Northern Flying Squirrel (Glaucomys sabrinus) Species Guidance Family: Sciuridae – the squirrels
Species of Greatest Conservation Need (SGCN)
State Status: SC/P (Special Concern/Fully Protected) State Rank: S3S4
Federal Status: None Global Rank: G5
Wildlife Action Plan Counties with documented locations Mean Risk Score: 3.2 of northern flying squirrels in Wildlife Action Plan Area of Wisconsin. Source: Natural Heritage Photo by Ryan Stephens Importance Score: 2 Inventory Database, April 2013.
Species Information
General Description: The northern flying squirrel and its sister species, the southern flying squirrel (Glaucomys volans), both occur in Wisconsin. The northern flying squirrel is slightly larger than the southern flying squirrel, but is small compared to other tree squirrels. Adult northern flying squirrels in the Great Lakes region weigh 70-130 g (2.5-4.6 oz) (Kurta 1995). Total length (including tail) ranges from 245-315 mm (10-12 in), tail length 110-150 mm (4.3-5.9 in), hindfoot length 35-40 mm (1.4-1.6 in), and ear height 18-26 mm (0.7-1.0 in) (Jackson 1961, Kurta 1995). Pelage (fur) is silky and usually cinnamon–colored, but can range from dark brown to red. Belly hair is white at the tips and gray at the base. The northern flying squirrel uses its patagium (loose flap of skin between the front and hind legs; Fig. 1) for gliding between trees. A cartilaginous projection called a styliform process extends from the wrist (Fig. 1) to widen the patagium and enhance its effect (Wells-Gosling and Heaney 1989).
Similar Species: The flying squirrels can easily be distinguished from the other eight Wisconsin squirrels by the presence of a furry patagium (flap of skin) that runs from the wrist to the ankle, and also by a cartilaginous projection on the wrist called a styliform process. Both flying squirrel species have silky pelage, an extremely wide dorso-ventrally flattened tail, and exceptionally large eyes. Flying squirrels are also almost exclusively nocturnal, whereas all other squirrels are largely diurnal. The northern flying squirrel closely resembles its congener, the southern flying squirrel, but can be distinguished by several characteristics. The most diagnostic feature is the color of the belly fur – the southern flying squirrel has white hairs to the base, whereas the northern flying squirrel has white tips with a gray base (Fig. 2b,c). The northern flying squirrel is usually larger (< 80 g in G. volans and > 70 g in G. sabrinus; Fig. 2a) with more cinnamon-colored pelage and a larger hind foot (≥ 34 mm in G. sabrinus and ≤ 32 mm in G. volans; Wells- Gosling and Heaney 1989). The tail of the northern flying squirrel is also longer Figure 1. Northern flying squirrel specimen. © Ryan (≤ 115 mm in G. volans) and has a darker tip, whereas the southern flying squirrel Stephens has a uniformly colored tail (Jackson 1961, Wells-Gosling and Heaney 1989).
a b c
Figure 2. a) Study skin of southern flying squirrel (top) and northern flying squirrel (bottom); b) belly fur of the northern flying squirrel, showing hairs with gray color at base; and c) belly fur of the southern flying squirrel, showing hairs that are white to the base. © Ryan Stephens.
Northern Flying Squirrel Species Guidance 1 of 9 PUB ER-677 (last updated June 23, 2017) Associated Species: Predators of the northern flying squirrels in Wisconsin include American marten (Martes americana), weasels (Mustela spp.), coyotes (Canis latrans), foxes, domestic cats, barred owls (Strix varia), great horned owls (Bubo virginianus), northern goshawks (Accipiter gentilis), raccoons (Procyon lotor), and red-tailed hawks (Buteo jamaicensis; Jackson 1961, Wells-Gosling and Heaney 1989, Kurta 1995, Wilson and Carey 1996).
State Distribution and Abundance: The northern flying squirrel is restricted to the northern forest regions of Wisconsin. Its southern limit is roughly marked by the tension zone (Curtis 1959) and extends from Burnett County in western Wisconsin, through Clark and Portage Counties in central Wisconsin, and into Outagamie and Door Counties in eastern Wisconsin (Jackson 1961, Long 2008). It can be locally common, but often has a spotty distribution and is usually not captured in abundance anywhere across its range (Long 2008). Research is needed to more precisely characterize the northern flying squirrel’s distribution and local abundance in Wisconsin, and therefore current distribution information for this species may not reflect its full extent in Wisconsin.
