The first sonogram shows just over half a second of sound from the social calls which Martin referred to, made at the Luton Hoo hibernaculum last month. There is a rapid series of calls lasting about one tenth of a second (remember to divide the times on the scale by 10 to get the true times), and the series is repeated several times. The bat may have been stationary because the volume of the calls does not vary, and there’s no sign of any echolocation calls. The second sonogram shows one series of calls (the third series from the first sonogram), on a bigger time scale.
The question is: which species? We know there were Natterer’s bats around at the time, but we can’t be sure that this was a Natterer’s calling