Variation in Summer and Winter Microclimate in Multi-Chambered Bat Boxes in Eastern Australia: Potential Eco-Physiological Implications for Bats

Abstract

Bat boxes are commonly used as a conservation tool. Detailed knowledge on the influence of box elements on microclimate is lacking, despite eco-physiological implications for bats. Summer and winter box temperature and relative humidity patterns were studied in narrow multi-chambered plywood and wood-cement boxes in eastern Australia. Box exteriors were black or white and plywood boxes comprised vents. Relative humidity was higher in white boxes than black boxes and box colour, construction material, chamber sequence and vents influenced temperatures. Maximum box temperature differences between designs varied by up to 9.0 °C in summer and 8.5 °C in winter. The black plywood box consistently recorded the warmest temperatures. This design comprised a temperature gradient between chambers and within the front chamber (influenced by vent). During the 32-day summer sampling period, the front chamber rarely recorded temperatures over 40.0 °C (postulated upper thermal tolerance limit of bats), while the third and fourth chamber never reached this threshold. At the study site, the tested black boxes are considered most thermally suitable for bats during average summer conditions. However, during temperature extremes black boxes likely become too hot. Wood-cement, a durable material not previously tested in Australia should be considered as an alternative construction material.

Full text

environments
Article
Variation in Summer and Winter Microclimate in
Multi-Chambered Bat Boxes in Eastern Australia:
Potential Eco-Physiological Implications for Bats
Niels Rueegger
School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia;
niels_ruegger@hotmail.com
Received: 9 December 2018; Accepted: 25 January 2019; Published: 28 January 2019


Abstract:
Bat boxes are commonly used as a conservation tool. Detailed knowledge on the influence of
box elements on microclimate is lacking, despite eco-physiological implications for bats. Summer and
winter box temperature and relative humidity patterns were studied in narrow multi-chambered
plywood and wood-cement boxes in eastern Australia. Box exteriors were black or white and
plywood boxes comprised vents. Relative humidity was higher in white boxes than black boxes and
box colour, construction material, chamber sequence and vents influenced temperatures. Maximum
box temperature differences between designs varied by up to 9.0
◦
C in summer and 8.5
◦
C in winter.
The black plywood box consistently recorded the warmest temperatures. This design comprised a
temperature gradient between chambers and within the front chamber (influenced by vent). During
the 32-day summer sampling period, the front chamber rarely recorded temperatures over 40.0
◦
C
(postulated upper thermal tolerance limit of bats), while the third and fourth chamber never reached
this threshold. At the study site, the tested black boxes are considered most thermally suitable for
bats during average summer conditions. However, during temperature extremes black boxes likely
become too hot. Wood-cement, a durable material not previously tested in Australia should be
considered as an alternative construction material.
Keywords: artificial hollow; box humidity; box temperature; roost box; tree cavity-roosting bat
1. Introduction
Microhabitat selection can be critical for small-bodied animals [
1
,
2
]. One factor that influences
microhabitat suitability is microclimate. Temperature affects an animal’s energy budget, particularly when
they occur outside the animal’s thermal neutral zone (TNZ), that is, the zone in which an animal’s metabolic
rate can be maintained passively [
3
,
4
]. In order to minimise metabolic costs, small heterothermic mammals
can combat temperature induced metabolic costs through two mechanisms: behavioural adaptation such
as seeking microclimates that are favourable, or, using physiological adaptation such as torpor [5–10].
One animal group where microclimate is central to their life cycle is echolocating bats, with many
species using tree cavities for roosting [
11
]. Few studies have been conducted on microclimate roost
selection by heterothermic tree-cavity roosting bats. There is some evidence that roost temperature
preferences change among seasons and between sexes. For example, studies reported the selection of
thermally unstable roost sites and roosts that allowed for passive rewarming [
12
,
13
]. In contrast, during
the maternity season, energy requirements of females are likely to be high due to milk production,
so roost temperatures close to or within the TNZ may be favoured to maintain normothermia and
facilitate the growth of young [
14
–
16
]. Studies on artificial roosts using bat boxes in the Northern
Hemisphere have documented that reproductive female bats, particularly lactating females, selected
warm boxes [
17
–
19
], although more recent studies documented the use of torpor by pregnant and
lactating females and use of thermally labile roosts [10,20,21].
Environments 2019,6, 13; doi:10.3390/environments6020013 www.mdpi.com/journal/environments

Environments 2019,6, 13 2 of 19
Bat boxes are frequently used for conservation and research purposes [
22
,
23
]. However, their
use has outpaced the understanding of suitable designs and factors influencing box uptake [
22
–
24
].
One factor that is poorly described is the influence of the thermal profile within a box, despite the likely
importance of microclimates for tree-cavity roosting bats. Some Northern Hemisphere studies have
investigated bat box temperatures [
17
,
19
,
25
–
27
] but few data are available on bat box thermal profiles
in Australia [
28
–
30
]. In addition, studies that compared nest boxes to tree hollows showed that boxes
differed significantly in temperatures and raised concerns about the suitability of box temperatures,
particularly during summer [31,32].
Knowledge of the influence of box design elements on temperature is crucial to provide suitable
artificial roosts and to allow desired box microclimates to be attained, such as for maternity roost boxes.
This roost type is considered particularly important to support viable local populations, yet records of
maternity roosts in boxes are scarce, restricted to only a few species [
22
]. Box design elements and box
placements that may influence box thermal profiles include: multiple large chambers, vents, box size,
exterior colour, type of box construction material, thickness of exterior walls, box aspect and extent
of shading [
17
–
19
,
27
,
30
,
33
,
34
]. Another potentially important aspect of box microclimate is humidity.
Little is known about the significance of humidity in roosts for tree-cavity roosting bats but humidity
has been reported to influence evaporative water loss in bats [
35
]. In addition, humidity has been
identified to differ vastly between tree hollows and timber nest boxes [31].
This study compared temperature and relative humidity (RH) of two bat box types during
warm (summer) and cool (winter) periods. One type was a multi-chambered plywood box adapted
from a North American design [
34
]. This type contained four fissure-type chambers and vents
in an attempt to provide a wide temperature gradient within the box. The other box type was a
multi-chambered box with a wood-cement shell. Wood-cement boxes may last several decades [
36
,
37
]
and are commonly used in Europe [
22
]. This material has not been widely trialled elsewhere, however,
the longevity of these boxes makes wood-cement an attractive option where bat boxes are installed
as a long-term conservation measure. The objectives of the study were to investigate the influence
of box elements (exterior colour, box construction material, multiple chambers and vents) on box
microclimates and to discuss the potential eco-physiological implications of these box elements for
bats. Black boxes were hypothesised to provide warmer temperatures to that of white boxes [
18
,
19
]
and multiple-chambers and vents were expected to influence temperatures within the box [
17
,
34
].
The influence of box construction material on box microclimate was uncertain, as was the influence of
box colour, multiple-chambers and vents on box humidity.
2. Materials and Methods
2.1. Study Area and Climate
The study was conducted within a habitat offset area of a coal mine near Muswellbrook in New
South Wales, Australia. The vegetation of the study area comprised eucalypt woodland and grassland
that had formerly been grazed (see [
38
] for more details). The climate experienced at the site during the
monitoring of the box microclimates was warm during summer 2015 (mean maximum: 29.7
◦
C; mean
minimum: 17.2
◦
C) and relatively cool during winter 2014 (mean maximum: 17.4
◦
C; mean minimum:
3.9
◦
C; data obtained from the mine’s on-site weather station at 2 m above ground). The longer-term
temperature averages (1991 to 2018) for the region during the summer months is 31.6
◦
C (maximum)
and 16.9
◦
C (minimum) and 16.6
◦
C (maximum) and 3.3
◦
C (minimum) during the winter months
(data obtained from a weather station, approximately 35 km away from the study site [39].
2.2. Bat Box Designs
Multi-chambered bat boxes were installed that differed in construction material and design
elements. Boxes were made from either plywood or wood-cement, contained entrances measuring
1.5 cm or 2.0 cm and were either painted black or white. Black and white boxes were used in an

Environments 2019,6, 13 3 of 19
attempt to achieve a maximum possible difference in internal temperatures between exterior colour
treatments. The external panels of the plywood box were made from 1.9 cm thick marine grade plywood.
The plywood box contained four chambers that were divided by 0.9 cm thick plywood panels. This box
type contained a 45
×
2 cm horizontal vent across the front panel and a
2×6 cm
vertical vent on one of
the side panels at the location of the fourth chamber (adapted from [
34
]). Each chamber was open at the
bottom. The internal dimensions of the plywood box were: 61 cm (height)
×
45 cm (width) (box depth
was made up of the size of the four chambers (either 1.5 cm or 2.0 cm)).
The wood-cement box comprised four wooden chambers enclosed by a 2 cm thick wood-cement
shell. The same exterior colours and chamber widths were used as for the plywood box. The height
of the wood-cement box was 42 cm and the internal diameter was 15 cm. The lid of the plywood
box extended 5 cm beyond the front panel and 2 cm beyond the side and back panels, whereas the
wood-cement box did not have a roof overhang (Figure 1). The wood-cement shell was constructed
from a mixture of sawdust and cement. The volume ratio of moist sawdust to dry cement was 1:1.
The sawdust (obtained from Eucalyptus oreades (Blue Mountains ash) chainsaw shavings) was thin and
less than 5 mm in length. A sieve was used to exclude larger shavings from the wood-cement mix.
The shavings were soaked in cold water for at least 12-h prior to box construction. Calcium chloride was
added to the water when mixing the sawdust and cement to accelerate the cement setting process and
increase the bonding ability [
40
]. A mould made from timber was used to shape the wood-cement box.
Environments 2019, 6, x FOR PEER REVIEW 3 of 20
2.2. Bat Box Designs
Multi-chambered bat boxes were installed that differed in construction material and design
elements. Boxes were made from either plywood or wood-cement, contained entrances measuring
1.5 cm or 2.0 cm and were either painted black or white. Black and white boxes were used in an
attempt to achieve a maximum possible difference in internal temperatures between exterior colour
treatments. The external panels of the plywood box were made from 1.9 cm thick marine grade
plywood. The plywood box contained four chambers that were divided by 0.9 cm thick plywood panels.
This box type contained a 45 × 2 cm horizontal vent across the front panel and a 2 × 6 cm vertical vent on
one of the side panels at the location of the fourth chamber (adapted from [34]). Each chamber was open
at the bottom. The internal dimensions of the plywood box were: 61 cm (height) × 45 cm (width) (box
depth was made up of the size of the four chambers (either 1.5 cm or 2.0 cm)).
The wood-cement box comprised four wooden chambers enclosed by a 2 cm thick
wood-cement shell. The same exterior colours and chamber widths were used as for the plywood
box. The height of the wood-cement box was 42 cm and the internal diameter was 15 cm. The lid of
the plywood box extended 5 cm beyond the front panel and 2 cm beyond the side and back panels,
whereas the wood-cement box did not have a roof overhang (Figure 1). The wood-cement shell was
constructed from a mixture of sawdust and cement. The volume ratio of moist sawdust to dry
cement was 1:1. The sawdust (obtained from Eucalyptus oreades (Blue Mountains ash) chainsaw
shavings) was thin and less than 5 mm in length. A sieve was used to exclude larger shavings from
the wood-cement mix. The shavings were soaked in cold water for at least 12-h prior to box
construction. Calcium chloride was added to the water when mixing the sawdust and cement to
accelerate the cement setting process and increase the bonding ability [40]. A mould made from
timber was used to shape the wood-cement box.
Figure 1. Paired plywood design (left) and paired wood-cement design (right) installed on poles
about 1.5 m above ground.
2.3. Field Setup of Boxes
Boxes were installed across four sites in a landscape dominated by grassland that contained
isolated trees. The boxes were installed 1.5 m above ground on either hardwood poles or isolated
trees. Only microclimate data of boxes installed on poles are reported (Figure 1). Each site comprised
two plots. Each plot contained eight bat boxes: paired plywood boxes (one black, one white)
installed on a pole and on a tree and paired wood-cement boxes (one black, one white), also installed
on a pole and on a tree. Because black boxes aimed to provide warmer box temperatures than white
boxes, black boxes were installed to face a north-westerly aspect (afternoon sun) and white boxes
faced a south-easterly aspect (morning sun). No other box aspects were tested. Therefore, when box
colour is reported and discussed, it is inferred that box aspect would likely have contributed to the
difference in microclimate between black and white boxes.
Figure 1.
Paired plywood design (
left
) and paired wood-cement design (
right
) installed on poles about
1.5 m above ground.
2.3. Field Setup of Boxes
Boxes were installed across four sites in a landscape dominated by grassland that contained
isolated trees. The boxes were installed 1.5 m above ground on either hardwood poles or isolated trees.
Only microclimate data of boxes installed on poles are reported (Figure 1). Each site comprised two
plots. Each plot contained eight bat boxes: paired plywood boxes (one black, one white) installed on
a pole and on a tree and paired wood-cement boxes (one black, one white), also installed on a pole
and on a tree. Because black boxes aimed to provide warmer box temperatures than white boxes,
black boxes were installed to face a north-westerly aspect (afternoon sun) and white boxes faced a
south-easterly aspect (morning sun). No other box aspects were tested. Therefore, when box colour is
reported and discussed, it is inferred that box aspect would likely have contributed to the difference in
microclimate between black and white boxes.
2.4. Microclimate Monitoring
Temperature/humidity data loggers (iButton, Dallas TX, USA) (hereafter ‘loggers’) were used to
monitor box microclimates in summer and winter. Some loggers recorded both RH and temperature
(Hygrochron DS1923) and others only temperature (Thermochron DS1921G). The logger recording
interval was one per hour and the logger resolution was 0.5
◦
C and 0.04% (RH). Loggers were attached

