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2007 SOUTHEASTERN NATURALIST 6(3):393–406
Effect of Woody Debris Abundance on Daytime Refuge
Use by Cotton Mice
Travis M. Hinkelman1,2,* and Susan C. Loeb3
Abstract - Daytime refuges are important to nocturnal rodents for protection from
predators and environmental extremes. Because refuges of forest-dwelling rodents
are often associated with woody debris, we examined refuge use by 37 radio-collared
Peromyscus gossypinus (cotton mice) in experimental plots with different levels of
woody debris. Treatment plots had six times ( 60 m3/ha) the volume of woody
debris as control plots ( 10 m3/ha). Of 247 refuges, 159 were in rotting stumps
(64%), 32 were in root boles (13%), 19 were in brush piles (8%), and 16 were in logs
(6%); 10 refuges could not be identified. Stumps were the most common refuge type
in both treatments, but the distribution of refuge types was significantly different
between treatment and control plots. Root boles and brush piles were used more on
treatment plots than on control plots, and logs were used more on control plots than
on treatment plots. Refuge type and vegetation cover were the best predictors of
refuge use by cotton mice; root bole refuges and refuges with less vegetation cover
received greater-than-expected use by mice. Abundant refuges, particularly root
boles, may improve habitat quality for cotton mice in southeastern pine forests.
Daytime refuges are important to nocturnal rodents for protection from
environmental extremes, predator avoidance, and rearing young (Frank and
Layne 1992). In the absence of large burrowing vertebrates such as
Gopherus polyphemus Daudin (Gopher Tortoise) or prominent physical
structures such as rock piles, refuges of forest-dwelling rodents are frequently
associated with woody debris (McCay 2000).
In the southeastern United States, forest management practices (e.g.,
short harvest rotations) and a humid climate result in low volumes of
woody debris (McCay et al. 2002). The relative scarcity of woody debris,
large burrows, and rock structures in managed Pinus spp. (pine) stands
(McCay 2000, McCay et al. 2002) suggests that refuges may function as a
limiting factor for rodents in pine forests in the Southeast. Although woody
debris is a resource that is amenable to management, little is known about
the relationship between woody debris abundance and refuge use by rodents
Peromyscus gossypinus LeConte (cotton mouse) is one of the most abundant
terrestrial rodents in southeastern pine forests (Clark and Durden 2002,
1Department of Forestry and Natural Resources, Clemson University, Clemson, SC
29634. 2Current address - School of Biological Sciences, University of Nebraska,
Lincoln, NE 68588. 3United States Forest Service, Southern Research Station, Department
of Forestry and Natural Resources, Clemson University, Clemson, SC
29634. *Corresponding author - firstname.lastname@example.org.
394 Southeastern Naturalist Vol. 6, No. 3
Loeb 1999, Mengak and Guynn 2003). Further, in managed pine stands in
South Carolina, cotton mouse abundance is positively associated with woody
debris abundance (Loeb 1999), and 92% of day refuges of cotton mice are
associated with woody debris (McCay 2000). The association with woody
debris and relatively high abundance makes the cotton mouse an important
species in which to investigate the relationship between woody debris abundance
and refuge use by rodents in southeastern pine forests.
If increasing woody debris increases the number of available refuges,
competitive interactions may be reduced (Loeb 1996). Cotton mice use
many refuges over a short period of time (Frank and Layne 1992, McCay
2000), and thus, increasing the availability of refuges may reduce constraints
associated with trade-offs in the costs (e.g., parasite infestation) and
benefits (e.g., site familiarity) of refuge fidelity, and the costs (e.g., predation
risk) and benefits (e.g., proximity to food) of refuge switching (Banks et
al. 2000, Lewis 1995, Norrdahl and Korpimäki 1998). Abundant refuges
may also permit greater selectivity by mice for refuge attributes such as type
and size (Frank and Layne 1992, Hall and Morrison 1997, McCay 2000,
Wolff and Hurlbutt 1982) and attributes of the refuge neighborhood such as
vegetation cover (Kalcounis-Rüppell and Millar 2002, Morzillo et al. 2003,
Wagner et al. 2000).
