-
Use of articial tree hollows by Australian birds and bats
Ross L. GoldingayA,B and Jane R. StevensA
ASchool of Environmental Science and Management, Southern Cross
University,PO Box 157, Lismore, NSW 2480, Australia.
BCorresponding author. Email: [email protected]
Abstract. Articial tree hollows (nest or roost boxes) may be of
considerable importance to the conservation andmanagement of
Australian hollow-using birds and microbats. This is suggested by
recognition that the rate of collapse ofhollow-bearing trees may
exceed replacement in some landscapes. We review the published
literature to synthesise currentinformation on the use of articial
hollows by Australian birds and bats, and to provide guidance to
future research andmanagement. The use of articial hollows has been
documented in some detail for 15 native bird and eight microbat
species.A range of hollow designs has been employed but there is a
limited understanding of favoured designs. General designs(e.g.
front-entry plywood boxes) have been used extensively by some
species and should continue to be used until moreeffective designs
are identied. Species tend to use articial hollows that have
entrance sizes just sufcient for their body size,and this should
guide hollowdesign.Competitive interactionswith a range of
non-target species (native and non-native)mayhave a pronounced
inuence on articial hollow use andmust be considered in
anymanagement program involving articialhollows.Wehighlight
somedesign elements thatmay reduce interference bynon-target
species. Temperature inside articialhollowsmay have a particular
inuence on their use by bats due to the role ofmicroclimate in bat
thermoregulation. Trials areneeded to investigate this factor and
to inform general approaches to positioning of articial hollows.
Several distinctmanagement uses exist for articial hollows,
including assisting threatened species recovery, e.g. Kangaroo
Island glossyblack-cockatoo (Calyptorhynchus lathami halmaturinus)
and orange-bellied parrot (Neophema chrysogaster).
Articialhollowsoffer an interim solution to hollow shortage but
their full potentialwill only be realisedwhenpreferences for
differentdesigns are better understood. This will require a
commitment to monitoring and should be conducted in an
adaptivemanagement context. Increased knowledge of the use of
articial hollows by Australian birds and bats should be of
globalrelevance to the management of hollow-using species because
it provides an independent test of ideas and strengthens
anygeneralisations.
Introduction
Species of wildlife throughout the world use tree hollows
forprotectionwhen inactive and as breeding sites (e.g. Saunders et
al.1982; Mackowski 1984; Newton 1994; Nowak 1999; Kunz andLumsden
2003; Zinner et al. 2003). In Australia, as many as 300native
vertebrate species (birds, bats, arborealmarsupials, reptilesand
frogs) use tree hollows (Gibbons and Lindenmayer 2002).This
corresponds to a far greater proportion of wildlife
speciesdependent on tree hollows for survival compared to that on
othercontinents (see Saunders et al. 1982; Newton 1994; Gibbons
andLindenmayer 2002). This prevalence of hollow dependenceamong
Australian wildlife should result in land managers andresearchers
leading the way internationally in understanding thehollow
requirements of species and devising effectivemanagement programs
for them. At present, this does notappear to be the case with
widespread concern that theabundance of tree hollows has declined
within manylandscapes in Australia (Joseph et al. 1991; Bennett et
al.1994; Mawson and Long 1994; Lindenmayer et al. 1997; Pelland
Tidemann 1997a; Gibbons et al. 2002; Heinsohn et al. 2003;Eyre
2005; Harper et al. 2005a; Courtney and Debus 2006).As a
consequence,manyhollow-dependent species are now listed
as threatened (Gibbons and Lindenmayer 2002). Managementprograms
in response to this appear to be in their infancy.
Articial hollows (nest and roost boxes) can potentiallysimulate
the tree hollow environment for many hollow-usingspecies (Menkhorst
1984; Boyd and Stebbings 1989; Petty et al.1994; Smith and Agnew
2002; Harley 2004; Beyer andGoldingay 2006; Goldingay et al. 2007)
and this is wellrecognised in Europe and North America (Stebbings
andWalsh 1991; Newton 1994). Indeed, understanding factors thatmay
inuence the use of articial hollows is an active area ofresearch in
Europe and North America for birds (e.g. Pogue andSchnell 1994;
Ardia et al. 2006) and bats (e.g. Kerth et al. 2001;Flaquer et al.
2006). Articial hollows have long been recognisedas an important
research and management tool for Australianarboreal marsupials
(Menkhorst 1984; Beyer and Goldingay2006). In contrast, the use of
articial hollows by Australianbirds is poorly documented in the
published literature despite thedeployment of articial hollows as a
management tool for over adecade (e.g. Olsen 1996; Mooney and
Pedler 2005). There isincreasing evidence that roost boxes will be
used by Australianmicrobats (Golding 1979; Irvine and Bender 1995;
Ward 2000;Smith and Agnew 2002) but the extent to which this can
result in
CSIRO PUBLISHINGwww.publish.csiro.au/journals/wr Wildlife
Research, 2009, 36, 8197
CSIRO 2009 10.1071/WR08064 1035-3712/09/020081
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valuable research and management applications is not
wellunderstood.
This paper reviews published information on the use ofarticial
hollows by Australian birds and bats. The largenumber of
hollow-using species in Australia means that anyincrease in
knowledge and understanding can benet themanagement of a signicant
component of biodiversity.Specically we aim to: (i) synthesise
available publishedinformation on the use of articial hollows; (ii)
examinedifferent applications of articial hollows; and (iii)
identifygaps in our knowledge so as to stimulate future research.
Thepresent review complements one by Beyer andGoldingay
(2006)concerning the use of articial hollows by Australian
arborealmarsupials. We make extensive reference to studies in
thenorthern hemisphere because there is a substantial literaturefor
that area that can greatly inform our understanding of
therequirements and behaviour of Australian species. Furthermore,an
increased understanding of Australian species can
provideindependent tests of various hypotheses about the use of
articialhollows, which will allow greater generalisation for
anyhollow-using birds and bats.
Use of articial hollows by Australian birds and microbats
To review the literature on the use of articial hollows
byAustralian birds and bats, we conducted searches of the Webof
Science as well as the Australian journals Australian Journalof
Zoology, Emu and Wildlife Research, using webpage searchtools and
keywords relating to articial hollows. The journalAustralian
Mammalogy was searched manually. Theses wereonly included when
commonly referred to by published studies.Some studies and most
books on this topic have documentedspecies observed using articial
hollows but have provided fewdetails of such use. We restrict our
attention to studies thatdescribe more than one observation of nest
and roost box useby birds or bats, and inwhich some details of the
articial hollowsused were described.Where possible we have collated
data on allspecies referred to in studies, regardless of whether
one species orwildlife group was targeted.
Only 27 studies have been published during the last 32 yearson
the use of nest boxes by birds, with 14 published during19962000
(Fig. 1). This included 15 native and two introducedspecies. Nest
box use has been described for seven parrot species,three
passerines, one nocturnal bird and two waterfowl species.The use of
articial hollows by microbats has fared much morepoorly with just
ve studies covering eight species published inthe last 32 years
(Fig. 1).