Environments 2019,6, 13 4 of 19
with a short piece of string. One logger was deployed in each box chamber, that is, for the plywood
boxes, loggers were installed 10 cm from the top of the box and for the wood-cement box, loggers
were installed 5 cm from the top. During a second investigation, an additional logger was installed
in each chamber of the black plywood box at a lower position (i.e., 15 cm from the bottom of box) to
investigate a potential thermal gradient within chambers of this box design. Each logger faced the
same way, that is, the top plane of the loggers faced the back panel of the chamber. Boxes were not
closed-off for bats to access the box during the temperature/humidity measurements. Because box use
was infrequent and predominantly by solitary bats (unpublished data), it was assumed that bats did
not influence logger measurements. Ambient temperatures during the box monitoring were obtained
from the mine’s on-site weather station.
Temperature and RH data were obtained during the austral summer and early part of autumn
(5 February to 8 March 2015) and winter (30 July to 17 August 2015). A subsequent, more detailed
investigation was undertaken for the black plywood box only for the warmest day during 18 November
2015 to 17 January 2016 to test the thermal profile within this box (see Table 1for details). The following
variables were collated from the data: ‘maximum day’ temperature (T
box_max
), ‘mean warmest
day period’ temperature (1000–1900 h; T
box_warmest
), ‘mean warmest day period’ RH (1000–1900 h;
RH
box_warmest
) and ‘mean night’ temperature (2000–0700 h; T
box_night
). Details and justification of the
type of analyses performed are outlined in Table 1and in the ‘statistical analysis’ section. Replication
of individual chambers per box design in which temperature/RH data were recorded was four, except
for winter RH where chamber replication for both black box designs was six. Pairs of boxes installed
on poles were selected randomly to obtain temperature and RH data. A preliminary comparison was
made between T
box_max
on the warmest summer day of the same box designs but differing in chamber
width (1.5 cm vs 2.0 cm). No significant differences were recorded between boxes comprising different
chamber widths (F1, 7 = 0.148, P= 0.714; File S1) and chamber widths was not considered further.
Table 1.
Details and justification of the type of microclimate variables analysed. All four chambers
within a box were analysed, except for T
box_night
and RH where only the front chambers were monitored.
RH data were arcsine transformed for statistical analyses. Replication per chamber was four except
for winter RH where chamber replication in black boxes was six. Statistical comparisons of chamber
temperatures among box designs were restricted between chambers of the same order. For the randomly
selected 5-day periods, the variable means over five days were used for the analysis.
Variable Periods
Investigated Reason
Tbox_max &
Tbox_warmest
(1000–1900 h)
(i) Warmest
summer & winter
day of sampling
period;
(ii) Coolest winter
day of sampling
period;
(iii) Randomly
selected 5-day
period during the
sampling period
(summer & winter).
Tbox_max & Tbox_warmest were considered the most relevant variables to
investigate box temperature as they are considered to be most influential with
regard to eco-physiological implications for bats.
Summer & winter temperature data were collected as these seasons allowed
the investigation of box temperatures among & within box designs during both
warm & cool ambient temperatures.
A randomly selected 5-day period during summer & winter was used to
investigate the ‘average’ box microclimate experienced in these seasons.
Investigating temperature among & within box designs during the periods of
investigation (i.e., warmest day, coolest day & 5-day period) is of particular
relevance to test whether boxes have the potential to cause heat stress (i.e., box
temperatures exceeding the upper thermal tolerance limit) in summer [32,41]
and/or provide beneficial conditions for bats to passively rewarm in summer &
winter [28,42] during both average ambient temperatures & ambient
temperature extremes.
The black plywood box recorded the warmest temperature of the box designs.
After the initial box temperature monitoring, a detailed investigation was
undertaken for this design on the warmest day
(20 November 2015)
during the
subsequent monitoring period. This investigation tested whether a vertical
temperature gradient existed within chambers (using loggers in an upper &
lower position). Of particular interest was whether the vents in the front &
back chambers influenced temperature.

Environments 2019,6, 13 5 of 19
Table 1. Cont.
Variable Periods
Investigated Reason
Mean night
Tbox_night
Randomly selected
5-day period
(2000–0700 h)
during the
maternity season
Tbox_night during the maternity season is of interest as heat retention may
benefit the development of young if boxes are used for maternity
roosting [14,43,44]. An investigation of a 5-day night period was undertaken.
However, the differences between night temperatures were minimal among
box designs (ranging between 0.2 ◦C & 0.9 ◦C) and were considered
inconsequential with regard to bat box selection & box night temperature.
Therefore, this temperature variable was not modelled & is not
considered further.
RHbox_warmest
(1000–1900 h)
Randomly selected
5-day period
during the
sampling period
(summer & winter).
Humidity is of interest as it has the potential to influence evaporative water
loss of bats [
35
]. Humidity has also been identified to differ vastly between tree
hollows & timber nest boxes [31]. The warmest day period was used because
this period was considered to be most relevant for potential eco-physiological
implications for bats.
2.5. Thermal Limits
Reported lower TNZs of Australian tree-cavity roosting bats are scarce. Willis et al. [
45
] reported
a lower TNZ threshold for Vespadelus vulturnus (little forest bat) of 28
◦
C and Morris et al. [
46
] a lower
TNZ for Nyctophilus gouldi (Gould’s long-eared bat) of 30
◦
C. Similarly, little information is known
about the upper thermal tolerance limit of Australian bats. There is some evidence that exposure to
a temperature of >40
◦
C increases body temperature, resting metabolic rates, thermal conductance
and water loss through evaporation [
47
–
49
], although some bats have been observed using roosts
exceeding 40
◦
C [
49
–
51
]. To discuss the documented box temperatures during summer in relation to
thermal limits of bats, a postulated lower TNZ threshold of 30.0
◦
C and an upper thermal tolerance
limit of 40.0 ◦C were used.
2.6. Statistical Analysis
Data were analysed for the variables outlined in Table 1. For the randomly selected 5-day periods,
the five day means of T
box_max
, T
box_warmest
, and RH
box_warmest
were used. The primary samples for
the analysed data were sets of box pairs. Linear mixed effects models [
52
] were employed to separate
the random variation among the samples of box pairs from the random variation among the individual
boxes. When only one measurement was taken on each box, the variation among the individual
boxes comprised the residual variance. Consequently, in models of this type, two random variances
were estimated: the variance among box pairs and the residual variance. In many cases, however,
multiple measurements were taken on each box. In models on data with this structure, three random
variances were estimated: the variance among the box pairs, the variance among the individual boxes
in each pair and the residual variance among the measurements on each box. In some cases, multiple
measurements were taken on each box on each of a sample of days. A further random effect for the
variation among days was fitted in the analyses of such data rather than a fixed effect for day as the
mean differences between days were not of interest. Models were fitted using the Mixed procedure in
SPSS (Version 25).
A model-reduction procedure was employed to identify the final model for each analysis. In each
case, a full-factorial model was initially fitted (including the main effects and all interaction effects up
to third order) which was systematically reduced by elimination of non-significant (
p> 0.05
) effects.
Non-significant effects were eliminated one at a time starting with those of the highest order of
interaction and the highest P-value. If a third order interaction effect was retained in the final model,
its subsidiary two-way effects were also retained and if a two-way effect was retained, its subsidiary
main effects were also retained. The fixed and random effects and their test statistics are reported
for the final model from each analysis (Supplementary Material File S1). Multiple comparison tests
among the levels of factors included in the final models were adjusted for their multiplicity by Sidak’s
method [
53
]. The Sidak correction gives similar, but generally more powerful, results than the better

