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Nearctic Brown Lemming

Lemmus trimucronatus

French: Lemming brun / German: Brauner Lemming / Spanish: Lemming neartico

Other common names: Brown Lemming

Taxonomy. Arvicola trimucronata [sic] J. Richardson, 1825, Point Lake, District of Mackenzie, Canada.

In the past, L. trimucronatus was synonymized with L. sibiricus . Ten subspecies recognized, but the subspecies chrysogaster may be synonymous with alascensis.

Subspecies and Distribution.

L.t.trimucronatusJ.Richardson,1825—NYukon,NorthwestTerritories,Nunavut,includingPrinceofWales,Somerset,KingWilliam,Baffin,andSouthamptonIs,andNManitoba(Canada).

L.t.alascensisMerriam,1900—NcoastalAlaska.

L.t.chrysogasterJ.A.Allen,1903—NWRussianFarEastEtoChukchiPeninsula.

L.t.harroldiSwarth,1931—NunivakI(offshoreAlaska).

L.t.helvolusJ.Richardson,1828—SYukon,NBritishColumbia,andNWAlberta(Canada).

L.t.minusculusOsgood,1904—SWAlaska.

L.t.magripesTrue,1894—PribilofIs(offshoreAlaska).

L.t.phaiocephalusManning&Macpherson,1958—BanksandVictoriaIs(CanadianArcticArchipelago).

L.t.subarcticusBee&Hall,1956—NAlaska.

L. t. yukonensis Merriam, 1900 — C & SE Alaska.

Descriptive notes. Head-body 115-133 mm, tail 11-18 mm; weight 51-90 g. Males are 1-6% larger than females. Maximum weight recorded in laboratory reared individuals is 131-4 g. The Nearctic Brown Lemming is slightly smaller than the Siberian Brown Lemming ( L. sibiricus) but has similar body proportions. Females have four pairs of nipples. Pelage is monochromatic, and spinal streak is occasionally retained on front of head but always absent from back. Dorsal fur is brownish gray, posteriorly with rusty shades; flanks are buffy or ocherous; and underparts are gray-washed buff. Winter fur is lighter. Melanistic and albino individuals have been reported in the wild. Skull and molar pattern are similar to those of the Norway Brown Lemming ( L. lemmus).

Habitat. High Arctic tundra with freezing temperatures for at least eight months of the year. In Alaska, Nearctic Brown Lemmings were recorded up to elevations of 1500 m. They prefer raised, drained areas, with vegetation 20-40 cm high; they avoid damp meadows. Dwarf woody perennials, graminoids, forbs, and mosses include: dwarf willows ( Salix arctica and S. pulchra, both Salicaceae); arctic white heather ( Cassiope tetragona) and bog bilberry ( Vaccinium uliginosum), both Ericaceae; white mountain-avens ( Dryas integrifolia, Rosaceae); longstalk starwort ( Stellaria longipes, Caryophyllaceae); arctic lupine ( Lupinus arcticus) and Maydell’s oxytrope ( Oxytropis maydelliana), both Fabaceae; mountain sorell ( Oxyria digyna, Polygonaceae); tussock cottongrass ( Eriophorum vaginatum, Cyperaceae); wideleaf polargrass ( Arctagrostis latifolia), boreal alopecurus ( Alopecurus borealis), and arctic bluegrass ( Poa arctica), all Poaceae; horstail (Equaisetum, Equisetaceae); and ribbed bog moss (Aulacomnium). At high densities, Nearctic Brown Lemmings are ubiquitous across habitat types. Suitable summer habitats are generally widespread on Arctic tundra, but winter habitats are more localized and patchy. Nearctic Brown Lemmings prefer snow depths of 60 cm or more, but average maximum snow depth is less than 50 cm across most of the North American Arctic. Greatest snow accumulations occur with wind in lees of topographic barriers.

Food and Feeding. Staple summer diets of Nearctic Brown Lemmings consist of grasses, sedges, and mosses; monocotyledons are the most important. Winter diet on Bylot Island (Nunavut Territory, Canada) was 65% dicotyledonous plants, 26% mosses, and 9% monocotyledonous plants. Nearctic Brown Lemmings did not strongly prefer or avoid particular species, but not all plants were palatable. Bark and twigs of willows and birch ( Betula, Betulaceae) are consumed in winter. In years of peak abundance, they can reduce tundra vegetation, and on some spots, more than 99% of standing vegetation may be clipped under snow. Wandering individuals feed on carcasses of conspecifics. During winter, excrement is deposited in heaps, c¢.13 cm to one side of a runway. Deposits can be 12 cm in diameter and 6 cm high.