The most commonly encountered species in articialhollows, in
terms of the number of individuals or boxesoccupied and the number
of studies in which they featured,were the crimson rosella
(Platycercus elegans), chestnut teal(Anas castanea), common myna
(Acridotheres tristis), Gouldswattled bat (Chalinolobus gouldi) and
the large forest bat(Vespadelus darlingtoni) (Table 1). Welcome
swallows(Hirundo neoxena) used at least 800 plastic drum nest
boxesin Western Australia but no further details were
provided(Norman and Riggert 1977). The chestnut teal (Anas
castanea)accounted for 363 boxes occupied in Victoria (Norman
andRiggert 1977). This and one other study (Briggs 1991) are
the
only ones that have targeted waterfowl despite the use of
treehollows for nesting by 10 Australian species (Saunders et
al.1982; Marchant and Higgins 1990) and the common use of nestboxes
to studywaterfowl in theUSA (seeEadie et al. 1998; Evanset al.
2002). Sample sizes in Australian studies exceeded 50(either boxes
occupied or individuals encountered) for just sixspecies (Table 1),
though some studies did not document thenumber of individuals. The
endangered orange-bellied parrot(Neophema chrysogaster) and
Kangaroo Island glossy black-cockatoo (Calyptorhynchus lathami
halmaturinus) have usednest boxes repeatedly but the details of
this are not welldocumented (Mooney and Pedler 2005; Orange-bellied
ParrotRecovery Team 2006).
Factors that affect the use of articial hollows
Several factors will inuence the use of nest and roost boxes.Of
particular importance are hollow design and placement,natural
hollow availability, and competition with other species.Breeding
patternswill produce seasonal patterns of use, and thesemay differ
across taxa. Temperature is also a key factor and mayproduce a
seasonal response in the timing of use. These factorshave not been
well studied and represent signicant gaps in ourunderstanding of
articial hollow use.
Hollow design and placement
The main design elements that may inuence the use of
articialhollows are entrance size, hollow volume, hollow depth
belowentrance and wall thickness. A great amount of general
literatureis available recommending detailed box designs for birds
andbats (McCulloch and Thomas 1986; Stebbings and Walsh 1991;Grant
1997; Franks and Franks 2003). However, manyrecommendations appear
to have been developed in an ad hocway. Understanding whether
species show preferences forparticular design elements and
placement positions is centralto all research andmanagement
applications of articial hollows.Despite this only a few published
studies have provided a choiceof hollow types or design elements
for birds and bats in Australia(see section Research
applications).
In the absence of preference studies (e.g. Lumsden 1989;Radunzel
et al. 1997) it is likely that future studies will simplyfollow
designs used elsewhere and be unable to state whether low
0
2
4
6
8
10
12
14
16
197680 198185 198690 199195 199600 200105 2006+
Year of publication
Num
ber o
f stu
dies
MicrobatsBirds-ManagementBirds-Research
Fig. 1. The number of studies on the use of articial hollows by
birds andmicrobats published in 5-year periods since 1976.
82 Wildlife Research R. L. Goldingay and J. Stevens
-
Tab
le1.
Cha
racteristics
ofarticial
hollo
wsused
bydifferen
tspeciesof
bird
andba
tFrequency
ofuseofvariablecategories:X
X=frequentlyused
(>20%ofboxesu
sedatasiteorinastudy);X
=know
ntohave
been
used;
hasnotbeenused
orabsentfrom
studies.Notallvariablecategorieswere
presentw
herespeciesused
nestboxes.Sam
plesizeshave
been
pooled
acrossstudies.Som
estudiesmay
notgiveprecisedataso
>isused
toindicatethetrue
valueexceedsthatshow
n.Species
body
sizes,
Simpson
andDay
(1993),C
hurchill(1998).R
eferences:1,Norman
andRiggert(1977);2,M
illedge
(1978);3,G
olding
(1979);4,C
alderetal.(1983);5,Menkhorst(1984);6,Q
uinandBaker-G
abb(1993);
7,Irvine
andBender(1995),R
.BenderandR.Irvine
(unpubl.data),R.Bender(unpubl.data);8,
Trainor
(1995a,1995b);9,
Emison
(1996);10,Olsen
(1996);11,Pedler(1996);12,P
ellandTidem
ann
(1997a,1
997b);13,K
rebs
(1998,
1999),Krebs
etal.(1999);14,G
leeson
(1999);15,H
oman
(1999);16,W
ard(2000);17,S
mith
andAgnew
(2002);18,H
arperetal.(2005b);19,O
range-bellied
Parrot
RecoveryTeam
(2006);20,G
oldingay
(2007)
Box
variable
Australian
owlet-nightjar
NorfolkIsland
boobookowl
White-throated
treecreeper
Greyshrike-thrush
Striatedpardalote
Crimsonrosella
Easternrosella
Rainbowlorikeet
Red-rumped
parrot
Glossy
black-cockatoo
Red-tailed
black-cockatoo
Galah
Orange-bellied
parrot
Chestnutteal
Turquoiseparrot
Commonstarling
Commonmyna
Gouldswattled
bat
Goulds
long-earedbat
Easternfalse
pipistrelle
Lesser
long-earedbat
Largeforestbat
Southernforestbat
Chocolate
wattledbat
White-striped
freetailbat
Bodysize
birds(cm),
bats(g)
2430
1524
1235
3028
2748
6336
2148
2022
2512
921
77
58
38
Entrancediam
eter
12
X
X
XX
XX
XX
Entrancelocatio
nSlit
below
XX
XX
X
XX
XX
Front/to
pXX
XX
XXX
XX
XX
XXX
X
XX
X
XX
X
XX
XX
X
Spout
XX
XX
X
Volum
e(m
3)
Small(
0.03)
XX
XXX
X
XX
XX
XX
XX
X
X
XX
X
Heightaboveground
6m
X
XX
X
XX
X
X
X
XX
X
Aspect
North
X
XX
X
XX
X
XX
XX
South
X
XX
X
X
XX
XX
East
X
X
X
XX
X
West
X
X
Sam
plesizes
Individuals
24>2
21
4>8
5
5
>3
0>3
602
>250
50
56>1
00>2
>1>5
Boxes
occupied
24>2
213
4>9
58
64
415
228
>360
212
8130
243
10
10
References
3,4,
5,8
103,4,
5,8
52
3,4, 5,
12,13
8,12,
14,15
178
119
8,18
191
612,14,
1512,15,
183,4,7
17,
203,4,
163,4,
7,16
7,16
7,16
77
Use of articial tree hollows by Australian birds and bats
Wildlife Research 83
-
usage was due to the design or local habitat factors.
Studiesreporting use of articial hollows by bats are a good example
ofthis. Golding (1979) used 22 sawn-timber boxes and 143 adaptedlog
hollows. Both designs were of similar volume and had a6.5 cm
diameter circular front entrance. He reported use of 23boxes by 260
bats of ve species but did not report whether onedesignwas
favoured.Menkhorst (1984) reportednousebybats of240 front-entry
boxes with circular entrances of 515 cmdiameter. Irvine and Bender
(1995) recorded 34 bats in 5 of 10boxes with a slit-entry at the
base. Ward (2000) used a small boxwith a slit-entry under the lid
and reported 73 captures of fourspecies of bats. Smith and Agnew
(2002) found that 17 of 48wedge-shaped boxes with a basal
slit-entry were used by bats attwo sites. It is impossible to
determine from these studiesspanning a broad latitudinal range
whether one design ordesign element (e.g. slit v. circular entry)
might be favoured.Given the inuence of temperature on roost
selection by bats (seebelow), it is also likely that box
temperature has played a role inthese results.
