A cautionary tale
I am having such fun with my ultrasonic microphone that I made a special journey to a known Barbastelle site. This is a rare species with only a few known maternity roosts in the entire country.
I arrived in good time before sunset to get my bearings. The site turned out to be a National Trust owned woodland with a network of public footpaths plus a convenient lay-by for parking; absolutely ideal!
Firstly, I selected a mature Oak tree in a hedgerow where I deployed my heterodyne detector, tuned to 36kHz, feeding the signal to an unattended recorder.
Then for my full-spectrum kit, I found a glade within the main wood with a gap in the canopy and some understory, which I correctly assumed would be good for biodiversity.
I was blasé about the machines working in the harvest fields nearby and amplified music from some distant village. I never worry about such distractions when targeting bats as the frequency difference is enough to separate the valid signal from ambient noise.
However, this is a cautionary tale for unbeknown to me, a male bush-cricket (Pholidoptera griseoaptera) was sitting close to the microphone. I cannot hear them nowadays and as I explained, I had just parked my bionic ear.
Then I retreated and sat bravely in my folding chair for an hour, serenaded by Tawny Owls and a Muntjac, as the light faded.
File size limitations
I mention the time duration because on my system, the maximum WAV file size is 2GB which equates to 62 minutes at 192/24 on one channel.
This is more than enough for my purposes and a quantum improvement over the niggardly < 2 seconds available on the early time-expansion machines.
Later at home when I had transferred the files to my PC, I was pleased to find that the Barbastelles had performed on cue and I had numerous well-modulated ecolocation sequences.
Unfortunately, my bush-cricket had also made known his presence, stridulating without a single pause masking Barbastelle pulses, on the sonograms. Mmm! Of course officially, I am in favour of biodiversity! Doubtless, the bat recordings are repeatable and next time I will be more circumspect!
I cannot do justice to sonograms here but instead, I include a Tawny Owl protesting at my presence. Full-spectrum recording captures normal audio as well, so here is a ‘by product’ of the session.
The main problem with ultrasonic recording is the need to review all the material back home on a PC when it is a forensic and painstaking job checking through the file visually. But then, how better to spend an evening ?
Finally, I would encourage mainstream wildlife recordists to cast their net more widely and target the ultrasonic world. It is a rewarding genre and new discoveries await.
But one final word of warning… Remember, nothing propinks like propinquity!