Leisler's bat (Nyctalus leisleri)
Ialtóg Leisler
The Leisler’s bat is Ireland’s largest, with a wingspan up to 320mm. It is also the third most common bat species in the country. This is unusual in that it is extremely rare elsewhere in Europe. Even in the UK, it is rarely encountered. The reason for its abundance in Ireland is probably due to lack of competition from the noctule (Nyctalus noctula) which is thought to be absent from the country. However, if the latter species does occur here, it is much rarer than in Britain. Another factor is that Leisler’s bat has adapted to roosting in buildings which has offset its dependence on trees.
This species is quick to emerge at dusk and is sometimes abroad long before it. It is conspicuous, being so large, and also because it can be readily heard as it echolocates. The lower range of its calls fall within human hearing range so that its 'tick, tick, tick' is very apparent.
In the hand, the species is extremely timid. The fur is shaggy, giving a 'lion's man' appearance on the back. The hair is bi-coloured, being dark brown at the base and lighter towards the tip. The fur also extends onto the forearm and wing and, because of this, the species used to be called the 'hairy-armed bat'. The tragus, of the ear, is mushroom shaped.
Leisler’s bat is a woodland species. Flying high, it often makes shallow dives to ground level to catch the moths, beetles and flies on which it preys. In summer, it roosts predominantly in buildings but sometimes is found in trees and bat boxes. It seldom stays for long periods in any given site, and is notorious for moving roosts. The audible chatter of the bats within the roost is sometimes obvious on hot days when the bats are active. In winter, the species is found hibernating in trees and buildings but it may also be migratory.
As with the other Irish bat species, mating takes place in the autumn, with the male holding a harem of several females. The young are born in June or July. Nursery roost size in tree holes is usually in the region of 20 - 50 animals. However, in buildings, nursery roosts may exceed 300.
The species is considered as internationally important and occurs throughout the county.