Science Spin January 2008

Survey Sheds Light on Lives of Irish Bats

By Anthony King

The bat most commonly encountered in Ireland is the pipistrelle, which weighs the equivalent of just five paperclips. They fly at head height, swooping irregular 'loop-the-loops' in jerky manoeuvres as they chase midges. A single bat can chomp through three thousand in one night.

The image here is of a Brown Long-Eared Bat, one of Ireland's native bat species [Picture credit: Austin Hopkirk]

Bat expert Conor Kelleher said the pipistrelle bat's habit of feeding around streetlights makes them obvious in urban areas. They roost in attics and under roof slates. A modern house in the Lee Valley in Cork boasts the largest bat colony in Ireland with about 2,000 individuals. For the last 30 years, bats from the surrounding countryside and villages have flown to this house to have their babies.

It makes for an impressive sight in the morning, said Conor: "They can't all fit in, so they tend to flock around the house, so you get a swarm of 200 to 300 bats." Pipistrelle colonies, he said, usually have less than 100 bats and other species roost in much smaller numbers.

Social

Bats are social animals and on warm days and just before venturing out, the pipistrelles can be heard chattering to one another. They also use sound to navigate. Bats emit very loud calls as they fly and use the returning echo to build up an acoustic picture of their environment; they can discern distance, speed and direction of a moth. The calls of Irish bats are an ear-splitting 110 decibels, as loud as a passenger jet taking off; fortunately the pitch of these calls is too high for us to hear. Having their own sonar system and being the only mammals to fly has made bats an evolutionary success story. One-quarter of all mammals are bats - over 1,000 species. Found throughout the world, they are especially numerous in the tropics, where fruit bats are important pollinators.

Hunters

Of the ten species of bat in Ireland, Leisler's bat is the largest. Conor said this bat is known as "the Irish bat" on the continent because we have the highest national population. They are doing well in urban areas, and can be seen flying up and down Dollymount and Sandymount Strand in Dublin. "They come out of the town houses along the strand and feed along the beaches and over the sea," he said.

Built for speed, they have long narrow, sickle-shaped wings; they fly high, but make shallow dives to bag flies and beetles. "Because they are large and fast, they are not worried about being picked off by crows and so can be seen flying in the early evening before the sun goes down."

Our smaller bats come out after sunset and are dark brown or grey in colour and, to our ears, silent. For bat watchers, a bat detector is thus essential kit. These handheld devices cost as little as fifty euros and convert bat calls to audible frequencies. Bats occur in urban areas; the lough in Cork City for instance is home to five species.

Echolocation

Over 65 million years ago, bats evolved the ability to detect moths and other insects by echolocation. This rendered night-flying moths easy targets; an evolutionary arms race followed, and many moths and other night-flying insects evolved hearing organs on their bodies to detect approaching bats. Once these moths detect bat calls, they take evasive action, zigzagging or by dropping to the ground. To counter this insect surveillance, some bats evolved whispering calls.

The brown long-eared bat is one such bat; they can pass very close to detectors without being heard. Their enormous bat ears, up to one-third their body length, allow them listen to the low returning echoes of their whispers.

Conor Kelleher said the best way to see this bat is to look upwards into a broadleaf tree and look for a bat moving from leaf to leaf, with two huge ears sticking out against the night sky. They sneak up on moths and have such fantastic hearing that sometimes they don't even echolocate. "He can hover in front of leaves and hear the footsteps of an insect or spider as they crawl," explained Kelleher. They, thus, glean prey from the canopy and may use their large eyes.

Surveys

Members of Bat Conservation Ireland (BCI) this summer surveyed sixteen roosts of brown long-eared bats. Three types of buildings were looked at: castles, churches and cathedrals, and 18th-century mansions. Tina Aughney of Bat Conservation Ireland says these bats like big, open, complex roof spaces and avoid heated buildings. "They use the attic space to fly around, doing acrobatic exercises and testing the air to make sure climatic conditions are right for foraging." If conditions are unsuitable, they will feed on whatever insects are in the building, she said.

Nursing colonies form a roosting ball, said Tina , with the adults on the perimeter offering insulation and protection for the young bats within.

Since 2003, BCI members and the animal ecology group at the National Park and Wildlife Service have recorded pipistrelle and Leisler's bats using advanced detectors attached to cars. But last year, Bat Conservation Ireland offered members of the public the opportunity to get involved in bat research. Hundreds of volunteers surveyed canals and rivers, counting the number of times Daubenton's bats flew past. These bats are easily identified because they skim low over waterways - they can use their tail to scoop insects from the water surface. With a bat detector tuned to 45 KHz, volunteers could also hear the bats approaching. Bat Conservation Ireland now has plans to survey and map the distribution of all Irish bats.

The only well documented bat species in Ireland is the lesser horseshoe bat, said Tina. "It is our only Annex II bat species and therefore has a much higher priority for conservation under the EU habitat directive," she said.

It is the only Irish bat that must free hang in its roost -- it can't bend its knees. This makes it easier to count and the population in Ireland, restricted to six western counties, is estimated at 12,500. The other nine species are more crevice dwelling and so not easy to count in roosts. "We don't have any information that comes close to estimating the population of these species," said Tina.

During winter, many species hibernate in underground sites or outhouses, though some will hide under roof tiles or behind loose tree bark. They reduce their body temperature to conserve energy and disturbance at this time can be very harmful.

