, MW used a band pass filter of 1500 to 7500 Hz.)

I think that some ultrasonic interference is picked up from my laptop when typing.

Manual analysis of the second recording by MW suggests presence of common pipistrelle peak 4682Hz and soprano pipistrelle 5533Hz (clearest call) and maybe a Noctule 2408Hz after FD.

MW's Analysis

In order to be able to repeat MW's segmentation for his manual analysis of a few days ago, I installed SoX on my Mac with:

% brew install sox

I ran MW's command to extract matching 15s segments:

% sox 200928_0125.flac 200928_0125.wav sinc 1500-7500 trim 0 15 : newfile : restart

I used ffmpeg to retain just the left (frequency-division) channel and convert to mono (I converted to FLAC first, but it could have been done in one step I think):

% ffmpeg -i INPUT.flac -map_channel 0.0.0 OUTPUT.flac

A low bit-rate MP3 was made from each with:

% ffmpeg -i INPUT.flac -aq 9 OUTPUT.mp3
FileAudioSpeciesPeak frequency after FD10
200928_0124009
15s "200928_0124009" Uploaded . Download mono MP3 clip 62kB, hi-fi mono FLAC clip 516kB.
Com pip4682Hz
200928_0124020
15s "200928_0124020" Uploaded . Download mono MP3 clip 63kB, hi-fi mono FLAC clip 524kB.
Sop pip5300Hz
200928_0124022
15s "200928_0124022" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 516kB.
Sop pip5300Hz
200928_0125004
15s "200928_0125004" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 515kB.
Com pip4829Hz
200928_0125011
15s "200928_0125011" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 515kB.
?Com pipNoisy
200928_0125013
15s "200928_0125013" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 515kB.
?Com pipNoisy
200928_0125017
15s "200928_0125017" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 513kB.
Com pip4784Hz
200928_0125020
15s "200928_0125020" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 514kB.
?Com pipNoisy
200928_0125022
15s "200928_0125022" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 514kB.
?Com pipNoisy
200928_0125023
15s "200928_0125023" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 516kB.
?Sop pip5533Hz
200928_0125031
15s "200928_0125031" Uploaded . Download mono MP3 clip 64kB, hi-fi mono FLAC clip 515kB.
Com pip4394Hz
200928_0125035
15s "200928_0125035" Uploaded . Download mono MP3 clip 61kB, hi-fi mono FLAC clip 513kB.
Com pip4662Hz
200928_0125056
15s "200928_0125056" Uploaded . Download mono MP3 clip 62kB, hi-fi mono FLAC clip 515kB.
Com pip4716Hz
200928_0125078
15s "200928_0125078" Uploaded . Download mono MP3 clip 62kB, hi-fi mono FLAC clip 516kB.
Com pip4664Hz
200928_0125103
15s "200928_0125103" Uploaded . Download mono MP3 clip 64kB, hi-fi mono FLAC clip 516kB.
Com pip4680Hz
200928_0125113
15s "200928_0125113" Uploaded . Download mono MP3 clip 63kB, hi-fi mono FLAC clip 519kB.
Com pip4718Hz
200928_0125123
15s "200928_0125123" Uploaded . Download mono MP3 clip 62kB, hi-fi mono FLAC clip 523kB.
Com pip4718Hz
200928_0125138
15s "200928_0125138" Uploaded . Download mono MP3 clip 62kB, hi-fi mono FLAC clip 519kB.
Com pip4658Hz
200928_0125161
15s "200928_0125161" Uploaded . Download mono MP3 clip 60kB, hi-fi mono FLAC clip 518kB.
???Noctule2408Hz

File 200928_0124 started at 7:05pm BST (18:05Z). File 200928_0125 started at 7:14pm BST (18:14Z).

2020-09-29: Anti-Social Calls

Starting just before 7pm BST, a little over an hour close to 16WW with many bats, maybe more than 10. Lots of common pipistrelles, but sopranos and maybe a Nathusius also around.

Apparently the 'social' calls of the common pipistrelle are also 'anti-social', used this evening to drive away the sopranos apparently!

(Is a bat at 20:19 a soprano pipistrelle, for example?)

There's a bit of extra crunching noise from me walking around, and some break-in from me chatting with a couple of people I was with. The chat sounds somewhat like a badly tuned short-wave radio.

