Roost‐boxes as a tool in the conservation of
tree roosting microbats (Microchiroptera) in
a highly‐modified agricultural landscape
Quarry Life Award Research Project, Australia
Project Topic: Biodiversity and Rehabilitation
Stephen Griffiths
July 2012
Department of Zoology
The University of Melbourne
Victoria 3010 Australia
Telephone: +61 3 8344 6244
Fax: +61 3 8344 7909
Roost-boxes as a tool in the conservation of tree roosting microbats
1
Abstract
The loss, modification and fragmentation of natural habitats constitute a major threat to bat
populations worldwide. This is particularly relevant in Australia where extensive loss of
native habitat since European settlement has resulted in significant negative pressure on
microbats (Microchiroptera), the majority of which rely on tree hollows for roosting.
However, because microbats are small, nocturnal and remain hidden in roosts during the
day, few people are aware of the diversity or abundance of bats that roost in trees in both
urban and rural areas. I used bat detectors to examine activity of microbats at two sites in a
highly-modified agricultural matrix. The species assemblage recorded comprised the
majority of microbat species known to occur in the Western Volcanic Plains region of
Victoria. A total of 6,214 echolocation call sequences were recorded over 39 consecutive
nights at the two sites. Considerable variation in activity was documented both within and
between nights. The echolocation data revealed minimal levels of foraging activity. At one
site, social calls were recorded in the hour prior to civil twilight (i.e. prior to nightfall) on
17 nights, providing indirect evidence of bats roosting diurnally in tree hollows within an
isolated stand of mature Eucalyptus cladocalyx. Artificial roosting boxes (bat-boxes) were
installed to provide supplementary roosting habitat as an initial step toward investigating
the efficacy of bat-boxes as a targeted conservation tool within the framework of a long-
term ecological management and restoration plan. The presence and activity of microbats
recorded in this study, and specifically the detection of social calls produced by diurnally
roosting bats, has implications for the management and rehabilitation of isolated patches of
land within highly-modified agricultural landscapes. Increasing the awareness of land
managers and decision makers to the benefits of these species (e.g. regulation of
herbivorous insect abundance), will enhance knowledge of this faunal group in the
community and provide further reasons for prioritising the management and conservation
of scattered trees within urban and rural environments.
Roost-boxes as a tool in the conservation of tree roosting microbats
2
Introduction
A wide variety of vertebrate taxa use tree hollows (also referred to as tree holes or cavities)
for shelter and as breeding sites (Goldingay 2009). Worldwide there are approximately 260
species of bird and 360 species of non-flying mammals that use tree cavities (Newton 1994;
Novak 1999), while in Australia, as many as 300 native vertebrate species (birds, bats,
arboreal marsupials, reptiles and frogs) use tree hollows (Gibbons and Lindenmayer 2002;
Kunz and Lumsden 2003; Goldingay and Stevens 2009).
Bats are among the most threatened fauna in Australia, with 36 species listed under The
Action Plan For Australian Bats (Duncan et al. 1999). Day-roost sites have been identified
as a key limiting resource for microbat conservation, but we know almost nothing about the
causes and consequences of roosting in different types of tree hollows or artificial nesting
boxes (Turbill 2006; Goldingay 2011). The dramatic decline of Australian native habitats
since European settlement has led to a growing awareness of the impact of habitat loss on
native fauna, and revegetation efforts, both in farmland (Kavanagh et al. 2007) and in
suburbia (Harper et al. 2005a,b), are increasingly common. However, trees planted now
may take up to 100 years to develop hollows suitable for use by wildlife (Lindenmayer et
al. 1993; Weinberg et al. 2011). Therefore, while revegetated areas can provide foraging
habitat for bats soon after planting, the lack of hollows may limit colonisation of these areas
as roosting habitat.