We have summarised information on the range in box
designelements used by bird and bat species (Table 1), which
provides abroad indication of preference in the absence of direct
testing. Thematerials that boxes are made from have varied
substantiallyamong studies. Hollows have been made from
woodenammunition boxes and plastic drums for use by
waterfowl(Norman and Riggert 1977), salvaged tree hollows placed
intrees for turquoise parrots (Quin andBaker-Gabb 1993) or in
treesand on powerpoles for red-tailed
black-cockatoos(Calyptorhynchus banksii graptogyne) (Emison 1996;
Fig. 2),polyvinyl chloride (PVC) pipe for use by glossy
black-cockatoosonKangaroo Island (Pedler 1996) (Fig. 3),
andplywoodboxes foreastern rosellas (Fig. 4) and crimson rosellas
(Krebs 1998) and forbats (Fig. 5). In Britain, plastic drums have
been used extensivelyby barn owls (Petty et al. 1994). Bat boxes
have been made frommarine ply (Smith and Agnew 2002) or from pine
(Irvine andBender 1995).
No detailed studies have been conducted in Australia toexamine
the inuence of roost box design on bat occupancy.A variety of bat
box designs have been used overseas, and often inthe context of
providing alternative roost sites to bats displacedfrom roof spaces
(Neilson and Fenton 1994). Brittingham andWilliams (2000) tested a
vertical and a horizontal box of the samedimensions and found a
preference for the horizontal box. Theyalso suggested that boxes
needed to experience high internaltemperatures. Flaquer et al.
(2006) compared single- and double-compartment bat boxes installed
on houses, posts and trees. Theyfound greater use of the
double-compartment box, and boxesattached to houses and posts, and
recorded the highest occupancyby bats of any studies using bat
boxes. Their single-compartmentboxwas similar to that used by
Irvine and Bender (1995) but witha 1.5-cm rather than a 3-cm slit
opening at the base.
Entrance size is a key design element, possibly enabling boxesto
be designed to target species and it is one element that is
easilyvaried. Most species generally prefer a minimum entrance size
toallow access (i.e. one close to bodywidth) but avoid predation
bylarger species. Menkhorst (1984) found that crimson
rosellaspreferred one entrance size (8 cm) compared to three
others.Several studies found that the Australian
owlet-nightjar(Aegotheles cristatus) occupied a range of entrance
diameters,
though it was more frequently encountered in boxes withentrances
of 58 cm diameter (Table 1) (Fig. 6). Entrance sizemay be important
to exclude some predatory species. Krebs(1998) implicated pied
currawongs (Strepera graculina) inhigh levels of predation on
crimson rosella chicks that ceasedwhen she used a 10 cm-long PVC
tube to create a spout entrance.
Most studies (Table 1) have found that bats generally use
small(20mm were found occupied by competinglarger mammals such as
the sugar glider (Petaurus breviceps),introduced black rat (Rattus
rattus) and common ring-tailedpossum (Pseudocheirus peregrinus) (R.
Bender and R. Irvine,unpubl. data) or by feathertail gliders
(Acrobates pygmaeus),sugar gliders and squirrel gliders (Petaurus
norfolcensis)(Smith and Agnew 2002; Goldingay et al. 2007).
(a)
(b)
Fig. 2. (a) An articial hollow installed for red-tailed
black-cockatoos inwestern Victoria. Metal ashing was attached near
the base of the pole toexclude access by brushtail possums. (b)
This articial hollow consisted of asalvaged tree hollow attached to
a powerpole at a height of approximately12m. Photos: R.
Goldingay.
84 Wildlife Research R. L. Goldingay and J. Stevens
-
Volume and depth are thought to inuence the suitability
ofarticial hollows to birds and bats (Trainor 1995a) butinformation
on this is limited. These parameters of naturalhollows inuence
selection of hollow sites (Saunders et al.1982; Gibbons et al.
2002), and are known to affect thebreeding success of birds (Newton
1994). Nest box depth mayprovide security from predators (Trainor
1995a).
The insulating ability of nest boxes is determined by the
typeand thickness ofmaterials used. Insulation is thought to affect
nest
box use (Calder et al. 1983; Menkhorst 1984), leading to
naturalhollows being favoured when available. Menkhorst
(1984)postulated this to explain the relative absence of nest box
useby the Australian owlet-nightjar and white-throated
tree-creeper(Cormobates leucophaea) at one site where natural
hollows wereabundant compared to another with low abundance where
boxeswere used. Trainor (1995a) hypothesised that low
insulatingproperties may affect the breeding success of birds.
Commonmynas showed no preference for insulating properties
(25-mmrough-sawn pine or 12-mm plywood) in one study (Harper et
al.2005b). The insulating ability of nest boxes may be signicant
tothe requirements of bats, which are thought to use hollows
thatfacilitate thermoregulation (Gibbons and Lindenmayer
2002;Lourenco and Palmeirim 2004). R. Bender (unpubl.
data)suggested no greater use of 10 roost boxes with a thick
wall(45mm) designed for winter roosting by bats compared to
otherboxes (19mm), though the extent to which this changed
themicroclimate inside these boxes is unknown.
Aspect is likely to inuence temperature changes withinnest and
roost boxes (Stebbings and Walsh 1991; Brittinghamand Williams
2000; Ardia et al. 2006). Its inuence may differbetween birds and
bats due to the thermoregulatory requirementsof bats (see below).
No preference for nest box aspect has beendetected in any
Australian study (Table 1), though few specieshavebeenassessed and
sample sizeshavebeensmall (Calder et al.1983; Menkhorst 1984; Smith
and Agnew 2002). Furthermore,the actual position of boxes on trees
may not have provided anadequate test of aspect (Menkhorst 1984).
Stebbings and Walsh
(a) (b)
Fig. 3. (a) A polyvinyl chloride articial hollow installed for
glossy black-cockatoos on Kangaroo Island. (b) The same designof
articial hollow (~90 cm tall, 30 cmdiameter; entrance16 20 cm)
installed for red-tailed black-cockatoos inwesternVictoriaon a
powerpole. Photos: (a) E. Sobey; (b) R. Goldingay.
Fig. 4. Nestling eastern rosellas in a plywoodnest
box.Photo:R.Goldingay.
Use of articial tree hollows by Australian birds and bats
Wildlife Research 85
-
(1991) recommended choosing aspects for bat boxes that allowthe
sun to fall directly on the box for part of the day, as well
asproviding boxes with various aspects in case overheating
shouldoccur. Preference trials are needed to resolve this issue.
Placementshould also consider the surrounding habitat because
somespecies may be inuenced by habitat variables in their choiceof
suitable nest boxes (e.g. Willner et al. 1983; Pogue andSchnell
1994).
Few studies have tested whether bird or bat species show
apreference for the height at which boxes are placed in trees.
