Critter Curriculum
Short-Tailed Weasel (Ermine) Mustela erminea The short-tailed weasel (Mustela erminea) is the second smallest member of the weasel family. Like the long- tailed weasel and its other relatives, the short-tailed weasel, also known as the ermine, is a predator. The short-tailed weasel occupies a wider variety of habitats than the long-tailed weasel, which include wetlands, forests, and fields. It is trapped for its fur, but not avidly.

Physical Description Like all members of the weasel family, the short-tailed weasel has a long, slender body, short legs, and a long neck. It can grow to a length of seven to 13 inches and a weight of one to seven ounces. The male is noticeably larger than the female.

The short-tailed weasel is capable of quick, agile movements. The coat is reddish brown on its back, head, sides and tail. However, it is white in color under the chin and on its belly. The tip of its tail is black, similar to that of a long-tailed weasel. In the summer an excellent field marking, besides the obvious tail length, is that the short-tailed weasel has a white line down its hind legs and the long tailed does not. In winter, the short-tailed weasel will molt to an all white coat, except for the tip of its tail, which remains black. It is referred to as an ermine in this color phase.

Life Cycle Short-tailed weasels breed form late spring to early summer, but development of the embryos does not begin until the following spring. After mating, the fertilized egg remains in limbo through a process known as delayed implantation. During this process, all development of the embryo ceases for approximately eight to nine months. After this time, the fertilized egg is implanted into the uterus wall and development of the embryo begins. In March, as the days begin to lengthen, the development of the fetus will resume. This unique process is thought to benefit the weasel by allowing the female to give birth when environmental conditions are at their most favorable.

After a total gestation period of 280 days, the young are born in April and May.

A litter can range in size from four to 15 but averages six to seven young, or kits. When the tiny weasels are born, they have fine white fur, and their eyes and ears are sealed.

The kits grow rapidly. At three weeks, they have a well developed mane and their eyes are open by five weeks. The youngsters are soon travelling short distances with their mother, who has the responsibility of raising the kits. Young males at seven weeks are as big as their mother and, by the eighth week, the male and female kits are able to hunt on their own. The female kits reach sexual maturity when they are two months old, and it is not uncommomn for them to breed the first summer of their lives. The male kits, however, do not mature until one year old.

Food Items Like the rest of the weasel family, the short- tailed weasel is a carnivore, preying on a variety of animals. The short-tailed weasel takes voles, shrews, cottontail rabbits, rats, chipmunks and nesting birds. Male short-tailed weasels normally take larger prey items than the females.

Short-tailed weasels will also store, or cache, extra food for later use. When their preferred food supply is low, they will eat prey that is easier to catch, like fish, birds or insects. In summer, they also eat fruit and berries.

Habits & Habitat Short-tailed weasels can be found in a variety of habitats ranging from wooded areas to grasslands. Short-tailed weasels require areas of heavy cover but tend to avoid dense forests. Weasels will burrow, or build, a nest in rock or wood piles, in a hollow tree, or under a building. Often, rather than building their own nest site, they will simply take over one of their prey's. Weasels are not social animals. With the exception of the breeding season, it is rare to find a male and female together. Although these fierce predators are active during the day, they are considered to be nocturnal. They are quite aggressive and will defend their territories from any intruder. They are skilled hunters having great speed and agility. They can also swim and climb.

Abundance Short-tailed weasels are common throughout their range. They prefer open woodlands and transitional areas between forests and fields located near a water source.

History The short-tailed weasel has proven itself as an adaptable species. As the landscape changed over the last 150 years, from intensive farming to abandonment, the short-tailed population fluctuated, but has remained an important species in Vermont’s ecological community.

Resource Utilization Short-tailed weasels are an important predator. They play a vital role in controlling populations of rodents that might otherwise damage agricultural crops or transmit disease. Humans also hunt them for their pelts. The ermine's pelt (i.e. winter coat) is considered to be of greater value in the fur industry than its brown summer pelage.

Management Efforts Continued monitoring is conducted to ensure that the short-tailed weasel remains healthy and abundant in Vermont.