Leisler's bat

(Nyctalus leisleri )

The Leisler's is the second largest bat in UK and is instantly recognizable in Ireland as it is our largest bat. It is rare all over Europe but its stronghold is Northern Ireland, probably due to less intensive agriculture.

What to look for

The Leisler is a large shaggy haired bat that can fit comfortably across the palm. It has a mane of hair from the back of the head to past the shoulders. The tragus, the flap of skin inside the ear, is the shape of a mushroom and very squat. All our other bats have a pointed tragus. The ears are short and slightly rounded. Exposed skin areas are almost black. The fur underneath extends onto the wing membrane hence the old name 'hairy armed bat'. Leisler's have a very swift, direct flight and are very maneuverable.

Forearm 38 - 47mm / 2½ inches
Length 50 - 70mm / 2½ inches
Weight 12 - 20g / ½ oz

• Heterodyne: The loudest frequency for Leisler's bat is around 25kHz and sounds like an irregular popping 'chip chop' similar to slow clapping with cupped hands. A male Leisler's bat advertising for females has a very characteristic call which is very loud and is done from a bare tree trunk. It sounds similar to two stones being hit together. Leisler's bat produces two calls, which may be produced in sequence. In this case they sound like a 'chip chop' sound. At around 25 kHz the sound is extremely loud and 'bubbly'. As you sweep up the range of frequencies the call will develop into a 'click'. However, this is not always easy to hear due to the volume of the call. Pulse repetition rate is irregular and slow - much slower than many other Irish or British species. Social calls can be heard occasionally. They sound similar to pipistrelle social calls but are much louder and sharper - usually heard without the aid of a bat detector. The mating call is easy to spot, even without a detector. When a bat will be stationary in a tree, for example, all that can be heard is a series of sharp 'clicks' (without the detector) repeated every 0.5 to 1 second.

• Time expansion: On this setting the Leisler's bat has a short, repeated almost monotone whistle. In open situations this bat uses an almost pure CF, of long duration at around 23 kHz, while in a closed environment the call is almost pure FM. In this situation the frequency of maximum energy may be as high as 29 kHz. However, the most common calls are the CF call at around 23 kHz and a 'pipistrelle shaped' call with a tail at 27 kHz.