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Least Weasel

Mustela Nivalis

The world’s smallest carnivore, the least weasel is also the world’s most widespread mustelid. It is found throughout the Palearctic and Nearctic regions of the world, with the exception of Ireland, the Arabian Peninsula and the Arctic Islands. Like its close relatives, the long-tailed weasel and ermine, it changes colour from brown to white in the winter months. A population of least weasels has also taken up residence in New Zealand, where it has become a serious threat to native bird populations.

A highly adaptable predator, the least weasel lives in most habitats, avoiding only deserts and very deep forests. This weasel is capable of killing animals much larger than itself due to its strength and powerful bite. It prefers small prey, however, such as mice, lemmings, voles, frogs, small birds and eggs. Usually hunting at night, the least weasel relies on a highly-developed sense of smell to find prey above or below ground, and then dispatches its victim with a bite to the head or neck.

Like most mustelids, least weasels are highly territorial, and adults are seldom to be found in each other’s company except at mating time. Intruders are faced with aggression, and a pitched battle often ensues when there is a dispute. These contests are seldom fatal, however, and intruders usually beat a hasty retreat.

Least weasels occupy a range of 1.5-2.5 acres where food is abundant, but may range up to 60 acres when it is scarce. Males occupy a larger range than females, and may have many within their range. They will try to mate with multiple females during the breeding season.

The least weasel can breed throughout the year, but usually does so between spring and late summer. Gestation lasts about 35 days, and a litter of 1-7 is born. In more northern regions, litter size tends to be higher to ensure a greater survival rate. Young least weasels rely on their mother for food, and spend a much of their time play fighting to prepare for real fights with prey, predators and other weasels later in life. Males usually reach maturity in about eight months, and females in about 4. At this time they leave their mother and try to set up territories of their own.

Canadian range of least weasel shown in orange.

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