Southern flying squirrel
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The southern flying squirrel (Glaucomys volans), sometimes called the assapan,<ref>Template:Cite web</ref><ref>Template:Cite book</ref> is a species of squirrel in the family Sciuridae. G. volans is one of three species of flying squirrels found in North America. It is found in deciduous and mixed woods in the eastern half of North America, from southeastern Canada to Florida. Disjunct populations of this species have been recorded in the highlands of Mexico, Guatemala, and Honduras. There are 11 subspecies that are recognized as being valid, including the nominotypical subspecies.
Description and ecology
Template:Multiple imageSouthern flying squirrels have grey-brown fur on top with darker flanks and are a cream colored underneath. They have large dark eyes and flattened tails. They have a furry membrane called a patagium that extends from the front to the rear legs and is used to glide through the air. Total length (including tail) is Template:Cvt. The tail can be Template:Cvt.
They are nocturnal and feed on fruits and nuts from trees such as red and white oak, hickory, and beech. They store food, especially acorns, for winter consumption. They also dine on insects, buds, mushrooms, mycorrhizal fungi, carrion, bird eggs, nestlings, and flowers. Their predators include snakes,<ref>E.g. rat snakes, namely Elaphe obsoleta: Medlin & Risch (2006)</ref> owls, hawks, and raccoons. Domestic cats can also be potential predators.
Both in the wild and in captivity, they can produce two litters of young each year (with 2–7 young per litter). The gestation period is approximately 40 days. Young are born without fur or any capabilities of their own. Their ears open at 2 to 6 days old, and fur grows in by 7 days. Their eyes do not open until they are 24–30 days old. Mothers wean their young 65 days after they are born. The young then become fully independent at around 120 days of age.
Southern flying squirrels show substantial homing abilities and can return to their nests if artificially removed to distances of up to a kilometer. Their home ranges may be up to Template:Cvt for females and double that for males, tending to be larger at the northern extreme of their range.
Exposure to southern flying squirrels has been linked to cases of epidemic typhus in humans.<ref>eMedicine - Typhus: Article Excerpt by Jason F Okulicz</ref> Typhus spread by flying squirrels is known as "sylvatic typhus" and the Centers for Disease Control and Prevention has documented a total of 39 such cases in the U.S. from 1976 to 2001.<ref>Sylvatic Typhus Fact Sheet, Pennsylvania Department of Health Downloaded on 24 January 2010.</ref> The squirrel acts as host to the Rickettsia prowazekii bacteria and transmission to humans is hypothesized to occur via aerosolized feces of the fleas and lice associated with G. volans.<ref>Kondratieff, B.C., Marquardt, William C..; Biology of Disease Vectors. pg 72.</ref>
Gliding
Flying squirrels do not actually fly, but rather glide using a membrane called a patagium.<ref name="Banfield 1974" /><ref name="Forsyth 1999" /> From atop trees, flying squirrels can initiate glides from a running start<ref name="Forsyth 1999" /> or from a stationary position by bringing their limbs under the body, retracting their heads, and then propelling themselves off the tree.<ref name="Banfield 1974">Banfield AWF. (1974). The mammals of Canada. Toronto: University of Toronto Press.</ref><ref name="Forsyth 1999" /> It is believed that they use triangulation to estimate the distance of the landing area as they often lean out and pivot from side to side before jumping. Once in the air, they spread their long arms forward and out and their long legs backward and out, causing their membrane to stretch into a square-like shape<ref name="Walker and Paradiso 1975">Walker EP, Paradiso JL. (1975). Mammals of the world. Baltimore: Johns Hopkins University Press.</ref> and glide down at angles of 30 to 40 degrees. They maneuver with great efficiency in the air, making 90-degree turns around obstacles if needed.<ref name="Forsyth 1999" /> Just before reaching a tree, they raise their flattened tails to abruptly change their trajectory upward, and point all of their limbs forward; this creates a parachute effect with the membrane in order to reduce the shock of landing. The limbs absorb the remainder of the impact, and the squirrels immediately run to the other side of the trunk or to the top of the tree in order to avoid any potential predators.<ref name = "Walker and Paradiso 1975" /> Although graceful in flight, they are very clumsy walkers, and if they happen to be on the ground in the presence of danger, they will prefer to hide rather than attempt to escape.<ref name = "Banfield 1974" /><ref name = "Forsyth 1999" />