The objectives of this study were to: (1) identify refuge types used by
cotton mice and determine if the distribution of types differed between areas
of low and high woody debris, (2) test if fidelity differed between areas of
low and high woody debris, and (3) model refuge selection as a function of
refuge attributes and the refuge neighborhood.
Study site and experimental design
This study was conducted on the Savannah River Site (SRS) from May to
September 2002 and February to September 2003. The SRS is a 78,000-ha
National Environmental Research Park in the upper Coastal Plain of South
Carolina located in Aiken, Allendale, and Barnwell counties. Study plots
consisted of six 9.3-ha plots situated in 50-yr old Pinus Taeda Linnaeus
(loblolly pine) stands. Soils were sandy and well drained (Workman and
Although loblolly pine was the dominant overstory species, Quercus spp.
(oak), Carya spp. (hickory), Liquidambar styraciflua Linnaeus (sweetgum),
and Morella cerifera Linnaeus (wax myrtle) were also found throughout the
plots in the overstory and midstory. Numerically dominant understory species
included Toxicodendron pubescens P. Miller (poison oak), Anthemis
cotula Linnaeus (dog fennel), and Lespedeza spp. (lespedeza).
In August 2001, trees on the three treatment plots were felled with
feller-bunchers to increase log volumes to approximately six times the level
on the three control plots. Feller-bunchers typically cut trees at the base
creating stumps and logs, but occasionally trees were felled by uprooting,
2007 T.M. Hinkelman and S.C. Loeb 395
which produced root boles and logs. Both methods of felling trees generated
an influx of fine woody debris. The newly created stumps and logs
were generally sound, i.e., in an early stage of decay. About a quarter of
the trees on the control plots were girdled with a chainsaw in spring 2001
so that the basal area of live trees on all six plots was about 15 m2/ha.
Treatment activities (i.e., log and snag creation) yielded open stands with
well-developed understory vegetation. The control and treatment plots
were paired, which yielded three blocks of two treatments. All 6 plots were
burned in January to March of 2000 or 2001 prior to the implementation of
Percent volume of understory vegetation (below a height of 3 m) was
estimated during the growing season of each year within twenty-five 0.04-ha
sampling plots arranged on each of the six study plots in a 5-by-5 grid with
50-m spacing. The length and diameter at midpoint of all logs 10 cm in
diameter was measured within eight randomly selected 0.25-ha subplots on
each of the control and six randomly selected 0.25-ha subplots on the three
treatment plots. Log volume was estimated with the formula for the volume
of a cylinder (V = *r2*length), and the total volume of logs was summed for
each subplot. A year was divided into growing (1 April to 30 September) and
non-growing (1 October to 31 March) seasons, which hereafter will be
referred to as summer and winter, respectively.
An 8-by-8 trapping grid with 20-m spacing was placed at the center of
each plot. The grids were at least 50 m from the plot borders. One folding
aluminum Sherman live trap (7.5 x 9.0 x 25.5 cm) was placed on the ground
and in the nearest tree at each station (Loeb et al. 1999). Ground traps were
baited with sunflower seeds to limit the attraction of Solenopsis wagneri
Santschi (red imported fire ant), and tree traps were baited with peanut
butter. Bimonthly trapping was conducted during the course of this study as
part of a larger, long-term effort to monitor small-mammal populations
within the plots. Trapping sessions spanned seven nights centered on the
new moon phase. Additional trapping was conducted as time permitted to
augment the number of cotton mice tracked.
