Stoat, Short-tailed weasel, Bonaparte weasel
Ermine is the common name given to this small northern weasel with a short, black-tipped tail, long body and short legs. Its fur is dark brown in summer but white in snowy, winter conditions. The white fur is called "ermine," and even where the animal called a "stoat," when it has its winter coat it may be known as ermine, or being "in ermine." Commercially, this animal has been of importance for the fur trade, particularly its valuable winter coat of white. This highly prized fur has been used to adorn royal robes in Europe and in art was used as a symbol of virginity or purity.
Ermine are found across the northern subarctic, Arctic and temperate regions of Asia, Europe, and North America. Across the New World, they are distributed from west to east in a wide belt running from the Arctic Ocean and nearby islands in the Canadian Archipelago south to the northern United States. They are not found on the Great Plains. These animals prefer riparian woodlands, shrubby fencerows, marshes and open areas near forests or shrub borders.
This species is largely crepuscular or nocturnal but is sometimes active during the day. Ermine are good climbers and they use trees when escaping predators, resting, and searching for food. They are largely solitary. They are territorial and intolerant of other ermine in their range, particularly those of the same gender. Within their range, they typically use several dens, often those of their prey species. They usually travel alone, except when mating mothers with their older offspring. Adult males will dominate females and young. The females generally remain in the area of their birth throughout their lives. The males disperse and secure a large territory that usually encompasses or overlaps females' territories. This species maintains exclusive boundaries that they patrol and mark with scent. They have keen senses of sight, hearing, smell, and touch that help to locate prey.
Ermine are carnivores and prey on small, warm-blooded vertebrates, particularly mammals the size of rabbits or smaller. When mammals are scarce, they eat birds, eggs, fish, frogs, and insects.
Ermine are polygynandrous (promiscuous), with both males and females mating with multiple partners. They mate from late spring to early in the summer. Females bear 1 litter only per year. After gestation of around 280 days, young are born during April or May. Gestation includes a period of developmental delay of 8 to 9 months. Litter sizes range from 3 to 18 and average 4 to 9. Young grow quickly and can hunt with their mothers when 8 weeks old. Weaning takes place at around 10 weeks. Females reach adult size by about 6 weeks after birth, and are able to mate at 60 to 70 days of age, often before being weaned. Males gain adult size during their second summer.
Potential threats include increasing access and the unrestricted trapping by people, habitat fragmentation and loss, interactions with introduced species, as well as changes in prey availability. Generally, mustelids are very vulnerable to trapping, not only to traps that are set specifically for them. Ermine may be less threatened than other furbearers by habitat change from fire disturbances or timber harvest due to the preference for communities with early-successional stages and their aversion to dense forest. Clear-cut logging, however, may be a threat in Alaska, particularly in the unproductive, mid-successional regrowth forest areas which seem to be favored habitat. Another concern is loss of genetic integrity and the transmission of pathogens (like canine distemper) and parasites from native or introduced stocks of other carnivores.
Ermine is an abundant species and it has a wide circumpolar distribution, but no overall population estimate is available. Currently this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today remain stable.
Ermine are important predators of small mammal communities within the ecosystems where they live.