I had a quite clear view against the sky of bats patrolling back and forth. A couple of times one passed right in front my face, low and fast!

spectrogram of 70 minutes near 16WW, batsounds are the vertical yellow streaks
Spectrogram of 70 minutes near 16WW from just before 7pm BST, many bats, see the vertical yellow streaks.

Raw mono frequency division output only from the Batbox Duet:

4311s "20200929T17:53Z near 16WW Batbox Duet L only FD10" Uploaded . Download mono MP3 clip 26250kB.

(The heterodyne frequency on the Duet was kept at ~20kHz most of the time, in the hope of catching a Nathusius, though in the end I listened to the FD channel almost exclusively, via the field recorder.)

2020-09-30: Rain

It's raining this evening, so I'm not expecting much activity to end my bat-induction month with!

But close passes at 7:14pm BST, 7:21 and 7:22, when I had the bat detector at my open front window for about 20 minutes, suggests that they bats still didn't get the memo.

2020-10-01: October

Opened the front window at 7:10pm BST, and almost immediately had a faint pass! It's about 12°C out, so the window isn't staying open very long tonight.

More at 7:17 (faint), 7:19 (faint).

Closed window because I was getting cold at 7:30.

2020-10-03: Chilly

Opened the front window at 7:09pm BST, first faint pass at 7:11. It's about 12°C out.

More passes at: 7:12 (sounding different to common pip at 45kHz), 7:26, 7:32 (loud), 7:38 (loud), 7:42/7:43 (several loud passes).

I switched to the field recorder and the Duet just after the 7:12 pass, with the heterodyne set to 20kHz.

20201003T18:25Z 16WW front window Batbox Duet 20kHz het spectrogram
7:25pm BST (18:25Z) bat activity spectrogram, from front of 16WW, likely all common pipistrelle, mixture of echolocation and social calls.

Some excerpts from the full recording:

Full Recording

20201003T18:12Z 16WW front window Batbox Duet FD10 mono waveform
Full recording from 7:12pm BST (18:12Z) frequency-division (FD10) channel mono lossy, waveform/amplitude.
1935s "20201003T18:12Z 16WW front window Batbox Duet FD10 mono" Uploaded . Download mono MP3 clip 11582kB.

Closed window at 7:45.

2020-10-04: Cold Drizzle

Opened the front window at 7:04pm BST. It's about 10°C out. Not expecting activity tonight.

Closed window at 7:15.

2020-10-05: Cold but Dry

Opened the front window at 7:02pm BST. Faint pass at 7:04. It's about 14°C out.

Pass at 7:08, much higher pitched, maybe soprano?

Loud passes at 7:14, 7:15, 7:27, 7:29; likely common pipistrelle.

Closed window at 7:41.

2020-10-06: Still Cold but Dry

Opened the front window at 6:45pm BST, checking for earlier activity. It's about 13°C out.

Loud pass at 6:52, 6:53 (very faint), 6:59, 7:07, all likely common pipistrelle.

Closed window at 7:10. (Getting cold, and joining a webinar!)

2020-10-07: Hogsmill

Tonight's first treat was to see a soprano pipistrelle release. Then later, by the Hogsmill, to hear at least one completely new species!

Snapshot of abundant bat activity on Hogsmill Lane by the river 2020-10-07 evening
Snapshot of abundant bat activity on Hogsmill Lane by the river 2020-10-07 evening c/o Alison F who said there were at least two passes that would qualify as Natterer’s bat according to [Jon] Russ.
2020-10-07 evening at the Hogsmill River: two bat species?
Brief snapshot of sound from the Hogsmill River (Hogsmill Lane) with what may be mainly soprano pipistrelle (Pipistrellus pygmaeus, ~55kHz constant frequency) to start, then Daubenton's Bat (Myotis daubentonii) with much higher bandwidth and lower peak-energy yellow streaks in the second half.
4s "20201007T18:15Z Hogsmill Lane Hogsmill River two bat species" Uploaded . Download stereo MP3 clip 119kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 29kB, hi-fi stereo FLAC clip 520kB.

A busy minute from about 7:25pm with continuous activity and multiple bats (FD channel bandpass filtered 1500Hz to 7500Hz per MW's suggestion):

60s "20201007T18:25Z Hogsmill Lane Hogsmill River multiple bats FD10 bandpass 1500 to 7500Hz" Uploaded . Download mono MP3 clip 1004kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 326kB, hi-fi mono FLAC clip 2747kB.