One short to medium term method of compensating for limited roosting sites is to install
nesting boxes (bat-boxes) as substitutes for natural hollows (Arnett and Hayes 2000;
Brittingham and Williams 2000; Flaquer et al. 2005; Lesinski et al. 2009). There have been
few studies of bat-box use in Australia, particularly in agricultural regions, and
consequently relatively little is known of the use and preferred designs of bat-boxes by
Australian tree roosting microbats (Irvine and Bender 1995; Smith and Agnew 2002;
Goldingay and Stevens 2009). My objective in the present study was to examine microbat
activity in a highly-modified agricultural landscape and conducted a preliminary
assessment of the efficacy of bat-boxes as a targeted conservation tool within the
framework of a long-term ecological management and restoration plan. Specifically, I
investigated: (1) temporal patterns (hourly and nightly) in bat activity; (2) the diversity of
Roost-boxes as a tool in the conservation of tree roosting microbats
3
species present; (3) the level of foraging activity; and (4) the potential value of deploying
bat-boxes as a short to medium term conservation tool.
Methods
Study sites
I conducted fieldwork at two former sheep grazing properties located in the Western
Volcanic Plains of Victoria, Australia. The region is characterised by temperate grassland
and grassy eucalypt woodland, now dominated by introduced grassland species, with
sparsely scattered paddock trees and occasional trees planted along fence lines as
windbreaks (DEWHA 2008). In 2008, the Australian government upgraded the listing of
the natural temperate grassland and the grassy eucalypt woodland of the Volcanic Plains of
Victoria to critically endangered, the most protected conservation status under the Federal
Environment Protection and Biodiversity Conservation Act 1999 (DSEWPC 2011). The
climate of the Western Volcanic Plains is temperate with warm to hot summers (average
summer maximum 24.6°C) and cool to cold winters (average winter maximum 12.6°C).
Rainfall on the plains ranges from 600 to 800 mm per annum and occurs mostly between
April and November. Annual average rainfall at the Australian Bureau of Meteorology
Hamilton Airport monitoring station (37°38'39.04'' S, 142°00'47.74'' E) is 685.7 mm
(Australian Bureau of Meteorology 2012).
The Warrayure Conservation Offset Site (37°44'05.65'' S, 142°12'47.93'' E) is located 230
km west of Melbourne, 14 km south-west of Dunkeld and 17 km east of Hamilton. The
Warrayure site has an area of 58 hectares, comprised predominantly of degraded grassland
with small patches of mature Eucalyptus cladocalyx. The site is on the north shore of Lake
Linlithgow, and it adjoins the Lake Linlithgow Nature Reserve. The Strathkellar
Conservation Offset Site (37°43'24.48'' S, 142°07'50.02'' E) is located 10 km west of the
Warrayure site, 20 km south-west of Dunkeld and 12 km east of Hamilton. The Strathkellar
site has an area of 80 hectares, comprised of highly degraded grassland and creek line
tussock grassland. Native tree species are limited to a small patch of Acacia melanoxylon
along the southeast boundary. The property is bordered by the Glenelg Highway to the
south and Rhooks Road to the northeast. Both the Warrayure and Strathkellar Conservation
Offse
the im
Acou
I use
Cons
bat d
Elect
levels
Detec
heigh
(Figu
time
FigurWarr
I dow
manu
www
echol
2008
file (
softw
ident
et Sites are
mprovement
ustic sampli
ed echoloca
servation Of
detectors (A
tronics, Law
s against an
ctors were p
ht of approx
ure 1). Reco
the detector
e 1. AnaBatayure Conser
wnloaded e
ually analy
w.hoarybat.c
location pul
). Each call
(Hayes 2000
ware (Gibso
ify call seq
Roo
covered by
t of native g
ing of bat c
ation calls a
ffset Sites. I
naBat II ba
wnton, Quee
n ultrasound
placed insid
ximately 1.
ordings bega
rs were trigg
t II bat detervation Offse
echolocation
ysed calls
com). A sing
lses (frequen
l sequence,
0). Files tha
on and Lum
quences to
ost-boxes as
a conservat
grasslands, p
calls
as an index
I surveyed b
at detector c
ensland). De
d frequency
de weatherp
.5 m, with
an 60 minut
gered autom
ector and At Site and b) t
n call data
s using
gle call sequ
ncy sweeps
separated b
at passed th
msden 2003
taxa by ex
s a tool in th
tion covena
plus restorat
x of bat act
bat activity a
connected to
etectors wer
y generator
roof plastic
the microp
tes before su
matically by
naBat ZCAIthe Strathkel
to a comp
AnalookW
uence was d
) identified
by more tha
hese criteria
). AnaSche
xtracting a r
he conservat
ant and have
tion of degr
tivity at the
at both sites
o an AnaBa
re calibrated
(AnaBat C
c boxes secu
phone facing
unset and e
ultrasonic n
IM storage ullar Conserva
puter using
version
defined as a
as bat echo
an 5 second
a were then
eme uses re
range of ca
tion of tree
e manageme
raded areas.