Environments 2019,6, 13 6 of 19
known Bonferroni correction [
54
]. Apart from presenting the effects and test statistics, the results
are reported in terms of the multiple pairwise comparison tests. Multiple pairwise comparison tests
were conducted in two families: between box designs and between chambers of the same designs.
Records of RH of >70% RH were adjusted to compensate for the reported saturation drift as per
the manufacturer’s equation [
55
]. All RH data were arcsine transformed prior to statistical analysis.
Given the large extent of statistical analysis output, only a summary of the most pertinent data is
provided in the result section to ensure succinctness. References are made to File S1 in which the final
models of all the analyses are shown. The study was carried out with approval from Southern Cross
University Animal Care and Ethics Committee under permit 14/23.
3. Results
3.1. Summer Temperature
3.1.1. Randomly Selected 5-Day Period—Hourly Temperatures
The mean hourly temperature over the 5-day period in summer (16–20 February 2015) showed
that the box designs were warmer than ambient during the night. During the day-period, white box
temperatures followed ambient temperatures closely, whereas the temperatures of the black boxes
were warmer than the white boxes and ambient temperatures (Figure 2).
Environments 2019, 6, x FOR PEER REVIEW 6 of 20
A model-reduction procedure was employed to identify the final model for each analysis. In
each case, a full-factorial model was initially fitted (including the main effects and all interaction
effects up to third order) which was systematically reduced by elimination of non-significant (p >
0.05) effects. Non-significant effects were eliminated one at a time starting with those of the highest
order of interaction and the highest P-value. If a third order interaction effect was retained in the
final model, its subsidiary two-way effects were also retained and if a two-way effect was retained,
its subsidiary main effects were also retained. The fixed and random effects and their test statistics
are reported for the final model from each analysis (Supplementary Material File S1). Multiple
comparison tests among the levels of factors included in the final models were adjusted for their
multiplicity by Sidak’s method [53]. The Sidak correction gives similar, but generally more powerful,
results than the better known Bonferroni correction [54]. Apart from presenting the effects and test
statistics, the results are reported in terms of the multiple pairwise comparison tests. Multiple
pairwise comparison tests were conducted in two families: between box designs and between
chambers of the same designs. Records of RH of >70% RH were adjusted to compensate for the
reported saturation drift as per the manufacturer’s equation [55]. All RH data were arcsine
transformed prior to statistical analysis. Given the large extent of statistical analysis output, only a
summary of the most pertinent data is provided in the result section to ensure succinctness.
References are made to File S1 in which the final models of all the analyses are shown. The study
was carried out with approval from Southern Cross University Animal Care and Ethics Committee
under permit 14/23.
3. Results
3.1. Summer Temperature
3.1.1. Randomly Selected 5-Day Period – Hourly Temperatures
The mean hourly temperature over the 5-day period in summer (16–20 February 2015) showed
that the box designs were warmer than ambient during the night. During the day-period, white box
temperatures followed ambient temperatures closely, whereas the temperatures of the black boxes
were warmer than the white boxes and ambient temperatures (Figure 2).
Figure 2. Warmest chamber temperature in each box design and ambient temperature over 24-h.
Hourly means (±SE) are for the 5-day summer period. ply = plywood; wc = wood-cement.
15
17
19
21
23
25
27
29
31
33
35
37
0 2 4 6 8 10 12 14 16 18 20 22
Temperature (oC)
Hours
Ambient
Black ply
White ply
Black wc
White wc
Figure 2.
Warmest chamber temperature in each box design and ambient temperature over 24-h.
Hourly means (±SE) are for the 5-day summer period. ply = plywood; wc = wood-cement.
5-Day Comparisons—between Designs
The 5-day mean maximum day ambient temperature was 29.3
◦
C
±
1.0 and 27.2
◦
C
±
0.3 for the
mean warmest day period. The final model showed that the two-way interaction effect of box design
by chamber was significant (T
box_max
: F
9, 288.00
= 11.060,
P= <0.001
; T
box_warmest
: F
9, 288.00x
= 12.751,
P= <0.001
). The highest T
box_max
was in the black plywood box (T
box_max
: 35.6
◦
C
±
2.0; T
box_warmest
:
31.6
◦
C
±
1.3), followed by the black wood-cement box (T
box_max
3.2
◦
C cooler and T
box_warmest
2.1
◦
C
cooler) and the two white box designs (T
box_max
~6.0
◦
C and T
box_warmest
~4.5
◦
C cooler than the black
plywood box; Figure 3).
The mixed effect models showed that the comparisons of both T
box_max
and T
box_warmest
between
black (warmer) and white (cooler) designs were significantly different for most chamber comparisons
(File S1). The pairwise comparisons between designs of the same chambers showed that the
black plywood box comprised the most comparison differences. All chambers of this design were
significantly warmer than all chambers of the other three box designs except the fourth (back) chamber
of the black wood-cement design. There were no significant differences between the two white box
designs between any chambers (File S1). The greatest differences were between the front chambers

Environments 2019,6, 13 7 of 19
of the black plywood and the white wood-cement box (5-day T
box_max
difference: 6.3
◦
C; df = 19.82,
P= <0.001; 5-day Tbox_warmest difference: 4.6 ◦C; df = 15.05, P= <0.001; Figure 3; Table 2).
Environments 2019, 6, x FOR PEER REVIEW 7 of 20
5-Day Comparisons—between Designs
The 5-day mean maximum day ambient temperature was 29.3 °C ± 1.0 and 27.2 °C ± 0.3 for the
mean warmest day period. The final model showed that the two-way interaction effect of box design
by chamber was significant (Tbox_max: F9, 288.00 = 11.060, P = <0.001; Tbox_warmest: F9, 288.00x = 12.751, P =
<0.001). The highest Tbox_max was in the black plywood box (Tbox_max: 35.6 °C ± 2.0; Tbox_warmest: 31.6 °C ±
1.3), followed by the black wood-cement box (Tbox_max 3.2 °C cooler and Tbox_warmest 2.1 °C cooler) and
the two white box designs (Tbox_max ~6.0 °C and Tbox_warmest ~4.5 °C cooler than the black plywood box;
Figure 3).
Figure 3. Summary of comparisons of mean (±SE) front chamber temperatures for each box design (n = 4)
during the periods of examination: Tbox_max on warmest summer day (ambient: 35.4 °C), 5-day Tbox_max
(ambient: 29.3 °C ± 1.0) and 5-day Tbox_warmest (ambient: 27.2 °C ± 0.3). ply = plywood; wc =
wood-cement.
The mixed effect models showed that the comparisons of both Tbox_max and Tbox_warmest between
black (warmer) and white (cooler) designs were significantly different for most chamber
comparisons (File S1). The pairwise comparisons between designs of the same chambers showed
that the black plywood box comprised the most comparison differences. All chambers of this design
were significantly warmer than all chambers of the other three box designs except the fourth (back)
chamber of the black wood-cement design. There were no significant differences between the two
white box designs between any chambers (File S1). The greatest differences were between the front
chambers of the black plywood and the white wood-cement box (5-day Tbox_max difference: 6.3 °C; df
= 19.82, P = <0.001; 5-day Tbox_warmest difference: 4.6 °C; df = 15.05, P = <0.001; Figure 3; Table 2).
Table 2. Pairwise comparison of temperatures in front chambers (n = 4) between box designs for
5-day Tbox_max, 5-day Tbox_warmest and warmest day Tbox_max. ply = plywood; wc = wood-cement.
Box design
comparisons
5-day Tbox_max 5-day Tbox_warmest Warmest day Tbox_max
Mean
difference
(°C)
P
Mean
difference
(°C)
P
Mean
difference
(°C)
P
Black ply
White
ply 6.0 <0.001 4.1 <0.001 8.3 0.001
Black wc 3.2 <0.001 2.1 0.004 3.1 0.360
White wc 6.3 <0.001 4.6 <0.001 9.0 <0.001
White
ply
Black wc −2.7 0.001 −2.0 0.007 −5.1 0.033
White wc 0.3 0.997 0.5 0.933 0.8 0.998
25
30
35
40
45
50
Ply black Wc black Ply white Wc white
Temperature (oC)
Warmest day max. T.
5-day max. T.
5-day warmest day period T.
Figure 3.
Summary of comparisons of mean (
±
SE) front chamber temperatures for each box design
(n
=
4) during the periods of examination: T
box_max
on warmest summer day (ambient: 35.4
◦
C), 5-day
T
box_max
(ambient: 29.3
◦
C
±
1.0) and 5-day T
box_warmest
(ambient: 27.2
◦
C
±
0.3). ply = plywood;
wc = wood-cement.
Table 2.
Pairwise comparison of temperatures in front chambers (n = 4) between box designs for 5-day
Tbox_max, 5-day Tbox_warmest and warmest day Tbox_max. ply = plywood; wc = wood-cement.
Box Design Comparisons
5-Day Tbox_max 5-Day Tbox_warmest Warmest Day Tbox_max
Mean
Difference (◦C) PMean
Difference (◦C) PMean
Difference (◦C) P
Black ply
White ply 6.0
<0.001
4.1
<0.001
8.3 0.001
Black wc 3.2
<0.001
2.1 0.004 3.1 0.360
White wc 6.3
<0.001
4.6
<0.001
9.0
<0.001
White ply Black wc −2.7 0.001 −2.0 0.007 −5.1 0.033
White wc 0.3 0.997 0.5 0.933 0.8 0.998
Black wc White wc 3.0
<0.001
2.5 0.007 5.9 0.016
5-Day Comparisons—Chambers within Designs
The greatest difference between chambers within a box design was between the front and
back chamber of the black plywood box (5-day T
box_max
difference: 3.7
◦
C; df = 288.00, P= <0.001;
T
box_warmest
difference: 2.1
◦
C; df = 288.00, P= <0.001; Table 3). Comparisons of 5-day T
box_max
and
5-day T
box_warmest
between chambers within the same box design showed that the black plywood box
comprised the most differences (11 (92%) out of the 12 pairwise comparisons). The black wood-cement
box comprised a significant temperature difference among six comparisons (50%), while the white
plywood box comprised one and the white wood-cement none.
Table 3.
Statistically significant (P= <0.05) pairwise comparison between chamber temperatures within
each box design for 5-day T
box_max
, 5-day T
box_warmest
and warmest day T
box_max
(n = 4 for each
chamber). ply = plywood; wc = wood-cement; 1 = front chamber; 4 = back chamber.
Box Design Chamber
Comparisons
5-day Tbox_max 5-day Tbox_warmest Warmest day Tbox_max
Mean
Difference (◦C) PMean
Difference (◦C) PMean
Difference (◦C) P
Black ply
1
2 1.0 0.015 - - - -
3 2.8
<0.001
1.3
<0.001
3.6 0.001
4 3.7
<0.001
2.3
<0.001
4.5
<0.001
23 1.8
<0.001
1.0
<0.001
- -
4 2.7
<0.001
1.8
<0.001
2.9 0.011
3 4 0.9 0.032 0.8
<0.001
- -

