2012 NORTHEASTERN NATURALIST 19(2):165–176
Distribution and Roost Selection of Bats on Newfoundland
Allysia C. Park! and Hugh G. Broders2,*
Abstract - We studied the distribution and ecology of male and female Myotis lucifugus
(Little Brown Bats) and M. septentrionalis (Northern Long-eared Bats) on Newfoundland,
where conditions (e.g., resource availability, abiotic conditions) were expected to
be less favorable than in areas where most studies of conspecifics have occurred. We
found that both species were patchily distributed and that Northern Long-eared Bats were
more widely distributed across the island than previously documented. We located and
characterized 36 roost trees from 14 female (6 lactating and 8 non-lactating) Northern
Long-eared bats and found that, relative to conspecific populations on mainland North
America, female Northern Long-eared Bats on the northern peninsula of Newfoundland
roosted in shorter trees with smaller diameters. We also found that roosts used by lactating
Northern Long-eared females were in cavities of large-diameter trees that maintained
more stable microclimates compared to roosts used by non-lactating females.
Introduction
Characterizing population dynamics in relation to resource availability and
abiotic conditions permits inference on factors that may be important for understanding
evolutionary patterns and processes (Bahn et al. 2006, Holt and Keitt
2005). Peripheral populations may contain unique, heritable traits that permit
persistence under conditions that conspecific populations in the core of a species’
distribution would find challenging (Kurta et al. 1996). If such populations
remain isolated, speciation may occur (Lesica and Allendorf 1995).
In Newfoundland, Canada, only 2 species of bats are believed to be abundant:
Myotis lucifugus LeConte (Little Brown Bat) and M. septentrionalis
Trouessart (Northern Long-eared Bat). Little Brown Bats are known to exist
across Newfoundland (van Zyll de Jong 1985), whereas Northern Long-eared
Bat records are thought to be restricted to the southwest portion of the island
(Caceres and Barclay 2000), although systematic research has not been conducted
beyond this area. The only previous study of bats on Newfoundland
recorded few individuals and noted that foraging occurred at low ambient
temperatures (<10 °C) relative to areas located more centrally within the distribution
of these bats (Grindal 1999).
The biotic and abiotic conditions on Newfoundland appear less favorable than
those of other areas where these species have been studied previously. For example,
approximately 83% of the forest in Newfoundland is dominated by just 2
species, Abies balsamea (L.) Mill. (Balsam Fir; Singh 1977) and Picea mariana
Mill. (Black Spruce; DNR 2008), and this low diversity likely is due to the island’s
!Department of Biology, Saint Mary’s University, Halifax, NS, B3H 3C3. 2Department of
Biology, Saint Mary’s University, Halifax, NS, B3H 3C3. *Corresponding author - hugh.
broders@smu.ca.
166 Northeastern Naturalist Vol. 19, No. 2
cool and moist climate (Roberts 1983). Neither species of tree is typically used for
roosting by bats in other areas. In addition to its forest composition, Newfoundland
has low average summer temperatures (13 °C), is adjacent to the foggiest waters in
the world (Rogerson 1983), and has very strong winds. Average wind speed on the
island is 22 km/hr, but mean velocities up to 34 km/hr occur in some coastal areas
(Khan and Iqbal 2004). Therefore, a study of the resource use and distribution of
bats on Newfoundland potentially can provide insight into the factors that limit the
distribution of these species.
Little Brown and Northern Long-eared Bats are sympatric throughout much
of their distribution, ranging from as far south as Florida to as far north as the
Yukon (Caceres and Barclay 2000, Fenton and Barclay 1980). However, the species
differ in their foraging and roosting behaviors. Little Brown Bats may forage
in a range of site types (LaVal et al. 1977), whereas Northern Long-eared Bats
appear to be forest specialists (Broders et al. 2003, Henderson and Broders 2008).
Northern Long-eared Bats roost almost exclusively in trees (Broders and Forbes
2004, Caceres and Barclay 2000, Jung et al. 2004), whereas Little Brown Bats
typically roost in buildings (Fenton and Barclay 1980), though there are records
of roosts in natural structures (Barclay and Cash 1985, Fenton and Barclay 1980,
Kalcounis and Hecker 1996). Both species are sexually segregated during summer,
with males and non-reproductive females typically remaining solitary and
rarely roosting with the maternity colony (Broders and Forbes 2004, Jung et al.
