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Overview

Brief Summary

The weasel is so small, that it can follow mice into their own network of tunnels. Of all the Wadden Islands, the weasel is only found on the island of Sylt. In the past,you could find weases on Ameland and Terschelling, but are no longer found there. Weasels are also having a hard time surviving in many places on the mainland. This is often because many of their hunting grounds are mowed, resulting in fewer voles and therefore, fewer weasels.   
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Biology

Weasels are active at any time of day or night, and intersperse periods of activity with a rest period (3). They feed mainly on small rodents, rabbits, birds and eggs (3), killing prey with a bite to the neck (1). Their small size enables them to enter the tunnels of mice and voles whilst hunting (2), and they often take over the nests of their prey, lining their dens with fur from prey during cold weather (2). A number of dens will be used within the home range. Males and females occupy separate territories, and defend these against members of the opposite sex (2). During spring, males move around in search of a mate (2). The male and female often fight prior to copulation, and the male grabs the female by the neck before he mates (1). A single litter of between 4 and 6 (2) naked, blind and deaf (1) kits is produced each year; the kits are weaned after 3 to 4 weeks and begin to hunt well by 8 weeks of age (2), often accompanying their mother to hunt in 'gangs' (2). By 9 to 12 weeks after birth the family group starts to split up (1). Historically, weasels were believed to have magical powers, and were said to be able to bring their dead young back to life. It was also thought that they hypnotised their prey by dancing (4); in fact 'dancing' behaviour is thought to be a response to discomfort caused by internal parasites (2).
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Description

Britain's smallest native carnivore (2), the weasel has a long slender body, and a short tail. The fur is ginger to a rich chocolate-russet brown in colour, and the underparts are creamy-white (2). The narrow head is supported on a long neck, and the legs are short (1). The large eyes are black, and the ears are rounded (1). In northern parts of the range, weasels turn white in winter, but they do not do so in the UK (2).
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Description

The smallest carnivores usually burn energy the fastest and have the most active lifestyles, so it is no surprise that the Least Weasel, the miniature among mustelids, consumes roughly half its body weight each day—equal to about two deer mice and a vole. As with other weasels, adult females may be half the size of adult males, and they mature much more rapidly; females are sexually mature at four months, males at eight months. Females produce two litters each year, unlike the larger, slower-breeding Ermine and Long-tailed Weasel. In the north, the fur of the Least Weasel turns from brown to white in winter, camouflaging them in the snow.

Adaptation: Large, shearing carnassial teeth at the back dominate the jaw structure of the Least Weasel, Mustela nivalis, as they do in all members of the weasel family.

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account
  • Original description: Linnaeus, C., 1766.  Systema Naturae per regna tria naturae, secundum classis, ordines, genera, species cum characteribus, differentiis, synonymis, locis. Twelfth Edition, p. 69.  Laurentii Salvii, Uppsala, 1:1-532.
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Distribution

occurs (regularly, as a native taxon) in multiple nations

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National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: Circumboreal, Holarctic distribution. Western Hemisphere: most of Canada and Alaska south to British Columbia, Montana, Wyoming, Oklahoma, Missouri, Ohio, Virginia, and along the Appalachians to the Great Smoky Mountains (North Carolina, Tennessee). Range has expanded southward in the Great Plains since the mid-1960s as the climate has become cooler and more mesic (Frey 1992). Thought to be rare (though sometimes locally fairly common) throughout the range in the southeastern U.S., but actual status is uncertain (Handley 1991). Introduced in New Zealand, Malta, Crete, the Azore Islands, and apparently also Sao Tome off west Africa (Sheffield and King 1994). Ranges to 3660 m in mountains of Eurasia.

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Range Description

This species has a circumboreal, Holartcic distribution, taking in much of Europe and North Africa, Asia and northern North America. It has been introduced in New Zealand, Malta, Crete, the Azore Islands, and apparently also Sao Tome off west Africa (Sheffield and King 1994). It is found throughout Europe and on many islands, including the Azores, Britain (but not Ireland), and all major Mediterranean islands. The populations on the Azores and Mediterranean islands (Malta and Crete) are widely considered introduced (Dobson, 1998; McDonald pers. comm.). It is also found on Honshu, Hokkaido, Kunashiri, Etorofu, and Sakhalin Islands in Japan (Abe et al., 2005) and northern Mongolia (Bannikov, 1954; Dulamtseren, 1970).
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Geographic Range

Least weasels are native to the Nearctic and Palearctic regions and have been introduced to the Australian region. They are found throughout Europe and northern Asia (excluding Ireland, the Arabian Pennisula, and Artic islands), in Japan, and throughout North America. In North America they range from Alaska and northern Canada south to Wyoming and North Carolina. A population of least weasels was introduced to New Zealand as well.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); australian (Introduced )

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Geographic Range

Least weasels are found throughout the Palearctic region (excluding Ireland, the Arabian Pennisula, and the Arctic Isles), in Japan, and in the Nearctic, from Alaska and northern Canada south to Wyoming and North Carolina (Honacki, 1982). A population of least weasels was introduced to New Zealand as well (Sheffield, 1994).

