6 September 2014: Bat Walk – Abingdon

Leader: Ben Carpenter

We gathered at the Health and Welfare Centre car park in Abingdon at 19.45 for a brief introduction from Ben before setting off with the light dimming in the direction of the Abbey Meadows to our first stop at the little up-and-over bridge at the Mill Stream. There, many acoustic bat detectors materialised from David’s rucksack. So with some clarification of the expected frequencies of the various bat species echo location, we all tuned-in. The 20kHz group listened in for the Noctules, while the 40-50kHz group listened-in for Pipistrelles. A solitary Common Pipistrelle was the first to break the silence. From there, we progressed clockwise round the Abbey Meadows picking up what we could hear on the detectors and looking out for bats flying past. We stopped at intervals while Ben gave us more information about bats – the various species of bat and the ones we were most likely to see/hear, the anatomy of their wings, where they roosted, what they ate and how (catching with their feet, enfolding with wings or with their mouth). Also, Ben had his laptop with him and was able to show us pictures of the species we were trying to observe and samples of their echo location calls. We stopped to listen for Noctules at the river’s edge near a narrow boat where Ben had been successful earlier. We did not hear Noctules but we did surprise the boat owner when he came out to find fifteen people pointing gadgets at him. He apologised for not being able to offer us all chairs! A little further on, we picked up Daubenton’s which completed the species tally for the night.

On the way back along the Mill Stream, we picked up many strong signals in the 40kHz-50kHz interval. One bat in particular was patrolling up and down the Stream. Also, in the 20kHz region, we heard a lot of the ‘social’ communications, but not the echo location of the Noctules. Back at the bridge, we had a chance for further questions. Ben explained more about detectors – heterodyne, frequency division, and time expansion – their cost and the software required to exploit them fully back home on the computer. Also there was fascinating discussion about the ability of Horseshoe bats to exploit the Doppler Effect and travel on intercept courses – quite remarkable adaptations.

So an excellent and fascinating walk in the gloaming with a super guide. Thanks again to Ben.

Common Pipistrelle, Soprano Pipistrelle, Daubenton’s.
Chris Biggs, Bridget Biggs, Graham Bateman, Hugh Summers, Vivienne Summers, Adrian Allsop, Joanne Wetton, Karolis Kzlanskis, Evelina Savickaite, David Guyoncourt, Carina Morris, Caroline Gregory, Nigel Gregory, Bob Evans, Rachael Everett (15 total)

Hugh Summers