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Ermine and Least Weasel

THE SPECIES: Mustela erminea and Mustela nivalis 

weasel.jpgA small, white face pushes up through the snow, its black eyes gleaming brightly. Next comes the body, long and slender, ending in a black-tipped tail. Built to squeeze into nooks and crannies, this ermine and its cousin, the least weasel, are two of the world's most efficient mousers. And, as anyone who's seen them will attest, these two weasels are also among the boldest and most agile of all Yukon mammals.

DISTRIBUTION

The ermine and least weasel inhabit northern countries around the world. In North America, ermine range from the Canadian high arctic to south of the Great Lakes and into the mountainous western states. Least weasels occur throughout most of the same range, but are absent from the arctic islands and western states.

Both least weasels and ermine range throughout the Yukon, avoiding the depths of mature forests and preferring instead to sniff and snoop in forest edges, meadows, brushy areas, marshes, bogs, and tundra. Based on winter track surveys, Yukon ermine are fairly abundant. However, least weasels are uncommon, though not endangered, throughout most of their North American range.

CHARACTERISTICS

There are two ways to tell our two weasels apart: size and tail color. Ermine reach over 30 cm in length, while least weasels are usually less than 25 cm long. Least weasels are also the smallest members of the weasel family. Ermine have black-tipped tails in both summer and winter, while least weasels have short, stubby tails without black tips.

In general, male weasels are larger and heavier than females. Male ermine are several centimetres longer and, at 70-200 grams, about twice as heavy as females. Male least weasels are also a couple of centimetres longer than females and weigh 60-90 grams to females 35-70 grams.

The striking size difference of male and female ermine makes the best use of available resources. Since raising young is totally up to the female, she needs to save every bit of energy she can. Her small size is not only the best size for hunting voles, her favourite food, it also means that she needs to eat less to keep herself going while raising a family.

On the other hand, being large gives male ermine a better chance of winning confrontations with other males. And, since males are too big to hunt in some rodent tunnels and burrows, their larger size also leaves food available to the female that raises their young.

Long and slender, both of our weasels can slip in and out of cracks and tunnels in their search for food and to escape predators. Their movements in tight spaces are made easier by short legs and fur, small ears, and long, sensitive whiskers.

Ferocious hunters, weasels are muscular and quick, sometimes taking on prey much larger than themselves. Indeed, the least weasel is hardly bigger than the small rodents it normally feeds on. Both ermine and least weasels have keen ears and noses, along with good night vision. Though weasels climb trees in pursuit of prey, to escape predation, or even just for a snooze, they are most at home on and under the ground. Ermine hunt by day or night, while the even more agile least weasels are active mostly at -night.

THE HUNTING WAY OF LIFE

Northern lights dance in the moonlit sky over a dainty trail printed on snow. Twin tracks, small and round, head this way, then that, and often turn back on themselves. Ahead, an ermine pauses in its investigation of holes, stumps, bushes, and logs. It lifts its head, then stands upright to better check the surroundings. Then it is off again, zigging and zagging; its erratic movements thought to deter predators.

Though the ermines fur is white in winter, an owl may still spot it moving against the snow. However, the ermine's black tail tip may draw the owls attention and fool it into attacking the tail.

As the female ermine lopes off, her long, thin body humps in the middle like a caterpillar's. Suddenly she dives into the soft snow, leaving only a neat, round hole behind. A few yards beyond, her head pops up through the snow. It swivels like a periscope on a long, snaky neck, then ducks into the snow again.

Most of the ermine's prey are small rodents that live beneath the snow in winter. To hunt them effectively, she must go where they go: into their runways, tunnels, and burrows. Shes the perfect size for hunting meadow voles, as her body diameter is almost exactly the same as the voles. Other vole species are also eaten, including brown and collared lemmings.

Male ermine, being much larger than females, are less efficient vole hunters. However, they still rely on voles, mice, and lemmings for most of their food. Both sexes also occasionally hunt shrews, chipmunks, pikas, red squirrels, ground squirrels, young hares, and birds.

Because least weasels are less common and more elusive than ermine, their habits are not well known. Both sexes are thought to spend much of their hunting time in the runways, burrows, and nest chambers of small rodents.

When ermine and least weasels live in the same area, they tend to hunt different prey in different habitats -- a good thing for the smaller weasel, since ermine sometimes eat them. The ermine hunt larger voles in meadows, boggy, or shrubby habitats, while the least weasels hunt deer mice and red-backed voles in forested habitats.

Weasel numbers are greatly affected by ups and downs in numbers of their prey species, particularly voles, lemmings, and mice. Such fluctuations in prey numbers create feasts and famines during which the chances of raising young to maturity range from excellent to zero. Our two very similar-looking weasels have developed two very different strategies for coping with changes in prey availability.

