Atypical Den Use of Carolina Northern Flying Squirrels
(Glaucomys sabrinus coloratus) in the Southern Appalachian
Mountains
Corinne A. Diggins, Christine A. Kelly, and W. Mark Ford
Southeastern Naturalist, Volume 14, Issue 3 (2015): N44–N49
Full-text pdf (Accessible only to subscribers.To subscribe click here.)
2015 Southeastern Naturalist Notes Vol. 14, No. 3
N44
C.A. Diggins, C.A. Kelly, and W.M. Ford
Atypical Den Use of Carolina Northern Flying Squirrels
(Glaucomys sabrinus coloratus) in the Southern Appalachian
Mountains
Corinne A. Diggins1,*, Christine A. Kelly2, and W. Mark Ford3
Abstract - Glaucomys sabrinus coloratus (Carolina Northern Flying Squirrel) is a federally endangered
subspecies that occurs in high elevation forests of the southern Appalachian Mountains.
Denning sites may be a limiting factor for this subspecies in areas where cavity trees are not abundant
or where interspecific competition from other tree squirrels occurs. This shortage can result in use of
unusual denning sites, such as subterranean dens. Herein, we report atypical denning habits of radiocollared
Carolina Northern Flying Squirrels in southwestern Virginia and western North Carolina
from 2008 to 2011 and 2014. Increased knowledge of denning habitats may be beneficial for conservation
and habitat management of this subspecies, particularly in sub-optimal or degraded habitats.
Glaucomys sabrinus coloratus Howell (Carolina Northern Flying Squirrel) is a federally
endangered subspecies of Northern Flying Squirrel that occurs in disjunct sky islands
of montane conifer–northern hardwood forests in the southern Appalachian Mountains
(USFWS 1990, Weigl et al. 1992). This subspecies is considered a secondary cavity nester
in both live trees and snags, but also uses external dens called dreys (Ford et al. 2014;
Hackett and Pagels 2003; Weigl and Osgood 1974; Weigl et al. 1992, 2002). Dreys are
constructed of twigs, leaves, and shredded bark and typically located between branches in a
tree (Cowan 1936, Weigl et al. 1992). Flying squirrels use den sites as shelter from predators
and weather, cache sites, and natal dens (Bendel and Gates 1987, Cowan 1936, Weigl 1978,
Weigl and Osgood 1974).
In other parts of the range, den types used by Northern Flying Squirrels vary between
cavities and dreys depending on the forest-stand type and structure, season, geographic
location, and ecological community as well as on the age, sex, and reproductive condition
of individual squirrels (Bakker and Hastings 2002, Carey et al. 1997, Cotton and Parker
2000, Holloway and Malcolm 2007, Menzel et al. 2004, Meyer et al. 2005, Smith 2012,
Urban 1988). Den availability is considered a possible limiting factor for Northern Flying
Squirrels (Carey et al. 1997, Holloway and Malcolm 2007, Pyare et al. 2010, Smith 2012),
potentially influencing squirrels to be behaviorally plastic opportunists (Weigl 2007) adaptable
to a wide variety of conditions in various habitats. This opportunistic behavior may
be exhibited as flexibility in den-site selection (Cotton and Parker 2000), especially where
past land use (e.g., timber harvesting) has influenced den availability or where competition
for denning sites is high due to intra- and interspecific competition (Bendel and Gates 1987,
Carey et al. 1997, Hackett and Pagels 2003, Pyare et al. 2010, Smith 2012, Weigl 1978).
In addition to cavities and dreys, Northern Flying Squirrels use dens in low structures
(e.g., downed woody debris) and subterranean dens, but the number of observations of
such alternative den sites reported in the literature are limited (Bakker and Hastings 2002,
Carey et al. 1997, Gerrow 1996, Hacket and Pagels 2003, Weigl et al. 2002). Other types of
1Department of Fisheries and Wildlife Conservation, Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061. 2Wildlife Diversity Program, North Carolina Wildlife Resources
Commission, Asheville, NC 28803. 3US Geological Survey, Virginia Cooperative Fish and Wildlife
Research Unit, Blacksburg, VA 24061. *Corresponding author - cordie1@vt.edu.