Biogeographic Regions: nearctic (Native ); palearctic (Native ); australian (Introduced )

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Range

Widespread throughout mainland Britain, and on large islands around the UK, but absent from Ireland (3). They also occur throughout much of Europe, reaching into Asia as far east as Japan, as well as in North America (3).
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Physical Description

Morphology

Physical Description

Least weasels are long and slender, with a long neck, a narrow head, and short limbs. They have large, black eyes and large, round ears. The feet have five fingers with sharp claws. The mass of least weasels varies depending upon their location. In North America least weasels range in weight from 30 to 55 grams, with males being slightly larger than females. Total length ranges from 165 to 205 mm, tail length ranges from 22 to 40 mm. Fur color is chocolate brown on their back and white with brown spots on the underparts. The summer coat is about 1 cm in length. The winter coat, which is about 1.5 cm in length, turns to all white in northern populations and remains brown in southern populations.

Range mass: 30.0 to 55.0 g.

Range length: 165.0 to 205.0 mm.

Other Physical Features: endothermic ; bilateral symmetry

Sexual Dimorphism: male larger

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Physical Description

The body of least weasels is long and slender, with a long neck; a flat, narrow head; and short limbs. This animal has large black eyes and large, round ears. The feet have five fingers with sharp claws. Mass is dependent upon location, North American populations are the smallest and those found in northern Africa have the largest mass. Fur color is chocolate brown on the back and white with brown spots on the underparts. The summer coat is about 1 cm in length. The winter coat, which is about 1.5 cm in length, turns to all white in northern populations and remains brown in the southern populations (Sheffield, 1994).

Range mass: 30.0 to 55.0 g.

Range length: 165.0 to 205.0 mm.

Other Physical Features: endothermic ; bilateral symmetry

Sexual Dimorphism: male larger

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Size

Length: 21 cm

Weight: 50 grams

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Size in North America

Sexual Dimorphism: Males are larger than females.

Length:
Range: 180-205 mm males; 165-180 mm females

Weight:
Range: 40-55 g males; 30-50 g females
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Ecology

Habitat

Comments: Habitat varies geographically and includes open forests, farmlands and cultivated areas, grassy fields and meadows, riparian woodlands, hedgerows, alpine meadows, scrub, steppe and semi-deserts, prairies, coastal dunes, and sometimes rural residential areas; snow cover is not an obstacle; generally avoids deep dense forest and sandy desert. When inactive, occupies burrow made by vole or mole, or rests in nest in hole in wall of building or under corn shock or similar site. Den site may change often. Young are born in abandoned underground burrows made by other mammals (or similar secluded sites).

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Habitat and Ecology

Habitat and Ecology
Weasels tolerate a wide range of habitats, including forests, farmlands and cultivated fields, grassy fields and meadows, riparian woodlands, hedgerows, alpine meadows and forests, scrub, steppe and semi-deserts, prairies, and coastal dunes (Sheffield and King, 1994; Pulliainen, 1999). This species occurs from sea level to at least 3,860 m. It forms dens in crevices among tree roots, in hollow logs, or in abandoned burrows of other species. This species is a specialist diurnal predator of small mammals (especially rodents), although it will also occasionally feed on birds’ eggs, lizards, frogs, salamanders, fish, worms, and carrion (Sheffield and King, 1994). Food may be stored for the winter (Danzig, 1992). Habitat selection is usually determined by local distribution of rodents. Foraging individuals avoid open spaces, where they are most vulnerable to predation by raptors (Sheffield and King, 1994). They prefer dense, rank grassland where microtines (voles and lemmings) are abundant (McDonald pers. comm.).

Systems
  • Terrestrial
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Least weasels do well in a wide variety of habitats, including open forests, farmlands, meadows, prairies, steppe, and semi-deserts. Least weasels avoid deep forests, sandy deserts, and open spaces. They are well adapted for the tundra regions.

Habitat Regions: temperate

Terrestrial Biomes: tundra ; taiga ; forest ; rainforest

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Least weasels can survive in a wide variety of habitats, including open forests , farmlands, meadows, prairies, steppe, and semi-deserts. Least weasels avoid deep forests, sandy deserts, and open spaces. They are well adapted for the tundra (Sheffield, 1994).

Habitat Regions: temperate

Terrestrial Biomes: tundra ; taiga ; forest ; rainforest

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Found in a range of habitats where there is good cover and plentiful prey, including woodland, grassland, sand dunes, mountains (3), urban areas, marshes and moors (2).
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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: Specialist predator of small mammals, especially voles, lemmings, and other mice. When small rodents are scarce, may consume other small vertebrates, insects, or worms. Young are adept at killing mice at 7 weeks.

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Food Habits

The diet of least weasels is composed of small mammals, mainly rodents like Peromyscus leucopus and Microtus pennsylvanicus. When rodents are scarce, weasels will eat Aves, Insecta, and Squamata. The size of prey that least weasels are able to hunt depends on burrow size of the prey. If the weasel is too large to fit into the burrow it is unlikely that they will be able to hunt those animals. Because females are smaller, they are able to hunt smaller prey than males. Least weasels will kill more prey than they can eat at the time and will store this surplus in their burrows for later consumption.

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Food Habits

The diet of least weasels is composed of small mammals, mainly rodents. When rodents are scarce, weasels will eat birds' eggs and nestlings. Their diet also ranges from insects to lizards. In the extreme northern populations they will eat the carcasses of brown lemmings. Males are better hunters and are more likely to hunt larger prey, while females will continue looking for small rodents (Sheffield, 1994).

Primary Diet: carnivore (Eats terrestrial vertebrates)

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Associations

Ecosystem Roles

Least weasels play an important role in controlling rodent populations.

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Predation

Least weasels are aggressive and fierce and will attack animals much larger than themselves. Young in nests are preyed on by Squamata, while adults may be preyed on by large birds of prey, such as Strigiformes and Accipitridae.

