BATS IN THE
Dr. Niamh Roche
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
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
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,
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
"In days of old, people thought that bats were half
mice and half birds, and the countryfolk yet speak of the
pipistrelle or common bat as the 'flittermouse', but they
have no affinity whatsoever with the birds, and not much with
Frances Pitt in her article 'Wild Animals of the Countryside'
from the Countryside Companion, published by Odham's Press
Coincidentally the German word for bat is 'fledermaus' the
image and name being used with great effect by Johann Strauss
in his operetta 'Die Fledermaus'.
By contrast the Irish word for bats is 'sciathán',
presumably derived from the Irish word for shield, 'sciath'.