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least weasel

Mustela nivalis

What do they look like?

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.

  • Sexual Dimorphism
  • male larger
  • Range mass
    30.0 to 55.0 g
    1.06 to 1.94 oz
  • Range length
    165.0 to 205.0 mm
    6.50 to 8.07 in

Where do they live?

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.

What kind of habitat do they need?

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.

  • These animals are found in the following types of habitat
  • temperate

How do they reproduce?

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.

  • How often does reproduction occur?
    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
  • Average number of offspring
    5
    AnAge
  • 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

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.

How long do they live?

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
    AnAge

How do they behave?

Males and females live apart from each other except during the breeding season. Because home ranges of females are smaller than male home ranges, one or more females may live within a male's range. Females have the ability to fend off other females and males from their home range. Males, once out of the breeding season, display dominance over females.

Least weasels are very active, both day and night. The young spend their time play fighting and play mating. Weasels watch the movement of their prey before they attack. When they kill they wrap their body and limbs around the victim and kill with a bite to the base of the skull. Least weasels use abandoned burrows rather than making their own.

How do they communicate with each other?

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.

What do they eat?

The diet of least weasels is composed of small mammals, mainly rodents like white-footed mice and meadow voles. When rodents are scarce, weasels will eat birds' eggs and nestlings, insects, and lizards. 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.

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates

What eats them and how do they avoid being eaten?

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.

What roles do they have in the ecosystem?

Least weasels play an important role in controlling rodent populations.

How do they interact with us?

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.

  • Ways that people benefit from these animals:
  • controls pest population

Are they endangered?

Least weasel populations are not considered threatened.

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Toni Lynn Newell (author), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that generate their own body heat through metabolic processes.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

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).

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

polygynous

having more than one female as a mate at one time

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Climbing plants are also abundant. There is plenty of moisture and rain, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

taiga

this biome is characterized by large expanses of coniferous forest, there is an extended cold season and heavy snowfall.

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).

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 found in very cold places -- either close to polar regions or high on mountains. Part of the soil stays frozen all year. Few kinds of plants grow here, and these are low mats or shrubs not trees. The growing season is short.

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Honacki, J.H., ed.; Kinman, K.E., ed.; Koeppl, J.W., ed. 1982. mammal Species of the World; A Taxonomic and Geographic Reference. Association of Systematic Collections, U.S.A.

Sheffield, J.R.; King, C.M. (2 June 1994). "Mustela nivalis." Mammalian Species. The American Society of Mammalogists, 454.

 
University of Michigan Museum of ZoologyNational Science Foundation

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Newell, T. 1999. "Mustela nivalis" (On-line), Animal Diversity Web. Accessed April 23, 2014 at http://www.biokids.umich.edu/accounts/Mustela_nivalis/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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