Known Predators:

  • owls (Strigiformes)
  • hawks (Accipitridae)
  • snakes (Serpentes)

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Ecosystem Roles

Least weasels are important predators of small mammals in the ecosystems in which they live.

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Predation

Least weasels are aggressive and fierce and will attack animals much larger than themselves. Young in nests are preyed on by snakes, while adults may be preyed on by large birds of prey, such as owls and hawks.

Known Predators:

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Known predators

Mustela nivalis is prey of:
Buteo lagopus
Squamata
Strigiformes
Accipitridae

Based on studies in:
Russia (Tundra)

This list may not be complete but is based on published studies.
  • T. Dunaeva and V. Kucheruk, Material on the ecology of the terrestrial vertebrates of the tundra of south Yamal, Bull. Soc. Nat. Moscou (N.S., Zool. Sect.) 4(19):1-80 (1941).
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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Known prey organisms

Mustela nivalis preys on:
Microtus
Microtus xanthognathus
Clethrionomys glareolus

Based on studies in:
Russia (Tundra)

This list may not be complete but is based on published studies.
  • T. Dunaeva and V. Kucheruk, Material on the ecology of the terrestrial vertebrates of the tundra of south Yamal, Bull. Soc. Nat. Moscou (N.S., Zool. Sect.) 4(19):1-80 (1941).
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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General Ecology

Home range size varies with conditions; up to 26 ha in males, up to 7 ha in females; in England, average home range was 7-15 ha for males, 1-4 ha for females (King 1975). Basically solitary, except during breeding season and when females have young. High dispersal rate, good ability to colonize vacant habitat when rodent populations increase.

Density fluctuates with rodent populations; 0.2-1.0/ha in favorable conditions, average as low as 1-7/100 ha over wider areas (Erlinger 1974, Golley 1960, Sheffield and King 1994).

Mortality rate is high (overall annual rate is 75-90%); average age at death is less than one year. Predators include various Carnovora, raptors, and possibly snakes.

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Life History and Behavior

Behavior

Communication and Perception

Least weasels possess keen senses of smell, hearing, touch, and sight. As with most mammals they rely heavily on their sense of smell, communicating among themselves and locating prey by detecting scents.

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Communication and Perception

Least weasels possess keen senses of smell, hearing, touch, and sight. As with most mammals they rely heavily on their sense of smell, communicating among themselves and locating prey by detecting scents.

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Cyclicity

Comments: Active day or night throughout the year.

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Life Expectancy

Lifespan/Longevity

Least weasels probably only live for several years after reaching adulthood and most die before reaching adulthood.

Range lifespan

Status: captivity:
9.1 (high) years.

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Lifespan/Longevity

Least weasels probably only live for several years after reaching adulthood and most die before reaching adulthood.

Range lifespan

Status: captivity:
9.1 (high) years.

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Lifespan, longevity, and ageing

Maximum longevity: 9.1 years (captivity) Observations: One wild born specimen was still alive at 9.1 years of age (Richard Weigl 2005). Anecdotal reports of animals living more than 10 years are plausible but remain unverified.
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Reproduction

May breed throughout the year but mainly in spring and late summer. When rodents are plentiful, may breed in winter under snow. Gestation lasts 34-37 days, including the 10-12 days between fertilization and implantation. Litter size averages 4-5 in temperate zone, higher in arctic latitudes. Commonly two litters/year. Young are tended by both parents, weaned by 6-7 weeks. Family groups break up when young are about 9-12 weeks old. Spring-born females are sexually mature in 3-4 months (may produce a litter in their first summer), males in 8 months. Reproductive output increases when food is abundant (more young are born, greater survivorship).

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Mating System: polygynous

Pregancy in least weasels lasts from 34 to 37 days. Litters may range from 1 to 7 young. A higher number of offspring per litter can be found in northern populations. In the wild it is possible to have two litters per year, but there is a high death rate in the second litter.  Females that are born in the spring are mature in four months and may breed in their first summer. Summer and autumn born females are not as well developed and cannot breed until the next summer. Males reach sexual maturity at 8 months old.

Breeding interval: Least weasels can breed once or twice each year.

Breeding season: Least weasels breed in spring and late summer.

Range number of offspring: 1.0 to 7.0.

Range gestation period: 37.0 (high) days.

Range weaning age: 18.0 (low) days.

Range age at sexual or reproductive maturity (female): 4.0 to 8.0 months.

Range age at sexual or reproductive maturity (male): 4.0 to 8.0 months.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous

Average birth mass: 2.6 g.

Average number of offspring: 5.

Newborns weigh from 1.1 g to 1.7 g and are naked, blind, and deaf. They are nursed and cared for in the burrow by their mother. After 49 to 56 days, they have reached their adult length. By week 6, males are larger than females. In 9 to 12 weeks the family groups begin to break up, and in 12 to 15 weeks the weasels reach their adult weight.

Parental Investment: altricial ; female parental care

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Mating System: polygynous

In North America, central Europe, and the former USSR, breeding can occur throughout the year, but the most breeding occurs in the spring and late summer. Gestation in least weasels lasts from 34 - 37 days. Litters may range from 1 - 7. A higher number of offspring per litter can be found in northern populations. Newborns weigh from 1.1 g to 1.7 g and are wrinkled, pink, naked, blind, and deaf. After 49 - 56 days, they have reached their adult length. By week 6 males are larger than females. In 9 - 12 weeks the family groups begin to break up, and in 12 - 15 weeks least weasels reach their adult mass. Females that are born in the spring are sexually mature in three months and may breed in their first summer. Summer and autumn born females are not as well developed and cannot breed until the next summer (Sheffield, 1994).

