CHAPTER 1
BAT SPECIES IN SCOTLAND
S. M. SWIFT
1. INTRODUCTION
In general, bat numbers and species diversity decrease with increasing latitude, and this is
the case in Britain; of the 16 or 17 British bat species, only nine occur in Scotland, and the
number of species decreases still further towards the north of the country. At high latitude,
bats have to contend with problems such as long, severe winters, short, rather unreliable
summers and few hours of darkness available for foraging in summer.
In Scotland, five species are considered to be common and/or widespread, and a further four
(or possibly five) are rare and/or with restricted distribution. One of these (Pipistrellus
nathusii) was formerly considered to be a migrant, but recent evidence suggests there may
also be a resident population. A further four species have been recorded as occasional
vagrants.
2.1 Common / widespread species
Pipistrelles (Pipistrellus pipistrellus and P. pygmaeus),
Brown long-eared bat (Plecotus auritus)
Daubenton's bat (Myotis daubentonii)
Natterer's bat (M. nattereri)
2.2 Rare / restricted distribution
Whiskered bat (Myotis mystacinus). Brandt's bat (M. brandtii) has been recorded once in
Scotland, and may also be present
Noctule (Nyctalus noctula)
Leisler's bat ((N. leisleri)
Nathusius' pipistrelle (Pipistrellus nathusii)
2.3 Vagrants
Serotine (Eptesicus serotinus) – European (native in southern Britain)
Northern bat (E. nilssonii) - northern European
Parti-coloured bat (Vespertilio murinus) - European
Savi's pipistrelle (Pipistrellus savii) - southern European
Hoary bat (Lasiurus cinereus) - north American
3. PIPISTRELLES (PIPISTRELLUS PIPISTRELLUS AND P. PYGMAEUS)
Until recently, the two common pipistrelles were considered to be a single species,
Pipistrellus pipistrellus, and therefore the vast bulk of available literature does not separate
them. The existence of two distinct phonotypes (ie groups which call at different
frequencies) was first recorded by Jones & van Parijs (1993), who also noted small
morphological differences between the phonotypes and suggested they may constitute
separate species. The existence of two cryptic, sympatric species was subsequently proved
using the technique of mitochondrial DNA analysis (Barratt et al 1995), and these are now
known as P. pipistrellus (the 45kHz pipistrelle, also called the common or bandit pipistrelle)
and P. pygmaeus (the 55kHz pipistrelle, also referred to as the soprano pipistrelle because
of its higher pitched call). Small but distinct differences have been shown in their
morphology (Haussler et al 2000), foraging behaviour (Glendell & Vaughan 2002; Vaughan
et al 1997) and diet (Barlow 1997); these have been detailed below, although not all
references dating prior to 1996 differentiate the species.
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3.1 Recognition
Distinguished from most other Scottish species (except Nathusius' pipistrelle) by their small
size (forearm length less than 35mm), uniformly mid-brown pelage dorsally and ventrally,
and the presence of a post-calcarial lobe. Distinction from P. nathusii relies on the ratio of
fifth digit : forearm length (less than 1.25) and lack of pale tips to dorsal hairs. P. pipistrellus
and P. pygmaeus are most easily distinguished from each other in flight - maximum energy
of echolocation calls is concentrated around 45kHz in P. pipistrellus and around 55kHz in P.
pygmaeus. P. pipistrellus often (but not always) has a mask-like band of dark pigment
around the eyes and muzzle, while P. pygmaeus usually has exposed pinkish skin on its
face; this species also has a typically strong, musky odour.
3.2 Distribution
3.2.1 In Europe
The two species occur sympatrically over much of Europe, although P. pygmaeus has been
found mainly in Scandinavia and in countries bordering the Mediterranean, while P.
pipistrellus is more frequent at central latitudes (Jones 1997; Barratt et al 1997).
3.2.2 In Britain
Both species are common and widespread, although it has been suggested that one or the
other may be more common locally in some areas.
3.2.3 In Scotland
Both species are common and widespread, resident pipistrelles having been recorded
throughout the mainland, on Orkney (but not Shetland) and on most of the Hebrides,
including outlying islands (Haddow & Herman 2000; Yoxon 1993). There is, however, some
evidence from bat group records that the pipistrelles on more remote islands, including
Orkney, Harris and the north coast of Skye, are mostly P. pipistrellus, while P. pygmaeus are
more likely to be found in river valleys on the mainland. A recent study of the two species in
Perth & Kinross (Swift et al 2001) found that, while both occurred throughout the study area,
45kHz pipistrelles were more likely to roost in remote, upland places and foraged both close
to and away from rivers, while 55kHz pipistrelles roosted and foraged mainly in lowland
valleys with abundant riparian vegetation.
3.3 Conservation status
3.3.1 Worldwide: The IUCN (World Conservation Union) lists the two species together as
Lower Risk: Least Concern (Hutson et al 2001). A taxon is Lower Risk when it has been
evaluated and does not satisfy the criteria for any of the categories Critically Endangered,
Endangered or Vulnerable. Taxa included in the Lower Risk category are separated by the
IUCN into three subcategories:
1. Conservation Dependent, for groups which, were they not the subjects of specific
conservation programmes, would qualify for one of the Threatened categories within
five years.
2. Near Threatened, which includes taxa not qualifying as Conservation Dependent, but
close to qualifying as Vulnerable.
3. Least Concern, which includes taxa not included in the Near Threatened or
Conservation Dependent categories.
3.3.2 In UK: Not Threatened (Hutson 1993a). Pipistrelles are the commonest and most
widespread species throughout the UK. There is some evidence from the Annual Bat
Colony Survey that their numbers may have declined nationally in the last 50 years, but this
is not the case in Scotland. Speakman et al (1991a) report that, historically, the pipistrelle
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population in north-east Scotland appears to have been much lower than it is today. Given
the dependence of pipistrelles on warm, occupied houses as nursery roosts (see below), it is
possible numbers have increased as houses in Scotland have become warmer.
3.3.3 UK BAP (Biodiversity Action Plan) status: Priority species for both species.
3.4 Population size
The most recent population estimates for the UK are between three million (Speakman
1991a) and about two million, of which 550,000 are in Scotland (Harris et al 1995). The
minimum population density in north-east Scotland has been calculated, from counts at
known nursery roosts, at approximately 18.2 bats per km2 (Speakman et al 1991a).
Pritchard & Kiggins (1995) reported a total of 1060 registered pipistrelle roosts in the former
SNH south-east Scotland region. The average colony size, for both species together, has
been estimated at 180 (Swift et al 2001), and this gives a total population size for the region
of around 190,000-200,000 bats. On this basis, a very rough estimate for the whole country
(allowing for high mountains and other areas unsuitable for bats) is between 0.55 and 0.75
million. Because it is accepted that most estimates of bat population sizes make
assumptions based on incomplete or inaccurate data, Harris et al (1995) used an index
(referred to as a reliability of population estimate) in conjunction with their figures. This
ranges from 1 (highly reliable) to 5 (very low). For pipistrelles, Harris et al (1995) assigned a
reliability index of 3 to their figure.
3.5 Social behaviour and organisation
3.5.1 Summer
Nursery colonies are formed and move into summer roosts, usually in early May in Scotland
(Swift 1980; author's data). Parturition is highly synchronised and begins around mid June
in most years, although it can be accelerated in very warm springs or delayed by poor
weather conditions (Racey & Swift 1981). Juveniles begin to fly at 3-4 weeks, and emerge
from the roost for the first time between 10th and 20th July (bat group data). Weaning is
complete in most colonies by early to mid August, and nursery colonies break up soon after.
However, juveniles tend to remain in nursery roosts, and may still be in residence in
September in warm weather. Adult males do not appear to be tolerated in pipistrelle nursery
colonies, since the few males found there are immature (Avery 1991).
