Short-tailed weasels, also known as ermine or stoats, are circumboreal in their distribution; in North America, they are found across Alaska and Canada, extending southward to the Northern Sierra, through the higher Rockies to New Mexico, across the Upper Great Lakes region and into New England. These small mustelids favor taiga, stunted timberline forest and open, brushy woodlands along streams; there they hunt for voles, mice, pikas, chipmunks, rabbits and small birds.
Solitary for much of the year, short-tailed weasels mate in summer and, after a period of delayed implantation, an average of 6-8 kits are born the following spring; able to fend for themselves within 2 months, the young disperse by late summer. Adult short-tailed weasels are generally 10-12 inches long and sport a brownish coat with white underparts during the spring and summer months; come fall, they molt to a white pelt to blend with their snowy surroundings though the tip of their tail remains black in all seasons. Like many predators, these energetic and aggressive hunters are primarily nocturnal but may be encountered early or late in the day.
The population of short-tailed weasels tends to wax and wane with that of their major prey species; most live less than two years but some survive for six years or more. Owls, gyrfalcons, coyotes and fox are their primary natural predators and humans have trapped them for their white winter pelts over the centuries. Introduced in New Zealand during the 1800s, these mustelids have since been decimating native bird populations, reminding us that human manipulation of natural ecosystems is frought with danger.