Breeding interval: Least weasels can breed once or twice each year.

Breeding season: Least weasels breed in spring and late summer.

Range number of offspring: 1.0 to 7.0.

Range gestation period: 37.0 (high) days.

Range weaning age: 18.0 (low) days.

Range age at sexual or reproductive maturity (female): 4.0 to 8.0 months.

Range age at sexual or reproductive maturity (male): 4.0 to 8.0 months.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous

Average birth mass: 2.6 g.

Average number of offspring: 5.

Newborns weigh from 1.1 g to 1.7 g and are naked, blind, and deaf. They are nursed and cared for in the burrow by their mother. After 49 to 56 days, they have reached their adult length. By week 6, males are larger than females. In 9 to 12 weeks the family groups begin to break up, and in 12 to 15 weeks the weasels reach their adult weight.

Females care for and nurse their young until they become independent.

Parental Investment: altricial ; female parental care

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Mustela nivalis

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 2 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ATGTTCATTAATCGATGATTATTTTCCACTAATCACAAAGACATCGGCACCCTTTACCTCTTATTTGGTGCATGAGCCGGAATAGTAGGTACTGCCCTCAGTCTACTAATCCGCGCTGAACTTGGTCAACCTGGCGCTCTATTAGGAGACGACCAGGTTTATAACGTGATCGTGACTGCTCACGCATTTGTAATAATTTTCTTCATAGTAATACCTATCATGCTTGGGGGTTTTGGGAACTGACTTATTCCCTTAATAATTGGCGCACCTGATATAGCATTCCCACGAATAAATAACATAAGCTTCTGACTTCTTCCACCCTCTTTTCTTCTCCTACTGGCCTCCTCTATGGTAGAAGCGGGTGCAGGGACTGGATGAACTGTATACCCTCCTCTAGCAGGGAACCTGGCACATGCTGGAGCATCCGTAGACCTAGCAATCTTTTCTCTTCACTTAGCTGGTGTTTCATCTATTTTAGGGTCAATTAACTTCATCACCACTATTATCAACATAAAACCACCTGCTATATCACAGTACCAAACCCCATTATTCGTATGATCAGTCTTAATTACAGCTGTACTTCTTCTCCTATCTCTGCCAGTTTTAGCAGCCGGCATCACCATATTACTTACAGATCGAAATCTAAACACTACTTTCTTCGACCCGGCCGGAGGAGGAGACCCTATCTTGTACCAACACCTATTTTGATTTTTTGGGCACCCGGAAGTATATATCCTAATTCTTCCAGGGTTTGGTATTATTTCACACGTTGTAACATATTACTCAGGAAAAAAAGAACCATTCGGTTACATGGGGATAGTATGAGCAATAATATCAATTGGTTTCCTAGGATTTATCGTATGAGCCCACCATATATTTACCGTAGGCTTAGACGTTGACACACGAGCATATTTCACCTCAGCTACCATGATCATCGCCATCCCCACTGGAGTAAAAGTATTCAGCTGACTTGCCACCCTACATGGAGGAAATATCAAATGATCCCCTGCTATGTTATGAGCCTTGGGGTTTATTTTTCTATTTACAGTAGGGGGTCTAACGGGCATTGTACTATCAAATTCATCACTAGACATTGTCCTTCACGACACATATTATGTAGTAGCACACTTCCACTACGTCCTCTCAATAGGGGCAGTGTTTGCAATTATAGGCGGATTCGTTCACTGATTCCCACTATTCACAGGCTATACCCTAAATGATGTATGAGCAAAAATTCATTTCACAATTATATTTGTAGGAGTAAACACAACATTCTTTCCTCAACATTTCCTAGGCCTATCAGGTATGCCTCGACGCTACTCCGATTACCCAGATGCTTATACAACATGAAATACAGTATCCTCCATAGGATCGTTCATCTCATTAACAGCAGTTATACTAATAATCTTCATGATTTGAGAAGCCTTCGCATCCAAACGAGAAGTATTGACAGTAGAACTAACCTCAACTAATATCGAATGACTACATGGATGCCCTCCTCCATATCACACATTCGAAGAACCAACCTATGTACTATCAAAATAA
-- end --

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Statistics of barcoding coverage: Mustela nivalis

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Specimens with Barcodes: 7
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2008

Assessor/s
Tikhonov, A., Cavallini, P., Maran, T., Kranz, A., Herrero, J., Giannatos, G., Stubbe, M., Conroy, J., Kryštufek, B., Abramov, A., Wozencraft, C., Reid, F. & McDonald, R.

Reviewer/s
Duckworth, J.W. (Small Carnivore Red List Authority) & Schipper, J. (Global Mammal Assessment Team)

Contributor/s

Justification
This species is listed as Least Concern in view of its wide distribution, presumed large population, occurrence in a number of protected areas, tolerance to some degree of habitat modification, and because it is unlikely to be declining at nearly the rate required to qualify for listing in a threatened category.
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Least weasel populations are not considered threatened.

