Lemmus lemmus

Geographic Range

Norway lemmings are distributed across Fennoscandia, a region stretching from the Russian Kola Peninsula to the west coast of Norway and from the northern coast of Norway south to the Baltic Sea. However, Lemmus lemmus may migrate further south if the species goes through a population boom.

• Biogeographic Regions
• palearctic palearctic
  • native native

• Other Geographic Terms
• holarctic holarctic

Habitat

Norway lemmings are found in tundra and alpine regions. During the winter they live in insulated spaces under the snow. This provides them with warmth, shelter, access to food, and protection from predators. Having this shelter gives young lemmings a better chance of survival. In times without snow cover, Norway lemmings may live in a variety of bogs, marshes, and other moist terrestrial habitats. They also inhabit heathland where dwarf shrubs are the main vegetation. Norway lemmings find safety by digging shallow burrows or by occupying already formed spaces underground.

• Habitat Regions
• temperate temperate
• polar polar
• terrestrial terrestrial

• Terrestrial Biomes
• tundra tundra

• Wetlands
• marsh marsh
• swamp swamp
• bog bog

Physical Description

Norway lemmings weigh between 20 and 130 g. Body length ranges from 8 to 17.5 cm. They have thick bodies with heavy coats for maintaining body heat against the cold. Fur color is black and brown with some golden-yellow streaks. The underbelly is a lighter color than the rest of their fur. Norway lemmings retain the same fur color, regardless of season, and the males and females are generally similar in size and color. They do not have a conspicuous tail. Their teeth are characteristic of their subfamily, Microtinae : 12 molars, 4 incisors, and flattened crowns. Their limbs are short and mostly tucked under the body. The claw of the first digit on each paw is larger and flatter than the rest of the claws. This modification helps lemmings to tunnel through snow. Their basal metabolic rate is 1.0710 W.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

Norway lemmings breed year round. Although they generally live independently of each other, they will encounter one another briefly for mating. Lemmings may become aggressive toward one another when there are too many other lemmings in close proximity, and male Norway lemmings have been observed engaging in boxing and wrestling behavior. In other species of lemmings, boxing and aggression are parts of the mating system, so it may be that this occurs in Norway lemmings as well. No information was found in the scientific literature indicating whether Norway lemmings are monogamous or polygynous or polygynandrous; however, considering characteristics of other lemmings and the independent nature of Norway lemmings, they are not likely to be monogamous. Females of the genus Lemmus undergo post-partum estrous, so a female may be receptive to mating shortly after giving birth to a litter.

• Mating System
• polygynous polygynous
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Norway lemmings are able to reproduce rapidly and they breed year round. On average, sexual maturity is reached at 3 weeks for females (although a 2 week old pregnant female has been recorded) and at one month for males. They can produce a litter every 3 to 4 weeks with a gestation period of 16 days. Members of the genus Lemmus may have gestation periods lasting between 16 and 23 days. Each litter of Norway lemmings yield between 5 and 13 young. Time to weaning for this genus is usually 14 to 16 days, and the birth weight of Lemmus young is 3.3 grams. Members of this genus also experience post-partum estrous, so the female may be pregnant with her next litter while still caring for the young from her previous litter.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous
• post-partum estrous

No information is currently available on parental investment in Norway lemmings. Generally, however, vole and lemming females are the caregivers and males do not play a role in care giving, except in a few monogamous species. Females in subfamily Microtinae are usually very protective of their young and will keep their offspring close to them. Females in the genus Lemmus wean their young in 14 to 16 days.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

The oldest recorded Norway lemming was a specimen in captivity which lived for 3.3 years. Lemmus species generally live for 1 to 2 years.

Behavior

Norway lemmings are active during the day as well as the night. They spend their waking periods (6 hours on average) foraging and moving about. As a species of the northern latitudes, they can be exposed to up to 24 hours of daylight in the summer, so having active periods during the day and night is most likely an adaptive response to their environment. Norway lemmings prefer to live independently of each other, and they can become aggressive toward each other during periods of overcrowding. Male lemmings are known to engage in boxing, wrestling, and threatening behavior. Their independent nature may be one of the driving factors in dispersal during their population peaks. During these peaks the lemming population will disperse beyond their normal range in search of more space and more food. They may even move into the taiga and forests which are not their preferred habitat. This great abundance of lemmings can decimate the heath shrubs, mosses and lichens which they most commonly feed upon. Generally, the population peaks occur every 3 to 5 years. However, some studies have found that the number of years between the peaks have been increasing and peaks are less regular in occurrence. This irregularity is attributed to climate change. With shorter winters, there is less snow cover and lemmings rely on the snow cover during the winter to provide safe access to food and shelter while breeding and raising their young.

• Key Behaviors
• terricolous
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• territorial territorial

Home Range

When populations are low there may be 3 to 50 Norway lemmings per ha (1.2 to 20 lemmings per acre), and when the population is high there may be up to 330 lemmings per ha (134 lemmings per acre).