The two species differ with respect to colony size, P. pygmaeus colonies having been
reported to be significantly larger than those of P. pipistrellus in Scotland (Swift et al 2001)
and elsewhere (Barlow & Jones; 1999). Mean colony sizes were 126 (n=27 roosts) for P.
pipistrellus and 237 (n=58 roosts) for P. pygmaeus in Perth and Kinross (Swift et al 2001),
and median sizes 76 (n=33 roosts) for P. pipistrellus and 203 (n=40 roosts) for P. pygmaeus
in England (Barlow & Jones 1999). Both species are reported to be strongly philopatric to
nursery roosts (Thompson 1992; 1987), and to return over distances of at least 80 km if
removed from roosts (author's data). Frequent roost moving during summer has recently
been reported in P. pipistrellus (Feyerabend & Simon 2000) in Germany, where a colony
used eight roosts over two summers and moved, on average, every 11.7 days. There do not
appear to be similar reports for P. pygmaeus, and records from Scotland indicate that most
colonies of this species stay in one nursery roost for the whole pregancy and lactation
period.
Summer roosts are concentrated in river valleys (Racey 1998) and both pipistrelle species
are highly dependent on occupied buildings for summer roosts. Almost all registered
nursery roosts in Scotland are in buildings, and pipistrelles are the species which encounter
by far the largest numbers of problems with unsympathetic householders. There has been
only one verified report of a nursery colony in a tree roost (Howe 1997), although groups of
males and non-breeding females make use of tree holes (Swift 1995), bat boxes (Park et al
1996) and bridges (Rydell et al 1994). Although roosts of P. pygmaeus are often surrounded
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by more wooded areas than similar houses not used as roosts, there is little evidence so far
that pipistrelles select buildings for any particular structural feature (Jenkins et al 1998),
unlike brown long-eared bats (see below). However, the above study did not test the effects
of temperature or humidity, and a constant feature of pipistrelle nursery roosts seems to be
high temperature - most are in south or south-west facing parts of buildings and many are
close to chimneys or other sources of warmth. Especially at high latitude such as in
Scotland, it seems more than likely they need high roost temperatures to rear young
successfully. Recent research on bat box design (Swift, unpublished; Rebelo et al 2002;
Lourenço et al 2002) has emphasised the need for high temperatures and wide temperature
ranges in bat boxes before they will be used by bats. Both species prefer to roost in
crevices, such as in cavity walls, between sarking and slates or beneath flat roofs.
3.5.2 Winter
While winter behaviour is still poorly understood, pipistrelles appear to make more use of
buildings for hibernation than do other Scottish species, and are rarely found in underground
sites (Herman & Smith 1992; 1995). Haddow (1992) observed a number of pipistrelles in
crevices in a vaulted ceiling of a castle cellar, and their use of this site has been constant
over several winters (J. Haddow, pers. comm.). A mild winter during 2002-3, combined with
heightened public awareness of bats following the EBL case, has brought to light a number
of winter observations. Fifteen bats, likely to be pipistrelles from the greenkeeper's
description, were found in a tree cavity on a golf course at Blair Atholl when the tree was
felled in February 2003 (SNH report), although all had flown away by the time an expert
arrived. Thirty pipistrelles were found during building work in a house in Tayside in early
March (S. Pritchard, pers. comm) and several roost owners have reported bats remaining in
summer roosts into January and February and being found in living spaces during mild
spells. It is probable, therefore, that most Scottish pipistrelles hibernate, in small numbers,
in crevices in unheated parts of buildings and that at least some of them stay in or close to
their summer roosts. This finding may well affect advice given concerning exclusion from
roosts in future.
3.5.3 Mating and swarming
Both species show a mating system based on resource defence polygyny, in which males
defend a mating territory which is visited by females (Gerell & Lundberg 1985). Numbers of
females in mating groups is dynamic, although in one study some females remained in a
male's group for up to six weeks, and were also found with the same male in successive
years. In the same study, the number of females in each group averaged 1.2 for P.
pipistrellus and 1.8 for P. pygmaeus (Park et al 1996). Mating territories are commonly
found around trees, bat boxes or bridges, but not in buildings (Gerell & Lundberg 1985).
Males advertise their territory and defend it from other males using songflight, made up of
low frequency (14-40kHz) calls. Songflight calls of P. pipistrellus typically have four
components, while those of P. pygmaeus typically contain three and are of higher frequency.
Swarming is defined as ‘the flights of bats through hibernacula in late summer and early fall’
(Fenton 1969), and has only recently been described in British bats (Parsons et al 2003).
The behaviour is also referred to as autumnal swarming, to distinguish it from dawn
swarming, which occurs at entrances to roosts in summer. Although commonest among bats
of the genus Myotis, it has been described in 26 species from seven genera. There is
usually a strong male bias among swarming bats and it is associated with social behaviour
involving calling, chasing and copulating, leading to the widely supported hypothesis that its
function is concerned with mating (Parsons et al 2003). While swarming does not appear to
be common in pipistrelles, there are reports of the behaviour in these species in continental
Europe (Kreutzschmar & Heinz 1995) and at a church in England (Bat News, February
1995).
3.6 Habitat and foraging
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Both pipistrelle species forage aerially, frequently on regular flightpaths or beats, and mainly
in riparian woodland and parkland; they may travel up to 5.1km from roosts to foraging areas
(Racey & Swift 1985). Pipstrelles fed along roads illuminated by street lamps in north-east
Scotland, and foraged at higher densities in villages lit by mercury-vapour lamps than in unlit
villages or those lit by sodium lamps (Rydell & Racey 1995). P. pygmaeus activity was
highest over rivers and lochs in south-west England (Vaughan et al 1997) and in Perthshire
(Swift et al 2001), and riparian vegetation was also reported to be the dominant habitat
around roosts of this species in SW England (Oakley & Jones 1998). However, in one study
(Glendell & Vaughan 2002), semi-natural woodland and tree-lines were also selected. P.
pipistrellus appears to have broader habitat preferences, since bats of this species foraged
over riparian vegetation, unimproved grassland, villages and semi-natural woodland in SW
England (Vaughan et al 1997), and in woodland both close to and away from water in
Perthshire (Swift et al 2001). In Northern Ireland, P. pipistrellus also foraged in a wider
variety of habitats than did P. pygmaeus (Russ & Montgomery 2002). The diets of the two
differ, as may be expected from the variation in habitat. The main prey of P. pipistrellus in
June and July was Diptera of the families Chironomidae, Ceratopogonidae and
Scathophagidae, while P. pygmaeus ate mainly chironomid midges (Barlow 1997). In
Scotland, small caddis flies were also very important food items (Swift et al 1985). The
differences in diet reflect the greater dependence of P. pygmaeus on riparian habitats. Prey
was found to be hunted unselectively in a study in Scotland carried out before the species
were separated (Swift et al 1985).
4. BROWN LONG-EARED BAT (PLECOTUS AURITUS)
Many bats worldwide have large ears, and the names ‘big eared’ and ‘long eared’ have been
applied to species in no fewer than nine microchiropteran species. However, the European
vespertilionid long-eared bats of the genus Plecotus, together with their close relatives in
North America, are unique in their ability to fold their ears when they are at rest. They are
among the most distinctive and easily recognised European bats, and their reliance on
occupied buildings for roosting brings them constantly into contact with humans. There are
four species in Europe, one of which, P. alpinus, has been recognised only within the last
year. Two occur in Britain, but one of these, the grey long-eared bat, P. austriacus, is found
only in the extreme south of England.
4.1 Recognition
The brown long-eared bat can be distinguished from all other Scottish species by its very
long ears (>25mm) which are joined at the base. At rest, the ears may be curved
backwards, resembling rams' horns, which are also distinctive. If the bat is torpid, the ears
may be folded and tucked under the wings. The tragus remains erect, and can superficially
resemble the ear of other species. Closer inspection will, however, reveal it for what it is.
4.2 Distribution
4.2.1 In Europe
Widespread in the Palearctic Region, and occurs eastward as far as the Ural and Caucasus
mountains (Swift 1998). It is common throughout northern Europe, including higher latitudes
up to 64oN in Scandinavia, and is also found in cool, mountainous areas in southern
Europe.
4.2.2 In Britain
Common and widespread, although absent from the Channel Islands.
