Inside the bat cave
Greater horseshoe bat numbers may be on the up, but the species remains one of the rarest in the UK.
Are greater horseshoe bats making a comeback in the UK?
With a clearly well-loved toy bat clutched in his hand, a young boy is torn between my display table and the adventure playground behind. “He really loves bats,” his mum tells me. “We’re on the waiting list to borrow a bat detector.” I am at a Bat Day organised by Devon Greater Horseshoe Bat Project (an initiative led by Devon Wildlife Trust) and, despite the inclement weather, there is no shortage of bat enthusiasts here. “We lend out bat detectors to local people to help us discover more about how the bats are using the landscape,” explains project manager Ruth Testa. “Knowing where the bats fly is important if we are to maintain suitable habitat in those areas. The location of these flight paths also helps inform planning decisions.” There’s clearly a need to develop local strategic plans to protect the flyways and foraging areas of greater horseshoes in the face of ever-increasing pressure to build new houses.
The Bat Day is in Buckfastleigh, near Dartmoor. Tucked away on the edge of this south Devon town is Rock Farm: the largest known maternity roost of greater horseshoe bats in western Europe. Up to 2,000 individuals – an eye-watering number by British standards – use this complex of disused agricultural buildings set in an abandoned limestone quarry. It is more picturesque than it sounds.
In Britain, the number of greater horseshoe bats is on the up. In fact, they are increasing faster than any other British bat species currently being
monitored by the Bat Conservation Trust’s National Bat Monitoring Programme, a citizen-science project involving many hundreds of volunteers each year.
This increase is most definitely a cause for celebration, but the rise comes after a catastrophic crash – estimated at more than 90 per cent – during the 20th century. With numbers today estimated at 13,000, the greater horseshoe remains one of our rarest bats ( for comparison, there are around three million common pipistrelles). There is still much to do to prevent this bat from becoming just a memory at dusk. There are a few factors that have contributed to increasing greater horseshoe numbers: national legislation that protects all bats and their roosts; a series of mild winters since the mid-1980s has seen a higher rate of juvenile survival; and conservation action by dedicated individuals and organisations.
Choosy roosters
Pregnant females each give birth to a single baby in July, with spring temperatures determining the peak birth period. When born, the pups weigh less than a heaped teaspoon of sugar, but by about four weeks they have perfected the horseshoe’s butterfly-like flight and fly short distances to hunt their own prey. At around two months, they are fully independent of their mother.
Greater horseshoe bats are not easy to please. Historically, they roosted in caves, but nowadays they will use buildings for all or part of the year. They have a particular fondness for stone-walled, slateroofed structures. Rock Farm – the ultimate gated apartment complex for greater horseshoes – fits the bill. For 40 years, the site has been managed by the mammal conservation charity, Vincent Wildlife Trust. The trust has around half of all Britain’s greater horseshoe bats using roost sites under its wing.
The most robust roost sites are those with a well-stocked bat bistro outside. The bats prefer a mix of broadleaf woodland interspersed with permanent cattle-grazed pasture. It is here that they find their favoured fare: cockchafers (large beetles), early in the year; larger moths, such as the yellow underwing, in the summer; and
dung beetles to provide a hearty meal in autumn and winter.
Despite the conservation input from Vincent Wildlife Trust and others, threats to the bats remain. Reduction in prey availability as a result of modern farming practices and a decline in suitable roosting sites continues. Habitat fragmentation is also a major problem – not just the loss of important features such as hedgerows, but the effects of landscape barriers, such as road infrastructure, noise and artificial lighting. Greater horseshoes are particularly light-shy. The bats are also vulnerable to climatic events, especially severe winters and cold springs. So much is stacked up against them.
Greater and lesser horseshoes have two fundamental differences from other British bats. First, they are the only species to hang free from surfaces. The bats dangle by their feet, with their papery wings cloaked around them, wrapped even more tightly in cold weather. Other British bats have the ability to crawl into crevices if they choose to, but horseshoes do not have the skeletal design for this option.
Second, horseshoes echolocate using a horseshoe-shaped ‘noseleaf’ – a built-in megaphone to help them find their supper. It gives them the look of a rugby player who has fared badly in a scrum. On a bat detector, the sound emitted by horseshoes converts to a symphonic warbling, reminding me of the haunting vocalisation of whale song. It’s also been likened to the sound of the Clangers.
