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Conservation of bats in British woodlands



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Conservation of bats in British woodlands
February 2008 British Wildlife 161
Conservation of bats
in British woodlands
David A Hill and Frank Greenaway
Broadleaved woodlands are probably the
most important of British habitats for bat
conservation. For most of the year they
support a great variety and abundance of inverte-
brates for bats to feed on. They also offer a huge
selection of tree cavities – crevices, bark flaps,
fissures and woodpecker holes – where bats can
rest during the day and where females can gather
in maternity colonies, to give birth and nurse their
young. All 16 British species of bat make regular
use of trees and wooded areas, and some of our
rarest bats are woodland specialists.
Yet, in spite of their importance, there is a
distinct lack of knowledge about bats in wood-
lands. Even most bat specialists know much less
about the distribution, behaviour or conservation
status of bats inhabiting woodlands than about
bats that roost in buildings or caves. The main
reason for this is that bats are particularly difficult
to find or record in woodlands, which has made
them very hard to survey or study.
In this article we describe a technique which
we have developed that overcomes some of these
difficulties and makes it possible, for the first
time, to survey woodlands for bats in a systematic
way. In 2005 and 2006, we used this technique to
survey bats in woods in the south-east of England.
The results of those surveys strongly suggest
that the number of bats and diversity of species
found in a woodland are related to the predomi-
nant tree species and the structure of the wood.
We shall summarise these findings, discuss some
of their implications for woodland management,
and conclude by arguing that woodlands should
become a major focus of future efforts to monitor
bat populations and promote their conservation.
The rare Bechstein’s Bat has proved
difficult to survey in woodlands using
traditional methods. Frank Greenaway
Conservation of bats in British woodlands
162 British Wildlife February 2008
Conservation of bats in British woodlands
February 2008 British Wildlife 163
Current status of bats and woodlands
Bat populations have declined in Britain, as they
have in many other parts of the world (reviewed
in Racey & Entwistle 2003). In most cases, it is
impossible to quantify the scale of the decline
because of a lack of reliable historical data on
population sizes or distributions. But the accu-
mulated evidence provides a compelling argument
that numbers of most British bat species, and the
ranges of some, have shrunk substantially, nota-
bly during the last century (Harris et al. 1995). In
recent years, populations of Greater and Lesser
Horseshoe Bats Rhinolophus ferrumequinum and
R. hipposideros have shown signs of increasing,
but there is no evidence of recovery in populations
of other species (BCT 2006). In recognition of the
declines and the continuing threats that they face,
all British bat species and their roosts are now
protected by national and European legislation.
A variety of factors is thought to have contrib-
uted to the decline of bat populations, including
the loss of roosting sites and hibernacula, and
the loss and degradation of feeding habitats. One
habitat which has suffered major losses is wood-
land. Broadleaved woods once covered most of the
British Isles, but the total area has been decreasing
since widespread clearance of land began in the
Neolithic era. Loss of semi-natural woodlands has
continued into modern times, reaching a low point
at the beginning of the 20th century, when only
5.4% of Britain’s land area supported woodland.
Woodland now occupies a total of 13.1%, but
more than half consists of planted conifers. Broad-
leaved woodlands cover just 5.6% of Britain, and
much of that is in small fragments scattered across
the landscape (statistics from Forestry Commis-
sion 2007 and Watts 2006).
Given their importance to bats, and the fact that
they have been in decline, broadleaved woodlands
would seem to be an obvious target on which to
focus bat conservation work. In fact, this has not
been the case. Although efforts to survey bats and
promote bat conservation in Britain have gained
considerable momentum over the past 15 years,
relatively little has been done to assess bat popula-
tions, or their habitat requirements, in woodlands.
Even the National Bat Monitoring Programme
(see Box 1), which is a major initiative to survey
Britain’s bats, has placed little emphasis on bats in
woodlands. The reason for this is very simple: bats
are extremely difficult to study, or even to find, in
woodlands by means of standard techniques.
Surveying methods for bats
Being small, fast-moving and most active during
the hours of darkness, bats are generally difficult
to survey. One of the most common methods is
to count individuals as they exit from a commu-
nal roost site. This can be particularly useful with
species that form maternity roosts in buildings,
as they commonly use the same roost site year
after year. The bats leave the roost around dusk
on most days, and often via one or two defined
exit points. In most cases it is possible to watch
and count the bats as they emerge without enter-
ing the roost and with little danger of causing
disturbance. As the method is non-invasive, no
licence is required. This means that surveys can be
conducted by volunteers, and counts can be safely
repeated several times in a season, as well as in
successive years.
Bats can also be surveyed by monitoring the
ultrasonic calls which they produce for echoloca-
tion. These can be converted to audible sound by
using a portable bat-detector. Different bats give
different kinds of calls and, in many cases, the
species of bat can be identified from characteris-
tics of the calls. However, identification to species
is not always possible because bats often adjust
the structure of their echolocation calls in relation
Box 1 The National Bat Monitoring Programme
In 1995, the Bat Conservation Trust initiated a five-year
programme of research to develop and apply methods
for systematically monitoring bat populations in the
UK. Data collection began in 1996 and has continued
annually since. The National Bat Monitoring Programme
(NBMP) uses trained volunteers from local bat groups
to make annual surveys of specific sites throughout the
UK. The main methods used are winter counts of bats at
hibernation sites, counts of bats emerging from known
maternity roosts, and field and waterway surveys with
bat-detectors. Different methods are suited to different
subsets of species. Emergence counts focus on colonies
of six species roosting in buildings. The field surveys
focus on four species – Noctule Nyctalus noctula,
Serotine Eptesicus serotinus, Common Pipistrelle and
Soprano Pipistrelle – and the waterway survey on
Daubenton’s Bat Myotis daubentoni. Two woodland
bats, Natterer’s Bat and the Brown Long-eared Bat, are
surveyed, but only those colonies that roost in buildings.