Environments 2019,6, 13 8 of 19
Table 3. Cont.
Box Design Chamber
Comparisons
5-day Tbox_max 5-day Tbox_warmest Warmest day Tbox_max
Mean
Difference (◦C) PMean
Difference (◦C) PMean
Difference (◦C) P
Black wc 1
2 1.2 0.002 0.7 0.001 - -
3 2.0
<0.001
1.2
<0.001
2.5 0.035
4 1.4
<0.001
0.7 0.001 - -
White ply 1 3 - - 0.6 0.008 - -
3.1.2. Maximum Temperature Comparisons on Warmest Day
Between Designs
On the warmest summer day during the sampling period (8 February 2015; max. ambient
35.4
◦
C), the black plywood box recorded the highest T
box_max
, followed by the black wood-cement
box. The two white box designs comprised T
box_max
slightly below that of the maximum ambient
temperature. The greatest temperature difference between ambient and a box design was in the front
chamber of the black plywood box (7.0
◦
C; Figure 3). The final model showed that the two-way
interaction effect of box design by chamber was significant (F9, 36.00 = 2.631, P= 0.019).
The pairwise chamber comparisons of T
box_max
showed that the black plywood box comprised
significantly warmer chambers than the white boxes in chambers one (front), two and three, whereas
there were no significant differences between the chambers of this box compared to the chambers
of the black wood-cement box. The black wood-cement box comprised a significantly warmer front
chamber to that of the front chambers of the two white box designs, while chamber two, three and four
(back) were not significantly different between this design and the white box designs. There were no
significant differences between the two white box designs between any chambers (File S1). The greatest
temperature difference between chambers was within the front chambers of black plywood box and
the white wood-cement box (9.0 ◦C; df = 18.14, P= <0.001; Table 2).
Within Designs
The pairwise chamber comparisons of T
box_max
within the same box design on the warmest
summer’s day during the sampling period showed that the black plywood box comprised the most
significant differences with three of the six pairwise comparisons being significantly different. The black
wood-cement boxes comprised one significantly different chamber comparison and none for the two
white box designs. The greatest difference between chambers within a box design was between the
front and back chamber of the black plywood box (difference: 4.5 ◦C; df = 36.00, P= <0.001; Table 3).
3.1.3. Detailed Investigation of the Black Plywood Box
The detailed investigation of the black plywood box took place following the ones described
above. This investigation examined whether there was a vertical gradient in temperature within
chambers of the box design that recorded the warmest temperatures. On the warmest day during this
sampling (20 November 2015), the T
box_max
measured within the box chambers was close to or above
the ambient temperature of 39.5
◦
C. There was a marked temperature gradient across the chambers
with the rear chamber (chamber 4) being the coolest. The T
box_max
at the upper chamber position was
higher than at the lower position across all chambers. The temperature gradient was less apparent at
the lower position presumably due to the influence of the vent in the first chamber (Figure 4). The final
model showed that there was a significant difference temperature between the upper (42.1
◦
C
±
0.4)
and lower (40.1
◦
C
±
0.4) logger within the front chamber (df = 21.00, P= <0.001), whereas there were
no significant differences within upper and lower logger position in the other three chambers (File S1).

Environments 2019,6, 13 9 of 19
Environments 2019, 6, x FOR PEER REVIEW 9 of 20
The pairwise chamber comparisons of Tbox_max within the same box design on the warmest
summer’s day during the sampling period showed that the black plywood box comprised the most
significant differences with three of the six pairwise comparisons being significantly different. The
black wood-cement boxes comprised one significantly different chamber comparison and none for
the two white box designs. The greatest difference between chambers within a box design was
between the front and back chamber of the black plywood box (difference: 4.5 °C; df = 36.00, P =
<0.001; Table 3).
3.1.3. Detailed Investigation of the Black Plywood Box
The detailed investigation of the black plywood box took place following the ones described
above. This investigation examined whether there was a vertical gradient in temperature within
chambers of the box design that recorded the warmest temperatures. On the warmest day during
this sampling (20 November 2015), the Tbox_max measured within the box chambers was close to or
above the ambient temperature of 39.5 °C. There was a marked temperature gradient across the
chambers with the rear chamber (chamber 4) being the coolest. The Tbox_max at the upper chamber
position was higher than at the lower position across all chambers. The temperature gradient was
less apparent at the lower position presumably due to the influence of the vent in the first chamber
(Figure 4). The final model showed that there was a significant difference temperature between the
upper (42.1 °C ± 0.4) and lower (40.1 °C ± 0.4) logger within the front chamber (df = 21.00, P = <0.001),
whereas there were no significant differences within upper and lower logger position in the other
three chambers (File S1).
Figure 4. Mean (±SE) Tbox_max recorded in four black plywood boxes on 20 November 2015 when the
ambient temperature reached a maximum of 39.5 °C. Loggers were placed in each of the four
chambers at an upper and lower position (15 cm and 45 cm from top respectively). 1 = front chamber;
2 = second chamber; 3 = third chamber; 4 = back chamber.
3.1.4. Comparison of Box Temperatures Vs Thermal Limit Thresholds
The 32-day summer period in which four replicates per box design were monitored resulted in
128 Tbox_max and 128 Tbox_warmest chamber records. The lower TNZ threshold of local bats was hypothesised
to be 30.0 °C. The number of times in which chamber Tbox_warmest exceeded this threshold was highest
for the black plywood box design, followed by the black wood-cement design and the two white box
designs (Figure 5). A few chambers of the black plywood boxes exceeded 35 °C during Tbox_warmest,
whereas only one chamber of the black wood-cement boxes exceeded this threshold and none of the
chambers of the two white box designs (Figure 5). Tbox_warmest did not exceed 40.0 °C (hypothesised
upper thermal tolerance limit) in any of the box designs (Figure 5). A similar pattern was
documented for Tbox_max over the 32-days monitoring period, although, as would be expected, the
frequency of chambers for all designs exceeding the 30 °C and 35 °C thresholds was higher. The only
39
40
41
42
43
1234
Temperature (oC)
Chambers
lower upper
Figure 4.
Mean (
±
SE) T
box_max
recorded in four black plywood boxes on 20 November 2015 when the
ambient temperature reached a maximum of 39.5
◦
C. Loggers were placed in each of the four chambers
at an upper and lower position (15 cm and 45 cm from top respectively). 1 = front chamber; 2 = second
chamber; 3 = third chamber; 4 = back chamber.
3.1.4. Comparison of Box Temperatures Vs Thermal Limit Thresholds
The 32-day summer period in which four replicates per box design were monitored resulted
in 128 T
box_max
and 128 T
box_warmest chamber
records. The lower TNZ threshold of local bats was
hypothesised to be 30.0
◦
C. The number of times in which chamber T
box_warmest
exceeded this threshold
was highest for the black plywood box design, followed by the black wood-cement design and the
two white box designs (Figure 5). A few chambers of the black plywood boxes exceeded 35
◦
C during
T
box_warmest
, whereas only one chamber of the black wood-cement boxes exceeded this threshold and
none of the chambers of the two white box designs (Figure 5). T
box_warmest
did not exceed 40.0
◦
C
(hypothesised upper thermal tolerance limit) in any of the box designs (Figure 5). A similar pattern
was documented for T
box_max
over the 32-days monitoring period, although, as would be expected, the
frequency of chambers for all designs exceeding the 30
◦
C and 35
◦
C thresholds was higher. The only
records of chambers exceeding a T
box_max
of 40
◦
C during the 32-day monitoring period were in the
first (17%) and second (8%) chambers of the black plywood design (Figure 5).
Environments 2019, 6, x FOR PEER REVIEW 10 of 20
records of chambers exceeding a Tbox_max of 40 °C during the 32-day monitoring period were in the
first (17%) and second (8%) chambers of the black plywood design (Figure 5).
Figure 5. Percentage of chambers where chamber temperatures during Tbox_warmest (left) and Tbox_max
(right) reached >30.0 °C (white bars), >35 °C (black bars) and >40 °C (red bars) during the 32-day
monitoring period (5 February–8 March 2015). X-axis: 1 = front chamber; 2 = second chamber; 3 =
third chamber; 4 = back chamber; ply = plywood; wc = wood-cement.
3.2. Winter Temperature
3.2.1. Randomly Selected 5-Day Period – Hourly Temperatures
Similar to the summer investigation, the winter mean hourly temperature over the 5-day period
(10–14 August 2015) showed that the box designs were warmer than the ambient temperature
during the night. During the day, the temperatures of the two white box designs and the black
wood-cement box closely resembled ambient temperature, whereas the temperature of the black
plywood box was higher than the other box designs and ambient temperature (Figure 6).
Figure 6. Warmest chamber mean (±SE) temperature in each box design and ambient temperature
over 24-h. Hourly means are for the 5-day winter period. ply = plywood; wc = wood-cement.
5-Day Comparison – between Designs
The 5-day mean maximum day ambient temperature was 18.3 °C ± 0.8 and 15.6 °C ± 0.4 for the
mean warmest day period. The final model showed that the two-way interaction effect of box design
by chamber was significant (Tbox_max: F9, 288.000 = 48.070, P = <0.001; Tbox_warmest: F9, 288.000 = 27.497, P =
-2
0
2
4
6
8
10
12
14
16
18
20
22
24
26
0 2 4 6 8 10121416182022
Temperature (oC)
Hours
Ambient
Black ply
White ply
Black wc
White wc
0
10
20
30
40
50
60
70
80
90
100
1234123412341234
Black
ply
White
ply
Black wc White wc
Chambers (%)
Box types and chambers
0
10
20
30
40
50
60
70
80
90
100
1234123412341234
Black
ply
White
ply
Black wc White wc
Chambers (%)
Box types and chambers
Figure 5.
Percentage of chambers where chamber temperatures during T
box_warmest
(left) and T
box_max
(right) reached >30.0
◦
C (white bars), >35
◦
C (black bars) and >40
◦
C (red bars) during the 32-day
monitoring period (5 February–8 March 2015). X-axis: 1 = front chamber; 2 = second chamber; 3 = third
chamber; 4 = back chamber; ply = plywood; wc = wood-cement.

