Southern flying squirrel (Glaucomys volans) COSEWIC assessment and status report: chapter 11
Limiting Factors and Threats
J. Bowman (pers. comm. 2005) suggested that overwinter survival is dictated primarily by availability of stored food, finding a numerical response to changes in oak and beech mast with an approximately 1-year lag. They proposed that winter temperatures affect the amplitude of year-to-year fluctuations.
Doby (1984) concluded that food played a critical role in the species’ winter ecology and population levels fluctuated with food availability in North Carolina. Similarly at Point Pelee National Park, the reintroduced southern flying squirrel population dropped from at least 100 individuals in fall of 1994 to only 43 individuals captured in a 1997 census following a reported mast crop failure in 1995 (Adams 1997).
Others have proposed that climate dictates the species’ northern range limit, either mean January isotherm (Muul 1968) or a minimum daily temperature of -15°C (Stapp et al. 1991). The southern flying squirrel has high energetic demands as they are nocturnally active year-round (the coldest time of day) with a gliding locomotion that increases heat loss. Over-wintering aggregations and torpor are adaptations which help minimize energy expenditures (Stapp et al. 1991; Stapp 1992; Merritt et al. 2001).
At what point nesting cavity availability becomes limiting to southern flying squirrel is unclear. In Point Pelee National Park, availability of nesting cavities was not a limiting factor to reintroduced southern flying squirrels (Adams 1995). Work in South Carolina also found that nest sites were not limiting to southern flying squirrel (Brady et al. 2000). Widespread removal of mature trees and snags can be expected to be detrimental to flying squirrels; they are obligate cavity nesters in Canada.
Habitat loss is the major threat facing southern flying squirrels. Activities that reduce overall forest cover (e.g. conversion of forested land to urban development) or remove forest structure attributes within a stand (e.g. removal of nesting trees or harvesting of mature mast-producing hardwoods) are key threats to southern flying squirrel survival at both the individual and population levels.
Reduction of forest cover, particularly in southern Ontario, likely reduced G. volans abundance in the core of its Great Lakes population. The loss of habitat in southern Ontario has been documented (see Habitat Trends: Great Lakes); however, there are no population data (historical or current) to support whether this reduced southern flying squirrel numbers.
Other flying squirrel species are at risk due to habitat loss. Northern flying squirrel subspecies, G. sabrinus coloratus and G. s. fuscus, found in the Appalachian Mountains are listed as Endangered in the USA (US Fish & Wildlife Service 2004). The European flying squirrel (Pteromys volans) is declining in Finland (Hanski 1998).
A minimum woodlot size and distance from other occupied habitat required to maintain southern flying squirrels is not known. They are found in small woodlots (<10 ha) in Norfolk County, but many of these areas are proximal to, and well-connected with, much larger forested tracts.
Nupp and Swihart (2000) found southern flying squirrels present only in forest tracts >6 ha and in close proximity to other woodlots in Indiana. Woodworth et al. (2001) found southern flying squirrels in 28 of 30 “forest fragments” in southern Illinois. However, the sites were within a “primarily forested landscape” where maximum distance between fragments was 643 m and the two patches not inhabited by flying squirrels were the most isolated.
Habitat fragmentation is known to disrupt southern flying squirrel ecology. Taulman et al. (1998) reported that population densities in Arkansas declined following forest harvesting, while populations in adjacent mature stands increased. In the same study, nest box use in “greenbelt” corridors (primarily unharvested riparian buffer strips) also increased. Squirrels used these “greenbelts” as corridors for travel between fragmented mature stands (Taulman and Smith 2004).
Industrial forestry that converts mixedwood hardwoods to conifer plantations in Nova Scotia has been identified as a threat to the Atlantic population (Lavers pers. comm. 2004). G. volans strongly selected for mixedwood sites in Nova Scotia and avoided conifer-dominated stands (Lavers 2004).
Mortality threats facing flying squirrels are primarily fur trapping by-catch and domestic cats. There is no commercial trapping for either species of flying squirrel and by-catch data are not kept. However, large numbers of northern flying squirrels are known to be caught in traps set for other species (primarily marten) across much of the species’ range (I. Adams pers. obs.). Limited records exist for southern flying squirrel killed by trappers in Québec (C. Genest pers. comm. 2004) and Nova Scotia (Lavers 2004).
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