Alaska Fish & Wildlife News
Wolverines: Behind the Myth
The wolverine’s reputation precedes it.
In Mark Trail’s Book of Animals, Ed Dodd writes: “Savage ferocity combined with mischievous cunning has made the wolverine an object of hate and dread among trappers.”
In Mammals of North America, Vic Cahalane recounts the legendary prowess of the wolverine as fact: immensely strong and known to drive bears and mountain lions off their kills (two or three at a time, even); capable of taking down a bear in a fight; and bad-tempered loners that will destroy a cabin out of sheer deviltry.
Fact and Fiction
Fish and Game researchers Howard Golden and Mike Harrington are studying wolverines in South-central Alaska. In recent years they’ve captured 18 wolverines and equipped them with GPS tracking collars to better understand their movements and numbers. Wolverines are impressive, but much of the reputation is exaggerated.
“They’ve got such a bad rap,” Harrington said. “I've had people ask, ‘will they chase you down? Aren’t they dangerous?’ People wonder if we’re afraid of them.”
“A lot of myths about them are way overblown,” Golden said. “People attribute magic powers to them, but they’re just doing their thing, looking for food. They are curious, smart animals and they figure stuff out pretty quick. They are smart enough to run down a trap line, and that’ll make trappers mad. But it makes sense that they’d do that – there’s always food on these trap lines. They’re not extra aggressive, they avoid trouble.”
Wolverines are weasels, Golden said, and have the weasel nature. “That whole family is pretty similar, just the size is different. Ermine can be bold; weasels are an intelligent family of animals and they know how to survive.”
While wolverines are usually solitary, the “bad tempered loner” stereotype gives the impression they are downright antisocial. Golden visited a facility in Washington that’s home to about 40 wolverines. They shared a large common area and he said they were quite tolerant and social with each other.
“If resources are limited that can cause conflict, but they can be social,” Golden said. “If food is plentiful, they’ve got no reason to worry about each other. We’ve seen them in April from the air wrestling and playing with each other, they weren’t fighting, they’re socializing.”
They are territorial, in the general sense of the word, but Harrington and Golden use the term “home use area” to describe the area they favor. “They pick areas they maintain and keep to themselves, males will overlap with females, but males don’t overlap much with males, or females with females,” Harrington said. “They need resources, and they pick an area where they can make a living and survive.”
They have scent glands, a ventral gland near the belly button, anal glands, and they also have little scent glands on the bottom of the pads of their feet, and when they walk they leave scent. They also scent-mark through urination. “They basically maintain territory this way through active marking,” Golden said. “We have found some that have been in fights and are scarred up, they do get into tussles. “
He said a wolverine can defend itself pretty well, but it’s no match for larger predators. “Two wolves can kill one,” he said. “You hear stories about them chasing bears off, I’ve never seen that happen, or known anyone who has.”
Their eyesight and hearing are not especially good, but they have an outstanding sense of smell.
“They’ve got a pretty good set of tools on them; a really good nose, they can smell food over long distances or buried well under the snow,” Golden said. “They can climb trees. They have a really warm coat. They’ve got strong claws for digging and defense, and incredibly strong jaws for biting and crushing bone and frozen meat - not the same crushing power as a wolf, but they’re not as big, a big wolverine is 40 pounds and small wolf is 60 pounds.”
“You look at them, they’re mostly built for scavenging,” Golden said. “But they’re very opportunistic and regularly kill small game. They’re not as fast as wolves, and they don’t work in packs, but they can be more predator than scavenger if the situation allows for it.”
Wolverines hunt snowshoe hares and voles, and in summer ground squirrels and marmots are important prey items. “We’ve got documentation of them killing smaller Dall sheep. In Scandinavian countries they lose domestic sheep and reindeer to wolverines, and the government provides compensation to herders. The herders are required to hire rangers to document wolverine den sites and reproduction, and that’s one reason they have great reproductive data.”
It is true that wolverines are very strong for their size and have incredible stamina. Golden said a wolverine can cover 30 miles in a night, working a circuit in search of food. They will den up and rest for brief periods, and then get back on the move. That ability to travel through incredibly rugged mountainous terrain is not exaggerated.
