Nathusiusís pipistrelle (Pipistrellus nathusii) / Feascarluch Nathusius

The Nathusiusís pipistrelle is the newest addition to the fauna list of Ireland, having been discovered in Antrim in 1997. Since its discovery, it has been located in five other counties; Armagh, Derry, Down, Laois and Wicklow. Due to confusion with the other two pipistrelle species (Pipistrellus pipistrellus and Pipistrellus pygmaeus), it is easily overlooked and is probably far more widespread than the present records would indicate.

This bat is found from Ireland to Asia Minor and is one of the most migratory of all the species in Europe. It is possible that the numbers fluctuate throughout the year as individuals arrive during autumn and winter from Scandinavia. The records of its presence are also dependent on the number of active bat workers "on the ground". As bat workers increase, the known distribution of this species is sure to expand to other counties.

Nathusiusís pipistrelle is slightly larger than either of the two Common pipistrelles weighing in at just 6 to 15.5 grams. The dorsal fur colour is a red or chestnut brown and the ventral a lighter brown often with grey tips. The upper surface of the tail is well haired and the fur on the lower side often extends along the wing membrane to the wrist. The length of the fifth finger (that furthest from the thumb) is diagnostic being over 42mm when measured from the outside of the wrist. The same finger on the other pipistrelle species is less than 42mm.

This bat is usually associated with both woodland and river habitats. It is a frequent visitor to farmland and parkland where, in summer, it roosts in crevices and hollows in trees, bat boxes and deer culling towers. It is occasionally found in buildings. In winter, it hibernates in cracks in walls, trees and sometimes caves. Like all other Irish species, the Nathusiusís pipistrelle is an insect feeder and can, like the other pipistrelles, consume in excess of 2000 midges and other small prey each night.

Emerging from its roost soon after dusk, the Nathusiusís pipistrelle forages along woodland edges, paths and above water, at a height of 4 to 15 metres. Its echolocation call begins with a Frequency Modulated sweep and levels off to a Constant Frequency of between 36 and 41 kHz (Ahlén 1990). On a heterodyne detector, the rhythm of the calls is noticably slower than that of the other pipistrelles.

These bats are known to mate from late July to early September on the continent. The males hold territories and mate with several females. As with the other Irish bats, the female stores the male sperm in her body throughout the winter and, when temperatures rise in the spring, the development of the young begins. There is no fixed gestation period as the growth of the foetus depends on external conditions so that the birth is often delayed during poor weather. This ensures that the young bat is born at the optimum time of insect emergence, usually late June, so that the mother can gain the necessary food energy to supply her baby with milk.

The young bat, although blind and helpless at birth, grows rapidly and is capable of flight within four weeks. Although it is not known how long the young bat remains with its mother, it is thought that she shows the juvenile where to find the favoured roosting and feeding sites. The species is known to live up to seven years.

This species is regarded as rare in Europe and vulnerable elsewhere. As with all our bat species, it is protected by law and it is illegal to knowingly disturb these animals without the appropriate licence. However, much unlicenced bat work can be conducted in the field, such as roost counts, which can provide useful data without affecting or intruding on the animalsí behaviour.

Nathusius's pipistrelle has yet to be discovered in County Cork!