IUCN Red List of Threatened Species: least concern

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

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Least weasels are generally widespread and abundant. Localized populations may be threatened by habitat destruction, but these animals are generally not threatened.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

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Status

Classified as a species of conservation concern by the UK Biodiversity Action Plan, although not a priority species. Listed under Appendix III of the Bern Convention (7).
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Population

Population
In the European part of its range, there are documented population declines in some areas (e.g. Britain: Battersby, 2005), and suspected declines in others. Although it has a wide distribution, it is considered rare in North America (Sheffield and King, 1994). In Eurasia, it is relatively common, but not often seen (Sheffield and King, 1994). Local densities of 0.2 to 1.0 individuals per hectare can occur in favored habitats when prey are abundant (Sheffield and King, 1994). However, over wider areas, the average density may be as low as 1 to 7 per 100 hectares (Goszczynski, 1977). Populations fluctuate both seasonally and annually, sometimes involving large increases of up to 10-fold, concurrently or within 9 months of a population peak of small rodents, and lasting 6 to 18 months (Sheffield and King, 1994). Thought to be rare (though sometimes locally fairly common) throughout the range in the southeastern U.S., but actual status is uncertain (Handley 1991).

Population Trend
Stable
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Threats

Major Threats
Threats include incidental poisoning with rodenticides (Sheffield and King, 1994) and persecution. The weasel prefers open agricultural habitats, which are declining owing to changes in agricultural practices (rural abandonment) in parts of Europe, as open fields undergo succession.
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Populations of weasels are controlled because they take gamebird eggs and chicks (3). Likely threats include habitat loss and simplification, as well as predation by foxes. Agricultural changes have led in many areas to the loss or reduction of rough grasslands, which is prime habitat for the field vole, a key source of food for weasels (3). Evidence is building that rodenticides are having an effect on weasels and stoats, as they eat poisoned rodents (5).
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Management

Conservation Actions

Conservation Actions
This species is found in many protected areas. It is listed on Appendix III of the Bern Convention (Pulliainen, 1999), and is protected under national and sub-national legislation in a number of range states (e.g. Sichuan, China: Yi-Ming et al., 2000). Monitoring is required to quantify the population trend in Europe.
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Conservation

Research is currently being carried out to determine whether the populations of weasels and stoats, our smallest carnivores are in decline (4). Weasels are not legally protected in the UK (2).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Positive

Least weasels have been hunted and trapped by humans throughout the world. They help keep in check the populations of many species of rodents that are potentially harmful to agriculture.

Positive Impacts: controls pest population

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Economic Importance for Humans: Positive

Least weasels have been hunted and trapped by humans throughout the world (Sheffield, 1994). The help keep in check the populations of many species of rodents that are potentially harmful to agriculture.

Positive Impacts: controls pest population

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Wikipedia

Least weasel

The least weasel (Mustela nivalis), or simply weasel in the UK,[2] is the smallest member of the genus Mustela and of the family Mustelidae (as well as the smallest of the Carnivora), native to Eurasia, North America and North Africa, though it has been introduced elsewhere. It is classed as being of Least Concern by the IUCN, due to its wide distribution and presumed large population.

Least weasels from various parts of its range vary greatly in size. The body is slender and elongated and the legs and tail are relatively short. The colour varies geographically, as does the pelage type and length of tail. The dorsal surface, flanks, limbs and tail of the animal are usually some shade of brown while the underparts are white. The line delineating the boundary between the two colours is usually straight. At high altitudes and in the northern part of its range, the coat becomes pure white in winter. Eighteen subspecies are recognised.

Small rodents form the largest part of the least weasel's diet, but it also kills and eats rabbits and other mammals, and occasionally birds, birds' eggs, fish and frogs. Males mark their territories with olfactory signals and have exclusive home ranges which may include several female ranges. Least weasels use pre-existing holes to sleep, store food and raise their young. Breeding takes place in the spring and summer, and there is a single litter of about six kits which are reared exclusively by the female. Due to its small size, fierce nature and cunning behaviour, the least weasel plays an important part in the mythology and legend of various cultures.

Taxonomy and evolution[edit]

The least weasel was given its scientific name Mustela nivalis by Carl Linnaeus in his 12th edition of Systema Naturae in 1766. The type locality was Westrobothnia in Sweden. As an animal with a very wide distribution, the morphology of the least weasel varies geographically. The species was reviewed by Reichstein in 1957 and again by van Zyll de Jong in 1992 and Reig in 1997. Youngman (1982) placed it in the subgenus Mustela while Abramov (1999) considered it should be included in the subgenus Gale. Based on skull characteristics, Reig (1997) proposed that the taxon should be split into four species, M. subpalmata, M. rixosa, M. vulgaris and M. eskimo. Abrimov and Baryshinikov (2000) disagreed, recognising only M. subpalmata as a separate species.[3]

Within the genus Mustela, the least weasel is a relatively unspecialised form, as evidenced by its pedomorphic skull, which occurs even in large subspecies.[4] Its direct ancestor was Mustela praenivalis, which lived in Europe during the Middle Pleistocene and Villafranchian. M. praenivalis itself was probably preceded by M. pliocaenica of the Pliocene. The modern species probably arose during the Late Pleistocene.[5] The least weasel is the product of a process begun 5–7 million years ago, when northern forests were replaced by open grassland, thus prompting an explosive evolution of small, burrowing rodents. The weasel's ancestors were larger than the current form, and underwent a reduction in size to exploit the new food source. The least weasel throve during the Ice Age, as its small size and long body allowed it to easily operate beneath snow, as well as hunt in burrows. It probably crossed to North America through the Bering land bridge 200,000 years ago.[6]

Subspecies[edit]

Various least weasel subspecies; (from left to right) M. n. pygmaea, M. n. nivalis, M. n. pallida, M. n. vulgaris, M. n. boccamela, M. n. heptneri

