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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

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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. 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