Wolverines expanding range in North Cascades

YAKIMA— Wildlife biologist Aja Woodrow has a system to get one of the Northwest’s most elusive animals— the wolverine— to pose for pictures.

The trick is to rig a roadkill deer in a remote tree, forcing the smart scavenger to climb to a narrow pole and then stand on its hind legs to reach the carcass, located next to a camera with a motion sensor. The resulting photos can capture the creature’s unique chest markings for later identification. Clamps also snag a small clump or two of hair for DNA analysis.

Woodrow, a biologist for the U.S. Forest Service, learned these techniques from other scientists, but he’s put them into action on the Cle Elum Ranger District to figure out how many wolverines are moving south and making themselves at home again in Washington’s Central Cascades decades after nearly being wiped out.

The key for wolverines is having vast swaths of remote, snowy terrain, Woodrow said. The largest member of the weasel family, wolverines are scavengers, occasional predators, and one of the few high-elevation animals that stays active all winter long.

Most of the wolverines known to live in Washington are found in the North Cascades, but Woodrow and other scientists believe that the animals are now making their way down the Cascades from British Columbia.

“They are in the process of expanding their range southward, but where that might end, we don’t know,” said Keith Aubry, a scientist with the Forest Service’s Northwest Lab in Seattle.

Their range now seems likely to end at Interstate 90, Woodrow said. To test that theory, he’s established a network of camera trap sites around the Cle Elum District, mostly north of the highway but with a few to the south as well.

The busy interstate is just one of the many ways the Cascades have changed since wolverines, grizzly bears and other nearly vanished species regularly roamed the area. The highway has been a total barrier for most species, said Craig Broadhead, a wildlife biologist for the state Department of Transportation.

It’s a problem for individual animals because the highway can block them from good habitat. But on a larger scale it limits mating options and limits genetic diversity in a population, Broadhead said. That genetic diversity is crucial to prevent inbreeding and helping populations avoid disease and adapt to changes in the environment.

It’s especially critical for at-risk species such as the wolverines, which exist in low numbers living in high mountain habitats that can be so isolated that Aubry compares the sites to islands.

Wolverines need deep snow that lasts until late spring, he said. That’s because females give birth in snow caves and they need the snow to persist until the kits are weaned, typically in mid- to late April.

For the past decade, Aubry has used GPS collars to study a population of about 20 animals in the northern Cascades. Wolverines have a reputation as solitary animals, but Aubry said his data show that they have more complex social behaviors than previously believed.

A century ago, the greatest threat to wolverines was poison from trappers who saw them as a nuisance. Today, the threat is climate change for the animals that rely on plentiful and long-lasting snow for successful reproduction, Aubry said. Last year, the U.S. Fish and Wildlife Service considered listing the species as endangered because of the threat of climate change, but decided not to.

“In that archipelago of high mountain conditions, as climate warms, not only will that habitat shrink in extent, but it will become more isolated from each other as well. That’s the greatest concern,” Aubry said.

Reconnecting habitat for wolverines and other wildlife large and small is why the state transportation department is spending millions on crossing structures as part of the large I-90 improvement project.

These include the completed underpass near Gold Creek and an overpass planned several miles to the east, which will be 150 feet wide and planted with native plants to mimic the forests it connects.

“We think of it as a landscape bridge; we’re trying to connect the landscape, not just the wildlife,” Broadhead said. “Slugs and snails might move 20 feet in their lifetime; we want to use the crossing structure as habitat for them as well, to connect the whole ecosystem.”

The transportation department is working with the Forest Service to look for wolverines on the Cle Elum District this winter in order to help learn how effective the bridges will be for these highly mobile animals.

“These are 25- to 30-pound animals that have territories of 200 to 500 square miles, scavenging for food in a very resource-poor environment,” Woodrow said. “Wolverines are just starting to come back to the Cascades, so we want to see if the crossing structures will restore connectivity.”

The crossings would likely also restore connectivity for the Cascades’ northern and southern black bear populations, which haven’t been able to mingle or mate easily for decades, Broadhead said.

Volunteers with Conservation Northwest have to set up and monitor wildlife cameras to help agency scientists watch more wilderness. Last year, they snapped photos of wolverines and lynx, but no grizzlies or wolves, said spokesman Chase Gunnell.

The wolverine camera traps can only be up for a few winter months each year, Woodrow said, because the dead deer used for bait could attract bears when they emerge from hibernation. This winter, the lack of snow is limiting access to some of his remote sites, but so far he’s got photos of two animals and some additional hair and scat samples for genetic analysis.

Aubrey is compiling the wolverine data from the Conservation Northwest volunteers, from Woodrow’s camera traps on the Cle Elum District, and his own work in the North Cascades with GPS tracking to learn as much as he can about how the animals are making themselves at home in Washington again.

That way, someday scientists will know how to help them, if need be, he said. So far, they are quietly, slowly coming back on their own.

“To me, they are the truly iconic wilderness species, roaming around these high elevations and somehow managing to eke out an existence in an area that seems impossible,” Aubry said. “They really speak to the wilderness that North America used to be.”