2004, Kunz and Lumsden 2003, Thomas 1988).
For the forest-dependent Northern Long-eared Bat, certain characteristics of
forest landscapes, stands, and roost trees presumably are essential for survival,
especially for reproductive females, which have the greatest energetic demands
(Barclay 1989, Racey and Entwistle 2003). However, few studies characterize
roosting patterns relative to reproductive stage of females. Stable, warm microclimates
within cavities of roost trees promote normothermic body temperatures
(Foster and Kurta 1999), offspring development during gestation, and milk production
during lactation (Hamilton and Barclay 1994, Jung et al. 2004, Kerth
et al. 2001b, Wilde et al. 1999). The warmest roosts tend to be located close
to the canopy in the tallest and largest-diameter trees (Crampton and Barclay
1998, Kunz and Lumsden 2003). These roosts receive more solar radiation, have
greater insulative properties, and house more individuals than roosts in shorter
and smaller trees (Foster and Kurta 1999, Garroway and Broders 2008). Because
of variation in energetic requirements during different reproductive stages (specifi
cally non-lactating versus lactating), roost-site characteristics selected by
females should vary to maximize energetic efficiency and increase fitness (Garroway
and Broders 2008).
The goal of this study was to gain a preliminary insight into the biology of
bats in an area where environmental conditions and resource availability appear
to be less favorable relative to sites where conspecific populations have been
studied previously. Specifically, our first objective was to determine the extent
of the summer distribution of Little Brown and Northern Long-eared Bats on
2012 A.C. Park and H.G. Broders 167
Newfoundland. Our second objective was to characterize roost-site selection of
female lactating and non-lactating Northern Long-eared Bats and compare roosttree
selection and roost-temperature profiles between the groups.
Methods
Field-site description
Newfoundland lies within the wet boreal forest region, which supports
dominant conifer stands (Thompson et al. 2003). These stands consist primarily
of Balsam Fir and Black Spruce (Campbell and Laroque 2007), which
thrive on moisture accumulated from high amounts of precipitation and fog
(Thompson et al. 2003). Betula papyrifera Marsh. (White Birch) is the only
major hardwood species in this region (Roberts et al. 1998). However, Picea
glauca (Moench) Voss (White Spruce), Populus tremuloides Michx. (Trembling
Aspen), Prunus pensylvanica L.f. (Pin Cherry), and Sorbus americana
Marsh. (American Mountain Ash) are also present (Thompson et al. 2003).
Distribution of bats on Newfoundland
From 3 June to 4 August 2008, we conducted surveys using harp traps (Austbat
Research Equipment, Lower Plenty, Victoria, Australia) along forested trails
at 14 areas on Newfoundland (Fig. 1). Forested trails are used by bats for commuting
(Downs and Racey 2006) and are an ideal site for trapping (Henderson
et al. 2008). Research on Prince Edward Island, Canada, found rivers to be a
key predictor of the presence of Northern Long-eared Bats (Henderson et al.
2008), so only areas that contained at least 1 river were included in our study.
Harp traps were deployed before sunset and checked every 0.5 h for 3 h. At
each of the 14 areas, we trapped bats at 1–5 locations along trails, for a total of
35 sampled locations.
All captured bats were identified to species, weighed, aged (Anthony
1988), sexed, and had their reproductive condition assessed. Bats were identified
as pregnant by palpating the abdomen and as lactating via the presence of
exposed skin around the nipple and/or presence of milk (Racey 1988). All bats
were released at the site of capture after processing. Sampling did not occur
on nights with heavy rain. Methods for capturing and handling bats followed
the guidelines of the American Society for Mammalogists (Gannon and Sikes
2007) and were approved by the Saint Mary’s University Animal Care Committee,
Parks Canada, and the Newfoundland and Labrador Department of
Environment and Conservation.
Roost selection by female Northern Long-eared Bats
From 15 June to 10 August 2009, we fitted female Northern Long-eared
Bats on the northern peninsula of Newfoundland, near the community of River
of Ponds (50°32´N, 57°24´W), with 0.42-g radio-transmitters (model LB-2N,
Holohil Systems, Carp, ON, Canada), representing, on average (± S.E.), 4.8 ±
0.15 % of the bat’s mass. All bats were located every day until the transmitter
fell off or failed.
