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. (Haim, et al., 2004; Hamel, et al., 2013; Henttonen, 2012) Biogeographic Regions

palearctic native

Other Geographic Terms

holarctic

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. (Jordan, 2004; Macdonald, 1984; Nowak, 1999; Tacutu, et al., 2013) Other Physical Features

endothermic

homoiothermic

bilateral symmetry Sexual Dimorphism

sexes alike Range mass 20 to 130 g 0.70 to 4.58 oz

Range length 8 to 17.5 cm 3.15 to 6.89 in

Average basal metabolic rate 1.0710 cm3.O2/g/hr

Average basal metabolic rate 1.071 W AnAge

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. (Jordan, 2004; Macdonald, 1984; Nowak, 1999) Mating System

polygynous

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. (Jordan, 2004; Kausrud, et al., 2008; Macdonald, 1984; Nowak, 1999) Key Reproductive Features

iteroparous

year-round breeding

gonochoric/gonochoristic/dioecious (sexes separate)

sexual

viviparous

post-partum estrous Breeding interval Norway lemmings can produce a litter every 3 to 4 weeks.

Breeding season Norway lemmings will breed year-round.

Range number of offspring 5 to 13

Average number of offspring 7 AnAge

Average gestation period 16 days

Average gestation period 19 days AnAge

Range age at sexual or reproductive maturity (female) 2 to 4 weeks

Average age at sexual or reproductive maturity (male) 4 weeks

Average age at sexual or reproductive maturity (male)

Sex: male 44 days AnAge 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. (Macdonald, 1984; Nowak, 1999) Parental Investment

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. (Nowak, 1999) Range lifespan

Status: captivity 3.3 (high) years

Average lifespan

Status: captivity 2.0 years Max Planck Institute for Demographic Research

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. (Haim, et al., 2004; Henttonen, 2012; Jordan, 2004; Macdonald, 1984; Moen, et al., 1993) Key Behaviors

terricolous

diurnal

nocturnal

motile

sedentary

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). (Macdonald, 1984)

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. (Macdonald, 1984) Communication Channels

tactile

acoustic

chemical Other Communication Modes

scent marks Perception Channels

visual

tactile

acoustic

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. (Jordan, 2004; Macdonald, 1984; Nowak, 1999) Primary Diet

herbivore folivore lignivore

Plant Foods

leaves

wood, bark, or stems

seeds, grains, and nuts

bryophytes

lichens

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. (Hamel, et al., 2013; Kausrud, et al., 2008; Macdonald, 1984) 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. (Hamel, et al., 2013; Kausrud, et al., 2008; Macdonald, 1984; Ravolainen, et al., 2011) 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. (Macdonald, 1984)

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. (Henttonen, 2012; Jordan, 2004; Macdonald, 1984; Nowak, 1999)

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

Glossary Palearctic living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa. acoustic uses sound to communicate bilateral symmetry having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria. bog a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum. chemical uses smells or other chemicals to communicate cryptic having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect. diurnal active during the day, 2. lasting for one day. endothermic animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds. female parental care parental care is carried out by females folivore an animal that mainly eats leaves. herbivore An animal that eats mainly plants or parts of plants. holarctic a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions. Found in northern North America and northern Europe or Asia. iteroparous offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes). marsh marshes are wetland areas often dominated by grasses and reeds. motile having the capacity to move from one place to another. native range the area in which the animal is naturally found, the region in which it is endemic. nocturnal active during the night polar the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south. polygynandrous the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females. polygynous having more than one female as a mate at one time scent marks communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them sedentary remains in the same area sexual reproduction that includes combining the genetic contribution of two individuals, a male and a female swamp a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation. tactile uses touch to communicate temperate that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle). terrestrial Living on the ground. territorial defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement tundra A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short. visual uses sight to communicate viviparous reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female. year-round breeding breeding takes place throughout the year