Nyctalus noctula; the Noctule
This bat is the largest (so long as you conveniently ignore the last greater mouse-eared bat (Myotis myotis)) resident bat, and often the first to emerge at night. It seems to prefer roosting in mature beech (Fagus sylvatica) trees and as mentioned on the entry for Leisler's bat (Nyctalus leisleri) it does roost with this species sometimes. The calls of this bat sound like a regular, quite loud, 'chip-chop' sound that can be detected at 25khz and they can be seen flying higher than other bats, where they feed on high flying invertebrates.