Montana Field Guide

Northern Bog Lemming - Synaptomys borealis

The northern bog lemming has a grizzled reddish-brown coat on the back that grades to gray on the belly; the coat is relatively long and loose. The ears extend noticeably beyond the body fur and are sparsely haired on the edge. The tail is extremely short. There are 16 teeth in the skull (dental formula: I 1/1, C 0/0, P 0/0, M 3/3), with the upper incisors broadly grooved. Body measurements are: total length 120 millimeters, tail 21 to 23 millimeters, hind foot 18 to 19 millimeters, and mass 22 to 25 grams (Foresman 2001a).

The northern bog lemming can be distinguished from all other mice and voles in Montana by a combination of a very short tail (equal to or only slightly longer than the hind foot), broad shallow grooves on the outer surface of the upper incisors, and the deep reentrant angles on the outer side of the upper cheek teeth and the inner side of the lower cheek teeth (Foresman 2001a, 2001b).

Montana Range

No information on movement is available for Montana.

Northern bog lemmings in Montana have been found in at least nine community types, including Engelmann spruce, subalpine fir, birch, willow, sedge (Carex), spike rush (Eleocharis), or combinations of the above, often occurring in wet meadows, fens, or bog-like environments. Wright (1950) captured lemmings in a swampy area containing spruce trees, timothy, alder and other moist-site plants (Wright 1950). The Upper Rattlesnake Creek specimen was captured in a wet-sedge/bluejoint meadow near subalpine fir (Adelman 1979). Areas with extensive moss mats, primarily sphagnum, are the most likely sites in which to find new populations (Wright 1950, Reichel and Beckstrom 1994, Reichel and Corn 1997, Pearson 1999, Foresman 2001a).

Throughout their range a variety of habitats are occupied, especially near the southern edge of the global distribution, and include sphagnum bogs, wet meadows, moist mixed and coniferous forests, montane sedge meadows, krummholz spruce-fir forest with dense herbaceous and mossy understory, alpine tundra, mossy streamsides, and even sagebrush slopes in the case of S. b. artemisiae in British Columbia (Clough and Albright 1987, West 1999). Typically, occupied habitat has high moisture levels. The northern bog lemming occupies burrow systems up to a foot deep, and also surface runways. Young are born in nests that may be underground or on the surface in concealing vegetation.

Northern bog lemmings feed on grasses, sedges, and other herbaceous vegetation, but also snails, slugs, and other invertebrates (West 1999, Foresman 2001a). In Montana, diet (7 stomachs from 7 sites) includes at least 17 moss species, making up an average 59% of the stomach contents (Reichel et al. in preparation).

The northern bog lemming is active throughout the year, and apparently during both day and night. It maintains a home range of probably less than 1 acre, although data regarding movements are unavailable. Population densities may range up to 36 per acre. It is very sociable and may be found in small colonies. Other small mammals present at bog lemming sites in Montana include shrews (Sorex vagrans, S. palustris) and voles (Microtis pennsylvanicus, M. richarsoni, M. longicaudus, Clethrionomys gapperi) (Wright 1950, Reichel and Beckstrom 1994). Predators in Montana include pine martens (Martes americana) and garter snakes (Thamnophis elegans) (Hoffmann et al. 1969, B. Maxell personal communication).

Information on reproduction in Montana is very limited. Scrotal males have been captured on June 16, July 26 and August 29 in Lincoln County, and pregnant females in Lewis and Clark County on August 31 (Reichel and Beckstrom 1994, J. D. Reichel unpublished data). One litter from Montana numbered 3 (Reichel and Beckstrom 1993). Information from other portions of their range indicates northern bog lemmings breed from late April to early October, with most occurring May through August (based on 178 museum specimens from across the global range) (J. D. Reichel unpublished data). Gestation probably lasts 3 weeks. Litter size ranges 2 to 9, with an average of 4 (mean of 3.98 embryos and 3.75 placental scars in 69 museum specimens) (J. D. Reichel unpublished data). Two or three litters per year are capable of being produced (West 1999); at least some individuals breed during the summer of their birth.

No special management activities have been developed or implemented for this species in Montana. Nevertheless, some populations on U.S. Forest Service lands are provided added protection through special management/conservation policy guidelines applied to peatlands, including Research Natural Area (RNA) designation (Chadde et al. 1998). Peatlands with RNA designation typically disallow manipulative management, such as timber harvest and livestock grazing, and water quality of these peatlands is protected under the Clean Water Act and state water quality standards. Protection guidelines (Reichel and Corn 1997) should be applied to all sites where northern bog lemmings are known to occur, as well as potential peatland sites not yet surveyed for them. Guidelines include 1) assumption that northern bog lemmings are present at sphagnum or fen moss habitat patches unless site-specific surveys indicate otherwise, 2) restriction of timber harvest to a zone beyond a 100 meter buffer surrounding sphagnum or other fen moss mats, or associated riparian areas which could provide corridors for dispersal to adjacent patches of suitable habitat, 3) minimizing livestock grazing in drainages with unsurveyed moss mats present, and maintaining range conditions there and in those with populations present at good to excellent, and 4) elimination of management activities that could destroy moss mats (road-building, pothole blasting, trail construction, dam construction, alteration of surface and subsurface waterflow, recreational vehicle use in fen habitats). Additional surveys should be undertaken to better understand the macro- and micro-distribution in Montana, and known sites should be monitored routinely to determine population persistence and trends.