“That’s the big thing to come out of the GPS work for Mike and I, and it’s pretty amazing when you see it,” Golden said. “We get locations every 20 minutes, you can see how fast they move around terrain, they go up and down really steep, icy, rocky slopes like they’re not even there. You could never hike it – you’d need climbing gear. It’s like they see the world as two-dimensional, the way they move up and down these snow-covered slopes.”
Tracks in the snow
An innovative technique to assess population size has partly driven the research. ADF&G biometrician Earl Becker developed a method to estimate wolf populations based on aerial surveys of tracks in snow. Called SUPE, Sample Unit Probability Estimator, Becker worked out the technique for wolves and he worked with Golden and Harrington to apply it to wolverines. Given some basic assumptions, it works like this: biologists survey an area after fresh snowfall and identify sets of tracks. The track lines can be extrapolated to population numbers. Some basic assumptions must be met, for example, all animals of interest move during the study, tracks are continuous, they’re recognizable from the air, and pre and post snowstorm tracks can be distinguished.
Wolverines behave differently from wolves, and they don’t run in packs. An important difference is that a wolverine may sometimes sit tight for two or three days, in a den site or on a kill, and that needs to be factored in.
“For two or three days out of 20 they might not be moving, and if we did a SUPE at that time we might miss 10 or 15 percent that weren’t moving after a fresh snowfall,” Golden said. “That’s a correction factor we need to apply to the calculated estimate.”
“The other thing about SUPE, it only works in some areas,” he added. “It wouldn’t work in Southeast; the canopy cover is too thick. You have to meet that set of assumptions, and normally we can verify them while we’re flying.”
Collaring and tracking wolverines allowed researchers to ground truth the technique – and learn a lot about wolverines in the process. Results from a cooperative study with Chugach National Forest indicated a wolverine density of 4.5 to 5.0 wolverines per 1,000 square kilometers in Kenai Mountains and Turnagain Arm area, which is typical for other areas of South-central where SUPES were conducted.
“Different techniques are suitable for certain areas,” Golden said. “In some areas you’re just looking for occupancy – do we even have wolverines?”
The researchers pointed out two other methods used to study wolverines. Hair snares subtly snag a tuft of fur from a passing animal, and the DNA in the follicles enables biologists to identify individual animals, their gender and relatedness, and multiple samples over time can provide a population estimate (mark-recapture). Photo identification uses remote, motion-triggered trail cameras to photograph animals in specific poses that reveal distinctive markings that can identify individuals – much as tail fluke marks are used to identify humpback whales.
Catching wolverines: traps and darts
The researchers captured 18 different wolverines between September 2007 and March 2014. Including recaptures, animals were live-trapped 14 times and helicopter-darted 10 times. Among the 18 wolverines captured, there were five juvenile (1–2 years old) females, five adult females, four juvenile males and four adult males. Wolverines were captured in the Chugach Mountains east of Anchorage (in the state park), on the Elmendorf-Richardson joint base (JBER) and south of Anchorage in the Kenai Mountains. The capture work was done in cooperation with Chugach State Park, JBER Natural Resources Department, and Chugach National Forest.
Three wolverines did not yield data – they slipped their collars right away, or for some other reasons researchers were unable to detect signals. All the telemetry work was done in late winter and early spring to better understand how wolverines move during the period when SUPES are conducted.
Cameras proved to be a valuable tool for trapping and darting. Motion-triggered trail cameras were set up near the live traps, and researchers wore helmet-mounted video cameras when helicopter darting to help them learn from capture attempts. That helped them solve an equipment malfunction at one point in the project - they slowed the video down and watched it frame by frame, revealing a problem with the dart design they were able to correct.
Darting can be really efficient under ideal conditions, and Golden said one day they caught four wolverines. That was exceptional, some days they found wolverines they couldn’t catch. Aircraft searched for roaming wolverines, and then called the capture team.
“Wolverines are never very abundant, even when they’re abundant for the species,” Golden said. “You need good conditions to track them, we had two fixed-wing aircraft just looking for animals, sometimes for hours, and then we’re sitting on a ridge with the helicopter, waiting. Then we get the call and go after them.”
Darting a moving animal from a moving helicopter is clearly a challenge. Harrington said the mountainous terrain and relatively small size of the target added to the difficulty. One thing played to their advantage, he said when pursued, wolverines tended to run uphill. In deep snow that really hampered their speed.
