In the middle of the night, the nave of a Breton church resounds with shrill chirps: the building is hosting an annual check-up of great bats, one of the 1,400 species of bats demonised by humans who do not know what they owe them. The latest babies are marked so that their movements from site to site can be tracked and to understand how to better protect the bats, which are threatened by human activity. Another team of scientists from Ireland is studying a surprising feature of chiropterans: their exceptional longevity. IMAGES AND SOUNDBITES ARRANGED IN SEQUENCES