Wildlife Act 1976 / 2000
EU Directive 92/43 Annex IV
Bern Convention Appendix II
Bonn Eurobats Convention Appendix II
Key Identification Features
Natterer’s bats are a medium sized species but they are one of the smaller bats found in Ireland. They are a bi-coloured species with a light brown colouration on the upperbody which changes to a pale white fur on the underbelly. The face is long and pink with little fur covering, the ears are long and narrow and can extend below the nose when folded forward during sleep and hibernation. Head and body together measure up to 5cm in fully grown adults who can weigh 12 grams at their heaviest in autumn. They will slim down to 6 grams when they first emerge after the winter hibernation. The wing design is relatively broad which tapers to a point at the tips and generally span to 30cm which contain brown coloured wing membranes. Their flight style is moderately fast and maneuverable at lower speeds when they are closer to ground level, they can also hover for short periods. When in slow flight the long tail will be held straight down which it utilizes to snatch prey off vegetation, the tail measures 4.7cm in length when the bat is fully grown. Natterer’s bats are a relatively vocal species and can communicate with a series of chirps and squeaks which change to high shrill calls when in flight. A deep humming sound is emitted if alarmed. They will use echolocation when hunting in the 40 – 60 kHz range with their ultrasonic calls being relatively weak in comparison to other Irish bat species.
Traditionally the natterer’s bat is a woodland occupying species which can now be found in parklands, farmlands, along river valleys and sometimes in urban areas. They require habitats with access to hunting grounds over open water and open woodlands. Summer roosts are established in tree hollows, old buildings and under bridges. Summer roost colonies are small in size and often shared with other bat species particularly brown long-eared bats and daubenton’s bats. Natterer’s bat colonies in summer will be composed of breeding females, their offspring and immature non-breeding females in maternity roosts. Male bats will remain alone during the summer months. For the winter hibernation roosts the natterer’s bat require areas which can retain high humidity therefore such sites are usually located in very damp areas often underground in caves, abandoned mines and cellars. This bat species is considered to be very sedentary so an individual’s home range will be quite small in size.
Food and Feeding Habits
Natterer’s bats only emerge after dark late in the evening usually one hour after sunset. They will use regular flight paths around trees along traditional hunting sites. Two different hunting strategies are used by this species. Smaller insect prey is taken when in flight usually over water such as caddis flies and moths while they can also glean insects from vegetation or directly off the ground. When a prey item is identified the bat can hover over it’s target before dipping down to catch it with it’s feet or scoop it up using the long flexible tail. Such prey items taken in this way are flightless beetles, centipedes and spiders or insect species which are only in flight during the day such as flies, froghoppers and yellow dung flies. This hunting technique greatly increases the type of insect prey which can be consumed and allows for later emergence times which can deter daytime birds of prey. Larger insects are brought back to the roost to be eaten later. On warm nights numerous hunting trips will be undertaken with several bouts of feeding activity occurring on such nights. The natterer’s bat will return to the roost site a few hours before dawn.
Reproduction and Life Cycle
The mating season for natterer’s bats begins in autumn but can continue through a mild winter, roosts at this time will contain a mix of males and females. The male bat will establish a set location in the roost and attempt to attract females to him by emitting calls. Once mating is complete the female will delay fertilization of her eggs until after the winter hibernation ends in spring. Females will gather together in maternity colonies by May where they will remain until September. Females will give birth to usually one offspring by June or early July. When born, young natterer’s bats will develop a light grey to brown fur colour until they are one year of age. Young bats are cared for exclusively by their mothers and are fully weaned after six weeks. They will begin to forage for themselves after only three weeks. The average lifespan of a natterer’s bat in Ireland is 7 years but some individuals have been recorded as having lived for 20 years.
The oldest fossils which 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. 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 natterer’s bat species belongs to the Vespertilionidae family in the Chiroptera order which include the brown long-eared bat, Daubenton’s bat, leisler’s bat and the whiskered bat species found in Ireland. The natterer’s bat is geographically widespread in Ireland but they are not present in abundant numbers. They are currently found in most European countries and are located in isolated pockets in Russia and Korea. They are absent from most of Scandinavia. They were present in Britain 6,000 years ago and may have also have been in Ireland at this time but the species was not identified here until 1845. They are currently considered to be one of our rarest bat species.
As the natterer’s bat is one of our rarest bat species its presence in Ireland is described as vulnerable and of an indeterminate threat status. The main issue in relation to the species is its loss of traditional mature woodland habitats and suitable locations for establishing summer roosts sites within large tree hollows. They are vulnerable to chemical treatment of attic timbers and the increased use of pesticides has reduced the abundance of its insect prey on which they are totally reliant. As the natterer’s bat species usually only produce one offspring each year any losses suffered are harder to recover from. Recent re-forestation projects will in time see a restoration of its natural habitats but these plantations need time to mature. The natterer’s bat species vulnerable status is now reflected in its strict protection under international, European and national legislation.