Pity the wolverine (Gulo gulo). This tough, antisocial, wandering predator (also known as the "skunk bear" or the "carcajou") has been on the decline in the U.S. for more than a century. Currently, according to the U.S. Fish and Wildlife Service (FWS), there are fewer 300 of these critters in the country, and last week the FWS acknowledged that the species deserved protection under the Endangered Species Act (ESA). But the FWS also said that wolverines won't be getting that insurance just yet. Instead, the service has added the wolverine to the ESA candidate list, citing that other species have a "higher priority."

The FWS's denial is the latest result of a long chain of lawsuits and court rulings as environmental groups have spent more than a decade seeking to protect the wolverine under the ESA.

Long the victim of fur hunters and habitat fragmentation, the wolverine's greatest threat these days is climate change. The FWS review "found that the wolverine in the contiguous U.S. is primarily threatened by the impact of climate warming on its alpine habitat." The wolverine is well adapted to snowy, alpine conditions, and females depend on deep snow to dig dens and raise their young.

The wolverine's status will be reviewed by FWS on an annual basis. But as has been the case many times in recent years, candidate animals rarely make it onto the endangered species list.

Meanwhile, does the wolverine have enough time to wait for annual reviews and the long chain of decision-making that would follow each year's findings? When I last wrote about wolverines in 2008, the U.S. population for the species was estimated at 500 to 1,000 animals. A 2006 study in the journal Conservation Genetics suggested that the wolverine gene pool in the U.S. was already too small and spread out, making it vulnerable to genetic drift—the loss of key genetic material as individuals lose the chance to breed. According to that study's authors, wolverines require conservation management and the introduction of animals from Canada (where most wolverines live) in order to survive. Specifically, "at least 400 breeding pairs, or one to two effective migrants per generation, would be needed to ensure genetic viability in the long-term for each of the populations in the United States."

If the FWS is correct and there are now just 300 wolverines remaining in the U.S., we are well below the 800 breeding wolverines needed for the species to survive in this country.

Where did all of those wolverines go? Trapping is still legal and, according to a study published in the September 2007 issue of the Journal of Wildlife Management, accounted for a 30 percent annual drop in wolverine populations in Montana alone between 2002 and 2005.

Of course, even if the wolverine were ESA-protected, actually implementing that protection is a tall order. We're talking about a species that doesn't like to be around its own kind and thinks nothing of taking a 300-kilometer walk to find a suitable lunch. Wolverines aren't exactly an easy species to protect.

The other problem is that wolverines are a most difficult species to study due what the Wolverine Foundation calls their "elusive nature, small population size and uncanny mobility"—not to mention the logistical challenges of gathering information in remote, frozen areas like Glacier National Park. So solid scientific information on their habits, habitats and threats is expensive to gather, and agencies lack the money necessary to do the job well. Without better information, getting the wolverine on the endangered species list seems unlikely.

No matter what happens with the ESA, climate change will take a massive toll on wolverines over the next 90 years. According to the FWS:

"Data and analysis requested from the University of Washington Climate Impacts Group and the U.S. Forest Service Rocky Mountain Research Station predict a reduction of wolverines' cold and snowy habitat of 63 percent by 2099. As wolverine habitat is reduced, the Service expects the remaining habitat will become more fragmented, with distances growing between habitat 'islands'. Evidence suggests this diminished and fragmented habitat will support fewer wolverines with reduced connectivity between populations. The impact of climate warming may exacerbate the impact of other threats, such as recreational use of habitat, infrastructure development and transportation corridors."

Once found throughout the northwestern U.S., wolverines are currently only located in Montana, Idaho and Wyoming, along with Alaska. (California and Utah each have a single known wolverine.) The species has also largely disappeared from eastern Canada, leaving most of the Western Hemisphere population in the nation's west, where about 15,000 to 19,000 wolverines still reside. A separate wolverine subspecies also exists in Russia's Siberia and Nordic Europe; its population is around 3,500 animals.

Photo by Steve Kroschel © U.S. Fish and Wildlife Service Mountain Prairie, via Flickr