Moststudies placed boxes at heights of 26m, presumably
becausearticial hollows placed at lowheightswill be quicker and
safer to
monitor. These relatively low heights may have limited the use
ofboxes but for the species detected there is little evidence as
yet thatgreater heights will be preferred (Table 1). Stebbings and
Walsh(1991) suggested that some bat species in Great Britain
preferboxes to be at least 5mhigh. The height atwhich boxes are
placedmay inuence rates of predation (Milledge 1978; Menkhorst1984)
but this remains to be tested. Lumsden et al. (2002a)found that a
large proportion of tree roosts of lesser long-earedbats were
5mhigh.However, the latter species accounted for 91%ofbats present
in boxes placed 46m high in Organ Pipes NationalPark (Irvine and
Bender 1995; R. Bender, unpubl. data).
(a)
(b)
Fig. 5. (a) Awedge-shaped articial hollow for bats (26 20 18 cm;
1.5-cm slit-entry). (b) Goulds wattled bats in a wedge-shaped bat
box. Photos: (a) R. Goldingay; (b) M. Grimson.
(a)
(b)
Fig. 6. (a)Anarticial hollowdesigned for rosellas (45 20 15 cm;
6.5-cmentrance).No research has addressed the need forperches on
these hollows. (b) An owlet-nightjar roosting in this articial
hollow. Photos: R. Goldingay.
86 Wildlife Research R. L. Goldingay and J. Stevens
-
The actual spacing of boxes may inuence their frequency ofuse.
Nest boxes located too close together may be subject tointraspecic
competition and nesting failure of birds (see Krebs1998). Among
North American waterfowl, nest boxes placed athigh density can lead
to high levels of conspecic broodparasitism (multiple females
depositing eggs into one clutch),which can have adverse population
effects (Eadie et al. 1998).Studies of tree hollow use in
white-tailed black-cockatoos(Calyptorhynchus latirostris) and Major
Mitchells cockatoos(Cacatua leadbeateri) suggest that conspecic
interactions leadto a wide spacing of nest trees (Saunders et al.
1982).
Given the lack of proper testing of elements of hollowdesign and
placement, there is a great need for research on thistopic. The
effective use of articial hollows in research andmanagement will
depend on sound knowledge of hollowdesign and placement.
Hollow availability
The availability of natural hollows is commonly assumed to havea
strong inuence on the frequency of use of articial hollows(e.g.
Newton 1994). However, few studies in Australia haveconsidered this
issue in detail with many studies having beenconducted where it was
apparent that a dearth of natural hollowswas precluding use of an
area (e.g. Irvine and Bender 1995) orhindering reproduction (e.g.
Orange-bellied Parrot RecoveryTeam 2006). Three studies in Victoria
(Ambrose 1982; Calderet al. 1983; Menkhorst 1984) each installed
boxes at severallocationswhere natural hollow abundancewas either
lowor high.In all studies boxes were used more frequently by
Australianowlet-nightjars where natural hollows were scarce.
White-throated tree-creepers and crimson rosellas showed higheruse
where natural hollows were scarce in two studies but nodifference
in one study (crimson rosella) or higher use wherenatural hollows
were abundant (white-throated tree-creeper).Ambrose (1982) found
box use by barn owls (Tyto alba) to bemore frequent in forest with
few hollows whereas boobook owls(Ninox novaeseelandiae) showed no
difference between siteswith few or many hollows. Menkhorst (1984)
found that greyshrike-thrushes (Colluricincla harmonica) only used
boxeswhere natural hollows were abundant.
Few studies have been conducted of bats in this context.Golding
(1979) found that 8% of boxes were used by thelesser long-eared bat
and Goulds wattled bat where hollowswere abundant, compared to 3%
where no hollows occurred and43% where hollows were in low
abundance. Ambrose (1982)reported a single bat detection in a
boxwhereasMenkhorst (1984)reported none. Smith andAgnew (2002)
found thatGoulds long-eared bat used boxes frequently at two sites
with no hollows andthere was little or no use where natural
hollowswere either in lowor high abundance. Goldingay et al. (2007)
observed low use ofbat boxes across ve locations that varied in
abundance of naturalhollows including the two sites where Smith and
Agnew (2002)reported frequent use. For both birds and bats, it
appears that sitefactors (habitat, competitors) may have a strong
inuence on boxuse that may mask a species response to natural
hollowabundance and that properly replicated studies are required
tobetter understand whether natural hollow abundance inuencesuse of
articial hollows. Due to the mobility of birds and bats it is
likely that they can readily colonise areas devoid of
naturalhollows if nest and roost boxes are installed.
Seasonal patterns related to breeding
Many species of hollow-using birds only use hollows forbreeding,
so their breeding patterns will determine when nestboxes are used.
This may require frequent checking of articialhollows during the
year to accurately document use as well as todetermine the adequacy
of the articial hollows provided forbreeding. The crimson rosella,
white-throated tree-creeper(Calder et al. 1983; Menkhorst 1984),
grey shrike-thrush(Menkhorst 1984), eastern rosella (Platycercus
eximius) andred-rumped parrot (Psephotus haematonotus) (Trainor
1995a)used nest boxes in the spring and summer periods for
breeding,althoughnest site preparation (hole chewing andnest
building) bythe crimson rosella (Calder et al. 1983; Pell
andTidemann 1997a;Krebs 1998) and white-throated tree-creeper
(Calder et al. 1983)was observed during winter. In Victoria,
crimson rosellas usedarticial hollows until chicks were edged in
mid-January, aperiod of 56 days following egg laying (Golding
1979). Orange-bellied parrots laid eggs betweenNovember and
January, and hadan incubation period of 24 days and a nestling
period of 35 days(Orange-bellied Parrot Recovery Team 2006). Glossy
black-cockatoos on Kangaroo Island laid eggs from late January
tolate July, and had an incubation period of 30 days and a
nestlingperiod of 90 days (Garnett et al. 1999). Red-tailed
black-cockatoos laid eggs during September to December, and hadan
incubation period of 30 days and a nestling period of 87
days(Commonwealth of Australia 2006). Maned or wood
ducks(Chenonetta jubata) bred in nest boxes near Canberra
betweenJuly and December with a 34-day incubation period
(Briggs1991). The nocturnal Australian owlet-nightjar used nest
boxesprimarily in spring and summer for breeding, but as a diurnal
roostsite throughout the year (Calder et al. 1983; Menkhorst
1984;Trainor 1995a). Thewhite-throated tree-creeper was found to
usenest boxes for roosting all year except during summer
(Ambrose1982). The boobook owl and barn owl used nest boxes
duringwinter and spring, and less frequently during summer
(Ambrose1982). The abovedata indicate that seasonal patterns of use
can behighly variable among bird species and consequently the
designof monitoring programs will need to accommodate this.
Few data are available for bats but if articial hollow
usemirrors natural hollow use then the requirements of some
speciesmaydiffer during the breedingperiod fromother timesof
theyear,when females aggregate into maternity colonies when
breeding(e.g. Churchill 1998). For example, females of the lesser
long-eared bat preferred enclosed hollows with ssure entrances
invery large-girth trees during breeding periods compared to
whennot breeding (e.g. Lumsden et al. 2002a). Golding (1979)
foundthat individual or small groups of Goulds wattled bat used
roostboxes throughout most of the year but female-dominated
groups(up to 39 bats) occurred in spring and for the lesser
long-eared bat(10 bats) in December in a few boxes. Smith and Agnew
(2002)observed small numbers (four to eight) of Goulds long-eared
batin several months but one aggregation of 16 females with youngin
October. R. Bender (unpubl. data) observed a summer peak inbreeding
by Goulds wattled bats in boxes. The frequency withwhich patterns
of use mimic those within natural hollows by
Use of articial tree hollows by Australian birds and bats
Wildlife Research 87
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catering for non-breeding females as well as
breedingaggregations should indicate the effectiveness of
articialhollows. Studies that involve a choice of box size and
locationare needed to better understand the potentially varied
seasonalrequirements of bats.
