BATS IN THE IRISH LANDSCAPE

This paper will cover some of the major developments in the Irish landscape, from prehistoric to contemporary times and hypothesise, based on knowledge of present bat behaviour, the effects these changes have had on the Irish bat species.

All bats are mammals, they give birth to live young and suckle their babies. There are approximately 970 known bat species (Corbet and Harris, 1991). These are divided into two groups: The Megachiroptera (Mega-bats or Flying Foxes) and the Microchiroptera (Micro-bats). The flying foxes are confined to old world, tropical and sub-tropical regions while the Microchiroptera have a more widespread distribution stretching from equatorial regions where diversity is greatest to cool temperate areas where species are fewer (Findley, 1993). All of the 9 species of bat in Ireland
(Russ and O'Neill, 1997) are insectivorous and all can echolocate (Stebbings, 1993). Echolocation is a method of navigation by producing high frequency sounds and listening for echoes. Bats used echolocation to find prey and to avoid obstacles.

In a bat community made up of several species, each has different flight and echolocation capabilities (Norbert and Rayner, 1987). As a result there is little competition between species. Examples of two differing strategies may be found when comparing the brown long-eared bat (Plecotus auritus) to the Leisler's bat (Nyctalus leisleri) both of which are resident in Ireland. The long-eared bat has broad short wings resulting in slow flight and greater manoeuvrability, large ears and very quiet echolocation (Schober and Grimmberger, 1997). This enables the long-eared bat to fly in more cluttered and glean prey from vegetation. In contrast the Leisler's bat has long narrow wings, short ears and sleek fur so that it is a streamlined fast flier and not very manoeuvrable (Schober and Grimmberger, 1997). The Leisler's also has very loud echolocation calls so that it can detect prey from long distances. The Leisler's therefore hunts for prey in open spaces such as over fields and parklands and high over woodland.

Bats exploit a relatively short window of activity when insect availability is at its peak (Racey, 1982), usually during the summer months from May to August. Females gather together in maternity roosts to give birth to a single baby in June each year and hibernation takes place from the cold autumn months to warmer spring months. The habit of gathering together in maternity and hibernation roosts means that they are prone to sudden drops in population levels if roosts are destroyed. The low rate of reproduction results in very slow recovery from such instances. Bat species have undergone serious declines in the past thirty years (Stebbings, 1988).

Since humans first arrived on Irish shores around nine thousand years ago (Mitchell and Ryan, 1997) they have been sharing the landscape with bats. However, until as recently as the last century bats were rarely documented, despite the fact that many bats must have been sharing their homes with great writers and historians.

It is unknown what species were present in Ireland during the development of woodland which occurred after the last ice age. The earliest known reference to bats in Ireland is made in a list of Irish fauna in a tract of the Fionn MacChumail saga. Legends of Fionn and the Fianna may have begun before the Neolithic development of agriculture although the first written references to the legendary heroes were not made until the 11th century (Moriarty, 1997). The fauna list comes from the ransom demanded for Fionn after he was abducted by the King of Tara, the ransom was said to have been a pair of each of the wild creatures of Ireland. The list includes a geographical reference to where each pair should be found. Two bats are referred to and these are to be taken from the Cave of the Nuts (Moriarty, 1997).

In Britain, where cave bones have been analysed in detail it has been found that the relative abundance of bat species present in Neolithic Britain was quite different from that of today. For example, in Dowel Cave, Derbyshire, lesser horseshoe bats and Natterer's bats, both species which forage mainly in woodland dominated the cave fauna in Neolithic times (Yalden, 1968). Today the lesser horseshoe bat is only found in southern England and in Wales. Sot their presence in the Peaks may reflect the more wooded nature of the Peak District at the time (Yalden, 1968). If this is the case then by extrapolation we may assume that during the peak of woodland cover in Ireland 7500 BC to Neolithic times 4500 BC when woodland clearance began in earnest, the bat species present in Ireland would have reflected the predominance of woodland. Lesser horseshoe bats, today found only in the south west of Ireland (McAney, 1994) may have had a wider distribution. Climate for the first Neolithic farmers in Ireland was approximately 2 degrees warmer than today (Mitchell and Ryan, 1997) and this may also have facilitated the spread of species like the lesser horseshoe bats in a more northerly and easterly direction.

Riparian habitats and woodlands support greatest bat activity (Walsh and Harris, 1996). Only 7% of the Irish land surface is today covered in forest and much of this is the non-native coniferous variety. Deciduous trees, in particular, support a wide range of potential insect prey. In a large area of mature deciduous woodland with a combination of glades, openings and dense vegetation, most of our species are able to find a niche in which to forage. Openings and glades for our fast flying less manoeuvrable species and more dense woodland for the slow flying gleaning species.