Global Distribution and Abundance: The northern flying squirrel is a boreal species whose range extends from the tree line in Alaska and Canada to mountainous regions of California, Utah, Virginia, Tennessee, and North Carolina. It is generally common in most of the northwest portion of its range), but populations (sub-species) in the Appalachian Mountains of Virginia (G. s. fuscus) and North Carolina (G. s. coloratus) are federally endangered.
Distribution of the northern flying squirrel in Range of Northern flying squirrel in North America. (Redrawn by Wisconsin. Dots represent museum records. Stephens in 2012 from Wells-Gosling and Heaney 1989) (Stephens, unpublished data, 2012)
Diet: The northern flying squirrel is omnivorous. It consumes fungi (known as mycophagy) and feeds on mushrooms and truffles, which are the subterranean fruiting bodies of hypogeous mycorrhizal fungi and release a strong scent when ripe (Thysell 1997, Lehmkuhl 2004, Weigl 2007). These foods are especially important in the spring and fall (Thysell 1997, Lehmkuhl 2004), and lichens are an important food source during the winter months (Thysell 1997, Smith 2007, Lehmkuhl et al. 2006). Northern flying squirrels in Wisconsin and the eastern US may have a more diverse diet than in other parts of their range; they eat acorns, hazelnuts, beechnuts, other hardwood mast or nuts, conifer seeds, fruits, tree buds, insects, and bird eggs, and readily consume meat when available (Jackson 1961, Wells-Gosling and Heaney 1989, Mitchell 2001). Northern flying squirrels may hoard winter foods, but this practice is not well documented and appears to be practiced less than the southern flying squirrel, which relies on cached hardwood mast (acorns or other nuts) to make it through the winter.
Reproductive Cycle: Mating occurs from late March to late May (Jackson 1961). Gestation lasts about 37-42 days. The mother typically gives birth to two to three pups between May and July, but may produce as many as six (Carey 2002). Usually only one litter is born per year, but a second litter may be born in mid-summer, especially in the southern portion of the species’ range or upon failure of the first litter (Vernes 2004, Long 2008). Young are born naked with a membrane covering their eyes and ears, but the patagium is clearly visible (Wells-Gosling and Heaney 1989). Weaning is completed at about two months (usually by the end of September even if two litters are reared), but young may stay with the mother for several additional months (Wilson and Ruff 1999, Vernes 2004).
Ecology: The northern flying squirrel does not hibernate, but does reduce its time outside the nest during the colder months (Vernes 2004). It is completely nocturnal and has two daily activity peaks, one around sunset to a few hours after dark and the other in the early morning (Weigl 1974, Vernes 2004, E. Anderson unpublished data); the earlier period may account for most of the evening’s activity (E. Anderson unpublished data). Inclement weather may delay departure from the nest for foraging, but does not prevent it, and early cloud cover can induce early departure (Weigl 1974). The name “flying squirrel” is a misnomer because the flying squirrel
Northern Flying Squirrel Species Guidance 2 of 9 PUB ER-677 (last updated June 23, 2017) does not actually possess true flight like bats. Rather it volplanes (glides), aided by its patagium, from the trunk of one tree to a lower trunk of another tree. These glides can be as far as 90 m (295 ft) but are normally about 19.7 m (64.6 ft; Wells-Gosling and Heaney 1989). Northern flying squirrels are relatively long lived (three to four years) and have low reproductive rates compared to other small mammals (Weigl 2007). This species usually produces only one litter per year between May and October, whereas the southern flying squirrel usually produces two litters (Long 2008).
Active Season (does not hibernate)
J F M A M J J A S O N D
Breeding Young-rearing
The northern flying squirrel also has an ecologically important relationship with fungi on which it feeds, and spreads mycorrhizal fungi by excreting fungal spores after feeding on the fruiting bodies, or truffles (Lehmkuhl et al. 2004, Weigl 2007). These fungi are an important part of the forest ecosystem, and contribute to nutrient and water uptake by many coniferous tree species (Smith 2007). This relationship is most evident in the Pacific Northwest but also occurs in Alaska and eastern North America, and therefore may exist in Wisconsin as well. The northern flying squirrel is considered a “keystone species” in the Pacific Northwest (Wilson and Ruff 1999) because of this obligate symbiotic association with forest fungi and because of its importance as a primary food source for the federally endangered spotted owl (Strix occidentalis).
