Earth Notes: Bats Around our Home aka 16WW (2020)

Updated 2024-03-25.
Learn how I became active observing and recording the various local bats...
From hearing bats outside my gaff in September, and borrowing some detectors, I started observing them more systematically...

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" (captions) Uploaded . Downloads:
[Noises from bat detector and chat between DHD and AF.]

So we're getting a few social calls actually.


So I think that we last spring, feeding, feeding,


when you get those bits of tree,


there's all those, that's a lot, a social call, there.


chonk, chonk.


So we've got one of that here,


and we've got another bat flying around making social calls.


And at this time of year, it's showing an aspiration to mate.


Because bats mate in September or October or whatever,


they have this delayed implementation of a social call,


a lovely social call to life.


There, did you see that?


Lovely social call.




And a feeding buzz.


You had a feeding buzz on your bat detector,


which is like a little raspberry,


and it's the point at which the bat takes its prey.


Right, that's homing in, presumably.


Get that one.


We've got a lot going on there.


We've got more than one bat.


Well, that's carry on up the alleyway.


There's no bats on this day.


I would say that, especially in dark alleyways,


Western boundary, the green at Willingham Way,


you can have bats feeding all through the night.


Yes, I wouldn't have any way of knowing, of course,


because I wouldn't be able to see them.


How do they cope with street lighting like this?


When they don't like it.


No, well, I'm...


Yes, they're going to be a problem when you say,


"It's practice streets."


I could leave the static bat detector in the garden, though.


Should we do that?


We could do.


What does that do?


Well, I'll leave it for a week in the garden


and then I'll analyse the results.


Oh, it's actually just records, yes?


I mean, I think that's fine.


If you tell me, I'm sure Jean will have no problem with it.


You've got a tree in the garden I can strap it to?


Well, there's that one at the back that got set fire to.


It's a party!


How [] is it?




You've got a trunk?


It's not very thick.


It's not.


It goes that high.


It goes a bit higher than that, but it's a bit slender,


so it depends how heavy your thing is.


I can strap it on.




Next week is going to be brilliant, weather.




Always backs here.


You've a chance of getting quite a rare bat here.


This is a common pipistrelle.


So it goes like that, as if it's catching when it's homing in, I guess.


It's where the echolocation is speeding up.


Yeah, yeah.


That's the point where it takes its prey.


Yeah, there I can hear it.


So an insect bites the dust every time that's on my eyes.


It does indeed.


But it's still part of the echolocation, so you'll see the buzz on...


Just tighten up.


On 45.




And when it goes down to 30, 20 or 30, it's the social call.


Oh, OK. Interesting.


I'm not getting any social calls here.




But when the Nathusius pipistrelle, we'll be echolocating at 39 kilohertz,


and it sounds slightly hysterical, so it's more bubbly and louder quite often,


because they're flying at a different height, to be honest.


The common pipistrelles fly and soprano pipistrelle, flying at mid-canopy height.


Remember when we were on the western boundary,


and Sim and I were discussing about where the bat was actually flying.


So these bat detectors can only detect 45 kilohertz from a distance of 20 meters,


which is about the mid-canopy on these trees.


Nathusius pipistrelle will fly in a more open area,


and is not so worried about these street lights.


These are orangy anyway.


They're not sort of broad-spectrum white lights,


and these orangy lights aren't as much of a nuisance to, you know,


the more amber spectrum, they're not so much of a nuisance as a white light,


which can have a UV component.


Well, look, look, these, the ones down this street are much lighter.


Yeah, look.


These are much newer LED ones.


I know, the new LEDs are a bit of a nuisance.




Ha! You're picking up the engine.


I am, I'm going with the exhaust.




All right, thank you. I'll stop.