Woodland habitats are not a focus of the NBMP,
presumably because of the extreme difficulties involved
in surveying them, as explained in the main text.
Conservation of bats in British woodlands
162 British Wildlife February 2008
Conservation of bats in British woodlands
February 2008 British Wildlife 163
to the environment in which they are flying, and
there is some overlap between the calls of different
bat species under certain conditions. Nevertheless,
it is an extremely useful non-invasive method for
identification of bats in flight, and for obtaining
comparable measures of bat activity. In recent
years, several inexpensive bat-detectors have
become available and the monitoring of echoloca-
tion calls has now become one of the main meth-
ods used to survey patterns of activity and habitat
use by bats.
Both of these methods are difficult to use in
woodlands, for a variety of reasons. In woodlands,
roosts are usually in holes and cracks in trees or
under loose flaps of bark. A maternity colony
usually uses the same roosts in consecutive years,
but it may use several roosts in a season, moving
to a different one every few days or so. In many
cases, whether occupied or not, roost sites are
indistinguishable from a multitude of other holes,
cracks and crevices in trees that are not used by
bats. So, visual searching for tree roosts in woods
is not a viable method.
Bat-detectors are also less useful in wood-
lands than in more open habitats, because bats
flying in a cluttered environment normally give
quiet echolocation calls. Also, in these condi-
tions, several species use calls
that are very similar in struc-
ture, so that, even when their
quiet calls are detected, species
identification can be difficult
or impossible. In these cases, it
is necessary to catch the bats to
identify species unambiguously.
Once caught, they can also be
examined to determine sex and
reproductive condition. This
is important information, as
the presence of a reproductive
female indicates that there is a
maternity colony in the vicinity,
whereas the presence of a male
does not. Unfortunately, bats
are also quite difficult to catch
inside woodlands. The ‘tradi-
tional’ method is to try to catch
them by setting mist nets or harp
traps over paths and rides or
over small streams. However,
while some species routinely use
such features for commuting routes or for forag-
ing, others do so infrequently and so are much
less likely to be caught. What is really needed is a
method for catching bats inside the interior of the
wood itself, and ideally one that will attract bats
down from the canopy. And this is what we have
Lured by the siren’s call
Our technique involves using simulated bat calls
as a lure so that the bats can be captured. As well
as the ultrasonic echolocation calls used to navi-
gate and to locate prey, bats produce a variety
of other vocalisations, which are thought to be
used to communicate with other bats. These calls,
commonly referred to as ‘social calls’, usually
include lower frequencies than echolocation calls,
and some are even audible to humans. They are
also given less frequently than echolocation calls,
and at irregular intervals. Work on the function of
social calls is still at an early stage, but indications
are that the way in which other bats respond to
them depends on the type of call and the context
in which it is given. For example, when record-
ings of Common Pipistrelle Pipistrellus pipistrel-
lus social calls were played back, they appeared
to repel other bats from feeding areas when insect
The Sussex Autobat speaker mounted on a pole beside a harp trap in
an upland oakwood. Frank Greenaway
Conservation of bats in British woodlands
164 British Wildlife February 2008
Conservation of bats in British woodlands
February 2008 British Wildlife 165
prey was in short supply, but not when it was plen-
tiful (Barlow & Jones 1997). By contrast, ‘alarm
calls’ given by Common Pipistrelles can be used
to elicit an approach response from other bats of
the same species, possibly representing a form of
predator-mobbing behaviour (Russ et al. 1998).
We wondered whether social calls could be used
to attract woodland bats into a mist net or harp
trap, in much the same way as some bird-ringers
use recordings of birdsong to lure birds. Most of
the species that are difficult to catch in woodlands
give social calls much more rarely and unpredict-
ably than do Common Pipistrelles. This makes it
very difficult to obtain good-quality recordings
for use in playback. As an alternative, we devel-
oped a programmable ultrasound synthesiser, the
Sussex Autobat, that we use to produce simula-
tions of bat social calls. Our preliminary work
indicated that the calls produced by the Autobat
could be very effective in attracting a variety of
bats in woodlands, and we went on to demon-
strate this experimentally (Hill & Greenaway
2005). Over 16 nights at different woodland sites,
23 bats were caught while the Autobat calls were
playing, compared with only one bat caught when
the Autobat was silent. The stimulus call used in
this experiment was modelled on a social call of
the rare Bechstein’s Bat Myotis bechsteinii, which
had proved impossible to survey with other meth-
ods (Hill & Greenaway in prep.). The calls proved
effective for attracting Bechstein’s Bats, but we
also caught bats of three other species: Brown
Long-eared Bats Plecotus auritus, Whiskered Bats
Myotis mystacinus, and Soprano Pipistrelles Pipis-
trellus pygmaeus. Having demonstrated the effec-
tiveness of the Autobat lure for catching bats in
woodlands, the next step was to apply the tech-
nique across a large sample of sites to demonstrate
how it could be used to conduct systematic surveys
of woodland bats at a regional level.
Preliminary surveys of bats in woodlands of
south-east England
In 2005 and 2006, we used the Autobat to conduct
two systematic surveys of bats in woodlands
in south-east England. In the first, we looked at
sites scattered across the counties of Hampshire,
Surrey, West Sussex, East Sussex and Kent. Then,
in 2006, we made a more intensive survey of East
and West Sussex, with the aim of having survey
data for one wood in every 10km square in which
a suitable site could be found. In both cases the
primary target was the rare Bechstein’s Bat, and
the detailed results for this species are described
elsewhere (Hill & Greenaway in prep.). However,
in both surveys we caught a variety of species that
were attracted to the lure, and this provided a
unique set of data on variation in bat diversity in
relation to woodland quality.
