Temporal range: Early Oligocene – Recent
|Northern flying squirrel (Glaucomys sabrinus)|
Flying squirrels are not capable of flight like birds or bats; instead, they glide between trees. They are capable of obtaining lift within the course of these flights, with flights recorded to 90 meters (295 ft). The direction and speed of the animal in midair is varied by changing the positions of its limbs, largely controlled by small cartilaginous wrist bones. The wrist is connected to the styliform cartilage, which forms a wing tip used during gliding. After being extended, the wing tip may adjust to various angles, controlling aerodynamic movements. The wrist also changes the tautness of the patagium, a furry parachute-like membrane that stretches from wrist to ankle. It has a fluffy tail that stabilizes in flight. The tail acts as an adjunct airfoil, working as an air brake before landing on a tree trunk.
The colugos, Petauridae, and Anomaluridae are gliding mammals which are similar to flying squirrels because of convergent evolution. These mammals can glide through the trees, but they do not actually fly (like birds and bats). They have a membrane of skin on either side of their body.
Prior to the 21st century, the evolutionary history of the flying squirrel was frequently debated. This debate was clarified greatly as a result of two recent molecular studies. These studies found support that flying squirrels originated 18–20 million years ago, are monophyletic, and have a sister relationship with tree squirrels. Due to their close ancestry, the morphological differences between flying squirrels and tree squirrels reveal insight into the formation of the gliding mechanism. By comparing northern and southern flying squirrels to tree squirrels of similar size, flying squirrels show lengthening in bones, such as those of the lumbar vertebrae and forearm, while the feet, hands, and distal vertebrae are reduced in length relative to the tree squirrels. Such differences in body proportions reveal the flying squirrels’ adaptation to minimize wing loading and allow for more maneuverability while gliding.
There are multiple hypotheses that attempt to explain the evolution of the gliding mechanism in flying squirrels. One possible explanation is related to energy efficiency and foraging. Gliding is an energetically-efficient way to progress from one tree to another while foraging, as oppose to climbing down trees and maneuvering on the ground floor or executing dangerous leaps in the air. Flying squirrels are also able to rummage through a greater area of forest more quickly than tree squirrels due to gliding at high speeds. In fact, they are adapted to gliding long distances by increasing their aerial speed and producing more lift. Other hypotheses state that the mechanism evolved to avoid nearby predators and prevent injuries. If a dangerous situation arises on a specific tree, flying squirrels have the ability to glide to another, typically assuring safety from the previous danger. Furthermore, take-off and landing procedures during leaps, implemented for safety purposes, may explain the gliding mechanism. While leaps at high speeds are important to escape danger, the high force impact of landing on a new tree could be detrimental to a squirrel’s health. Yet the gliding mechanism of flying squirrels involves structures and techniques during flight that allow for great stability and control. If a leap is miscalculated, a flying squirrel may easily steer back onto the original course by using its gliding ability. A flying squirrel also creates a large glide angle when approaching their target tree, decreasing its velocity due to an increase in air resistance and allowing all four limbs to absorb the impact of the target.
The largest of the species is the woolly flying squirrel (Eupetaurus cinereus). The two species of the genus Glaucomys (Glaucomys sabrinus and Glaucomys volans) are native to North America, and the Siberian flying squirrel is native to parts of northern Europe (Pteromys volans).
Thorington and Hoffman (2005) recognize 15 genera of flying squirrels in two subtribes.