4.2.3 In Scotland
Occurs everywhere except in exposed mountainous regions in the north and north-west. The
northernmost record in the country is of a nursery colony in a bat box 25km west of Lairg in
Sutherland (Canham 1992). It is found in the Inner Hebrides (Haddow & Herman 2000) and
5
has been recorded in Orkney (Booth & Booth 1994) although this was not confirmed as a
breeding roost, but is absent from the outer islands and Shetland. Its absence from these
islands, and from exposed parts of the mainland, may well be connected with the lack of
woodland in such places, in view of the dependence of the species on trees as foraging
habitat (Swift 1998).
4.3 Conservation status
4.3.1 Worldwide: Lower Risk : Least Concern (Hutson et al 2001).
4.3.2 In UK: Not Threatened (Hutson 1993a). This is generally considered to be the second
commonest bat in Britain after pipistrelles. However, its abundance in relation to species
which make less use of houses (such as Daubenton's bat) may well have been
overestimated - P. auritus almost always roost in roof apices and is therefore easily visible to
householders and likely to be reported to conservation organisations. There is evidence in
Scotland (Speakman et al 1991a) that numbers have declined over the last 100 years,
probably due to loss of woodland habitat and to modern house construction being less
suitable for roosting than that of older ones. A recent survey in Perthshire (Swift 1999)
concluded that, while the population has remained stable over the short term in the area, the
species is under pressure from loss of habitat and roost sites and requires protection if
numbers are to be maintained.
4.3.3. UK BAP status: Species of conservation concern.
4.4 Population size
Speakman et al (1991a) estimated the population density of brown long-eared bats in an
area in north-east Scotland to be 1.66 bats per km2, or less than a tenth that of pipistrelles.
Using this figure, the overall British population has been estimated at around 200,000
individuals (Harris et al 1995). Of these, possibly 20-30,000 are in Scotland, with a low
reliability of population estimate of 4.
4.5 Social behaviour and organisation
4.5.1 Summer
Together with pipistrelles, this is the Scottish species most closely associated with houses
as summer roosts, although churches and barns are also used. Nursery colonies are
occasionally found in trees and bat boxes (Boyd & Stebbings 1989). Further south in its
range, tree holes are used widely by P. auritus (Bauer 1960), and thus its reliance on
occupied buildings in Scotland is probably connected with its need for warmth to rear young.
Entwistle (1994) found that tree holes and farm buildings were used as temporary roosts at
times when food was in short supply and bats became torpid to save energy, but that
nursery roosts were almost always in houses. Roosts sites are in apices above a roof void
large enough to provide a space for flying. A study in Scotland (Entwistle et al 1997) has
shown that long-eared bats are selective in the houses in which they roost, and that they
select large, old houses (average age 150 years) close to abundant woodland. They also
select buildings which are warmer than others nearby and which contain several roof
compartments, thus giving the bats a variety of microclimates in which to roost. It therefore
appears that buildings suitable as roost sites may be in limited supply, and it cannot be
assumed that excluded colonies will easily find an alternative site.
Females move into nursery roosts around mid May, and are palpably pregnant by the end of
May. Gestation lasts 60-70 days (Speakman & Racey 1987), depending on weather
conditions in spring. Birth of a single infant takes place in late June to mid July.
Synchronisation of births is less marked in this species than in others in Scotland (Entwistle
1994), with births being spread out over about a month, both within and between colonies.
In Scotland (Swift 1981) and in southern England (Howard 1995), juveniles leave the roost
for the first time at around 30 days of age and make trial flights within the roost for up to ten
6
days before this. Weaning is completed by around 42 days of age (Swift 1991). Most young
are independent by late August, but bats remain in summer roosts well into autumn; it is not
uncommon for them still to be in residence in November, and some remain even longer.
Nursery colonies are small in P. auritus, with the number of bats visible in roosts averaging
15-20 (Entwistle et al 2000; Swift 1999), although a capture-mark-recapture study showed
that actual colony size is approximately twice the number visible at any time (Entwistle et al
2000). Colonies consist mainly of females in spring, but adult males move in progressively
through summer, probably to take advantage of the warm conditions in nursery roosts in
order to maintain a constantly high body temperature during spermatogenesis (Entwistle et
al 2000). Both males and females show a high degree of roost fidelity, and a fifteen year
ringing study (Entwistle et al 2000) has demonstrated that P. auritus in Scotland is an
immobile species. Of 720 ringed bats recaptured, only five (less than 0.7%) were found in
roosts other than those in which they were originally ringed. The implications of this finding
for the genetic structure of the population were investigated by Burland et al (1999; 2001),
who found that most offspring were fathered by males originating from a colony other than
their own. This suggests extensive mixing of individuals from different colonies during
mating, which prevents inbreeding but allows both males and females to take advantage of
using long-term and successful roost sites and of maintaining long-term associations with
other members of their colony.
4.5.2 Winter
Long-eared bats enter hibernation relatively late, and frequently stay in summer roosts at
least until November. They hibernate singly or in small groups, generally within crevices
(Horacek 1975). They are reported to use caves, both natural and man-made ones such as
mines and quarries, and to choose relatively low temperatures (-3 to 11oC, average 7oC).
However, surveys of undergound hibernation sites in southern Scotland (Herman & Smith
1992; Smith 2000) reported finding very low numbers of long-eared bats (maximum of five
individuals in any one site). In Europe, they are among the bats most likely to be found in
buildings, particularly cellars (Horacek 1975; Rydell 1989). However, again there are few
reports in Scotland of these bats being found in buildings in winter. It is possible they rely
largely on tree holes, but there are as yet few reliable reports to substantiate this. Longeared bats are reported to fly frequently in winter (Hays et al 1992), and may arouse on
nights when ambient temperature rises above 4oC, when they are able to feed by gleaning.
4.5.3 Mating and swarming
The most likely mating system in P. auritus is considered to be a random, promiscuous one
in which swarming occurs and females mate with many males (Entwistle 1994). Since
intermittent mating occurs throughout winter and spring in this species (Strelkov 1962), the
energy males would need to expend defending females would not guarantee them
reproductive success since they could not defend females all winter. A promiscuous mating
system thus seems most likely. Park (2000) found long-eared bats, predominantly males,
swarming at mines in southern Scotland during September and October. However, mating
has also been reported to occur in summer roosts (Entwistle 1994); it thus begins in autumn
and continues in hibernacula during winter and spring.
4.6 Habitat and foraging
Brown long-eared bats are strongly associated with tree cover (Entwistle et al 1996) and
select roosts within 0.5km of deciduous woodland. They are found in villages but very rarely
in towns or cities, and in Scotland roosts are concentrated in lowland valleys, where most
woodland is situated. They select deciduous woodland as foraging habitat (Entwistle et al
1996), but also feed in mixed woodland and on the edges of coniferous plantations. They
forage close to the roost (usually within 1.5km) and regularly use a series of sites, between
which they move along flyways such as hedges or treelines ( Entwistle et al 1996). They
emerge later than pipistrelles (Swift & Racey 1983; Entwistle et al 1996), when it is almost
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dark, and remain active all night. They capture much of their prey by gleaning and their diet
contains a high proportion of moths (Swift & Racey 1983). By switching off echolocation and
using their huge ears to listen for prey-generated sound, they are able to avoid the problems
of tympanate moths detecting their approach and of the echoes from prey being confused
with those from the clutter of vegetation among which they forage (Anderson & Racey 1991;
1993).
5. DAUBENTON'S BAT (MYOTIS DAUBENTONII)
Also known as the water bat, Daubenton's bat is strongly associated with water and almost
always roosts close to, and forages over, lochs or rivers. It generally avoids urban areas,
roosts mainly in trees and bridges or tunnels, and has little contact with humans. Although a
common bat throughout Europe, relatively little is known of its behaviour, particularly in
roosts.
5.1 Recognition
A medium-sized bat recognisable by its even length fur, uniformly dark dorsal hair from base
to tip and large feet (more than half the length of the tibia). It has a long, straight calcar and
small rounded ears set on the side of the head.
