Bats sometimes change roosts!

There is a building on a site that we have obtained planning permission and a European Protected Species licence to demolish. There had been a single Common Pipistrelle in there last year and we had designed and constructed new roosting opportunities on site for the Common Pips using the building. The bats were roosting between the underfelt and the large interlocking concrete roof tiles. Access was through a gap in the verge where the concrete had fallen out at the junction between the roof tiles and the ridge tile.

The demolition, originally scheduled for the early part of 2008, was put on hold because of funding issues, so the building was put into the monitoring programme for this year. It was quite a surprise therefore to find 11 bats emerging during mid July from the same spot. The bat detectors showed that they were all Common Pipistrelles. Because of the possibility of them being part of maternity roost we thought it best not to hand net them until late August, when the juveniles would all be flying.

So, there we were last night on the roof waiting for the bats. The building has two adjoining pitched roofs with a large, 1.5 metre wide, valley gutter between them. Plenty of space when we’d got up on the roof to move around safely. Luckily the interlocking tiles are all laid on a shallow pitch so it was possible to walk up the tiles and lie down close to the ridge. I could then hold the hand net just below the entrance to the roost without getting too close myself. It was much easier than trying to hold a hand net in place from the ground. With 5 metres of extensions on to reach the ridge hand nets soon get very heavy, and they also wobble a lot, putting off bats they may be waiting to emerge.

The weather was good. 16 degrees Centigrade, light winds and overcast, but dry. A perfect night to find out more about the bats in the roost. It was still a good night an hour and a quarter later when I was still lying on the roof and Anna was listening to a Noctule and Common Pipistrelles on the bat detector, but no bats had emerged. All the preparation and the bats had moved on!