Temperature
The inuence of temperature on hollow use will vary dependingon
whether a species requires hollows throughout the year(bats,
hollow-roosting birds) or just during the breedingseason
(hollow-breeding birds). Temperature within hollowsmay be critical
to the daily thermoregulation of individuals orin promoting faster
rates of growth by developing young(e.g. Dawson et al. 2005). The
temperature inside articialhollows can be an important factor in
their use if hollows eitherexceed or do not reach a preferred
thermal zone. There may be aseasonal element to this due to the
poor insulative properties ofarticial hollows (Calder et al. 1983;
Kerth et al. 2001), so theymay be ignored inwinterwhen temperatures
are lowor ignored insummerwhen temperatures are high (R.Goldingay,
unpubl. obs).This seasonalpattern is likely tovary
latitudinallywithclimateandmay lead to variation in the preferred
orientation of entrances tonests (e.g. Burton 2007) or the
preferred position of an articialhollow (full sun v. shade).
Furthermore, elevational gradients intemperaturemayalsohavean
inuence.Therefore,wherewereferto studies from different geographic
locations below, weacknowledge that some ndings may be location
specic.
In Australia, the inuence of the thermal environment inarticial
hollows has not been well studied. Norman andRiggert (1977) found
that temperatures inside black plastic-drum nest boxes in southern
Western Australia were an averageof 12Chotter than ambient.
Temperatures in the boxes commonlyexceeded 35C in October but were
not assessed later in the yearwhen they might have been much
hotter. Menkhorst (1984)suggested that reduced survival of
white-throated tree-creeperhatchlings in his study may have
resulted from overheatingwithin nest boxes. Calder et al. (1983)
have shown that aspect,wall thickness, entrance position and box
depth can all haveprofound inuences on temperatures within articial
hollows.Overly high summer temperatures may not be such a
problemfor hollow-breeding birds that breed in spring, but the
young ofsome species (e.g. crimson rosella, white-throated
tree-creeper)may not edge until JanuaryFebruary (Calder et al.
1983). Somebird speciesmay choosewarmhollows in springdue to the
positiveinuence that temperature can have on incubation andnestling
development (e.g. Ardia et al. 2006). Consistentwith this was the
observation that Bechsteins bats (Myotisbechsteinii) in Germany
preferred sun-exposed boxes duringlactation whereas shaded boxes
were preferred pre-lactation(Kerth et al. 2001).
Temperature is a critical issue for microbats in roost
selection(Boyles 2007) and therefore roost box
selection.Manymicrobatsare quite small in size (
-
for some target species. Competition may arise from native
ornon-native species. The impacts of displacement by
non-nativespecies is relatively well documented. The common myna
(Pelland Tidemann 1997a; Homan 1999; Harper et al. 2005b),common
starling (Sturnus vulgaris) (Ambrose 1982; Trainor1995a; Pell and
Tidemann 1997a, 1997b) and introducedhoneybee (Ambrose 1982;
Trainor 1995b; Emison 1996; Pelland Tidemann 1997a; Homan 1999;
Harper et al. 2005b) are thespecies of most concern, though the
black rat could also be aproblem at some locations. These species
have the potential todeter native species from using nest boxes and
reduce the numberof available hollows (Trainor 1995b; Pell and
Tidemann 1997b;Smith and Agnew 2002). The common myna was found to
out-compete several species of native parrot and the common
starlingcan cause nest failure of native species (Ambrose 1982;
Trainor1995a; Pell and Tidemann 1997b; Gleeson 1999;
Orange-belliedParrot Recovery Team 2006). Harper et al. (2005b)
found thatmynas occupied 45 of 120 nest boxes in Melbourne over
a7-month period, and rebuilt their nests following removal.Although
competition for nest sites with the starling has led tofew declines
among cavity-nesting birds in the USA (Koenig2003), the longer-term
effects of starlings and mynas onAustralian birds are unknown.
The invasion of both articial and natural hollows by
feralhoneybees can be a signicant management issue (e.g.
Trainor1995b; Wood and Wallis 1998). The recovery plans of
theKangaroo Island glossy black-cockatoo and orange-belliedparrot
have identied the need for regular maintenance to deterand remove
feral honeybees from articial and natural hollows(Mooney andPedler
2005;Orange-bellied ParrotRecoveryTeam2006). Feral honeybee
invasionhas been reported inmany studiesof nest boxes (e.g. Wood
and Wallis 1998; Harper et al. 2005b;Goldingay et al. 2007) and
needs to be documented in detail so itsincidence and treatment can
be better understood. For example,the use of carpet (Franks and
Franks 2003) and insecticide strips(Irvine andBender 1995;
Soderquist et al. 1996) inside nest boxeshave been trialled to
prevent honeybee infestations but fewdetailshave been reported.
Nest box design may mitigate the impact of pest species
andreduce the need for costlymaintenance. Lumsden (1989)
reportedthat starlings did not use nest boxes painted white inside.
In apreliminary study by Homan (2000), the use of a bafe
installedon the front of nest boxes successfully excluded the
commonmyna without excluding native species. A slit entrance for
batboxes has been suggested to exclude competition and predationby
introduced birds (Smith and Agnew 2002). Small nest boxvolumemay
reduce hive building by honeybees (Goldingay et al.2007). The
inuence of pest species is relevant to the success andeconomic cost
of articial hollows in management, and furtherinvestigation using
an experimental approach is needed.
Some native hollow-using species will displace others.
Boxesinstalled in Australia for use by bats may be used by
arborealmammals (Smith andAgnew2002;Goldingay et al. 2007).
Irvineand Bender (1995) reported that 2 of 10 bat boxes had nests
ofsugar gliders but over time all of these boxes had sugar
gliderspresent either often or occasionally (R. Bender and R.
Irvine,unpubl. data). Small entrance sizewill not overcome this
problembecause feathertail gliders will use entrances of 1.5 cm and
theirnests can completely ll a box (Fig. 7a). Goldingay et al.
(2007)
reported that 6 of 12 bat boxes at locations in
south-eastQueensland had feathertail gliders or their nests and
only fourboxes were used by bats. This may require a reliance on
open-bottom roost boxes for bats that preclude the construction of
a leafnest inside (Fig. 7b, c).
Arboreal marsupials are likely to compete with birds as wellbut
the extent of this is not well documented. Menkhorst (1984)provided
circumstantial evidence that two bobucks (Trichosuruscaninus)
discouraged the use of many nest boxes by othermammals and birds.
Common brushtail possums (Trichosurusvulpecula) will kill nestlings
present in articial hollows. OnKangaroo Island, this has required
placing metal guards aroundtrees containing hollows used by glossy
black-cockatoos toprevent possums gaining access (Garnett et al.
