All UK bats hibernate through the winter – it’s one of the first things we learn when getting interested in bats. Winter hibernation counts in caves, mines and tunnels are an important part of the National Bat Monitoring Programme survey suite used to monitor bat populations. However we also soon learn that bats will emerge on mild evenings in winter to forage and drink; there are occasional evening sightings in most winters.

To find out just how often bats were flying around in December I put one of the Group’s Anabat Express detectors out in my South Derbyshire garden throughout the month. It was mild, with temperatures at sunset not dropping below 2 °C and averaging 6.7 °C. Wind was not a factor, never above Beaufort force 2 and there was rain at sunset on only 5 nights and that persisted well into the night only twice.

I recorded bats on 24 nights with a total of 199 bat passes by common pipistrelles, soprano pipistrelles and Myotis species. Bat passes were recorded at all hours through the night over the month.

On 3rd December there were 54 passes, nearly all by one or more common pipistrelles in the first hour after sunset, with a lot of foraging activity indicated by feeding buzzes.

On 19th December the detector recorded 59 passes, mostly in the three hours before sunrise; again mostly one or more common pipistrelles but this time with persistent social calling, probably a male in song flight.

Perhaps the most surprising record was at 02:17 on the 10th December when the temperature was minus 0.5 °C; a Myotis, probably a Natterer’s bat, made two passes – what on earth was it doing out in those temperatures?

Results are shown in the charts above and the detector is still out so I will update this with the January results when they are all in.

Alan Roe

Derbyshire Bat Group Recorder

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