The protocol used in both surveys was as
follows. Within each target wood, two survey sites
were selected that were at least 200m from each
other and 20m from the nearest woodland edge.
On the survey night, a 6m net was set at one of
the two sites and surveying began one hour after
civil twilight. The Autobat speakers were mounted
on a pole about 2m above the ground, halfway
along the length of the net and about 50cm away
from it. Three different sequences of stimulus calls
were played in succession, two modelled on calls
of Bechstein’s Bat and one on calls of the Barbas-
telle Barbastella barbastellus. Each call sequence
was played for two minutes and followed by a 30-
second interval of silence. This was continued for
1.5 hours at the first site, after which the equip-
ment was moved to the second site, which was
likewise surveyed for 1.5 hours. In cases of heavy
rain, or when the temperature dropped below
10°C, sampling of the second site was completed
on a subsequent night. For all bats captured a
record was made of species, sex, whether adult
or juvenile, reproductive status of adults and the
forearm length (measured with dial callipers).
All woods that were surveyed for bats were
visited again during daylight hours to make a basic
classification of the woodland, in which we used
predetermined categories based on the predomi-
nant canopy species, percentage canopy cover and
percentage understorey cover. These were deter-
mined by walking the perimeter of the woodland
block and one or more paths that crossed the inte-
rior. For very large woodland blocks, the vegeta-
tion was surveyed over an area of approximately
25ha that included the two netting sites.
The 2005 survey
From June to August of 2005, a wood was
surveyed in each of 52 10km squares scattered
fairly evenly across Hampshire, Surrey, West
Sussex, East Sussex and Kent. The selecting of the
target woods was done by Dr Patrick Fitzsimons in
collaboration with Forest Research at Alice Holt.
Conservation of bats in British woodlands
164 British Wildlife February 2008
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February 2008 British Wildlife 165
It involved the use of three GIS database resources:
the National Inventory of Woodland and Trees,
the Ancient Woodland Inventory and Ordnance
Survey maps. For each square, a wood was chosen
that was larger than 25ha, and that appeared to
have a high proportion of broadleaved trees. Other
criteria used to select woods were a record of the
site in the Ancient Woodland Inventory, presence
of, or proximity to, surface water and proximity
to other areas of woodland.
Characteristics of the surveyed woods
The 52 sites surveyed included a great variety
of woodlands, in terms of both predominant
tree species and structure of the wood. The GIS
databases used in the selection process provided
limited information on the nature of the woods.
It was not possible to distinguish, for example,
between a young, even-aged Beech Fagus sylvatica
plantation and a mature semi-natural oak Quer-
cus woodland. Eight woodland types were distin-
guished on the basis of predominant species in the
canopy (Fig. 1). Three predominant tree species
accounted for over three-quarters of the woods
surveyed: predominantly oak (42%), predomi-
nantly Beech (23.1%) and predominantly Sweet
Chestnut Castanea sativa (11.5%). At two sites
planted conifers were the predominant canopy
species, although both also contained areas of
broadleaved trees.
The GIS databases also gave no information
about the structure of the woods in terms of the
extent of cover in the canopy or understorey. At
most sites canopy cover was good, but 12 sites had
less than 50% cover, of which three had less than
25% (Fig. 2). Lack of cover in the understorey was
more common, a third of woodlands having 25%
or less.
Bats captured in 2005
Bats were caught in 45 (87%) of the woods
surveyed. In total, 143 bats of 11 species were
caught (Table 1). The first five species listed in
Table 1 are usually associated with woodland
habitats, and will be referred to as ‘woodland
bats’ in the discussion below. Unsurprisingly, four
of these woodland bats were caught in the greatest
numbers, and in the largest number of woods. Of
these, Brown Long-eared Bats accounted for more
than half of the bats captured, and were caught
in almost two-thirds of the woods. The next most
frequently caught species was Natterer’s Bat
Myotis nattereri, which was caught in over a quar-
ter of woods, followed by the Whiskered Bat.
Ten Bechstein’s Bats were caught in eight woods,
and all of these were new records for this rare and
elusive species. Nine of the ten were adult females.
This means that there is likely to be a breeding
colony nearby, as females rarely travel far from
the maternity roost and are reluctant to cross open
ground. The maximum number of bats caught in
Common name Woods with species Number
of bats
Number %
Brown Long-eared * 32 62 76 1:1
Natterer’s* 14 27 25 4:1
Whiskered* 10 19 11 2:1
Bechstein’s* 8 15 10 1:9
Brandt’s* 2 4 3 2:1
Daubenton’s 2 4 2 1:1
Common Pipistrelle 6 12 6 5:1
Soprano Pipistrelle 3 5 3 3:0
Noctule 2 4 4 1:3
Serotine 1 2 2 1:1
Barbastelle 1 2 1 1:0
Total 143
Figure 1 Predominant tree species in the canopy of
52 woods surveyed in 2005.
Figure 2 Estimated cover in the canopy and
understorey of woods surveyed in 2005.
Table 1 Bats captured during July and August 2005.
* = ‘woodland bats’
Conservation of bats in British woodlands
166 British Wildlife February 2008
Conservation of bats in British woodlands
February 2008 British Wildlife 167
one wood was 13, with a mean capture rate of 4.4
bats per wood. More than one species was caught
in over half of the woods surveyed (Fig. 3), with a
maximum of five species caught in one wood, and
a mean of 1.6 species.
There were no apparent associations between
the extent of canopy cover and the number or
diversity of bats captured. However, this result
should be interpreted with caution, as the sample
included very few woods with sparse canopy, and
the vast majority of surveyed woods had canopy
cover of 50% or more.
