Weasel (Mustela erminea and M. rixosa)

Introduction

Weasels represent the smallest members of the Mustelidae. Both the Mustela erminea, short-tailed weasel and M. rixosa, the least weasel are found in most of the lower forty- eight states and Alaska. The short-tailed weasel is much larger than the least weasel. It can be as long as fifteen inches in length. The least weasel, is the smallest living carnivore, and rarely exceeds ten inches in length. I have seen some full grown least weasels in Pennsylvania that were five inches long or less. Both weasels look identical in coloration which is medium brown above, with yellowish (urine stained) white underneath, and a brown tail with a black tip. The tail of the least weasel usually has fewer black hairs than the short-tailed weasel. Both weasels can turn pure white in winter, but the tail tip remains black, hence the reference to ermine. Weasels are a powerful animal for their size, and can take down large rabbits easily. They have a long slender head similar to the mink, and a sinuous body. Female weasels are approximately three fourths the size of males.

Like other members of the Mustelidae, weasels may be bred by more than one mate, and the implantation of the fertilized eggs in the uterus is often delayed. Mating in the farthest northern climates of Canada and Alaska typically takes place in mid to late summer, but delayed implantation of the fertilized eggs might last for six months or more. Total gestation can be as long eight to ten months. However, in the milder climates of the lower forty-eight states delayed implantation might not occur for the least weasel, and in their farthest southern range they might have three litters a year.

Litter size varies from three to ten young, which are born in a nest under old buildings, rock outcroppings, or hollow stumps and logs. The nest is often lined with rabbit or mouse fur. Survival of the young until weaning generally depends on the availability of food in the mother’s home range.

May

The pregnant female spent several days preparing her nest for the birth of her young. She lined the nest with field mice fur from her daily kills, and recently made a kill of a large rabbit whose fur contributed greatly to the comfort and warmth of her nest. During the night she gave birth to seven weasels, four males and three females. The tiny youngsters would remain in the den for almost forty days before emerging into their new world. The mother weasel was kept especially busy during this time, because she required almost forty percent of her body weight in mice, rabbits, shrews, insects and other small animals to remain healthy and nurse her young. That was not too difficult as she located her nest in an area rich with field mice and other small prey animals. She hunted both day and night. Weasels hunt during the daylight hours, though many of their successful predatory kills are during the night.

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June/July

After the young finally emerged from their nest, they remained close to the den for several weeks before accompanying their mother on hunting trips where they would learn the fine art of being a successful weasel. The family forages and training continued for a little more than five weeks. Each young weasel became adept at catching field mice and young rabbits. Like other members of the Mustelidae, their curiosity was boundless, and they rapidly learned what they needed to know to survive.

August

By mid August the last of the kits, which were now fully grown, left their mother’s den area and dispersed on their own. At least four would make it to sexual maturity during the next spring, but three were lost to winged predators during the winter.

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