By Toni Lynn Newell
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 ).
Habitat
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).
These animals are found in the following types of habitat:
temperate .
Terrestrial Biomes:
tundra ; taiga ; forest ; rainforest .
Physical Description
(1.06 to 1.94 oz)
(6.5 to 8.07 in)
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).
Some key physical features:
endothermic ; bilateral symmetry .
Sexual dimorphism: male larger.
Reproduction
Least weasels can breed once or twice each year.
Least weasels breed in spring and late summer.
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).
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (internal ); viviparous .
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 .
Lifespan/Longevity
Least weasels probably only live for several years after reaching adulthood and most die before reaching adulthood.
Behavior
Males and females live apart from each other except during the breeding season. Because the range of a female is smaller than a male's, one or more female may live within one male's range. Females have the ability to fend off other females and males from her 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 go for the neck of the victim.
The dens of the weasel are not permanent but are those taken from the prey.
(Sheffield, 1994).
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.
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).
Predation
- owls (Strigiformes)
- hawks (Accipitridae)
- snakes (Serpentes)
Ecosystem Roles
Least weasels are important predators of small mammals in the ecosystems in which they live.
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.
Ways that people benefit from these animals:
controls pest population.
Conservation Status
IUCN Red List: [link]:
Lower Risk - Least Concern.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
State of Michigan List: [link]:
No special status.
Least weasels are generally widespread and abundant. Localized populations may be threatened by habitat destruction, but these animals are generally not threatened.
For More Information
Find Mustela nivalis information at
Contributors
Toni Lynn Newell (author), University of Michigan.
Tanya Dewey (editor), Animal Diversity Web, University of Michigan Museum of Zoology.