The least weasel has a high geographic variation, a fact which has historically led to numerous disagreements among biologists studying its systematics. Least weasel subspecies are divided into 3 categories:[7]

  • The pygmaea–rixosa group (small weasels): Tiny weasels with short tails, pedomorphic skulls, and pelts that turn pure white in winter. They inhabit northern European Russia, Siberia, the Russian Far East, Finland, northern Scandinavian Peninsula, Mongolia, northeastern China, Japan and North America.[7]
  • The boccamela group (large weasels): Very large weasels with large skulls, relatively long tails and lighter coloured pelts. Locally, they either do not turn white or only partially change colour in winter. They inhabit Transcaucasia, from western Kazakhstan to Semirechye and in the flat deserts of Middle Asia. They are also found in Morocco, Algeria, and Tunisia.[7]
  • The nivalis group (average weasels): Medium-sized weasels, with tails of moderate length, representing a transitional form between the former two groups. They inhabit the middle and southern regions of European Russia, Crimea, Ciscaucasus, western Kazakhstan, southern and middle Urals and montane parts of Middle Asia, save for Koppet Dag.[7]

As of 2005,[8] 18 subspecies are recognised.

Physical description[edit]

Skulls of a long-tailed weasel (top), a stoat (bottom left) and least weasel (bottom right), as illustrated in Merriam's Synopsis of the Weasels of North America

The least weasel has a thin, greatly elongated and extremely flexible body with a small, yet elongated, blunt-muzzled head which is no thicker than the neck. The eyes are large, bulging and dark coloured. The legs and tail are relatively short, the latter constituting less than half the body length. The feet are armed with sharp, dark-coloured claws, and the soles are heavily haired.[19] The skull, especially that of the small rixosa group, has an infantile appearance when compared with that of other members of the genus Mustela (in particular, the stoat and kolonok). This is expressed in the relatively large size of the cranium and shortened facial region.[20] The skull is, overall, similar to that of the stoat, but smaller, though the skulls of large male weasels tend to overlap in size with those of small female stoats.[21] There are usually four pairs of nipples but these are only visible in females. The baculum is short, 16 to 20 mm (0.6 to 0.8 in), with a thick, straight shaft. Fat is deposited along the spine, kidneys, gut mesentries and around the limbs. The least weasel has muscular anal glands under the tail, which measure 7 by 5 mm (0.3 by 0.2 in), and contain sulphurous volatiles, including thietanes and dithiacyclopentanes. The smell and chemical composition of these chemicals are distinct from those of the stoat.[21] The least weasel moves by jumping, the distance between the tracks of the fore and hind limbs being 18 to 35 cm (7 to 14 in).[22]

Skeleton, as illustrated in Lydekker's The New Natural History

Dimensions vary geographically, to an extent rarely found among other mammals. Least weasels of the vulgaris group, for example, may outweigh the smaller races by almost four times. In some large subspecies, the male may be 1.5 times longer than the female. Variations in tail length are also variable, constituting from 13–30% of the length of the body. Average body length in males is 130 to 260 mm (5 to 10 in), while females average 114 to 204 mm (4.5 to 8.0 in). The tail measures 12 to 87 mm (0.5 to 3.4 in) in males and 17 to 60 millimetres (0.7 to 2.4 in) in females. Males weigh 36 to 250 g (1.3 to 8.8 oz), while females weigh 29 to 117 g (1.0 to 4.1 oz).[23]

The winter coat is conspicuous when there is no snow on the ground.

The winter fur is dense, but short and closely fitting. In northern subspecies, the fur is soft and silky, but coarse in southern forms. The summer fur is very short, sparser and rougher. The upper parts in the summer fur are dark, but vary geographically from dark-tawny or dark-chocolate to light pale tawny or sandy. The lower parts, including the lower jaw and inner sides of the legs, are white. There is often a brown spot at the corner of the mouth. The dividing line between the dark upper and light lower parts is usually straight but sometimes forms an irregular line. The tail is brown, and sometimes the tip is a little darker but it is never black. In the northern part of its range and at high altitudes, the least weasel changes colour in the winter, the coat becoming pure white and exhibiting a few black hairs in rare circumstances.[20][24]

Behaviour and ecology[edit]

Reproduction and development[edit]

The least weasel mates in April–July and there is a 34- to 37-day gestation period. In the northern hemisphere, the average litter size consists of 6 kits and these reach sexual maturity in 3 to 4 months. Males may mate during their first year of life, though this is usually unsuccessful. They are fecund in February–October, though the early stages of spermatogenesis do occur throughout the winter months. Anestrus in females lasts from September until February.[25]

The female raises its kits without help from the male. They are 1.5 to 4.5 g (0.05 to 0.16 oz) in weight at birth. Newborn kits are born pink, naked, blind and deaf, but gain a white coat of downy fur at the age of 4 days. At 10 days, the margin between the dark upper parts and light under parts becomes visible. The milk teeth erupt at 2 to 3 weeks of age, at which point the young start to eat solid food, though lactation can last 12 weeks. The eyes and ears open at 3 to 4 weeks of age, and by 8 weeks, killing behaviour is developed. The family breaks up after 9 to 12 weeks.[25] There is a single litter each year and least weasels can live for 7 or 8 years.[24]

Territorial and social behaviours[edit]

