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  Least Weasel - Scientific name Mustela nivalis 

Distribution & Abundance  |  Habitat  |  Habits  |  Foods  |  Reproduction  |  Conservation

- Image courtesy of James F. Parnell © - -- Image courtesy of James F. Parnellę --

Two species of weasels live in Illinois--the long-tailed weasel and the least weasel. The long-tailed weasel is two to three times larger than the least weasel. Both have long, slender bodies, short legs, and a broad, slightly flattened head that's barely larger around than the neck.

Male long-tailed weasels are larger (13 to 16 inches in length; 6 to 16 ounces) than females (11 to 14 inches in length; 3 to 9 ounces). The tail is nearly half as long as the head and body combined and has a distinctive black tip.

The least weasel is the smallest living carnivore in Illinois. Males are up to 10 inches in length (including the tail) and weigh 2.1 to 3.2 ounces. Females are up to 9 inches in length and weigh 1.2 to 2.5 ounces. The tail is less than one-fourth of the length of the head and body combined.

Both species have a summer coat that's reddish-brown or tan except for a yellowish-white belly. Weasels begin shedding their summer coats during early fall and replace them with winter coats that tend to be lighter in color. In parts of northern Illinois, the winter coat is nearly all white, helping them to blend in with a snowy background and avoid detection by predators like hawks and owls. Further south (where snow cover is uncommon), the winter coat can have patches of brown and white or remain mostly brown like the summer coat. Weasels molt again in the spring, replacing their winter coats with darker summer colors.

Distribution & Abundance
Long-tailed weasels are found throughout Illinois. Least weasels are found only in the northern half of the state. Populations of both species tend to be scattered, occurring mainly in areas with good habitat and high numbers of rodents.

Long-tailed weasels can be found in a wide variety of habitats, but prefer forests, woodlands, thickets and brushy fence rows. Least weasels tend to be found in more open areas like meadows, grasslands and river bottoms. Both species do best in areas with access to water and high rodent populations. Their dens are usually found in rock piles, junk heaps, abandoned buildings and burrows dug by mice, ground squirrels, moles or chipmunks. They sometimes line their nest chambers with grass or fur and feathers from their prey.

Both species make a wide range of sounds. A loud, harsh chirp or a screech can be heard when a weasel is disturbed or ready to attack. A low trill often signals a friendly meeting between a male and a female. A trill also helps a female to call her young. Baby weasels make high-pitched squeaks. At about four weeks of age, their squeaks get lower-pitched and raspier, eventually reaching a chirp similar to the adults'.

Weasels can be seen during daytime, but are most active at night. The size of the area they live in depends on the amount of food found there. For example, the home range of a least weasel might be as small as 1.7 to 2.5 acres where food is abundant or as large as 37 to 65 acres where food is scarce. The home ranges of long-tailed weasels can vary from 25 to 400 acres depending on food supplies.

Both species follow regular hunting routes, covering only parts of their home ranges during a single night. Hunting routes usually start and end at a den. Total distances covered in a night can be less than a tenth of a mile up to 3 1/2 miles for long-tailed weasels. Males travel farther than females. Not much is known about the daily movements of least weasels. They probably travel much shorter distances than long-tailed weasels.

Small prey like mice are killed with a few quick bites to the back of the neck--where the neck joins the skull. Weasels also stalk larger prey, trying to take them by surprise. If the stalk is successful, the weasel rushes in and grasps onto the prey animal with its front and hind feet. During the struggle that follows, the weasel tries to position itself on the animal's back for a series of bites to the base of the skull. Prey found in tunnels are attacked head-on and killed by a crushing bite to the windpipe.

Weasels bound or lope with the back arched and tail held straight out or slightly higher than the plane of the back. They swim well and climb trees easily. Their small girth (1 to 1 1/2 inches) lets them slip through small knotholes, crevices and tunnels when chasing prey.

Long-tailed weasels eat mice, rats, voles, squirrels, chipmunks, shrews, moles and rabbits. Less common foods include birds, bird eggs, snakes, frogs and insects. Least weasels specialize in taking small prey such as mice and voles. They do most of their hunting in tunnels made by these rodents.

Long-tailed weasels have only one litter per year. They mate in July or August. The fertilized eggs develop for eight days, then enter a dormant period. About 7 1/2 months later, the eggs attach to the wall of the uterus and resume development. The young are born 23 to 27 days later, usually during April or May. Litter sizes vary from one to nine and average four to five young. Young long-tailed weasels begin hunting with their mother at 6 to 7 weeks and are ready to leave her at about 11 to 12 weeks.

Least weasels can breed year-round. They produce more young when rodent numbers are high. For example, they might have one litter per year when food is scarce and two or even three per year when prey is abundant. The gestation period (pregnancy) is about 35 days long. There may be as few as one or as many as ten young in a litter, but the average is four to five. The young develop quickly when food is plentiful, reaching sexual maturity at 3 to 4 months. Under normal food conditions, females reach sexual maturity at 4 months and males at about 8 months.

Illinois allows a limited trapping season for weasels, but very few (usually fewer than 20) are harvested each winter because populations are scattered and few trappers attempt to catch them unless they're causing damage like killing poultry.

Few people manage habitat specifically for weasels. However, they benefit from broader soil, water and wildlife conservation practices. Planting grass strips along creeks, streams and rivers provides habitat for weasels and their prey while reducing soil erosion and runoff from heavy rains. Woody fence rows provide wildlife habitat and act as windbreaks that reduce soil erosion. Once common in Illinois, many fence rows have disappeared because large fields with few obstacles are more efficient for modern farm equipment. Some have been removed because trees shade and wick away moisture from nearby crops, causing lower yields. In these cases, a root plow can be used to trim tree roots next to fence row and improve crop yields. Building brush or rock piles can provide denning areas for weasels and other wildlife.

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