Northern bog lemming (Synaptomys borealis)

The vast peatlands of northern Minnesota are home to a tiny and rarely seen mammal, the northern bog lemming. Uncommon wherever it is found, and threatened by habitat loss, climate change, and more, this small rodent is being considered for federal threatened or endangered status.

Appearance. The northern bog lemming is a small burrowing rodent, drab gray-brown in color and about 5½ inches in length. Its stumpy tail is an inch long at most. It closely resembles the southern bog lemming (Synaptomys cooperi). Only differences in their tooth pattern can reliably separate the two species.

Behavior. Northern bog lemmings live in small colonies in underground burrows in summer and, in winter, in nests under the snow. They construct paths called runways to provide routes between nests, food, and other resources. They make “hay” piles of clipped vegetation and produce bright green droppings. They are active day and night all year.

Habitat. Northern bog lemmings are creatures of peatlands, those wet environments composed of living plants and dead plant material and defined by a delicate balance of water, plants, and chemistry. These lemmings have been found in open meadows and tamarack and black spruce forests. Their habitat is typically dominated by sphagnum moss, bearberry, wintergreen, Labrador tea, and grasses and sedges.

Distribution. Northern bog lemmings are one of several boreal species that are on the southern fringe of their range in northern Minnesota. They’re broadly distributed across Canada and Alaska, as well as a few places in Maine, New Hampshire, Montana, Idaho, Washington, and Minnesota. In Minnesota, they have been found in Lake of the Woods, Roseau, Clearwater, Beltrami, Koochiching, Itasca, and St. Louis counties—all within the unique patterned peatlands region.

Life cycle. Gestation lasts about three weeks and typically results in four young per litter. The young lemmings reach reproductive age at five to six weeks, and adult females can breed the day after giving birth. 

Status. The northern bog lemming’s obscurity is one of the biggest threats to its survival. Populations can be small and isolated from each other, meaning entire colonies can quickly be wiped out. Northern bog lemmings can be threatened by extractive activities, climate change, and invasive species. Snow compacted by snowmobiles can cut off tunnel systems that connect them to their food sources. Northern bog lemmings are listed as a species of special concern by the Minnesota Department of Natural Resources and in other states. The U.S. Fish and Wildlife Service will decide by September 30, 2023, whether to list the species as threatened or endangered.