Traps were checked in the early morning of every day of a trapping
period. All captured animals were marked with ear tags, weighed, and
identified by species, sex, age, and reproductive condition. Age of cotton
mice was determined by a combination of pelage characteristics and mass
(adult: 18 g). An animal that was obviously in reproductive condition (e.g.,
descended testes) was recorded as an adult regardless of mass or pelage. All
non-target captures were released without handling during the additional
Adult cotton mice weighing 20 g with at least one previous capture were
selected for radio-tracking. The minimum-mass criterion was incorporated to
396 Southeastern Naturalist Vol. 6, No. 3
limit the effect of the transmitter on the mouse’s behavior, and the previouscapture
criterion increased the likelihood that an individual was a resident of
the plot. Individuals selected for transmitter attachment were anesthetized
with a mixture of halothane and mineral oil and fitted with a radiocollar
(M1420 transmitter, Advanced Telemetry Systems, Inc., Isanti, MN; MD-2C
transmitter, Holohil Systems Ltd., Carp, ON, Canada). Transmitter attachment
took less than 10 min per mouse. Radiocollars weighed about 1.3 g and
averaged 5.4% of the mass of the radiotagged mice (mean = 23.9 g). Mice
were held for > 1 hr to recover from anesthesia and then released at the
One location was taken each day between sunrise and sunset for each
collared mouse by homing with a TR-2 receiver and RA-2A two-element
antenna (Telonics, Mesa, AZ). Cotton mice are not active on the surface
during the day (McCay 2000). Tracking began on the day following transmitter
attachment and continued for the life of the transmitter ( 30 days).
When locating refuges, we attempted to limit any preconceived biases about
refuge types by marking the location of the strongest signal even if no
apparent refuge substrate was present.
We used the total number of locations per mouse as a measure of tracking
effort. Refuge fidelity for each mouse was calculated as the number of
locations divided by the number of refuges used. Thus, fidelity is an estimate
of the average number of days that a mouse spent in a particular refuge
whether they were consecutive or not. Fidelity is an attribute of the mouse,
not the refuge.
We recorded the type (stump, root bole, log, tree base, or brush pile) and
measured the dimensions (e.g., diameter, length, height) of each refuge. To
standardize refuge size across types, we selected one dimension for each
refuge type to reflect the size of that refuge. We used diameter for logs and
stumps, diameter at breast height (dbh) for tree bases, circumference for root
boles, and depth for brush piles. (We use the term “tree base” to emphasize
that all refuges in trees were located at the base of the tree.) We created a
standardized continuous variable for refuge size (i.e., mean = 0 and SD = 1)
by subtracting the mean and dividing by the standard deviation for each
The structural cover surrounding each refuge (i.e., neighborhood) was
characterized with nested sampling plots. Within a 4-m radius plot (50 m2)
centered on the refuge, we recorded the dbh of all trees 5 cm dbh, the
height and diameter of all stumps, and the length and diameter of the
portions of logs that were within the sampling plot. Within a 1.78-m radius
plot (10 m2) nested in the larger sampling plot, we estimated the percent
ground cover of grass, forbs, shrubs, bare ground, and litter. To represent
structural cover at each refuge, we calculated total percent cover of ground
vegetation (i.e., sum of grass, forb, and shrub cover), area of stumps, volume
of logs, and basal area of trees.
2007 T.M. Hinkelman and S.C. Loeb 397
We tested for differences in the total number (summed across plots) of
refuge types between treatment and control plots with a likelihood-ratio test
(PROC FREQ; SAS Institute, Inc. 2000). We used mixed-model analysis of
variance (ANOVA) to test for differences in log volume, understory vegetation,
tracking effort, and refuge fidelity by treatment and season (PROC GLM;
SAS Institute, Inc. 2000). The ANOVA follows a split-plot design with three
blocks, two treatments, two years or three seasons, and sub-samples comprised
of either log subplots, vegetation sampling plots, or individual mice. Variables
were logarithmically transformed to satisfy the assumptions of the ANOVA.
Refuge selection was modeled using negative binomial (NB) regression.
Although Poisson distributions are typically used to model counts of animal
locations (Millspaugh et al. 2006), our data exhibited overdispersion, indicating
that NB regression was more appropriate than Poisson regression. NB
regression models the probability of refuge use and circumvents the need to
classify refuge sites as either used or unused as in logistic regression
(Keating and Cherry 2004, Millspaugh et al. 2006). The modeling approach
treated the data as survey observations rather than imposing any specific
experimental-design constraints. The refuge was the experimental unit for
the NB regression analysis.
