Dicrostonyx groenlandicus

34.

Nearctic Collared Lemming

Dicrostonyx groenlandicus

French: Lemming du Groenland / German: Nordlicher Halsbandlemming / Spanish: Lemming neértico de collar

Other common names: Bering Collared Lemming, Greenland Collared Lemming, Northern Collared Lemming, Northern Hoofed Lemming, Northern Varying Lemming

Taxonomy. Mus groenlandicus Trail, 1823, Jamesons Land, Greenland.

Dicrostonyx groenlandicus is in the subgenus Dicrostonyx. Opinions on the number of species of collard lemmings varied in the past from a single species (D. torquatus) to the current seven species. Taxonomic scope of D. groenlandicus is still not generally accepted. Some authors regard vinogradovi as independent species; others include nelsoni, nunatakensis, richardsoni, and unalascensis under groenlandicus. Phylogeographic analyses retrieved two clusters among Nearctic populations, separated by the Mackenzie River. Six subspecies recognized.

Subspecies and Distribution.

D.g.groenlandicusTrail,1823—ENunavut,includingEQueenElizabethIs,PrinceofWalesI,SomersetI,NBaffinI,andSouthamptonI(Canada)andGreenland.

D.g.clarusHandley,1953—WQueenElizabethIs.

D.g.kilangmiutakR.M.Anderson&Rand,1945—NYukon,NorthwestTerritories,andWNunavut(NWCanada),includingBanks,Victoria,andKingWilliamIs(SWCanadianArcticArchipelago).

D.g.lentusHandley,1953—SBaffinIs.

D.g.rubricatusJ.Richardson,1839—NAlaska.

D. g. vinogradovi Ognev, 1948 — Wrangel I (Russia).

Descriptive notes. Head-body 113-151 mm, tail 11-22 mm; weight 52-114 g. Average weight of the Nearctic Collared Lemming is greater in years of peak abundance than in intermediate years. Winter morphs are significantly longer, heavier, and rounder than summer morphs. The Nearctic Collared Lemming is chunky; it has a short tail and relatively large head. Ears are reduced to low folds of skin and entirely concealed in fur. Feet are short and broad, with densely haired soles and palms and five digits on each. Claws of third and fourth front digits are normal size during summer but enlarge in winter. Winter claws are c.1 cm long, broad, and bifurcate. They are used for digging through ice and snow. Females have eight nipples, two pairs of pectoral and two pairs of inguinal. Pelage is long, dense, and very soft, and winter fur is longer and thicker than summer fur. Tail is densely haired and well pencilled. Summer pelage is brilliantly colored, gray to brownish or rusty on back, fulvous on flanks, and light gray on belly. Back is speckled blackish, reddish, or light gray. Ventral side is frequently washed buff or fulvous, and there is distinct yellowish orange collar. Head is normally darker than posterior fur, and back has more or less distinct spinal strike. Winter pelage is white throughout, occasionally with light buffy gray blotches and similarly tanned forehead. Skull is broad and deep, with convex dorsal profile, constricted interorbital region, widely separated supraorbital ridges, and prominent squamosal pegs that project forward. Mandible is slender, and coronoid process is short and blunt. Upper incisors show no peculiarities; lower incisors are short and posteriorly terminate at level of M”. Molars are rootless and lack cement in reentrant folds. Enamel folding pattern is complex, with vestigial angles on posterior end of M' and M? and anterior end of M, and M,.

Habitat. Arctic tundra with short snow-free period and winter temperatures up to —40°C. Typical habitat of the Nearctic Collared Lemming is flat, gently sloping, or undulating landscape with relatively dry and rocky hillocks, densely covered by willows (Salix lanata and S. arctica, Salicaceae), white dryas (Dryas octopetala, Rosaceae), and cottongrass (Eriophorum, Cyperaceae). Areas with sparse vegetation are less suitable. Summers are mostly spend in upland dry heaths dominated by shrubs and select moist transitional habitats with early accumulation of snow for wintering.

Food and Feeding. Summerdiet of the Nearctic Collared Lemming consists of grasses, sedges, bearberries (Arctostaphylos, Ericaceae), and cottongrass. Twigs and buds of willows are eaten in winter under snow. In peak years, biomass of willows is reduced by 34-54%. On Wrangel Island, 68 plant species were identified in the diet. In late July and early August, Nearctic Collared Lemmings on Wrangel Island store food in caches that contain up to 10-2 kg of fresh plants (usually 5-8 kg), or 2:5 kg of dry matter. Floral composition of cached plants was diverse, and 53 species were identified. Excrement is deposited in piles, containing up to 890 pellets each (300 on average). In a 1m by 1000m transect in Alsaka, 154 fecal piles were counted.

