Tree-dwelling bats in Brittany (France) : typology of 60 tree roosts, and fragments of an ecology of the observed species. From 1992 to 1999, prospecting in woodlands in the Northwest of Brittany has allowed the discovery of 60 natural roosts for tree-dwelling bats. Various kinds of occupied hollows have been found inside trees, but those created by the partial healing of narrow cracks, mainly resulting of storm and/or frost (especially in
oaks), are so particularly sought out by bats, that systematic inspection inside this kind of hollows (with ladders, light and small mirrors), quickly turned out to be a really « productive » method, as to the discovery of bats : at least 58 % of the suitable narrow crevices are used by bats (results needing an average of 2,2 visits per crevice). Five bat species have been recorded : the brown long-eared bat (or sp.) [Plecotus auritus (or sp.)] ; the Natterer’s (Myotis nattereri), Daubenton’s (Myotis daubentoni), and whiskered bat (Myotis mystacinus) ; the Pipistrelle sp. (Pipistrellus sp.). The tree roosts can be occupied all through the year, reproduction and hibernation included. Besides, it has been noticed that tree-dwelling bats often move around, from one roosting site to another, probably according to similar trips every year. The observed numbers (bats inside trees, or flying off) go from 1 up to 26 individuals, and several nursery roosts are recorded. Some protective measures for suitable trees are now being taken in a few national forests.