168 Northeastern Naturalist Vol. 19, No. 2
To characterize roost-site selection, a 17.8-m-radius plot (0.1-ha), centered on
roost trees, was surveyed when bats were known to be not roosting in the tree.
Within each plot, both live trees and snags were counted, and diameter (dbh) of
the roost tree was measured. Canopy height was defined as the average height
of 5 representative trees and determined using a clinometer (model PM-5/1520,
Suunto, Vantaa, Finland). Roost height relative to the canopy was calculated by
subtracting canopy height from roost height.
Based on a review of the literature on roosting behaviors of female Northern
Long-eared Bats (e.g., Carter and Feldhamer 2005, Garroway and Broders
2008), we created a set of 9 a priori logistic models, each representing alternative
hypotheses to differentiate roosts used by lactating and non-lactating bats.
Because only 36 roosts and their respective stand plots were analyzed, all but
1 model contained only 1 or 2 predictive variables (Hosmer and Lemeshow
Figure 1. Distribution of male and female Little Brown and Northern Long-eared Bats on
Newfoundland during summer 2008, as determined by systematic harp-trap surveys.
2012 A.C. Park and H.G. Broders 169
2000). The candidate models and respective variables were ranked by secondorder
Akaike’s information criterion (AICC ; Burnham and Anderson 2002)
using SYSTAT 12 (SYSTAT software, Inc. 2001), and the 95% confidence set
was used for inference. Model-averaged parameter estimates (βi) and unconditional
standard errors (S.E.) were calculated (Burnham and Anderson 2002),
and only those variables for which the parameter estimate ± S.E. did not overlap
zero were used for inference.
To characterize the temperature profile of roosts, ambient temperature (± 1
°C) was measured every hour within the study areas using data loggers (iButton,
Dallas Semiconductor Corporation, Dallas, TX). Loggers were placed directly
on tree trunks, shaded under canopy cover to eliminate direct exposure to solar
radiation, at 1.5 m above ground level. Data loggers were also placed in different
roosts (once bats were known not to be using the roost) for 6–18 days to facilitate
comparison of roost temperature to ambient temperature. A generalized linear
model was used to determine whether variation in roost temperature profile, relative
to ambient, varied between trees used by lactating and non-lactating bats
(Crawley 2007).
Results
Distribution of bats on Newfoundland
In 2008, 22 Little Brown (7 male:15 female) and 29 Northern Long-eared Bats
(10:19) were captured. Little Brown Bats were caught in only 5 of the 14 areas,
and Northern Long-eared Bats were captured at 9 of 14 areas (Fig. 1). No pregnant
Little Brown Bats were caught; however, the first occurrence of a lactating
Little Brown Bat was on 18 July, and the first record of a volant young-of-theyear
was on 28 July. The only records for pregnant Northern Long-eared Bats
occurred on 22 June and 4 July. The first lactating Northern Long-eared Bat was
trapped on 7 July, and all females of this species caught after that date showed
signs of lactation. No juvenile Northern Long-eared Bats were caught.
Roost selection by female Northern Long-eared Bats
In 2009, 18 female Northern Long-eared Bats (8 lactating and 10 non-lactating)
were caught, 14 of which (6 lactating and 8 non-lactating) were tracked for 1 to 11
days to 36 roost trees (Table 1), for 60 bat-days, with a bat-day defined as 1 radiotracked
bat roosting in 1 tree for 1 day. During the lactation period (10–31 July
Table 1. Sample size and mean characteristics (S.E.) of roosts used by lactating and non-lactating
Northern Long-eared Bats near River of Ponds, Newfoundland, in 2009.
Roost-site characteristics Lactating Non-lactating
n bats 6 8
n roost trees 13 23
Roost-tree diameter (cm) 31.7 (2.2) 22.7 (2.0)
Canopy height relative to roost height (m) 12.8 (1.9) 11.3 (1.3)
Total number of live trees (number/ha) 144.5 (19.5) 96.1 (9.4)
Total number of snags (number/ha) 13.9 (1.7) 14.1 (1.4)
170 Northeastern Naturalist Vol. 19, No. 2
2009), 2 of the 8 females tracked were non-lactating. Nine roost trees were used on
>1 day by either the same or different individuals, with 1 roost occupied for 11 batdays
by 4 bats; 3 roost trees were used by more than 1 tracked bat.