e Warrayur
s concurrent
at ZCAIM s
d by adjustin
Chirper 2, T
ured to the t
g upward a
ended at sun
noise.
units securedation Offset S
g CFCread
3.8s (C.
a file contai
olocation cal
s, was desig
processed
egional iden
all paramete
roosting mi
ent plans re
re and Strat
tly using ult
storage unit
ng their sen
Titley Electr
trunk of a tr
at an angle
nrise, during
d to trees atite.
version 4.3
Corben
ining at lea
lls (Houriga
gnated as a
using AnaS
ntification k
ers (Lumsd
icrobats
4
equiring
thkellar
trasonic
, Titley
nsitivity
ronics).
ree at a
of 45º
g which
t a) the
3s then
2011,
st three
an et al.
unique
Scheme
keys to
den and
Roost-boxes as a tool in the conservation of tree roosting microbats
5
Bennett 2005; Adams et al. 2010). I used an existing identification key developed to
identify the species in the Grampians region of Victoria (Arthur Rylah Institute for
Environmental Research 2012). Using the Grampians key, AnaScheme identifies call
sequences to species, except for Nyctophilus and Mormopterus, which are grouped by
genus. A list of microbat species known to occur in the Western Volcanic Plains of Victoria
is provided in Appendix 1.
Call sequences for all taxa recorded were grouped to investigate activity patterns of the
entire microbat community. Hourly activity patterns were recorded as the mean number of
call sequences recorded per hour after civil twilight for all species during the survey period.
Civil twilight times were accessed from Geoscience Australia (2012). Call sequences were
screened manually for buzz calls associated with pursuit and capture of prey. Foraging buzz
calls are characterised by a rapid increase in pulse repetition rate, slope, frequency and
speed (Griffin et al. 1960; Schnitzler et al. 1987). Call sequences were also examined for
social calls: distinctive audible contact calls made by bats from within roost sites before
leaving for the night to forage (Aldridge et al. 1990; Pfalzer and Kusch 2003; Arnold and
Wilkinson 2011).
Results
Bat activity
Over 39 consecutive nights from 20 April to 28 May 2012 (78 detector-nights) I identified
6,214 bat call sequences from 11,531 files (53.9%). A total of 5,474 and 740 call sequences
were recorded at the Warrayure and Strathkellar sites respectively. Bat activity was
recorded on every night at Warrayure, and on the majority of nights at Strathkellar (zero
call sequences recorded on 4 nights (10.3%)). Considerable variation in the nightly number
of bat call sequences was documented at both sites. An average (± standard error) of
140.4±26.7 call sequences per night was recorded at Warrayure, with a nightly maximum
of 775 calls (20 April 2012) and minimum of 15 (21 May 2012). At Strathkellar an average
of 19±5.2 call sequences per night was recorded, with a nightly maximum of 163 calls (20
April 2012) (Figure 2).
FigurStrath Hour
Hour
hour
more
sites.
hour
Figurthe Wcivil tw
e 2. Numbehkellar Conse
rly activity
rly activity p
after civil tw
e than 60%
A total of
prior to civi
e 3. Mean (±sWarrayure an
wilight.
