As wolverines return to Washington, another threat looms
People who drove through Snoqualmie Pass in early January came back talking about the grass still poking up through the meager snowpack on downhill ski runs. Skiers are on the well-covered slopes at Snoqualmie now, but climate change — if that's what we're seeing — doesn't bode well for folks who make a living from low-elevation ski areas. Nor does it bode well for animal species that make a living in deep snow around here.
The risk goes well beyond this region, of course. The plight of polar bears faced with less Arctic sea ice on which to hunt seals has been well publicized. (A recent report suggests that the big bears are developing a taste for snow goose eggs.)
But here, in the upper corner of the country, the looming change may soon give us a new federally listed species: the wolverine, Gulo gulo, the world's largest terrestrial weasel. Many of the Northwest's most charismatic species rely on chilly water or deep snow. Salmon, which rely on cool spawning streams, may be driven from much of their current habitat. In the Columbia Basin, the only spawning streams with cool enough water may eventually be those that lie in the mountains of Idaho — a location that means fish are forced to run the gauntlet of the lower Snake River dams.
The Canada lynx, which lives in the North Cascades and the Selkirks, is adapted to living in snow. Its big feet keep it from sinking in. It dines primarily on the snowshoe hare, whose big feet keep it from sinking in, too. Take away reliable winter snow, and the snowshoe hare population disappears. And so does the lynx's evolutionary advantage. Other species' genetic equipment becomes more beneficial: The bobcat, which is less adapted to snow but is a larger, more competent generalist, starts displacing the lynx.
And then there's the wolverine. The return of wolverines to Washington and the discovery two years ago that they're breeding here has been big news. Scientists know there are at least 18 of them in Washington, mostly in the North Cascades, although they've started appearing south of Highway 2 and a single male has been seen around Mount Adams.
For unknown reasons, male wolverines sometimes take off on long solo journeys. One currently lives in the southern Sierra Nevada and another in the southern Rockies, far from any established population. Because females evidently don't have the same wanderlust, these males aren't likely to start new populations.
Once upon a time wolverines lived all across the northern tier of states and way down into the Rockies and Sierra Nevada. They were exterminated before 1950, partly through deliberate trapping, but probably mostly as collateral damage when people set out to poison coyotes and wolves. (Not that people were above poisoning wolverines directly. "Some trappers intentionally poisoned them to prevent the destruction of more valuable furbearers," Keith Aubrey of the U.S. Forest Service's Pacific Northwest Research Station in Olympia and colleagues wrote in 2007. They noted that intentional poisonings even occurred in Yellowstone National Park in the late 1800s.)
Then, 20 or 30 years ago, new wolverines started walking south across the Canadian border. Most came down from Alberta into the northern Rockies, where they've established breeding populations. A smaller number has come down from British Columbia's Coast Range into the North Cascades.
The animals have no physical adaptations as obvious as the big feet of the lynx or snowshoe hair, but wolverines, too, are adapted to snow. I have an old top-of-the-line Eddie Bauer parka, heavy with down filling and topped with a wolverine fur ruff. Why wolverine? Because it's the only fur that, exposed to damp human breath in super-cold temperatures, won't ice up.
Behaviorally, they are largely confined in places where the snow gets deep and lasts well into spring. They make dens and raise their young in deep snow caves. "Virtually all reported wolverine reproductive dens (sites where kits are born and raised prior to weaning) are relatively long, complex snow tunnels that may or may not be associated with large structures, such as fallen trees or boulders," the Aubrey paper explained. J.P. Copeland and colleagues surveyed wolverine populations around the northern hemisphere and found virtually all of them in areas where deep snow lasted until at least May 15.
Because of the threat posed by climate change, the U.S. Fish and Wildlife Service has proposed listing wolverines in the Lower 48 states as threatened. A decision is due this summer.
To be sure, despite the threats posed by climate change, the service may propose delisting grizzly bears in the Greater Yellowstone ecosystem. There are more bears than there used to be, although just how many can get you an argument, but one of their main foods is being threatened by disease and bugs given a foothold by higher winter temperatures. The Yellowstone bears eat pine nuts. But the pines are dying en masse. That forces the bears lower, where they are more likely to come into conflict with human beings, and forces them into more of a meat diet, with the same result.
Some Western state governments have urged the FWS not to list the wolverines. There are, in recent historical terms, lots of wolverines, they argue, and it makes sense to wait and see what climate change will do. Wyoming's Gov. Matt Mead wrote federal officials, "There is no evidence suggesting that wolverines will not adapt sufficiently to diminished late spring snow pack (assuming there is any) to maintain viability." ("Assuming there is any": The governor wouldn't want to let anyone suggest he's in cahoots with those climate change alarmists, would he?)
Of course, there is no evidence yet, but the spatial logic is pretty simple: Let's start with the premise that there will be higher average temperatures and less snow. The governor of Wyoming may regard this as conjecture, but "at the most fundamental level, I think there's no uncertainty about the fact that it's going to get warmer," says Amy Snover, who heads the University of Washiington's Climate Change Group. "Where the questions come in is how much, how fast." This is hard to gauge, because we live in a highly variable climate and "that's not predictable." She explains that in the near term, natural variations may either mute or amplify the long-term patterns. But look far enough down the road, and bare ski slopes at Snoqualmie will be the norm.
And it's already starting to happen. "Climate change impacts to wolverine habitat are occurring now," says the U.S. Fish and Wildlife Service's Shawn Sartorious, a biologist based in Montana. "The point at which we're likely to see impacts to wolverines are down the line, but the habitat is being affected now."
If you're a species that wants colder weather, you either move up in latitude or move up in altitude. If it's latitude, that pushes habitat up above the Canadian border. If it's altitude, that pushes habitat farther up into the mountains. Think of a wide plain with mountains poking from it here and there. If critters are forced from the plain to the mountains, their habitat shrinks and fragments; they have effectively been isolated on islands.
Or, if they have already been living on islands of altitude, the pieces of their archipelagos become smaller and farther apart. This means that they have less habitat and more trouble maintaining connections among populations. Over the long term, preserving "connectivity" is key to preserving the genetic diversity that a population needs in order to survive.
At this point, Sartorious says, we still have substanial blocks of habitat that but, because a male wolverine's territory is so large, 100 square miles, those areas don't support a lot of individual animals. For that reason, he says — even in, say, the North Cascades, where snowpack will probably remain adequate throughout this century — "there's reason to think that maintenance of genetic diversity over a long term is going to be a concern."
What — apart from reducing greenhouse gas emissions — could government do for the wolverine if it were listed? It could keep people from deliberately killing them. In Montana, recreational trapping of wolverines is legal. It could preserve habitat and corridors between islands of habitat. Most is already protected in national parks and wilderness areas. And maybe it could shuttle wolverines among those islands, to prevent inbreeding of isolated populations. Consider it a kind of government dating service.
The politics, at least, seem relatively simple, says Tim Preso, managing attorney for Earthjustice's Northern Rockies office: Unlike wolves, wolverines don't evoke fears of dead sheep and cattle or family pets torn limb from limb. However, there's "always this jockeying between the states and the federal government" over regulatory control.
And there are state-level political considerations. For example, "Montana has this fish and wildlife agency that is supported by fisher and hunter dollars." Nevertheless, Preso says, listing wolverines "should be a no-brainer."