Manuscript Editor: Andrew Edelman
Notes of the Southeastern Naturalist, Issue 14/3, 2015
N45
2015 Southeastern Naturalist Notes Vol. 14, No. 3
C.A. Diggins, C.A. Kelly, and W.M. Ford
atypical dens, such as unusually placed dreys, are also rare or absent from the literature; the
majority of studies only report use of cavities as den sites (e.g., Baker and Hasting 2002,
Cotton and Parker 2000). Herein, we provide observations of unusual diurnal denning sites
utilized by Carolina Northern Flying Squirrels in the southern Appalachians.
Methods. Our study sites occurred in secondary and old-growth forests in the southern
Appalachian Mountains in southwestern Virginia and western North Carolina. Sites were in
high-elevation Tsuga canadensis (L.) Carr (Eastern Hemlock)-northern hardwood forests
on Whigg Cove and Hooper Bald in the Unicoi Mountains (UM) Graham County, NC;
Picea rubens Sarg. (Red Spruce)-northern hardwood forests on Whitetop Mountain (WM),
Grayson County, VA; northern hardwood forest with a minor component of recovering Red
Spruce on Little Sam Knob (LSK) in the Great Balsam Mountains, Haywood County, NC;
and Red Spruce-Abies fraseri (Pursh) Poir (Fraser Fir) forest along the Cloudland Trail, and
Red Spruce-northern hardwood forests on Carver’s Gap in the Roan Mountain Highlands
(RMH), Mitchell County, NC and Carter County, TN (Fig. 1). All stands were subjected to
clearcutting in the late 1880s through the mid-20th century and, in some areas, experienced
subsequent fires following the industrial logging period. The lone exception was the stand
on WM, which is an old-growth stand containing trees ~180 y old (T. Blevins, USDA Forest
Service, Mt. Rogers National Recreation Area, Marion, VA, pers. comm.). We captured
Carolina Northern Flying Squirrels using live-trapping (UM, WM, RMH) and nest-box
checks (UM, LSK, RMH). Sampling was conducted in winter 2008–2011 (UM), spring
Figure 1. Study-site locations where Carolina Northern Flying Squirrels were tracked to atypical
den sites. UM = Unicoi Mountains, LSK = Little Sam Knob, RMH = Roan Mountain Highlands, and
WM = Whitetop Mountain. The predicted range of the Carolina Northern Flying Squirrel is from Ford
et al. (2015).
2015 Southeastern Naturalist Notes Vol. 14, No. 3
N46
C.A. Diggins, C.A. Kelly, and W.M. Ford
2009 (UM), and winter and spring 2014 (WM, LSK, RMH). We used Tomahawk 201 live
traps (14 cm x 14 cm x 41 cm; Tomahawk Live Trap Co., Hazelhurst, WI) baited with a slice
of apple with a peanut butter or peanut butter–molasses–bacon-grease topping. We placed
polyfil batting in each trap and wrapped traps with plastic and duct tape to help reduce trap
stress and risk of hypothermia. We set traps on the ground, along log runs, and on the bole
of trees to increase captures of arboreal mammals (Loeb et al. 1999). We set traps at sunset,
checked them at sunrise, and, to reduce captures of diurnal species, closed traps during the
day. We acquired additional captures by checking wooden nest boxes (30 cm x 18 cm x 15
cm with 5 cm x 5 cm entrance) established by the North Carolina Wildlife Resources Commission,
Asheville, NC. Nest boxes were hung approximately 3.6 m high on the trunks of
trees with nails and wire (Kelly et al. 2013). We differentiated between the Carolina Northern
Flying Squirrel and the parapatric G. volans L. (Southern Flying Squirrel) by measuring
the hind foot (>34 mm in length for Northern Flying Squirrels) and examining the fur on
the abdomen (Wells-Gosling and Heaney 1984). We measured, weighed, sexed, aged, and
tagged individuals with a uniquely numbered Monel 1005-1 tag (National Band and Tag
Co., Newport, KY). We radio-collared adult squirrels with 3.4-g or 4.5-g PD-2C transmitters
(Holohil Systems Ltd., Carp, ON, Canada). We did not anesthetize squirrels during
handling or collaring, and no individual squirrel was handled for more than 10 minutes. To
track radio-collared squirrels to den sites, we used TR42000S receivers (Wildlife Materials,
Carbondale, IL) and 2-element folding yagi antennas. We tracked squirrels to diurnal dens
on a bi-weekly to monthly basis for UM and LSK, and on a daily to weekly basis for WM
and RMH. We identified den sites by type (cavity, drey, subterranean), tree or shrub species
(for cavities and dreys), and nest height (for arboreal nests).