5.2 Distribution
5.2.1 In Europe
One of the most widely distributed of all bat species (Kruskop 2002), it occurs throughout
eastern and western Europe.
5.2.2 In Britain
Common and widespread, although relatively few roosts have been recorded. Most records
are of foraging bats by electronic detector (Richardson 2000), since this is probably the
easiest British species to identify in flight.
5.2.3 In Scotland
Recent distribution maps (Haddow & Herman 2000) indicate that Daubenton's bat is also
common and widespread in Scotland, although there are relatively few records from the
north and north-west. This may, however, be due to there being few recorders in these
areas. The northernmost record is from Caithness, and the species has not so far been
found on Shetland, Orkney or the Outer Hebrides.
5.3 Conservation Status
5.3.1 Worldwide: Lower Risk : Least Concern (Hutson et al 2001).
5.3.2 In UK: Not Threatened (Hutson 1993a).
Considerably increased numbers of Daubenton's bats have recently been reported from
hibernacula in the Netherlands (Weinrich & Oude Voshaar 1992), Czech and Slovak
republics (Cerveny & Bürger 1990), Poland (Kokurewicz (1995) and Germany (Harrje 1994),
and Kokurewicz (1995) has postulated that this Europe-wide increase may be due to
eutrophication and canalisation of waterways resulting in increased availability of chironomid
midges. Daubenton's bats feed over water and rely heavily for food on insects, such as
chironomids (Swift & Racey 1983), which have aquatic larvae.
5.3.3 UK BAP status: Species of conservation concern.
5.4 Population size
Because M. daubentonii relies mainly on tree holes as summer roost sites (see below) and
such roosts are notoriously difficult to locate, it is likely that its population size has been
underestimated, since estimates such as that by Speakman et al (1991a) have been based
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on counts at roosts. Speakman's survey found only four house roosts in a study area in NE
Scotland, all situated in river valleys. In this area, he calculated the density of M. daubentonii
at 2.4 bats per km2. Using a similar method, the British population has been estimated at
150,000 and that of Scotland at 40,000 (Harris et al 1995), both with a low reliability rating of
4. Warren et al (1997) measured bat activity by means of bat detectors along a stretch of the
River Wharfe in Yorkshire and estimated the mean number of Daubenton's bats to be 8.9
per km of water, only slightly lower than that of pipistrelles (11.2 bats per km). In Scotland,
bat detector records show Daubenton's bats can be found on most calm stretches of rivers
in lowland areas. This species may therefore be more numerous than roost records suggest
and could be at least as common as P. auritus. Population trends are unknown in Scotland,
but the population may be increasing here, as elsewhere in Europe. A study in
Aberdeenshire (Racey et al 1998) provided some support for Kokurewicz's (1995) theory of
eutrophication providing increased food for Daubenton's bats; the small, eutrophic River
Ythan supported as many foraging bats, mostly Daubenton's, as did the larger, oligotrophic
River Dee.
5.5 Social behaviour and organisation
5.5.1 Summer
Across its range, Daubenton's bat is reported to be predominantly a tree roosting species
(Nyholm 1965), but because tree roosts are difficult to locate, relatively few have been
recorded. This holds true in Scotland, where there are fewer recorded roosts than for
pipistrelles or brown long-eared bats, despite the apparent abundance of the species from
detector records. One nursery roost was found in a beech tree in Perthshire (Swift 1995)
and two more in oaks in Strathclyde (Howe 1997). Another tree roost was reported in
Aberdeenshire in 2002 (R. Raynor, pers. comm.); this was found when a tree containing a
large cavity was felled and a number of Daubenton's bats escaped. There is evidence
colonies are selective (Boonman 2000), preferring oak to beech trees and selecting trees
situated on the edge of woodland. They also prefer tree cavities which are narrow and have
high ceilings (van der Wijden et al 2002). In general, the only way to find tree roosts is by
time-consuming detector studies or by attaching radio transmitters to individuals caught
while foraging, and more will undoubtedly come to light as survey effort increases. The
colonies occupying the tree roosts found so far have been nursery ones. Small numbers of
nursery colonies are also found in houses in rural areas (Speakman et al 1991; Swift 1995;
Swift & Racey 1983), barns or derelict buildings (Swift 1995), castles (Haddow 1997) and
bridges (author's data), although bridges do not seem to be used to the same extent as they
are in northern England (Racey 1998). It is likely most are not warm enough for rearing
young at our higher latitude. Most colonies in bridges consist of groups of males (both adult
and immature; Swift 1995; Warren et al 1998), and such groups also live in culverts and lade
tunnels. In addition, males are found in nursery colonies (Swift & Racey 1983). The
existence of male groups has also been reported in Germany (Encarnação et al 2002) and
elsewhere. Both male and female groups move roost frequently (Warren et al 1997; Rieger
1996), with one colony in Switzerland using up to seven different roost sites and moving, on
average, every second day. Roosts are always situated close (most within 50m) to water
bodies (Racey 1998), and are connected to lochs and rivers by flyways such as hedges or
overgrown burns (Herman et al 1991; Swift 1995), since this species appears to avoid flying
in open spaces except over water.
Nursery colony size in Scotland varies between 18 (SNH records) and 112 (Swift 1981), with
a mean of 68. This is much higher than in northern England, where mean maternity colony
size was 16 (Jones et al 1996); the difference could be due to relatively few maternity
colonies having been found in Scotland, since larger colonies are more likely to come to light
first. Male groups are smaller, numbering between 4 and 26 in Scotland (SNH records). In
a colony in Inverness-shire (Swift 1981), bats moved into the nursery roost in the second
week in May, parturition began between 21st June and 10th July (in a year with a very cold
9
spring), and juveniles flew for the first time between 9th July and 31st July. Weaning is
normally completed by mid August.
5.5.2 Winter
Hibernacula appear to be predominantly in caves and mines, and M. daubentonii is one of
the more numerous species reported from mines and limestone quarries in southern
Scotland (Herman & Smith 1992; Smith 2000a). Bats were found to hibernate singly and in
crevices. This was the only widespread Scottish species not found by Haddow (1992) in an
important building hibernaculum at Doune Castle and there have, to date, been no other
reports of Daubenton's bats hibernating in buildings in Scotland. In Germany, individuals
aroused at regular intervals during hibernation and moved position (Harrje 1994). Intervals
between arousals became longer as winter progressed.
5.5.3 Mating and swarming
Swarming at entrances to caves used as hibernacula appears to be a regular occurrence in
this species (Harrje 1994; Parsons et al 2003) and has recently been documented in
Scotland (Park 2000). Swarming during late summer and early autumn involves mostly male
bats and is considered to be associated with mating. All reports of swarming in Scotland
have been at sites used as hibernacula. Mating is promiscuous, and observations to date
indicate it occurs only at hibernacula (Harrje 1994; Strelkov 1969).
5.6 Habitat and foraging
Foraging is almost exclusively over water and the diet is mainly insects such as chironomids
and caddis flies, which have aquatic larvae (Swift & Racey 1983) caught aerially within 0.5m
of the water . Water bugs and beetles, moths and other insects, and possibly also small fish,
may be gaffed from the surface using the feet (Siemers et al 2001). Bats select stretches of
smooth water with canopy trees on both banks for foraging (Warren et al 2000; Swift 1995) such stretches produce significantly more insects than treeless ones. A radio tracking study
in Yorkshire (Altringham et al 1998) showed bats foraged on beats involving regularly used
sites such as pools along a river, some of which were up to 14km from roosts . Night roosts
may be used, particularly on wet or cold nights (Ruedi 1993), and in Scotland are mainly in
culverts or lade tunnels (Swift 1995 ).
6. NATTERER'S BAT (MYOTIS NATTERERI)
A shy, elusive bat, often overlooked in roosts particularly when these are shared with other
species such as pipistrelles or long-eared bats, Natterer's bat is one of the least studied
European species. It was first recorded in Scotland as late as the 1980’s, and its recorded
range in the country has expanded as bat work has progressed over the last 20 years.
