Bats without borders: The Nathusius’ pipistrelle
by Matthew Beattie
Populations of Nathusius’ pipistrelle can be found across much of continental Europe; however, it was 1940 before this migratory species was first officially recorded as a rare visitor to the United Kingdom. Subsequent studies of these shy creatures have since revealed that populations are far more established, prolific and widely traveled than anyone could have imagined.
A Nathusius' pipistrelle being held. Fully grown bats are not much larger than the tip of a human thumb. (Photo: alamy)
The Nathusius’ pipistrelle is one of several European migratory bat species. It is tiny – around the size of your thumb – and weighs just seven or eight grams. Depending on the time of year, it can be found at dusk using its sonar to hunt for insects close to estuaries, lakes, rivers and canals across much of continental Europe. While a number of bat species hibernate over the lean winter months, the Nathusius’ pipistrelle is known to migrate significant distances to reach milder climates and areas where food is more plentiful. Yet until relatively recently, it was assumed that this was a continental species and that the North Sea was the natural limit to its westward range.
At home on land and at sea
The UK’s first Nathusius’ pipistrelle bat was officially recorded in 1940, on the remote Shetland Islands, 168 kilometers northeast of the British mainland. Nature experts concluded it was a vagrant: a rare visitor that had reached the UK from the continent by chance. However, other sightings of the species followed on the mainland: infrequent sightings, yet enough of them to suggest somewhat greater numbers. As a consequence, its status was raised to that of a migratory visitor. Today, Nathusius’ pipistrelles have been recorded across the UK, Ireland and even on oil platforms out in the middle of the North Sea. A small number of maternity colonies – temporary groups of pregnant reproductive female bats that form to raise their young – have also been found in both mainland Britain and Northern Ireland, suggesting that some groups of bats have chosen to remain rather than migrate back to the continent.
Nobody is certain whether the increase in both the frequency and number of recorded UK Nathusius’ pipistrelle sightings is the result of the bats adjusting their migratory paths or whether it is due to an increase in bat research. Both are plausible explanations, according to Daniel Hargreaves, who has been passionate about bats for thirty years. Today he is a volunteer with the Bat Conservation Trust and is among the UK’s foremost experts on the Nathusius’ pipistrelle: “I think it’s definitely the case that people are paying more attention to bats nowadays,” he explains. “We do generally feel that there are more individuals migrating here and some of that may be linked to climate change. A scientific study several years ago suggested that Nathusius’ pipistrelles are moving their migration trajectories slightly north, but we don’t know this for a fact.”
Hermaness Nature Reserve, the Isle of Unst, in the Shetland Islands. These remote islands to the northeast of Scotland were the location for the UK's first recorded Nathusius' pipistrelle sighting in 1940. (Photo: shutterstock)
A happy team of UK bat volunteers holding a captured Nathusius' pipistrelle that was previously ringed in Latvia. (Photo: Daniel Hargreaves)
Indeed, there is still a great deal we do not know about the Nathusius’ pipistrelle and bats in general. While birds have been extensively studied, bat research is still in its infancy and is very much the preserve of passionate volunteer experts like Hargreaves. “It's a good animal group to study,” he says. “Every year new species are discovered, which is unusual for mammals.”
Since the early 20th century, habitat losses and human activity have had a significant impact on both UK and global bat populations. “The post-war period was especially bad,” Hargreaves explains. “We had heavy losses and lost a lot of colonies. We know this from limited historical data.” Fortunately for British bats, the UK was among the vanguard of countries to introduce powerful legislation to protect bats and their roosts when it passed the Wildlife and Countryside Act in 1981. This has helped slow the decline, but so little is known about bats, it is difficult to put a number on losses or populations. Britain’s bats gained a powerful ally in 1991, when the Bat Conservation Trust was established to educate the public about bats, coordinate research and encourage conservation efforts. Today it has more than 6,000 members and is the UK’s leading non-governmental organization dedicated solely to bats. It also works closely with similar bat groups elsewhere in Europe – particularly when it comes to the research and monitoring of migratory bat species such as the Nathusius’ pipistrelle.