Roo
er of echoloervation Offse
patterns wer
wilight (Wa
of all calls
45 call seq
il twilight, i
s.e.) number d Strathkella
ost-boxes as
cation call set Sites.
re similar at
arrayure 18.
were record
quences (0.8
i.e. prior to n
of bat call sear Conservati
s a tool in th
sequences re
t both sites w
.9% and Str
ded in the f
8% of total
nightfall (Fi
equences per ion Offset Sit
he conservat
ecorded each
with greates
rathkellar 41
first four ho
calls) were
igure 3).
night detectetes. The -1 ca
tion of tree
h night at t
st activity re
1.6% of call
ours after civ
recorded at
ed each hour ategory refers
roosting mi
the Warrayu
ecorded in t
l sequences)
vil twilight
t Warrayure
after civil tws to the hour
icrobats
6
ure and
the first
), while
at both
e in the
wilight at prior to
Spec
Using
level
ident
to me
not b
were
tasma
timor
austr
flaviv
(16.2
Figurof calgouldiNyctopV. regSacco
Fora
One h
(2% o
ies diversit
g the AnaS
(or to genu
ified either
eet the mini
be distinguis
identified
aniensis, M
riensis, Vesp
ralis, and
ventris. Vesp
2%), while V
e 4. Echolocall sequences ii; Cm, C. mphilus geoffrogulus; Vv, V
olaimus flavive
aging activit
hundred and
of total calls
Roo
ty
Scheme prog
us for Nycto
as a result
imum criter
shed betwee
d: Vespert
Minopteurs
padelus dar
Mormopter
padelus dar
V. vulturnus
ation call seqwere not ide
morio; Ft, Faoyi/N. gouldi/V. vulturnus;entris.
ty
d fifteen fee
s) and 13 at
ost-boxes as
gram, 2828
ophilus sp.,
of being a
ria, or havin
en two speci
tilionidae:
schreibers
rlingtoni, V
rus species
rlingtoni wa
dominated
uences identientified at Stalsistrellus ta/N. timoriensi; Ta, Tadarid
eding buzze
t Strathkella
s a tool in th
8 (45.5%) c
and Mormo
short seque
ng the majo
ies (Gibson
Chalinolob
sii bassani
V. regulus,
s 4/M. spe
as the most c
calls at Stra
ified to specietrathkellar anasmaniensis; is; Sb, Scotoreda australis;
es were reco
ar (1.8% of t
he conservat
call sequenc
opterus sp.)
nce with in
ority of puls
n and Lumsd
bus gouldi
ii, Nyctoph
and V. vult
ecies 2; E
commonly r
athkellar (43
es or genus bnd WarrayurMsb, Miniopepens balston
M, Mormop
orded during
total calls) (
tion of tree
ces were ide
). The rema
nsufficient g
ses with par
den 2003). T
ii, C. mo
hilus geoff
turnus; Mol
Emballonuri
recorded sp
3.9%) (Figu
by AnaSchemre respectivepterus schreibni; Vd, Vespadpterus specie
g this study,
(Figure 5).
roosting mi
entified to
ainder could
good quality
rameters tha
The followi
orio, Falsi
ffroyi/N. go
lossidae: Ta
idae: Sacco
ecies at Wa
ure 4).
me; 25.8% andely. Cg, Chalbersii oceanedelus darlingtes2/M. specie
, 112 at Wa
icrobats
7
species
d not be
y pulses
at could
ng taxa
istrellus
ouldi/N.
adarida
olaimus
arrayure
d 58.4% linolobus ensis; N, toni; Vr,
es 4; Sf,
arrayure
FigurStrath
Socia
Socia
provi
matur
separ
Strath
speci
regio
Warr
FigurWarr
e 5. Numberhkellar Conse
al calls
al calls wer
iding indire
re E. clado
rate occasio
hkellar site.
ies level, as
on are not
rayure are pr
e 6. Number ayure Conser
Roo
r of echolocaervation Offse
re recorded
ect evidence
ocalyx at th
ons at Wa
It was not p
reference s
available. E
resented in
of microbat rvation Offse
ost-boxes as
ation foraginet Sites.
in the hour
e of bats ro
his site. A m
arrayure (F
possible to
social calls p
Examples o
Appendix 2
social calls ret Site.
s a tool in th
ng buzz calls
r prior to c
osting diurn
maximum o
igure 6). N
identify the
produced by
of two soci
2.
