I returned home to be find a grinning Mrs D holding out a full poop-scoop bag for me. I took it with some suspicion, but it was lightness itself, seemingly a bag of air, and on inspection contained the corpse of a bat. Not just any bat, but a Brown Long-Eared Bat.
Its ears are indeed very long. I got wondering why it has big ears, because if its just for sonar, then why doesn't every bat have huge ears?
Well I read here that its because this species specialising in mugging passing moths, so it has to be very quiet, and hence needs large ears to capture its very weak signal. So there you have it!