Environments 2019,6, 13 10 of 19
3.2. Winter Temperature
3.2.1. Randomly Selected 5-Day Period—Hourly Temperatures
Similar to the summer investigation, the winter mean hourly temperature over the 5-day period
(10–14 August 2015) showed that the box designs were warmer than the ambient temperature during
the night. During the day, the temperatures of the two white box designs and the black wood-cement
box closely resembled ambient temperature, whereas the temperature of the black plywood box was
higher than the other box designs and ambient temperature (Figure 6).
Environments 2019, 6, x FOR PEER REVIEW 10 of 20
records of chambers exceeding a Tbox_max of 40 °C during the 32-day monitoring period were in the
first (17%) and second (8%) chambers of the black plywood design (Figure 5).
Figure 5. Percentage of chambers where chamber temperatures during Tbox_warmest (left) and Tbox_max
(right) reached >30.0 °C (white bars), >35 °C (black bars) and >40 °C (red bars) during the 32-day
monitoring period (5 February–8 March 2015). X-axis: 1 = front chamber; 2 = second chamber; 3 =
third chamber; 4 = back chamber; ply = plywood; wc = wood-cement.
3.2. Winter Temperature
3.2.1. Randomly Selected 5-Day Period – Hourly Temperatures
Similar to the summer investigation, the winter mean hourly temperature over the 5-day period
(10–14 August 2015) showed that the box designs were warmer than the ambient temperature
during the night. During the day, the temperatures of the two white box designs and the black
wood-cement box closely resembled ambient temperature, whereas the temperature of the black
plywood box was higher than the other box designs and ambient temperature (Figure 6).
Figure 6. Warmest chamber mean (±SE) temperature in each box design and ambient temperature
over 24-h. Hourly means are for the 5-day winter period. ply = plywood; wc = wood-cement.
5-Day Comparison – between Designs
The 5-day mean maximum day ambient temperature was 18.3 °C ± 0.8 and 15.6 °C ± 0.4 for the
mean warmest day period. The final model showed that the two-way interaction effect of box design
by chamber was significant (Tbox_max: F9, 288.000 = 48.070, P = <0.001; Tbox_warmest: F9, 288.000 = 27.497, P =
-2
0
2
4
6
8
10
12
14
16
18
20
22
24
26
0 2 4 6 8 10121416182022
Temperature (oC)
Hours
Ambient
Black ply
White ply
Black wc
White wc
0
10
20
30
40
50
60
70
80
90
100
1234123412341234
Black
ply
White
ply
Black wc White wc
Chambers (%)
Box types and chambers
0
10
20
30
40
50
60
70
80
90
100
1234123412341234
Black
ply
White
ply
Black wc White wc
Chambers (%)
Box types and chambers
Figure 6.
Warmest chamber mean (
±
SE) temperature in each box design and ambient temperature
over 24-h. Hourly means are for the 5-day winter period. ply = plywood; wc = wood-cement.
5-Day Comparison—between Designs
The 5-day mean maximum day ambient temperature was 18.3
◦
C
±
0.8 and 15.6
◦
C
±
0.4
for the mean warmest day period. The final model showed that the two-way interaction effect
of box design by chamber was significant (T
box_max
: F
9, 288.000
= 48.070, P= <0.001; T
box_warmest
:
F
9, 288.000
= 27.497, P= <0.001). The highest 5-day box temperatures were in the black plywood box
(T
box_max
: 2
5.3 ◦C±1.5
; T
box_warmest
: 19.8
◦
C
±
0.6), followed by the black wood-cement box (5.5
◦
C
(T
box_max
) and 2.9
◦
C (T
box_warmest
) cooler) and the two white box designs (~7.5
◦
C (T
box_max
) and
~5.0 ◦C (Tbox_warmest) cooler than the black plywood box; Figure 7).
Environments 2019, 6, x FOR PEER REVIEW 11 of 20
<0.001). The highest 5-day box temperatures were in the black plywood box (Tbox_max: 25.3 °C ± 1.5;
Tbox_warmest: 19.8 °C ± 0.6), followed by the black wood-cement box (5.5 °C (Tbox_max) and 2.9 °C
(Tbox_warmest) cooler) and the two white box designs (~ 7.5 °C (Tbox_max) and ~5.0 °C (Tbox_warmest) cooler
than the black plywood box; Figure 7).
Figure 7. Summary of comparisons of front chamber mean (±se) maximum temperatures for each
design (n = 4) during the periods of examination: Tbox_max on warmest winter day (ambient: 24.0 °C),
Tbox_max on coolest winter day (ambient: 12.5 °C), 5-day Tbox_max (ambient: 18.3 °C ± 0.8) and 5-day
Tbox_warmest (mean ambient 15.6 °C ± 0.4). ply = plywood; wc = wood-cement.
The mixed effect models showed that the pairwise comparisons of both Tbox_max and Tbox_warmest
between black and white box designs were significantly different for all comparisons (File S1). As for
the summer 5-day investigation, the pairwise comparisons showed that all chambers of the black
plywood design were significantly warmer than all chambers of the other three box designs except
the fourth (back) chamber of the black wood-cement design. Comparisons between the two white
box designs did not result in significant temperature differences between any chambers (File S1).
The greatest differences were between the front chambers of the black plywood and the white
wood-cement box (5-day Tbox_max difference: 7.9 °C; df = 34.44, P = <0.001; 5-day Tbox_warmest difference:
4.8 °C; df = 23.57, P = <0.001; Figure 7; Table 4).
Table 4. Pairwise comparison of temperature in front chambers between box designs for 5-day
Tbox_max, 5-day Tbox_warmest, Tbox_max warmest day and Tbox_max coolest day. ply = plywood; wc =
wood-cement.
Box design
comparisons
5-day Tbox_max 5-day Tbox_warmest Tbox_max warmest day Tbox_max coolest day
Mean
difference
(°C)
P
Mean
difference
(°C)
P
Mean
difference
(°C)
P
Mean
difference
(°C)
P
Black
ply
White ply 7.4 <0.001 4.7 <0.001 4.7 <0.001 8.1 <0.001
Black wc 5.5 <0.001 2.9 <0.001 3.1 <0.001 6.1 <0.001
White wc 7.9 <0.001 4.8 <0.001 4.9 <0.001 8.5 <0.001
White
ply
Black wc −2.0 <0.001 −1.8 <0.001 −1.6 0.005 −2.0 0.002
White wc 0.5 0.656 0.1 0.997 0.1 1.000 0.4 0.973
Black
wc White wc 2.4 <0.001 19 <0.001 1.8 0.002 2.4 <0.001
10
15
20
25
30
Ply black Wc black Ply white Wc white
Temperature (oC)
Warmest day max. T.
5-day max. T.
5-day warmest day period T.
Coolest day max. T.
Figure 7.
Summary of comparisons of front chamber mean (
±
se) maximum temperatures for each
design (n = 4) during the periods of examination: T
box_max
on warmest winter day (ambient: 24.0
◦
C),
T
box_max
on coolest winter day (ambient: 12.5
◦
C), 5-day T
box_max
(ambient: 18.3
◦
C
±
0.8) and 5-day
Tbox_warmest (mean ambient 15.6 ◦C±0.4). ply = plywood; wc = wood-cement.

Environments 2019,6, 13 11 of 19
The mixed effect models showed that the pairwise comparisons of both T
box_max
and T
box_warmest
between black and white box designs were significantly different for all comparisons (File S1). As for the
summer 5-day investigation, the pairwise comparisons showed that all chambers of the black plywood
design were significantly warmer than all chambers of the other three box designs except the fourth
(back) chamber of the black wood-cement design. Comparisons between the two white box designs
did not result in significant temperature differences between any chambers (File S1). The greatest
differences were between the front chambers of the black plywood and the white wood-cement
box (5-day T
box_max
difference: 7.9
◦
C; df = 34.44, P= <0.001; 5-day T
box_warmest
difference: 4.8
◦
C;
df = 23.57, P= <0.001; Figure 7; Table 4).
Table 4.
Pairwise comparison of temperature in front chambers between box designs for 5-day T
box_max
,
5-day T
box_warmest
, T
box_max
warmest day and T
box_max
coolest day. ply = plywood; wc = wood-cement.
Box Design
Comparisons
5-Day Tbox_max 5-Day Tbox_warmest Tbox_max warmest day Tbox_max coolest day
Mean
Difference
(◦C)
P
Mean
Difference
(◦C)
P
Mean
Difference
(◦C)
P
Mean
Difference
(◦C)
P
Black ply
White ply 7.4 <0.001 4.7 <0.001 4.7 <0.001 8.1 <0.001
Black wc 5.5 <0.001 2.9 <0.001 3.1 <0.001 6.1 <0.001
White wc 7.9 <0.001 4.8 <0.001 4.9 <0.001 8.5 <0.001
White ply Black wc −2.0 <0.001 −1.8 <0.001 −1.6 0.005 −2.0 0.002
White wc 0.5 0.656 0.1 0.997 0.1 1.000 0.4 0.973
Black wc White wc 2.4 <0.001 19 <0.001 1.8 0.002 2.4 <0.001
5-Day Comparison–Chambers within Designs
Comparisons between chambers within the same box design showed that the black plywood box
comprised the most significant 5-day T
box_max
and T
box_warmest
temperature differences, with 10 (83%)
of the 12 comparisons being significant. The black wood-cement box comprised four (33%) significantly
different chamber comparisons, whereas none of the chambers significantly differed in temperature
within the white boxes. The greatest temperature difference between chambers within a box design
was between the front and back chamber of the black plywood box (5-day T
box_max
difference: 5.7
◦
C;
df = 288.00, P= <0.001; Tbox_warmest difference: 2.9 ◦C; df = 288.00, P= <0.001; Table 5).
Table 5.
Statistically significant (P= <0.05) pairwise comparison between chambers within each box
designs for 5-day T
box_max
, 5-day T
box_warmest
, warmest day T
box_max
, coolest day T
box_max
, (
n=4
for each chamber). ply = plywood; wc = wood-cement; 1 = front chamber; 4 = back chamber.
Box
Design
Chamber
Comparison
5-Day Tbox_max 5-Day Tbox_warmest Tbox_max warmest day Tbox_max coolest day
Mean
Difference
(◦C)
P
Mean
Difference
(◦C)
P
Mean
Difference
(◦C)
P
Mean
Difference
(◦C)
P
Black ply 1
2 2.5 <0.001 1.3 <0.001 1.3 <0.001 2.4 <0.001
3 5.0 <0.001 2.5 <0.001 3.2 <0.001 5.4 <0.001
4 5.7 <0.001 2.9 <0.001 3.3 <0.001 6.4 <0.001
23 2.5 <0.001 1.2 <0.001 1.9 <0.001 3.0 <0.001
4 3.2 <0.001 1.6 <0.001 2.0 <0.001 4.0 <0.001
Black wc 1 2 1.1 0.001 0.7 0.003 - - - -
2 4 −0.9 0.003 −0.6 0.014 - - - -
3.2.2. Maximum Temperature Comparisons on Warmest and Coolest Day
Between Designs
On the warmest day (max. ambient 24.0
◦
C) and coolest day (max. ambient 12.5
◦
C) in winter,
the chambers of the black plywood box recorded the highest T
box_ max
and were up to 3.5
◦
C on the
warmest and 8.2
◦
C on the coolest day above maximum ambient temperature. The T
box_max
of the