Results. We tracked 2 individuals to subterranean dens at UM. In February and March
2008, we tracked an adult male at Hooper Bald to a subterranean den under a rock (1.4 m
x 1.5 m x 0.9 m) on 3 occasions. The rock was covered with moss and ferns with a double
trunked Acer rubrum L. (Red Maple) adjacent to the rock. We also found this male denning
in a cavity higher up on the same Red Maple adjacent to the rock. In 2008, we located an
adult female from UM at Whigg Branch denning in a subterranean den in the root mass of
a live Eastern Hemlock on 18 occasions from March to June. Because this was the only
den where we located her during this period, we initially suspected that she had dropped
her radio-collar. However, nighttime telemetry observations showed the female exiting
the den and exhibiting normal movement behaviors of radio-collared flying squirrels, and
afterwards she returned to the subterranean den site. We recaptured this female and radiocollared
her the following year, although she did not use any subterranean dens during a
12-week tracking period in spring 2009.
In 2008 at UM, the same adult female who utilized a subterranean den site also denned in
downed coarse woody debris. She was denning in the log (diameter ~17 cm at den entrance)
or underground beneath the log in a subterranean den on 5 occasions in February and March,
including 3 consecutive days at the same den site. There was a fractured-rock crevice at the
entrance to the rotting log, so we were unable to determine whether she was denning in the
log or underneath it, although we saw shredded Yellow Birch bark in the rotten log.
During February 2014 at LSK, we observed a juvenile male using a subterranean den under
a boulder (1.5 m x 1 m x 0.5 m) in a northern hardwood forest. Approximately 15.3 cm
of wet snow was on the ground for the 1 occasion the male was found under the boulder. We
tracked the male 3 days later and found his collar but no evidence of predation. We found
this same juvenile male in a drey in a Rhododendron maximum L. (Rosebay Rhododendron)
canopy ~4 m in height. The outside of the drey was predominantly made of shredded Betula
alleghaniensis Britton (Yellow Birch) bark and twigs. This male denned in the drey for 2
consecutive days in February 2014.
N47
2015 Southeastern Naturalist Notes Vol. 14, No. 3
C.A. Diggins, C.A. Kelly, and W.M. Ford
We captured an adult female in a live trap in February 2014 at WM, released her at
the capture site in the Red Spruce-northern hardwood ecotone with a thick Rosebay Rhododendron
shrub stratum, and observed her retreating into a subterranean den in a rotten
root-wad at the base of a live Yellow Birch. The subterranean den appeared to be a smallmammal
burrow that went down into the root mass of the Yellow Birch. We did not collar
this particular female and therefore could not determine if she remained in the subterranean
burrow for the rest of the day.
At RHM, we tracked an adult male to a subterranean den in a root mass at the base of a
live Red Spruce tree with a diameter at breast height of 33.6 cm. We observed the squirrel
denning there in May 2014 for 1 day, although there was a 3-day gap between the observation
at that den site and the next denning location. Additionally, we only gathered denning
locations for 2 weeks at RMH, so the duration and frequency of use for this particular den
site is unknown. The tree was along an ephemeral headwater stream on the Tennessee side
of Carver’s Gap at RMH.
In April 2014, near the Cloudland Trail at RMH, we found an adult male denning in a
downed Fraser Fir log suspended approximately 1 m off the ground. The diameter of the log
was 36 cm. The male appeared to access the den site by a network of hollow cavities near
the uprooted end of the tree. We found the male using this den site on 1 occasion, although
he utilized several cavities in different trees within 15 m of this den site.
