Echolocation
Noctules have the loudest call of any British bat, ranging from 20 to 45 kHz, peaking at 20 kHz. The lower part of the call is audible to children and some adults. In open habitats the call sequence has a loud ‘chip-chop’ sound on a bat detector with occasional clicks. In closed habitats and in clutter, calls vary from this pattern. In noctule the peak frequency can be higher and may be difficult to separate from Leisler’s or serotine bats.
Habits
Noctules are very dependent on trees, but can be found foraging in a wide range of open habitats, especially over deciduous woodland, parkland and pasture. Both summer and winter roosts are mainly in trees in rot-holes and woodpecker holes, and occasionally in bat boxes, but noctules are found only very rarely in buildings in the UK.
Beetles, in particular chafer and dung beetles, are an important part of their diet, though they will take other smaller insects, including mayflies and winged ants, at certain times of the year.
Reproduction and life cycle
Colonies start to gather in April and often break up into smaller groups prior to setup of nursery roosts. The mothers change roost frequently, carrying the young between roosts during lactation. Single males establish a mating roost during late summer, usually a tree hole, calling with loud shrill calls from the roost entrance, attracting a harem of usually four to five females which stay for one or two days.
Due to the difficulty of finding tree roosts, most of the records of this species are of bats in flight.
Distribution, status and conservation
Although widespread in England and Wales, increasing concern for this species led to its addition to the UK Priority Species list. According to the NBMP 2024, the species has experienced a significant long-term decline, as well as a decline in the short term.
During the 1980s large numbers of noctules were observed at certain times of the year in Kent, but a decline in their numbers was noted and commented on in the early nineties, before it was recognised in other parts of the country. These bats are now considered scarce in the county with only single bats or small numbers seen occasionally. As this is the most easily observed of all our bats, due to its early emergence, size, and flight pattern, this is a matter of real concern. The loss of thousands of trees to make way for transport links and building developments, together with agricultural changes which have led to the loss of the chafers and dung beetles dependent on cattle grazing, have all played a part in the species’ decline. Wind turbine collision is also recognised nationally as a significant pressure for noctules.
Up to 2012, only three tree roosts had been recorded by the KBG, and the status of these roosts had not been confirmed. More recent data shows continued scarcity, but a few additional flight records and occasional tree roosts have been recorded.