Natural Community Associations (WDNR 2005 and WDNR 2009, but modified by R. Stephens based on unpublished data, Jackson 1961, and Long 2008): Significant: boreal forest, northern mesic forest, northern wet-mesic forest, black spruce swamp, tamarack poor swamps Moderate: northern dry-mesic forest, mesic cedar forest, muskeg, pine barrens, northern dry forest, and great lakes ridge, swale Minimal: northern hardwood swamps
Habitat: The northern flying squirrel occupies a wide variety of habitats across its range. Although this species has long been considered an old-growth forest specialist, old-growth habitat may not be essential (Waters and Zabel 1995, Ransome and Sullivan 1997, Smith et al. 2005, E. Anderson unpublished data). Nevertheless, northern flying squirrels are associated with some factors generally consistent with older forests, such as wooded areas with standing live and dead trees, an abundance of decaying coarse woody debris, diverse understory, and high truffle abundances (Smith et al. 2005, Smith 2007). Conifers and moist forests are also important components in nearly all of this species’ range (Jackson 1961, Weigl 1978, Ford et al. 2004, Smith 2007). In Wisconsin, the northern flying squirrel often occurs in pure stands of spruce, northern white cedar, or tamarack (Jackson 1961, R. Stephens pers. obs.). Conifers are associated with higher abundances of truffles and lichens, which are staples of the squirrel’s diet (Loeb et al. 2000). There is some speculation that northern flying squirrels may also consume the staminate cones and needles of conifers as a natural remedy to purge themselves of the parasitic nematode Stongyloides robustus (see “Threats” section below), which can be fatal (Payne et al. 1989). In Wisconsin, and in the eastern portion of the northern flying squirrel’s range, mixed stands of conifers and hardwoods are the most commonly used habitat type, and ecotones (boundaries) between conifer forests and hardwood forests appear to be particularly important habitat (Jackson 1961, Payne et al. 1989, Kate Witkowski pers. comm.). Pure stands of hardwoods may also be acceptable habitat in some cases, but northern flying squirrels rarely use them (Jackson 1961). This avoidance may arise from interspecific competition with the southern flying squirrel, which is known to aggressively displace the northern flying squirrel (Smith 2007). In areas where the two species co-occur, the southern flying squirrel is associated with hardwood forest cover and the northern flying squirrels with coniferous cover (Weigl 1978, Holloway and Malcolm 2006, E. Anderson unpublished data).
a b c d
Photos illustrating natural community associations used by the northern flying squirrel (left to right): a) Black spruce swamp (Clark Co. WI), b) Tamarack poor swamp (Clark Co. WI), c) Northern wet mesic forest (Lincoln Co. WI), d) Northern mesic forest (Vilas Co. WI). © Ryan Stephens.
Density and home range: Relatively little is known about the home range of northern flying squirrels in Wisconsin (Long 2008). Home range elsewhere varies from 2-3 acres but may be as large as 31.5 acres (Wells-Gosling and Heaney 1989, Long 2008). Densities of northern flying squirrels in Wisconsin are also poorly studied, but densities in the west range from about 0.2-1.6 squirrels
Northern Flying Squirrel Species Guidance 3 of 9 PUB ER-677 (last updated June 23, 2017) acre (Waters and Zabel 1995, Lehmkuhl et al. 2006, Smith 2007). Males may travel great distances in search of females in the early spring (Weigl 2007).
Nesting: Northern flying squirrels may nest in hardwoods or conifers. Unlike southern flying squirrels, which are strictly cavity nesters, northern flying squirrels use cavities but also construct external nests known as dreys (Cowan 1936, Weigl 1974). Cavity nests may be as low as 0.9-1.5 m (3-5 ft) (Cowan 1936), but most nests are much higher, averaging 11.5 m (37.7 ft) above the ground in British Columbia (Cotton and Parker 2000). Northern flying squirrels are not known to nest in course woody debris lying on the ground. Cavities are used all year long but are used most during the winter. Cavity nests are often excavated by woodpeckers, but natural cavities in live trees or snags are also used (Cowan 1936, Weigl 1974). Northern flying squirrels have been observed to congregate in cavities during the winter for thermodynamic reasons, but this species is generally more solitary than the southern flying squirrel (Weigl 1974). Cavity nests can be over 20° C warmer than the outside temperature (Weigl 1974). Dreys are built almost exclusively in conifers and are primarily used during the summer for young-rearing and resting or feeding (Cowan 1936, Weigl 1978, Smith 2007). Dreys are often built in witches’ brooms (branch deformity resulting in dense growth of shoots), tree boles, branches on conifers, or in clumps of broken branches (Cowan 1936, Kate Witkowski pers. comm.). In Wisconsin, witches’ brooms are common in black spruce and are caused by a mistletoe species (Arceuthobium pusillum). They may provide important nesting sites in black spruce swamps that have few large-diameter trees. Dreys can also be made from modified bird nests (Cowan 1936). These types of nests may be especially important in areas of sympatry where the more aggressive southern flying squirrel may displace northern flying squirrels from tree cavities (Weigl 1978, Smith 2007).