Soundwalk 2020-09-12 near 16WW
September 2020 snapshot of activity on CRE near 16WW at end of Soundwalk, by 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 . Downloads:
81s "20200921T18:40Z 16WW back garden common pipistrelle 45kHz" Uploaded . Downloads:
28s "20200921T18:45Z 16WW back garden common pipistrelle 45kHz" Uploaded . Downloads:
47s "20200921T18:47Z 16WW back garden common pipistrelle 45kHz" Uploaded . Downloads:

2020-09-22: Out Front

2020-09-22 ~9pm BST common pipistrelle distribution by 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 . Downloads:

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 . Downloads:

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!)

Amazingly, 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 . Downloads:

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 . Downloads:
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
15s "200927_0122015" Uploaded . Downloads:
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 . Downloads:
2488s "20200928T18:14Z 16WW front window Batbox Duet FD10" Uploaded . Downloads:

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 . Downloads:

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 . Downloads:

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
15s "200928_0124009" Uploaded . Downloads:
Com pip4682Hz
15s "200928_0124020" Uploaded . Downloads:
Sop pip5300Hz
15s "200928_0124022" Uploaded . Downloads:
Sop pip5300Hz
15s "200928_0125004" Uploaded . Downloads:
Com pip4829Hz
15s "200928_0125011" Uploaded . Downloads:
?Com pipNoisy
15s "200928_0125013" Uploaded . Downloads:
?Com pipNoisy
15s "200928_0125017" Uploaded . Downloads:
Com pip4784Hz
15s "200928_0125020" Uploaded . Downloads:
?Com pipNoisy
15s "200928_0125022" Uploaded . Downloads:
?Com pipNoisy
15s "200928_0125023" Uploaded . Downloads:
?Sop pip5533Hz
15s "200928_0125031" Uploaded . Downloads:
Com pip4394Hz
15s "200928_0125035" Uploaded . Downloads:
Com pip4662Hz
15s "200928_0125056" Uploaded . Downloads:
Com pip4716Hz
15s "200928_0125078" Uploaded . Downloads:
Com pip4664Hz
15s "200928_0125103" Uploaded . Downloads:
Com pip4680Hz
15s "200928_0125113" Uploaded . Downloads:
Com pip4718Hz
15s "200928_0125123" Uploaded . Downloads:
Com pip4718Hz
15s "200928_0125138" Uploaded . Downloads:
Com pip4658Hz
15s "200928_0125161" Uploaded . Downloads:

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 . Downloads:

(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 . Downloads:

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 by 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 . Downloads:

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 . Downloads:

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" (captions) Uploaded . Downloads:

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 (faint, 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" (i) Uploaded . Downloads:

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 . Downloads:

The Batbox Duet was generally pointing towards the back of the garden, though I did sometimes 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.

By contrast, listen to the following segment captured by AF later the same evening, common and then soprano pipistrelles with maybe a social call or three and some break-in from a nearby het detector (broadband 256ksps, after 30kHz high-pass filter) slowed down 10x:

150s "20201022T17:28:39Z pipistrelles 10x slow AF" Uploaded . Downloads:


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 . Downloads:
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 by 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 harshly 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 . Downloads:

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

25s "20201022T17:50:43Z Daubenton 10x slow AF" Uploaded . Downloads:

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 . Downloads:

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 . Downloads:

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

40s "20201022T18:23:27Z Daubenton 10x slow AF" Uploaded . Downloads:

2020-10-23: Near 16WW

First (pipistrelles, 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 (multiple, 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 . Downloads:

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 . Downloads:

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.

2020-11-01: No(vember) Bat?

Opened the front window at 4:51pm GMT. (Sunset 4:33.) It's about 16°C out. It has been raining today, stopped now.

Possible pass at 4:54 (faint).

Closed window at 5:21.

2020-11-02: November Bat

Opened the front window at 4:30pm GMT. (Sunset 4:32.) It's about 12°C out. It has been sunny, with a burst of rain this afternoon.

Battery died without me noticing so may have missed something: replaced 4:49!

Pass at 5:09 (loud, probably pip).

Closed window at 5:20.

2020-11-03: November Bats

Opened the front window at 4:37pm GMT. (Sunset 4:30.) It's about 9°C out. It has been sunny today.

