LEISLER’S BAT Nyctalus leisleri

 

Status: Native; Scarce (but relatively common in Yorkshire)

 

Habitats:  Woodland; Grassland; River/Lake; Semi-urban

 

A relatively large bat, with characteristically shaggy hair around the shoulders, leading to its alternative name of Hairy armed bat.  The dorsal (upper) surface is golden brown with dark roots (giving it a bicoloured appearance); the underside is a paler grey-brown. 

 

This species feeds predominantly in deciduous woodland habitats; particularly along rides and woodland edges.  Radio-tracking surveys in Kent have shown that this habitat is preferred, even when the woodland abuts a major road.  Pasture and riparian habitats are also used, and this species has even been found feeding over sand dunes in Ireland (where it is one of the commonest species).

 

Like the Noctule bat, to which it is related, this species can forage over large areas.  Average home ranges can approach 18 square kilometres, and foraging flights can be 13 km from the roost.  As with Noctules, flight is rapid and direct; Leisler’s bats tend not to stoop in pursuit of insect prey to the same degree as Noctules, instead making rather shallow dives, followed by more gradual climbs. Roosts are left shortly after dusk; two or three feeding bouts occur in a typical night.

 

Unlike the Noctule, Leisler’s bats roost mainly within buildings in the summer (although bat boxes and tree-roosts can also be used).  During autumn and winter this species is thought to roost mainly in tree-holes; in the autumn the males are said to emit a sweet, rather pungent smell (allowing it to be separated from the female by small alone in certain cases).

 

Nursery roosts typically comprise 20-50 females bats (but in Ireland roosts ten times this size are known).  Young are born in June-July; males form batchelor groups at this time.  Like many other bats, male Leisler’s set up ‘mating roosts’ in August-September.  Males select ‘calling perches’, repeating a narrowband FM sweep once every second for -10 minutes.  Harems of up to 9 females are established at this time, which are keenly defended by the male concerned.

 

This species has a very similar ‘chip chop’ call to the Noctule, but it is most clearly heard at 24-28 KHz on a bat detector (rather than 22-25 KHz with the Noctule).

 

The British population of Leisler’s bats is estimated to be around 10,000.  This species is relatively common in Yorkshire, including within urban environments..