Threats: Loss of suitable habitat is among the greatest threats to northern flying squirrels. The northern flying squirrel depends on forested habitat, especially forests with conifers and older-forest characteristics, and the amount of forest cover within the Great-Lakes region has been reduced since European settlement by over one third (Frelich 1995). Large roads (e.g., two-lane highways) that bisect forested areas, clear-cut harvesting, and conversion of forests to agricultural lands reduce and fragment the type of forest that this species needs, and limit or prevent dispersal (Smith 2007, Weigl 2007). Roads and logging also increase the amount of edge habitat and raise predation risks (Smith 2007). Logging, regardless of the forest practice used, seems to temporarily reduce northern flying squirrel habitat both in quantity and quality, as indicated by lower densities (Bowman et al. 2005, Waters and Zabel 1995, Holloway and Malcolm 2006, Lehmkuhl et al. 2006, Herbers and Klenner 2007). One important negative effect of logging on northern flying squirrels might arise indirectly from logging’s tendency to benefit the more aggressive southern flying squirrel (Holloway and Malcolm 2006), and therefore favor its intrusion into the site. Southern flying squirrels in turn occupy nest cavities, reducing nest site availability, and actively displace the northern flying squirrel into less suitable habitat (Weigl 1978). In addition, hybridization between the two species has also been documented in a broad area where the species are increasingly coming into contact because of climate change and other human influences; whether this phenomenon represents a threat to local populations is not yet known.
Expansion of the southern flying squirrel into areas occupied by the northern flying squirrel presents additional indirect impacts beyond physical displacement. Southern flying squirrels carry the parasitic nematode Stongyloides robustus, which has little impact on them but can be extremely debilitating or even fatal to the northern flying squirrel (Wetzel and Weigl 1994). The parasite is spread through fecal material. Southern flying squirrels defecate in nests, whereas northern flying squirrel maintain separate nests as latrines (Wetzel and Weigl 1994). This critical difference between the two species increases the chances that northern flying squirrels will contract the parasite when their nests are also used by southern flying squirrels.
Much is known about the ecology of the northern flying squirrel in the southern Appalachians, where it is listed as endangered, and on the west coast where it is the primary food source for the endangered northern spotted owl. However, little is known about the natural history of the northern flying squirrel in the Midwest, and this lack of knowledge poses a significant barrier to conservation of this species in Wisconsin. Live trapping can be used to help increase our understanding and locally ascertain the presence of the northern flying squirrel.
Climate Change Impacts: Indirect effects of climate change on the northern flying squirrel may be significant and will test the plasticity of the species. After a disturbance or logging, forests naturally regenerate back to native vegetation through succession; however logging, coupled with climate change and invasive species, may disrupt ecological succession after a disturbance and ultimately change forest landscapes (Smith 2007). Climate change coupled with drought conditions may also create more xeric conditions in parts of the state (WICCI 2011). Warming may decrease the productivity of fungi, which are one of the main northern flying squirrel food sources (Mitchell 2001). Lichens are another important winter food, and climatic drying may also limit the amount of lichen growth on trees (Lehmkuhl et al. 2006, Weigl 2007). Predicted warming trends, especially warmer winters (WICCI 2011, Swanston et al. 2011), suggest that many northern forest types will move further north, and reduce the size and extent of suitable habitat for the northern flying squirrel in Wisconsin (Bachelet et al. 2001, Iverson and Prasad 2001). Northern white cedar (Thuja occidentalis), red pine (Pinus resinosa), and spruce (Picea spp.), are predicted to be especially affected by climate change (Iverson and Prasad 2001). These species are particularly important components of natural communities such as boreal forest, northern dry- mesic forest, northern mesic forest, northern wet-mesic forest, and black spruce swamps, all of which are habitats for the northern flying squirrel.