1999). Sugargliders compete with orange-bellied parrots for nest
sites andmay even kill incubating birds (Orange-bellied Parrot
RecoveryTeam2006).This requires specic research to identifymethods
toreduce this impact. For example, squirrel gliders and sugar
glidersmay favour rear-entry nest boxes (the entrance occurs on the
backof thebox; seeBeyer andGoldingay2006) andbe less likely
touseother front-entry box types (with the entrance on the front or
sideof the box) when a choice is provided (Goldingay et al. 2007;R.
Goldingay, unpubl. obs). Loeb and Hooper (1997) found thatthe
provision of nest boxes reduced the use of natural cavitiesrequired
by endangered red-cockaded woodpeckers (Picoidesborealis) by
competing cavity users.
Crimson rosellas on Norfolk Island competed for nest boxeswith
endangered Norfolk Island boobook owls (Olsen 1996) andfor natural
hollows with endangered Norfolk Island greenparrots (Cyanoramphus
novaezelandiae cookii) (Hill 2002).Galahs (Cacatua roseicapilla)
have been implicated in theloss of eggs and little corellas
(Cacatua pastinator)implicated in the loss of nestlings of the
glossy black-cockatoo (Garnett et al. 1999). Deployment of decoy
nestboxes may help to alleviate competition and provide
easieraccess to these species for control.
Emison (1996) recorded yellow-tailed
black-cockatoos(Calyptorhynchus funereus), long-billed corellas
(Cacatuatenuirostris), maned ducks and owls using articial
hollowserected for red-tailed black-cockatoos. The expansion in
thegeographic ranges of common hollow-nesting parrots may
putcompetitive pressure on other hollow-using native
species.Clearly, competition from non-target species can have
asubstantial inuence on the effectiveness of any articialhollow
program. However, although the problem is wellacknowledged by many
authors it remains poorly documentedand this will hamper attempts
to reduce its impact. Therefore,research must be conducted to
understand the magnitude of theproblem and how it might be
managed.
Articial hollow applications
Articial hollows have been used in a variety ofways for
researchand management. Beyer and Goldingay (2006) recognised
forarboreal marsupials that nest boxes had three
researchapplications (detection of species, ecological
studies,investigation of nest-box design and placement) and
threemanagement applications (threatened species recovery,
speciesintroductions, strategic placement). These also apply to
birds and
Use of articial tree hollows by Australian birds and bats
Wildlife Research 89
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bats. In addition, we also recognise species
establishmentthrough habitat enhancement and hollow-bearing tree
offset.These research and management applications are discussed
indetail below.
Research applications
Species detection
Nest boxes have been used as a survey tool to determine
thedistribution and abundance of cryptic arboreal mammal
species(Beyer and Goldingay 2006). Using articial hollows in
this
way may not be of great importance for birds and bats, whichmay
be detected more readily using conventional surveytechniques,
particularly sonar detection for bats (but seeFlaquer et al. 2007).
Homan (1999) installed 12 nest boxesto survey for small parrots but
eight were quickly occupied bycommon starlings and common mynas.
However, the value ofnest and roost boxes is that they can be left
in place for longperiods and may provide insights not readily
gained fromperiodic survey using other techniques. In Great
Britain, theplacement of large numbers of bat boxes has
producedsignicant range extensions for some species (Stebbings
and
(a)(b)
(c)
Fig. 7. (a) A feathertail glider nest completely lled this
wedge-shaped bat box. (b) An open-bottom designbat box (42 17 15
cm; front panel 32 cm). (c) Goulds long-eared bats in an
open-bottom box. Photos: (a, b)R. Goldingay; (c) J. Lindsay.
90 Wildlife Research R. L. Goldingay and J. Stevens
-
Walsh 1991). Articial hollows could be deployed to
identifyspecies that might respond to hollow provision, as a
precursor toa management application.
Ecological research
Nest boxes have been used extensively to investigate thebreeding
biology and life histories of hollow-using birds inNorth America
and Europe (Koenig et al. 1992; Evans et al.2002). InAustralia,
only a small numberof published studies haveused articial hollows
to investigate the ecologyof birds andnonehave investigated the
ecology of bats. Norman (1982) used nestboxes to study egg laying
and incubation in the chestnut teal.Briggs (1991) used nest boxes
to investigate intraspecic nestparasitism in maned ducks. Pell and
Tidemann (1997a) used nestboxes to study factors that affect the
breeding success of thecrimson rosella, and eastern rosella when in
competition withintroduced hollow-using birds. Pell and Tidemann
(1997b)investigated the ecology of the common myna using nestboxes.
Nest boxes have allowed detailed investigation ofbreeding biology,
patterns of food allocation in broods, andnestling growth and
survival in the crimson rosella (Krebs1998, 1999, 2001; Krebs et
al. 1999, 2002; Krebs andMcGrath 2000). Nest box use by the glossy
black-cockatoohas allowed aspects of its breeding ecology to be
described(Garnett et al. 1999). Baltz and Clark (1999) used nest
boxesto investigate the inuence of conspecics on nest choice
inbudgerigars (Melopsittacus undulates) in captivity. The
abovestudies highlight the value of nest boxes as a research
tool,in providing access to animals that may not be available
anyother way.
Articial hollow preferences
The design of articial hollows can have a pronouncedinuence on
their frequency of use (see above). Despite this,fewpreference
studies have been conducted inAustralia.Normanand Riggert (1977)
examined the use by waterfowl of eight nestbox types that differed
in construction material and dimensions.This revealed greater use
of a thick wooden box (ammunitionbox) but few of some types were
installed and it appears thata direct choice of different box types
was not provided.
Menkhorst (1984) provides the rst example of a
properlyreplicated choice experiment in which combinations of
fourentrance sizes, three height placements and two aspect
typeswere used. He cautioned about the comparison of aspect
becauseboxes were placed on the east or west side of a tree and
likely tohave received approximately equal exposure to the sun.
Heidentied a preference by crimson rosellas for entrance sizebut
sample sizes for owlet-nightjars, white-throated tree-creepers and
grey shrike-thrushes were too low to demonstrateany choice. No bats
were detected in this study.
R. Bender and R. Irvine (unpubl. data) explored therelationship
between entrance size and bat body size with asmall number of roost
boxes. They suggested that Gouldswattled bat (10 g) preferred a
slit entrance size >15mm,whereas smaller species, the large
forest bat (7 g) and thesouthern forest bat (Vespadelus regulus) (5
g), preferred slitentrance sizes
-
success similar (and in some years greater) to that in
naturalhollows (Mooney and Pedler 2005). This program could
informthe use of articial hollows in other recovery programs.
Articial hollows consisting of hollows cut from fallen treeshave
been used to supplement the breeding habitat of the south-eastern
red-tailed black-cockatoo. A programwas trialled for thissubspecies
and included erecting some nest boxes on 12m-highpower poles
(Emison 1996). Nest boxes were quickly occupied,and over a 2-year
period 30% of all articial hollows were used(Emison 1996).
Approximately 60 articial hollows, comprisingboth PVCplumbing pipe
and natural hollows cut from fallen trees(Figs 2, 3) have been
installed on power poles in the last 5 yearsbut only salvaged
natural hollows (at least seven) were used(R. Hill, pers. comm.).