Breeding. Summer reproduction starts when snow melts, but Nearctic Brown Lemmings can also reproduce under snow and raise litters in winter nests. Captive individuals can reproduce throughout the year. Gestation lasts 20-21 days. Due to postpartum estrus, interval between successive litters averages 21 days but can be as short as 17 days. Captive females produce 9-12-4 litters/year. Mean litter sizes under laboratory conditions are 4-2—4-4 young (range 1-10). Primiparous females have the same size litters as multiparous females. On Chukchi (Russian Far East), overwintered females have an average of 8-3 embryos, and numbers of embryos in Alaska varied between years from 4-7 to 8-1. Numbers were higher in females from spring litters (6-9) than in those from summerlitters (5). Neonates are naked, blind, and deaf. Dorsal pelage is apparent at 2-3 days old, and eyes open at 6-11 days old. Young become active at 8-9 days old, start eating solid food at 12-14 days old, and are weaned at 14-18 days old. Birth weights are 3-5-2 g (mean 4). Young weigh an average of 20-6 g at weaning and 59-5 g at 140 days old when growth rate stabilizes. Until then, young gain weight at mean biweekly rates of 1-2-4 g. Females mature at an early age; in the laboratory they were inseminated at 14-19 days old and delivered litters at 35-39 days old. Males have spermatozoa in the epididymis at 22 days old. Wild Nearctic Brown Lemmings attain reproductive maturity at 3—4 weeks old for females and 4-5 weeks for males. Laboratory reared individuals lived up to two years. Populations fluctuate with ¢.3—4 year cycles of peak abundance.

Activity patterns. Nearctic Brown Lemmings are active day and night throughout the year. During summer, they move around using tunnels and surface runways through vegetation. Lengths of tunnels from entrance to chamber are 5-100 cm (mean 22 cm). Under snow, they build roofed-over tunnels where they feed and reproduce throughout winter. They dig through snow making very brief appearances on the surface. At high densities, however, tracks of activity on the snow crust become numerous. Vertical tunnels through snow are used only once. Nests are built with sedges, grasses, and other vegetation. Outer two-thirds of a nest are made with coarse vegetation, and inner one-third is lined with lemming hair. Nest chambers are underground in summer and at ground level or higher up in the snow column in winter. Summer nests are at various depths, ranging from more than 0-5 m on the elevated polygonsto as little as 9 cm when they rest on permafrost. In a winter nest, heat from an occupant’s body melts surrounding snow, and it freezes into a thin icy layer surrounding the nest. Chambers used for resting and as temporary shelters are usually unlined. Ice chambers are placed below permafrost in active ice; they serve as protection from predators and to maintain body temperature during the hottest parts of the day .

Movements, Home range and Social organization. Activities and home range sizes of Nearctic Brown Lemmings vary among years. In Alaska, summer home ranges were 0-0004-2-8 ha for males (means for consecutive years 1-3 ha and 0-98 ha) and 0-01-1-7 ha for females (0-68 ha and 0-41 ha). Males were more active than females, spending 75% of time moving, feeding, and grooming and 69% of time outside of burrows; these proportions for females were 67% and 55%, respectively. Mass movements are typical at peak populations in early summer. Snow melt and collapse of winter tunnels force Nearctic Brown Lemmings to patches of newly uncovered tundra. On barren and frozen ground that is largely inundated by water from melting snow, they are exposed to weather and predators what results in haphazard dispersal. These erratic movements have no direction although peripheral parts of a population can be pushed onto ocean ice up to 16 km from shore. Under such conditions, a female forced to move traveled 2-4 km in 80 minutes (1800 m/h). Nearctic Brown Lemmings are socially tolerant even at peak densities.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Nearctic Brown Lemming is a species of conservation concern in Alberta (Canada), the Magadan Region (Russia), and on Pribilof Islands, USA ( ssp. nigripes).

Bibliography. Banks et al. (1975), Bee & Hall (1956), Chernjavskij (2016d), Rausch & Rausch (1975), Reid et al. (2012), Shenbrot & Krasnov (2005), Soininen et al. (2015).