Two least weasels fighting

The least weasel has a typical mustelid territorial pattern, consisting of exclusive male ranges encompassing multiple female ranges. The population density of each territory depends greatly on food supply and reproductive success, thus the social structure and population density of any given territory is unstable and flexible.[26] Like the stoat, the male least weasel extends its range during spring or during food shortages. Its scent marking behaviour is similar to that of the stoat; it uses faeces, urine and anal and dermal gland secretions, the latter two of which are deposited by anal dragging and body rubbing. The least weasel does not dig its own den, but nests in the abandoned burrow of another species such as a mole or rat.[27] The burrow entrance measures about 2.5 cm (1 in) across and leads to the nest chamber located up to 15 cm (6 in) below ground. The nest chamber (which is used for sleeping, rearing kits and storing food) measures 10 cm (4 in) in diameter, and is lined with straw and the skins of the weasel's prey.[28]

The least weasel has four basic vocalisations; a guttural hiss emitted when alarmed, which is interspersed with short screaming barks and shrieks when provoked. When defensive, it emits a shrill wail or squeal. During encounters between males and females or between a mother and kits, the least weasel emits a high-pitched trilling. The least weasel's way of expressing aggression is similar to that of the stoat. Dominant weasels exhibit lunges and shrieks during aggressive encounters, while subdominant weasels will emit submissive squeals.[27]

Diet[edit]

Taxidermy exhibit showing a least weasel attacking a European hare, in the Natural History Museum of Genoa

The least weasel feeds predominantly on mouse-like rodents, including mice, hamsters, gerbils and others. It usually does not attack adult hamsters and rats. Frogs, fish, small birds and bird eggs are rarely eaten. It can deal with adult pikas and gerbils, but usually cannot overcome brown rats and sousliks. Exceptional cases are known of least weasels killing prey far larger than themselves, such as capercaillie, hazel hen and hares.[29] In England, a favoured prey item is the field vole (Microtus agrestis). These have fluctuations in population size, and in years of abundance may form up to 54% of the weasel's diet. In years of scarcity, birds form a greater proportion of the diet and female least weasels may fail to breed.[30]

Despite its small size, the least weasel is a fierce hunter, capable of killing a rabbit five to ten times its own weight.[31] Although they are commonly taken, the rabbits are usually young specimens, and become an important food source during the spring, when small rodents are scarce and rabbit kits are plentiful. Male least weasels take a higher proportion of rabbits than females, as well as an overall greater variety of prey. This is linked to the fact that being larger, and having vaster territorial ranges than females, males have more opportunities to hunt a greater diversity of prey.[32]

The least weasel forages undercover, to avoid being seen by foxes and birds of prey. It is adapted for pursuing its prey down tunnels, though it may also bolt prey from a burrow and kill it in the open.[32] The least weasel kills small prey, such as voles, with a bite to the occipital region of the skull[29] or the neck, dislocating the cervical vertebrae. Large prey typically dies of blood loss or circulatory shock.[32] When food is abundant, only a small portion of the prey is eaten, usually the brain. The average daily food intake is 35 g (1 oz), which is equivalent to 30–35% of the animal's body weight.[29]

Predators and competitors[edit]

Least weasels driven from a mountain hare carcass by a stoat, as illustrated in Barrett-Hamilton's A History of British Mammals

The least weasel is small enough to be preyed upon by a range of other predators.[33] Least weasel remains have been found in the excrement of red foxes, sables, steppe and forest polecat, stoats, eagle owls and buzzards.[34] The owls most efficient at capturing least weasels are barn, barred, and great horned owls. Other birds of prey threatening to the least weasel include broad-winged and rough-legged buzzards. Some snake species may prey on the least weasel, including the black rat snake and copperhead.[28] Aside from its smaller size, the least weasel is more vulnerable to predation than the stoat because it lacks a black predator deflection mark on the tail.[33]

In areas where the least weasel is sympatric with the stoat, the two species compete with each other for rodent prey. The weasel manages to avoid too much competition by living in more upland areas, feeding on smaller prey and being capable of entering smaller holes. It actively avoids encounters with stoats, though female weasels are less likely to stop foraging in the presence of stoats, perhaps because their smaller size allows them to quickly escape into holes.[35]

Diseases and parasites[edit]

Ectoparasites known to infest weasels include the louse Trichodectes mustelae and the mites Demodex and Psoregates mustela. The species may catch fleas from the nests and burrows of its prey. Flea species known to infest weasels include Ctenophthalmus bisoctodentatus and Palaeopsylla m. minor, which they get from moles, P. s. soricis, which they get from shrews, Nosopsyllus fasciatus, which they get from rodents and Dasypsyllus gallinulae which they get from birds.[33]

Helminths known to infest weasels include the trematode Alaria, the nematodes Capillaria, Filaroides and Trichinella and the cestode Taenia.[33] Least weasels are commonly infected with the nematode Skrjabingylus nasicola, adults of which are found in the nasal sinuses and can damage the skull. There is no evidence that this has serious detrimental effects on even heavily infested animals.[36]

Distribution and habitat[edit]

Alaskan weasel Mustela n. eskimo

The least weasel has a circumboreal, Holarctic distribution, encompassing much of Europe and North Africa, Asia and parts of northern North America, where it occurs mainly in places where the stoat isn't found, though it has been introduced in New Zealand, Malta, Crete, the Azore Islands and also Sao Tome off west Africa. It is found throughout Europe and on many islands, including the Azores, Britain (but not Ireland), and all major Mediterranean islands. It also occurs on Honshu and Hokkaido islands in Japan and on Kunashir, Iturup, and Sakhalin Islands in Russia.[1]

The least weasel occupies a similar type of habitat as the stoat but it less often frequents wet places. It can be found in fields, open woodland, bushy or rocky areas, parks and gardens, and at altitudes of up to about 3,000 metres (9,800 ft).[24]