As conifers shift northward, habitat suitability for mast-producing hardwoods such as oak (Quercus spp.) and hickory (Carya spp.) in
Northern Flying Squirrel Species Guidance 4 of 9 PUB ER-677 (last updated June 23, 2017) northern Wisconsin is predicted to improve (Bachelet et al. 2001, Iverson and Prasad 2001). Southern flying squirrels are restricted by both cold temperatures and mast availability (Bowman et al. 2005, Smith 2007); average daily minimum temperatures in January and February below -18˚ C may be enough to halt northward expansion, especially when coupled with a failed mast crop (Bowman et al. 2005). Warming conditions, in particular, a decline in the frequency of extremely cold nights (WICCI 2011), are expected to allow southern flying squirrels to expand northward into northern flying squirrel range wherever landscape connectivity and mast availability allow. Canada, Michigan, and Wisconsin have documented northward expansion of southern flying squirrels and declines of northern flying squirrels (Bowman et al. 2005, Holloway and Malcolm 2006, Long 2008, Myers et al. 2009), and this sister-species range expansion presents additional risks associated with disease and, potentially, genetic threats to northern flying squirrel populations (see “Threats” section).
Survey Guidelines: Live trapping for the northern flying squirrel should only be attempted by individuals experienced in trapping and handling small mammals, and state permits must be obtained before commencing trapping (see Linked Websites section below). If surveys are being conducted for regulatory purposes, survey protocols and surveyor qualifications must also first be approved by the Endangered Resources Review Program (see Contact Information).
Trapping is best done during the summer (after mid-July) and fall when the squirrels are more susceptible to capture and populations are at their highest (Vernes 2004). Mortality can be reduced by putting nest boxes with bedding in traps and avoiding cold nights (< 40˚ F), especially when there is a chance of precipitation – which greatly increases the likelihood of trap mortality (Vernes 2004). Mortality can also be reduced by adding sufficient nesting material and food in the traps and affixing a protective covering to the trap to displace rain. Northern flying squirrels spend substantial time on the forest floor in search of food, but they are largely arboreal and therefore traps on the ground often produce relatively low capture rates (Engel at el 1992, Vernes 2004). To help increase capture probability, traps are often attached to large trees approximately 1.5 meters above the ground (Smith et al. 2005, Holloway and Malcolm 2006, Lehmkuhl et al. 2006). Northern flying squirrels are larger than many of the other small-mammal species, and therefore traps such as a Tomahawk 201 or Havahart 1025 should be used (Wilson and Carey 1996, Holloway and Malcolm 2006, Lehmkuhl et al. 2006). Sherman live traps are also effective, but present a higher mortality risk on cold nights because they have more exposed metal surfaces; adding nesting material can help reduce the risk of hypothermia and mortality. Common baits include a combination or singular elements of peanut butter, apple, molasses, oats, nuts, and grain (Wells-Gosling and Heaney 1989, Lehmkuhl et al. 2006).
Summarize results, including survey dates, times, weather conditions, number of detections, detection locations, and behavioral data, and submit via the WDNR online report:
Management Guidelines The following guidelines typically describe actions that will help maintain or enhance habitat for the species. These actions are not mandatory unless required by a permit, authorization or approval.
Northern flying squirrels are linked to components of mature conifer forest habitat, generally under mesic conditions with abundant coarse woody debris, diverse understory vegetation, and the presence of lichens and truffles (fruiting bodies of underground fungi) as food sources. Northern flying squirrel response to forest harvest practices has not been well documented in Wisconsin, but studies elsewhere show that a range of forest-harvest and site-preparation methods reduce northern flying squirrel abundance, regardless of harvest intensity and pattern (Herbers and Klenner 2007). For example shelterwood cuts reduce the abundance of squirrels (Waters and Zabel 1995, Holloway and Malcolm 2006, Herbers and Klenner 2007). Heavy logging and site preparation reduce basal area and canopy cover and may create more xeric conditions. These impacts can reduce the productivity of truffles, basal area for lichens to grow, and the diversity of understory vegetation (Waters and Zabel 1995, Lehmkuhl 2004, Lehmkuhl et al. 2006).