Big babies
The two British horseshoe bat species look remarkably similar, but, as so eloquently described by horseshoe expert Dr Roger Ransome, the lesser horseshoe has a body that would fit comfortably on a teaspoon, whereas the greater horseshoe would need a tablespoon.
Roger has studied greater horseshoes for more than 60 years, and I met up with him and his team of volunteers at Woodchester Mansion. This gothic country house in Gloucestershire is home to a very wellstudied colony of greater horseshoe bats. The building itself is expertly cared for by the Woodchester Mansion Trust (and well worth a visit, with a chance of watching bats live on camera from the ‘bat room’).
“This bat is amazing in so many respects,” Roger tells me. His passion for these bats is unequivocal. “Newborn babies are about a third of their mother’s weight, they grow to full size in two months and can live for up to 30 years.” I find myself imagining a human mother giving birth to a baby of these proportions.
More than six decades of ringing data has given Roger a remarkable insight into all aspects of greater horseshoe ecology, so we now know so much more about bat behaviour. It was, for example, his seminal 1971 research paper that put paid to the idea that bats all spend the winter asleep.
Further south, another ringing programme has been underway for 19 years in disused stone mines around Bath. Amazingly, this area holds up to 10 per cent of Britain’s hibernating greater horseshoes. The programme, run by the Wiltshire Bat Group, is investigating the movement of bats during the hibernation period. “We’ve discovered that the bats use a multitude of different sites, moving frequently between them,” explains professor Fiona Mathews of the University of Sussex, who leads the project. “It’s probably to take advantage of varied microclimates at different stages of hibernation.”
Research is also underway at the mines to look at the bats’ social behaviour, an area still not fully understood.
Perfect conditions
With Bat Day visitors thinning out,
I take a break and walk over to Rock Farm with Tom Kitching, one of Vincent Wildlife Trust’s bat ecologists. Rock Farm’s five-star status means that it is one of the few sites in the country where greater horseshoe bats are found in significant numbers year-round.
The buildings have been enhanced by the trust to create a natural air-conditioning system, with areas of different temperature and humidity. “Warm areas are needed for the growth and survival of young, while stable, cool and humid conditions are needed for periods of torpor and hibernation,” explains Tom. “When the weather cools, the bats’ winter hibernation quarters are ready and waiting in the limestone caves in the adjacent quarry face.” In the face of climate change, roost sites such as this have built-in resilience.
Quite how climate change will impact on the bats is open for debate, though there are signs of range expansion.
Core populations remain in the southwest of England and South Wales, but small groups are now found in Mid and North Wales, the West Midlands and West Sussex. Recently, the species has also been discovered in Kent for the first time in more than 100 years. Undoubtedly, these bats have benefited from milder winters, but more extreme weather events are likely to have detrimental consequences.
As we tour the reserve, I’m surprised that the noise from the nearby A38 does not deter the bats. “It is likely that they put up with the noise because of the quality of the restaurant on their doorstep,” Tom tells me. Domhnall Finch at the University of Sussex is investigating the effects of human-modified landscapes on greater horseshoes. “We are looking not just at road noise but at all environmental variables, including the composition and configuration of the habitat around a roost,” explains Domhnall. “This will help inform conservation initiatives for this species.”
Roost protection has played a critical role in reversing the fortunes of this species, but it is vital to focus on the wider environment, too. As professor Fiona Mathews says, “Bats have a very
long lifespan, so there can be significant time lags before the consequences of environmental problems become evident.”
What has become clear to me is that the greater horseshoe bat’s success story is all about people – scientists, volunteers, landowners, conservation professionals and local communities.
Bat Day is winding down when Richard Hibbert calls by. Richard is Deputy Head at the Greater Horseshoe School nearby, which caters for children with complex needs. “The bats roost in our roof,” he tells me. “They’re happy to co-exist with our amazing young people. The students are proud to know that they share their environment with a very special animal.”
The day’s event has been incredibly inspiring. Later, at sunset, Buckfastleigh’s Millennium Green will be filled with bat watchers, gazing aloft at a stream of shadows silhouetted against the night sky. I do hope our little bat enthusiast, and his toy bat, will be there.
HILARY MACMILLAN recently retired as head of communications for Vincent Wildlife Trust, and is studying for an MA in travel and nature writing.
FIND OUT MORE Visit vwt.org.uk/ species/greater-horseshoe-bat