6.1 Recognition
A medium sized bat distinguished from all other species by its conspicuous fringe of stiff
hairs, about 1mm long, along the outer edge of the tail membrane. It is further distinguished
from other Scottish Myotis species by its relatively long ears, which reach beyond the end of
the muzzle if folded forward, and by the S-shaped bend in the calcar.
6.2 Distribution
6.2.1 In Europe
Widespread to the extreme south of Scandinavia (Hutson 1993a).
6.2.2 In Britain
Widely distributed. Clusters of records reflect the results of intensive surveys of the species,
suggesting that more roosts will be found as surveying effort increases (Richardson 2000).
6.2.3 In Scotland
10
Forty-six roosts have been recorded to date (Haddow & Herman 2000), including on Islay,
Skye and Arran, and north to the Black Isle. The northernmost record is of two Natterer's
bats hibernating in a cave in Inverness-shire (Canham 1993). Records appear to be
concentrated in southern and central Scotland and in Perthshire, probably due to more
intensive survey work in these areas, but possibly also indicating that the species is
approaching the northern border of its distribution in Scotland.
6.3 Conservation status
6.3.1 Worldwide: Lower Risk : Least Concern (Hutson et al 2001).
6.3.2 In UK: Not Threatened (Hutson 1993a). Although widespread in Scotland, summer
records are still scarce and do not reflect the relatively high numbers found in hibernacula.
6.3.3 UK BAP status: Species of conservation concern.
6.4 Population size
The pre-breeding population has been estimated at 70,000 in England, 17,500 in Scotland
and 12,500 in Wales, but these estimates are based on very limited information and are
likely to be inaccurate (Harris et al 1995; reliability estimate =4). Many roosts are in trees,
and even those in buildings are difficult to find, which probably means the population size
has been underestimated. There are insufficient data to draw any conclusions regarding
population trends.
6.5 Social behaviour and organisation
6.5.1 Summer
Nursery colonies, consisting mainly of females although some contain around 25% adult and
immature males (Swift 1997), number 25-200 (Smith 2000b) and may live in buildings or
trees. Mean size of nursery colonies in Perth & Kinross is 40 (SNH database). Groups of
males and non-breeding females (8-28 bats) have also been reported in Scotland (Swift
1997), although such groups have not been found further south in the species' range (Smith
2000b). These groups roost in trees or in farm buildings, and one was found in a crevice in a
garden wall (Swift 1997). Nursery colonies live in occupied houses or in bridges, barns and
farm buildings (about half the known roosts in Scotland are in occupied houses), but a radio
tracking study in Wales has shown that about two thirds of maternity roosts are in trees
(Smith 2000b). It is likely trees are also widely used in Scotland, although to date only one
tree roost used by a nursery colony has been reported (Howe 1997). A second tree roost
was found during summer 2002 (author's data), when radio-tracked females took refuge in a
narrow cavity in a birch following exclusion from their nursery roost. However, it is doubtful
whether this would have been used by reproducing bats under less adverse circumstances,
and within two days of the exclusion, all bats had abandoned the tree. Within buildings, bats
hide in crevices, often between end beams and gable walls, and one colony roosted deep in
the cavity between a stone gable and a lathe-and-plaster wall (author's data). Roosts are
frequently shared with other species, mainly brown long-eareds in Scotland (J.Haddow,
pers. comm.). Because Natterer's bats roost in crevices and are relatively quiet in the roost,
their colonies can be overlooked in buildings, particularly when they are shared with more
obvious bats such as long-eareds.
In a captive colony and in the wild, births of single young began in the first week in July in
central Scotland (Swift 2001). First flight in the captive colony took place at 20 days of age,
juveniles could fly well by 22 days and weaning was completed by 39-40 days. In the wild,
nursery roosts are occupied by mid May, juveniles first fly early in August and weaning is
completed by late August (Swift 1995). Frequent roost moving is a constant feature of the
behaviour of M. nattereri. Smith (2000b) found that one colony in Wales moved roost, on
average, every three days during lactation, and mothers must therefore have carried young
in flight on a regular basis, and roost moving has also been reported in Germany (Siemers et
11
al 1999) and in Scotland (Swift 1997). Even in captivity, mothers moved between roost
boxes in a flight room on a regular basis (Swift 2001). Transport of young in flight is well
documented in this species, and stranded infants, presumably dropped by their mothers and
not retrieved, are regularly reported to bat conservation groups. This must be an additional
hazard to survival, and the reason for the behaviour has yet to be addressed.
Bats emerge to forage late in the evening (average 60 minutes after sunset at light
intensities of less than 3.5lux; Swift 1997), and circle continuously in a dark space close to
the roost before departing (Swift 1997); a requirement for this dark space (such as a nearby
barn or the shadow under a bridge) also seems to apply to Natterer's bats in Scotland,
although this may not hold true further south (Smith & Racey 2002). Bats also return to this
dark space at intervals through the night and circle for several minutes before moving off
again (Haddow 1995; Swift 1997), suggesting the behaviour has a social communication
function, possibly connected with group foraging.
6.5.2 Winter
M. nattereri is the most numerous species found at hibernacula in mines and limestone
quarries in southern Scotland (Herman & Smith 1992; Smith 2000a). At one mine, 38 were
counted on one occasion (Smith 2000a). They appear to prefer the cool entrance areas, and
are the species most likely to be found in any small, exposed cave-like site in winter (eg
Canham 1993). In Poland, they select temperatures of 6-10oC (Harmata 1969). In
hibernation, individuals are usually solitary, but small groups are not uncommon and one
cluster of around 150 bats has been recorded in Hampshire (Stebbings 1993). There is no
evidence trees or buildings are used for hibernation.
6.5.3 Mating and swarming
Natterer's bats were the most numerous species caught at mine entrances in September
and October in Scotland (Park 2000), and the bias towards males suggests they were
swarming. They were also the most numerous species captured during swarming at
underground sites in southern England (Parsons et al 2003). Mating is probably
promiscuous, as in most species which display swarming, and takes place in hibernacula.
Copulation has been observed in a cave during December (Gilbert & Stebbings 1958), but
may continue intermittently through winter and spring, as in Daubenton's (Strelkov 1969).
6.6 Habitat and foraging
Compositional analysis revealed that bats selected semi-natural broad-leafed woodland and
tree-lined river corridor in a radio tracking study in Wales (Smith 2000b), but also foraged
over grassland. In Scotland, foraging has been observed in woodland edge, parkland, trees
on a loch shore and roadside vegetation (Swift 1997). Most observations have been in areas
with medium-length grass under widely spaced coniferous trees such as larch or Scots pine
(author's data). Coniferous woodland was also reported to be widely used by a colony in
southern Germany (Siemers et al 1999). Night roosts are used within foraging areas (Swift
1997).
Natterer's bats have low wing-loading and frequently hover. They forage close to
vegetation, and are able to hunt by echolocation in cluttered environments by using FM calls
of exceptionally broad bandwidth (Siemers & Schnitzler 2000). They glean prey from
vegetation using the tail membrane as a net (Swift & Racey 2002), and continue to
echolocate throughout gleaning attacks. There is evidence they may rely more on gleaning
in Scotland than in Germany (Siemers & Swift, unpublished), consistent with the cooler
climate and less reliable supply of flying insects further north. The diet includes non-flying
arthropods such as spiders and harvestmen, diurnal flies such as dungflies, earwigs, beetles
and longhorn flies. This species has one of the most varied diets of all British bats, reflecting
its ability to forage adaptably. Compared with long-eared bats, which also glean, it eats
12
relatively few moths, possibly because it does not switch off echolocation during foraging
and so its approach can be detected by tympanate species.
7. WHISKERED (MYOTIS MYSTACINUS) AND BRANDT'S (M. BRANDTII) BATS
These are cryptic species which were clearly identified as separate species only 30 years
ago (Hanák 1970), and records previous to this date all referred to M. mystacinus. The two
are extremely difficult to tell apart and confusion still exists. There is only one confirmed
record of M. brandtii in Scotland. This was collected in the Rannoch area in 1874, and the
specimen is in Perth Museum. There are no more recent records, and it is doubtful whether
this species occurs in Scotland. However, because of confusion in identification, it is
possible more will be recorded in future. The two are considered together in this account.
