Alaska Mammals: Least Weasel

alaska is home to many mink

The Mustelidae, or weasel family is a large group of mammals. In Alaska there are eight types of Mustelidae. They include the wolverine, fisher, river otter, sea otter, marten, short tailed weasel, least weasel, and the mink.


There are two species of weasels in Alaska: the short-tailed weasel or ermine (Mustela erminea) and the least weasel (Mustela rixosa). These weasels range over North America and are found throughout most of Alaska. Neither weasel is found on the offshore islands of the Bering Sea or the Aleutian Islands west of Unimak Island. In addition, the least weasel does not occur on the Kodiak Archipelago or on most islands in Southeast Alaska. The short-tailed weasel occurs in the Old World where it is known by the name of “stoat.”

In summer, both weasels are medium to dark brown above, with yellowish white underparts. Both species turn white in winter. The larger of the two is the short-tailed species. It can reach 15 inches (38 cm) in length and 7 ounces (198 g) in weight.

The least weasel is the smallest living carnivore. Least weasels are dark brown with light underparts in the summer. They characteristically turn entirely white in the winter but retain a few black, brown, and white hairs on their tail during all seasons. Least weasels are much smaller than Ermine, averaging 8 to 10 inches long and weighing only three ounces. The least weasel well deserves its title of the smallest living carnivore.

The short-tailed weasel's tail is one-fourth to one-third of the total body length while the least weasel's tail length comprises only about 15 percent of total body length. During all seasons the tip of short-tailed weasel's tail is black. The tail of the least weasel contains only a few black hairs.Long slender skulls and sinuous bodies equip the weasel for its niche in life. If the head can fit into a burrow, then the remainder of the body can easily fit as well. Weasels are powerful animals for their size. A weasel is capable of running 300 yards (274 m) while carrying a large mouse in its mouth. In both species the males are about 25 percent larger than females.

Weasels are primarily solitary animals except during the mating and whelping seasons. Reproductive pairing is usually temporary. Females may be bred by more than one male. Mating typically occurs in mid-to late summer. Fertilization of the ova is followed by a period during which the eggs do not implant in the uterus. No development occurs during this period. This process is called delayed implantation. After 6 to 7 months the fertilized ova implant in the uterus and embryos begin to develop. The total gestation span is 8 to 10 months. Least weasels apparently do not always experience delayed implantation. In the southern portion of their geographic range they can produce three litters per year.In Alaska, litters of 3 to 10 young are born from early May through June. Variations in time of breeding and birth depend in part on the latitude. Weasels in northern Alaska breed about two weeks later than those in the south.

Weasels usually nest in small rodent burrows, stumps, rock outcroppings, or under old buildings. The nest is often lined with mouse fur. The number of young born and the number that survive until weaning depend in large part on the abundance of food in the mother's home range.Young weasels remain in the den for 30 to 45 days, at which time they are about two-thirds grown. After emerging, they stay near the home den for a week or two before beginning to accompany their mother on foraging trips. At 80 to 85 days of age (early fall) they reach full size. At this time, they disperse away from their mother's home range. Sexual maturity is reached by the following spring.

The presence of weasels is almost always indicative of substantial rodent populations. Weasels must have almost daily access to rodents in order to survive. They prefer mice. When mice are not abundant, weasels will also take shrews, pikas, birds, fish, and insects. Short-tailed weasels can also kill young snowshoe hares.Weasels have a high metabolic rate which drives them in search of prey. They eat 40 percent or more of their body weight daily.

During the whelping period, female weasels kill and consume an average of four mice per day. Their fast and furious pace allows only short periods of inactivity. Total daily rest time averages a few hours.Weasels hunt both at night and during the day. They locate prey chiefly by scent. Weasels typically pounce on their prey with their forefeet. They kill with bites to the back of the neck. They occasionally emit a shriek when seizing prey.Nature seldom provides a steady source of food. The weasel's mode of survival involves killing whatever it can, whenever it can. When confronted with an abundance of mice, the voracious weasel follows the only pattern it knows and will kill more than it can eat at one time. Dens often have a side chamber used as a store room for surplus slain mice.






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Alaska Mammals:

With 112 mammal species, Alaska ranks 12th of the 50 U.S. states in mammalian diversity.

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Shrews Bats Cats
Canines Bears Weasels
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Alaska Least Weasel

Alaska least weasel