Bats roosted an average of 1136 m (range: 71–2375 m) from the capture site.
At least 3 species of trees were used as roosts. Thirteen roosts were in Balsam
Fir, 1 was in Black Spruce, and 10 were in White Birch. The remaining 12 trees
Table 2. Ranked Akaike weights (wi) and sum of Akaike weights (Σwi) for all a priori selected candidate
models for differentiating characteristics of sites and roosts used by lactating and non-lactating
Northern Long-eared Bats. The first four models formed the 95% confidence set.
Model wi Σwi
Canopy relative to roost, roost-tree diameter 0.534 0.534
Canopy relative to roost, roost tree-diameter, total number of live trees 0.247 0.781
Canopy relative to roost, total number of live trees 0.107 0.888
Canopy relative to roost 0.071 0.959
Roost tree diameter 0.022 0.981
Roost tree diameter, total number of snags 0.013 0.994
Total number of live trees 0.005 0.998
Total number of live trees, total number of snags 0.001 1.000
Total number of snags 0.000 1.000
Figure 2. Temperature inside roosts occupied by lactating and non-lactating Northern
Long-eared Bats versus ambient temperature, near River of Ponds, Newfoundland.
2012 A.C. Park and H.G. Broders 171
were not identified due to advanced decay. Roosts used by lactating and nonlactating
bats were predominately snags (87 and 92%, respectively). Exit counts
were performed on 39 occasions. Mean group size was 9.0 (range: 1–19, n = 12)
for lactating bats and 7.6 (range: 1–28, n = 27) for non-lactating females.
The 95% confidence set of models to differentiate roosts used by lactating
and non-lactating Northern Long-eared Bats consisted of 4 models (Table 2).
At the local level, for every 2.0-cm increase in diameter of a roost tree (βDBH =
0.105 ± 0.051), the odds that it was a tree used by a lactating Northern Longeared
Bat increased by 1.23 (95% CI: 1.01–1.51). At the stand level, for every
increase of 5 trees (βTREES = 0.007 ± 0.008) within a 0.1-ha plot, the odds that it
was used by a lactating Northern Long-eared Bat increased by 1.05 times (95%
CI: 0.97–1.14).
Roost microclimate
On average, lactating Northern Long-eared females used roost trees that were
significantly larger (dbh = 31.7 ± 2.2 cm, n = 12) than the roost trees used by nonlactating
females (dbh = 22.7 ± 2.0 cm, n = 23; ANOVA, F1, 33 = 9.0, P = 0.005).
Microclimate temperature patterns, relative to ambient, also differed between
roost-sites used by lactating and non-lactating bats (Fig. 2). Variation in the slope
of the regression lines of ambient vs. roost temperature for trees used by lactating
vs. non-lactating bats was significantly different from one another (P < 0.001).
On average, the slope was 0.60 ± 0.04 (n = 2, r2 = 0.68–0.88) for roosts used by
lactating bats (n = 2, r2 = 0.68 and 0.88) and 1.35 ± 0.05 (n = 4, r2 = 0.62–0.86)
for roosts used by non-lactating bats, suggesting that lactating bats selected cavity
roots in large trees that had lower temperature fluctuations than roosts used
by non-lactating bats.
Discussion
Consistent with other studies of bats in eastern Canada (Farrow and Broders
2010, Henderson et al. 2008), both Little Brown and Northern Long-eared Bats
were patchily distributed on the island of Newfoundland. Surprisingly, despite
the more generalist nature of Little Brown Bats, they were caught at fewer locations
than Northern Long-eared Bats, and the only location where only Little
Brown Bats were caught was on the Avalon Peninsula at Salmonier. Northern
Long-eared Bats were found farther east and north than previously reported (Caceres
and Barclay 2000).
Throughout the core of their geographic distribution, female Northern Longeared
Bats roost in a variety of tree species that typically are larger than those
found on Newfoundland (e.g., Broders and Forbes 2004, Foster and Kurta 1999,
Sasse and Pekins 1996). On Newfoundland, softwood species (particularly Balsam
Fir) were most commonly used as roost trees (58% of identified roosts).