By contrast, there were associations between
bats captured and the extent of cover in the under-
storey. When woodland species were consid-
ered separately, there was a positive correlation
between understorey cover and the number of bats
captured (r=0.274; p=0.049), and a much stronger
correlation with the number of species captured
(r=0.413; p=0.002). When all bat species were
included in the analysis there were still positive
correlations, but they did not
reach statistical significance.
Only oak and beechwoods
were sampled in sufficient
numbers to allow statistical
comparisons to be made of the
numbers and diversity of bats
caught in them. There was no
significant difference in the
number of bats caught in the
two types of wood. However,
the number of species caught
in oakwoods was significantly
higher than that in beechwoods
(t-test: t=2.26, df=32, p=0.031).
This difference was stronger
when only the number of wood-
land bat species was considered
(t=2.4, df=32, p=0.022).
There was less understorey cover in the beech-
woods than in the oak, which may explain some
of the difference. Unfortunately, the sample sizes
were too small to allow us to control for the effect
of understorey, but experience at a variety of other
sites leads us to conclude that oakwoods really do
support a greater diversity of bat species than do
beechwoods, irrespective of understorey cover.
The 2006 survey
The results from 2005 suggested that oakwoods
with good canopy cover and a well-developed
understorey were associated with the highest
numbers of individuals and species diversity of
bats. In the following year we decided to make a
more comprehensive survey of Sussex, focusing,
so far as possible, on woodlands with these char-
acteristics. We wanted data for a wood in every
Figure 3 Distribution of number of species caught
per wood.
Figure 4 Estimated cover in the canopy and
understorey of woods surveyed in 2006.
A Sussex oakwood with a Hazel understorey. Frank Greenaway
Conservation of bats in British woodlands
166 British Wildlife February 2008
Conservation of bats in British woodlands
February 2008 British Wildlife 167
10km square in East and West Sussex. As the main
aim of the exercise was to maximise our coverage
of squares in Sussex with survey data for breeding
populations of Bechstein’s Bat, we decided not to
resurvey any square for which we already had a
record of one or more female Bechstein’s Bats. For
each of the remaining squares, potential woodland
sites were identified from OS maps, and woods
were then visited to establish which most closely
matched the required characteristics.
Characteristics of woods surveyed
Of the 39 squares considered, 11 had no suit-
able woodland sites and for one we were unable
to obtain permission to survey.
A wood was surveyed in each
of the remaining 27 squares. On
the whole, we were successful in
finding woods that matched the
characteristics for which we were
looking. In 23 of the woods the
canopy was predominantly oak,
and in the remaining four the
canopy was a mix of oak and
other species. All of the woods
had 50% or greater canopy cover
(Fig. 4), and over three-quarters
had 50% or greater cover in the
Bats captured in 2006
In total, 128 bats of 11 species
were caught in the 2006 survey
(Table 2). One or more bats were
caught in every wood surveyed.
The four species caught in the
greatest numbers, and in the greatest number of
woods, were same as in the 2005 survey. Brown
Long-eared Bats accounted for almost half of the
bats captured, and were caught in almost three-
quarters of the woods. The next most frequently
caught species was Bechstein’s Bat, which was
caught in 44% of woods, followed by the Whisk-
ered Bat and Natterer’s Bats, both caught in about
one third of the woods.
Both the mean number of bats and the mean
number of species caught per wood were greater in
2006 than in 2005. These differences were statisti-
cally significant both for all bat species (species:
t=3.4, p=0.001; number of bats: t=3.76, p<0.001)
and for woodland bats alone (species: t=2.88,
p=0.005; number of woodland bats: t=2.98,
p=0.002). For two of the main woodland species,
the catch in 2006 also included a higher propor-
tion of females than in the 2005 survey. This trend
was significant for Natterer’s Bats (Chi sq.=5.33,
p=0.02), but not quite for Brown Long-eared Bats
(Chi sq.=3.39, p=0.07).
Woodland structure and the bat community
The two surveys were done at the same time of
year and using the same survey methods. The
same species were caught in both years, and yet
the 2006 survey yielded both greater numbers
and greater diversity of bats per wood. The fact
Common name Woods with species Number
of bats
Number %
Brown Long-eared * 20 74 61 1:2
Natterer’s* 9 33 15 2:3
Whiskered* 10 37 13 9:4
Bechstein’s* 12 44 15 1:3
Brandt’s* 1 4 1 0:1
Daubenton’s 2 7 3 3:0
Common Pipistrelle 5 19 7 5:2
Soprano Pipistrelle 5 19 6 4:1
Noctule 3 11 4 3:0
Serotine 2 7 2 2:0
Barbastelle 1 4 1 1:0
Total 128
In the 2006 survey, Brown Long-eared Bats accounted for more than
half of the individuals captured. Frank Greenaway
Table 2 Bats captured during July and August 2006.
* = ‘woodland bats’
Conservation of bats in British woodlands
168 British Wildlife February 2008
Conservation of bats in British woodlands
February 2008 British Wildlife 169
that more females were caught is also indicative of
higher-quality habitat, as breeding females appear
to be more demanding in their habitat require-
ments than are males (Senior et al. 2005; Hill &
Greenaway in prep.). A major difference between
the two years was in the nature of the woods
surveyed. In 2005 the sites selected from GIS data
were heterogeneous in both predominant tree
species and degree of cover. By contrast, in 2006,
sites were selected by visiting several potential
woods in advance. We set out to target oakwoods
with good cover in both canopy and understorey
layers, and the vast majority of the sites which
we surveyed fitted this description. The extent to
which each of these characteristics influences the
bats present in a wood cannot be determined from
our data. Nevertheless, it seems clear that overall
the woods which we selected for the 2006 survey
represented better-quality habitat for bats than
those we surveyed in 2005.
