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Synaptomys cooperi - Southern Bog Lemming

Photo by Roger W. Barbour:

Physical Description:

S. cooperi, a vole-like member of the Muridae family, is mostly brown with a white or silver ventral region.  It is described as having a grizzled appearance and a short tail that is no longer than its hind leg.  S. cooperi exhibits a well-defined squamosal crest, thick rostrum, small ears and feet with no hair on soles (Ellermann 1966).

Pelage in S. cooperi becomes darker and duller as it matures and has been noted to be softer, longer and lighter in color during winter (Linzey 1983).  The following ranges of body measurements of S. cooperi are taken from Krupa 1995: total length: 110-140mm; tail length: 18-24 mm; hind foot length: 16-20 mm; ear height: 10-13mm and weight: 20-45 g.  Males and females do not significantly differ in size (Linzey 1983).

Though often confused with close relative the Northern Bog Lemming (Synaptomys borealis) and with true voles, S. cooperi has slightly grooved upper incisors that distinguish it.  S. borealis can also be distinguished by the rust colored hair at the ear base, which is not present in S. cooperi (National Wildlife Federation 2002).  A difference in number of triangles of dentine also distinguish these species; S. cooperi has four, while S. borealis only has three (Kurta 1995).


Synaptomys cooperi is distributed throughout the Midwestern and Eastern United States, through southeastern Canada, Nova Scotia and Cape Breton Island.  It can be found as far west as western Minnesota, south to northeastern Arkansas and southwestern North Carolina, and east to the Atlantic Ocean. S. cooperi can be found throughout Wisconsin (Kurta 1995 and Linzey 1983).

Fossil record:

Records show a distribution extending further south than present distribution.  Fossils from the Pleistocene have been found near Dallas and into Mexico. From this evidence it is thought that S. cooperi took over the distribution that was once occupied by S. borealis before it moved North where it is currently found (Patton 1963 and Linzey 1983).


Although breeding can occur in all seasons, in the Great Lakes region it is restricted to March through October due to food availability.  An average litter of 3, but a range of 1-8, neonates are born after a gestation period of 23-26 days (Linzey 1983).  Approximately three weeks after birth, young are weaned from the mother’s milk and she mates with another male. Subsequent litters will be cared for in the same nests as previous (Linzey 1983).  This reproductive behavior allows for 2 or 3 litters each breeding season (Kurta 1995).  The young are born with little fur, closed eyes, folded ear pinnae and weighing an average of 4 grams.  By the second day, ear pinnae will be unfolded, lower incisors break through after 6-8 days and eyes of young open after 10-11 days (Linzey 1983).  Southern bog lemmings can live over two years in captivity, but rarely live more than one year in the wild (Kurta 1995).


In contradiction to the common name “bog lemming”, Synaptomys cooperi found in the Great Lakes region occupy mostly grassy meadows. In Canadian parts of its range, S. cooperi can be found in deciduous and coniferous forests. They will also occupy sphagnum bogs where available; especially near Atlantic coast; and wet meadows, fields and clear cut areas where they are not; especially in parts of range found in the Appalachian Mountains (Linzey 1983).  They also occupy wet forest areas with cedar, tamarack and spruce (Kurta 1995).

Feeding primarily on vegetation, S. cooperi consumes grasses, moss, roots, fruit, bark and leaf litter found in its habitat.  Slugs, snails and fungus are occasionally eaten as well (Kurta 1995).

Home ranges of S. cooperi are estimated at 0.11 for males and 0.14 for females, but may vary depending on habitat (Lowell 1959).

High predation rates by various owls, housecats, badgers, weasels and foxes may account for a decreased distribution area (Kurta 1995).  Along with predators, S. cooperi must compete in some areas with the meadow vole (Microtus pennsylvanicus), which is more aggressive and has been found to invade the preferred habitat and food sources of the Southern bog lemming.  A trend of deforestation and cooler climates may have contributed to the expansion of M. pennsylvanicus in southeastern Kentucky, which may explain a decrease in the population of S. cooperi in areas where the meadow vole occurs (Krupa and Haskins 1996).


When feeding S. cooperi obtains the fleshy part of a plant by biting at the bottom until the plant falls and the top part can be consumed.  This method results in numerous even-sized “cuttings” that are left behind.  Runways are built to connect feeding, nest and waste sites.  In addition to cuttings and runways, bright green scat may indicate the presence of S. cooperi (Kurta 1995).

Active primarily at night, the Southern bog lemming is also out in the afternoon and evening. The Southern bog lemming is not found to hibernate (Linzey 1983).

Observation in captive and research settings have found that S. cooperi is mostly docile and handled with ease.  Its passive behavior has been found to occur in the field as well.  During both interspecific and intraspecific competition, S. cooperi has exhibited submissive behavior, often resulting in dispersal (Linzey 1983).


Seen as rare and elusive, S. cooperi may suffer from declining populations due to competitive exclusion by Microtus pennsylvanicus in much of its range. Deforestation and a change to grasslands in the Eastern part of its distribution are also working against S. cooperi because this habitat favors M. pennsylvanicus (Krupa and Haskins 1996).  However, areas that have been clear cut favor S. cooperi. This competition may not be seen in populations of S. cooperi in the Midwest because they are thought to have coevolved with Microtus ochrogaster and exhibit habitat partitioning (Linzey 1983).

Literature Cited:

Ellermann, J.R. 1966. The Families and Genera of Living Rodents. Trustees of the British Museum, London. 558-559.

Getz, L.L. 1960. Home Range of Bog Lemming. American Society of Mammalogists.  41:404.
Krupa, J.J. and K.E. Haskins. 1996. Invasion of the meadow vole (Microtus pennsylvanicus) in southeastern Kentucky and its possible impact on the southern bog lemming (Synaptomys cooperi). The American Midland Naturalist. 135: 14-22.

Kurta, A. 1995. Mammals of the Great Lakes Region. University of Michigan Press. Ann Arbor, MI. 180-183.

Linzey, A. 1983. Mammalian Species: Synaptomys cooperi. American Society of Mammalogists. 210:1-5.

National Wildlife Federation. 2002 “Southern Bog Lemming: Synaptomys cooperi” <>.  Accessed October 25, 2003.

Patton, T. 1963. Fossil remains of southern bog lemming in Pleistocene deposits of Texas. Journal of Mammalogy. 44:275-276.

Reference written by Sarah Johnston, Biol 378: Edited by Chris Yahnke.
Page last updated 4-29-04.

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