Habitat
The southern flying squirrel is found in eastern deciduous forests or mixed forests of North America.<ref name = "Forsyth 1999">Forsyth A. (1999). Mammals of North America: Temperate and Arctic regions. Willowdale: Firefly Books.</ref> Large hickory<ref name = "Fridell and Latvaitis 1991">Template:Cite journal</ref> and beech trees<ref name = "Fridell and Latvaitis 1991" /><ref name = "Holloway and Malcolm 2007">Template:Cite journal</ref> are more abundant in intensively used areas of their home ranges. Also, maple and poplar,<ref name="Banfield 1974"/><ref name = "Forsyth 1999" /> as well as oak trees, make favorable habitats. Although southern flying squirrels may be present in heavily wooded suburban regions, they never occur in large numbers in these areas.<ref name = "Banfield 1974" />
The size of the home range of southern flying squirrels varies greatly. Average home range estimates are Template:Convert,<ref name="Bendel and Gates 1987">Template:Cite journal</ref> Template:Cvt,<ref name = "Stone et al. 1997">Template:Cite journal</ref> and Template:Cvt<ref name="Fridell and Latvaitis 1991"/> for adult males, Template:Cvt,<ref name = "Bendel and Gates 1987" /> Template:Cvt,<ref name = "Stone et al. 1997" /> and Template:Cvt<ref name = "Fridell and Latvaitis 1991" /> for adult females, and Template:Cvt for juveniles.<ref name = "Bendel and Gates 1987" /> Significant overlap exists among the home ranges.<ref name = "Fridell and Latvaitis 1991" /><ref name = "Bendel and Gates 1987" /><ref name = "Stone et al. 1997" /> Near the northern limit of the southern flying squirrels distribution, home range increases in size as mast-producing trees become more dispersed.<ref name = "Fridell and Latvaitis 1991" /> This trend is also observed in fragmented forests where nesting and foraging areas become widely spaced.<ref name = "Taulman and Smith 2003">Template:Cite journal</ref>
Home range is larger in males than females<ref name = "Fridell and Latvaitis 1991" /><ref name = "Bendel and Gates 1987" /><ref name = "Stone et al. 1997" /><ref name = "Taulman and Smith 2003"/> possibly to increase the chance of encountering potential mates.<ref name = "Fridell and Latvaitis 1991" /> Although males have a larger home range, female home ranges have been shown to increase by as much as 70 percent following the departure of the offspring.<ref name = "Bendel and Gates 1987" />
Number of nesting sites does not influence the total number of flying squirrels<ref name = "Brady et al. 2000">Template:Cite journal</ref> but may influence which sex will be present. Male home ranges contain more food as they have been associated with a higher than expected number of large red oaks and white oaks, whereas female home ranges contain lower food resources and more abundant nesting sites possibly to avoid contact with other squirrels while raising the young.<ref name = "Fridell and Latvaitis 1991" />
Southern flying squirrels nest in natural cavities and woodpecker holes,<ref name="Holloway and Malcolm 2007"/><ref name = "Brady et al. 2000" /><ref name = "Loeb et al. 2012">Template:Cite journal</ref> or build nest out of leaves and twigs.<ref name = "Holloway and Malcolm 2007" /><ref name = "Brady et al. 2000" /> Leaf nests are used as a refuge or a resting site and are used primarily in summer, whereas cavities are used for breeding and more intensively during winter.<ref name = "Brady et al. 2000" /> Cavities used by southern flying squirrels are found in small snags, average Template:Cvt in diameter at breast height, or large living trees, average Template:Cvt dbh, with entrances that average Template:Cvt in width by Template:Cvt in height, which are an average of Template:Cvt above the ground.<ref name = "Bendel and Gates 1987" />
Dens tend to be on the perimeter of the home range<ref name = "Bendel and Gates 1987"/><ref name = "Stone et al. 1997" /> and situated away from clearings.<ref name = "Bendel and Gates 1987" /> To cross disturbances such as plantations and logged areas, southern flying squirrels prefer to use mature forest corridors over younger ones, suggesting that they are more sensitive to forest disturbances than previously believed.<ref name="Taulman and Smith 2003"/>