The most striking feature of the results was the
clear association between a well-developed under-
storey and the number and diversity of woodland
bat species. Why should woodland bats appar-
ently favour habitats with a well-developed under-
storey? There is probably no one answer for all
species concerned. However, three possible factors
should be considered.
1) Understorey cover provides protection from
aerial predators hunting within the wood. Three
of the woodland bats feed primarily by gleaning,
often flying slowly or hovering to catch their prey,
and may be vulnerable to preda-
tors such as the Tawny Owl
Strix aluco.
2) The understorey may provide
a habitat for key prey species for
the bats.
3) The presence of the under-
storey produces a more benign
microclimate than would be
found without it, by acting as
a baffle to reduce wind speeds
within the wood, and generally
maintaining a higher tempera-
ture than that outside the wood
(see Greenaway 2001).
An alternative explanation
would be that there was no great
difference in bat communities in
the different woodlands, but that
bats were simply easier to capture in the clutter of
the understorey than in open woodland, because
they were less able to detect the net. Although we
cannot test this from the current data, our strong
impression is that it is not the case. On the basis of
extensive experience of surveying woodlands with a
variety of techniques, including monitoring activity
around Autobats with infrared video and bat-detec-
tors, we are sure that this link between understorey
and bat diversity and numbers is a real one.
Implications of the findings for woodland
Management of semi-natural habitats in Brit-
ain for conservation tends to follow established
guidelines that have been developed with partic-
ular species groups in mind. Such practices may
not always be beneficial to other groups. There
is a widely held view that the conservation inter-
est of many woodlands can best be maintained or
enhanced by a return to traditional management
practices, such as rotational coppicing, or restora-
tion of wood pasture (see e.g. Warren & Thomas
1992; Barkham 1992; Fuller & Warren 1995).
A common prescription is to let the light into
the wood, for example, by thinning or clearing
the understorey, and widening rides and glades.
While this is clearly necessary for conservation of
some groups, such as woodland butterflies and
many plants, it is not beneficial for all woodland
wildlife. For instance, Hambler & Speight (1995)
noted that many less charismatic woodland inver-
Natterer’s Bats were caught in about a third of the woods surveyed in
2006. Frank Greenaway
Conservation of bats in British woodlands
168 British Wildlife February 2008
Conservation of bats in British woodlands
February 2008 British Wildlife 169
tebrates that depend on dark damp conditions
would not be favoured by this approach. Simi-
larly, Barbastelles have been shown to choose tree
roosts that are surrounded by thick understorey
(Greenaway 2001), and may abandon roosts if the
understorey is cleared.
The results of this survey strongly suggest that
the entire community of woodland bats may be
adversely affected by the clearance of understo-
rey. Consequently, reinstatement of traditional
management practices in a ‘neglected’ wood should
be undertaken only after the site has been thor-
oughly surveyed for bats. Furthermore, the likely
negative impact of management on bat popula-
tions and diversity should be explicitly acknowl-
edged in any management plan for a semi-natural
woodland that involves substantial changes to the
structure of the canopy or understorey.
Looking to the future
This study has demonstrated that the Sussex Auto-
bat acoustic lure system opens up great possi-
bilities for rapid survey of woodland bats. Its use
makes it possible to conduct systematic surveys
of woodland bats over an extensive area within
a single season. Because the primary goal of the
survey reported here was to search for Bechstein’s
Bat, the calls we used were limited. We have devel-
oped a range of calls which, used in rotation, can
increase the mean diversity of bat species caught
on a single survey night. Applied in a systematic
way, this method would allow quite rapid assess-
ment of woodland bat diversity in relation to
woodland size, structure and other characteristics
over a large area within a workable timeframe.
Like many sampling methods, the inherent
biases are unknown. For example, some species
may respond to the acoustic lure much more read-
ily than others, so between-species comparisons
of abundance within a wood may not be justified.
However, within-species differences in capture
rates, whether at different sites, at the same site over
time, or before and after management, are likely to
reflect actual differences in abundance. This means
that, for the first time, we can collect meaning-
ful baseline data on the distribution of woodland
bat species in relation to habitat quality, and we
can begin to look at the diversity and structure of
woodland bat communities. By repeating system-
atic surveys at intervals of several years, it should
be possible to assess whether woodland bat popu-
lations are stable, declining or perhaps increasing.
This would add a new and important dimension
to the national survey approach, which currently
concentrates on bats in buildings, underground
hibernation sites, waterways and edge habitats.
Thanks to the Mammals Trust UK for providing
support for the survey. We also thank the follow-
ing friends and colleagues for their assistance at
various stages of the study: Patrick Fitzsimons,
Brenda Mayle, Stephanie Murphy, Kevin Watts and
Tony Whitbread. Dan Whitby of Whitby Wildlife
Conservation did the fieldwork for the 2005 survey
under contract and was also involved in the 2006
survey. Thanks to all of the landowners for giving
us permission to look for bats in their woods.