Least weasels, who eat small rodents almost exclusively, breed throughout spring and summer when food is plentiful. They can produce up to three litters a year, with four or five young per litter. For them, life is boom or bust and few live to see their first birthday. Ermine, rather more general feeders, produce only one litter a year with an average of six young. However, with a life expectancy almost twice as long as least weasels, ermine may scrape through the rodent lows to see better hunting times- ahead.

SEASONS OF THE SMALLEST HUNTERS

In April, when crocuses bloom on warm Yukon hillsides, ermine give birth to their young. Blind and naked, the newborns weigh about the same as a penny. Fine, white fur soon covers them and thick, dark manes appear at two weeks. These manes may provide a place for mothers to grasp if emergency evacuations are needed.

Brown and white coats with black tail tips make an appearance by two months of age, about the same time the young ermine start to play outside their nest. Weaning occurs at two to three months. By this time, or even earlier, female young may have already mated.

Although mating occurs early in summer, embryonic ermine do not develop in the uterus until the following March, a condition common to certain other members of the weasel family and known as delayed implantation.

Least weasels, however, do not have delayed implantation. Females produce young 35 days after mating. When food is abundant, both male and female offspring mature within three to four months.

During the warm, endless days of summer, young weasels gambol and romp, squeal and trill. They practice hunting by pouncing on each other, or on a vole that their mother brings to the nest. Killers by instinct, the youngsters do not need instruction on how to grasp prey at the nape of the neck and bite into the skull. By weaning time, they can kill their own food, and soon after are on their own.

Come autumn, young weasels disperse from their mothers' territories and may cover many hazardous kilometres before they are able to secure a territory of their own. Weasels lead solitary lives except at breeding time. Both males and females set up territories that exclude members of their own sex. Females avoid males where their territories overlap. Both sexes advertise their presence with the strong, musky odour so characteristic of the Mustelidae, or weasel family.

Female ermine are mature by late autumn; the males by the next spring. Only two in five ermine will survive their first year, though the odd old-timer may reach an age of seven years. Starvation kills most ermine, along with poor snow cover, cold temperatures, disease, or habitat disturbance. Predation by hawks, owls, coyotes, foxes, and larger members of the weasel family is another factor.

Since least weasels depend on small rodents for food even more so than ermine, they may suffer local extinctions when numbers of prey species plummet. Other causes of death are the same as for the ermine, with the addition of kestrels as predators.

When temperatures plunge and winter winds howl, weasels have acquired their white coats and get down to the business of staying warm. Being long and thin, they lose heat rapidly due to a large surface area and the inability to tuck themselves into a tight ball when resting. As well, weasels do not store much energy in the form of fat.

To save energy, weasels decrease activity, stay under snow, and arrange nest bedding for the greatest insulation. To make an acquired rodent nest of grasses or shredded leaves even warmer, weasels pluck fur from their prey and line the nest with a fur blanket up to an inch thick.

Even so, to stay warm, weasels must eat up to a third of their body weight in food each day. They burn energy at up to four times the rate of more rounded mammals of the same weight. How do they keep up with the demand? Instead of storing fat, they store mice and voles. Thus, the killing sprees of legend are not so much a weasel's lust for blood as the need to stockpile food in case poor future hunting cannot satisfy the voracious appetite of such a slender, active mammal.

WEASELS AND PEOPLE

Inquisitive and quite fearless, weasels often visit yards in rural areas and stick around to make the owner's acquaintance. They enter cabins and tents even when occupied. If curiosity gets the best of them, they will step right up onto a boot to take a closer look at who's attached to the foot inside. Since weasels are the best mousers in the boreal forest, trappers like to have them around cabins to help keep rodents down.

Occasionally, both ermine and least weasels are taken in traps set for other furbearers. Although the least weasel has no commercial value, trapping one is thought to bring good luck. Ermine fur is used both locally for parka and slipper trim, and exported to Europe where it is dyed and made into jackets and coats.

VIEWING OPPORTUNITIES

Both ermine and least weasels are small, solitary mammals that spend much of their time underground. Therefore, finding one is largely a matter of luck unless you know of a place -- such a yard or cabin -- where one regularly comes to visit.

In summer, weasels leave little sign, but watch for playful youngsters romping near a nest. In winter, look for a trail of twin prints in the snow. The small, round tracks often disappear into neat, round holes and reappear farther on. A short leap -- long leap -- short leap pattern is quite characteristic of weasel trails.

If you do spot a weasel in summer or winter, remember that the ermine has a black-tipped tail and is larger than the least weasel. A short, stubby tail without a black tip means you are looking at a least weasel. Remain still and see if the wee, bold hunter decides to check you out. If not, give it some encouragement by imitating a mouse squeak -- then guard your throat!

DID YOU KNOW?

 

Last Updated: December 31, 1969 | © 2008 Government of Yukon | Copyright | Privacy Statement | Disclaimer