Pass at 4:52 (loud, probably pip), 6:58 (multiple), 5:05 (faint, multiple), 5:06 (faint).

Closed window at 5:13.

2020-11-04: Reading Nature

I have just watched Reading Nature Episode 3: Bats about bats in Kingston and a little further up the Hogsmill.

Opened the front window at 4:35pm GMT. (Sunset 4:28.) It's about 9°C out. It has been sunny today.

Pass at 5:01 (loud, multiple, probably pip), 5:02 (multiple), 5:03, 5:05 (loud, multiple), 5:10 (multiple, maybe sop pip?), 5:14 (loud), 5:16 (loud, very different sound maybe sop?).

Closed window at 5:20.

2020-11-05: Fireworks

It's about 8°C out at sunset (4:26). It has been sunny today. I can see insects aloft from my window.

But it's cold, it's fireworks night, and I have to be on a video call from 5pm. So any "lockdown2" bats will remain unobserved by me this evening!

2020-11-06: Quiet

Opened the front window at 4:23pm GMT. (Sunset 4:25.) It's about 9°C out. It has been sunny today. I can see insects aloft from my window. (And fireworks are still happening, especially from 5pm...)

Pass at 4:53 (loud, 'bubbly' not pip-like), 5:17 (faint, pip?), 5:23 (loud).

Closed window at 5:27.

2020-11-07: Daubenton

bat detector handheld Pettersson D240x time expansion

Listening for Daubenton's (Myotis) at the Hogsmill. (Sunset 4:23.) It's about 12°C out. It has been sunny today.

I had a new toy on loan today, a Pettersson D240x with time expansion (x10), through which parakeets sound like cows, and with which it is possible to pick out the close and quietening clicks of a feeding buzz. And firework bangs are audible in slow motion too, like a beer fizz.

I didn't take the field recorder, so it was all experience and no data!

Arrived before 5pm, left about 6:30pm. First Daubenton detected ~5:04.

Lots of activity, from common and soprano pipistrelles. (The distinction seems clearer in the D240x at 45kHz than for other detectors.)

Lots of Daubenton's activity, possibly at least a couple of individuals.

A Nathusius was detected at 4:56.

Maybe a Natterer's too a couple of times (different sound).

In one spot at the end of Hogsmill Lane there was repeated Daubenton activity, back and forth skimming the water, in spite of lots of light spilling from the adjacent buildings and car park. I think that I got a glance of white belly fur.

Lots of swooping to the water which may have been pipistrelles drinking.

Other activity such as roosting parakeets and crows/jackdaws, and a mouse swimming.

2020-11-08: Warm, Busy

Opened the front window at 4:34pm GMT. (Sunset 4:21.) It's about 14°C out.

Pass at 4:49 (likely pip), 4:46 (loud), 4:47 (multiple), 4:48 (multiple), 4:49 (faint, multiple), 4:50 (multiple), 4:51 (loud, multiple), 4:52 (multiple), 4:53 (loud, multiple), 4:57 (multiple), 4:59 (loud), 5:00, 5:01 (multiple), 5:02 (loud, multiple), 5:03 (multiple), 5:04 (faint, multiple), 5:06 (loud, multiple), 5:07 (loud, multiple), 5:08, 5:09 (multiple), 5:10 (loud, multiple).

Closed window at 5:10.

CRE Roost?

Alison F tells me that she had a good night around Cambridge road estate ... I left the transect mark on so its possible to see where I went. ... The temperature actually increased while I was out.

20201108 Cambridge Road Estate bat observations AF
Activity on the Cambridge Road Estate 2020-11-08 observed by AF.

2020-11-09: No Observations Made

No time to make any observations this evening.

2020-11-10: Still Active

Opened the front window at 4:32pm GMT. (Sunset 4:18.) It's about 13°C out. It has been sunny today. I could see insects aloft from my window earlier.