ecorded each
he conservat
recorded ea
civil twiligh
nally in tree
of 16 socia
No social
e social calls
y species in
ial calls rec
h night in the
tion of tree
ach night at
ht on 17 nig
e hollows w
al calls was
calls were
s recorded d
n the Weste
corded on
hour prior t
roosting mi
the Warray
ghts at War
within the s
s recorded
e recorded
during this s
rn Volcanic
20 April 2
to civil twiligh
icrobats
8
yure and
rrayure,
stand of
on two
at the
study to
c Plains
2012 at
ht at the
Roost-boxes as a tool in the conservation of tree roosting microbats
9
Discussion
Considerable variation in activity was documented both within and between nights during
this study, however bats were present (as detected via echolocation calls) on every night at
Warrayure, and on the majority of nights at Strathkellar, albeit at lower levels (Figure 2).
The overall hourly pattern of bat activity featured a peak immediately after dusk, followed
by a steady decrease throughout the night and only minimal activity in the second half of
the night (Figure 3). Studies by Law et al. (1998) and Milne et al. (2005b) examining bat
activity in southeastern and northern Australia respectively have reported similar patterns.
In both studies, the majority of activity occurred in the first half of the night, with
considerably less activity from midnight to sunrise. Several lines of evidence suggest this
pattern is driven primarily by activity of nocturnal insects which also exhibit the greatest
peak of activity at twilight, with activity dropping off during the remainder of the night
until dawn (Rautenbach et al. 1988; Vaughaun et al. 1996; Jetz et al. 2003;
Wickramasinghe et al. 2003a,b; Weinbeer et al. 2006).
High levels of variation in bat activity between nights has also been identified in previous
studies (Hayes 1997; Milne et al. 2005b). A range of factors have been shown to influence
variation in nightly bat activity, including climate variables (Bullen and McKenzie 2005;
Turbill 2008; Brooks 2009), insect availability (Bell 1980; Avila-Flores et al. 2005;
Akasaka et al. 2009), and lunar phase (Fenton et al. 1977; Milne et al. 2005a). While
specific factors influencing activity patterns were not examined here, the findings clearly
show bats were consistently present in this highly-modified agricultural landscape. The
assemblage recorded comprised the majority of species known to occur in the Western
Volcanic Plains region of Victoria (Figure 4, Appendix 1). However, a conservative
approach should be taken when drawing inferences from a survey based solely on passively
collected echolocation data, as detection rates can differ significantly between species
(Hayes 2000; Sherwin et al. 2000). To provide greater confidence in recording an accurate
species inventory, capture techniques (e.g. harp trapping or mist netting) and physical
identification of animals should be employed in conjunction with bat detector sampling
(Australasian Bat Society 2006).
Roost-boxes as a tool in the conservation of tree roosting microbats
10
Minimal levels of foraging activity were recording during this study, predominantly at the
Warrayure site (Figure 5). Microbats are known to forage in a range of forested and rural
landscapes of southeastern Australia (Law et al. 1998; Lumsden and Bennett 1995), as well
as in highly-modified urban landscapes (Threlfall et al. 2012). Lumsden and Bennett (2000)
suggested bats are likely to play an important role in regulating populations of herbivorous
invertebrates around sparsely scattered trees, because insectivorous birds dependent on
good quality forest cover are often scarce in agricultural landscapes. Many land managers
are familiar with the beneficial role of birds as insectivores or pollinators (Reid and
Landsberg 1999; Lindemayer et al. 2011; Schirmer et al. 2012). However, because
insectivorous bats are small, nocturnal and remain hidden in roosts during the day, few
people are aware of the ecosystem services they provide by eating insects in rural
landscapes (Lumsden and Bennet 2005).
The presence and activity of microbats recorded in this study, and specifically the detection
of social calls produced by diurnally roosting bats (Figure 6), has implications for the
management and rehabilitation of isolated patches of land within highly-modified
agricultural landscapes. Across much of southeastern Australia, the amount of land
dedicated to conservation of biodiversity is generally small in size compared with the
extensive areas transformed for urbanisation, industrialisation and agricultural development
(Gobbons and Lindenmayer 2002; Lumsden and Bennett 2005; Rhodes et al. 2006).
Consequently, relatively small sites dedicated to conservation and restoration often exist
within a matrix of natural, semi-natural and highly modified habitats (Lindemayer et al.
