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Synaptomys borealisnorthern bog lemming

By Danielle Nicholas

Geographic Range

Northern bog lemmings (Synaptomys borealis) occur across North America from Labrador to southern Alaska. They are uncommon in northwestern and eastern Canada. There is an isolated population south of the St. Lawrence River in the Northern Appalachian Mountains (Banfield, 1974).

Their geographic range is thought to be explained by their high affinity for boreal habitats, these boreal forests have been retreating northward along with S. borealis.

The first fossil record of Synaptomys was found in the Wisconsin Glacial age deposits in the Great Basin, where they are no longer found. Evidence suggests that a glacial meltwater stream provided a local environment which was more mesic and supported a restricted population of lemmings in this canyon-bottom region (Mead et al, 1992). (Banfield, 1974; Mead, et al., 1992)

Habitat

Synaptomys borealis primarily live in burrows among sedges and grasses (Wilson et al, 1999). They can be found where moisture levels are high and growth of sedges and grasses are sufficient to provide cover as well as act as their food supply (Wilson et al, 1999). During the snow free months this species is active both above and below ground, though most activity at this time occurs below ground to avoid predation by the high diversity of mammalian and avian predators (Wilson et al, 1999). During the winter months this risk of predation is lowered and most activity occurs above ground. Lemmings construct globular nests composed of mosses, grasses, and sedges at ground level just beneath the snow in the winter months and build their nests underground in the summer months (Banfield, 1974). They remain active year-round.

Foraging activities are largely confined to runway systems where vegetation is harvested and either consumed or removed to underground nests via escavated burrow systems (Wilson et al, 1999).

Synaptomys borealis primarily frequent sphagnum-Labrador tea-black bogs but they are also found to live among deep, moist spruce woods, wet, subalpine meadows, and alpine tundra (Mead et al, 1992). (Banfield, 1974; Mead, et al., 1992; Wilson and Ruff, 1999)

Physical Description

Tail: 20-27mm

Hing foot: 18-21mm (Banfield, 1974)

Synaptomys borealis is a microtine rodent. They have a stocky build, with short legs and a tail which is slightly longer than their hind foot (Wilson et al, 1999). Their ears are relatively small and their nose is blunt. The pelage is coarse and appears ruffled, the colour varies from grayish brown to chestnut brown on their dorsal side and pale gray ventrally (Banfield, 1974). The bicoloured tail is brown above and white below (Wilson et al, 1999).

Synaptomys borealis can be identified by several cranial features. They have a short rostrum, projections on the upper incisors, and mandibular incisors which are thin and pointed. They can be differentiated from their closest relative, Synaptomys cooperi, (southern bog lemmings) by the absence of closed triangles on their mandibular molars and a palate which extends in a sharply pointed, backward projecting spine (Banfield, 1974).

Flank glands of adult males are often clearly marked by a patch of white hair (Banfield, 1974). Females possess eight teats of which two are pectoral pairs and two are inguinal pairs. Synaptomys cooperi has six mammae (Banfield, 1974).

Northern bog lemmings do not have any significant sexual dimorphism. (Banfield, 1974; Wilson and Ruff, 1999)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    27 to 35 g
    0.95 to 1.23 oz
  • Range length
    122 to 144 mm
    4.80 to 5.67 in

Reproduction

The breeding season for S. borealis extends from May to late August. Their litter sizes ranges from two to eight, with an average size of four to five young per litter (Wilson et al, 1999). Female S. borealis are capable of breeding one day after giving birth and are thus capable of having two or three litters per breeding season (Wilson et al, 1999). This indicates the potential for rapid population growth under ideal environmental conditions, though they tend to be uncommon throughout their range.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual

Behavior

S. borealis repeatedly leave fresh droppings along their runways, creating a scent 'signpost' which identifies it as an active runway (Wilson et al, 1999). They often share runway systems with meadow voles, Microtus pennsylvanicus (Wilson et al, 1999).

Communication and Perception

Food Habits

Northern bog lemmings primarily feed on sedges and grasses. They actively clip sedges, grasses, and leafy plants to line the above ground runways between burrow entrances (Wilson et al, 1999). Runways without clippings indicate an abandoned burrow system (Banfield, 1974).

Economic Importance for Humans: Positive

Positive effects are unknown, though it is likely that the presence of Northern bog lemmings contributes to a healthy ecological community.

Economic Importance for Humans: Negative

None known.

Conservation Status

Contributors

Danielle Nicholas (author), University of Toronto.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

References

Banfield, A. 1974. The Mammals of Canada. Toronto: University of Toronto Press.

Mead, J., C. Bell, L. Murray. 1992. Mictomys borealis (Northern Bog Lemming) and the Wisconsin Paleoecology of the East-Central Great Basin. Quaternary Research, 37, No. 2: 229-238.

Wilson, D., S. Ruff. 1999. The Smithsonian Book of North American Mammals. UBC Press.

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