The Leisler’s bat (Nyctalus leisleri) is similar to the noctule, but smaller, with longer fur, particularly around the shoulders and the upper back, giving it a lion’s mane appearance. It was formerly known as the hairy-armed bat.
The calls are occasionally audible to the human ear. On a bat detector a characteristic “chip chop” with clicks at the top of the range is heard, but the sounds are less loud and harsh made by those made by the noctule bat.
Leisler’s bat is naturally a forest species, roosting in tree holes and bat boxes. They also roost in buildings, both old and new. In houses they have been found around the gable ends in lofts, between tiles and underfelt, under ridge tiles, above large soffit boards, behind hanging tiles, under loft floor insulation, behind window shutters and in disused chimneys.
Leisler’s bat is a mobile species and one roost is often occupied for only a few days before the colony moves to another roost. The bats are very vocal prior to emergence and are particularly noisy on hot summer days. They usually fly high and fast in the open, frequently at or below tree top level, with shallow dives. Sometimes they fly close to the ground along lanes and well lit roads. In suburban areas they may be attracted to insects around street lights. They feed on flies, moths, caddis flies and beetles.
The Leisler’s bat has a golden-tipped or reddish-brown fur which is darker at the base. The head and body length is 50mm – 70mm and its wingspan is 260mm – 320mm. It weighs 12g – 20g.
Mating occurs from late summer until mid-autumn. Breeding males emerge from their holes at dusk and slowly fly around calling loudly every second or so. They keep within 300 m of their mating roost, returning to the roost after several minutes, where they continue to call and await the arrival of the females. If no females arrive, the males fly around calling again. These calls are audible to the human ear and are not like calls used in echolocation. The males do not feed during the courtship period. Male Leisler’s bats can have a harem of up to nine females; males give off a strong sweet odour during the autumn. In the summer, maternity colonies of females gather in tree holes and sometimes in buildings, particularly in Ireland where colonies may number 1,000. The young are born in mid-June.
In Britain all bat species and their roosts are legally protected, by both domestic and international legislation.
Many thanks to the Bat Conservation Trust for sharing this information; for more detailed reading please visit their website below.