Wolverine Distribution and Ecology in the North Cascades Ecosystem: 2014 Annual Report

The wolverine (Gulo gulo) is one of the rarest mammals in North America and the least known of the large carnivores (Banci 1994). The wolverine is considered a sensitive species in the Pacific Northwest Region by the U.S. Forest Service, and a candidate species for listing as threatened or endangered by the state of Washington. On 13 August 2014, the U.S. Fish and Wildlife Service (USFWS) withdrew their 2013 proposed rule to list wolverine populations in the contiguous U.S. as “Threatened” under the Endangered Species Act (ESA; U.S. Fish and Wildlife Service 2013, 2014). The USFWS stated that “while there is significant evidence that the climate within the larger range of the wolverine is changing, affecting snow patterns and associated wolverine habitat, the specific response or sensitivity of wolverines to these forecasted changes involves considerable uncertainty at this time” (U.S. Fish and Wildlife Service 2014). On 14 October 2014, a coalition of 8 conservation groups filed a lawsuit challenging the USFWS’s decision to withdraw their proposed rule to list the wolverine in the contiguous U.S. under the ESA.

The northern Cascade Range in Washington represents the southernmost extent of current wolverine range along the Pacific coast of North America (Aubry et al. 2007). Prior to our research, wolverines had never been studied in the field in this region, due partly to their low densities and extremely limited access into the unroaded wilderness areas where they occur during all periods of the year. Recent telemetry studies of wolverines in the Rocky Mountains of British Columbia (Krebs et al. 2007) and the United States (Copeland 1996, Copeland et al. 2007, Squires et al. 2007) indicate that wolverines are wide-ranging, inhabit remote areas near timberline, give birth to young during winter in subnivean dens, and may be sensitive to human disturbance at natal and maternal den sites. Winter recreation activities are widespread in the northern Cascade Range and often occur in suitable wolverine denning habitat. Such activities may affect wolverines or their use of preferred habitat.

Snowtracking and remote-camera surveys conducted from 1995 to 2005, coupled with a review of historical occurrence records in Forest Service files, resulted in a number of highly credible wolverine observations (many verifiable) from areas near the Cascade Crest on the Methow Valley Ranger District of the Okanogan-Wenatchee National Forest. Consequently, we chose this area to evaluate the feasibility of trapping wolverines during winter in the northern Cascade Range. The first year of the study (2005/06) was successful, so we have continued to use this area as the center of a greatly expanded study area that we are currently using to monitor wolverine movements with satellite telemetry, estimate home ranges, and investigate patterns of habitat use.

Although all verifiable records of wolverine occurrence in Washington obtained prior to 2005 were from areas near the Cascade Crest, DNA analysis confirmed that a sample of hair collected in 2005 in the Kettle Range near Danville in Ferry Co. was from a wolverine (C. Loggers, U.S. Forest Service, personal communication). This record suggested that wolverines may be more broadly distributed in Washington than we thought. Thus, an additional objective of our study was to expand our trapping area and establish trap sites as far east of the Cascade Crest as feasible, in hopes of capturing individuals or family groups that occur outside the Pasayten Wilderness. Also, findings from our research to date indicate that wolverines in the northern Cascades of Washington appear to be part of a larger population that includes portions of British Columbia and, possibly, Alberta.

As in Washington, however, relatively little is known about the population status or ecology of wolverines in southwestern Canada. Consequently, in year 4 (winter 2008/09), we expanded the geographic scope of our study by establishing a collaborative relationship with forest carnivore biologists at the B.C. Ministry of Environment (Eric Lofroth and Rich Weir) and at the B.C. Ministry of Forests, Lands and Natural Resource Operations (Cliff Nietvelt). Field crews in British Columbia follow our study protocols, and all data are sent to the Pacific Northwest Research Station to be integrated with data collected in Washington. This progress report is cumulative, and includes results from the first 9 years of research (winters of 2005/06 thru 2013/14) on wolverine distribution and ecology in the North Cascades Ecosystem.