Wolverines: New studies offer insight into behavior and natural history

Posted: Friday, November 12, 2010

Some friends recently gave me a new book called "The Wolverine Way" (by D. Chadwick), and reading that book perked up my interest in wolverines and the tremendous challenge of studying them in the wild. So, here is a little bit about them.

Courtesy Of Bob Armstrong
Courtesy Of Bob Armstrong

Wolverines belong to the weasel family, Mustelidae. They are the largest terrestrial weasels. Males usually weigh 25-40 pounds, but they can top out around 70 pounds. Females generally weigh 12-25 pounds. They have a flat-footed walk, like bears and humans. Their paws are huge for their body size - as big as those of a wolf weighing three times as much. The claws can be partly retracted (more than a dog and less than a cat). Although most illustrations show them in a somewhat crouched posture, their legs are not as short as they often look. They have dark brown fur with a blond "swoosh" stripe along the side.

An early naturalist, Ernest Thompson Seton, described wolverines this way, "The wolverine is a tremendous character ... a personality of unmeasured force, courage, and achievement so enveloped in a mist of legend, superstition, idolatry, fear, and hatred, that one scarcely knows how to begin or what to accept as fact."

Years later, detailed studies are yielding many new insights into wolverine behavior and natural history.

The wolverine is also known as the glutton, a name that conjures up an image of unrestrained gobbling of food, an image that is surely exaggerated. They have very powerful jaws, capable of gnawing into frozen meat and crushing bones. As in wolves and foxes, some of the molar teeth are modified into large, slicing blades called carnassial teeth. Wolverines take prey up to the size of a bobcat or a moose calf, but have been known to sometimes take larger animals. They also scavenge carcasses left by wolves, human hunters or winter-kills. However, much of their prey consists of rodents and hares. In the Yukon, they've been seen foraging on spawning salmon. They even eat berries in season.

In some circles, this large weasel has a reputation of total, malevolent ferocity. It is presumably this reputation that has led to its name being adopted by an avenging comic book character, a brand of tough boots and sports teams of a certain Midwestern state. Indeed, it can be a fierce creature, ripping up box traps made of logs and snarling aggressively while fighting back when threatened. They fight each other upon occasion, often with lethal consequences.

But there are other aspects of the animal as well. Wolverines in captivity can become very tame and docile, eating snacks offered by human hands and enjoying tummy-rubs like happy dogs and cats do. Family life is more social than previously imagined. Long thought to be solitary creatures, detailed studies reveal that family associations are sometimes prolonged, at least intermittently, for years. Duos of mother and grown-up offspring, or even father and grown-up son have been documented, keeping company for days at a time.

Wolverines are excellent climbers with great endurance. By intensive radio tracking and by satellite tracking of animals with special transmitters on collars or in surgical implants, researchers can follow the movements of individual animals for extended periods of time. A study in Montana recorded them as they climbed up nearly vertical cliffs and snow chutes near the tops of mountains where humans dare not go. One animal climbed almost five thousand feet in an hour and a half. They can travel twenty, thirty, forty miles or more in a day.

A male's home range covers two or three hundred square miles, or even five or six hundred, in some cases. Home ranges of males can also overlap those of several females. A male wolverine can cover hundreds of miles in a week as he patrols his home range, looking for patchy food sources or for females ready to mate.

Wolverines mate in summer, but the embryo is not implanted in the females' uterus until early winter. Two or three kits are born in winter or early spring. They have white fur when they are born, but gradually the fur darkens to deep brown. Dens are often located at the end of long tunnels in deep snow, sometimes on barren rocky hillsides above timberline, but seldom in the forest. One female used an old beaver lodge. Females often move the kits from one den to another.

Kits are weaned in about two and half months, but they stay near the mother at least into fall and often into winter. Wolverines mature at age two, but seldom breed successfully until age three. Breeding success is probably related to food supply.

Wolverines typically live at low densities on the landscape. Their food is often widely and patchily distributed. Their natural enemies include grizzly bears and other wolverines, but their principal predator is humankind.

In Alaska, wolverines are widespread, including Southeast. They occur in forested and alpine habitats all across northern reaches of Eurasia and North America, but American wolverines have been extirpated around the Great Lakes and St Lawrence River and in much of the mountainous west, where a few small, isolated populations still remain. Around Juneau, their tracks are occasionally seen near the glacier, on Mt Roberts and near Eaglecrest. A few lucky observers have reported a sighting in Spaulding Meadow.

At 7 p.m. on Nov. 14, there will be a Nature program on wolverines on Channel 10.

• Mary F. Willson is a retired professor of ecology.



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