Lesser horseshoe bat

The lesser horseshoe bat is a fussy bat that requires special conditions, explained Kate McAney of the Vincent Wildlife Trust. They used to be the bat of the big mansion house, but with so many of these now gone, they have moved down the property ladder. They roost in ruined buildings during the summer, preferring unoccupied cottages with thatch or slate roofs. With rising property prices, even these abandoned dwellings are under threat. The Vincent Wildlife Trust has bought or leased a number of the properties and the bats thrive in these reserves. Like all Irish bats, they feed on insects.

The lesser horseshoe needs to fly directly to its roost like a swallow; it is also unique in emitting an extremely high frequency call (110 KHz). Kate said this high frequency allows it to decipher extremely fine detail, but the call dissipates rapidly. This renders it an expert navigator in cluttered environments, but it avoids flying across wide open spaces. Linear landscape features such as hedges, tree lines and even stone walls are therefore essential to this bat, she said.

Conservation

Linear features like hedgerows are extremely important for most bat species. "My biggest concern is the loss of hedgerows and intensive use of pesticides," said Tina Aughney. She also cites the renovation of old buildings as having detrimental effects on bats. The effect of light pollution, especially for woodland species, may be of concern.

John Altringham, UK bat expert, who delivered the keynote address at the recent Irish Bat Conference, said habitat fragmentation is an important issue in Ireland and the UK. The biggest threats are the destruction of feeding areas and roosts and the separation of feeding areas from roosts, as well as the isolation of small populations, he says.

Anyone wanting to help bat conservation can put up bat boxes or plant trees and insect-friendly shrubs and become aware of developments in their area. "Bat boxes are only a foot high but you can get 70 to 80 bats squeezed into one," said Conor Kelleher. "It allows them more alternative roosting sites." He added that ponds in gardens and night-scented flowers like honeysuckle will encourage bats and their insect prey into gardens. Having bats in your garden can make barbeques more comfortable, since they will keep the midges away.

Conservationists advocate common sense mitigation measures for bats, such as hedgerow conservation and protection of roost sites. Tall trees either side of a road with light underneath will channel bats over a road and away from traffic, for example.

Bats are a mysterious group of animals and there is a great deal yet to be discovered. Intensive study only began in the 1960s when the technology to study them was developed. "Things like squirrels and pine martens have been studied for centuries. Bat studies are in their infancy, so it's a very good area for any budding naturalist," said Conor. "There's huge scope to make new discoveries." For example, pipistrelles were assigned to a single species until 1993, when it was discovered that there are in fact two species, the common pipistrelle (which echolocates at 45 KHz) and the soprano pipistrelle (55 KHz). They roost separately and appear to have different food and habitat preferences.

Molecular studies

Two other Irish species, the whiskered and Brandt's bat, are similarly difficult to tell apart: they echolocate in the same way and look similar. Dr Emma Teeling, UCD's School of Biological and Environmental Science, has been applying molecular techniques to such problems, using specific sequences of DNA to differentiate whiskered and Brandt's bats.

Dr Teeling previous work at the National Institutes of Health in the US led to a paper on the evolution of bats in the prestigious journal Nature. PhD students in her lab are now studying the evolutionary relationships of bats, the evolution of the senses in bats, and the genetics of the bumblebee bat.

The bumblebee bat is the smallest mammal in the world; a population in Thailand and a recently discovered population in Burma echolocate differently and Emma's research group is examining whether there are actually two species of this rare bat. The UCD group is also studying the genetics of the lesser horseshoe bat, research that may show how Irish and European colonies are related and where Irish colonies originated from after the Ice Age.

Dr Teeling said she is excited about the potential of molecular studies of bats to answer many fundamental biological questions. Her work in the US was linked to the human genome project and she believes genetic studies on bats can have biomedical implications and offer insight into human genes and diseases.

Myths

Bram Stoker created an image problem for bats. Vampire legends in Europe and Asia existed for hundreds of years, but vampires were never bats. The myth was born when Stoker's Count Dracula flitted around London as a large blood-sucking bat. Though there are over one-thousand bat species, there are just three species of vampire bat, all in South America, and just one species sucks the blood of mammals. Ironically, the vampire bat is also one of the few animals to show true altruistic behaviour. Bats will share a blood meal with a hungry roost mate.

The people at Bat Conservation Ireland state that it often explains to people that bats are not rodents and breed slowly. They have just one baby per year and can live up to 40 years. The group often gets calls from people claiming to have found a baby bat - it's usually an adult. Given that a pipistrelle can fit in a matchbox, the small size of Irish bats surprises most people. Bats are not blind and few are so accident prone as to tangle in hair. Indeed, researchers using fine mist nets to capture bats find themselves frequently outwitted by bat sonar.

Future

Bats are an easily overlooked but important member of our native fauna. Their numbers are under threat throughout Europe; habitat destruction, insecticides, and intensive farming may be impacting on Irish populations. Conor Kelleher said that he believes some bat species have gone extinct in Ireland in historical times, but hopes that some species such as the large noctule bat in Britain may yet return to our shores. Public interest in bats has increased enormously.

Anyone interested in bats can visit Bat Conservation Ireland and consider joining the organisation and volunteering for survey work. An interest in these intriguing animals, a bat detector and a warm jacket are all that's needed for some nocturnal fun.