“On hard packed snow, we couldn’t believe how fast they can run,” he said.
Pursuit was limited to 10 minutes. “Sometimes we had to say, ‘we’re not going to get this guy.’”
Once caught, wolverines were quickly processed. Throughout processing biologists monitored wolverines’ temperature, heart rate and respiration, and were prepared to provide supplemental oxygen if needed. They took samples of tissue (for DNA), hair and blood, the animals were weighed and measured, age estimated, and they were marked with an ear tag and equipped with a GPS/VHF collar.
The collars were programmed to record GPS locations at 20-min intervals, and were capable of maintaining that rate of data collection for about 3 months and then to continue VHF beaconing for about 100 days longer before battery failure. Collars also stored altitude and air temperature. Two types of GPS collars were used; both stored thousands of location data points onboard and allowed remote downloading of collar data from the ground or from the air. One model could be released remotely to drop-off, the other could not and required recapture to retrieve collars.
Golden and Harrington were successful live-trapping on JBER during the first two or three years while new animals were still coming into the trapsites. The researchers took advantage of a winter moose hunting season on the joint base - wolverines were attracted to kill sites and worked the hunt areas into their foraging circuits. However, it became very difficult to attract wolverines into traps during winter of 2012–13, which they attributed mostly to the lack of new wolverines visiting the area. From images gathered on the remote cameras, it seemed the animals were too wary to be caught.
“They remember where they’ve found food, but they got wise to the traps really quick,” Harrington said. “They’re hard to live trap in the first place, and really hard after that. You might fool them once, but how do you fool them again after that? We got creative with different kinds of bait - we tried chickens wrapped in bacon, and big wads of beef suet.”
Home range estimates for wolverines in South-central Alaska show females use about 300 to 600 square kilometers (115-230 square miles) and males use about 700 to 1,000 square kilometers (270 to 380 square miles.
Males and females traveled extensively throughout their home use areas. Both sexes occasionally went on exploratory trips and then returned to their primary areas. A look at the movements of five wolverines over the course of a year (two females and three males) showed great variation in distances traveled, some days they covered a lot of ground, others days not so much. The average distances traveled per day was about 12 kilometers for the females, and between eight and 21 kilometers for the males.
“One male had twice as big an area as other wolverines,” Golden said. “It may be that area had lost a male and this animal just took over the whole area, at least for the short time the collar was active.”
Because the focus of the study was movement in late winter and spring, the researchers did not track wolverines year-round. The far ranging male did provide some data in late spring – when he expanded his range even more.
“They do spend a lot of time in summer during the breeding season testing boundaries and trying to encounter females,” he said.
An important time in a wolverine’s life, and a time for significant movement, is when a young adult strikes out to establish its own home range. Wolverines are born in February or March, two to four kits that usually dwindle from mortality to one or two by fall.
“Mortality is pretty high for kits,” Golden said. “We’re finding females generally don’t have a litter before they’re about three years old, and then typically have a litter about every other year.”
The kits are essentially full grown by October or November and begin moving out. It can be tough for a young wolverine to find a territory that is unoccupied and suitable. “A daughter might stay with mom a couple years and inherit her area,” Golden said. “Young may try and stay relatively close to their natal area, and siblings may be more tolerant of each other.”
But wolverines have been known to disperse as far as 235 miles. Dispersal is important, that’s how wild areas that “produce” wolverines can supply them to potential home ranges elsewhere, good habitat where wolverines may have been harvested.
That balance is a model for sustainable yield – enough refugia from human activity, good habitat for wolverines that are producing young that will emigrate out.
Hunters and trappers in Alaska harvest about 550 wolverines each year. Because wolverine reproductive potential and survivorship is low it’s important to understand where and when animals are harvested to be sure the population is not overharvested. Wolverines disperse depending on availability of food and habitat resources, and animals dispersing from areas where they are not trapped replenish the population in areas where they are hunted and trapped.
A gallery of trail camera photos of wolverines is available, as well as a short video of a wolverine raiding the nest of a ground-nesting shorebird and eating the eggs.
Riley Woodford is the editor of Alaska Fish and Wildlife News.
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