More-or-less the whole half-hour-ish (37 min) at the Hogsmill starting from approximately 7:10pm, bandpass filtered and downsampled to 16ksps to save bytes (~50% for the FLAC):

2275s "20201007T18:10Z Hogsmill Lane Hogsmill River multiple bats FD10 bandpass 1500 to 7500Hz resampled 48ksps to 16ksps" Uploaded . Download mono MP3 clip 10861kB, hi-fi mono FLAC clip 48851kB.

2020-10-08: Hopeful

Opened the front window at 6:43pm BST. (Sunset 6:22.) It's about 14°C out.

First pass at 6:43 (likely pippip, ie common pipistrelle, Pipistrellus pipistrellus), 6:48 and 6:49 (multiple passes, pippip), 6:53 (faint), 6:58, 7:00 (a couple of passes).

Closed window at 7:10. (Getting cold, and already in a webinar!)

2020-10-10: Early

Opened the front window early at 6:27pm BST. (Sunset 6:17.) It's about 11°C out.

Passes at 6:49 (faint, likely pippip), 6:50 (faint), 6:51 (faint).

Closed window at 7:00. (Getting cold!)

2020-10-11: Less Early

Opened the front window at 6:47pm BST. (Sunset 6:15.) It's about 12°C out.

Pass at 6:52 (faint, likely pippip).

Closed window at 7:06. (Getting cold!)

2020-10-14: Sunset

I haven't been able to make dusk observations for the last couple of days.

Opened the front window at 6:09pm BST. (At sunset 6:09.) It's about 11°C out.

Pass at 6:23 (faint, likely pippip), 6:28 (loud), 6:29 (loud), 6:36 (faint, higher pitch?).

Closed window at 6:49. (Getting cold!)

2020-10-17: Ten After

Opened the front window at 6:12pm BST. (Sunset 6:02.) It's about 11°C out.

Pass at 6:18 (faint, likely pippip), 6:21 (loud), 6:28 (loud, very different sound, burbly and slower: maybe a Nathusius?), 6:29 (loud, pippip).

Closed window at 6:39. (Detector's rechargeable NiMH battery getting flat!)

2020-10-18: Ten After Too

Opened the front window at 6:10pm BST. (Sunset 6:00.) It's about 11°C out.

Pass at 6:17 (faint, multiple), 6:18 (faint), 6:19 (faint, multiple), 6:20 (faint, multiple), 6:21 (loud), 6:22.

Closed window at 6:35.

2020-10-19: Early

Opened the front window at 6:04pm BST. (Sunset 5:58.) It's about 13°C out.

Pass at 6:11 (faint), 6:13 (faint), 6:16 (very faint), 6:21 (loud, multiple), 6:23 (faint), 6:24 (loud), 6:25 (loud + faint), 6:26 (loud, multiple), 6:27 (loud, multiple), 6:28 (loud), 6:29 (faint), 6:30 (loud).

It sounded like the ones around 6:25 were successfully catching insects.

Closed window at 6:40.

2020-10-20: Warm

Opened the front window at 6:16pm BST. (Sunset 5:56.) It's about 16°C out, ie quite warm. Heterodyne on 45kHz as usual.

Pass at 6:17 (likely pippip), 6:19, 6:22 (multiple), 6:23, 6:24 (faint), 6:25, 6:27 (loud, patrolling right outside the window at points!), 6:28, 6:29 (multiple), 6:30, 6:32 (loud, very different bubbly sound), 6:33, 6:35, 6:36 (faint), 6:39 (faimt, multiple).

Plenty of visual contact around 6:30, with some swoops very close!

Closed window at 6:40.

2020-10-21: Still Warm

Opened the front window at 6:11pm BST. (Sunset 5:54.) It's about 15°C out, still quite warm. Has rained a lot today, but not raining now.

Pass at 6:16 (faint, likely pippip), 6:17 (faint), 6:18 (loud), 6:24, 6:29, 6:33 (faint then loud, bubbly as 6:32 yesterday), 6:35 (loud), 6:36 (faint), 6:37 (loud pippip, then 2x 'bubbly').

Closed window at 6:41.

2020-10-22: Back Garden Pip, and Myotis

In the back garden recording from ~6:12. (Sunset 5:52.) It's about 12°C out. Has rained a lot today, but not raining now.

Mainly one solo (common?) pip back and forth above our garden and nearby. Often very clearly visible against the sky, maybe ~2m above ground level.

I ended up with two recordings by accident (accidentally stopped the first).