Environments 2019,6, 13 12 of 19
black wood-cement box chambers were slightly above maximum ambient temperature, whereas the
white box designs were slightly below (Figure 7; File S1).
The final model showed that the two-way interaction effect of box design by chamber was
significant (warmest day T
box_max
: F
9, 36.000
= 20.492, P= <0.001; coolest day T
box_max
: F
9, 36.000
= 18.868,
P= <0.001). The black plywood box was significantly warmer compared to the black wood-cement
boxes in six (75%) of the eight chamber comparisons, whereas there were no significant differences
between the chambers of the two white box designs (File S1). The greatest temperature difference was
between the front chambers of the black plywood box and the white wood-cement box (warmest day
T
box_max
difference: 4.9
◦
C; df = 22.64, P= <0.001; coolest day; T
box_max
difference: 8.5
◦
C; df = 46.68,
P= <0.001; Figure 7; Table 4). The mixed effect models for T
box_max
showed that 11 (69%) pairwise
comparisons between the chamber temperatures of black (warmer boxes) and white box designs were
significantly different on the warmest day (88% (7) for black plywood; 50% (4) for black wood-cement)
and 12 (75%) pairwise comparisons on the coolest day (100% (8) for black plywood; 50% (4) for black
wood-cement; File S1).
Within Designs
On the warmest and coolest winter day, the pairwise comparisons among chambers within
the box designs significantly differed only within the black plywood box. The greatest difference
between chambers within this design was between the front and back chamber. On the warmest day,
the T
box_max
difference was 3.3
◦
C (df = 36.00, P= <0.001) and 6.4
◦
C on the coolest day (
df = 36.00
;
P= <0.001; Table 5).
3.3. Relative Humidity—Summer and Winter
Over the randomly selected 5-day summer and winter sampling periods, ambient RH was higher
at night than in boxes. In summer, the black plywood box (front chamber data) comprised a similar
RH during the daytime to that of ambient RH, whereas the other three box designs were slightly above
ambient RH during most parts of the daytime (Figure 8). In winter, the difference in RH between the
white (higher RH) and black (lower RH) box designs (particular the black plywood box) was markedly
higher during the daytime (Figure 8).
Environments 2019, 6, x FOR PEER REVIEW 13 of 20
the Tbox_max difference was 3.3 °C (df = 36.00, P = <0.001) and 6.4 °C on the coolest day (df = 36.00; P =
<0.001; Table 5).
3.3. Relative Humidity—Summer and Winter
Over the randomly selected 5-day summer and winter sampling periods, ambient RH was
higher at night than in boxes. In summer, the black plywood box (front chamber data) comprised a
similar RH during the daytime to that of ambient RH, whereas the other three box designs were
slightly above ambient RH during most parts of the daytime (Figure 8). In winter, the difference in
RH between the white (higher RH) and black (lower RH) box designs (particular the black plywood
box) was markedly higher during the daytime (Figure 8).
In summer, the ambient RH for the 5-day ‘warmest day period’ was 50.9% ± 2.2. The final
model showed that the effect of box design was significant for both summer (F3, 10.208 = 150.831, P =
<0.001) and winter (F3, 12.000 = 50.782, P = <0.001) during RHbox_warmest. The highest RHbox_warmest was
recorded in the white wood-cement box (55.8% ± 0.8), followed by the white plywood (2.1% lower),
the black wood-cement (5.0% lower) and the black plywood (10.1% lower). In winter, the 5-day
‘warmest day period’ ambient RH was 72.1% ± 2.0. The highest RHbox_warmest was in the white
wood-cement box (78.1% ± 0.4), followed closely by the white plywood (1.2% lower), the black
wood-cement (8.7% lower) and the black plywood (22.9% lower). The mixed effect models showed
that the pairwise comparisons were significant between the designs during both the summer and the
winter sampling periods, except between the two white boxes (Table 6).
Figure 8. Mean front chamber RH in each box design and ambient RH. Left: 5-day summer hourly
means (±SE) (n = 6 for each plywood box design; n = 4 for each wood-cement box design). Right:
5-day winter hourly means (±SE) (n = 4 for each box design). ply = plywood; wc = wood-cement.
Table 6. Pairwise comparison of box designs in front chambers for ‘warmest day period’ RH over the
5-day period for summer and winter. ply = plywood; wc = wood-cement.
Box design comparisons Summer RH Winter RH
Mean difference (%) P Mean difference (%) P
Black ply
White ply −8.0 <0.001 −21.7 <0.001
Black wc −5.1 <0.001 −14.2 <0.001
White wc −10.1 <0.001 −22.9 <0.001
White ply Black wc 3.0 0.014 7.5 0.010
White wc −2.1 0.086 −1.2 0.989
Black wc White wc −5.0 <0.001 −8.7 0.003
30
40
50
60
70
80
90
100
0246810121416182022
Relative humidity (%)
Hours
Ambient
Black ply
White ply
Black wc
White wc
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14 16 18 20 22
Relative humidity (%)
Hours
Ambient
Black ply
White ply
Black wc
White wc
Figure 8.
Mean front chamber RH in each box design and ambient RH.
Left
: 5-day summer hourly
means (
±
SE) (n = 6 for each plywood box design; n = 4 for each wood-cement box design).
Right
:
5-day winter hourly means (±SE) (n = 4 for each box design). ply = plywood; wc = wood-cement.
In summer, the ambient RH for the 5-day ‘warmest day period’ was 50.9%
±
2.2. The final
model showed that the effect of box design was significant for both summer (F
3, 10.208
= 150.831,
P= <0.001) and winter (F
3, 12.000
= 50.782, P= <0.001) during RH
box_warmest
. The highest RH
box_warmest

Environments 2019,6, 13 13 of 19
was recorded in the white wood-cement box (55.8%
±
0.8), followed by the white plywood (2.1%
lower), the black wood-cement (5.0% lower) and the black plywood (10.1% lower). In winter, the
5-day ‘warmest day period’ ambient RH was 72.1%
±
2.0. The highest RH
box_warmest
was in the
white wood-cement box (78.1%
±
0.4), followed closely by the white plywood (1.2% lower), the black
wood-cement (8.7% lower) and the black plywood (22.9% lower). The mixed effect models showed
that the pairwise comparisons were significant between the designs during both the summer and the
winter sampling periods, except between the two white boxes (Table 6).
Table 6.
Pairwise comparison of box designs in front chambers for ‘warmest day period’ RH over the
5-day period for summer and winter. ply = plywood; wc = wood-cement.
Box Design Comparisons
Summer RH Winter RH
Mean
Difference (%) PMean
Difference (%) P
Black ply
White ply −8.0 <0.001 −21.7 <0.001
Black wc −5.1 <0.001 −14.2 <0.001
White wc −10.1 <0.001 −22.9 <0.001
White ply Black wc 3.0 0.014 7.5 0.010
White wc −2.1 0.086 −1.2 0.989
Black wc White wc −5.0 <0.001 −8.7 0.003
4. Discussion
The deployment of bat box designs that differ in thermal profiles and the use of boxes that
offer a thermal gradient within the box itself is likely an important factor for boxes to be a suitable
artificial roost resource for heterothermic bats. Box microclimate is considered particularly important
during ambient temperature extremes [
32
,
41
,
56
] and for energy conservation, such as through
passive rewarming from torpor [
28
,
57
] and through warm roosts for dependent young and lactating
females [14,43].
The black plywood box provided the warmest box temperatures of the four designs, followed
by the black wood-cement box. Temperatures between the two black box designs were frequently
significantly different, particularly for the front chamber comparisons. The two white box designs
recorded similar box temperatures among them. Differing exterior colours (black boxes facing
afternoon sun and white boxes facing morning sun), box construction materials, multiple chambers
(chamber sequence) and chamber vents were shown to influence temperatures between box designs
and within box designs, both in summer and winter.
4.1. Box Colour
Box colour consistently influenced T
box_max
and T
box_warmest
, with black boxes being warmer
than white boxes in both summer and winter. The influence of box colour on temperature is expected
to have been amplified by box aspect with black boxes facing the afternoon sun and white boxes
facing the morning sun. Previous studies have shown that differing box colours influenced box
temperature significantly (Kerth et al. [
18
] comparing black and white wood-cement boxes; Lourenço
and Palmeirim [
19
] comparing black, green and white plywood boxes; Doty et al. [
28
] comparing black
and white plywood boxes; Griffiths et al. [
30
] comparing white and green plywood boxes). In contrast,
Goldingay [
58
] found no significant temperature difference between brown and green timber nest
boxes. The maximum difference in T
box_max
of boxes made from the same construction material but
differing in exterior colour was 8.3
◦
C (summer) and 8.1
◦
C (winter) between the plywood boxes and
3.3
◦
C (summer) and 2.4
◦
C (winter) between the wood-cement boxes. The difference between the
plywood boxes in summer is similar to that reported by Lourenço and Palmeirim [
19
] (mean maximum
temperature difference: 9.2
◦
C between black and white boxes; Portugal). In contrast, a study carried
out in Germany, Kerth et al. [18] reported that during summer, the maximum temperature difference

Environments 2019,6, 13 14 of 19
between sun-exposed white and black wood-cement boxes was up to 20
◦
C and up to 4.4
◦
C between
shaded boxes during summer.
4.2. Box Construction Materials
Bideguren et al. [
56
] investigated the internal temperatures of bat box designs made from
different construction materials in a Mediterranean climate. In other climates, the investigation
of box temperature differences between plywood, a commonly used construction material in Australia
and North America [
22
,
59
] and wood-cement, a commonly used material in Europe [
22
], has not been
assessed in detail. Rueegger et al. [
60
] reported that T
box_max
and T
box_warmest
of shaded and different
coloured nest boxes made from plywood, polyvinyl chloride and wood-cement boxes did not differ
significantly during cooler seasons. Studies reported that tree hollows are cooler and have a greater
buffer capacity from ambient temperature than timber boxes [
31
,
32
] or white and black wood-cement
boxes [18].
Wood-cement reduced the effect of black exterior colour for warm box temperature compared to
plywood. This resulted in the black wood-cement box adding an additional variation of available box
microclimate, recording lower temperatures to that of the black plywood box but higher temperatures
to that of the white boxes. The difference during the 5-day T
box_warmest
period between the black boxes
was greater during winter (5.5
◦
C) compared to summer (3.2
◦
C). In contrast, box material had little
influence on microclimate when painted white.
4.3. Multiple Chambers and Vents
This study investigated potential temperature gradients within box designs, that is, between
chambers and within chambers. Providing a temperature range within a box is likely important
for bats to select suitable temperatures throughout the day [
17
,
19
,
50
]. Temperature differences were
significant between chambers of the black plywood box (maximum difference: 6.4
◦
C), whereas
significant temperature differences between the chambers were sporadic for the black wood-cement
box and practically absent for the white box designs (Tables 3and 5). The detailed investigation of the
black plywood box during the warmest day of the sampling period showed that the front chamber of
this box comprised a 2.1
◦
C warmer maximum temperature in the upper section of the chamber to that
of the lower section. The localised cooling effect in the lower section of the chamber was likely due to
the chamber’s vent. A previous study conducted in the Midwest region of the USA also documented
temperature differences within boxes [
61
]. They found that two of their box designs could differ by
more than 10
◦
C between upper and lower portions of the boxes during warm and clear days. Both of
these designs used multiple chambers and one design also contained vents. These data show that
boxes can be designed to provide a large thermal range within the box and thus, reduce the likelihood
of the entire box comprising temperatures above the thermal tolerance limit of bats.
4.4. Suitability of Recorded Box Temperatures for Bats
4.4.1. Maternity Roosts
Given the importance of maternity roosts to sustain viable populations and the low use of bat
boxes to rear young by many species, designing bat boxes suitable for maternity roosting is crucial [
22
].
It is likely that a warm thermal profile of a box is one factor selected by breeding females. The data
indicate that at the study area, black painted boxes (facing the afternoon sun) are likely most suitable
for maternity roosting during average ambient temperatures. Black boxes, in particular the front
chamber of the black plywood box, most frequently provided temperatures within the postulated
thermal limits (30.0 to 40.0
◦
C) and for the longest day period. In addition, the vent for the front
chamber and the multiple chambers of the black plywood box resulted in a thermal gradient, providing
cooler areas to that of the upper section of the front chamber. In very warm climates, box designs