This research suggests that harvests may be beneficial in only limited circumstances where the management objective is to steer succession back toward older coniferous growth and thereby create future suitable habitat. In general, however, forest harvest practices reduce northern flying squirrel abundances, and a no action or no harvest plan is the best management practice for this species. If a no-harvest management strategy is not a viable option, there are a number of ways to minimize timber harvest impacts on the northern flying squirrel. If possible, avoid site disturbances during the breeding and rearing season (late May through September), and in particular avoid snags and trees with cavities, witches’ brooms (branch deformities resulting in dense growth of shoots; see “Habitat” section) and visible dreys, all of which may contain natal nests in the spring and summer. In optimal habitat, active forest management should avoid clearcut, seed tree, and over-story removals. If shelterwood harvest is necessary, maintain the highest basal area possible. Patch selection should be limited to areas with presently unsuitable or marginal habitats due to incompatible forest cover type or stand age, structure, and basal area. Leaving a mosaic of older growth stands (> 12 ha) at the forest landscape level will give refugia as the harvested areas regenerate. Maintaining habitat connectivity among these patches is also important for dispersal (Weigl 2007). Where habitat fragmentation is an issue, corridors should be as large as possible to provide maximum protection from predators. Conifers are an extremely important component to northern flying squirrel habitat and should be retained as much as possible, especially along ecotones with hardwoods. Hardwood buffers should be maintained around conifer swamps. Conifer swamps
Northern Flying Squirrel Species Guidance 5 of 9 PUB ER-677 (last updated June 23, 2017) are best left un-harvested due to their importance as habitat for the northern flying squirrel, but careful application of group and single- tree selection may be a compatible option within these swamps. In all cases of timber harvest, manage for maximum retention of basal area, canopy cover, coarse woody debris, understory vegetation, legacy and green trees (especially conifers in hardwood types), den trees, and snags. Landscape-level forest management can benefit the northern flying squirrel by maintaining a variety of habitat ages and composition over time and avoiding large (> 600 acre) clearcuts (Karl Martin pers. comm.).
Screening Procedures The following procedures should be followed by DNR staff reviewing proposed projects for potential impacts to the species.
Follow the “Conducting Endangered Resources Reviews: A Step-by-Step Guide for Wisconsin DNR Staff” document (summarized below) to determine if northern flying squirrels will be impacted by a project (WDNR 2012):
Is there a northern flying squirrel element occurrence No additional screening is
(within project area or a 1 mile buffer), regardless of “last required. Document No obs” date or element occurrence precision OR is there reason conclusions in project file
to believe northern flying squirrel s may be present (e.g., and continue screening for
recent reports of northern flying squirrels in the area)? other species.
Yes No Will the northern flying squirrel or suitable habitat for the northern flying squirrel be impacted by the project? (see “Habitat” section
for descriptions of suitable habitat.) No
Yes Yes (assume presence) (do not assume presence)
See the Avoidance Require/conduct surveys at the project to Yes Measures section to verify northern flying squirrel determine options for presence/absence (see Survey Guidelines). your project. Are northern flying squirrels present on site?
Avoidance Measures
The following measures are specific actions required by DNR to avoid take (mortality) of state threatened or endangered species per Wisconsin’s Endangered Species law (s. 29.604, Wis. Stats.) These guidelines are typically not mandatory for non- listed species (e.g., special concern species) unless required by a permit, authorization or approval.
The northern flying squirrel is a Protected Wild Animal under NR 10.02 Wis. Admin. Stats., which prohibits intentional killing. If you have not yet read through Screening Procedures, please review them first to determine if avoidance measures are necessary for the project.
1. The simplest and preferred method to avoid take of northern flying squirrels is to avoid directly impacting individuals, known northern flying squirrel locations, or areas of suitable habitat (described above in the “Habitat” section and in Screening Procedures).
2. If suitable habitat cannot be avoided, follow these time-of-year and management restrictions to avoid take: Avoid work during the squirrels breeding and rearing season (typically May 15 - September 30).
Northern Flying Squirrel Species Guidance 6 of 9 PUB ER-677 (last updated June 23, 2017) Avoid harvest of snags, trees with cavities, witches’ brooms, and visible dreys, which may contain natal nests. For nuisance cases, do not use one-way exclusion devices on buildings and other human structures when young may be trapped inside (typically May 15 – September 30). o Block entrances to human structures in the fall, after all animals have been excluded or otherwise removed.
3. Active forest management should avoid clearcut, seed tree, and overstory removal.
4. If northern flying squirrel impacts cannot be avoided, please contact the Natural Heritage Conservation Incidental Take Coordinator (see Contact Information) to discuss possible project-specific avoidance measures.
Additional Information
References Bachelet, D., R. P. Neilson, J. M. Lenihan, and R. J. Drapek. 2001. Climate change effects on vegetation distribution and carbon budget in the United States. Ecosystems 4:164-185.
Bowman, J., G. L. Holloway, J. R. Malcom, K. R. Middel, and P. J. Wilson. 2005. Northern range boundary dynamics of southern flying squirrels: evidence of an energetic bottleneck. Canadian Journal of Zoology 83:1486-1494.
Carey, A. B. 2002. Response of northern flying squirrels to supplementary dens. Wildlife Society Bulletin 30:547-556.
Cowan, I. M. 1936. Nesting habits of the flying squirrel Glaucomys sabrinus. Journal of Mammalogy 17:58-60.
