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Northern Bog Lemming
Synaptomys borealis
The northern bog lemming is one of Maine’s rarest mammals, and much like the Canada lynx, it is more numerous in the north and reaches the southern edge of its range here in Maine. The northern bog lemming has been listed as state-threatened since 1986, however, it has not received federal listing attention. The northern bog lemming plays a critical role in the population cycles of many larger carnivores that share habitat, providing food to a variety of wildlife and their young.
Habitat
The northern bog lemming usually occurs in moist, wet meadows or boggy areas, often in conjunction with arctic or alpine tundra and spruce-fir forests. Frequently it occurs near a spring or other source of water or near lush, mossy logs and rocks. Specimens found in Maine are associated with deep moist sphagnum, both in low and high-elevation settings.
The northern bog lemming is widely distributed across northern North America, ranging from Alaska to Labrador and south to Washington and Maine. This species has not been found in great numbers anywhere, with the exception of moderate sized populations in Alaska and around the Hudson Bay. It is less common at the southern extent of its range, which includes Maine and adjacent New Hampshire.
In Maine, the northern bog lemming has been found at five locations in western and northern Maine, including two sites in Baxter State Park. The species has also been captured in three locations in New Hampshire: along the Wild River, not far from the Maine/New Hampshire border, near the base of Mt. Washington, and on Mt. Mooselauke. Most occurrences are at elevations of 2,000 feet or greater. In other parts of the species’ range, it occurs at much lower elevations where its habitat needs are provided by a northern tundra-like habitat, rather than an alpine environment.
Diet
Northern bog lemmings are herbivores, primarily feeding on sedges and grasses, raspberry seeds, and the fungus Endogone.
Distinctive Characteristics
The northern bog lemming is a small mammal, about the size of a vole, or about one ounce and an average length of four inches. It has a blunt nose, short tail, and somewhat grayer coat than the common red-backed vole (Clethrionomys gapperi). The upper parts are dull brown and are slightly brighter on the hind part of the body. Toward the head the fur has a grizzled appearance, while the underside is grayish. The dorsal side of the tail is brown and paler on the ventral side, and feet are a dark grayish color. Bog lemmings have a groove along the outer edge of each incisor tooth, which similar-looking species of voles do not have.
Two species of bog lemmings, the northern and southern (S. cooperi), live in Maine. They are very similar in appearance and are difficult to distinguish. Unlike the southern bog lemming, the northern species has rusty-tipped fur at the base of the ears. Also, female northern bog lemmings have eight mammae (milk-secreting organ of females), while southern bog lemmings only have six. Tooth structures must be examined under magnification to confirm identification of the two species. The northern bog lemming does not have closed triangles on the outer surface of its molars, and it has a shark projection pointing back from the roof of the mouth.
Nocturnal/Diurnal
Northern bog lemmings are active during both day and night, maintaining a home range of likely less than one acre.
Seasonal Changes
Northern bog lemmings are active year-round and create runways through vegetation and dig burrows under the snow in the winter that allow regular movement.
Reproduction & Family Structure
Little is known about the northern bog lemming’s reproductive behavior, although it may be similar to that of the southern bog lemming, which breeds throughout the year and may produce several litters. The gestation period lasts 21-23 days, and a littler may contain one-eight young. When born, the young are blind, naked, and helpless, and weigh about a tenth of an ounce.
Survival & Threats
Predators may include mammals, hawks, owls and snakes. Because the northern bog lemming is found in so few sites and in such low numbers in Maine, it is vulnerable to extirpation. Suitable habitat is not abundant in Maine. Mountain elevations above 2,700 feet are subject to special regulations in Maine, but development of ski areas or wind power could be harmful. Wind power development has been proposed for one known site in western Maine. The discovery of northern bog lemmings at low-altitude spruce-fir forests in Baxter State Park may indicate broader habitat use. Sensitive microhabitats (especially wet, sphagnum ground cover within forests could be altered by logging equipment on non-frozen ground. Additional research is needed to better understand the full range of habitats used. Competition with other small mammals, like meadow voles, may also limit the species’ distribution.
Management & Conservation
The northern bog lemming was listed as threatened in Maine in 1986, because of its apparently low numbers and limited distribution. As yet, no specific conservation plans have been implemented for this species. Further information on habitats used by the species in Maine is needed to develop appropriate conservation measures. Moist, high-elevation mossy areas seem to be optimal habitat. The northern bog lemming shares these habitats with other rare small mammals, including the yellow-nosed vole and rock shrew (both Species of Special Concern). Once the lemming’s habitat needs are better understood, land use should be carefully planned to protect the lemming and other rare species. Systematic small mammal surveys are needed. A recent small mammal inventory in the early 2000’s yielded two new records of northern bog lemmings collected near Sweeny Pond and Deboullie Public Lands in Aroostook County.
Recommendation for management and conservation:
- Prior to land development or forest harvesting, consult with a biologist from MDIFW to assist with planning.
- Deliver any bog lemming specimens to MDIFW to confirm identification. Note the site location as accurately as possible so MDIFW can locate and protect associated northern bog lemming populations.
- Minimize impacts to high elevation habitats that may potentially harbor northern bog lemmings and associated species (cool, moist, mossy areas of a boreal or alpine character). Survey these areas for the species’ presence.
- To preserve the vegetation and physical structure required by the northern bog lemming, do not stray off marked trails, especially in fragile alpine areas on Mt. Katahdin, Bigelow Mountains, and high elevation areas on the Appalachian Trail.