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Management of Coppice Woodlands (pp 115-147). Chapman & Hall
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data and a playback experiment. Animal Behaviour 53 (5): 991-999
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woodlands. British Wildlife 7: 26-37
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science replacing tradition. British Wildlife 6: 137-148
Harris, S, Morris, P, Wray, S, & Yalden, D 1995 A Review of British
Mammals: population estimates and conservation status of British
mammals other than cetaceans. JNCC, Peterborough
Hill, D A, & Greenaway, F 2005 Effectiveness of an acoustic lure for
surveying bats in British woodlands. Mammal Review 35(1): 116-122
Hill, D A, & Greenaway, F in prep. Putting Bechstein’s bat on the map: A
systematic regional survey for a rare woodland bat. (To be submitted
to Biological Conservation)
Racey, P A, & Entwistle, A C 2003 Conservation ecology of bats. In: T
H Kunz & M B Fenton (eds) Bat Ecology (pp 680-744). University of
Chicago Press, Chicago
Russ, J M, Racey, P A, & Jones, G 1998 Intraspecific responses to
distress calls of the pipistrelle bat, Pipistrellus pipistrellus. Animal
Behaviour 55(3): 705-713
Senior, P, Butlin, R K, & Altringham, J D 2005 Sex and segregation
in temperate bats. Proceedings of the Royal Society B 272(1580):
Warren, M S, & Thomas, J A 1992 Butterfly responses to coppicing. In:
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249-270). Chapman & Hall
Watts, K 2006 British Forest Landscapes – The legacy of woodland
fragmentation. Quarterly Journal of Forestry 100 (4): 273-279
David Hill is a lecturer in Ecology and
Conservation at the University of Sussex. His
research investigates the behaviour, ecology and
conservation of woodland bats in Britain and
Japan. Frank Greenaway, now retired from the
Natural History Museum, divides his time between
bat research, bat consultancy, and photography.
... For many insectivorous species, woodlands provide a key habitat for their arthropod prey (e.g. Hill & Greenaway, 2008). The way in which different bat species will use these environments will therefore often depend on the distribution of different plant or prey species and this may vary seasonally (e.g. ...
... However re-coppicing over-mature coppice areas that have been undermanaged for some time has been suggested may have a detrimental effect on some species (e.g. Lassauce et al., 2012;Murphy, Greenaway & Hill, 2012;Hill & Greenaway, 2008). ...
... Ancient woodlands are areas of high biodiversity and are often habitats for rare and endangered species, making them a high conservation priority (Peterken, 1993). They are also thought to be extremely important habitats for bats in Britain and are usually regarded as superior over non-native conifer plantations in terms of species diversity and abundance (Hill & Greenaway, 2008). However, conifer plantations may still offer suitable habitats for vulnerable species (e.g. ...
Full-text available
I investigate tools for studying bat species’ assemblages in woodlands, at varying spatial scales; including species distribution modelling (MaxEnt) for Myotis bechsteinii in Britain at a broad-scale, and an investigation into the use of an acoustic lure (the Sussex AutoBat) as a method for increasing capture rates of bats in woodlands at a local scale. M. bechsteinii is limited in its distribution due to unsuitable climatic and habitat conditions and new colonies are likely to be found in broad-leaf or mixed woodlands where there are relatively warm winters and low summer precipitation. Future work should focus on further delineating the range for M. bechsteinii using habitat suitability maps produced in this study; and further investigation into factors limiting its distribution, for example summer and winter diet. I also found that an acoustic lure is likely to be a valuable tool for monitoring bat species’ presence and assemblages in woodlands. Bat species were disproportionately responsive to different lure call playbacks, some playbacks being more generalist and others more species-specific in their ability to elicit a response. I therefore suggest that the lure be used as part of a carefully considered integrative approach to woodland monitoring, along with other methods. Lure call playbacks should be chosen on a case-by-case basis, to minimise bias and limit disturbance on bat species populations where possible. I conclude that it is important to use multi-scale tools to study bats, from the broad level of the species range, down to the fine scale of how they use specific habitats. Only then, can effective management guidelines and practices be put in place and habitats protected, to safeguard the future of bats in the landscape.
... Many bat species, including most of the rarest and endangered, are linked to forest environments. Forest habitats perform three fundamental functions for bats, in that they offer roosting opportunities to many species, produce a wide variety of prey (insects) [32], and can be used as a spatial reference for commuting, also due to higher insect densities and the chance of shelter from predators and wind [33]. Tree roosts can be abandoned woodpecker holes, hollows produced by xylophagous insects, flaking bark, broken and cracked branches and trunks [34]. ...
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Megaprojects radically change the landscape due to their large-scale and high investments. Forests are often one of the most affected habitats, as they are frequently included in megaproject construction sites. These habitats support rich animal communities that the new settlement may threaten. Among all species present in any construction site, those listed in the Habitats Directive (92/43/CEE) deserve particular attention as they are protected throughout Europe. Here, we present a case study related to the expansion of an industrial site, part of the megaproject Turin–Lyon high-speed railway, where forest compensations were used to reverse biodiversity loss. The site expansion scheduled for 2020 included mature forests and clearings that used to host a butterfly species and at least 15 bat species protected by the Habitats Directive and other taxa of conservation concern. Forest compensations are usually used to finance tree plantations and forest improvements. In this case study, for the first time, we used them to maintain local biodiversity, which otherwise would have been severely compromised by the site expansion. Indeed, our approach has made it possible to allocate forest compensation funding to restore or improve habitats to favor biodiversity. This approach may be exported to other megaprojects to support local biodiversity.
... Dead wood availability is important for B. barbastellus (Russo et al. 2004, Carr et al. 2019) because individuals frequently switch roosting locations (Russo et al. 2005). Their higher occupancy in irregular stands potentially reflects the abundance of retained deadwood (Görföl et al. 2019) and feeding habitat across patches of dense understorey (Zeale et al. 2012, Hill & Greenaway 2008. We found a negative association in limited intervention stands with deadwood snags; interestingly Tillon et al. (2016) did not identify a relationship between B. barbastellus and deadwood presence. ...