The recovery plan for this species hasrecognised that although the
availability of natural nest hollows isnot currently limiting the
population, dead nest trees arecollapsing at a rate of 47% per
year, and this is likely to be aserious threat in years to come
(Commonwealth of Australia2007). The recovery plan recommends for
the situation to bemonitored and the articial hollow program
expanded only ifsignicant nest tree losses are observed
(Commonwealth ofAustralia 2006). Articial hollows made from fallen
brancheswere installed to supplement the breeding habitat of the
turquoiseparrot (Neophemapulchella) inChiltern Park, Victoria (Quin
andBaker-Gabb 1993). Twowere used for nesting. Articial hollowsmade
from salvaged tree hollows and erected in known breedingareas have
been used in breeding by Norfolk Island green parrots(Hill
2002).
Nest boxes were installed in two studies in Tasmania totarget
the endangered forty-spotted pardalote (Pardalotusquadragintus) but
were only successful in enabling the striatedpardalote (Pardalotus
striatus) to breed (Milledge 1978;Woinarski and Bulman 1985). Nest
boxes are currently beingtrialled as part of the recovery plan for
this species (ThreatenedSpecies Section 2006).
Roost boxes could play an important role in the recovery
ofthreatened bats but existing studies are inadequate to guide
thisapplication. The recovery plan for theChristmas Island
pipistrelle(Pipistrellus murrayi) proposes to install roost boxes
tosupplement the natural roosts of this species, which mayinclude
beneath tree bark, under dead palm fronds, beneathtree canopies,
and in tree hollows (Schulz and Lumsden 2004).The eastern false
pipistrelle (Falsistrellus tasmaniensis), avulnerable species in
New South Wales, has been recordedusing nest boxes in Victoria
(Golding 1979; Ward 2000),suggesting there is potential to use
roost boxes in the recoveryof this species.
Existing studies demonstrate the usefulness of articialhollows
to threatened species recovery. However, there is aneed for further
research to improve and expand current use.This application has
potential for threatened bats but will dependon a dramatic increase
in our understanding of preferred roostbox designs.
Species introductions
We recognise this application as distinct from threatenedspecies
recovery because it may not always involve such speciesand the
approach may be quite different. It involves installing
articial hollows at a location where a species is to
beintroduced. The deployment of articial hollows to introducea
species at a site has been documented for just one species.Several
nest boxes were installed on Norfolk Island in 1987 forthe
reintroduction of the endangered Norfolk Island boobookowl (Ninox
novaeseelandiae undulata) (Olsen 1996). Malebirds from the closest
extant subspecies, the New Zealandmorepork (Ninox novaeseelandiae
novaeseelandiae), weretranslocated to the island. The nest boxes
enabled successfulbreeding to occur.
Species establishment through habitat enhancement
Because birds and bats are highly mobile it is quite possibleto
attract and establish species at a location by the installation
ofarticial hollows. This is as a form of habitat enhancementwhere
the decline or disappearance of hollow-using species isrecognised
and articial hollows have been installed to preventthe permanent
loss of biodiversity. Currently, the onlysuccessful example of this
management application is that byIrvine and Bender (1995) for bats.
Bat boxes were installed inOrgan Pipes National Park in Victoria in
1992 to facilitate theestablishment of bat populations within
regenerating forest inthe park where habitat restoration had
commenced in 1972(Irvine and Bender 1995). Bat boxes were not
occupied for30 months, which is in stark contrast to within 3
months ofinstallation documented by Smith and Agnew (2002) in boxes
inQueensland. The number of bats in Organ Pipes National
Parkincreased from 15 per check in 199495 to >100 per check
in200405 from 34 boxes (R. Bender, unpubl. data). Gouldswattled bat
comprised 91% of records but a small number oflarge forest bats
also consistently used the boxes. Boyd andStebbings (1989) reported
a doubling over a 10-year period in apopulation of brown long-eared
bats (Plecotus auritus)supported by roost boxes in managed forest
in Great Britain.These observations suggest that the local bat
population inOrgan Pipes National Park increased in size over time
so theinitial delay may have been due in part to a small
localpopulation.
Harper et al. (2005b) installed nest boxes as habitatenhancement
(~3 per ha) for vertebrate fauna across remnantvegetation within
the urban and suburban landscape ofMelbourne. Although nest box
design favoured large arborealmammals (large entrance and volume),
a small numberwere usedby rainbow lorikeets (six), an eastern
rosella (one) and a galah(one). The provision of articial hollows
may also allow hollow-using species lost from urban areas to
recolonise. Other studiesthat install articial hollows as habitat
enhancement have beenplanned and will target a range of birds and
bats (B. Law andR. Kavanagh, pers. comm.; R. Goldingay, unpubl.
data).
This management application has considerable merit but
iscurrently hamperedby the lackofunderstandingof the factors
thatinuence the use of articial hollows (see above). Many trials
areneeded todeterminewhichhollowdesigns shouldbe installed,
thenumber of eachdesign, themost effective placement,
andwhetherparticular species have beneted from such habitat
enhancement.Evidence that this application has been successful
would be theon-going use and breeding in articial hollows (Petty et
al. 1994),rather than only sporadic use by species. Such trials
should be
92 Wildlife Research R. L. Goldingay and J. Stevens
-
conducted in an adaptivemanagement framework so that changescan
be made as information accumulates on factors that
improveeffectiveness.Monitoringwill be fundamental to such studies
andneeds to be continued for 25 years to provide the best
insights.
Hollow-bearing tree offset
Another management application that has been used by
landmanagers (e.g. local government, road agencies, powercompanies)
is to install articial hollows to compensate forhollow-bearing
trees lost during authorised clearing (Fig. 8).This might occur
either adjacent to the development site orpossibly away from the
site if a landscape approach is taken tomanaging hollow-using
species.We stress that the potential valueof articial hollows
should not be used to justify the removal ofhollow-bearing
trees.Themerit of this application is that birds andbats can be
highly mobile and providing some replacementhollows may assist some
species as an interim solution whileother longer-term measures are
devised. If such a managementapplication is used there needs to be
monitoring over a 25-yearperiod to document the outcome. Currently,
information islacking to demonstrate the value of such a use of
articialhollows to hollow-using species so there is an obvious
needfor research on this application.
Strategic placement
This management application emphasises the speciclocations where
articial hollows are placed. This might be aspecic location in a
landscape suchaswithinwildlife corridorsorit might be a location
where a specic objective is to be achievedsuch as to attract
particular kinds of hollow-using species(Beyer and Goldingay 2006).
Although it will be concernedwith establishing species in an area
it primarily differs fromspecies establishment because fewer
hollows will be used,their installation will be highly targeted and
a more specicobjective will be stated.
In Europe there is increasing recognition of the value of
nestboxes to attract hole-nesting birds as ameans of controlling
insectpests in forests and orchards (Mols and Visser 2002). Smith
and
Agnew (2002) hypothesised that small mammals, particularlybats,
could control insects in farm forests and therefore provide ahealth
benet to the trees. They installed bat boxes in smallhardwood
plantations in south-east Queensland and had successin attracting a
small number of bats to their sites but better successwith
attracting feathertail gliders and squirrel gliders, which mayhave
discouraged greater use of the boxes by the bats. Thework inOrgan
Pipes National Park provides insight to the potential ofstrategic
placement with regard to bats. In 200405, >100 batswere captured
per round of box checks from 34 roostboxes scattered through 5 ha
of regrowth forest (R. Bender,unpubl. data).