Cotton, C. L. and K. L. Parker. 2000. Winter habitat and nest trees used by northern flying squirrels in subboreal forests. Journal of Mammalogy 81:1071-1086.
Curtis JT. 1959. The Vegetation of Wisconsin. University Wisconsin Press: Madison, WI.
Engel, T. C., M. J. Lemke, and N. F. Payne. 1992. Live capture of sympatric species of flying squirrel. Transactions of the Wisconsin Academy of Sciences, Arts and Letters 80:149-152.
Ford, M. W., S. L. Stephenson, J. M. Menzel, D. R. Black, and J W. Edwards. 2004. Habitat characteristics of the endangered Virginia northern flying squirrel (Glaucomys sabrinus fuscus) in the central Appalachian mountains. American Midland Naturalist 152:430-438.
Frelich, L. E. 1995. Old forest in the lake states today and before European settlement. Natural Areas Journal 15:157-167.
Garroway, C. J., J. Bowman, T. J. Cascaden, G. L. Holloways, C. G. Mahan, J. R. Malcolm, M. A. Steele, G. Turner, and P. J. Wilson. 2010. Climate change induced hybridization in flying squirrels. Global Change Biology 16:113-121.
Herbers, J., and W. Klenner. 2007. Effects of logging pattern and intensity on squirrel demography. The Journal of Wildlife Management 71:2655-2663.
Holloway, G. L., and J. R. Malcolm. 2006. Sciurid habitat relationships in forests managed under selection and shelterwood silviculture in Ontario. The Journal of Wildlife Management 70:1735-1745. Iverson, L. R., and A. M. Prasad. 2001. Potential changes in tree species richness and forest community types following climate change. Ecosystems 4:186-199.
Jackson, H. 1961. Mammals of Wisconsin. The University of Wisconsin Press, Madison, Wisconsin, USA.
Kurta, A. 1995. Mammals of the Great Lakes Region. University of Michigan Press, Ann Arbor, Michigan, USA.
Lehmkuhl, J. F., L. E. Gould, E. Cazares, and D. R. Hosford. 2004. Truffle abundance and mycophagy by northern flying squirrels in eastern Washington forests. Forest Ecology and Management. 200:49-65.
Lehmkuhl, J. F., K. D. Kistler, J. S. Begley, and J. Boulanger. 2006. Demography of the northern flying squirrels informs ecosystem management of western interior forests. Ecological Applications 16:584-600.
Long, C. A. 2008. The wild mammals of Wisconsin. Pensoft Publishers, Sofia, Bulgaria.
Northern Flying Squirrel Species Guidance 7 of 9 PUB ER-677 (last updated June 23, 2017)
Loeb, S. C., F. H. Tainter, and E. Cázares. 2000. Habitat associations of hypogeous fungi in the southern Appalachians: implications for the endangered northern flying squirrel (Glaucomys sabrinus coloratus). American Midland Naturalist 144:286-296.
Myers, P., B. L. Lundrigan, S. M. G. Hoffman, A. P. Haraminac, and S. H. Seto. 2009. Climate-induced changes in the small mammal communities of the Northern Great Lakes Region. Global Change Biology 15:1434-54.
Mitchell, D. 2001. Spring diet of the endangered West Virginia northern flying squirrel (Glaucomys sabrinus fuscus). American Midland Naturalist 146:439-443.
Pauli, J. N., S. A. Dubay, E. M. Anderson, and S. J. Taft. 2004. Stongyloides robustus and the northern sympatric populations of northern (Glaucomys sabrinus) and southern (G. volans) flying squirrels. Journal of Wildlife Diseases 40:579-583.
Payne, L. J., D. R. Young, and J. F. Pagels. 1989. Plant community characteristics associated with the endangered northern flying squirrel, Glaucomys sabrinus, in the southern Appalachians. American Midland Naturalist 121:285-292.
Ransome, D. B., and T. P. Sullivan. 1997. Food limitation and habitat preference of Glaucomys sabrinus and Tamiasciurus hudsonicus. Journal of Mammalogy 78:538-549.
Smith, W. P., S. M. Gende, and J. V. Nichols. 2005. The northern flying squirrel as an indicator species of temperate rain forest: test of an hypothesis. Ecological Applications 15:689-700.
Smith, W. P. 2007. Ecology of Glaucomys sabrinus: habitat, demography, and community relations. Journal of Mammalogy 88:862- 881.