Changing economics in the 20th century led to losses and fragmentation of semi-natural woodland in Britain and to a reduction in active woodland management with many becoming increasingly neglected, even-aged and with closed canopy. Lack of woodland management is known to contribute to declines in some taxonomic groups, for example birds. However, the response of bats to changes in woodland structure are poorly understood. We compared two measures of bat activity, derived from static acoustic recorders across 120 sample plots in coppice, irregular high forest (uneven-aged, continuous cover) and limited intervention (under-managed, even-aged) management stands, within a large tract of ancient woodland in southern England. Bat species richness was highest in irregular high forest stands, and there were significant differences in occupancy rates for most bat species across stand management types. Coppice recorded low activity of several bat species and irregular high forest showed high occupancy rates, including for Barbastelle Barbastella barbastellus, which is IUCN listed as near threatened. The occupancy rates in stand management types differed for some bat species between mid- and late summer counts, suggesting seasonal variation in habitat use. Within stands, most bat species were associated with opened canopy, lower growing stocks and reduced densities of understorey, and to a lesser extent, with large-girthed trees and presence of deadwood snags. In some cases, species responded to a given habitat variable similarly across the three stand management types, whereas in others, the response differed among stand management types. For example, increased numbers of large-girthed trees benefitted a number of bat species within coppice where these were least common, but not in irregular stands. Irregular silviculture high forest appears to provide many of the structural attributes that positively influence occupancy of several woodland bat species, including Barbastella barbastellus.
... The Sussex Autobat acoustic lure was developed in 2001 to improve capture rates for bats in British woodlands, and particularly for the elusive Bechstein's bat Myotis bechsteinii. Once the effectiveness of the technique had been demonstrated by field experiment and pilot surveys (Hill and Greenaway, 2005;2008) it was incorporated into a systematic survey, coordinated and run by the Bat Conservation Trust, which mapped the national distribution of Bechstein's bat in the UK (Miller, 2012;Barlow et al., 2013). ...
... The degree to which understory cover affects the use of forests by bats depends greatly on their wing morphology and foraging behaviour, with some bats benefitting from a more open forest with little in the way of cover, while other species rely heavily on a well-developed dense understory (e.g. Hill and Greenaway 2008;Müller et al. 2012). Vegetation structure revealed by LiDAR in Germany indicated that while high levels of understory cover were preferred by edge-space and gleaning species, open-space foragers were more associated with relatively open forest stands (Jung et al. 2012). ...
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Forests are one of the most important habitats for insectivorous bats as they offer the potential for both roosting and foraging. We reviewed silvicultural literature from North America, Australia, and Europe and found that diverse research approaches have revealed commonalities in bat responses to forest silviculture . Almost all silvicultural treatments evaluated were compatible with some use by forest bats, though different bat ensembles respond in different ways. Ensemble ecomorphology was a consistent predictor of how bats respond to vegetative clutter and its dynamic changes as forests regenerate and develop a dense structure following harvesting. Sustaining high levels of bat diversity in timber production forests requires a mix of silvicultural treatments and exclusion areas staggered across the landscape, regardless of forest type or geographic region. Use of edge habitats, exclusion areas/set-asides, and riparian corridors for roosting and foraging by bats were consistent themes in the literature reviewed, and these habitat elements need to be considered in forest planning. Densities of hollow or dead trees sufficient to support large populations of roosting bats are unknown and remain a major knowledge gap, but will likely be species contingent. New paradigm shifts in forest management away from the use of even-aged systems to multi-spatial scale retention of mature forest including trees with cavities should be beneficial to bats, which are influenced by landscape-scale management. Such an approach is already in use in some regions, though there is a limited guidance on what constitutes a reasonable landscape threshold for retention. The effectiveness of such an approach will require long-term monitoring and research, especially with population studies which are currently lacking.
... Our results suggest that such management could have a negative impact on P. auritus, as its patterns of foraging were strongly associated with a well-developed understorey layer. There is also evidence that cover in the understorey is positively correlated with abundance and species diversity in the woodland bat community as a whole (Hill & Greenaway, 2008). Clearly, woodland bats have already survived centuries of traditional management. ...
Full-text available
Reinstating forestry practices, such as coppicing, thinning the understorey and grazing, has become a key element of proposals for improving the conservation value of broadleaved woodlands in Europe. However, the consequences of such woodland management for bats are poorly understood because of a lack of knowledge concerning their habitat requirements. We studied the brown long‐eared bat Plecotus auritus in South East England to determine how their patterns of habitat use could inform conservation management. Radio‐tracking of 38 adult females showed that they foraged primarily in woodland and that each had a foraging area (mean = 4.4 ha) that they returned to on successive nights. Core foraging areas (mean = 2.1 ha) were characterized by more cover and greater species diversity in the understorey layer than more peripheral areas. Hedgerows were also used for foraging in the late summer and autumn. Most conservation activities for this species have focused on protecting roosts in houses and other buildings. While such protection is important for bat conservation, efforts should also be made to protect foraging habitats in woodlands by maintaining cover of native species in the understorey layer and hedgerows that provide connectivity between woodland patches. Common conservation management practices, such as reinstating coppicing or grazing in semi‐natural broadleaved woodlands, could be detrimental for P. auritus and other woodland bats. Their impact on bats should be tested experimentally before they are widely promoted as a woodland conservation strategy.
... Behavioural studies have demonstrated that broadcasting bat-feeding buzzes and social calls can attract both conspecific and heterospecific bats (Russ et al. 1998;Wilkinson and Boughman 1998); this led to the development of an acoustic lure, the Sussex AutoBat (Hill and Greenaway 2005). Field testing showed that the capture rate of different bat species, including the rare M. bechsteinii, increased with the use of the lure (Hill and Greenaway 2005;Goiti et al. 2007;Hill and Greenaway 2008); however, the extent to which this enhances capture rates in comparison to traditional trapping techniques has not, to our knowledge, been systematically tested. ...