Balsam Fir is a short-lived species, and “old growth” conditions for this conifer
typically last only 20–30 years (Thompson et al. 2003). On Newfoundland, the
amount of old-growth forest has declined considerably since the 1940s because
of logging, and infestations of both Lambdina fiscellaria Guenee (Hemlock
172 Northeastern Naturalist Vol. 19, No. 2
Looper) and Choristoneura fumiferana Clemens (Spruce Budworm) (Thompson
et al. 2003). Therefore, relative to roosts available to females in central
areas of the distribution of Northern Long-eared Bats in North America, only
smaller and shorter roost trees are widely available in Newfoundland and are
selected by the bats.
Energetic requirements of bats not only differ by gender, but also by reproductive
status. Non-reproductive females, like males, have less energetic cost
associated with reproduction and should therefore have greater flexibility in
roost-site selection (Barclay 1991, Mills et al. 1996, Thomas 1988). Gestation,
however, may result in bats selecting warmer roosts to reduce the amount of
energy required to sustain normothermic body temperature and facilitate fetal
growth (Kerth et al. 2001a, Kunz and Lumsden 2003, McLean and Speakman
1999, Wilkinson 1992). During lactation, the most energy-intense period for
both mother and offspring (Kurta et al. 1989, Racey and Swift 1981), females
allocate most energy reserves not spent on foraging to milk production (Wilde et
al. 1999). In our study, roost-tree characteristics selected by lactating Northern
Long-eared Bats appeared to coincide with energetic demands, relative to those
of bats that were non-lactating. Lactating bats roosted in trees that were larger in
diameter, presumably to decrease energy expenditure.
The relationship between roost-tree diameter and reproductive status is supported
by prior studies that compared characteristics of roost trees used by female
Northern Long-eared Bats to those of randomly selected trees (Sasse and Perkins
1996) or trees occupied by males (Perry and Thill 2007), and characteristics of
trees used by maternity colonies to those used by solitary females (Lacki and
Schwierjohann 2001). Garroway and Broders (2008) found that, during lactation,
roosts of Northern Long-eared Bats were exposed to increased solar radiation and
had less surrounding clutter (i.e., roosts were situated high in tall trees that were
surrounded by an open canopy and a low number of trees in the stand). These
roosts were expected to be warmer due to greater exposure to sunlight (Betts
1998, Vonhof and Barclay 1996), which is especially important when the growing
season for young is short (Kerth et al. 2001b, Lewis 1993).
Insulation and temperature of roost cavities is also largely dictated by the size
of the tree in which it is located. Large-diameter trees provide more insulation
and are less affected by ambient conditions, enabling them to maintain more stable
microclimates than trees with smaller diameters (Coombs et al. 2010, Nicolai
1986, Vonhof and Barclay 1997). Roost microclimate has not been widely studied
in the past due to difficulty of access. For studies that have been successful,
reproductive bats seem to select roosts with more stable microclimates relative
to roosts used by non-reproductive females (Burnett and August 1981, Kalcounis
and Hecker 1996, Sedgeley 2001).
This study examined the distribution of bats on Newfoundland and provided
insight into roost selection at the periphery of a species’ range. We have revealed
factors that likely influence roosting- and foraging-site selection for forestdependent
Northern Long-eared Bats and show that roost-site selection differs
here from that in the interior of their North American distribution. However, even
2012 A.C. Park and H.G. Broders 173
at the northeastern extreme, which contains forest features that are less likely to
be chosen by Northern Long-eared females at the core of their distribution, the
overall trend of roost-site selection is similar. Females that were lactating and
undergoing conditions that required significant energy resources selected roost
cavities in large diameter trees that provided warmer, more stable microclimates
than those used by bats that were non-lactating. This finding supports the contention
that lactating females are more sensitive to distribution-limiting factors than
non-lactating females.
Acknowledgments
We are grateful to all private park-owners and landowners in the community of
River of Ponds, who granted access to their land. Logistic support was provided by
Newfoundland and Labrador’s Parks and Natural Areas Division, Parks Canada, and
the Newfoundland and Labrador’s Forest Resources and Agrifoods Division in the Department
of Natural Resources. Funding was provided by the Wildlife Division of the
Newfoundland and Labrador Department of Environment and Conservation, the Animal
Health Division of the Newfoundland and Labrador Department of Natural Resources,
and Saint Mary’s University. Field assistants included G. Bateman, L. Burns, S. Caines,
S. Chessel, K. Letto, M. Makowska, and A. Wells.
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