Discussion. Our observations of atypical den usage by Carolina Northern Flying Squirrels
highlight the plasticity of den selection by this subspecies in the southern Appalachians
(Hackett and Pagels 2003, Menzel et al. 2004). We found that Carolina Northern Flying
Squirrels utilized subterranean and low structure-dens during the winter and spring, confirming
1 previous observation that Carolina Northern Flying Squirrels used underground
dens during the colder months of the year in the Appalachians (Weigl et al. 2002). Hackett
and Pagels (2003) found 27% of nests used by Carolina Northern Flying Squirrels in Virginia
were subterranean. However, they only observed males using these dens in the summer
time, whereas we observed females and males using subterranean dens during colder times
of the year. Gerrow (1996) documented increased use of subterranean dens in New Brunswick,
Canada, during colder months when snowfall occurred. However, because we tracked
the majority of our radio-collared squirrels in the winter and spring, we cannot determine if
use of subterranean dens varies with season. Nonetheless, similar to observations in other
parts of the Northern Flying Squirrel’s range, we found Carolina Northern Flying Squirrels
using subterranean dens in rock colluvium and root structures, and low-structure dens in
downed coarse woody debris (Bakker and Hastings 2002, Carey et al. 1997, Gerrow 1996,
Hackett and Pagels 2003).
One of the most unusual observations was the drey in the Rosebay Rhododendron used
by the juvenile male at LSK. Although dreys are common denning structures in the Appalachians
(Hackett and Pagels 2003, Menzel et al. 2004, Urban 1988, Weigl et al. 1992), they
are typically found in living deciduous or coniferous trees. This is first known observation
of a drey occurring in the ericaceous shrub layer.
Increased understanding of how past land-use, competitors, and predators may influence
Carolina Northern Flying Squirrel denning ecology is important for the conservation of this
species (Hackett and Pagels 2003, Menzel et al. 2004, Weigl 2007). Examining stand-level
and intra-stand level characteristics that influence den selection could help indicate how and
why this subspecies selects certain den sites. These observations could aid in habitat management
for Carolina Northern Flying Squirrels because denning sites are likely important
for the long-term persistence of this subspecies in the Southern Appalachians.
2015 Southeastern Naturalist Notes Vol. 14, No. 3
N48
C.A. Diggins, C.A. Kelly, and W.M. Ford
Acknowledgments. We would like to thank P. Curtin, K. Parker, D. Brown, and H.B.
Hound for field support. We also thank K. Weeks, S. Jones, and P. Weigl. Funding was provided
by the North Carolina Wildlife Resources Commission (NCWRC) and the US Fish
and Wildlife Service, Asheville, NC, Field Office. This work was conducted under NCWRC
Permit #14-ES00401 and Virginia Tech IACUC Permit #11-120-FIW. N. Castleberry, A.
Edelman, and 2 anonymous reviewers provided helpful comments which improved the
manuscript. The use of any trade, product or firm names does not imply endorsement by the
US government.
Literature Cited
Bakker, V.J., and K. Hastings. 2002. Den trees used by Northern Flying Squirrels (Glaucomys sabrinus)
in southeastern Alaska. Canadian Journal of Zoology 80:1623–1633.
Bendel, P.R., and J.E. Gates. 1987. Home range and microhabitat partitioning of the Southern Flying
Squirrel (Glaucomys volans). Journal of Mammalogy 68(2):243–255.
Carey, A.B., T.M. Wilson, C.C. Maguire, and B.L. Biswell. 1997. Dens of Northern Flying Squirrels
in the Pacific Northwest. Journal of Wildlife Management 61(3):684–699.
Cotton, C.L., and K.L. Parker. 2000. Winter habitat and nest trees used by Northern Flying Squirrels
in subboreal forests. Journal of Mammalogy 81(4):1071–1086.
Cowan, I.M. 1936. Nesting habits of the flying squirrel Glaucomys sabrinus. Journal of Mammalogy
17(1):58–60.
Ford, W.M., C.A. Kelly, J.L. Rodrigue, R.H. Odom, D. Newcomb, L.M. Gilley, and C.A. Diggins.
2014. Late winter and early spring home-range and habitat use of the endangered Carolina Northern
Flying Squirrel in western North Carolina. Endangered Species Research 23:73–82.