Bat research on a national scale
One of the Bat Conservation Trust’s most significant endeavors at present is the Nathusius’ Pipistrelle Project. This citizen science project involves dozens of volunteer bat groups working together across the length and breadth of the UK. Its aim is to increase our collective understanding of this fascinating bat species, and it is already yielding interesting results: “There had been probably only around a hundred recorded firsthand sightings of individuals in the UK when we started the study in 2012. It was a relatively rare species here, which was one of the reasons it sparked our interest,” says Daniel Hargreaves. “We didn’t know whether populations were increasing or decreasing – we still don’t, actually. We don’t know a lot about them at all.” It is hoped that the Nathusius’ Pipistrelle Project will change this by allowing research to be conducted on a national scale and generate meaningful volumes of information.
The project volunteers collect data about the Nathusius’ pipistrelle using a range of different methods, including the capture and release of bats under special license from the government. Individual bats are caught in flight using harp traps: “These are a bit like giant steel frames, about three meters tall by about one to two meters wide,” Hargreaves explains. “The frames then have banks of fishing line set vertically. At the bottom is a cloth bag. The bats fly into the fishing line and they land in the bag at the bottom of the trap. It doesn't hurt them at all.” Bats are lured into the traps with recordings of the male Nathusius’ pipistrelle’s mating call, which are played though speakers. The captured bats are then sexed, recorded and ringed before being released.
It is the rings that are put onto the captured bats that have yielded some of the most fascinating insights into the Nathusius’ pipistrelle: most notably, its phenomenal ability to migrate significant distances across land and sea. Volunteers in the UK have captured individual bats that have been ringed by international bat groups in Latvia and Lithuania – proving that bats have traveled up to 1,499 kilometers from their traditional maternity colonies in the Baltic region. Additionally recaptured individuals from the UK have been found in Holland and Belgium. “The bats don't know how long it's going to take before they reach land,” Hargreaves explains. “Some of these animals are setting off on their journeys at around three-to-four months old. They just head on this southwest trajectory and seemingly keep flying until their unknown destination.”
With each year it is running, the Nathusius’ Pipistrelle Project is adding significantly to the number of recorded sightings of the Nathusius’ pipistrelle in the UK, transforming our understanding of its place in the country’s ecosystems. Ultimately, by better understanding the lifecycle, habits and migratory patterns of the species, we will be better able to find ways of ensuring it survives and thrives well into the future. For example, we still do not understand what sort of impact offshore wind farms may have on migrating bats: “We might be able to use the data we gather on this project to help the people developing wind energy with mitigating the impact of turbines on migrating bats,” Hargreaves explains. “We know that massive numbers of bats are migrating. Some scientists in Europe have even indicated that it could be one of the largest movements of mammals in the world.”
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The Nathusius’ pipistrelle
Head and body length:
46mm – 55mm
228mm – 250mm
6g – 16g
Reddish-brown, occasionally with frosted tips on the belly. The ears, membranes and face are usually very dark.
Medium-sized flying insects, mosquitoes and caddis flies
Nathusius’ pipistrelles favor roosting in cracks in walls, fissures in rocks and in crevices. Roosts are generally found close to stretches of water such as freshwater lakes, rivers and canals.
Nathusius’ pipistrelles migrate southwest across Europe in late fall and winter before returning to major breeding grounds and established maternal colonies in Latvia, Lithuania and western Russia the following spring. In the UK it appears that a small summer breeding population is supplemented by migratory individuals from continental Europe during the winter.
During breeding season toward the end of summer, male Nathusius’ pipistrelles sing to attract females. They will fly or find a roost, from which they will call for hours – all night long, if necessary – until they find a mate.
Learn more about the Bat Conservation Trust and how you can get involved:
Bat Conservation Trust: www.bats.org.uk
Listen to a slowed down recording of a male bat singing here:
male bat singing
Support valuable bat research by donating to the Nathusius’ Pipistrelle Project: