Nathusius' pipistrelle Pipistrellus nathusii
© Phil Richardson
Nathusius' pipistrelle is one of the newest additions to the bat fauna of Ireland, having been discovered in Antrim in 1996. Since its discovery, it has been located in several other counties; Armagh, Cork, Derry, Down, Fermanagh, Kerry, Laois and Wicklow. Due to confusion with the more widespread pipistrelle species, 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.
Nathusius’ pipistrelle is slightly larger than either of the two more 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 Common pipistrelles 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 Nathusius’ 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 Nathusius’ 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. On a heterodyne detector, the rhythm of the calls is noticeably slower than that of the Common 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. This 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.