Recent studies indicating wolverines could lose their snowy habitat due to climate change prompted the U.S. Fish and Wildlife Service (FWS) to propose listing the rare carnivores as a threatened species last February.
Last week, FWS reopened the public comment period on the proposal, in part due to questions about how federal wildlife officials interpreted the impacts of climate change on wolverines.
During the initial comment period, which ended May 6, FWS received comments questioning whether the survival of wolverines depends on late spring snow packs. Climate change models predict those snow packs will recede as Earth’s temperature rises. In order to take additional information on those issues, FWS is accepting further comment until Dec. 2.
In its proposal to protect wolverines as a threatened species, federal wildlife officials relied on studies that show wolverines rely on deep winter snow that lasts into May to build dens where they raise their young. Research for some of those studies is being conducted here in the mountains surrounding the Methow Valley, where the North Cascades Wolverine Study has been underway for eight years.
The study has resulted in the capture and radio collaring of 13 wolverines, some of which have been captured more than once. Led by Keith Aubry, a research biologist with the Pacific Northwest Research Station in Olympia, the study is providing information about wolverine behavior and habitat.
Based on research by Aubry and other biologists, FWS concluded that  “deep, persistent, and reliable spring snow cover (April 15 to May 14) is the best overall predictor of wolverine occurrence in the contiguous United States.”
In announcing its decision to reopen public comment on the proposal to list wolverines as threatened, FWS said some commenters questioned “our determination that wolverines are dependent on persistent late spring snow.”
Two winters ago, researchers with the North Cascades study documented two high-elevation den sites dug into deep snow by females that had previously been captured through the study. These were the first documented wolverine dens in the Northwest, and cameras set near the dens caught video of one female, named Xena by the researchers, emerging from her den carrying a kit.
The research team plans to set eight or nine traps this winter in the mountains around Harts Pass, along the North Cascades Highway, and up Twisp River, said John Rohrer, a U.S. Forest Service biologist in the Methow Valley and field coordinator for the study.
The team monitors the traps and when a wolverine is captured, the researchers travel to it on snowmobiles with the goal of examining it and placing identifying ear tags and a radio telemetry collar on the wolverine before releasing it. The collar allows researchers to monitor the animal for several months.
The team also installs wildlife cameras in known wolverine territory, and one of those cameras produced some intriguing footage last winter, Rohrer said. The video showed Rocky, the first wolverine captured by the researchers when they began the study in 2006, traveling with a younger male wolverine that had been captured the previous winter and named Dasher by the biologists.
The biologists believe that Dasher is the offspring of Xena and Rocky, based on DNA samples taken from the wolverines. “We’re pretty much 99 percent sure they’re father and son,” Rohrer said.
That discovery has biologists questioning their previous assumptions that male wolverines are “quintessential solitary carnivores,” Aubry said.
There was no evidence that wolverines involved in the North Cascades study gave birth last year. “Bringing off kits is a pretty physiologically expensive deal, so they don’t do it every year,” Rohrer said.
Research indicates wolverines need the deep snow to last into late spring to maintain their dens while their kits are young and vulnerable.
The likelihood of reduced snow pack and earlier spring snow melt predicted by climate change models was a key reason for the decision by federal officials to propose protecting wolverines as threatened.
FWS said it is specifically interested in comments on issues related to wolverines’ reliance on late spring snow and whether projected impacts of climate change will result in loss of wolverine habitat.
Copies of the notice and proposed rules are online at http://www.regulations.gov. Copies of the proposed rules are also available at http://www.fws.gov/mountain-prairie/species/mammals/wolverine/.