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Glaucomys sabrinus - Northern Flying Squirrel

Description:

The northern flying squirrel (Glaucomys sabrinus) is one of two flying squirrels found in Wisconsin, the other being the southern flying squirrel (Glaucomys volans).  The northern flying squirrel averages a body mass of around 70-130 grams while the southern flying squirrel is much smaller with average body mass of around 50-75 grams (Kurta 1995).  Besides size, the two squirrels can be distinguished by their colorings, especially along the belly of the animal.  The northern flying squirrel has belly hairs that are slate gray at the base (with some variety in shades and color) with white or cream-colored tips.  On the other hand the southern flying squirrel has a distinct belly with white hairs.  The northern flying squirrel also has larger feet and longer tails (Jackson 1961 and Kurta 1995).  The bottom of the tails  generally are much darker in G. sabrinus than G. volans (Jackson 1961).  Both flying squirrels have the dental formula 1/1 0/0 2/1 3/3 = 22 total teeth (Heaney and Wells-Gosling 1984).  Both these squirrels have a loose fold of skin known as a patagium, which runs the along each side of the body (from the ankle of the hind leg to the wrist of the foreleg).  The patagium allows the squirrels to “fly” from tree to tree.  The squirrel really doesn’t fly, but glides in the air.  This type of motion is energetically cheap to perform and the squirrel can cover a greater distance with less energy (Vernes 2001).  The squirrel can conserve its energy for more important activities like foraging and mating.

Distribution:

The northern flying squirrel, G. sabrinus, has a very wide distribution across North America.  G. sabrinus inhabits almost all of Canada , extending near the artic circle and into Alaska.  The northern flying squirrel has three key geographic regions in the continental United States.  The first of these areas are the Rocky Mountains.  The squirrels’ distribution follows the Rocky Mountains and extends its distribution west to the Pacific coast, including California, Oregon and Washington.  The second key area follows the Appalachian Mountains in the Eastern part of the United States.  The final key area is the Great Lakes region including Northern Minnesota, most of Michigan and Northern Wisconsin.  The Appalachian Mountain region and the Great Lakes region are areas of interest for research since the northern flying squirrel, G. sabrinus, and the southern flying squirrel, G. volans, both inhabit these regions.  In Wisconsin, the beginning of the ecological tension zone, between the northern and southern flying squirrel, occurs in the central part of Wisconsin, around Wood and Portage counties.  This area is the southern most extent of the northern flying squirrels distribution (in Wisconsin), while the southern flying squirrels distribution extends north to the Upper Peninsula of Michigan and the northern border between Minnesota and Wisconsin (Jackson 1961 and Kurta 1995).

Ontogeny and Reproduction:

Mating starts towards the end of March and may last until the middle to late part of May.  About 40 days later, the female will give birth to between 2 and 4 offspring that are born with eyes and ears shut, hairless, cylindrical shaped tail, toes fused together and a visible patagium (Heaney and Wells-Gosling 1984).  The young weigh around 5-6 grams at birth.  Northern flying squirrels generally only have one litter per year.  The young take about 30 days or so before opening their eyes, and wait until around 40 days to leave the nest.  The young will typically nurse on its mother’s milk for about 2 months.  Overall, northern flying squirrels take about 10 weeks to fully mature and fend on their own (Jackson 1961, Kurta 1995 and Malamuth 1996).

Ecology and Behavior:

Nutrition-

The northern flying squirrel has a very wide-ranging diet.  Though mostly omnivorous, Glaucomys sabrinus has been documented consuming bird eggs, small birds and insects.  They consume a large variety of nuts, fruits, and other omnivorous meals.  In Wisconsin, they may eat hazelnuts, and beechnuts along with seeds from spruce, balsam and maple trees.  Fruits such as pin cherry, June berry, huckleberry, mountain ash berry and a variety of other berries make up their diet in Wisconsin when these fruits are available (Jackson 1961 and Kurta 1995).  The northern flying squirrel will even consume mushrooms, lichens and other fungi (in some areas fungi are a very important food source).  They are also believed to hoard, or store larger quantities of food for winter use, but that has not been confirmed, as of yet (Malamuth 1996). 