Tribe Pteromyini – flying squirrels
- Subtribe Glaucomyina
- Genus Eoglaucomys
- Kashmir flying squirrel, Eoglaucomys fimbriatus
- Genus Glaucomys – New World flying squirrels (American flying squirrels), North America
- Genus Hylopetes, Southeast Asia
- Particolored flying squirrel, Hylopetes alboniger
- Afghan flying squirrel, Hylopetes baberi
- Bartel's flying squirrel, Hylopetes bartelsi
- Gray-cheeked flying squirrel, Hylopetes lepidus
- Palawan flying squirrel, Hylopetes nigripes
- Indochinese flying squirrel, Hylopetes phayrei
- Jentink's flying squirrel, Hylopetes platyurus
- Sipora flying squirrel, Hylopetes sipora
- Red-cheeked flying squirrel, Hylopetes spadiceus
- Sumatran flying squirrel, Hylopetes winstoni
- Genus Iomys, Malaysia and Indonesia
- Javanese flying squirrel (Horsfield's flying squirrel), Iomys horsfieldi
- Mentawi flying squirrel, Iomys sipora
- Genus Petaurillus – pygmy flying squirrels, Borneo and the Malay Peninsula
- Genus Petinomys, Southeast Asia
- Basilan flying squirrel, Petinomys crinitus
- Travancore flying squirrel, Petinomys fuscocapillus
- Whiskered flying squirrel, Petinomys genibarbis
- Hagen's flying squirrel, Petinomys hageni
- Siberut flying squirrel, Petinomys lugens
- Mindanao flying squirrel, Petinomys mindanensis
- Arrow flying squirrel, Petinomys sagitta
- Temminck's flying squirrel, Petinomys setosus
- Vordermann's flying squirrel, Petinomys vordermanni
- Genus Eoglaucomys
- Subtribe Pteromyina
- Genus Aeretes, northeastern China
- Groove-toothed flying squirrel (North Chinese flying squirrel), Aeretes melanopterus
- Genus Aeromys – large black flying squirrels, Thailand to Borneo
- Genus Belomys, Southeast Asia
- Hairy-footed flying squirrel, Belomys pearsonii
- Genus Biswamoyopterus, India and Bangladesh
- Namdapha flying squirrel, Biswamoyopterus biswasi
- Genus Eupetaurus, Kashmir; rare
- Woolly flying squirrel, Eupetaurus cinereus
- Genus Petaurista, Southeast Asia
- Red and white giant flying squirrel, Petaurista alborufus
- Spotted giant flying squirrel, Petaurista elegans
- Hodgson's giant flying squirrel, Petaurista magnificus
- Bhutan giant flying squirrel, Petaurista nobilis
- Indian giant flying squirrel, Petaurista philippensis
- Chinese giant flying squirrel, Petaurista xanthotis
- Japanese giant flying squirrel, Petaurista leucogenys
- Red giant flying squirrel, Petaurista petaurista
- Genus Pteromys – Old World flying squirrel, Finland to Japan
- Genus Pteromyscus, southern Thailand to Borneo
- Smoky flying squirrel, Pteromyscus pulverulentus
- Genus Trogopterus, China
- Complex-toothed flying squirrel, Trogopterus xanthipes
- Genus Aeretes, northeastern China
- Mechuka giant flying squirrel (Petaurista mechukaensis)
- Mishmi Hills giant flying squirrel (Petaurista mishmiensis)
- Mebo giant flying squirrel (Petaurista siangensis)
The life expectancy of flying squirrels in the wild is about six years, but flying squirrels can live up to fifteen years in zoos. The mortality rate in young flying squirrels is high because of predators and diseases. Predators of flying squirrels include tree snakes, raccoons, owls, martens, fishers, coyotes, bobcats, and feral cats. In the Pacific Northwest of North America, the northern spotted owl (Strix occidentalis) is a common predator of flying squirrels.
Flying squirrels are usually nocturnal, since they are not adept at escaping birds of prey that hunt during the daytime. They eat according to their environment; they are omnivorous, and will eat whatever food they can find. The North American southern flying squirrel eats seeds, insects, gastropods (slugs and snails), spiders, shrubs, flowers, fungi, and tree sap.
The mating season for flying squirrels is during February and March. When the infants are born, the female squirrels live with them in maternal nest sites. The mothers nurture and protect them until they leave the nest. The males do not participate in nurturing their offspring.
At birth, flying squirrels are mostly hairless, apart from their whiskers, and most of their senses are not present. Their internal organs are visible through the skin, and their sex can be signified. By week five, they are almost fully developed. At that point, they can respond to their environment and start to develop a mind of their own. Through the upcoming weeks of their lives, they practice leaping and gliding. After two and a half months, their gliding skills are perfected, they are ready to leave the nest, and are capable of independent survival.
Flying squirrels can easily forage for food in the night, given their highly developed sense of smell. They harvest fruits, nuts, fungi, and birds' eggs. Gliding conserves energy. Many gliders have specialized diets and there is evidence to believe that gliders may be able to take advantage of scattered protein deficient food. Additionally, gliding is a fast form of locomotion and by reducing travel time between patches, they can increase the amount of foraging time.
- Daxner-Höck G. (2004). "Flying Squirrels (Pteromyinae, Mammalia) from the Upper Miocene of Austria". Annalen des Naturhistorischen Museums in Wien 106A: 387–423. PDF.
- Malamuth, E. & Mulheisen, M. (1995–2008). "ADW: Glaucomys sabrinus – Northern flying squirrel". University of Michigan Museum of Natural History. Retrieved 14 July 2009.
- Asari, Y; Yanagawa, H.; Oshida, T. (2007). "Gliding ability of the Siberian flying squirrel Pteromys volans orii" (PDF). Mammal Study 32 (4): 151–154. doi:10.3106/1348-6160(2007)32[151:GAOTSF]2.0.CO;2. Retrieved 2009-07-14.
- Johnson-Murray, Jane L. (1977). "Myology of the Gliding Membranes of Some Petauristine Rodents (Genera: Glaucomys, Pteromys, Petinomys, and Petaurista)". Journal of Mammalogy 58: 374–384.
