The species was unknown in this part of the world until comparatively recently. ‘Only seven (bat) species occur in Ireland’ declared Fergus O’Rourke in his Fauna of Ireland, published in 1970. ‘The pipistrelle, the smallest of our bats, is by far the most abundant’, he added. No wonder it was so numerous; three species, it turned out, were masquerading as one. ‘Pipistrelle’ is derived from Latin meaning ‘little squeaker’; children, whose hearing is better than adults’, can just detect some of its calls.
Like all insect-catching bats, pipistrelles transmit powerful high-pitched pulses which bounce off objects around them, sending echoes back to the sender. From these, the bat builds up a ‘sound picture’ of its surroundings, as detailed as the ones our eyes provide in daylight. Luckily, bat pulses are transmitted at frequencies much too high for us to hear; they are so loud that, were we able to detect them, we would be deafened.
During the 1950’s, our knowledge was transformed by the invention of bat detectors. These devices respond to the high pitched sounds bats make and shift them down to our hearing range. Pulses differ in frequency and duration depending on the species of the sender. Detectors can display the ‘shapes’ of pulses and their frequencies. Modern portable ones, about the size of mobile phones, have become essential tools for bat identification in the field.
When the pulses of pipistrelles were monitored, an odd pattern emerged. The bats were using two separate frequency ranges. Some individuals transmitted at around 45kHz, while the pulses of others were 10kHz higher. DNA comparisons showed that the bats from the two groups differed genetically; there were two species, not one. The higher pitched bat was named the ‘soprano’ pipistrelle.
The confusion, however, did not end there. Another pipistrelle species had been described in Germany in 1839. It was named in honour of the Magdeburg naturalist Hermann Engelhard von Nathusius, whose main contribution to science was a book on pigs. His bat was slightly bigger, and had broader wings, than the common pipistrelle. The configuration of its teeth was different and it had a hairier back. What could not be known back then was that it emits pulses at around 40kHz. A woodland species, it roosts in hollow trees and holes in the walls of derelict buildings.
Nathusius’ bat is found from Ireland to Russia, but populations in western countries are small and scattered. It was first recorded here in 1996 and breeding was confirmed in Antrim the following year. Winter roosts have been found near Lough Neagh and in counties Down and Wicklow. Although one site had 150 bats, the Nathusius’ remains one of our scarcest species. Did it arrive here recently or is it an old resident whose presence just went unnoticed?
None of our Irish bat species migrates. Is the Nathusius’ pipistrelle an exception? It’s a long-distance migrant in mainland Europe; populations move southwards in autumn and return in spring. A Russian bat travelled 1,600km. Ireland is at the western extremity of the species’ range. Thanks to the warm waters of the Gulf Stream, we have the mildest climate bats encounter anywhere in Europe. Nathusius’ pipistrelle should be able to hibernate here comfortably. Bats breeding in northern Europe might move southwards and westwards in the autumn. Do some of they spend the winter here? Nor is this just an academic question. Research in Canada showed that wind-farms can threaten migrating bats; lungs rupture due to the sudden drop in pressure as they fly between the rotating turbine blades.
Thirty countries are asked to focus on the Nathusius’ bat, making their citizens aware of its presence and implementing conservation measures. Answering the questions surrounding migration would be a valuable Irish contribution to 2015 Bat of the Year research.
DISCOVER MORE CONTENT LIKE THIS