Bats flying around in mid-winter! ...whatever next?
It may be relatively rare compared to the number of recordings made each night during the summer...
...but just one recording shows that there are bats out there.
Inspired by the Bats London project, I've been running my new automatic bat recording system for almost every dry night during January (plus a few where the weather forecast was wrong!) in the hope of capturing any bat activity. This is the system that uses a Dodotronic Ultramic 192k USB microphone connected to a Raspberry Pi 3.
Even in the absence of any real bat calls, its been a useful exercise for testing the software and fiddling with the detection sensitivity parameters. However, a few days ago my patience was rewarded when a common pipistrelle flew past, leaving me with this single 10 second recording.
|Common Pipistrelle recorded 25th Jan 2019 at 5.32pm|
On this particular night, the temperature was approximately 9'C according to the local weather forecast (from the BBC) at the time of the recording. So it was not particularly cold. You can see both echolocation calls, and the lower frequency social calls. It seems strange to me that this apparently solitary bat should waste energy producing social calls, as these are always considerably louder and of longer duration than the echolocation calls, and therefore must consume a lot more energy.
The other noticeable characteristic of this call sequence is the horrendous echo.
|Illustration shows 4 echolocation calls, the rest are believed to be just echos.|
This is an unfortunate problem created by my choice of microphone location.
|This is the view from my microphone's position on the 2nd floor.|
There are a lot of reflective surfaces on the surrounding buildings, and the widows directly behind the microphone may be a major contributor.
I plan to operate this system out in the open during the warmer, dryer summer months to see if I can get some 'clean' recordings.
In the meantime I also want to make a revised system using an electret mic insert which (unlike my old system) does not need batteries. On the old system, even with batteries providing some degree of power supply isolation, I still get a kind on switching noise which is not present on my new 'DodoPi'.
Here are the system details