Montana Trappers Association

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Furbearers Are A Natural Renewable Resource.

Least Weasel


Weasel Family

Classification: Non-game Wildlife Species

Mustela nivalis

Order: Carnivora
Family: Mustelidae

Status: Unprotected predator.


Identifying Characteristics: The smallest weasel and smallest carnivore in North America.  Similar to other weasels in color and body form.  Males are larger than females.  Fur is brown above and whitish below during summer.  Entirely white during winter.  No black tip at end of short tail.


Total length: less than 10 inches.  Weight: 1 to 3 ounces.


Habitat: Variety of habitats, including meadows, fields, brushy areas, and open woods.  Avoids dense forest, prefers ecotones.  Abundance of small mammals is important in determining the local distribution of least weasels.


Food Habits: Feeds almost entirely on mice.  Small enough to pursue rodents into runways, burrows, and nest chambers.


Life History: Most active at night.  With abundant food sometimes produces more than one litter per year.  Breeds year round; young born any time of the year; delayed implantation does not occur; litter size usually 4 to 5.


Similar Species: Much smaller than the short or long-tailed weasel.  Both short and long-tailed weasels have a black tip on tail.

The least weasel is considerable smaller, with a very short tail, and males may measure up to 8 inches in length, while females measure about 6 inches.


The least weasel also has a long, slender, muscular body with short legs. The head is small, with beady eyes, small ears and a pointed nose. They move with quick movements and a graceful, bounding gait. All three weasels change color with the seasons, and there is no color difference between the sexes. All the senses are well developed in the weasel.


The least weasel lacks the black tipped tail of the other two species.


Life Cycle
Both the short tailed and long tailed weasel females mature at 3 to 4 months and males mature at about one year. The breeding season is in July. There is a period of delayed implantation with a gestation period of 9 to 10 months. The period of active pregnancy is 23 to 17 days.


Litter sizes varies from four to thirteen, with an average of six to eight. The young are born in April or May in nests constructed in underground dens or hay piles. Mouse nests and burrows are often used and heavily lined with fine grass and mouse fur. The male begins to bring food to the den about 1 month after the young are born. The young are weaned at the end of 5 weeks and are able to hunt for themselves by 7 or 8 weeks of age. The family stays together until late summer and then disperses. The life expectancy of weasels is short, probably less than a year, although they are capable of living as long as 6 years.


The least weasel may have three to ten young, but averages five which may be born at any time of the year but most frequently are born in late winter.


Weasels prey on small rodents such as mice, rats, voles, hares, rabbits, and chipmunks. They also take shrews, birds, birds eggs, frogs, bats, insects, earthworms and may occasionally kill domestic chickens. The least weasel depends almost exclusively on mice for food.


The weasel hunts by tirelessly and persistently investigating every small hole, crevice, bush or rock pile it encounters. They will track prey by following their scent trails and generally attack prey by ambushing and pouncing on it. They are very quick and kill by piercing the base of the skull with their teeth. The weasel frequently kills more than it can eat and often caches leftover food. The weasel can consume up to one third of its own weight in a 24 hour period.

Weasels are curious, alert and bold. They are persistent hunters who seldom remain long in their dens and may be abroad hunting at any hour, although they are usually most active at night. Weasels are active year round. Weasels occasionally hunt in pairs but, for the most part, are solitary except during breeding and rearing season. They are good swimmers and can also climb trees. All species emit a strong musk odor when alarmed, and the weasel may stamp its feet when annoyed. Weasels may mark their trails with droppings. Home ranges very from 30 to 400 acres.


Weasel populations often cycle with mouse populations. Several parasites can infect weasels, such as guinea worm and kidney worms. These probably have little impact on the population.


Weasels are subject to predation from hawks, owls, foxes, coyotes, dogs, cats and man.


In agricultural areas, weasels are more common due to the practice of storing grain which provides ideal conditions for mice.


Weasels prefer woodlands or open country with hedgerows, thickets or fence rows. They are usually found near water but are not semi-aquatic as is the mink. They frequent stone piles, brush heaps, wood piles, hay stacks, log piles and old abandoned buildings.


The least weasel has a variety of habitats including meadows, fields, brushy areas, and open woods. It avoids dense forests.


The dens of weasels are shallow chambers about 6 inches underground with two to three entrances and are lined with mouse fur and grass.


Economic Value
The fur of the least weasel is seldom taken and is so small that it is of little or no value in the fur trade.


Weasels play an important role in helping to control rodent populations.

Did You Know?

Jim Bridger (1804-1881). Trapper, scout, mountain man. One of first white men to see the future Yellowstone Park and Great Salt Lake, which he believed to be an arm of the Pacific Ocean. Became partner of Rocky Mountain Fur Company in 1830 and established Fort Bridger in Wyoming Territory in 1842. Laid out routes for the Central Overland Stage and Pike's Peak Express Company. Returned to Missouri in 1867 where died on his farm on July 17, 1881.


Rendezvous were held on a yearly basis at various locations until 1840, mainly in Wyoming, but Pierre's Hole in Idaho and Bear Lake in northwest Utah were favorite sites as well.


Fort Manuel Lisa was established in 1807 by Manuel Lisa at the mouth of the Big Horn River near Hysham. This was the first permanent settlement in Montana and was occupied until 1811.


John Jacob Astor was the first prominent member of the Astor family and the first multi-millionaire in the US. He amassed his wealth through fur-trading, opium smuggling, and New York City real estate. Famed patron of the arts. At the time of his death, he was the wealthiest person in the US.


In 1919, the Hudson’s Bay Company was approaching its 250th year in business. What began in a coffee house in London, in 1670, had now grown to become the undisputed leader of the international fur trade.


The desire for beaver fur hats in European men’s fashions dates back centuries and spurred the development of the 17th century North American fur trade. Beaver fur was the most prized of the fur trade because of its water repellant qualities. Encouraged by European trade goods, natives hunted beaver to extinction in some areas.