Stephens, R. B. 2012. Small mammal assemblages in natural plant communities of Wisconsin. M.S. Thesis. Stevens Point, Wisconsin.
Swanston, C., M. Janowiak, L. Iverson, L. Parker, D. Mladenoff, L. Brandt, M. St. Pierre, A. Prasad, S. Matthews, M. Peters, D. Higgins, and A. Dorland. 2011. Ecosystem vulnerability assessment and synthesis: a report from the Climate Change Response Framework Project in northern Wisconsin, Version 1. US Department of Agriculture, Forest Service, Northern Research Station.
Thysell, D. R., L. J. Villa, and A. B. Carey. 1997. Observations of northern flying squirrel feeding behavior: use of non-truffle food items. Northwestern Naturalist 78:87-92.
Vernes, K. 2004. Breeding biology and seasonal capture success of northern flying squirrels (Glaucomys sabrinus) and red squirrels (Tamiasciurus hudsonicus) in southern New Brunswick. Northeastern Naturalist 11:123-136.
Waters, J. R., and C. J. Zabel. 1995. Northern flying squirrel densities in fir forests of northern California. The Journal of Wildlife Management 59:858-866.
Weigl, P. D. 1974. Study of the northern flying squirrel, Glaucomys sabrinus, by temperature telemetry. American Midland Naturalist 92:482-486.
Weigl, P. D. 1978. Resource overlap, interspecific interactions and the distribution of the flying squirrels, Glaucomys volans and G. sabrinus. American Midland Naturalist 100:83-96.
Weigl, P. D. 2007. The northern flying squirrel (Glaucomys sabrinus): a conservation challenge. Journal of Mammalogy 88:897-907.
Wells-Gosling, N, and R. H. Heaney. 1984. Glaucomys sabrinus. American Society of Mammalogists 229:1-8.
Wetzel, E. J., and P. D. Weigl. 1994. Ecology implications for flying squirrels (Glaucomys spp.) of effects of temperature on the in vitro development and behavior of Strongyloides robustus. American Midland Naturalist 131:43-54.
Wilson, D. E., and S. Ruff (eds). 1999. The Smithsonian book of North American mammals. Smithsonian Institution Press, Washington D.C.
Wilson, T. M., and A. B. Carey. 1996. Observations of weasels in second–growth Douglas-fir forests in the Puget Trough, Washington. Society of Northwestern Vertebrate Biology 77:35-39.
Northern Flying Squirrel Species Guidance 8 of 9 PUB ER-677 (last updated June 23, 2017) WDNR [Wisconsin Department of Natural Resources]. 2005. Wisconsin's Strategy for Wildlife Species of Greatest Conservation Need: A State Wildlife Action Plan. Madison, WI.
WDNR [Wisconsin Department of Natural Resources]. 2009. Wisconsin wildlife action plan species profile: Northern Flying Squirrel. (accessed May 27, 2012). Madison, Wisconsin, USA.
WDNR [Wisconsin Department of Natural Resources]. 2012. Conducting Endangered Resources Reviews: A Step-by-Step Guide for Wisconsin DNR Staff. Bureau of Endangered Resources. Wisconsin Department of Natural Resources, Madison, Wisconsin.
WDNR [Wisconsin Department of Natural Resources]. 2013. Natural Heritage Inventory database. (accessed April 15, 2013).
WICCI [Wisconsin Initiative on Climate Change Impacts]. Wisconsin’s Changing Climate: Impacts and Adaptation. 2011. Nelson Institute for Environmental Studies, University of Wisconsin-Madison and the Wisconsin Department of Natural Resources, Madison, Wisconsin.
Linked Websites: Incidental Take Permit and Authorization:
Funding Natural Resources Foundation of Wisconsin –
Contact Information Endangered Resources Review Program: WI Department of Natural Resources, Bureau of Natural Heritage Conservation ([email protected]) Refer to the Mammals contact on the Rare Species and Natural Community Expert List
Suggested Citation Wisconsin Department of Natural Resources. 2012. Wisconsin Northern Flying Squirrel Species Guidance. Bureau of Natural Heritage Conservation, Wisconsin Department of Natural Resources, Madison, Wisconsin. PUB-ER-678.
Developed by Ryan B. Stephens and Eric M. Anderson, primary authors Gregor W. Schuurman, primary editor
Wisconsin Department of Natural Resources Bureau of Natural Heritage Conservation PO Box 7921 Madison, WI 53707-7921 http://dnr.wi.gov, keyword “ER”
Northern Flying Squirrel Species Guidance 9 of 9 PUB ER-677 (last updated June 23, 2017)