7.1 Recognition
Whiskered / Brandt's bats are the smallest British Myotis species (forearm length less than
37mm), and may be further distinguished from Daubenton's bat by their smaller feet, which
are less than half the length of the tibia. Ears and face membranes are very dark, almost
black, and the dorsal fur is shaggy and dark grey. Ventral fur is pale grey, as in other
Myotis. Recognition from each other relies on small differences in dentition, although adult
Brandt's bats may have characteristically red-brown dorsal and buff ventral fur, and males of
this species have a club-shaped penis. Bats less than a year old have virtually identical
colouring in both species.
7.2 Distribution
7.2.1 In Europe
Whiskered bats are widely distributed, although rare in the extreme south-west. Brandt's
bats are distributed throughout northern Europe to central Scandinavia and southern Finland
(Hutson 1993a).
7.2.2 In Britain
Both species have a widespread, although patchy, distribution throughout England and
Wales and, with respect to M. mystacinus, as far north as southern Scotland (Richardson
2000).
7.2.3 In Scotland
There is one record of M. brandtii from Perthshire (see above). Records of M. mystacinus
have all been in the south except for one bat found in Aberdeen (Racey & Rydell 1995).
This may have been a stray from further south, since no roost has yet been found in the
area. There are a total of nine records from Borders, Midlothian, Ayrshire and Dumfries, but
none north of the central belt except for the one Aberdeen specimen (Haddow 1993). Since
the species occurs much further north in Scandinavia, it may yet be found more widely in
Scotland.
7.3 Conservation status
7.3.1 Worldwide: Lower Risk : Least Concern (Hutson et al 2001) for both species.
7.3.2 In UK: Both species are considered to be Vulnerable; scarce (Hutson 1993a). In
Scotland: M. mystacinus is rare and has restricted distribution. It is doubtful whether M.
brandtii is present at all.
7.3.3 UK BAP status: Species of conservation concern.
7.4 Population size
The most recent estimate for the British population of M. mystacinus is 30-40,000 (reliability
of estimate: 4; low), of which approximately 1500 are in Scotland (Harris et al 1995). Earlier
13
status of the species is uncertain, due to confusion with pipistrelles and Brandt's bat, but if
estimates from 100 years ago were accurate, whiskered bats have suffered significant
declines during the Twentieth Century. Numbers of M. brandtii have been estimated at
about 30,000 in Britain, with a reliability estimate of 5; very low (Harris et al 1995). The
Scottish population size is unknown.
7.5 Social behaviour and organisation
7.5.1 Summer
Nursery colonies consisting mainly of females are formed in May and move into summer
roosts. These are usually in buildings, often under slates or ridge tiles (Stebbings 1991).
Nursery colonies in Scotland appear to be small (Haddow et al 1989; Haddow 1993), since
the largest so far recorded consisted of 40 individuals and most of the others numbered 1420 (Haddow 1993). Phenology is probably similar to that of other Myotis species, with
juveniles flying by mid August. Adult males are thought to be solitary in summer (Stebbings
1991). Bats emerge from summer roosts early in the evening, at about the same time as
pipistrelles, and probably remain intermittently active all night.
7.5.2 Winter
As is the case for the other Scottish Myotis species, whiskered bats have not been found in
buildings in winter. They have been reported from hibernacula in underground sites in
southern Scotland (Herman & Smith 1992) and Dumfries (Haddow 1993) in very low
numbers; no more than one bat has been recorded from any site on a single visit. In
Europe, they have been found hibernating in cellars and caves, where they prefer the cooler
entrance regions (Bezem et al 1964). They may hibernate either hanging from the roof or in
crevices.
7.5.3 Mating and swarming
Mating is thought to be similar to that in other Myotis species, with a promiscuous mating
system, the main mating period in November and December and intermittent mating through
winter and spring (Strelkov 1962). No whiskered bats have so far been reported from
swarming sites in Scotland, but swarming by both M. mystacinus and M. brandtii, with peak
numbers occurring in late August, was recorded recently in England (Parsons et al 2003).
7.6 Habitat and foraging
Foraging is mainly in lightly wooded habitat, often along hedgerows, and flight is level with
occasional swoops (Stebbings 1991). Analysis of droppings from a nursery colony in
southern Germany in 2002 (Swift, unpublished) showed that the main items in the diet (in
order of importance) were small moths, flies (including chironomid midges and diurnal flies),
ichneumonid wasps, spiders and a few harvestmen. The harvestmen must have been
caught by gleaning, as could some of the spiders, showing that this species gleans some of
its prey, although it probably forages mainly by aerial capture.
8. NOCTULE (NYCTALUS NOCTULA)
Nyctalus is a small genus with six species, three of which occur in Europe. All have long,
narrow wings associated with fast, straight flight. There are two species in Britain (N.
noctula and N. leisleri), both of which are known to be migratory in parts of their ranges in
Europe, and both of which are found rarely in Scotland. A number of the records for both are
bat detector records, since Nyctalus bats emit distinctive, loud calls which have a
recognisable ‘plip-plop’ sound on a heterodyne detector. The calls of the two are, however,
difficult to distinguish from each other and thus most detector records have been attributed
to Nyctalus spp, rather than to either species.
8.1 Recognition
14
The noctule is easily the largest Scottish bat (forearm length more than 47mm), and may be
recognised in flight by its size, high, fast flight and early emergence, since it often flies well
before dusk. In the hand, it has sleek, reddish-brown fur and a mushroom-shaped tragus
which distinguishes it from all other species except Leisler's bat. It differs from Leisler's in its
larger size and the uniform colour of hairs from base to tip.
8.2 Distribution
8.2.1 In Europe
Widespread from south Scandinavia, but scarce in the south-west of Europe (Hutson
1993a).
8.2.2 In Britain
Widespread but local in England and Wales, and north to southern Scotland (Mackie 2002).
8.2.3 In Scotland
In-hand records are confined to the south-west of the country, from Dumfries & Galloway
(Haddow & Herman 2000) and Ayrshire (Potter 1997). There are also bat detector records
of N. noctula from East Lothian (P.Reynolds; unpublished time-expansion detector record
from 2001) and Borders (J.Haddow; unpublished record from 2001), and of Nyctalus spp
from Strathclyde and the Highlands; the latter seems unlikely to have been a noctule. In
addition, two bats, both adult females, have been recorded in 1980 and 1988 from the
Fulmar Alpha oil platform 312 km east of Dundee (P.A.Racey, pers. comm). These were
presumably blown off course from continental Europe, as was a specimen recorded in
Orkney (Racey 1977).
8.3 Conservation status
8.3.1 Worldwide: Lower Risk: Least Concern (Hutson et al 2001).
8.3.2 In UK: Vulnerable : relatively common in small numbers (Hutson 1993). It is believed
to be less numerous in Britain than in the past, probably due to loss of deciduous woodland,
on which it depends for foraging and roosting habitat (Hutson 1993a).
8.3.3 UK BAP status: Species of conservation concern.
8.4 Population size
The UK population has been estimated at 50,000 (Speakman 1991a), of which the Scottish
colonies make up a very small proportion (estimated at 250; Harris et al 1995). The
reliability of population estimate for this figure is 3 (Harris et al 1995) Population density in
woodland in Yorkshire was 0.015 per hectare (Jones et al 1996).
8.5 Social behaviour and organisation
8.5.1 Summer
The noctule is predominantly a tree bat and the vast majority of roosts are in tree holes. Rot
holes are used, but woodpecker holes are preferred (Boonman 2000; Mackie 2002), and
roosts are mostly in deciduous trees or Scots pine. Bats select holes which are larger,
further from the ground and in more open situations than random (Mackie 2002). In Europe,
colonies occasionally roost in houses (Zahn et al 2000) or in rock crevices (Gaisler et al
1979). In one house in Bavaria, between 200 and 500 bats roosted all year round behind
fascia boards (Zahn et al 2000). Tree roosts may be recognised by dark streaks of faeces
and urine which drain from the access hole, or by droppings scattered below the tree. Bats
also frequently vocalise in roosts before emergence. Tree holes may be shared with other
species, usually Daubenton's bats (Mackie 2002).
