With thick fur and snowshoe-like feet, wolverines are well-adapted to live in snow caves and run straight up mountains. Their high elevation lifestyles have helped them stay out of harm’s way in recent decades, and stage a slow comeback from the rampant carnivore persecution of the early 1900s. Though elusive and tenacious, they won’t be insulated from human impacts forever. They face a precarious future as climate change eats away at the snowpack they need.
That’s why the U.S. Fish and Wildlife Service is proposing to add them to the endangered species list, even as a handful of wide-ranging wolverines are venturing into states where they haven’t been seen for generations. The agency was slated to make a listing decision earlier this month as part of a legal settlement with environmental groups. But reputable wolverine biologists have criticized the scientific underpinnings of the agency’s proposed listing decision, especially the parts related to snowpack. Now, the FWS is delaying the decision for another six months so they can reconvene with scientists about wolverine habitat and climate impacts to it.
If wolverines are listed, they will join polar bears in having the dubious distinction of receiving federal protection in the name of climate change. Even if that can’t do much to curb climate impacts, it would renew discussions about federal and state wildlife managers reintroducing experimental populations of wolverines in higher elevation refuges like Colorado, to help maximize their survival prospects in the U.S.
A listing will also send a strong message about the fragile future of mountain snowpack that so many people depend on for water. But the prospect of a decision based on climate models, rather than more traditional, tangible, threats is already attracting attention. As Bob Inman, a wolverine biologist for the Wildlife Conservation Society in Montana wrote in his peer review comments, “The magnitude of the precedent that this ruling establishes warrants careful scrutiny.”
In an October letter to a U.S. House working group that’s looking at Endangered Species Act reforms, Alaska’s Fish and Game director expressed concern about listing based on models asking, “Ultimately, what species could not be listed due to future threats such as climate change?”
In addition to the controversial nature of a listing based on climate models, the current science on wolverines isn’t as complete as for other carnivores. Though wolverines are not at risk in Canada and Alaska, there are likely fewer than 300 of the naturally rare weasel-relatives in Idaho, Montana, Wyoming and the North Cascades. Since wolverine research is in its early days, due in part to the animal’s remote, rugged habitat, even biological basics like population estimates are sketchy. It’s clear that wolverines rely on snow for survival, but the arguments begin when you ask exactly why they need that snow, and how risky it is for them when it melts earlier in the spring.
Researchers have found evidence that wolverines need long-lasting spring snow cover for dens where they birth and raise their young. In late February and March females take to snow tunnels on talus slopes and avalanche ravines to give birth, and then wean their young in late April and May. In one study, satellite-based maps of late-April to mid-May snow cover were overlain with the locations of 562 wolverine dens in North America and Scandinavia. Ninety-five percent of the dens were in areas where the satellite map showed snow cover as late as May 15.
Though the study didn’t explain why that close relationship between wolverine dens and spring snowpack exists, the authors saw it as additional evidence that spring snowpack limits where wolverines can live. Scientists have even found that during summer wolverines stay in the areas that once had spring snow.
If wolverine survival depends on dens that provide warmth and protection from predators into spring, then climate change that reduces spring snowpack in the high country could harm wolverine populations. One study tried to predict those impacts by using climate models to describe how wolverine habitat, i.e. spring snow cover, will shrink in the next century. They estimated that between 2030 and 2059, warming will eat up 31 percent of today’s wolverine habitat in the Lower 48. Central Idaho was among the most impacted places, but parts of Montana, like the wolverine stronghold that is Glacier National Park, look poised to fare better, as do the North Cascades. Colorado’s high elevations also retained spring snow pack in the models, which encourages conservationists to consider a wolverine reintroduction there.
In their listing proposal the Fish and Wildlife Service stated that wolverine habitat is likely to get smaller and more fragmented, based on that latter study and other research focused on spring snowpack declines. The agency cited trapping as a secondary risk (Montana has a wolverine season, though it’s suspended in light of listing). Recreational impacts from backcountry skiing and snowmobiling, while poorly understood and being studied now, are not considered to be major problems for wolverines.
While five of the peer reviewers of the FWS proposal last February agreed with most of its scientific basis, two others were not pleased that the agency used the aforementioned studies. A particular sticking point was whether mid-May snowpack is the best measure to accurately predict future wolverine habitat.
Though he was a co-author on the paper that described the relationship between May snowpack and wolverine habitat, Bob Inman was highly critical of its use as the foundation for the listing rule. Though he wrote “Wolverines are linked to snow. This is not in doubt,” Inman has his own ideas about why they need it. He thinks wolverines may be limited by food, and thus the ability to hide and preserve scavenged meat in snow banks. If the explanation behind why wolverines need snowpack is not known, he said, “then we do not know how or when climate change will impact wolverines.” (It’s worth noting that there’s nothing to say that wolverines don’t need snowpack for denning and food storage.)
Inman’s critiques blindsided his colleague, Jeff Copeland, a former Forest Service scientist, now the director of the Idaho-based non-profit Wolverine Foundation. Copeland points out that Inman’s ideas about food storage are opinion-based – they haven’t been tested yet. Plus, the model that’s being criticized aligns with wolverine biology. “If the wolverine is capable of adapting to the snow-free environment we should see that happening,” he says. “You’d be seeing them at very low elevations where there isn’t persistent snow.”
Montana Fish Wildlife and Parks has taken up many of the arguments of critical reviewers in their opposition to wolverine listing.
The debate over why wolverines need snow, when they need it, or how much they need, isn’t likely to be settled before the U.S. Fish and Wildlife Service has to make a decision, with help from other scientists, in August. And while the agency doesn’t have as much certainty as they’d like about why wolverines need cold and snow, they do know this, as Shawn Sartorius, a Helena-based FWS biologist involved in the listing decision, puts it: “Where you don’t have those conditions you don’t have wolverines.”
Sarah Jane Keller is a correspondent for High Country News. She tweets @sjanekeller.