Leisler's bat  (Nyctalus leisleri)

In Great Britain, all bats are fully protected under Schedule 5 of the Wildlife and Countryside Act (1981) as amended, and by the Conservation (Natural Habitats etc) Regulations (1994). An agreement on the Conservation of Bats in Europe (EUROBATS) under the auspices of the Bonn Convention, also known as the Convention on Migratory Species (CMS) is in force, and all European bats are listed under Appendix II of the CMS (3).

This medium sized bat is similar in appearance to the noctule bat (Nyctalus noctula), but it is both darker and smaller (4). The fur is short, reddish-brown on the back and yellow-brown on the belly (2). Hairs on the back are dual coloured, being blackish-brown at the base, and reddish towards the tips (2). The wing membrane, face and ears are blackish-brown (2). Juveniles are darker in colour than adults (2).

Leisler's bat occurs in England and Wales, but is absent from Scotland. In Europe, although populations are fragmented, it has a wide distribution (4), but is found mainly in the south (5). The species is fairly rare in most European countries (2) except Ireland, where it is widespread and common (5).

This bat is largely a woodland species (4); maternity roosts occur in tree holes, buildings and bat boxes (2). Hibernation occurs in tree holes and cavities on and within buildings (2).

Bats are the only true flying mammals. In Britain they are insectivorous (eat insects), and contrary to popular misconception they are not blind; many can actually see very well (6). All British bats use echolocation to orient themselves at night; they emit bursts of sound that are of such high frequencies they are beyond the human range of hearing and are therefore called 'ultrasound' (5). They then listen to and interpret the echoes bounced back from objects, including prey, around them, allowing them to build up a 'sound-picture' of their surroundings (5).

Leisler's bats produce echolocation calls of frequencies between 18 and 45 kHz (4). They emerge just after sunset, and with fast, high flight they hunt for moths, beetles and a range of flying insects, making frequent dives (2).

Mating tends to occur towards the end of August and early September (2), but fertilisation is delayed until the following spring (6). During the mating season, a male holds a 'harem' of up to 9 breeding females in a mating roost (2). Hibernation occurs between the end of September and early April (2). The following summer, maternity roosts of 20 to 50 females form, with births occurring after mid-June (2). Leisler's bats are known to live to a maximum of 9 years (2).

Like all bats, Leisler's bat is vulnerable to a number of threats, including the loss of roost sites; in particular hollow trees are felled if thought unsafe or 'untidy'. Habitat change and loss, affecting the availability of insect prey and causing the fragmentation of feeding habitat is a serious problem for many bats, furthermore pesticide use has devastating effects, by causing severe declines in insect prey abundance, and contaminating food with toxins that may be fatal (3).

In Britain, bats benefit from a very comprehensive level of legal protection (3). Under the Wildlife and Countryside Act it is illegal to intentionally kill, injure, take or sell a bat, posses a live bat or part of a bat, to intentionally (or in England and Wales, recklessly) damage, obstruct or destroy access to bat roosts. Under the Conservation Regulations it is an offence to damage or destroy breeding sites or resting places. Fines of up to £5,000 for every bat affected, and up to six months imprisonment are in place for these offences (7). Several species of bat can also benefit by bat boxes put up by the public.

To find out more about the conservation of this and other British bats, see:

• The Bat Conservation Trust - Species Information Sheet - Leisler’s bat:
  http://www.bats.org.uk/publications_detail.php/218/species_information_sheet_leislers_bat
• The Bat Conservation Trust:
  http://www.bats.org.uk/
• The Vincent Wildlife Trust:
  http://www.vwt.org.uk/index.php

Amy Dunkley, The Bat Conservation Trust, London.
http://www.bats.org.uk

• Echolocation: detecting objects by reflected sound. Used by bats and odontocete cetaceans (toothed whales, dolphins and porpoises) for orientation and to detect and locate prey.
• Hibernation: a winter survival strategy characteristic of some mammals in which an animal's metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer. In insects, the correct term for hibernation is 'diapause', a temporary pause in development and growth. Any stage of the lifecycle (eggs, larvae, pupae or adults) may enter diapause, which is typically associated with winter.

1. Integrated Taxonomic Information System (ITIS) (October, 2009)
   http://www.itis.gov/
2. Schober, W. and Grimmberger, E. (1987) A Guide to Bats of Britain and Europe.Hamlyn Publishing Group Limited, London.
3. Morris, P. (1993) A Red Data Book for British Mammals.Mammal Society, Bristol.
4. Burton, J.A. (1991) Field Guide to the Mammals of Britain and Europe.Kingfisher Books, London.
5. Macdonald, D.W. and Tattersall, F.T. (2001) Britain's Mammals: The Challenge for Conservation.The Wildlife Conservation Research Unit, Oxford University. Available at: www.wildcru.org
6. Altringham, J.D. (1996) Bats: Biology and Behaviour.Oxford University Press, Oxford.
7. Bats and the Law - a quick guide. Bat Conservation Trust (August, 2002)
   http://www.bats.org.uk/