Nursery colonies may exceed 100 bats in Europe, but in England are much smaller and the
average colony size in one study was 14 (Howes 1979). No data are available with respect
15
to colony size in Scotland. Nursery colonies are formed by early June, gestation length is 7073 days in Europe (Eisentraut 1936), and young are born in the first half of June to early
July. Twins and occasionally triplets have been recorded (Kleiman & Racey 1969).
Weaning does not take place before August, and in some years the young may not fly until
September (Cranbrook & Barret 1965). Males may be solitary in summer, or may form small
groups. Both male and female colonies move roost frequently, and females regularly carry
infants in flight (Gaisler et al 1979).
8.5.2 Winter
Winter roosts are in trees or buildings, and large, mixed-sex colonies of up to 1000 bats
have been reported in Europe (Strelkov 1969; Petit et al 1999; Petit & Mayer 2000), although
colony size in the UK is much smaller. Tree holes which are occupied in winter are limited to
those in areas where the January temperature does not fall below -2 to -4oC (Gaisler 1979).
Severe winters are thought to result in high mortality, and this may well be a limiting factor to
the distribution of the species in Scotland.
Noctules are migratory in eastern Europe, moving up to 1600km between summer and
winter roosts (Strelkov 1969), but probably less so in western Europe and are not known to
move out of Britain, even during severe winters.
8.5.3 Mating
The mating system is resource defence polygyny, similar to that of pipistrelles, and
swarming associated with mating has not been recorded. Single males establish territories
in tree holes in September and defend them with vocalisations (Gaisler 1979). Females visit
the territory, and up to 18 females may be found with a single male (Sluiter & van Heerdt
1966). The main mating period occurs during September and October.
8.6 Habitat and foraging
Noctules are woodland bats and feed by fast aerial hawking over woodland, pasture next to
woodland, water and brightly lit areas, where they capitalise on insects accumulating round
street lamps (Rydell & Racey 1995). They emerge before sunset, and their early evening
foraging coincides with the dusk peak of flying insects (Cranbrook & Barret 1965). Most
important items in the diet include large beetles, especially chafers, flies and moths
(Vaughan 1997).
9. LEISLER'S BAT (NYCTALUS LEISLERI)
9.1 Recognition
Leisler's bat can be distiguished from the noctule by its smaller size (forearm length less
than 48mm) and distinctly bicoloured fur, with individual hairs much darker at the base than
at the tip, and from all other species by the mushroom shape of the tragus.
9.2 Distribution
9.2.1 In Europe
Widespread through central Europe, but sparse in the south and west.
9.2.2 In UK
Most colonies in England are in the central southern counties, and there are isolated records
from Wales and southern Scotland. It is common and widespread in Ireland.
9.2.3 In Scotland
The species has been recorded in Dumfriesshire in 1988 and 1991 (Arnold 1993), and in bat
boxes in Galloway in 1994 (Collin 1995). Rydell et al (1993) recorded Leisler's bats in the
Aberdeen area from several time-expansion bat detector recordings and one sighting. One
16
specimen found in Orkney was presumed to be a vagrant (Corbet 1970), and another
vagrant was recovered from a North Sea oil platform in 2002 (P.A.Racey, pers. comm.).
9.3 Conservation status
9.3.1 Worldwide: Lower Risk: Near Threatened ( Hutson et al 2001).
9.3.2 In UK: Vulnerable: scarce (except Ireland) and poorly known (Hutson 1993a).
There are no data on previous numbers, and lack of knowledge about Leisler's bat means
that specific threats have not yet been identified.
9.3.3 UK BAP status: Species of conservation concern.
9.4 Population size
Harris et al (1995) estimated the total pre-breeding population in Britain to be about 10,000,
of which 250 were in Scotland. The reliability of the population estimate for this figure was 4
(low).
9.5 Social behaviour and organisation
9.5.1 Summer
Although it is considered to be principally a tree-roosting species in Europe (Roer 1989), in
Britain and Ireland most nursery roosts are in roof spaces of buildings, mainly occupied
houses (McAney & Fairley 1990; Sullivan et al 1993; Heathcote & Heathcote 1990). Roost
moving has been reported, as for noctules. Non-breeding roosts have been located in tree
holes and bat boxes, and similar non-breeding groups are frequent occupants of bat boxes
in southern Germany (B. J. Siemers, pers. comm.). Vocalisation in the roost is loud for
about 15 minutes before emergence, and bats typically emerge about 18 minutes after
sunset in England (Jones & Rydell 1994). As in the noctule, this early evening flight
coincides with the dusk peak of flying insects.
Mean colony size in one study in England (Heathcote & Heathcote 1990) was 36, with the
largest colony numbering 164, and in Ireland colonies of up to 100 females are relatively
common (O'Sullivan 1994). Nursery roosts begin to form in April, and females give birth to a
single young from mid to late June (C. Shiel, unpublished). Juveniles begin to fly around 30
days after birth.
9.5.2 Winter
Winter behaviour is probably similar to that in noctules, but there are no data currently
available.
9.5.3 Mating and swarming
Essentially, the mating system is similar to that for noctules, with males defending mating
territories from August onwards, males emitting songflight and females visiting territories in
trees (C. Shiel, unpublished). Copulation is presumed to take place in autumn.
9.6 Habitat and foraging
A radio tracking study in Ireland (Shiel et al 1999) revealed that two thirds of foraging time
was spent over pasture or drainage canals. Other habitats included lakes, coniferous
woodland, areas under streetlights and estuaries. However, an earlier Irish study using bat
detectors (Shiel & Fairley 1998) suggested N. leisleri showed little habitat preference. Russ
et al (2003) have suggested this may have been because, since individuals forage at heights
of up to 150m, it is difficult to assign accurate habitats to them. Bats commuted up to
13.4km from roosts to foraging sites (Shiel et al 1999). Food is medium-sized and small
insects caught and eaten in flight. Midges (Chironomidae), flies, particularly dungflies,
caddis flies and moths are the most important components of the diet in Ireland (Sullivan et
al 1993).
17
10. NATHUSIUS' PIPISTRELLE (PIPISTRELLUS NATHUSII)
This uncommon bat, which is difficult to differentiate from its congeners P. pipistrellus and P.
pygmaeus, was considered until recently to be a migrant species, some of which may have
wintered in Britain. However, with the discovery of three maternity colonies, two in Northern
Ireland (Russ et al 1998) and one in England (BCT Bat Group Reports, Number 22, 1997), it
is now clear there is also a resident breeding population.
10.1 Recognition
This species is very similar to the two common pipistrelle species in Scotland, except in that
the ratio of the length of the fifth digit : forearm is greater than 1 : 1.25 and the length of the
third digit (including the wrist) is over 60mm. The fur is slightly longer and shaggier than in
the other species and may be darker brown dorsally and lighter ventrally, giving a ‘two-tone’
appearance. The echolocation calls can also be separated from those of 45 and 55kHz
pipistrelles. The maximum energy ‘tail’ in Nathusius' calls is typically around 37kHz and is
slightly longer than in the other species (Rydell & Swift 1995).
10.2 Distribution
10.2.1 In Europe
Nathusius' pipistrelle is found throughout northern continental Europe, extending westwards
into France and eastwards to Russia (Speakman et al 1991b). It is common in the Baltic
states and the range extends into Sweden and Finland, to latitude 58-59oN (Strelkov 2000).
10.2.2 In Britain
Initially classed as a vagrant (Stebbings 1988), on the basis of three documented records,
plus a fourth from the North Sea. By 1991, the number of records had increased to 21, with
clear peaks of recordings occurring in spring and autumn. Speakman et al (1991b)
proposed it be reclassified as a migrant species. It is well established in Europe that P.
nathusii is migratory (Strelkov 2000), leaving its breeding areas in Scandinavia and the
Balkans around late August and moving south-west into central Europe and France.