- Thorington Jr., R.W; Darrow, K.; Anderson, C.G. (1998). "Wing Tip Anatomy and Aerodynamics in Flying Squirrels" (PDF). Journal of Mammalogy (American Society of Mammalogists) 79 (1): 245–250. doi:10.2307/1382860. JSTOR 1382860. Retrieved 2009-07-14.
- Carraway, L.N.; Verts, B.J. (1994). "Sciurus griseus" (PDF). Mammalian Species 474 (474): 1–7. doi:10.2307/3504097. Retrieved 2009-07-14.
- Arbogast, B.S. (2007). "A brief history of the new world flying squirrels: Phylogeny, biogeography, and conservation genetics". Journal of Mammalogy 88 (4): 840–849. doi:10.1644/06-MAMM-S-322R1.1.
- Mercer, J.M.; V.L. Roth (2003). "The effects of cenozoic global change on squirrel phylogeny". Science 299 (5612): 1568–1572. doi:10.1126/science.1079705. PMID 12595609.
- Steppan, S.J.; B.L. Storz; R.S. Hoffmann (2004). "Nuclear DNA phylogeny of the squirrels (Mammalia : Rodentia) and the evolution of arboreality from c-myc and RAG1". Molecular Phylogenetics and Evolution 30 (3): 703–719. doi:10.1016/S1055-7903(03)00204-5. PMID 15012949.
- Thorington, Richard W.; Santana, Erica M. (2007). "How to make a flying squirrel: Glaucomys anatomy in phylogenetic perspective". Journal of Mammalogy 88: 882–896.
- Flaherty, E.A.; M. Ben-David; W.P. Smith (2010). "Quadrupedal locomotor performance in two species of arboreal squirrels: predicting energy savings of gliding". Journal of Comparative Physiology B-Biochemical Systemic and Environmental Physiology 180 (7): 1067–1078. doi:10.1007/s00360-010-0470-1.
- Norberg, Ulla M. (1985). "Evolution of vertebrate flight: an aerodynamic model for the transition from gliding to active flight". American Naturalist 126: 303–327.
- Paskins, Keith E.; Bowyer, Adrian; Megill, William M.; Scheibe, John S. (2007). "Take-off and landing forces and the evolution of controlled gliding in northern flying squirrels Glaucomys sabrinus". The Journal of Experimental Biology 210: 1413–1423.
- Scheibe, John S.; Figgs, Daylan; Heiland, Jeff (1990). "Morphological attributes of gliding rodents: a preliminary analysis". Transactions of the Missouri Academy of Science 24: 49–56.
- Byrnes, Greg; Spence, Andrew J. (2011). "Ecological and Biomechanical Insights into the Evolution of Gliding in Mammals". Integrative and Comparative Biology 51: 991–1001.
- Choudhury, A.U. (2007). A new flying squirrel of the genus Petaurista Link from Arunachal Pradesh in north-east India. The Newsletter & Journal of the Rhino Foundation for nat. in NE India 7: 26–34, plates.
- Choudhury, A.U. (2009). One more new flying squirrel of the genus Petaurista Link, 1795 from Arunachal Pradesh in north-east India. The Newsletter & Journal of the Rhino Foundation for nat. in NE India 8: 26–34, plates.
- Choudhury, A.U. (2013). Description of a new species of giant flying squirrel of the genus Petaurista Link, 1795 from Siang Basin, Arunachal Pradesh in North East India. The Newsletter & Journal of the Rhino Foundation for nat. in NE India 9: 30–38, plates.
- Thorington, Jr., R.W; Pitassy, D.; Jansa, S.A. (2002). "Phylogenies of Flying Squirrels (Pteromyinae)" (PDF). Journal of Mammalian Evolution 9 (1–2): 99–135. doi:10.1023/A:1021335912016. Retrieved 2009-07-14.
- Studelska, Rebecca. (1997). "Northern Flying Squirrels". Northern State University. Retrieved 2009-09-14.
- Patterson., Robert (2009). "Life Cycle". Retrieved 2009-09-14.
- North, M.; Trappe, J.; Franklin, J. (1995). "Standing crop and animal consumption of fungal sporocarps in Pacific Northwest forests" (PDF). Ecology 78 (5): 1543–1554. doi:10.1890/0012-9658(1997)078[1543:SCAACO]2.0.CO;2. Retrieved 2009-07-14.
- Byrnes, G.; A.J. Spence (2011). "Ecological and biomechanical insights into the evolution of gliding in mammals". Integrative and Comparative Biology 51 (6): 991–1001. doi:10.1093/icb/icr069. PMID 21719434.
- Thorington, R. W. Jr. and R. S. Hoffman. 2005. Family Sciuridae. pp. 754–818 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.
- Chisholm, Hugh, ed. (1911). "Flying-squirrel". Encyclopædia Britannica (11th ed.). Cambridge University Press.
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