(Will test using FD channel only, bandpass 1.5--7.5kHz, downsample to 16ksps, store as FLAC and mono mp3, to store efficiently with minimum loss of fidelity.)

20201022T17:13:24Z 16WW back garden common pipistrelle AudioMoth broadband partial spectrogram
Zoomed-in fragment of common pipistrelle spectrogram.

As well as the Duet, I had MW's audiomoth recording broadband (192ksps), here being a common pipistrelle:

5s "20201022T17:13:24Z 16WW back garden common pipistrelle AudioMoth 48kHz het MW" Uploaded . Download mono MP3 clip 39kB (i).

The heterodyne MP3 file was generated by mixing a 48343Hz sine wave with the WAV file because 48343Hz was the peak in the coefficients of a fast fourier transform of the WAV file.

The WAV files were converted by me to FLAC for more efficient (but still lossless) storage and serving.

(The AudioMoth was picking up some of the Duet het-downshifted output too, as they were close together on my garden table near the house.)

An approximately matching sample from the Duet with FD10 and ~45kHz het:

8s "20201022T17:13:24Z 16WW back garden common pipistrelle Batbox Duet L FD10 R het45kHz" Uploaded . Download stereo MP3 clip 205kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 52kB, hi-fi stereo FLAC clip 1143kB.

The Batbox Duet was generally pointing towards the back of the garden, though I did somtimes walk with it a few steps and point it. The AudioMoth stayed stationary, with its microphone pointing straight up.

Here is another broadband pass sample.

Myotis

Later, near 16WW, MW captured a Myotis with its much more vertical and wider-bandwidth frequency sweep (with heterodyne):

3s "20201022T18:05:56Z near 16WW Myotis sp broadband het MW" Uploaded . Download mono MP3 clip 24kB.
Myotis bat spectrogram
Myotis bat spectrogram.
Myotis bat FFT
Myotis bat FFT (Fast Frequency Transform) spectral power chart.

The original broadband (WAV, 200ksps).

AF reported first Myotis 6:48, last 7:23, social calls too.

20201022T18:04:23Z Daubenton 30kHz highpass spectrum AF
2s Daubenton's (Myotis daubentonii) spectrum c/o AF, broadband after 30kHz high-pass filter.

To remove our background chit-chat (and het output from my Duet for example), in Audacity I rather hashly applied a high-pass filter at 30kHz (Nyquist, roll-off 48dB/octave). That gets rid of most but not all of the crud visible in the spectrograms, without (I hope) distorting the Myotis waveform too much. I have left the sample rate of the originals at 256ksps.

I have also produced versions slowed down by 10x, a different sort of frequency division. Those are resampled to a relatively-widely supported 32ksps which should preserve all information in the original, eg waveform.

Short segment (broadband 256ksps, after high-pass filter) slowed down 10x, and I think that echoes are perceptible:

20s "20201022T18:04:23Z Daubenton 10x slow AF" Uploaded . Download mono MP3 clip 193kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 80kB, hi-fi mono FLAC clip 691kB.

Another, quiet, from about 14 minutes earlier (broadband, high-passed) slowed 10x:

25s "20201022T17:50:43Z Daubenton 10x slow AF" Uploaded . Download mono MP3 clip 184kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 99kB, hi-fi mono FLAC clip 486kB.

A much longer segment, 2 minutes later (broadband, high-passed) slowed 10x, with some common pipistrelles butting in towards the end:

150s "20201022T17:52:33Z Daubenton 10x slow AF" Uploaded . Download mono MP3 clip 1486kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 587kB, hi-fi mono FLAC clip 5269kB.

Immediately after (broadband, unfiltered) slowed 10x, then highpass at 15kHz, maybe preserving a social call at the end:

23s "20201022T17:52:51Z Daubenton 10x slow AF" Uploaded . Download mono MP3 clip 280kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 91kB, hi-fi mono FLAC clip 906kB.

Finally (broadband, high-passed) slowed 10x:

40s "20201022T18:23:27Z Daubenton 10x slow AF" Uploaded . Download mono MP3 clip 360kB (may not be available in data-saver/lite mode), download low-bandwidth mono MP3 clip 159kB, hi-fi mono FLAC clip 1393kB.

2020-10-23: Near 16WW

First (pippips, several at once) heard ~6:13pm BST, last ~1h13 later. ~12°C.