Articial hollows are being trialled in northern Australia
toincrease barn owl and masked owl numbers for the control ofrodent
pests in sugarcane crops (Gibbons and Lindenmayer2002). Studies on
the strategic use of articial hollows inAustralia are in their
infancy. Further research is needed forthis application.
Conclusion
In many landscapes across Australia the collapse of
hollow-bearing trees has outpaced the recruitment of
replacementhollows and future shortages in this resource are
inevitable(Saunders 1979; Lindenmayer et al. 1990, 1997; Saunderset
al. 2003; Courtney and Debus 2006; Commonwealth ofAustralia 2007;
Beyer et al. 2008). The provision of articialhollows is likely to
be the most appropriate interim solution tothis shortage but
existing information on the use of articialhollows is too limited
to enable this response to be effective andprogress in this eld has
been slow. Applying our criteria ofrequiring more than a single
record of articial hollow use andsome details of the hollows, we
found information wasdocumented for just 15 of 114 hollow-using
bird species and8 of 41 hollow-using microbat species.
The lack of information is most stark for microbat species.The
deployment of roost boxes for bats in Australia is clearly inits
infancy. Progress has in part been hampered by the
relativelyinfrequent use of articial hollows by bats, which may be
aconsequence of positioning roost boxes without regard forcreating
suitable thermal environments. Selecting roosts toenable passive
rewarming from daily torpor may be quitewidespread among Australian
tree-roosting bats (Turbill et al.2003a, 2003b; Turbill 2006) and
this will inuence theirability to use articial hollows. Correct
positioning ofarticial hollows poses a challenge because deployment
inforested habitats may preclude positioning boxes in
highlyfavourable microsites due to shading from canopy cover.Some
natural roosts of bats in mature forest may be locatedhigh in trees
(e.g. Herr and Klomp 1999; Lumsden et al. 2002a)and have low canopy
cover (e.g. Campbell et al. 2005) tominimise shading. However,
given that bats may commute overlong distances where tree hollows
are scarce (e.g. Lunney et al.1985, 1988; Lumsden et al. 2002b), it
may be appropriate totarget edge and forest gap sites to place
articial hollows wheresun exposure will be optimal.
A key deciency in deploying articial hollows inresearch and
management of hollow-using birds and bats is inunderstanding the
most effective designs to use. Research
Fig. 8. Bat boxes installed on powerpoles through a powerline
easement inBrisbane. Some poles also have parrot boxes attached.
These boxes wereinstalled after expansion of an existing powerline
easement. Photo:R. McLean.
Use of articial tree hollows by Australian birds and bats
Wildlife Research 93
-
suggests that most species favour articial hollows withentrances
just wide enough to enter. This enables avoidance oflarger
competitors and possibly predators. Other elements ofdesign have
not been properly investigated though guidancecan be provided by
research on natural hollows, which showthat hollow depth is also
important (e.g. Saunders et al. 1982;Gibbons et al. 2002). Some
bird specieswill use articial hollowsmade from salvaged tree limbs
but it is not well documentedwhether constructed hollows that
emulate these have been triedadequately. Batsmay have different
requirements during the year(breeding v. non-breeding periods) and
this might require theprovision of several designs. So few studies
have been conductedof bats using roost boxes in Australia that
suitable designsremain largely unknown. There is an obvious need
for manyeld experiments that compare different hollow designs
orwhich vary specic design elements for birds and bats. Thisshould
lead to better knowledge of designs preferred by
differentspecies.
Another aspect that requires further investigation is theextent
that competing species may pre-empt target speciesfrom articial
hollows. Many studies have described potentialcompetition among
hollow users but the seriousness of this tomanagement is not well
documented. In some cases competitorsmay favour a specic box design
(e.g. arboreal mammalsthat displace birds or bats) and exert less
interference if theirhollow needs are catered for. This requires
specic researchto address. Furthermore, there are various issues
that relate tothe maintenance of articial hollows, such as the
occupationby feral honeybees and the collapse of boxes (Beyer
andGoldingay 2006). This also must be addressed by researchwith
particular attention given to the cost of maintenance(see also
Harley 2006).
One aspect of articial hollow placement that is not
wellunderstood and in need of research is whether species show
apreference for the height at which boxes are placed on trees.
Thisis of considerable management relevance because this can
havecost and safety implications in effectively employing
articialhollows. Available information suggests that heights >5m
arerarely needed (Table 1). The only examples where hollows
havebeen placed very high is that of theKangaroo Island glossy
black-cockatoo with hollows at ~16m above ground (Pedler 1996)
andthe red-tailed black-cockatoo with hollows at 12m above
ground(Emison 1996). It appears that articial hollows have been
placedat an equivalent height to natural tree hollows (Pedler
1996). Suchhollows will require an enormous amount of time to check
andmaintain. Given that red-tailed black-cockatoos have used
treehollows at heights as low as 4.4m (mean height 7m) in
WesternAustralia (Saunders et al. 1982), it is possible that very
highhollows are not needed. Examples where bats select high
roosts(i.e. >10m) may reect their preference for suitable
thermalenvironments, which may be replicated by placing
articialhollows in canopy gaps (see above).
Studies inAustralia on the useof articial hollowshave
laggedbehind those conducted in Europe and North America (e.g.
Boydand Stebbings 1989; Newton 1994; Petty et al. 1994; Pogue
andSchnell 1994;BrittinghamandWilliams 2000;Kerth et al.
2001),which is surprising given that a greater proportion of
wildlifespecies in Australia compared to other continents is
dependent ontree hollows for survival (see Saunders et al. 1982;
Newton 1994;
Gibbons and Lindenmayer 2002). The small number ofAustralian
studies currently available is insufcient to allowmany
generalisations. Articial hollows have enormouspotential to become
an important management tool for hollow-using species in Australia
but this can only be realised byconducting many additional studies.
This needs to occuracross a range of species and landscapes to
maximise ourunderstanding of interactions between species and
differentenvironments. Furthermore, species of Australian birds
andbats are likely to respond to similar factors in
choosingarticial hollows as taxonomically equivalent species
overseas(e.g. parrots, vespertilionid bats), so investigations can
provideindependent tests of current hypotheses concerning inuences
onuse, or of management applications. This will allow
greatergeneralisation and can also lead to work conducted
inAustralia informing research and management of
hollow-usingspecies in other countries.
Acknowledgements
The comments of Brendan Taylor, Geoff Smith and two anonymous
refereeshelped improve this paper. This paper has been informed by
several nest boxprojects conducted in Brisbane and an articial
hollow project conducted atBrunswick Heads, NSW.We thank Brisbane
City Council for support of ourresearch inBrisbaneandAbigroup for
assistancewith theproject atBrunswickHeads. Matthew Grimson and
Geoff Smith are thanked for sharing ideas andeld work that have
provided background to this paper. We thank RobertBender and Robert
Irvine for their pioneering work with bat boxes in OrganPipes
National Park.
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