Southern flying squirrel (Glaucomys volans) COSEWIC assessment and status report: chapter 7

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Habitat

• Habitat Requirements
• Habitat Trends: Great Lakes
• Habitat Trends: Atlantic
• Habitat Protection/Ownership

Habitat Requirements

Stabb (1988) provided a thorough description of southern flying squirrel habitat requirements. These have been supported by more recent work (Fridell and Litvaitis 1991; Adams 1995; Taulman et al. 1998; Taulman 1999; Lavers 2004; Taulman and Smith 2004). Suitable habitat requirements are primarily mature mast-bearing trees for food and tree cavities for nesting.

In the northern part of their range, southern flying squirrels use forests dominated by hardwood, mast-bearing trees with some conifer, generally pine (Pinus spp.) (Doby 1984; Gilmore and Gates 1985; Adams 1995; Lavers 2004). In the Atlantic population, G. volans selected forests with American beech (Fagus grandifolia), eastern hemlock (species), red oak, white ash (Fraxinus americana) and white pine (Pinus strobus). Nest trees (dead or alive) also tend to be larger in diameter than trees without nests (Gilmore and Gates 1985; Adams 1995; Taulman 1999; Lavers 2004).

Recent work has shown that southern flying squirrels select older forest stands (Adams 1995; Taulman 1999; Lavers 2004; Taulman and Smith 2004). In Nova Scotia, stand age around nest trees averaged 87.9 years ±27.7 (n = 41), significantly older than random sites (Lavers 2004). In Point Pelee National Park, southern flying squirrels exhibited strong selection for the oldest stands in the park following reintroduction (Adams 1995). Stand age is not so important itself as the attributes found most commonly within those stands. Older hardwood trees produce more mast and older stands tend to have more cavities. Younger stands and those selectively harvested to retain nesting sites and enough mature mast-producing trees may support southern flying squirrels as well (note how many mast-producing trees is “enough” is not known). However, reported high densities from younger stands may include subordinate individuals or juveniles who have been displaced to a lower quality habitat (Goertz et al. 1975; I. Adams pers. obs.).

Proximity to water also may be important (Sonenshine et al. 1979; Taulman 1999). In Ontario’s Norfolk County woodlots, which were used as the source population for the Point Pelee National Park reintroduction, squirrels were most often captured in vernally flooded swamps dominated by silver maple (Acer saccharinum). Following release at Point Pelee, similar habitats were commonly used (Adams 1995). When flooded, these forests may provide protection to flying squirrels by deterring terrestrial predators from accessing the nest tree.

The southern flying squirrel is a secondary cavity nester. Downy (Picoides pubescens) and Hairy Woodpeckers (P. villosus) are the primary excavators of cavities used by G. volans (Sollberger 1940; Muul 1968). They also use cavities formed either from broken limbs or disease. Lavers (2004) found that only 28% of 46 nests were excavated by woodpeckers. Similarly, most cavity nests in Point Pelee, were in knotholes or broken branches of live trees (Adams 1995). Southern flying squirrels will readily use human structures for nesting, including attics, outbuildings and nest-boxes erected for birds. In the southern part of their range, southern flying squirrels will also build drays (Dolan and Carter 1977).

Cavity entrances are usually 3.5 to 5 cm in diameter (Muul 1968). Stabb (1988) reported nest cavity heights averaging 6.6 m (1.3 to 14.0 m). Cavities at Point Pelee and in Norfolk County tend to be toward the upper end of that range in the tree canopy of mature live trees or large snags (Adams pers. obs.). In Nova Scotia, nest height averaged 5.4 m ±3.3 (n = 46; Lavers 2004).

Habitat Trends: Great Lakes

Approximately 90% of southern Ontario’s original woodlands were eliminated by 1920 (Larson et al. 1999). About 13% of that land has since returned to woodland, in large part because they were marginal agricultural lands. Provincial efforts have helped protect other significant woodlots from development (Larson et al. 1999). Whether these woodlots are large, well-connected and mature enough, as well as containing required habitat elements, to support southern flying squirrels is not known.

Haldimand-Norfolk Region lost 80% of its forest cover by 1900 (Gartshore et al. 1987). Perhaps, southern flying squirrels presently found in the Norfolk township woodlots, which represent 17% of the region’s forest cover, recolonized them as habitat became available. A similar pattern of secondary forest use by southern flying squirrels seems to be occurring along the Niagara Escarpment forest in Hamilton, Ontario, which was bare in the 1920s. If reforestation continues, southern flying squirrels may increase in abundance in southern Ontario. However secondary forests will take time to mature and they will be under pressure from anthropogenic effects such as habitat fragmentation and urbanization.

Habitat trends may be positive in the Canadian Shield portion of forests used by southern flying squirrels. Limited agricultural and urban development, along with the practice of selective logging, may help preserve continuous tracts of forest (J. Bowman, pers. comm. 2004). Based on climate change models, mast-producing species are expected to slowly extend their range northward, potentially increasing southern flying squirrel habitat in the long term (J. Bowman, pers. comm. 2004).

Habitat Trends: Atlantic

The Atlantic population of southern flying squirrels appears to be closely tied to the distribution of red oak in Nova Scotia (Lavers 2004). Red oak is a common tree species in southwestern Nova Scotia, although another preferred species, American Beech, has suffered from disease and its distribution and individual tree size has been reduced (M. Elderkin pers. comm. 2004). Overall, rate of forest loss increased in southwestern Nova Scotia during 1997–2002, with forest loss exceeding forest gain (Rozalska and Colville 2003). Freedman et al. (1996) noted that a substantial reduction in standing live trees (snags), hollow live trees and coarse woody debris has accompanied conversion of original Acadian forests to earlier seral stages and agricultural fields.

Habitat Protection/Ownership

Habitat is protected by various national and provincial parks and wildlife reserves throughout their range (Table 4). In addition to these, Ontario has a system of Conservation Areas (e.g. Backus Woods in Norfolk County) which provide some protection to southern flying squirrel habitat. The parks in Table 4 represent areas capable of supporting an isolated G. volans population. There are numerous other protected areas throughout the species’ range where southern flying squirrels occur, most of which are small and isolated habitat fragments. Such smaller protected areas may help sustain southern flying squirrels in the highly developed and fragmented habitat mosaic of southern Ontario, SW Québec and Nova Scotia’s Annapolis Valley.

Areas given are for the entire protected area and do not necessarily represent total habitat area available to southern flying squirrels. (§ indates recent range expansion documented by J. Bowman et al. (unpubl. data)).

¹ Corresponding location on Figure 4.
² Note: habitat suitable to southern flying squirrels may be substantially less.

Figure 4: Locations of Protected Areas Identified in Table 5

Shaded area is current known distribution of southern flying squirrels.