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  • Writer's pictureMike Bullock

REVEIL 2021: Listening to Bats, 1-2 May

A Little Brown Bat at Arcadia, in a binaural decode from an ambisonic recording.

A Big Brown Bat, recorded in my back yard using an A/B stereo array.

Last year, as part of Soundcamp’s REVEIL festival, I had the great pleasure of moderating a discussion about the sound world of bats, and how listening to bats can help us better understand and protect them. This coming Saturday 1 May I’m looking forward to revisiting the topic as part of REVEIL 2021. Joining our discussion as last time will be researcher Erin Ruggiano, and this time Erin and I will be able to meet in person at the Massachusetts Audubon Arcadia Wildlife Preserve to hunt for bat sounds. Using sensors that can modulate a bat’s calls into the human hearing range, we hope to give REVEIL’s global audience an audible glimpse of the Big Brown Bat (Eptesicus fuscus), the Eastern Red (Lasiurus borealis), and with luck, the endangered Little Brown Bat (Myotis lucifugus). The discussion starts 7:30 PM Massachusetts time, UTC-4. For our UK and Europe friends that’s the wee small hours!

On a recent survey at Arcadia, I was able to pick up this recording of a Little Brown Bat using my Sennheiser ambisonic microphone. I wasn’t sure I’d get anything on that mic, which is only rated up to 20 kHz, but I was able to get some decent (if a bit noisy) recordings of this bat hunting at around 50 kHz.

Last night I set up a pair of LOM Uši Pro mics in an AB array in my backyard, and got some really clear recordings of a Large Brown Bat.

In both cases I recorded to a Sound Devices MixPre6 operating at 192 kHz sampling rate. I decoded the ambisonic recording using the Harpex-X plugin in Reaper, and did the pitch-shifting and filtering in Izotope RX. I generally prefer to pitch-shift bat recordings by changing the sampling rate and simply reading the file more slowly; that preserves the original data and doesn’t introduce artifacts. Also, it gives an interesting insight into how the bat might be listening, by letting you hear the reverb tails as the calls bounce off of objects (and, ideally, moths).

I plan to spend more time this spring testing different mic arrays for bats; my intention is to get bat recordings that are not only as clean as possible, but can also give us spatial information about the bats movements. I suspect that some of the quick echos we get from these recordings are the bat’s calls bouncing off of buildings.

Bats already had an undeserved bad reputation before the coronavirus pandemic, but since then, it’s been the easy – but unproven – assumption that humans got SARS-CoV-2 from bats. In fact, bat rescuers take precautious to avoid giving the virus *to* bats, though it’s not known whether bats can become ill from the virus.

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