Environments 2019,6, 13 15 of 19
that facilitate warm roosts, such as the black boxes tested here, are unlikely to be suitable during hot
ambient conditions [41,49,56] with dependent young particularly vulnerable to heat stress.
The tested box designs did not allow for bats to access different chambers internally
(following [
34
]). It is unknown if bats migrate to different chambers during the day through the
entrances at the bottom of the chambers. This aspect should be investigated to ensure bats are able to
make use of the thermal gradient within a multi-chambered box during the day. If access between
chambers within the box were to be provided, this may reduce the intended thermal differences among
chambers. Extending the external front and side panels by a few centimetres below the bottom edge of
the internal chamber panels would offer some protection for bats to switch chambers via the bottom
entrances during the day.
4.4.2. Day Roosts Other Than Maternity Roosts
There is evidence that heterothermic bats are well adapted to roosting in conditions where ambient
temperatures are below the TNZ [
62
] and are known to employ torpor extensively to reduce energy
costs [
28
,
62
,
63
]. Bats may select roosts that facilitate torpor [
64
,
65
]. Such roosts may be thermally
labile that allow passive rewarming from sun exposure [
12
,
57
,
62
]. Doty et al. [
28
] showed that
N. gouldi selected warm boxes in winter to passively rewarm from torpor to increase the time spent
normothermic and increase the active time at night. Therefore, the black boxes tested, particularly the
black plywood box, are likely to provide energy budget benefits for bats that use passive rewarming
during cool ambient temperatures.
4.4.3. Thermal Limits and Box Temperature
Little information is available on how well Australian tree-cavity roosting bats cope with high
temperature extremes. Bats in hot Australian regions are believed to cope well with warm roost
temperatures [
49
,
62
]. During the 32-day monitoring period in summer, no chamber of any box design
exceeded 40
◦
C during T
box_warmest
. T
box_max
exceeded 40
◦
C in the front chamber of the black plywood
box on 22 (17%) occasions and on eight (6%) occasions in the second chamber but never in the third and
back chamber or in the other box designs. In contrast, when the black plywood box was investigated
in more detail the following summer, T
box_max
on the warmest day exceeded 40
◦
C in the upper section
of all chambers and the loggers measuring temperatures at the lower section of the chambers were
either just above or just below 40 ◦C (Figure 4).
It is unclear if short durations of temperatures over 40.0
◦
C are detrimental to bats [
50
,
51
,
66
]
and likely varies between species and location [
19
,
49
]. Some bat box studies conducted in warm
climates have raised concerns that bat boxes become lethal during hot ambient conditions [
41
,
56
],
with Hoeh et al. [
61
] recording box temperatures of up to 61
◦
C. The data obtained in this study
indicates that at the study site, box temperatures experienced in black boxes (with an afternoon sun
aspect) installed on poles with a natural groundcover underneath, were suitable for bats on an average
summer day (mean maximum: 29.7
◦
C). However, during spells of very hot ambient temperatures or
in climates experiencing warmer ambient temperatures to that at the study site, the availability of box
designs buffering from very hot ambient temperatures and providing a thermal gradient are important.
This study indicated that: white boxes, box materials that buffer warm ambient temperature (e.g.,
wood-cement over plywood) and box designs that comprise a temperature gradient within the box
(e.g., multiple chambers with vents) can negate hot ambient temperature to some extent. Consideration
of these box design elements and identifying other design elements to further improve the buffering
capacity from extreme heat [
56
,
67
] may be particularly important given the predicted climate warming
and increased periods of extreme heat [68].
4.5. Relative Humidity
Humidity has the potential to influence the evaporative water loss of bats [
35
]. However, it
is unclear whether RH is a factor in roost selection with roost humidity likely influenced by the

Environments 2019,6, 13 16 of 19
presence of bats, particularly where bats congregate in colonies [
25
]. Both box colour and box material
influenced RH. Box material was shown to influence RH for black boxes but not for white boxes.
The black plywood and black wood-cement box differed significantly during the 5-day RH
box_warmest
(black plywood 5.1% (summer) and 14.2% (winter) drier than black wood-cement), whereas the white
plywood and the white wood-cement box did not differ significantly. In addition, the comparisons
showed that white boxes (with a morning sun aspect) provided higher RH conditions than black
boxes (with an afternoon sun aspect; maximum difference between the 5-day RH
box_warmest
in summer:
10.1%; winter: 22.9%). It is likely that the higher RH recorded in the white boxes mimic natural roosts
more closely. A previous study on timber nest boxes documented boxes to provide lower mean daily
RH (mean 76–78%) to that of tree hollows (mean 90%) [
31
], indicating that boxes do not closely mimic
RH of tree hollows.
5. Management Implications
Roost temperatures can influence bat thermoregulation and energy expenditure during both
summer and winter. This study showed that box design elements can be used to influence box
temperature. Bat thermoregulatory theory and some empirical evidence [
18
,
19
,
28
] support the view
that black boxes (facing an afternoon sun aspect) are likely more suitable for passive rewarming during
temperatures below the TNZ, as well as for maternity roosting in climates with cool and moderate
temperatures, except during periods of ambient temperature extremes. This is also supported by the
data obtained in this study. However, there is a lack of detailed knowledge of thermal roost preferences
by bats and preferences may differ between sexes, seasons and species.
When devising a bat box program in cool and moderate climates, the use of a variety of box designs
that provide differing microclimates and offer an internal thermal gradient should be considered.
Deploying paired black (comprising a thermal gradient) and white multi-chambered boxes may be
a suitable approach. In very warm climates, however, black boxes should be avoided altogether as
they can become ecological traps (see [
56
] for details). Even in moderately warm climates, such as at
the study site, the use of black box designs that provide limited internal thermal gradients should be
considered with caution, particularly in light of the predicted increase of days of extreme heat [
68
].
Furthermore, the placement of boxes should also be considered when deploying bat boxes, such as
installing boxes in a variety of aspects and a variety of sun and shade exposed locations [18,69].
This study used wood-cement as a bat box material for the first time in Australia. Black painted
wood-cement boxes were shown to diversify box microclimate compared to the other designs tested,
being warmer than the two white box designs and cooler than the black plywood design. Wood-cement
is likely a suitable alternative construction material to that of plywood in temperate Australia but its
use by bats remains to be documented. This material has the potential to reduce box maintenance costs
for long-term box programs compared to the commonly used plywood boxes [
22
,
60
]. More research
is required to test box design elements further, including wood-cement and voluminous-type boxes,
across differing climates. Additional artificial hollow provision methods such as mechanical creation
of hollows into trees [
70
,
71
] and large bat ‘houses’ [
34
,
56
] should also be further advanced and tested.
Supplementary Materials:
The following are available online at http://www.mdpi.com/2076-3298/6/2/13/s1.
Funding:
This research was financially supported by the Holsworth Wildlife Research Endowment and the MA
Ingram Trust.
Acknowledgments:
I thank Brad Law and Linda Rueegger for the review of the manuscript and Ross Goldingay
for his comments on sections of an earlier draft. I thank the mine’s land management officer for his support
throughout the project and three anonymous reviewers for their comments that greatly improved this manuscript.
Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the
study; in the collection, analyses or interpretation of data; in the writing of the manuscript or in the decision to
publish the results.

Environments 2019,6, 13 17 of 19
References
1.
Calder, C.A. Microhabitat selection during nesting of humming birds in the Rocky Mountains. Ecology
1973
,
54, 127–134. [CrossRef]
2.
With, K.A.; Webb, D.R. Microclimate of ground nests: The relative importance of radiative cover and
windbreaks for three grassland species. Condor 1993,95, 401–413. [CrossRef]
3. Schmidt-Nielson, K. Animal Physiology, 5th ed.; Cambridge University Press: Cambridge, UK, 1997.
4.
Speakman, J.R.; Thomas, D.W. Physiological ecology and energetics of bats. In Bat Ecology; Kunz, T.,
Fenton, M., Eds.; The University of Chicago Press: Chicago, IL, USA, 2003; pp. 430–492.
5.
Roverud, R.C.; Chappell, M.A. Energetic and thermoregulatory aspects of clustering behaviour in the
Neotropical bat Noctilio albiventris.Physiol. Zool. 1991,74, 1527–1541. [CrossRef]
6.
Sano, A. Postnatal growth and development of thermoregulative ability in the Japanese greater horseshoe
bat, Rhinolophus ferrumequinum nippon, related to maternal care. Mamm. Study 2000,25, 1–15. [CrossRef]
7.
Geiser, F.; Körtner, G. Thermal biology, energetics and torpor in the possums and gliders. In Possums and
Gliders; Goldingay, R., Jackson, S., Eds.; Surrey Beatty: Chipping Norton, Australia, 2004; pp. 186–198.
8.
Dietz, M.; Kalko, E.K. Seasonal changes in daily torpor patterns of free-ranging female and male Daubenton’s
bats (Myotis daubentonii). J. Comp. Physiol. B 2006,176, 223–231. [CrossRef] [PubMed]
9.
Willis, C.K.R.; Brigham, R.M. Social thermoregulation exerts more influence than microclimate on forest
roost preferences by a cavity-dwelling bat. Behav. Ecol. Sociobiol. 2007,62, 97–108. [CrossRef]
10.
Stawski, C.; Willis, C.; Geiser, F. The importance of temporal heterothermy in bats. J. Zool.
2014
,292, 86–100.
[CrossRef]
11.
Kunz, T.H.; Lumsden, L.F. Ecology of cavity and foliage roosting bats. In Bat Ecology; Kunz, T., Fenton, M.,
Eds.; The University of Chicago Press: Chicago, IL, USA, 2003; pp. 3–89.
12.
Turbill, C. Roosting and thermoregulatory behaviour of male Gould’s long-eared bats, Nyctophilus gouldi:
Energetic benefits of thermally unstable tree roosts. Aust. J. Zool. 2006,54, 57–60. [CrossRef]
13. Turbill, C.; Geiser, F. Hibernation by tree-roosting bats. J. Comp. Physiol. B 2008,178, 597–605. [CrossRef]
14.
Racey, P.; Swift, S. Variations in gestation length in a colony of pipistrelle bats (Pipistrellus pipistrellus) from
year to year. Reproduction 1981,61, 123–129. [CrossRef]
15.
Hoying, K.M.; Kunz, T.H. Variation in size at birth and postnatal growth in the insectivorous bat Pipistrellus
subflavus (Chiroptera: Vespertilionidae). J. Zool. 1998,245, 15–27. [CrossRef]
16.
McLean, J.A.; Speakman, J.R. Energy budgets of lactating and non-reproductive brown long-eared bats
(Plecotus auritus) suggest females use compensation in lactation. Funct. Ecol. 1999,13, 360–372. [CrossRef]
17.
Brittingham, M.C.; Williams, L.M. Bat boxes as alternative roosts for displaced bat maternity colonies.
Wildl. Soc. Bull. 2000,28, 197–207.
18.
Kerth, G.; Weissmann, K.; König, B. Day roost selection in female Bechstein’s bats (Myotis bechsteinii): A field
experiment to determine the influence of roost temperature. Oecologia 2001,126, 1–9. [CrossRef] [PubMed]
19.
Lourenço, S.I.; Palmeirim, J.M. Influence of temperature in roost selection by Pipistrellus pygmaeus
(Chiroptera): Relevance for the design of bat boxes. Biol. Conserv. 2004,119, 237–243. [CrossRef]
20.
Dzal, Y.A.; Brigham, R.M. The tradeoff between torpor use and reproduction in little brown bats
(Myotis lucifugus). J. Comp. Physiol. B 2013,183, 279–288. [CrossRef] [PubMed]
21.
Johnson, J.S.; Lacki, M.J. Summer heterothermy in Rafinesque’s big-eared bats (Corynorhinus rafinesquii)
roosting in tree cavities in bottomland hardwood forests. J. Comp. Physiol. B 2013,183, 709–721. [CrossRef]
22.
Rueegger, N. Bat boxes—A review of their use and application, past, present and future. Acta Chiropterol.
2016,18, 279–299. [CrossRef]
23.
Mering, E.D.; Chambers, C.L. Thinking outside the box: A review of artificial roosts for bats. Wildl. Soc. Bull.
2014,38, 741–751. [CrossRef]
24.
Goldingay, R.; Stevens, J. Use of artificial tree hollows by Australian birds and bats. Wildl. Res.
2009
,36,
81–97. [CrossRef]
25.
Bartoniˇcka, T.; ˇ
Rehák, Z. Influence of the microclimate of bat boxes on their occupation by the soprano
pipistrelle Pipistrellus pygmaeus: Possible cause of roost switching. Acta Chiropterol.
2007
,9, 517–526.
[CrossRef]

