Short-tailed weasels are one of the six mammals native to Kodiak Island. Weasels are known by three common names. In their summer phase in the U.S., they are called weasels, but in their white, winter phase, they are known as ermine, and in many other countries, the same animal is called a stoat. Two species of weasels exist in Alaska: the short-tailed weasel or ermine (Mustela ermine) and the least weasel (Mustela rixosa). The least weasel does not occur on the Kodiak Archipelago. Seven subspecies of Mustela ermine can be found in Alaska, and six of these are endemic to the state, including Mustela ermine kadiacensis, which is only found on the Kodiak Archipelago. Weasels belong to the family Mustelidae. Other Alaskan mustelids include river otters, sea otters, mink, marten, and wolverines.
Short-tailed weasels are found in North America, Europe, Siberia, Greenland, and Canada and have been introduced to other parts of the world. In North America, they range from Alaska and Canada south to central California, northern Arizona, northern New Mexico, Iowa, the Great Lakes, Pennsylvania, and northern Virginia. Short-tailed weasels occur throughout most of Alaska, except on the offshore islands of the Bering Sea and the Aleutian Islands west of Unimak Island.
A Short-tailed weasel has an elongated body, short legs, a long neck, and a triangular head with long whiskers and round ears. In the summer, a weasel’s fur is reddish-brown on the back and creamy white on the stomach, but in the winter, the fur is completely white except for the tip of the tail, which remains black all year. A short-tailed weasel can reach 15 inches (38 cm) in length and weigh seven ounces (198 g). A weasel’s long narrow skull and slender body allow it to squeeze into vole tunnels to chase its prey of choice.
Weasels mate in mid- to late summer in Alaska, and a female may breed with more than one male. In the southern part of their range a female produces three litters per year, but in Alaska, females give birth to only one litter a year. Like many other animals, weasels experience delayed implantation. After an egg is fertilized, it does not implant on the uterine wall for six to seven months. Once it does implant, the remaining gestation period lasts only four weeks. Females give birth from early May through June to litters of three to ten young.
Weasels nest under old buildings, in stumps, in rock outcroppings, or in rodent burrows. They often line their nests with mouse or vole fur. Young weasels remain in the den for 30 to 45 days after they are born, and after they first emerge, they stay near the den for a week or two before following their mother on foraging trips. They are full grown in the early fall when they are 80 to 85 days old, and at this time, they leave their mother. Weasels reach sexual maturity when they are one year old. Female weasels may survive three years, but males usually do not live that long.
Weasels eat a variety of animals, including birds, insects, fish and young rabbits, but rodents, especially mice and voles, are their food of choice. On Kodiak Island, weasels mainly eat tundra voles (Microtus oeconomus). Weasels have a very high metabolic rate and must eat at least 40% of their body weight every day. A pregnant female consumes an average of four voles per day. Weasels do not hibernate but hunt all year long. Their white fur provides them camouflage against the snow in northern climates, allowing them to sneak up on prey more easily. They hunt both night and day, and they locate their prey mainly by scent. A weasel usually pounces on its prey with its forefeet and then kills it by biting the back of its neck.
Weasels have few natural enemies; their speed and ability to squeeze into narrow spaces help them avoid most predators. Humans sometimes trap weasels in their white, winter phase and use this “ermine fur” as a trim on parkas and other clothing. In some western societies, ermine fur was once considered a badge of royalty. In Alaska, not many weasels are trapped, and only about 300-500 weasel pelts enter the fur market every year.
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