The logarithm of the number of locations for a refuge was modeled as a
linear combination of refuge, neighborhood, and plot variables. Refuge
variables (type and size) described the refuge, neighborhood variables described
the area surrounding the refuge, and plot variables (treatment and
block) described the plot where the refuge was located. The number of
locations for a refuge was log-linked to the expected number of locations for
a refuge as an offset term (Erickson et al. 2001). For example, if we obtained
50 locations for a plot with 25 refuges, then the expected number of locations
for each refuge on that plot was two. No selection would be inferred for
any refuges on that plot with two locations.
To identify significant predictors of selection, we used a backward elimination
procedure based on likelihood-ratio statistics for Type III analysis; no
interaction terms were included in the model. For the variables included in
the final model, pair-wise comparisons of parameter estimates were examined
with linear contrasts. NB regression analyses were conducted with
PROC GENMOD (SAS Institute, Inc. 2000).
Log volume was significantly different between treatment and control
plots (F = 20.94, d.f. = 1, P = 0.0446), but not between years (F = 2.43, d.f. =
1, P = 0.1941). Log volumes were approximately 6x greater on treatment
plots than on control plots (Table 1). Understory vegetation varied significantly
by year (F = 38.07, d.f. = 1, P = 0.0035), but not by treatment (F =
0.03, d.f. = 1, P = 0.8775). Understory vegetation increased by about 50%
from 2002 to 2003 (Table 1).
398 Southeastern Naturalist Vol. 6, No. 3
The number of cotton mouse captures per trapping period per plot was
similar between treatment and control plots with 1.4 ± 0.4 (SE) and 2.1 ± 0.6
captures, respectively, on control and treatment plots in 2002, and 4.4 ± 1.8
and 4.8 ± 0.8 captures, respectively, on control and treatment plots in 2003.
A total of 37 cotton mice were fitted with radiocollars; 9 individuals wore
2 collars. The number of telemetry locations for each mouse ranged from 1
to 44 because of slipped collars, transmitter failure, predation, and the
tracking schedule. To limit the effect of unequal tracking effort, we excluded
the 7 mice with < 9 locations from the analysis of tracking effort
and refuge fidelity.
We recorded an average of 21.01 ± 0.87 locations and 7.99 ± 0.70 refuges
for collared mice. We documented one male on a control plot using 15
different refuges in a span of 3 months. The number of refuges observed for
a mouse was positively correlated with the number of locations (Fig. 1).
Tracking effort (i.e., number of locations) was not significantly different
between treatment and control plots or among seasons (P > 0.20), but there
Table 1. Mean (± SE) log volume and understory vegetation on study plots by treatment and year.
Year Plot Log volume (m3/ha) Understory vegetation (volume percent)
2002 Control 9.82 ± 2.76 19.09 ± 3.88
Treatment 59.65 ± 6.95 19.60 ± 2.51
2003 Control 9.61 ± 2.48 28.81 ± 7.15
Treatment 57.34 ± 6.79 30.39 ± 2.51
Figure 1. Number of refuges as a function of number of telemetry locations.
2007 T.M. Hinkelman and S.C. Loeb 399
Figure 2. Mean (± SE) locations per refuge on study plots by treatment and season
(N = number of plots; n = number of mice).
was a significant treatment by season interaction (F = 14.26, d.f. = 2, P =
0.0294). There were no significant treatment, season, or treatment by season
effects on refuge fidelity (P > 0.10). However, the number of locations per
refuge, i.e., fidelity, was considerably higher on treatment (2.80 ± 0.44) than
control (1.83 ± 0.54) plots in summer 2002, and fidelity was considerably
higher on control (3.15 ± 0.25) than treatment (2.25 ± 0.13) plots in summer
2003 (Fig. 2).