Environments 2019,6, 13 18 of 19
26.
Fukui, D.; Okazaki, K.; Miyazaki, M.; Maeda, K. The effect of roost environment on roost selection by
non-reproductive and dispersing Asian parti-coloured bats Vespertilio sinensis.Mamm. Study
2010
,35, 99–109.
[CrossRef]
27.
Dodds, M.; Bilston, H.A. Comparison of different bat box types by bat occupancy in deciduous woodland,
UK. Conserv. Evid. 2013,10, 24–28.
28.
Doty, A.C.; Stawski, C.; Currie, S.E.; Geiser, F. Black or white? Physiological implications of roost colour and
choice in a microbat. J. Therm. Biol. 2016,60, 162–170. [CrossRef]
29.
Rhodes, M.; Jones, D. The use of bat boxes by insectivorous bats and other fauna in the greater Brisbane
region. In The Biology and Conservation of Australasian Bats; Law, B., Eby, P., Lunney, D., Lumsden, L., Eds.;
Royal Zoological Society of New South Wales: Mosman, Australia, 2011; pp. 424–442.
30.
Griffiths, S.R.; Rowland, J.A.; Briscoe, N.J.; Lentini, P.E.; Handasyde, K.A.; Lumsden, L.F.; Robert, K.A.
Surface reflectance drives nest box temperature profiles and thermal suitability for target wildlife. PLoS ONE
2017,12. [CrossRef]
31.
Maziarz, M.; Broughton, R.K.; Wesołowski, T. Microclimate in tree cavities and nest-boxes: Implications for
hole-nesting birds. For. Ecol. Manag. 2017,389, 306–313. [CrossRef]
32.
Rowland, J.A.; Briscoe, N.J.; Handasyde, K.A. Comparing the thermal suitability of nest-boxes and
tree-hollows for the conservation-management of arboreal marsupials. Biol. Conserv.
2017
,209, 341–348.
[CrossRef]
33.
Stebbings, R.E.; Walsh, S.T. Bat Boxes: A Guide to the History, Function, Construction and Use in the Conservation
of Bats; Bat Conservation Trust: London, UK, 1991.
34.
Tuttle, M.; Kiser, M.; Kiser, S. The Bat House Builder’s Handbook, 3rd ed.; Bat Conservation International:
Austin, TX, USA, 2013.
35.
Webb, P.I.; Speakman, J.R.; Racey, P.A. Evaporative water loss in two sympatric species of vespertilionid bat,
Plecotus auritus and Myotis daubentoni: Relation to foraging mode and implications for roost site selection.
J. Zool. 1995,235, 269–278. [CrossRef]
36. Bruns, H. The economic importance of birds in forests. Bird Study 1960,7, 193–208. [CrossRef]
37. Heise, G.; Blohm, T. Arbeit mit Fledermauskästen—sinnvoll oder nicht. Nyctalus 2012,17, 226–239.
38.
Rueegger, N.; Goldingay, R.L.; Law, B.; Gonsalves, L. Limited use of bat boxes in a rural landscape:
Implications for offsetting the clearing of hollow-bearing trees. Restor. Ecol. 2018. [CrossRef]
39.
BOM. Climate statistics for Australian locations. Bureau of Meteorology. 2019. Available online: http:
//www.bom.gov.au/climate/averages/tables/cw_061363.shtml (accessed on 5 January 2019).
40.
Eusebio, D.A.; Soriano, F.P.; Cabangon, R.J.; Evans, P.D. Manufacture of Low-Cost Wood-Cement Composites
in the Philippines Using Plantation-Grown Australian Species: I. Eucalypts; Australian Centre for International
Agricultural Research: Canberra, Australia, 1998; pp. 105–114.
41.
Flaquer, C.; Puig, X.; López-Baucells, A.; Torre, I.; Freixas, L.; Mas, M.; Porres, X.; Arrizabalaga, A.
Could overheating turn bat boxes into death traps. Barbastella 2014,7, 46–53.
42.
Geiser, F.; Körtner, G.; Turbill, C.; Pavey, C.; Brigham, R. Passive Rewarming from Torpor in Mammals and Birds:
Energetic, Ecological and Evolutionary Implications; University of Alaska: Fairbanks, AK, USA, 2004.
43.
Kunz, T.H.; Hood, W.R. Parental care and postnatal growth in the Chiroptera. In Reproductive Biology of Bats;
Crichton, E., Krutzsch, P., Eds.; Academic Press: London, UK, 2000; pp. 415–468.
44.
Sedgeley, J. Quality of cavity microclimate as a factor influencing selection of maternity roosts by a
tree-dwelling bat, Chalinolobus tuberculatus, in New Zealand. J. Appl. Ecol. 2001,38, 425–438. [CrossRef]
45.
Willis, C.K.R.; Turbill, C.; Geiser, F. Torpor and thermal energetics in a tiny Australian vespertilionid, the
little forest bat (Vespadelus vulturnus). J. Comp. Physiol. B Biochem. Syst. Environ. Physiol.
2005
,175, 479–486.
[CrossRef] [PubMed]
46.
Morris, S.; Curtin, A.; Thompson, M. Heterothermy, torpor, respiratory gas exchange, water balance and the
effect of feeding in Gould’s long-eared bat Nyctophilus gouldi.J. Exp. Biol. 1994,197, 309–335.
47.
Morrison, P. Body temperatures in some Australian mammals. I. Chiroptera. Biol. Bull.
1959
,116, 484–497.
[CrossRef]
48.
Baudinette, R.; Churchill, S.; Christian, K.; Nelson, J.; Hudson, P. Microclimatic conditions in maternity caves
of the bent-wing bat, Miniopterus schreibersii: An attempted restoration of a former maternity site. Wildl. Res.
1994,21, 607–619. [CrossRef]

Environments 2019,6, 13 19 of 19
49.
Bondarenco, A.; Körtner, G.; Geiser, F. Hot bats: Extreme thermal tolerance in a desert heat wave.
Naturwissenschaften 2014,101, 679–685. [CrossRef]
50.
Licht, P.; Leitner, P. Behavioural response to high temperature of three species of California bats. J. Mammal.
1967,48, 52–61. [CrossRef]
51.
Maloney, S.K.; Bronner, G.N.; Buffenstein, R. Thermoregulation in the Angolan free-tailed bat Mops
condylurus: A small mammal that uses hot roosts. Physiol. Biochem. Zool. 1999,72, 385–396. [CrossRef]
52.
Pinheiro, J.C.; Bates, D.M. Linear Mixed-effects Models: Basic Concepts and Examples. In Mixed-Effects
Models in S and S-Plus; Springer: New York, NY, USA, 2000.
53.
Šidák, Z. Rectangular confidence regions for the means of multivariate normal distributions. J. Am. Stat. Assoc.
1967,62, 626–633. [CrossRef]
54. Shaffer, J. Multiple hypothesis testing. Annu. Rev. Psychol. 1995,46, 561–584. [CrossRef]
55.
Maxim Integrated Products Inc. DS1923: iButton Hygrochron Temperature/Humidity Logger with 8KB Data-Log
Memory; 19-4991, Rev 7; Maxim Integrated Products Inc.: San Jose, CA, USA, 2013; p. 53.
56.
Bideguren, G.; López-Baucells, A.; Puig-Montserrat, X.; Mas, M.; Porres, X.; Flaquer, C. Bat boxes and climate
change: Testing the risk of over-heating in the Mediterranean region. Biodivers. Conserv. 2018. [CrossRef]
57.
Currie, S.; Noy, K.; Geiser, F. Passive rewarming from torpor in hibernating bats: Minimizing metabolic costs
and cardiac demands. Am. J. Physiol. Integr. Comp. Physiol. 2014,308, R34–R41. [CrossRef] [PubMed]
58.
Goldingay, R.L. Temperature variation in nest boxes in eastern Australia. Aust. Mammal.
2015
,37, 225–233.
[CrossRef]
59.
Beyer, G.L.; Goldingay, R.L. The value of nest boxes in the research and management of Australian
hollow-using arboreal marsupials. Wildl. Res. 2006,33, 161–174. [CrossRef]
60.
Rueegger, N.; Goldingay, N.; Brookes, L. Does nest box design influence use by the eastern pygmy-possum?
Aust. J. Zool. 2012,60, 372–380. [CrossRef]
61.
Hoeh, J.P.; Bakken, G.S.; Mitchell, W.A.; O’Keefe, J.M. In artificial roost comparison, bats show preference for
rocket box style. PLoS ONE 2018. [CrossRef]
62.
Geiser, F. Energetics, thermal biology, and torpor in Australian bats. In Functional and Evolutionary Ecology of
Bats; Zubaid, A., McCracken, G.F., Kunz, T.H., Eds.; Oxford University Press: New York, NY, USA, 2006;
pp. 5–22.
63.
Geiser, F.; Brigham, R.M. Torpor, thermal biology, and energetics in Australian long-eared bats (Nyctophilus).
J. Comp. Physiol. B 2000,170, 153–162. [CrossRef]
64.
Hamilton, I.M.; Barclay, R.M. Patterns of daily torpor and day-roost selection by male and female big brown
bats (Eptesicus fuscus). Can. J. Zool. 1994,72, 744–749. [CrossRef]
65.
Geiser, F.; Ruf, T. Hibernation versus daily torpor in mammals and birds: Physiological variables and
classification of torpor patterns. Physiol. Zool. 1995,68, 935–966. [CrossRef]
66.
Sanderson, K.; Jaeger, D.; Bonner, J.; Jansen, L. Activity patterns of bats at house roosts near Adelaide.
Aust. Mammal. 2006,28, 137–145. [CrossRef]
67.
Larson, E.R.; Eastwood, J.R.; Buchanan, K.L.; Bennett, A.T.; Berg, M. Nest box design for a changing climate:
The value of improved insulation. Ecol. Manag. Restor. 2018,19, 39–48. [CrossRef]
68.
Bellard, C.; Bertelsmeier, C.; Leadley, P.; Thuiller, W.; Courchamp, F. Impacts of climate change on the future
of biodiversity. Ecol. Lett. 2012,15, 365–377. [CrossRef] [PubMed]
69. Isaac, J.L.; Parsons, M.; Goodman, B.A. How hot do nest boxes get in the tropics? A study of nest boxes for
the endangered mahogany glider. Wildl. Res. 2008,35, 441–445. [CrossRef]
70.
Rueegger, N. Artificial tree hollow creation for cavity-using wildlife: Trialling an alternative method to that
of nest boxes. For. Ecol. Manage. 2017,405, 404–412. [CrossRef]
71.
Griffiths, S.; Lentini, P.; Semmens, K.; Watson, S.; Lumsden, L.; Robert, K. Chainsaw-carved cavities better
mimic the thermal properties of natural tree hollows than nest boxes and log hollows. Forests
2018
,9, 235.
[CrossRef]
©
2019 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).