Leisler's bat

GB: Nearly threatened

England: Nearly threatened

Scotland: Nearly threatened

Wales: Nearly threatened

Global: Least concern

Head & body length: 50mm - 70mm

Forearm length: 38mm - 47mm

Wingspan: 260mm - 320mm

Weight: 12g - 20g

Colour: Fur golden-tipped or reddish-brown, darker at base.

Leisler’s bats appear early in the evening, soon after the noctule, and have been observed emerging from houses at about sunset. They may stay away from the roost until dawn.

They usually fly high and fast in the open, frequently at or below tree top level, with shallow dives. Sometimes Leisler's bat fly close to the ground along lanes and well lit roads. In suburban areas they may be attracted to insects around street lights.

Leisler’s bat is naturally a forest species, roosting in tree holes. Bat boxes have proved in some areas to be a useful substitute for natural roost sites. They occasionally share roosts with noctules and pipistrelles.

They also roost in buildings, both old and new. In houses, Leisler's bat 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, producing a loud metallic sounding call.

Leisler’s bats hibernate in tree holes, in the cracks and cavities of buildings and occasionally in caves and tunnels. Elsewhere in Europe they sometimes hibernate in large groups in rock crevices.

Leisler's bat feeds on flies, moths, caddis flies, beetles.

Mating occurs from late summer until mid-autumn. Breeding Leisler's bat 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 female Leisler's bats gather in tree holes and sometimes in buildings, particularly in Ireland where colonies may number 1,000. The young are born in mid-June. Usually a single young is born, but twins are recorded more frequently in eastern Europe.

Leisler’s bats echolocation calls range from 15 to 45kHz and peak at 25kHz. 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 strident than those made by the noctule bat.

Leisler’s bat is found throughout the British Isles, with the exception of northern Scotland. Ireland is a stronghold; the species is the third most common here.

In view of its rarity in Britain, all known roosts are important and special care should be taken of roosts in buildings and of wooded areas where the species is known to occur. Bat boxes have been successful in encouraging the species in some areas.

The internationally important population of Leisler's bat in Ireland deserves special attention.