When humans first arrived in Ireland, the bats there would have been roosting in tree hollows and caves. At that time there would have been a wider variety of tree holes available, with some very large ancient trees with large hollowed out interiors (the kind that are presently removed from our landscape because of perceived dangers to humans and livestock). The first human colonists, as hunter gatherers would have had little impact upon the native bat populations. For over four thousand years these people may have moved with the seasons acting as an integral component of the ecosystem rather than as facilitators of ecosystem change (Feehan, 1997).

The onset of agriculture however, by clearing woodland and developing areas of pasture and tillage would have favoured our larger fast flying species - the Leisler's and impacted negatively upon our slow flying woodland foragers.

Originally, the temporary wooden buildings would probably have had only a minor impact on bats but by 3500 BC., bats may have been using the cave like burial tombs as a hibernacula. There are over 1000 megalithic tombs present in the Irish landscape, and their existence probably provided extra potential hibernacula, particularly in areas with few caves.

Periodic forest clearances took place from 4000 BC, followed by periods of forest regrowth. Farming waxed and waned, possibly as a result of climate changes. However, by 200 AD arable farming reached a new peak and later the development of new farming techniques by the early christians ensured a cessation of woodland encroachment (Mitchell and Ryan, 1997). By then the landscape would have been dotted with many more stone structures such as monasteries and ring forts. From this time on the common pipistrelle probably came into its own. As an adaptable forager of small midge sized insects, the agricultural landscapes proved sufficient for its lifestyle, where other species would have suffered a decline in abundance. The pipistrelle's adaptability has been exemplified by its use of many kinds of modern structure such as bungalows, flat pitch-roofed sheds and even concrete bridges. It can also be found roosting in trees and old houses (Corbet and Harris, 1991).

The use of buildings by bats probably increased with the coming of the Normans and with them, new architectural techniques. Some species of bat have adapted to a loss of suitable tree roosts and in many ways improved their chances of reproductive success by using man-made structures which heat up during the warm summer days, promote the growth of new born babies and improve their chances of survival through the Irish winter. The long-eared bat is one species which may have benefitted by the range of new potential roosting sites. It often favours buildings which were constructed prior to the turn of this century (Entwistle et al., 1997). Brown long-eared bats prefer a site with a high roof space, sometimes with walled sections but with enough room to conduct their sociable warm up flights before leaving to feed half an hour after dusk. This species probably used churches from early christian times spreading then into the high roofed norman towers, into the attics of mansion houses, haybarns and outbuildings in farmyards.

The lesser horseshoe bat has very specific roosting requirements. This species has thrived for hundreds of years in the large mansions and castles dotted around Clare, Cork, Kerry, Galway and Mayo. A small population is also present in Limerick. Attics in these buildings provide a choice of conditions to suit weather changes. The lesser horseshoe is very sensitive to disturbance and requires an opening in the building through which it can exit and enter without having to land (Vincent Wildlife Trust, 1996). However, as the mansions and castles in the west of Ireland gradually fall into greater disrepair or are renovated to an extent which excludes the bats, they have been moving to sub-optimal sites. Usually these are abandoned vernacular houses, traditional stone cottages roofed in thatch or galvanised. Most are in a poor state of repair (McAney, pers. comm.). This bat is now almost extinct in many parts of central Europe (Schover and Grimmberger, 1997). Our population of the lesser horseshoe is considered of international importance (While, 1993). The designation of the larger sites in Clare and Kerry as special areas of conservation under the Habitats Directive should help protect it.

The last great woodland clearances took place around the 17th century (Mitchell and Ryan, 1997). Much of the Irish landscape has since then been characterised by a hedgerow network. This system is essential to the present bat population because there is at least something of a continuous, if linear, woodland type system. This provides essential feeding and also important commuting routes. Very few bats fly over open land, preferring instead the protection of hedgerows against aerial predators like barn owls. Dutch researchers have found that bats fly three or even four times greater distances to foraging sites along linear landscape features rather than following a direct path over unprotected open land (Limpens and Kapteyn, 1991).

For the past six thousand years, bats have adapted to man induced changes in the landscape in order to improve their own chances of survival. The bat fauna which is present in Ireland today is, therefore, irrevocably linked to our own history. However, recent changes in agriculture, such as increased use of pesticides, scrubbing out of hedgerows, loss of permanent pasture, draining wetlands have all reduced the amount of foraging habitat available to bats. This, combined with the use of timber treatments in roosts, increased disturbance in hibernacula and changing building methods have contributed to an overall decline in bat numbers (Stebbings, 1988). The pipistrelle and the Leisler's bats are probably the only species which may benefit from modern building techniques. Over the past forty years, landscape changes have accelerated. Attitudes have also changed. Where once bats in the thatch or attic may have been reluctantly accepted as part of life in rural homes, now this is not the case. The future for many of our species in Ireland, therefore, remains uncertain unless there is increased awareness and more sympathetic landscape developments.