Speakman et al (1991b) suggested that, since available meterological data did not support
the probability of bats simply being blown off course, some may actually migrate into Britain
to spend the winter here. More recently, the increase in the number of records (91 by
2000) and the identification of three nursery roosts (Russ et al 2001) has established the
presence of the species in Britain all year round and led to the conclusion that at least a
proportion of the migrating population remains in Britain to breed each summer (Russ et al
2001).
10.2.3 In Scotland
Between 1940 and 2000, there were a total of 39 in-hand records of Nathusius' pipistrelle in
Scotland. Of these, 12 came from Shetland, 8 from the Scottish mainland and 19 from North
Sea oil installations (Russ et al 2001). Most of these were in late summer, autumn or spring,
suggesting they were migrating bats. A further two bats were found on oil platforms during
2001 (P.A.Racey pers. comm.). In addition, there have been five bat detector records of
Nathusius' pipistrelles foraging in Scotland in summer - one in Aberdeen and one near
Balmoral (Rydell & Swift 1995), and three near Stirling (J.Haddow, unpublished). This
suggests there is likely to be a breeding population in Scotland, although no nursery roosts
have yet been found.
10.3 Conservation status
10.3.1 Worldwide: Lower risk : Least Concern (Hutson et al 2001).
10.3.2 In UK: Not threatened: regular migrant, but rare (Hutson 1993a).
18
10.3.3 UK BAP status: Species of conservation concern.
10.4 Population size
There are no data available for the UK as a whole, nor for Scotland. The Northern Irish
population has been estimated at between six and twenty thousand, based on bat detector
surveys (J. Russ, unpublished).
10.5 Social behaviour and organisation
10.5.1 Summer
In Europe, this is essentially a tree-roosting species, with nursery roosts mainly in tree holes,
cracks in tree trunks, and bat boxes, but rarely in buildings (Schober & Grimmberger 1989).
However, the three roosts found in Britain have all been in cavity walls or under roof slates in
buildings, and individual males also roosted in crevices in buildings (Russ et al 1998).
Colony size at the two Northern Irish roosts was around 150 - 200, and the capture of
pregnant females on 1st May and lactating females on 22nd June (Russ et al 1998) suggests
the phenology of this species in similar to that of other pipistrelles in Britain. Males appear to
be solitary in summer, again similar to 45 and 55kHz pipistrelles.
10.5.2 Winter
There are no data available in Britain. In mainland Europe, winter roosts are in fissures in
rocks, cracks in walls and caves and in tree holes (Schober & Grimmberger 1997).
Nathusius' pipistrelle is a strongly migratory species, and the pattern of records from Britain
suggests it migrates from Scandinavia to avoid the harsh winters there, and overwinters in
the British Isles (Russ et al 2001).
10.5.3 Mating and swarming
The mating system is similar to that of the other pipistrelle species, with males defending
mating territories and advertising to attract females. However, P. nathusii spends about half
its time calling from the roost and the other half in aerial display, whereas the other species
call only on the wing (Gerell-Lundberg & Gerell 1994). Males defend territories from July to
late August and form mating groups with females (mean number of females per group was
4.5 in Sweden) in late August and September (Gerell-Lundberg & Gerell 1994). The
songflight calls of P. nathusii are distinctive, the main part having 5-8 components and
lasting about 50ms (Barlow & Jones 1996).
10.6 Habitat and foraging
In Northern Ireland, foraging occurs in riparian habitats, broadleafed and mixed woodland,
and parkland. Bats occasionally feed in farmland, but always near water (J. Russ,
unpublished). In England, foraging has been reported over lakes and rivers (Vaughan et al
1997). Both roosts in Northern Ireland have been in rural areas and approximately 50m from
a river (Russ et al 1998). The bat detector records in Scotland have been in parkland close
rivers (Rydell & Swift 1995) and over a small loch (J. Haddow, unpublished). The diet
consists mainly of insects, such as chironomid midges, with aquatic larvae (Vaughan 1997),
and all prey is probably caught by aerial hawking (Kalko 1995).
11. VAGRANT SPECIES
11.1 Serotine bat (Eptesicus serotinus)
This is a large species that occurs over much of central and western Europe, including
southern England. It is a bat of lowland parkland, pasture and woodland edge, where it
feeds mainly on beetles which it captures during sweeps close to the ground. Other insects
such as moths and flies are also taken. Maternity colonies are small (up to around 30
females) and are commonly located in buildings. Although serotines may commute up to
40km in a single night between the roost and several foraging sites, the species appears to
19
be a relatively sedentary and does not normally migrate over large distances (Altringham
2003). Nevertheless, there is a record of a single live serotine found on the island of
Whalsay (Shetland) in October 1991, although its origin is unknown.
11.2 Northern bat (Eptesicus nilssonii)
As its name implies, this occurs mainly in northern Europe, where it is one of the commonest
species. Its range extends to northern Scandinavia and Russia (Rydell 1993) and breeding
colonies have been found above the arctic circle (Rydell et al 1994). It is uncommon in
lowland further south, but has been recorded in mountainous areas in Germany and France.
There are only two British records, the first in Surrey in 1986, and the second from an oil
installation in the North Sea in August 1993 (Speakman et al 1995). The species is not
known to be migratory, and has not been reported to cross open water regularly, so these
two records probably represent vagrants. The northern bat lives mainly in forested areas,
but also in farmland, villages and towns. It forages in straight flight along treelines or over
water (Rydell 1986) and frequently feeds along lines of street lamps. Its diet is mainly small
flying insects such as Diptera, moths, mayflies and caddis flies (Rydell 1986). Maternity
colonies typically consist of 20-80 females and, in Scandinavia, are almost always in heated
houses. Males are solitary in summer, and hibernation sites are usually houses and cellars,
occasionally caves and mines (Rydell 1993).
11.3 Parti-coloured bat (Vespertilio murinus)
The parti-coloured bat occurs over a wide area in Europe, from eastern France and
Switzerland to southern Scandinavia, eastward through central Europe to Ukraine and into
Asia and southern Siberia (Rydell & Baagøe 1994). It is a migratory species in eastern
Europe (Strelkov 2000), and vagrants are frequently reported well outside its known range.
Until last year, there had been four records of single animals in England (Richardson 2000),
two on Shetland and three on North Sea oil platforms east of Shetland. The three North Sea
records were all within a two-month period in November/December 2001 (P. A. Racey, pers.
comm.). From 2001-2, three more grounded bats were reported in England, causing
speculation that the species may be increasing its range in Europe and that these may be
resident bats (Bat News, July 2002). However, so far it seems certain the Scottish records
were of vagrants. Nursery roosts are usually well hidden in crevices in roofs and walls, often
in modern and well insulated buildings (Rydell & Baagoe 1994), but in Russia tree holes are
also used (Strelkov 1969). Hibernation is in crevices in buildings and in rock fissures. In
Poland, tall buildings are frequently used for hibernation (Lesinki et al 2001). V. murinus
forage at heights of around 20-40m (Baagøe 1987) in open country and over woodland and
lakes. They also feed in suburban areas, especially around street lights. Insects are
captured only by aerial hawking and small dipterans, mainly chironomid midges, dominate
the diet (Rydell 1992).
11.4 Savi's pipistrelle (Pipistrellus savii)
This has been recorded once in Scotland, from Wick, and twice from southern coastal
locations in England (Richardson 2000). A southern European species, it is found mainly in
the Mediterranean region and is relatively common in SE France, where it is a typical rock
dwelling bat (Hutson 1993b). In the Pyrenees it roosts in crevices in cliffs and rocky slopes,
and migratory behaviour has not been reported. It seems an unlikely vagrant without the
unwitting help of humans, and ship-assisted passage is likely to have been involved in all the
British records.
11.5 Hoary bat (Lasiurus cinereus)
The only British record of the hoary bat, a north American species, is from Orkney in 1847
(Stebbings 1986). It has also been recorded four times in Iceland, each time in autumn and
early winter, suggesting the Orkney individual may well have been a migrant blown far off
course. It is a high-flying migrant and the only bat to have colonised Hawaii from the
American mainland.
20
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