Pass at 4:48 (multiple, probably pip), 4:49 (multiple), 4:50, 4:51 (loud), 4:56 (loud, multiple), 4:57 (faint), 5:01 (faint, multiple, bubbly), 5:03 (loud, bubbly), 5:05 (faint), 5:07 (loud, multiple), 5:08 (loud, multiple), 5:09 (faint), 5:10 (loud, multiple).

Closed window at 5:11.

2020-11-11: Visual Contact

Opened the front window at 4:06pm GMT. (Sunset 4:17.) It's about 13°C out.

Pass at 4:39 (probably pip), 4:47 (loud), 4:48 (loud, multiple), 4:49 (loud - saw it!).

Closed window at 4:59.

2020-11-12: Got the Memo?

Opened the front window at 4:26pm GMT. (Sunset 4:15.) It's about 12°C out.

No passes heard before window closed ~40 minutes after sunset.

Closed window at 4:58: only had a brief time to listen this evening...

2020-11-13: AudioMoth

I have placed an order for an AudioMoth field recorder, that can do broadband ultrasonic for bat detecting!

The AudioMoth is a low-cost, full-spectrum acoustic logger, based on the Silicon Labs Gecko processor range. Just like its namesake, AudioMoth can listen for sound from audible frequencies, well into ultrasonic frequencies. It is capable of recording uncompressed audio to micro SD card at up to 384,000 samples per second.

(USD60 for the AudioMoth, USD35 for the waterproof case, plus other bits.)


Opened the front window at 4:22pm GMT. (Sunset 4:14.) It's about 11°C out.

Pass at 4:41 (multiple, pip), 4:42, 4:49 (loud, multiple), 4:50 (loud, multiple), 4:54 (loud, multiple), 4:55 (loud, multiple), 4:56 (loud), 4:57 (loud, bubbly), 4:59 (loud).

Closed window at 4:59.

2020-11-14: Raining

It's about 14°C out, but raining (and has been all day). So I won't be listening out for bats tonight. Nor likely tomorrow night given heavier rain forecast, along with temperatures around 10°C by sunset.

2020-11-15: Briefly Stopped Raining

Opened front window 4:30pm GMT. (Sunset 4:11.) It's about 9°C out, has been raining all day, even some sleet.

No passes heard.

Closed window at 5:08.

2020-11-16: Raining

Opened front window 4:24pm GMT. (Sunset 4:10.) It's about 11°C out, but raining.

No passes heard.

Closed window at 5:00.

2020-11-17: Not Raining Today

Opened front window 4:26pm GMT. (Sunset 4:09.) It's about 13°C out.

Pass at 4:39 (pip), 4:48.

Closed window at 5:00.

2020-11-18: Rain Stopped Play

Opened front window 4:05pm GMT. (Sunset 4:07.) It's about 12°C out.

Pass at 4:42 (loud, multiple, pip including feeding buzz), 4:49 (just after rain started).

Closed window at 4:55, a few minutes after rain started.

2020-11-19: Cooler

Opened front window 4:20pm GMT. (Sunset 4:06.) It's about 7°C out.

No passes heard.

Closed window at 4:51, quite cold!

2020-11-21: Cooler

(No attempt to observe yesterday.)

Opened front window 4:04pm GMT. (Sunset 4:04.) It's about 11°C out.

No passes heard.

Closed window at 4:40. Battery had already run down, whoops!

2020-11-23: Cooler

(No attempt to observe yesterday.)

Opened front window 4:00pm GMT. (Sunset 4:02.) It's about 9°C out.

No passes heard.

Closed window at 4:37.

2020-11-28: Speculative

(No attempt to observe for last several days as cold and unpromising!)

Opened front window 4:20pm GMT. (Sunset 3:58.) It's about 9°C out.

Pass at 4:34 (pip).

Closed window at 4:45.

2020-12-21: Solstice Chancer

(No attempt to observe on intervening days; it has been cold and wet!)

Opened front window 4:05pm GMT. (Sunset 3:55.) It's about 14°C out.

Pass at 4:26 (loud, pip).

Closed window at 4:45.