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Long-tailed Weasel
(Mustela frenata Emmons)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry.  216pp.

Family: Mustelidae

Description: The long-tailed weasel resembles the ermine but has a longer tail, 9.5-16 cm (3.6-6.3 in) in length and greater than 44 percent of the head-body length. This is the only other member of the weasel family in the Adirondacks to develop a white coat in winter (December-March or April). The terminal one-fourth to one-third of the tail remains black throughout the year. Except for the tip, the tail and upper parts of the body are brown with the chin, throat, belly and inner areas of the legs white to yellow in the summer. The total length of an adult is from 30-45 cm (12-18 in), and weight varies from 72-270 g (2.5-9.5 oz). The sexes differ substantially in size with the smallest females only one-fourth to one-half the size of the largest males.

Range and Habitat: The range is southern Canada, all of the U.S. except for parts of the Southwest, most of Mexico, Central America, and northern South America. The range, habitat preference, and relative abundance of the long-tailed weasel in the Adirondack Park are not well known. This species is a likely resident of all terrestrial habitats, perhaps at all elevations, but is probably least abundant at elevations above 610 m (2000 ft) and in dense forest. The long-tailed weasel is found in the same areas as the ermine but is less common. Long-tailed weasels modify the nests and burrows of prey as homes. 

Food and Feeding Behavior: The long-tailed weasel is carnivorous and its diet is similar to the ermine’s, but includes a greater portion of larger prey which is taken primarily by males. Small rodents such as mice and voles are the preferred prey but long-tailed weasels also eat moles, shrews, tree squirrels, chipmunks and snowshoe hares. Both sexes may consume insects, earthworms, frogs, snakes, birds and bird’s eggs, especially when small mammals are scarce. The hunting method is typical of many mustelids, with an individual coursing over large areas, exploring every nook and canny. The long-tailed weasel kills by leaping or pouncing on an animal, severing major blood vessels in the region of the throat or the spinal column at the base of the skull with a series of quick bites. This species may also kill more prey than it can consume at one time, usually storing the surplus in or near the nest for later consumption. The myth that a weasel is a wanton killer derives both from this practice, and from the habit of eating only small portions of some prey, for example, the brain. The long-tailed weasel requires about 20-30 percent of its weight in food each 24-hour period.

Activity and Movement: The long-tailed weasel forages both day and night and throughout the year. It travels by walking, bounding or running over the ground or snow, by burrowing through deep, soft snow; and may cover distances of up to 11 km (7 mi) during a single excursion. Long-tailed weasels swim well, and ascend trees, sometimes to great heights when pursuing prey.

Reproduction: The breeding season is from mid to late summer. Males mate with adult females that are still nursing litters or shortly after they have weaned them. The gestation period is 205-337 days with much of the development of the embryos taking place during the last 23-27 days of pregnancy. Females bear their litters in April or May, and the average litter size is 5-8 but may vary from 1-12. A newborn long-tailed weasel weighs about 3 g (0.1 oz), is blind and mainly pink in color possessing only a few white hairs. The eyes open at 35-36 days, and weaning begins at about this age. The young disperse before winter. Females are sexually mature during the first summer; males a year later. The potential lifespan is at least 5 years. 

Predators: Avian predators include the barred and great-horned owls, and the northern goshawk. Coyotes and both red and gray foxes are documented mammalian predators. Few, if any, predators prey consistently on the long-tailed weasel because of its speed of movement, aggressiveness, and scent glands.

Social Behavior:

  • Social system - This aspect of the life history of the long-tailed weasel is not well known. Adults are mainly solitary except during the breeding season when pairs form, at least temporarily. Adults occupy home ranges which overlap and vary in size with the availability of prey. Home ranges vary from 12-160 ha (30-400 acres), and males have larger ranges than females. Little is known about the densities of long-tailed weasel populations, but information from a few studies in different parts of the range gives estimates of one weasel per 2.5-256 ha (6.25-640 acre).
  • Communication - Scent and vocalizations play important but undetermined roles in regulating social encounters and defining the social organization of long-tailed weasels. Adults screech, hiss, purr, and also produce a repetitive “took-took-took” sound. Adults, when threatened or startled, often discharge the contents of their large anal glands, the products of which yield an odor that is nauseating to humans. These scent glands probably serve in marking and defining home ranges, as they do in the ermine.

Additional References 

Hamilton, W.J., Jr. 1933. The weasels of New York: Their natural history and economic status. American Midland Naturalist, 14:289-344.

Svendson, G.E. 1976. Vocalizations of the long-tailed weasel (Mustela frenata). Journal of Mammalogy, 57:398-399.

Wright, P.L. 1948. Breeding habits of captive long-tailed weasels (Mustela frenata). American Midland Naturalist, 39:338-344.

Order: Carnivora


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