Southern flying squirrel (Glaucomys volans) COSEWIC assessment and status report: chapter 8
Biology
G. volans may reach sexual maturity after six months (Wells-Gosling 1985), although females producing a litter in their first year is unusual (Giacalone-Madden 1976). G. volans are polyestrous (Banfield 1974) and may produce two litters in a season (Dolan and Carter 1977). Although this is more likely to occur in the southern parts of the species’ range, females have been observed to rear two litters at Point Pelee National Park (Adams 1995). Mean litter size from American studies is 2.75 (sd= 0.59, n=11 studies, range= 1-6; source: Stabb 1988). Canadian litter size data are limited to Point Pelee (3.45 ± 0.66 SD, n = 11; Adams 1995) and Norfolk County (3.66, n = 3; Stabb 1988).
Survival data for G. volans are scarce. Giacalone-Madden (1976) reported a mean “annual disappearance rate” of ~50% with wide variance for southern flying squirrels on Long Island, NY. Doby (1984) found a substantial drop in nest box recaptures after three years of age in North Carolina. At Point Pelee National Park, the oldest captured squirrel was four years, representing <1% of the population (Bednarczuk 2003). Two of 42 (4.8%) squirrels captured there in 1997 were ≥3 years old (Adams 1997) and 10 of 58 (17.2%) squirrels captured in 2003 were originally tagged in 2001 (Bednarczuk and Stephens 2004).
Generation time is estimated to be 1.5 years: most females rear their first litter at age one and few survive to three years of age.
Parturition starts as early as late April and as late as August. Parturition dates appear linked to food availability and weather conditions. For example, unusually cold winter temperatures and a potential lack of mast crop food resources due to a drought the preceding year likely resulted in a delayed onset of reproduction and an omission of the second litter at PPNP in 2003 compared to 2001 (Bednarczuk and Stephens, 2004).
G. volans aggressively outcompetes the larger G. sabrinus for nesting sites (Weigl 1978; Muul 1968). G. volans also carries a strongilid nematode that is lethal to G. sabrinus. Competitive exclusion of G. sabrinus has been suggested to be at least partially mediated by this parasite (Wetzel and Weigl 1994; Weigl et al. 1999 in Lavers 2004). Previously thought to be only marginally sympatric because of behaviour, parasites and habitat selection differences (Weigl 1978), the two species are now known to have substantial range overlap throughout much of G. volans’ Canadian distribution, with the exception of southwestern Ontario (J. Bowman unpubl. data; Lavers 2004). The two species have also been found to occur in the same winter aggregations (Lavers 2004).
The diet of southern flying squirrels is varied. The main food is hardwood tree mast, particularly hickory (Carya spp.), oak (Quercus spp.) and American beech (Harlow and Doyle 1990; Sawyer and Rose 1985) although they also readily consume insects, eggs, nestlings and other foods when available (Dolan and Carter 1977; Wells-Gosling 1985; Stabb et al. 1989). Southern flying squirrels rely on stored mast crop for over winter food. Lavers (pers. comm. 2004) reports that in sympatric populations of G. volans and G. sabrinus in Nova Scotia, both species consume fungi year round. Mycophagy is well-known for northern flying squirrels (Maser et al. 1985; Maser et al. 1986) but is otherwise unknown for southern flying squirrels.
Predators of G. volans include owls, elaphid snakes, raccoon (Procyon lotor), opossum (Didelphus virginianus), weasels (Mustela spp.), mink (Mustela vison), marten (Martes americana), as well as red fox (Vulpes vulpes), domestic cat (Felis domesticus) and bobcat (Lynx rufus; see Stabb 1988). Flying squirrels may avoid predators such as owls which may watch them as they glide, by immediately running around to the back of the tree trunk following landing (Adams and Bednarczuk pers. obs.). Domestic and feral cats are common predators and may present a serious conservation challenge for southern flying squirrel. Cats likely contributed to the extirpation of G. volans from Point Pelee National Park (and other habitat fragments) in the early 1900s (Adams and Nudds 1992) and probably continue to limit isolated populations in forest fragments in rural southwestern Ontario and elsewhere. In Nova Scotia, 42% of 129 collected southern flying squirrel specimens were killed by domestic cats (Lavers 2004).
G. volans do not hibernate during winter but become much less active, and may form aggregations to reduce the costs of thermoregulation. Most aggregations are <10 individuals and consist of primarily family units, but as many as 50 individuals have been observed in one tree cavity (see Stabb 1988). The optimal group size for southern flying squirrels may be six individuals at which point energy expenditures are reduced by 50% at 0-9°C (Stapp et al. 1991).
Relatively little is known about the dispersal habits of southern flying squirrels. Juveniles appear to remain together throughout the winter with their mother and other conspecifics (Lavers 2004; Giacalone-Madden 1976; Muul 1968). Prior to winter, movements are limited compared to the breeding season.
Adults are capable of covering large distances in short periods of time. Mean male and female home ranges for Arkansas G. volans were 9.0 ± 2.5 ha (n = 7) and 3.9 ± 0.6 ha (n = 7) respectively (Stone et al. 1996). Adams (unpubl. data) observed radio-collared males moving >2 km in a single night following translocation to Point Pelee National Park. In similar linear forest habitat near Hamilton, ON, an adult male moved of 2.4 km in a single night (mean movement estimates not available) (Bednarczuk and Judge 2002).
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