Echolocation
In open habitats the call is similar to whiskered and Daubenton’s bats, with a rapid series of clicks, although the repetition rate is faster and the call quieter. The calls are extremely broadband in frequency.
Caution is needed when using heterodyne detectors to identify Myotis bats to species level. The call of pipistrelle bats flying in clutter can sound similar to Natterer’s bats.
Habits
Natterer’s bat is found in a varied range of woodland habitats, from dense woodland to more open parkland, gardens and coniferous forest. Frequently it forages in open meadows and woodland clearings, away from linear features. Prey includes flies, moths and lacewings, with a substantial number of spiders.
Whilst naturally a tree-roosting bat, most known summer roosts in the UK are in old stone buildings with timber beams, such as castles, barns and churches. It will adopt bat boxes and even use them as nursery roosts. Winter roosts are almost always in underground sites, where the bats tuck themselves away in small crevices, sometimes on their back.
Reproduction and life cycle
Maternity colonies are formed from May to June and bats can stay in these roosts until September to October. Bats may move regularly between roosts and sometimes include some adult and immature males.
Swarming occurs with other species in late summer and early autumn around cave and mine entrances, with some bats travelling as far as 65 km to the swarming site.
In winter Natterer’s bats are found in any small cave-like structure or even in exposed rock crevices.
Distribution, status and conservation
Natterer’s bat is found throughout most of the British Isles; this is generally a scarce and poorly known species, but the British population is internationally important.
The majority of Kent records are of hibernating bats, as Natterer’s bat is one of the two species most regularly found in underground sites in winter. Grounded bats feature in the records, and 15 new woodland sites were identified when Natterer’s bats were trapped during the 2009 BCT Bechstein’s Bat Survey.
Some maternity roosts are known to have been lost in the county as a result of the demolition or redevelopment of barns and other agricultural buildings as well as timber treatment, and effects of pesticides on their insect prey. To conserve summer roosts the conversion of barns should be discouraged or allow for bats’ continued use, and the maintenance and remedial timber treatment of other older buildings carefully monitored. Winter sites should be protected not only for hibernation, but also for the little-understood part they play in the bats’ social calendar as autumn swarming sites.
The NBMP long-term trend data now show Natterer’s bat increasing since 1999.