Conservation status[edit]

The least weasel has a very wide circumboreal range and a large total population and is therefore listed by the International Union for Conservation of Nature as being of "least concern". Its chosen habitat is in areas of coarse vegetation and in some regions its numbers may be decreasing because of changes in agricultural practices, but altogether its population trend is thought to be steady. It is relatively common in Eurasia but less abundant in North America and is thought to be rare in the southeastern United States. It is subject to considerable variations in numbers in areas where its main rodent prey is liable to large population fluctuations. In years of rodent population booms, the least weasel numbers may rise by up to ten-fold, only to slump again as prey becomes scarce again in the following years.[1]

In folklore and mythology[edit]

17th century print of a weasel confronting a basilisk

The Ancient Macedonians believed that to see a least weasel was a good omen. In some districts of Macedon, women who suffered from headaches after having washed their heads in water drawn overnight would assume that a weasel had previously used the water as a mirror, but they would refrain from mentioning the animal's name for fear that it would destroy their clothes. Similarly, a popular superstition in southern Greece had it that the least weasel had previously been a bride, who was transformed into a bitter animal which would destroy the wedding dresses of other brides out of jealousy.[37] According to Pliny the Elder, the least weasel is the only animal capable of killing the basilisk;

To this dreadful monster the effluvium of the weasel is fatal, a thing that has been tried with success, for kings have often desired to see its body when killed; so true is it that it has pleased Nature that there should be nothing without its antidote. The animal is thrown into the hole of the basilisk, which is easily known from the soil around it being infected. The weasel destroys the basilisk by its odour, but dies itself in this struggle of nature against its own self.[38]

The Chippewa believed that the least weasel could kill the dreaded wendigo giant by rushing up its anus.[39] In Inuit mythology, the least weasel is credited with both great wisdom and courage, and whenever a mythical Inuit hero wished to accomplish a valorous task, he would generally change himself into a least weasel.[40] According to Matthew Hopkins, a witch hunter general during the English Civil War, least weasels were the familiars of witches.[41]

References[edit]

  1. ^ a b c Tikhonov, A., Cavallini, P., Maran, T., Kranz, A., Herrero, J., Giannatos, G., Stubbe, M., Conroy, J., Kryštufek, B., Abramov, A., Wozencraft, C., Reid, F. & McDonald, R. (2008). Mustela nivalis. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 21 March 2009.
  2. ^ Shorter Oxford English dictionary. United Kingdom: Oxford University Press. 2007. p. 3804. ISBN 0-19-920687-2. 
  3. ^ Wilson, Don E.; Reeder, DeeAnn M. (eds.) (2005). Mammal Species of the World: A Taxonomic and Geographic Reference, Volume 12. JHU Press. pp. 616–617. ISBN 978-0-8018-8221-0. 
  4. ^ Heptner & Sludskii 2002, p. 972
  5. ^ Kurtén 1968, pp. 102–103
  6. ^ Macdonald 1992, p. 205
  7. ^ a b c d Heptner & Sludskii 2002, pp. 975–978
  8. ^ Wozencraft, W. C. (2005). "Order Carnivora". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  9. ^ Heptner & Sludskii 2002, p. 982
  10. ^ Rhoades, Samuel M. (1900). "A New Weasel from Western Pennsylvania". Proceedings of the Academy of Natural Sciences of Philadelphia 52: 751–754. JSTOR 4062685. 
  11. ^ Heptner & Sludskii 2002, p. 980
  12. ^ Swenk, Myron H. (1926). "Notes on Mustela campestris Jackson, and on the American Forms of Least Weasels". Journal of Mammology 7 (4): 313–330. doi:10.2307/1373581. JSTOR 1373581. 
  13. ^ Heptner & Sludskii 2002, p. 981
  14. ^ Kuroda, Nagamichi (1921). "On Three New Mammals from Japan". Journal of Mammalogy 2 (4): 208–211. doi:10.2307/1373554. JSTOR 1373554. 
  15. ^ Heptner & Sludskii 2002, p. 984
  16. ^ Heptner & Sludskii 2002, p. 978
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  20. ^ a b Heptner & Sludskii 2002, p. 969
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  24. ^ a b c Konig, Claus (1973). Mammals. Collins & Co. p. 167. ISBN 978-0-00-212080-7. 
  25. ^ a b Harris & Yalden 2008, p. 474
  26. ^ Erlinge, S. (1974). "Distribution, Territoriality and Numbers of the Weasel Mustela nivalis in Relation to Prey Abundance". Oikus 25 (3): 308–314. JSTOR 3543948. 
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Names and Taxonomy

Taxonomy

Comments: The North American population sometimes is treated as a separate species, Mustela rixosa. Confusion has existed for a long time regarding the taxonomic status of this species and its subspecies, particularly in Europe (see Sheffield and King 1994; Wozencraft, in Wilson and Reeder 2005).

Reig (1997) examined skull variation in samples from North America, Central Europe, and Siberia and concluded that the Old World subspecies subpalmata warrants consideration as a separate species. Reig also suggested that subspecies M. nivalis rixosa of the eastern United States and adjacent southern Canada may be specifically distinct from M. n. eskimo of Alaska and adjacent Canada. Abramov and Baryshnikov (2000) separated only M. subpalmata as specifically distinct from M. nivalis. Wozencraft (in Wilson and Reeder 2005) noted these proposals but retained all taxa within the species M. nivalis.

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