2011). The mobility of bats means they can traverse the rural landscape to exploit multiple,
isolated habitat patches (Lumsden and Bennett 2000). Therefore, the management of
sparsely scattered and even single trees in the agricultural landscape can provide significant
conservation outcomes for bats (Lumsden and Bennett 1995; Law et al. 1998).
In areas with limited roosting sites, bat-boxes can be installed as substitutes for natural
hollows. In Australia, relatively little is known of the use and preferred designs of bat-
boxes (Goldingay and Stevens 2009), however studies in the Northern Hemisphere provide
evidence that internal microclimate, height off the ground, construction material and design
can affect the attractiveness and suitability of a bat-box for the target species (Arnett and
Roost-boxes as a tool in the conservation of tree roosting microbats
11
Hayes 2000; Brittingham and Williams 2000; Kerth et al. 2001; Flaquer et al. 2005;
Bartonicka and Rehak 2007; Lesinski et al. 2009). Therefore, the design and placement of
roost boxes is likely to influence their usefulness to bats, and other wildlife, and their
effectiveness in allowing the maintenance of sustainable populations of native wildlife in
lower-quality, fragmented habitats.
Conclusions
The loss, modification and fragmentation of natural habitats constitute a major threat to bat
populations worldwide (Racey and Entwistle 2003). This is particularly relevant in
Australia where the majority of microbats rely on tree hollows to roost in during the day
(Churchill 2008). Echolocation data collected in this study provide indirect evidence of bats
roosting diurnally in a small, isolated patch of trees located within a highly-modified
agricultural matrix. Bat-boxes were installed at the Warrayure Conservation Offset Site as
part of an ongoing ecological management and restoration plan, with the intention of
providing supplementary microbat roosting sites (Appendix 3). Further work is planned to
incorporate 6-monthly manual checks of bat-box occupancy at Warrayure, paired with
additional bat detector surveys to examine seasonal patterns of activity at both the
Warrayure and Strathkellar Conservation Offset Sites. This research will provide insight
into the efficacy of bat-boxes as a management tool for the conservation of tree-hollow
roosting microbats in highly-fragmented rural landscapes.
Roost-boxes as a tool in the conservation of tree roosting microbats
12
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Appendix 1
Table A1. Microbat species known to occur in the Western Volcanic Plains region of Victoria*, with level of taxonomic identification achieved by the AnaScheme program. Scientific name Common name AnaScheme identification Vespertilionidae Chalinolobus gouldii Gould’s wattled bat Species level Chalinolobus morio chocolate wattled bat Species level Falsistrellus tasmaniensis eastern false pipistrelle Species level Miniopterus schreibersii oceanensis southern bent-winged bat Species level Nyctophilus geoffroyi lesser long-eared bat Genus: Nyctophilus sp. Nyctophilus gouldi Gould’s long-eared bat Genus: Nyctophilus sp. Nyctophilus timoriensis greater long-eared bat Genus: Nyctophilus sp. Scotorepens balstoni inland broad-nosed bat Species level Vespadelus darlingtoni large forest bat Species level Vespadelus regulus southern forest bat Species level Vespadelus vulturnus little forest bat Species level Molossidae Tadarida australis white-striped free-tailed bat Species level Mormopterus species 2 eastern free-tailed bat Genus: Mormopterus sp. Mormopterus species 4 southern free-tailed bat Genus: Mormopterus sp. Emballonuridae Saccolaimus flaviventris yellow-bellied sheath-tailed bat Species level
*Species distributions from Churchill (2008) and on advice from L. Lumsden (Department of Sustainability and Environment, Victoria).
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Appendix 2
a)
b)
Figure A1. Sonograms of social call sequences produced by microbats roosting diurnally in mature E. cladocalyx at the Warrayure Conservation Offset Site. Call frequency (kHz) is presented on the y-axis, with time in seconds on the x-axis (call a) 15 second duration; call b) 12 second duration). Both call sequences are comprised of short pulses of sound within the range 7-10 kHz.
App
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ost-boxes as
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at the Warracladocalyx at
he conservat
ayure ConserWarrayure o
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t Site. b,c,d) P012.
icrobats
19
Purpose-