Behavior
Southern flying squirrels are highly social mammals and have been observed flying and foraging together in large groups.<ref name="Banfield 1974"/> Additionally, they often aggregate together in dens, especially as seasonal temperatures decline<ref name = "Layne and Raymond 1994">Template:Cite journal</ref><ref name = "Reynolds et al. 2009">Template:Cite journal</ref> in order to conserve energy.<ref name = "Stapp et al. 1991">Template:Cite journal</ref><ref name = "Merritt et al. 2001">Template:Cite journal</ref> Compared to individuals who nest alone in winter, squirrels in aggregates can save 30 percent more energy.<ref name = "Stapp et al. 1991"/> Although southern flying squirrels do show a preference for relatedness, they are tolerant of nonrelated but familiar individuals, possibly because in addition to providing heat energy for the aggregation, outsiders will promote outbreeding.<ref name = "Thorington and Weigl 2011">Template:Cite journal</ref> However, in the summer months, they tend to forage and cache alone in their home range.
Muul<ref name = "Muul 1974">Template:Cite journal</ref><ref name = "Layne and Raymond 1994"/> stated that communal nesting may be detrimental during warm weather and is unnecessary in the southern parts of the species range. However, Layne and Raymond observed nest boxes in Florida and discovered that the southern populations also nest in large groups (up to 25 individuals) and that, compared to northern populations, the period of elevated communal nesting extended later in the spring. In this study, nest temperatures occasionally exceeded Template:Cvt<ref name = "Layne and Raymond 1994" /> while the normal body temperature of southern flying squirrels varies between Template:Cvt.<ref name = "Merritt et al. 2001"/> Since southern populations breed later in the spring than northern populations,<ref name = "Reynolds et al. 2009"/><ref name = "Raymond and Layne 1988">Template:Cite journal</ref><ref name = "Layne and Raymond 1994"/> these findings suggests that communal nesting serves more than a thermoregulatory function and may actually play a role in the social organization of populations. Proposed advantages of aggregation include increased likelihood of mating, increased defense against predators, or increased foraging success.<ref name = "Layne and Raymond 1994"/>
Populations which nest together were found to be more highly related than expected by chance and it is believed that this could be a form of kin selection since an individual's stored food may be beneficial for the survival of its relatives in the event of death.<ref name="Thorington and Weigl 2011"/><ref name = "Thorington et al. 2010">Template:Cite journal</ref>
Winterrowd and Weigl performed experiments in controlled conditions to determine whether memory, smell, random searching, or problem solving played a major role in retrieving hidden food. When burying dry nuts in dry substrate, no odors are present and spatial memory is the most effective retrieval mechanism, suggesting that there is no inclusive fitness involved in the hoarding behavior. However, once placed in a wet environment, smell becomes an effective means to retrieve the food and decreases the individuals' advantage over the other members of the group. Experiments to determine whether a squirrel would steal from others in the group revealed that no particular pattern exists and that the hidden food is recovered according to its availability.<ref name="Winterrowd and Weigl 2006">Template:Cite journal</ref>
Sports and popular culture
- Richmond Flying Squirrels - Eastern League affiliate of the San Francisco Giants. This Virginia-based team draws its name, logo, and mascot from the southern flying squirrel.
- The video games Pokémon Black and White take place in the Unova region (based on the eastern United States) and contain Emolga, an Electric/Flying type Pokémon based on the southern flying squirrel.
- The animated television series The Adventures of Rocky and Bullwinkle and Friends features the anthropomorphic flying squirrel Rocket J. ("Rocky") Squirrel.
Footnotes
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References
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- Fox, D. & Mulheisen, M. (1999): Animal Diversity Web - Glaucomys volans. Accessed May 20, 2005.
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