Ford, W.M., A.M Evans, R.H. Odom, J.L. Rodrigue, C.A. Kelly, N. Abaid, C.A. Diggins, and D.
Newcomb. 2015. Predictive habitat models derived from nest-box occupancy for the endangered
Carolina Northern Flying Squirrel in the Southern Appalachians. Endangered Species Research
27:131–140.
Gerrow, J.S. 1992. Home range, habitat use, nesting ecology, and diet of the Northern Flying Squirrel
in southern New Brunswick. M.Sc. Thesis. Acadia University, Wolfville, NS, Canada. 53 pp.
Hackett, H.M., and J.F. Pagels. 2003. Nest-site characteristics of the endangered Northern Flying
Squirrel (Glaucomys sabrinus coloratus) in southwest Virginia. American Midland Naturalist
150(2):321–331.
Holloway, G.L., and J.R. Malcolm. 2007. Nest-tree use by Northern and Southern Flying Squirrels in
central Ontario. Journal of Mammalogy 88(1):226–233.
Kelly, C.A., C.A. Diggins, and A.J. Lawrence. 2013. Crossing structures reconnect federally endangered
flying squirrel populations divided for 20 years by road barrier. Wildlife Society Bulletin
37(2):375–379.
Loeb, S.C., G.L. Chapman, and T.R. Ridley. 1999. Sampling small mammals in southeastern forests:
The importance of trapping in trees. Proceedings of the Annual Conference of Southeastern Association
of Fish and Wildlife Agencies 53:415–424.
Menzel, J.M., W.M. Ford, J.W. Edwards, and M.A. Menzel. 2004. Nest–tree use by the endangered
Virginia Northern Flying Squirrel in the central Appalachian Mountains. American Midland
Naturalist 151(2):355–368.
Meyer, M.D., D.A. Kelt, and M.P. North. 2005. Nest trees of Northern Flying Squirrels in the Sierra
Nevada. Journal of Mammalogy 86(2):275–280.
Pyare, S., W.P. Smith, and C.S. Shanley. 2010. Den use and selection by Northern Flying Squirrels in
fragmented landscapes. Journal of Mammalogy 91(4):886–896.
Smith, W.P. 2012. Flying Squirrel demography varies between island communities with and without
Red Squirrels. Northwest Science 86(1):27–38.
United States Fish and Wildlife Service (USFWS). 1990. Appalachian Northern Flying Squirrel
(Glaucomys sabrinus fuscus and Glaucomys sabrinus coloratus) recovery plan. Annapolis Field
Office, US Department of Interior, Annapolis, MD. 62 pp.
N49
2015 Southeastern Naturalist Notes Vol. 14, No. 3
C.A. Diggins, C.A. Kelly, and W.M. Ford
Urban, V. 1988. Home range, habitat utilization, and activity of the endangered Northern Flying
Squirrel. M.Sc. Thesis. West Virginia University, Morgantown, WV. 59 pp.
Weigl, P.D. 1978. Resource overlap, interspecific interactions, and the distribution of the flying squirrels
Glaucomys volans and G. sabrinus. American Midland Naturalist 100(1):83–96.
Weigl, P.D. 2007. The Northern Flying Squirrel (Glaucomys sabrinus): A conservation challenge.
Journal of Mammalogy 88(4):897–907.
Weigl, P.D., and D.W. Osgood. 1974. Study of the Northern Flying Squirrel, Glaucomys sabrinus, by
temperature telemetry. American Midland Naturalist 92(2):482–486.
Weigl, P.D., T.W. Knowles, and A.C. Boynton. 1992. The distribution and ecology of the Northern
Flying Squirrel, Glaucomys sabrinus coloratus, in the southern Appalachians. North Carolina
Wildlife Resources Commission Project Report, Raleigh, NC. 93 pp.
Weigl, P.D., R.S. Hughes, and D.C. Battle. 2002. Study of the Northern Flying Squirrel populations
along the Cherohala Skyway: Questions of fragmentation and ecology in the southernmost part of
the range. Report to the US Fish and Wildlife Service, Asheville, NC. 83 pp.