Mice used rotted stumps (N = 159), root boles (N = 32), brush piles (N = 19),
logs (N = 16), and tree bases (N = 11) as refuges. Another 10 refuges were
recorded as “unidentified” and were most likely associated with shallow
burrows (e.g., mole tunnels; McCay 2000). The 10 unidentified refuges, along
with 4 of the 11 tree-base refuges that were in live trees, represented the only
refuges that were not associated with woody debris. That is, 233 of 247 (94%)
refuges were associated with some form of woody debris. Several refuges were
used by 2 different mice with the following breakdown by type: stumps (N =
15), brush piles (N = 5), root boles (N = 4), tree bases (N = 2), and unknown
(N = 1). Only on 5 occasions were 2 mice found using the same refuge on the
same day; all observations of joint nesting were during the winter.
Of the 247 refuges, 115 were on control plots and 132 were on treatment
plots. Stumps were the most common refuge type in both control and
treatment plots. The distribution of refuge types was significantly different
between treatment and control plots (G2 = 29.71, d.f. = 5, P = 0.0001). The
differences were particularly evident in 3 types: root boles, brush piles, and
400 Southeastern Naturalist Vol. 6, No. 3
logs. More root boles and brush piles were used on treatment plots than in
control plots, whereas more log refuges were used on control plots than
in treatment plots (Fig. 3).
The NB regression model yielded two significant main effects: vegetation
cover (2 = 4.10, d.f. = 1, P = 0.043) and refuge type (2= 9.34, d.f. = 4,
P = 0.053). Increasing vegetation cover decreased the likelihood that a
refuge received greater than expected use. Linear contrasts for refuge type
indicated that root bole refuges were significantly more likely to receive
greater than expected use than log or stump refuges (Table 2).
The main premise of this study was that refuges might be a limited
resource for cotton mice in southeastern pine forests. However, capture
data suggest that refuges were not limited because mouse density in both
treatment and control plots was relatively low compared to previous years.
Bimonthly trapping has been conducted on the plots in this study since
1997. The total number of cotton mice captures in 2002 and 2003 was
10.3% and 22.2%, respectively, of total captures in 1997, the year with the
most captures (S.C. Loeb, unpubl. data). The decline in mouse populations
was most likely a consequence of an extended period of drought that ended
in 2003. Although there is probably a population threshold above which
refuge availability would limit cotton mice abundance, food availability is
the most likely factor limiting cotton mice populations during our study
Figure 3. Number of refuges on study plots by type and treatment.
2007 T.M. Hinkelman and S.C. Loeb 401
(T.S. McCay, Colgate University, Hamilton, NY, pers. comm.). Indeed,
based on a food supplementation study, Smith et al. (1984) concluded that
food is a limiting factor for cotton mice under natural conditions at the
Savannah River Site.
With only three experimental plots per treatment and few mice tracked
per plot over three seasons, small sample sizes may have limited our
ability to detect a significant effect of season or treatment on refuge
fidelity. However, within each season, differences between control and
treatment plots were evident but inconsistent (Fig. 2). We expected mice
on control plots to exhibit higher fidelity than mice on treatment plots
because of lower woody debris volumes on control plots, but this occurred
in only one out of three seasons. Our measure of refuge fidelity
may not have adequately reflected the refuge-use patterns of each mouse.
Further, due to small sample sizes, individual variation in refuge fidelity
may have been greater than the treatment effect. Even with large sample
sizes, between-individual variation and behavioral correlations across
situations could obscure patterns in refuge fidelity (Bolnick et al. 2003,
Sih et al. 2004). For example, consistent individual differences in boldness
(e.g., bold and shy behavioral types) may influence refuge fidelity
more than refuge abundance such that a shy individual may switch refuges
infrequently even when refuges are abundant.
