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The problem with being long and skinny

By Jack Souther,

Whistler Naturalists

A few towers up the Wizard, on my way to early morning powder, I spotted a tiny black dot moving mysteriously across the slope. Only when I was directly over it could I make out the body of a small white weasel which, except for the black tip of its tail, was almost invisible against the snow.

Though rarely seen, the short-tailed weasel or ermine ( Mustela erminea ) ranges from the high Arctic into the northern States. About 30 cm long and weighing from 2 to 5 ounces, it is the smallest true carnivore in the Whistler area – about a tenth the size of its larger relative, the Pine Marten, with whom it shares the local habitat.

Males are about twice as heavy as females, giving both sexes an advantage in their respective reproductive roles – the larger, stronger males in their competition for territory and mates, and the smaller females in their vole-hunting and reduced food requirement when raising young.

Ermine are polygamous and promiscuous. They mate in early summer but implantation is delayed until the following March. Litters of 4 to 9 pups are born in April. Naked and blind at birth the young quickly grow a covering of white fuzz which at two months is replaced by the rich brown dorsal fur, yellowish-white belly and black-tipped tail of a summer adult. Weaning occurs at two to three months when the young ermine begin to play outside the nest.

Squealing and romping, they practice hunting by pouncing on one another or by teasing and eventually killing a hapless mouse or vole that mom has dragged home for them to practice on. By the eighth week they are able to hunt with their mother and soon after are on their own – leading relatively solitary lives in exclusive territories, patrolled and marked with scent.

Ermine hunt mainly at night, killing small mammals up to the size of young hare by seizing their victim’s neck and biting into the base of the skull. Their long lithe bodies and short legs allow them to move swiftly through burrows and squeeze into nooks and crannies in search of mice and voles which form most of their diet.

But being long and skinny has its problems. The ermine's large surface area and small body mass leads to rapid heat loss and a need for almost constant feeding in order to meet their exorbitant energy demands.

The other catch in being skinny is lack of internal space for anything but a very small stomach. An ermine can eat less than an ounce of meat at a time, requiring it to feed every few hours in order to survive. This need for a constant food supply has given the little carnivore its reputation for being a wanton killer driven by blood-lust. In fact the animal is simply adding to its larder, storing the bodies of its victims inside cavities of its burrow and using their fur and feathers to line its sleeping chamber.

And why the black tip on its tail? One theory suggests it is a decoy, designed to take the hit if the ermine is attacked by an owl. Could be – it is certainly all I could see from the lift.

Upcoming Events

Saturday, January 5th — Monthly Bird Walk . Meet at the base of Lorimer Road at 8 a.m. Contact Michael Thompson (604-932-5010) for details.

Sightings and Memberships: NatureSpeak is prepared by the Whistler Naturalists. To become a member or to report noteworthy sightings of mammals, birds, or other species, contact Lee Edwards (604-905-6448; e-mail:

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