Field Event Reports

Saturday 15th September 2018: Bat hunting evening at Radley Lakes

Leader: Ben Carpenter

We met at the top of Barton Lane where we armed ourselves with bat detectors of varying sophistication and Ben gave us an overview of bat morphology, habits, the principal species to be found in the UK and those we might find on our field trip. Then our group of nine, led by Ben, set off from Barton Lane along cycle route 5 for Radley Lakes, just as the daylight was starting to fade. Bats were already leaving their roosts and circulating around Thrupp Cottage `social calling' - as inferred from our miscellaneous bat detectors. These were mostly Pipistrelles, but one substantially larger bat flew quite fast and straight over our heads. Ben identified it as a noctule. It was the only noctule we saw or heard during the evening. We paused at intervals along the path, as it darkened and the numbers of bats flying around us increased. Ben explained the echo-locations sounds and social calling of the different bats and their characteristic frequencies, so that we gradually `tuned-in'. It was noted that the noctule echolocates at quite a narrow frequency range ~21kHz while the pipistrelle social calling is upwards from ~25kHz. It was evident that the main species present was soprano pipistelles, echolocating at ~55kHz . As we turned and proceeded along the west bank of Thrupp Lake, it was becoming quite dark and by then there were very large numbers of bats flitting near the water's edge. By far the largest proportion was soprano pipistrelles, which favour a watery environment, with far fewer common pipistelles, echolocating at ~45kHz. Ben had a powerful search light which he shone over the water, hoping to illuminate Daubenton's (also known as water bats), echolocating at ~50kHz in short sharp clicks, flying just above the water's surface, but for some reason they seemed absent. We had just two sightings of Daubenton's, one on the North side and one at the East side flying fast and direct just above the surface. So soprano pipstrelles dominated the evening. As an extra, we did catch sight of two very small toads moving in the light of our torches.

Attendees:
Carina Morris + three friends, Lesley Bosley, Felicity Jenkins, Sally Gillard, Ian Smith and Hugh Summers.

Hugh Summers