Refuge fidelity in rodents has not received much attention, despite considerable
insights gained from studies of site fidelity in other taxa (e.g., roost
fidelity in bats; Lewis 1995), and has primarily been studied in the context of
seasonal variation. For example, Frank and Layne (1992) reported that both
cotton mice and Ochrotomys nuttalli Harlan (golden mice) tended to spend
more days at each refuge and switch refuges less often in the winter than the
summer. Rodents often respond to cooler winter temperatures by nesting
Table 2. Parameter estimates, standard errors, and test statistics for variables of negative
binomial regression model of refuge use by cotton mice. Parameter estimate indicates the
direction and magnitude of the difference between two types of refuge. For example, the
negative sign indicates that logs are only 0.68 (or e-0.35) times as likely as root boles to be used
more than expected.
Parameter Estimate SE 2 P
Vegetation cover . . 4.10 0.043
Refuge type . . 9.34 0.053
Tree base vs. log 0.46 0.34 1.86 0.172
Brush pile vs. tree base -0.19 0.33 0.33 0.567
Brush pile vs. log 0.27 0.32 0.73 0.390
Brush pile vs. stump -0.10 0.23 0.18 0.668
Tree base vs. stump 0.09 0.26 0.13 0.719
Log vs. stump -0.37 0.24 2.39 0.123
Brush pile vs. root bole -0.45 0.26 3.09 0.079
Tree base vs. root bole -0.26 0.28 0.84 0.359
Log vs. root bole -0.35 0.15 5.52 0.019
Stump vs. root bole -0.35 0.15 5.52 0.019
402 Southeastern Naturalist Vol. 6, No. 3
communally and underground (Frank and Layne 1992, Madison et al. 1984,
Wolff and Hurlbutt 1982). We documented joint nesting on 5 occasions, and
all occurred in winter. Less switching in the winter may suggest that refuges
that are able to accommodate communal nesting and insulate against temperature
fluctuations occur in low abundance. High winter fidelity could
also arise from reduced activity and short periods of torpor in response to
cold temperatures or low food availability (Tannenbaum and Pivorun 1984).
Similar to McCay (2000), we documented almost exclusive use of woody
debris as refuge sites by cotton mice; 94% of refuges were associated with
some type of woody debris. Stump refuges were the most used type on both
control and treatment plots, but stumps were used relatively more on control
plots (Fig. 3). The lower number of stump refuges used on treatment plots
may have resulted from the greater use of other refuge substrates (e.g., root
boles, brush piles). Alternatively, some stumps might have been destroyed
by heavy equipment while trees were felled on treatment plots, and the lower
use simply reflected the reduced availability of suitable stump refuges.
Treatment activities, by design, increased the abundance of logs, brush
piles, and root boles on treatment plots and mice exploited the increased
availability of brush pile and root bole refuges on treatment plots (Fig. 3).
However, cotton mice used more log refuges on control plots, probably
because the newly felled logs on treatment plots were not decayed enough to
provide access as refuges or nesting cavities. Frank and Layne (1992) noted
the versatile refuge selection behavior of cotton mice, which likely accounts
for the different distribution of refuge types on treatment and control plots.
Indeed, ephemeral refuges, such as brush piles, provided alternatives that
were readily used by cotton mice. However, ephemeral refuge substrates are
likely more important to refuge use and fidelity when refuges are limited
The refuge-selection analysis was based only on used sites to avoid
assumptions about non-used sites (Erickson et al. 2001). Further, although
we only tracked 37 mice, we identified 247 unique refuges, which was
important because the refuge was the experimental unit in the analysis of
refuge selection. Based on this analysis, we affirmed the importance of
refuge type in refuge selection by cotton mice (Frank and Layne 1992), and
identified a negative relationship between vegetation cover and refuge selection.
However, logs, stumps, and trees in the refuge neighborhood were not
significant predictors of refuge selection. Likewise, Wolff and Hurlbutt
(1982) failed to identify any aboveground features that were related to the
selection of underground refuge sites by Peromyscus.
Although nest site selection is related to protective cover in other
rodents (Kalcounis-Rüppell and Millar 2002, Morzillo et al. 2003,
Wagner et al. 2000), cover in the refuge neighborhood may actually
2007 T.M. Hinkelman and S.C. Loeb 403
provide ambush sites for sit-and-wait predators (Reinert et al. 1984).
