10-year study in North Cascades is coming to an end
By Ann McCreary
A healthy male wolverine was captured and fitted with a radio collar last week, the first wolverine to be captured this winter as part of an ongoing study of the elusive mammals in the North Cascades.
The 30-pound wolverine was caught in a trap near Easy Pass, west of Rainy Pass, on Super Bowl Sunday, said Scott Fitkin, a wildlife biologist with the Washington Department of Fish and Wildlife (WDFW), and part of the research team.
The wolverine is likely the same animal that was caught — strangely enough — on Super Bowl Sunday three years ago, Fitkin said. “That was an interesting anomaly,” he said.
The research team was unable to immobilize the animal well enough when it was first caught in 2012 to fit it with a collar, but obtained DNA samples at the time that will be analyzed to determine if it is the same wolverine, he said.
This winter is the tenth and final year of the North Cascades Wolverine Study, which has provided valuable insights into wolverine behavior and habitat.
Each winter researchers set sturdy wooden traps in high mountain locations, baiting them with deer or beaver parts and installing cameras.
When an animal enters and the trap closes, a satellite signal alerts the team, and members ride snowmobiles to the trap. The wolverines are immobilized and examined, DNA samples are taken, and they are fitted with radio collars and ear tags before being released.
“In the nine years we have 27 captures of 14 different animals,” said John Rohrer, a U.S. Forest Service biologist and field coordinator for the study. The team has named each captured animal and some have been trapped numerous times. This has allowed researchers to monitor them over an extended period of time.
Rocky, captured during the first winter of the study in 2006, was caught seven times and his son, Logan, has also been caught seven times. Although wolverines are notoriously ferocious, Rohrer says the team members are always glad when they see the familiar, snarling faces of wolverines they have monitored over the years.
The ongoing research has revealed much about the social lives of wolverines, Rohrer said. “That’s one of the most interesting things in the study for me,” he said.
Through DNA analysis, they know that several of the animals they have captured are related — part of an extended wolverine family.
Rocky is known through DNA to be the father of the most recently captured wolverine, named Special K, although the mother is not known, Rohrer said. Rocky fathered Logan with a female called Melanie, and fathered another male named Dasher with a female called Xena.
“The last time we saw Rocky was with Dasher at the Twisp River trap” in February of 2013, Rohrer said. The two were photographed by a camera at the trap. Dasher was less than a year old and researchers think Rocky would have been about 10 years old at the time — a ripe old age for a wolverine.
Observing Rocky traveling with his offspring provided evidence that has altered previous beliefs about the parenting style of wolverines, Rohrer said.
“We used to think wolverines, especially males, were totally solitary. More recent research, including ours, shows males actually do assist with parental duties. They don’t totally ignore their offspring,” Rohrer said.
The radio collar on Rocky provided insights into the movements of wolverines, who travel expansively throughout their habitat, Rohrer said. Rocky moved from the crest of the North Cascades into Canada, then appeared along the Highway 20 corridor, then was found in the Twisp River drainage, returned back to Canada and was last seen back in the Twisp River basin.
“They must shift around in relation to where the females are,” or look for territory not already inhabited by another male, Rohrer said.
“Logan took over his dad’s area and we didn’t see Rocky any more. We don’t know if Logan drove him off or if Rocky died,” Rohrer said.
Before his radio collar died last November, Logan appeared to have relocated to the headwaters of the Stehekin River. “And now we have this other big male,” that was captured last week and may have moved into the territory formerly occupied by Logan.
The research team was successful in documenting two high-elevation den sites in 2012, and captured photos of Xena emerging from her den, carrying a kit. This was the first documented wolverine den in the North Cascades.
The most significant aspect of the wolverine study is “documenting their recolonization of the Cascades,” Rohrer said.
“When we started out we weren’t sure if we could effectively trap wolverines, or whether satellite telemetry would work in this rugged country,” he said.
Believed to be totally extirpated in the North Cascades by the early 1900s by trapping, poisoning and shooting, wolverines appear to be re-establishing here, Rohrer said.
“Each year we’ve caught new wolverines, in addition to catching the same ones,” Rohrer said.
The current population may derive from wolverines in Canada, Rohrer said. DNA studies of museum specimens of wolverines from the Cascades show a different genetic lineage than the current residents, he said. “The original wolverines are gone,” he said.
Rohrer said the origination of today’s wolverines is among the questions that will likely be explored further by the study’s principal investigator, Keith Aubrey, a research biologist with the Pacific Northwest Research Station. Aubrey will be writing scientific papers about the project after it is completed, Rohrer said.
The impact of climate change on wolverines and their habitat is also a question to be further examined, Rohrer said.
To create natal dens and rear their young, wolverines require deep, high-elevation snowpack that lasts late into the spring. Climate change models predict that mountain snowpacks will shrink significantly as the planet warms.
“We think climate change is happening now and making it not as hospitable for wolverines,” Rohrer said. “Their range seems to be constricting. At the same time we’re seeing them re-colonize and expand. It’s a kind of dichotomy.”
The apparent expansion could be due to wolverines moving into an area that was empty after humans exterminated all the resident wolverines, he said.
“At some point it may be saturated. Maybe it is now,” Rohrer said.
From his own experience in making many trips on snowmobiles to check traps in the high mountains as part of the study, Rohrer said the winters appear to be changing. “It didn’t rain in February 10 years ago,” he said.
Some wildlife researchers are exploring ways to try to monitor wolverines in the summer, to continue gathering research after the winter trapping study comes to an end this year.
In the winter, the wolverines can be lured by their favorite meal — big hunks of decaying meat. In the summer, however, bears have come out of hibernation and will grab the bait first, making summer monitoring more challenging, Rohrer said.
Rohrer said the research team hopes to make a few more captures this winter. The team has two traps up Twisp River, two along the Highway 20 corridor, three at Hart’s Pass and one at Billygoat Trailhead.
The project has meant that Rohrer and Fitkin haven’t been able to travel far away during winter, because they need to be available to respond quickly if a wolverine is caught. Still, Rohrer said, he’ll be sad to see the study come to an end this spring.
“It’s been a great project. I’ll be sorry it’s over.”