Leisler's

Leisler's bat is widespread but rare in Europe, including the British Isles, Isle of Man, north to southern Scotland. A European stronghold is in Ireland, where the species is the third most common bat and where the Noctule does not occur. It is migratory in Europe with a record of 810 km. One British individual was found 250 km (157 miles) from where it had been ringed 4 years previously. It has also been found as a vagrant to the Shetland Isles.

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 some areas. The internationally important population in Ireland deserves special attention.

flight & ultrasound

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 treetop level with shallow dives. Sometimes they fly close to the ground along lanes and well-lit roads.

Leisler's bats' echolocation calls range from 15 to 45 kHz and peak at 25 kHz. The calls are occasionally audible to the human ear. On a heterodyne bat detector a characteristic 'chip chop' with clicks at the top of the range is heard but the sounds are les strident than that of the Noctule bat. Leisler's has a loud call that is similar to the Noctule ("chip-chop") but with many more "chips" than "chops". The Leisler's "chop" is normally heard best above 20 kHz (at around 25 kHz) as opposed to the Noctule's "chop" which is generally heard best below 20 kHz.

Leisler's calls can be confused with those of the Serotine or Noctule: 

Serotine's do not make the "chip-chop" 2-part call of the Leisler's but just a "chop" that is loudest at about 27 kHz. If a "chip-chop" sound is heard with a heterodyne detector set to 25 kHz Serotines can be discounted. Serotines are found more frequently at the edges of landscape features such as treelines or hedgerows whereas Noctules and Leisler's prefer a very open environment.

  Leisler's bat call on a Time Expansion bat detector.

breeding

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 females. If no females arrive then the males fly around calling again. These calls are audible to the human ear and are not the calls used in echolocation. The males do not feed during the courtship period.

Male Leisler's bats can have a harem of up to 9 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 reach 1,000. The young are born in mid-June. Usually a single young is born but twins are recorded more frequently in eastern Europe.

summer roosts

Leisler's bat is naturally a forest bat roosting in tree holes for which bat boxes have proved in some areas to be a useful substitute. They occasionally share roosts with Noctules and Pipistrelles and roost in old and new buildings. In houses they have been found around the gable end 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.

winter roosts

Description
Head and Body Length	50 - 70 mm
Forearm Length	38 - 47 mm
Wingspan	260 - 320 mm
Weight	12 - 20 g
Colour	Fur golden-tipped or rufous-brown, darker at base.
Life Cycle
Mating Period	End August - October
Maternity Colonies	Established late spring. Young: 1 born mid June.
Colony Size	20 - 50 bats
Longevity	Up to 16 years.
UK Status	Vulnerable
Habitat and Food
Summer Roosts	Tree holes, bat boxes, buildings.
Winter Roosts	Tree holes, buildings, occasionally caves and tunnels.
Feeding Habitat	Open deciduous and coniferous woodland, parkland, suburban areas and around street lamps.
Food	Flies, moths, caddisflies, beetles.