Wildlife Act 1976 / 2000
EU Directive 92/43 Annex II, Annex IV
Bern Convention Appendix II
Bonn Eurobats Convention Appendix II
Key Identification Features
The lesser horseshoe bat is one of Ireland’s smaller bats and is the smallest species of the horseshoe family in Europe. They have soft fluffy fur with their undersides coloured grey and white with the remainder of their bodies having a smokey brown colour with a slight reddish tint. Young lesser horseshoe bats have a more grey body colouration than adults. When fully-grown, adult’s head and body measure up to 4.5cm in length with a 3cm long tail. At their heaviest in autumn adults can weigh up to 9 grams but will slim down to 5 grams after the hibernation period in spring. The wingspan, which is composed of a thin web of skin stretched across long fingers can reach up to 25cm in length with a relatively broad wing design reflecting their fast highly maneuverable flight style. The distinctive horseshoe shaped nose is used when the bat is engaged in the echolocation of its prey and functions as a reflector to help locate small insects. A near constant frequency call is used when hunting which at the ultrasonic range of 110 – 115 kHz is higher than any frequencies used by other bat species in Ireland. Lesser horseshoe bats are a vocal species and when located within the roost site emit continual chattering calls to communicate.
The preferred habitat type for the lesser horseshoe bat is among sheltered valleys near wooded countryside and are often found in limestone areas in Ireland. Summer roosts are usually located in old unoccupied buildings which have wide entrances as this bat species requires a direct flight path into the site. Summer roosts are usually maternity colonies containing breeding females, their offspring and in some cases juvenile males. These colonies are often large and can contain up to one hundred individuals. Mature males and non breeding females will roost alone or gather in small groups. Winter roosts are established in old buildings, caves, mines or cellars as long as such sites provide humid conditions with this bat species preferring a temperature range of 6 – 9 degrees Celsius. Lesser horseshoe bats do not huddle together in clusters like most other Irish bat species but hang freely from horizontal surfaces by the feet and wrap their large wings around the body for warmth.
Food and Feeding Habits
Lesser horseshoe bats emerge from the roost to hunt thirty minutes to an hour after sunset, they will leave the colony one at a time unlike other bat species who emerge in groups. They generally remain active all night before returning to the roost about an hour before dawn. They hunt low to ground level and are extremely maneuverable fliers allowing them to hunt within vegetation or close to walls and hedgerows. Their diet consists of caddis flies, crane flies, lacewings, moths and midges. They will glean these insects from vegetation or directly off the ground but they can also catch prey on the wing. During a hunting trip they will generally not travel more than 3km from the roost site if their home range is located within a good quality habitat. Rest sites are used to perch on and eat larger insect prey with an individual bat having several regularly used sites usually on tree branches within its territorial range.
Reproduction and Life Cycle
The mating season for lesser horseshoe bats begins in September and runs until November. Brief mating chases occur within the winter roost prior to copulation where the male hangs behind the female from a horizontal surface by the feet. Once mating is complete fertilization is delayed until the female relocates to the nursery roost by spring time. Pregnancy length will depend on the weather with colder conditions slowing the fetus’s development. A single offspring will be born from the June to July summer period with young bats covered in fine hairs and weighing up to 2 grams. They will first open their eyes after three days and will be weaned by their mothers for the first five weeks of life. They will be capable of solo flight by six weeks of age and can be fully independent by their seventh week. As is the case for all Irish bat species parental care is given by the mother only. Both male and female lesser horseshoe bats will reach sexual maturity at one year of age. The average lifespan of a lesser horseshoe bat in Ireland is 5 years but some individuals have been recorded as having lived for 18 years.
Bats are believed to have evolved from small insect hunting mammals which occupied the tree canopy of forested areas of the Eurasian continent. The present day bat family tree now contains 950 different species divided into 17 families. The lesser horse shoe species belongs to the Rhinolophidae family in the Chiroptera order. The oldest fossils that gave rise to modern bats date from 50 million years ago. Past climatic changes such as the last Ice Age seriously affected the number and range of bats but they can now be found in most habitats throughout the world except for land areas near the poles. The lesser horseshoe bat species can now be found throughout southern Europe, south Russia, North Africa and around the Caspian Sea. They were once widespread throughout the entire European continent but their natural ranges have been in decline for some time. They are currently absent from Scotland, Denmark, Northern Germany and Scandinavia. This bat species was present in Britain 6,000 years ago and may also have been in Ireland at this time but they were not identified here until 1859. They are now found in western coastal counties in limestone areas with a density of four individuals per km2 in good quality habitats. The Irish lesser horseshoe bat population was estimated to number 12,000 individuals in the 1990’s.
The lesser horseshoe bats of Ireland are now Europe’s largest population of the species and as such their protection is vital. This bat species is very sensitive to disturbances when it is roosting both in summer and hibernation sites. If disturbed they will raise their metabolic rate which must be compensated for by increased feeding. Modern buildings are usually unsuitable for establishing roost sites as large unobstructed entrances are required by this species which most modern structures do not provide. Roost disturbance is an issue in Ireland due to building renovations and the bats roosting position of hanging freely from horizontal surfaces leaves them vulnerable. The European population of lesser horseshoe bat is in decline due to past changes in agricultural and forestry practices. The increased use of pesticides reduces the number of insect prey on which this species is totality reliant. The lesser horseshoe bat is now offered strict legal protection under Irish, European and international legislation.