Breeding. Reproduction starts under snow and lasts into September. Winter reproduction is important for populations where summeris short. Those on Wrangel Island have up to 5-6 litters under snow compared to 1-2 summerlitters. Reproductive effort might be prompted by photoperiod-regulated hormonal changes. Sex ratio is balanced (1:1). Ovulation can be induced in captivity and starts ¢.9 hours after copulation. Gestation lasts 19-21 days. Interval between litters is 26 days in captivity. Females normally have 2-3 litters/season, with up to eleven young. Winter litters are smaller (means 3-5-3-8 on Wrangel Island) than summer litters (5-6-6-4). Neonates are naked, blind, and with closed ears. They weigh 2-:7—4-8 g (mean 3-8 g) and are 20-27 mm long. Twelve-day-old young are coved with dense immature pelage, and they get subadult pelage at 26-30 days old. Ears open on day nine, eyes open on day twelve, and molars start erupting on day seven. Individuals born in summer have short summer claws on day 25; winter-born young at same age develop enlarged bifid claws on third and fourth digits of front feet. Young are weaned at 15-20 days old. At 22 days old, young weigh 16-5-34-6 g (mean 26 g). Smallest individuals captured in the wild weighed 11-5 g. Juveniles gain 0-2 g/ day. Females are sexually mature at 40 days old and males at 85 days. There is evidence for earlier breeding; e.g. a female gave birth at 49 days old and a male sired a litter at 47 days old. Although Nearctic Collared Lemmings can be mature at less than 20 g, weight of reproductively active individuals is normally more than 35 g. On Wrangel Island, summer litters attain maturity in the following year. Maximum longevity is 3-3 years, but survival beyond one year in the wild is uncommon. During population peaks, even maximum rate of growth cannot compensate for high predation rates (e.g. 3-4% of females/ day in Greenland). The Nearctic Collard Lemming exhibits remarkably regular 2-8-3-9year population cycles with variable amplitude.

Activity patterns. Nearctic Collared Lemmings are active throughout the day and year. Daily activity is polyphasic. Burrows are important because they can reduce detection by predators; females in particular center their activity on burrows. Up to 843 entrances to underground tunnels were counted per hectare. Underground gallery system of a family group on Wrangel Island extended more than 30 m* and had up to 30 exits. Tunnels descend 25 cm, frequently reaching permafrost level. Winter burrows are more complex, with 1-3 nest chambers (14-18 cm in diameter and 25-50 cm deep) lined with plant material. Digging is most common in mid-summer after soil warms up. Nearctic Collared Lemmings are particularly adept at digging at high densities; low densities restrict this activity to repairs of pre-existing galleries. A single individual unearths up to 25 kg of soil/season, bringing stones as heavy as 135 g to the surface. The Nearctic Collared Lemming has relatively high body temperature averaging 38-4°C.

Movements, Home range and Social organization. In Greenland, monthly means of daily movements were 23-6—41-8 m for males and 29-4-93-8 m for females. Mean home ranges were larger for females (2:7-0-46 ha) than for males (0-15-0-54 ha). In the Canadian Arctic, males had larger home ranges and moved over greater distances (47-4 m in two hours) than females (10-5 m). In Canada, home ranges are generally larger for non-breeding females and failed breeders than breeding females, larger males than smaller males, and at low and medium densities than at high densities. Female home ranges do not overlap; males’ often do. On Wrangel Island, home ranges of females were 800-900 m?*, and males were 3000-4000 m*. Males normally occupy home ranges of 2-3 females. Juveniles disperse from their natal burrows at an average rate of 53 m/ day and can travel 600 m/ day. Young of the subspecies vinogradovi start to disperse 10-14 days after weaning. Nearctic Collared Lemmings are often described as aggressive, but only 1:5% of individuals had apparent injuries even at high densities.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Subspecies vinogradovi from Wrangel Island was classified as a species distinct from groenlandicus as Data Deficient. Before 1996, subspecies vinogradovi was classified as Critically Endangered. This taxon is a species of special concern in Russia. Nearctic Collard Lemmings on Wrangel Island have restricted distribution and display dramatic population oscillations. Cyclicity of populations have been disrupted since the 1980s, with lower amplitude of fluctuations and prolonged periods of low population numbers. Nearctic populations may be threatened by climate change; modelling suggests that climate change could degrade and destroy c.60% of the habitat.

Bibliography. Bee & Hall (1956), Fedorov & Stenseth (2002), Gilg (2002), Hansen (1957), Krivosheev (1984), Predavec & Krebs (2000), Reynolds (1993), Travina (2016).