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Accurately estimating species’ population abundance is essential for wildlife and habitat management. We show that, for some bat species, acoustic monitoring can be used as a surrogate for trapping as a measure of relative abundance within woodlands, while the use of an acoustic lure can increase trapping efficiency. The use of these techniques can enhance surveying effectiveness, maximise the knowledge of diversity in an area, minimise wildlife disturbance and improve the accuracy of targeted conservation decisions
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• Bat populations are thought to have suffered significant declines in the past century throughout Europe. Fortunately, there are some signs of recovery; for instance, of the 11 species monitored in the UK, population trends of five are increasing. The drivers of past losses and recent trends are unclear; identifying them will enable targeted conservation strategies to support further recovery. • We review the evidence linking proposed drivers to impacts on bat populations in Europe, using the results of a previous cross‐taxa semi‐quantitative assessment as a framework. Broadly, the drivers reviewed relate to land‐use practices, climate change, pollution, development and infrastructure, and human disturbance. We highlight where evidence gaps or conflicts present barriers to successful conservation and review emerging opportunities to address these gaps. • We find that the relative importance or impacts of the potential drivers of bat population change are not well understood or quantified, with conflicting evidence in many cases. To close key gaps in the evidence for responses of bat populations to environmental change, future studies should focus on the impacts of climate change, urbanisation, offshore wind turbines, and water pollution, as well as on mitigation measures and the synergistic effects of putative drivers. • To increase available evidence of drivers of bat population change, we propose utilising advances in monitoring tools and statistical methods, together with robust quantitative assessment of conservation interventions to mitigate threats and enable the effective conservation of these protected species.
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Capture is essential for any field research on bats that requires confirmation of species, sex, maturity and reproductive status, or that involves radio-tracking or marking individuals. However, bats can be difficult to capture. We made a preliminary test of the effectiveness of an acoustic lure that produces ultrasonic simulations of bat social calls for enhancing capture rates in harp traps. Over 102 trap-hours at seven forest sites in north-eastern Queensland, 65 bats representing seven species were captured in traps with lures, while no bats were captured in paired control traps. The results indicate great potential for the development and application of acoustic lures to increase the efficiency of field surveys and research on Australian echolocating bats that involve capture.
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1. A field experiment was used to test the effectiveness of a synthesized bat call as an acoustic lure to attract bats into mist nets in woodlands in southeast England. The stimulus was modelled on a social call of the rare Bechstein's bat Myotis bechsteinii. 2. In the Test condition, when the synthesized call was played, 23 bats of four species were captured, including six Bechstein's bats. In the Control condition, when no calls were played, only one bat was caught. 3. The bat call synthesizer is an effective tool for increasing capture rates for bats. Used as part of a systematic survey programme, it has the potential to provide the first baseline data on the distribution of bats in British woodlands.
Full-text available
Responses of the vespertilionid bat Pipistrellus pipistrellus to five recently caught conspecifics confined to a wire-mesh cage, at distances of 50 and 5 m from their roosts, were recorded on 12 separate evenings at three roosts during pregnancy and lactation. When bats were confined 50 m from their roost, an almost 20-fold increase in the number of bats that passed across an open site around the cage was recorded and the strength of response (number of bat passes) increased with time. When the bats were 5 m from the roost there was an 80-fold increase in bat activity above the cage. Playbacks of recorded distress calls produced by single hand-held bats resulted in a more than three-fold increase in bat passes, but the response waned rapidly. The distress calls of recently caught P. pipistrellus were generally similar to those of individuals from the same colony held for longer in captivity, and differences in distress calls between two of the three colonies studied probably reflect differences in the physiological states of recorded bats, rather than the existence of colony-specific vocalizations. Distress calls probably function in attracting conspecifics which perform mobbing behaviour as an anti-predator response. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.
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Many temperate insectivorous bats show marked sexual segregation during the summer, but in spectacular, pre-hibernation swarming, gather at caves to mate. In many species, sexual segregation is probably due to a gradient in aerial insect availability that confines females to lower elevations, where high reproductive costs are met by an abundant and reliable food supply. In the hawking and trawling Myotis daubentonii, we show that alongside inter-sexual segregation, there is intra-male segregation and suggest that this results from the exclusion of most males from high-quality habitat. These apparently excluded males suffer reduced foraging efficiency and mating success relative to males that roost with the females in summer. Changes in resources and behaviour at the end of the summer lead to a change in strategy that gives all males a chance to mate during swarming, but this does not overcome the paternity advantage to males that spend the summer with the females.
  • F Greenaway
Greenaway, F 2001 The Barbastelle in Britain. British Wildlife 12: 327-334
  • C Hambler
  • M R Speight
Hambler, C, & Speight, M R 1995 Biodiversity conservation in Britain: science replacing tradition. British Wildlife 6: 137-148
D 1995 A Review of British Mammals: population estimates and conservation status of British mammals other than cetaceans. JNCC, Peterborough Hill, D A, & Greenaway, F 2005 Effectiveness of an acoustic lure for surveying bats in British woodlands
  • S Harris
  • P Morris
  • S Wray
  • Yalden
Harris, S, Morris, P, Wray, S, & Yalden, D 1995 A Review of British Mammals: population estimates and conservation status of British mammals other than cetaceans. JNCC, Peterborough Hill, D A, & Greenaway, F 2005 Effectiveness of an acoustic lure for surveying bats in British woodlands. Mammal Review 35(1): 116-122
Putting Bechstein's bat on the map: A systematic regional survey for a rare woodland bat
  • D A Hill
  • Greenaway
Hill, D A, & Greenaway, F in prep. Putting Bechstein's bat on the map: A systematic regional survey for a rare woodland bat. (To be submitted to Biological Conservation)