During the summer males roost in small groups, moving frequently, but in the autumn they establish breeding territories which are visited by females, sometimes in fairly large numbers. The small roost sites limit the number of individuals present: in the UK the average roost is only 14 bats, but in Europe they may exceed 100 animals. Noctules may move roosts in order to reduce the build up of parasites within the roost. Some bats may move between roosts, but in the same area, during the nursing phase, carrying their pup with them.

Both sexes assemble in roosts on emerging from hibernation in March but the females return to the roosts where they were born by June. Noctules mate in the autumn and the females give birth to a single pup in June or July. Noctules emerge from their roosts at around dusk, and can sometimes be seen flying around streetlights. However, in Cornwall the largest recorded noctule roost is in a building! This woodland bat hunts high and fast, searching for larger moths and beetles, even eating cockchafers - a substantial meal. Noctules roost almost exclusively in trees - using splits, holes, and rotted cavities, usually in mature deciduous trees or Scots pine. When the bats are hunting closer to the ground they may use only the frequency modulation call. The loud call can be heard at long distances and allows the noctule to detect prey at long ranges in the open. The pattern heard on a bat detector is a slow rhythmic ‘chip-chop’ alternating steep frequency modulation sweeps with short constant frequency calls. Noctules use a low frequency of 25 kHz to echolocate, so that their calls may be heard by children, or adults with good hearing. Males have conspicuous glands at the corner of the mouth producing a strongly smelling

The ears are short and broad and the tragus (the central ear lobe) is mushroom shaped. Span of as much as 450 mm. Their coat is a uniform golden brown, sometimes with a reddish tinge, and with the chest and belly being only a little lighter. Noctules weigh up to 40 g (6 times the weight of a pipistrelle) and have a wing Noctules are active hunters for larger beetles and moths and have been The largest Cornish bat, noctules are often active early in the evening and, with their long narrow wings, may be confused with swifts, as they fly fast and high above tree top level.

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