Communication and Perception

No information is currently available specifically on communication and perception in Norway lemmings. Voles and lemmings have well-developed senses, such as smell and hearing. Some species of lemmings use scents to mark boundaries, and many species of lemmings can recognize members of their own species by their scents. Voles and lemmings use different calls for distress, aggression, and mating. Each species has a unique set of calls.

• Communication Channels
• tactile tactile
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Norway lemmings are herbivorous. They mainly eat mosses, lichens, bark, and some grasses. Mosses thrive when there has been a sufficient amount of snow over the winter. Food may be difficult or dangerous to obtain just before winter when there are rains and freezing temperatures without snow cover.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • lignivore

• Plant Foods
• leaves
• wood, bark, or stems
• seeds, grains, and nuts
• bryophytes
• lichens

Predation

The population densities of Fennoscandian predators are shown to be tied to the population cycles of Norway lemmings and other small rodents with cyclic population changes. Common predators of Norway lemmings include red foxes , Arctic foxes , ermines , weasels , snowy owls , ravens , and other birds of prey. Fall is a particularly opportune time for lemming predators because there is no snow cover and plant food sources are scarce due to freezing temperatures. With less available food, lemmings may stray further away from their burrows than usual and leave themselves vulnerable to predation. Their burrows, whether in the ground or under the snow, are a lemming's main defense against predators. Aerial predators and larger predators have a more difficult time accessing the burrows. Predators such as ermines and weasels may be able to find their way into the lemmings' burrows.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

During population peaks, when there are up to 134 lemmings per acre, the damage that Norway lemmings inflict on vegetation can take the area up to four years to recover from. While the effect to the tundra landscape can be negative during these times, the effect on predator populations can be positive. For example, Arctic foxes ( Vulpes lagopus ) have a higher probability of recolonizing an area when lemmings are abundant and when their competitor,red foxes ( Vulpes vulpes ), do not live in the area. Norway lemmings are hunted by both of these foxes, and Arctic foxes specialize in hunting lemmings specifically. It has been suggested that having more information on Norway lemming populations could help understand how to support threatened Arctic fox populations.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Norway lemmings have been useful in studies of population cycling. Their population cycles were first noted in myths and legends as the Scandinavian people described hordes of lemmings marching across the land every 3 to 5 years. A Swedish Catholic priest named Olaus Magnus was the first to illustrate Norway lemming migrations in 1555 in his Historia de gentibus septentionalibus ("History of the Northern Peoples"). The woodcut shows horrific giant rodents descending from the skies (essentially appearing out of nowhere) and attacking smaller creatures. While this is an extreme exaggeration, it captures the spirit of fascination and curiosity which led to these animals being so well-studied in their population cycles. The cycles of lemmings and their relatives are the foundation for a lot of research in population dynamics, vegetation growth, and as an example of the effects of climate change.

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

Despite the legends, Norway lemmings have little to no negative impact on human agriculture or economics. Although the lemmings may migrate into more populated areas during years of high population density, they mainly live out of the way of human agricultural areas.

Conservation Status

The IUCN states that the populations of Norway lemmings are stable and of least concern for endangerment. Possible future threats include climate change and grazing of other herbivores which reduces lemming habitat. Overall, Norway lemmings are a rather successful species in the area where they live.

Other Comments

During population peaks, Norway lemmings exhibit large scale dispersal. While many other rodents experience population peaks, Norway lemmings are the only species that will embark on long distance migrations. Their migrations have become famous through legends and stories. One common misconception is that lemmings set out on these migrations with the intent to drown themselves in the sea. Although mass drowning of lemmings do occur on these migrations (it is the number one cause of death on the journey), lemmings are not suicidal. In normal conditions, lemmings are actually able to swim fairly well; however, the sheer number of lemmings and the impending obstacle before them seems to trigger a panic effect in the creatures causing them to drown during the crossing. This phenomenon is another reason why lemming population cycles are so well studied.

Additional Links

Encyclopedia of Life

Contributors

Alexandria Stubblefield (author), Sierra College, Jennifer Skillen (editor), Sierra College, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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Hamel, S., S. Killengreen, J. Henden, N. Yoccoz, R. Ims. 2013. Disentangling the importance of interspecific competition, food availability, and habitat in species occupancy: Recolonization of the endangered Fennoscandian arctic fox. Biological Conservation , 160: 114-120. Accessed March 06, 2013 at http://www.sciencedirect.com/science/article/pii/S0006320713000219 .

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Ravolainen, V., K. Bråthen, R. Ims, N. Yoccoz, J. Henden, S. Killengreen. 2011. Rapid, landscape scale responses in riparian tundra vegetation to exclusion of small and large mammalian herbivores. Basic and Applied Ecology , 12(8): 643-653. Accessed March 06, 2013 at http://www.sciencedirect.com/science/article/pii/S1439179111001228 .

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