Behavior-

Northern flying squirrel, like its close relative the southern flying squirrel, is strictly nocturnal, only being active two hours after sunset and an hour before sunrise (Kurta 1995 and Malamuth 1996).  The squirrels move from tree to tree by gliding.  They can glide from 3-45 meters.  Males will typically glide further than females (Vernes 2001).  Northern flying squirrels differ from southern flying squirrels in that they regularly leave the trees to forage on the ground, while southern flying squirrels rarely leave the trees (Kurta 1995).  Northern flying squirrels occupy a variety of forests types such as: pure conifers, mixed conifer and deciduous, and pure deciduous (rarely).  When northern and southern flying squirrels occupy a mixed stand together, the northern flying squirrel will typically select conifers while southern flying squirrels select deciduous trees (Anderson 2003).  Northern flying squirrels remain active during the winter even with temperatures below –20 °C.  During wintertime, northern flying squirrels have been documented to nest with other individuals in the same tree.  Up to nine individuals will nest in the same tree, with more nesting in trees near the main nest.  Winter nests can be up to 20°c warmer than outside temperatures.  Nest trees range in diameter and type, but larger conifers are preferred when available (Cotton et all 2000, Jackson 1961 and Kurta 1995).  Northern flying squirrels have even been known to emit a low chirp sound as a form of communication (Jackson 1961) and they will also make a cluck sound when distressed (Malamuth 1996).

Predators-

The most frequent predators of northern flying squirrels are feral and domestic house cats (Jackson 1961).  Other carnivores like foxes, weasels, martens, lynxes and coyotes have been known to prey on northern flying squirrels (Kurta 1995 and Malamuth 1996).  Raptors also prey on the squirrels.  Most owls have been known to prey on flying squirrels, with other raptors like hawks catching one occasionally.  The northern flying squirrel is one of the top prey items for spotted owls.

Economics-

Northern flying squirrels help disperse spores of mycorrhizal fungi and conifer seeds.   Some consider the northern flying squirrel a nuisance because they have been known to nest in the attics of houses, causing minor damage to the house as well as noise irritation to the owner of the house (Malamuth 1996).  A plus for anyone whose house the squirrels get into is that northern flying squirrels are fairly easy to trap (Jackson 1961).

Literature Cited:

Anderson, E.  2003.  Habitat Selection and Partitioning by Northern and Southern Flying Squirrels in Central Wisconsin.

Cotton, C.L. and K.L. Parker.  2000.  Winter Habitat and Nest Trees Used by Northern Flying Squirrels in Subboreal Forests.  Journal of Mammalogy 81(4): 1071-1086.

Jackson, H.  1961.  Mammals of Wisconsin.  The University of Wisconsin Press:181-183.

Heaney, L.R. and N. Well-Gosling.  1984.  Mammalian Species No. 229: Glaucomy sabrinus.  The American Society of Mammalogists.

Kurta, A.  1995.  Mammals of the Great Lakes Region: 131-134.  The University of Michigan Press, Ann Arbor.

Malamuth, E. and M. Mulheisen.  1996.  Glaucomys sabrinus, Northern Flying Squirrel. Animal Diversity Web.  <http://animaldiversity.ummz.umich.edu/>.

Vernes, K.  2001.  Gliding Performance of the Northern Flying Squirrel (Glaucomys sabrinus) in Mature Mixed Forests of Eastern Canada.  Journal of Mammalogy 82(4): 1026-1033.

Snyder, A.M., and Y.B. Linhart.  1997.  Porcupine feeding patterns: selectivity by a generalist herbivore.  Canadian Journal of Zoology 75: 2107-2111.

Sweitzer, A. R.  1996.  Predation or starvation: consequences of foraging decisions by porcupines (Erethizon dorsatum).  Journal of Mammalogy 77(4): 1068-1077.

Texas Parks and Wildlife Department.  1994.  Porcupine, The mammals of Texas online edition. <http://www.nsrl.ttu.edu/tmot1/eretdors.htm>.  Accessed 1 Dec 2003.

Ward, B.  2003.  Sedgvick county zoo, Erethizon dorsatum.  <http://www.scz.org/animals/p/prcpine.html>.  Accessed 2 Dec 2003.

Woods, C.A.  1973.  Erethizon dorsatum.  Mammalian Species 29: 1-6.

Zimmerling, N.T. and C.D. Croft.  2001.  Resource selection by porcupines: winter den site location and forage tree choices.  Western Journal of Applied Forestry 16(2): 53-63.

Reference written by Justin Riebe, Biol 378: Edited by Chris Yahnke. Page last updated 4-23-04.

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