Leisler's bat Nyctalus leisleri

Leisler' bat - click to enlargeThe Leisler's bat is the largest bat present in Northern Ireland where it is common except in upland areas. The fur is reddish-brown. Leisler's bats are the first bats to emerge in the evening, often before sunset. They fly very high with sharp dives. They are commonly found roosting in occupied buildings, particularly houses. Leisler's bats hibernate during the winter months. In Europe, this species is migratory. However, it is not known if the bats in Northern Ireland migrate.

SPECIES DESCRIPTION: The Leisler's bat is the largest of all the bat species in Northern Ireland and is very easily identified. Its ears are relatively short with a tragus that is short and mushroom shaped. The fur, chestnutty-brown in colour, may be slightly shaggy around the shoulders giving the effect of a mane. Leisler's bats used to be referred to as 'hairy-armed' bats due to the extension of the fur as far as the forearm. The head and body length is about 55-65mm and the length of the forearm is about 35-45mm. A small lobe (postcalcarial lobe) is present on the calcar of the tail membrane which separates Leisler's and pipistrelle bats from all other bats in N. Ireland. Leisler's bats emerge early, occasionally just before sunset. They are fast fliers, foraging high above the ground (10m, up to about 70m) in a straight line with fast turns and dives. Male bats are territorial and establish mating roosts in autumn that are visited by females. These 'harems' can contain from one to ten females. The exact mating period is not known, although it probably occurs from August to October. Fertilisation is delayed until the spring following the hibernation period. Females then form large maternity colonies and the young are born from the end of May to the middle of July. These maternity colonies are usually located in buildings, quite often of relatively recent construction, and generally inhabited by humans, It is not known where male bats roost at this time, although it is likely that they are solitary. Very few records of hibernating bats have been reported.

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© Jon Russ 2001. Text refereed by Angela Ross & Lynne Rendle.

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