Cotton mice on these plots often move through open areas and do not
constrain movements to maintain proximity to logs and vegetation cover
(Hinkelman 2004). High surface temperatures during the day (most mice
were tracked during summer) may have favored selection for refuge features
that buffered environmental extremes rather than provide protective
cover in the refuge neighborhood. In Florida, cotton mice use Gopher
Tortoise burrows more than tree cavities because tortoise burrows provide
a stable microclimate (Douglass and Layne 1978, Frank and Layne
1992). Cotton mice in our study may have selected root boles over logs
and stumps because of the stability of the microclimate.
Selection for refuge type is likely related to microclimate, but certain
refuge types may provide more points of escape to evade predators that enter
a refuge. McCay (2000) found no differences in entrance diameter between
stump refuges used by cotton mice and randomly sampled stumps, but
perhaps the more relevant (and difficult to assess) attribute is the number of
entrances. Decay stage may provide a surrogate measure for the number
of entrances in a woody debris refuge. If so, the number of entrances may
explain why cotton mice select stumps that are more highly decomposed
than random stumps (McCay 2000). In Africa, Parotomys brantsii A. Smith
(Brant’s whistling rat), which inhabits open areas, digs many more burrow
entrances than Parotomys littledalei Thomas (Littledale’s whistling rat),
which occupies areas of good plant cover (Jackson 2000). Given that cotton
mice in our study selected refuges with less vegetation cover, the number of
refuge entrances may be very important in refuge selection.
In contrast to an earlier study on SRS (McCay 2000), cotton mice in our
study did not select refuges based on size. Our analysis only incorporated
used refuge sites whereas McCay (2000) compared stumps and root boles
used as refuges to randomly sampled stumps and root boles. Among actual
refuge sites, size may not be an important criterion for refuge selection (our
analysis), but size may dictate whether a potential refuge substrate is used at
all (McCay 2000).
The limitations of our study prevented us from drawing strong conclusions
about refuge fidelity in cotton mice. However, we believe that future
research on refuge fidelity in rodents will yield interesting insights into
habitat selection, social behavior, and population and community dynamics
including predator-prey and host-parasite interactions. Nest boxes may
present a cheaper alternative to radiotelemetry for studying refuge fidelity
and are readily used by Peromyscus (Havelka and Millar 2000, Rose and
Walke 1988). Size, number of entrances, and neighborhood vegetation
cover, for example, could be easily manipulated with careful construction
and placement of nest boxes.
The high association of refuges with woody debris indicates that woody
debris is an important resource for cotton mice, but, as habitat generalists,
404 Southeastern Naturalist Vol. 6, No. 3
cotton mice readily exploit a variety of refuge types. Management prescriptions
that increase woody debris abundance should increase habitat quality
for cotton mice by increasing the number of refuges available, which allows
mice to exhibit greater selectivity in the type of refuges used. Even a small
increase in the number of refuge substrates, especially root boles, may yield
marked improvements in habitat quality. Further research is needed, though,
to understand how refuge type and abundance interact to influence refuge
use, and how food availability amplifies or negates the importance of woody
debris abundance to cotton mice.
Funding was provided by Sigma Xi and the Department of Energy-Savannah
River Operations Office through the USDA Forest Service Savannah River under
Interagency Agreement DE-IA09-00SR22188 and the USDA Forest Service, Southern
Research Station. V. Barko, D. Leput, M. Mengak, T. McCay, T. Mong, S.
Zarnoch, X. Bernal, R. Strauss, and 2 anonymous reviewers provided helpful comments
on an earlier version of the manuscript. We thank Charles Dachelet, Heather
Ferguson, Hope Bowles, Denise Jones, and Stephanie Junker for their assistance in
the field. Carolyn Wakefield, John Blake, John Kilgo, and Ed Olson provided
invaluable assistance throughout the project. Trapping and handling procedures were
approved by the Animal Research Committee at Clemson University under Animal
Use Protocol No. 20007.
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