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Southern Bog Lemming
(Synaptomys cooperi Baird)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry. 216pp.

Order: Rodentia

Family: Cricetidae

Description: The southern bog lemming is more closely related to the voles than to the true lemmings that inhabit higher latitudes. Grooved upper incisors and a relatively shorter tail, 17-21 mm (0.75 in), which is about the same size as the hind foot, distinguish this species from the other Adirondack voles. The long, shaggy fur is chestnut to brown on the upper parts of the body; silvery gray on the lower parts, and only slightly paler than the sides. The head is relatively large, the eyes small, and the ears barely show. The average length of an adult is 118 mm (4.6 in). Weight varies from 21-33 g (0.7-1.2 oz).

Two species of bog lemmings occur in the Adirondacks. Although there are several older records of the northern bog lemming, the only recent verified one is of a specimen taken near Whiteface Mountain (James Lackey, pers. Comm.). The northern part of the Adirondack Park is on the extreme southern boundary of the range of the northern bog lemming, but is probably more widespread in this area than the few records suggest. The two species of bog lemmings are so similar in appearance that they can only be separated by number of mammae and tooth structure (female S. borealis have 8 mammae; female S. cooperi have 6). The life history of the northern bog lemming is similar to the account that follows, and is not treated separately.

Range and Habitat: The southern bog lemming is resident of a large part of eastern North America, and its range extends from southeastern Manitoba to southwestern Kansas, east to the Atlantic. Although in some parts of the range the southern bog lemming actually lives in bogs, in the Adirondacks where it is known from an elevational range of 244-1341 m (800-4400 ft), this small mammal is more common in deciduous and mixed coniferous- deciduous forests. The grassy openings and edges of these forests, especially where sedges, ferns, and shrubs grow, and where the soil is loose and crumbly, are habitats the bog lemming prefers. It also inhabits wetter or drier sites when meadow voles are scarce or absent. Wherever the bog lemming lives, it creates a maze of interconnecting tunnels and runways 2.5-5 cm (1-2 in) wide, and builds nests 15-20 cm (6-8 in) in diameter from plant fibers. Summer nests are on the surface of the ground or in a clump of sedges or grasses but winter nests are usually underground in an enlarged tunnel.

Food and Feeding Behavior:  The bright green droppings, bunches of leaf blades, and piles of cut stems that litter the bog lemming’s runways offer clues to the presence and diet of this small rodent. (The droppings of other small mammals are black or brown, and other voles also cut green vegetation, they do not gather and transport this material in the large quantities typical of bog lemmings). Fresh vegetation, especially the leaves, stems, seed heads, and roots of grasses and sedges, is the main food of this species. Raspberries, blueberries, and other fruits, insects, fungi, and bark form a lesser part of the diet. Bog lemmings sever grass and sedge stems in 2.5-7.5 cm (1-3 in) sections and cache them in underground chambers.

Activity and Movement: This species travels and forages on the surface of the ground and in tunnels which may extend to depths of 30 cm (12 in). The shallow tunnels it makes appear as small ridges, and resemble mole runs. The southern bog lemming is active throughout the year. Individuals are most active during the night, but may move about during the day, too.

Reproduction: Breeding may occur during any month of the year, but at this latitude is unlikely during the winter. The gestation period is 21-23 days. Females bear multiple litters of 1-8 (average 3) young. At birth the newborns are hairless, mainly pink, their eyes closed, and each weighs about 3.9 g (0.14 oz). Young bog lemmings develop a full coat of fur at 7 days. Their eyes open at 10-11 days, and they are weaned at 21 days. Age at first breeding is unknown. The potential life span is 2.4 years, but it is unlikely few individuals survive this long in the wild.

Predators: The raccoon, coyote, red fox, ermine, long-tailed weasel, hawks, and owls are some of the predators of the southern bog lemming.

Social Behavior:

  • Social system - The behavioral relationships among breeding adults are unknown. Males occupy home ranges that overlap those of both sexes, but the home ranges of females do not. Home ranges are small, varying in size from 0.04-0.4 ha (0.1-1.0 acre) and average densities are 4-12 ha (1.6-4.8 per acre). Maximum densities for populations in Kansas and Michigan were 51 and 34 per ha (20 and 13.6 per acre) respectively. 
  • Communication - Unknown. The presence of hip glands, which in breeding males are often covered with white hairs, suggest a role for chemical communication

Additional References 

Buckner, C.H.  1957. Home range of Synaptomys cooperi. Journal of Mammalogy, 38:132.

Connor, P.F. 1959. The bog lemming Synaptomys cooperi in southern New Jersey. Publication of the Museum of Michigan State University Biology Service. Pp 161-248.

Linzey, A.V. 1983. Synaptomys cooperi. Mammalian species, 210:1-5.


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