2020-10-24: Front

Opened the front window at 5:57pm BST. (Sunset 5:48.) It's about 15°C out, but windy and raining slightly.

Pass at 6:19 (faint, likely pippip), 6:24 (loud).

Closed window at 6:37.

2020-10-25: Front

Opened the front window at 4:49pm GMT. (Sunset 4:46.) It's about 11°C out, fairly clear skies and still.

Pass at 5:10 (loud, likely pippip), 5:11 (loud, multiple).

Closed window at 5:19. (Cold, and rain started.)

2020-10-26: More Front

Opened the front window at 4:54pm GMT. (Sunset 4:44.) It's about 11°C out, fairly clear skies and still. Lots of insects about.

Pass at 5:11 (mutiple, likely pippip), 5:12 (faint), 5:13 (faint), 5:14 (faint), 5:15 (faint, multiple), 5:16 (faint, multiple), 5:17, 5:20 (loud), 5:22 (very loud, multiple).

Closed window at 5:28. (Cold!)

2020-10-27: Not Much Activity

Opened the front window at 4:53pm GMT. (Sunset 4:42.) It's about 12°C out.

Pass at 5:05 (loud, likely pippip), 5:07 (loud), 5:08 (faint and loud, multiple), 5:21 (loud).

Closed window at 5:30.

2020-10-28: Post Rain, Low Activity

Opened the front window at 4:56pm GMT. (Sunset 4:41.) It's about 11°C out. It has been raining very hard within the last hour or so, stopped now.

Pass at 4:58 (likely pippip).

Closed window at 5:20.

In these more recent sessions I'm trying to find out how soon after sunset I hear a pass, eg to gain some idea of how far from roosts 16WW may be.

I expect peak activity roughly 20 minutes after sunset.

2020-10-29: Hogsmill

20201029 caddis fly on hand

Set off for Hogsmill Lane at 4:52pm GMT, back 6:10. (Sunset 4:39.) It's about 14°C out.

Lots of (caddis?) flies. Lots of noisy roosting parakeets and jackdaws.

First bat heard 5:02 (pip?). The party really kicked off 5:14 and fairly solid until I left ~5:55.

Lots of what I think were common and soprano pipistrelles generally scooting around at eye level or above.

Maybe a handful of passes from a Daubenton's (Myotis) such as at ~5:40, larger and skimming the water and more machine-gun sound:

1s "20201029T17:40Z Hogsmill possible Daubenton" Uploaded . Download mono MP3 clip 8kB, hi-fi mono FLAC clip 49kB.

Lots of social calling too!

I crossed Villiers Road and checked for activity on the other side, which there was (at least a pipistrelle visible and echolocating).

Here is 55 minutes starting from ~5pm until I left:

3346s "20201029T17:00Z Hogsmill Lane bat partytime 55m" Uploaded . Download mono MP3 clip 12651kB, hi-fi mono FLAC clip 73703kB.

2020-10-30: Visual

I was out from about 5:10 to 5:55 watching bats near 16WW, a mixture of common and soprano pipistrelles I think from checking with a het detector at 45kHz and 55kHz.

It was warm at about 15°C, with some drizzle. Sunset was 4:37.

Daubenton's was heard down at the Hogsmill, I am told!

2020-10-31: Halloween Bats

Opened the front window at 4:57pm GMT. (Sunset 4:35.) It's about 12°C out. It has been raining very hard today, stopped now.

Pass at 5:07 ('bubbly').

Closed window at 5:20.

Dataset

name
16WW Bat Activty
description
Bat activity with audio and spectrograms, at or near 16WW, Kingston-upon-Thames, London, KT1 3JA, UK
version
1
keywords
bat, Chiroptera, urban, London, England, UK, ultrasonic, detection, Pipistrellus, pipistrelle, common pipistrelle, 45kHz, soprano pipistrelle, 55kHz, Myotis, audio, heterodyne, het, frequency division, spectrogram
variableMeasured
activity
date created
2020-09-18T14:20:37Z
date published
date modified
2020-10-31T17:20:17Z
temporal coverage
2018-10/..
spatial coverage
UK centre 51.406696N,-0.288789E elevation 16m
canonical URL
this descriptive text with markup
distribution
bat data folder
distribution
16WW ambient sound recordings: bats
licence
this dataset is licensed under CC0, ie it is effectively public domain; if you make use of this data, attribution is nice but not obligatory
creator
Alison Fure
Damon Hart-Davis