Wolverine Distribution and Ecology in the North Cascades Ecosystem

The wolverine (Gulo gulo) is one of the scarcest mammals in North America as well as the least known of the large carnivores. The species is considered sensitive in the Pacific Northwest Region  and is a candidate species for listing as threatened or endangered by the state of Washington in the United States.

The northern Cascade Range in Washington is the southernmost wolverine habitat in North America. However, due to the species’ low density and the extremely limited access to unroaded wilderness areas, no information about wolverines was available, which was one of the reasons this research project was initiated.

Wolverines prefer wide-ranging, uninhabited, remote areas near timberline. They give birth during winter in subnivean dens and are likely to be sensitive to human disturbance at natal and maternal den sites.

The study area was located in the northern Cascade Range, mainly on the Methow Valley Ranger District of the Okanogan-Wenatchee National Forest in Washington. During the study, the investigated area was enlarged due to the fact that wolverine populations may be more widely distributed in Washington than thought. The study area was expanded as far east of the Cascade Crest as possible and portions of southern British Columbia were included. Data in BC were collected on behalf of the BC Ministry of Environment and the BC Ministry of Forests, Lands and Natural Resource Operations. Data were sent to and evaluated in the Pacific Northwest Research Station.

Habitat vegetation involves bitterbrush/bluebunch wheatgrass at lower elevations, mixed-conifer forests at mid- to high elevations, and alpine meadows, rocky ridges, peaks, and small glaciers at the highest elevations.

In order to get an overview about wolverine behaviour, livetraps were installed: 12 traps were established in Washington and 15 in British Columbia. Traps were placed in locations that had been documented as wolverine habitat, and some of them were relocated due to poor wolverine activity.

Either prefabricated traps with milled lumber (BC) or traps directly built in the trapping spots (Washington) were used. Bait consisted of road-killed mule deer, beaver carcasses, and salmon carcasses. Traps were visited twice a week to check functionality. Captured wolverines were immobilized with a mixture of ketamine and medetomidine (Washington) or Telazol (BC). Tissue samples were taken from all wolverines for genetic profiling and data on sex, age, and condition was collected.

Furthermore, captured animals were marked with a small, colored plastic tag to each ear, and Sirtrack telemetry collars containing both Argos satellite transmitters and standard VHF transmitters.

Standardized photographs of wolverines’ throats and chest markings were captured to distinguish individuals.

Trapping season usually began in January and continued into late-march or early April.

In Washington, over 10 winter field seasons, 13 different wolverines were trapped at 39 occasions, whereas in British Columbia, during a 4-year period, 3 individuals were trapped. Two of the three in BC had also been captured in Washington. As several wolverines were captured more than once in the same area, the existence of a resident population is very likely in Washington. The first year consisted of a failing data collection, as the collars were not useful, which resulted in the development of better collars that were successfully used later on. Already in the second study year, reliable data could be documented. Two reproductive dens were located and both field and genetic research concluded that one of the males was the father of two females, as offspring was sampled as well. However, home ranges may be difficult to establish due to the wide spread of individuals.

The conservation of wolverines in the northwest of North America relies on sincere knowledge of their distribution, population status, and habitat relations. Thus, it is crucial that long-term field research is implemented and potential study area is expanded.

  • Source Keith B. Aubry, John Rohrer, Catherine M. Raley, Scott Fitkin. February 2016. Wolverine Distribution and Ecology in the North Cascades Ecosystem - Final Progress Report. Available at : https://wolverinefoundation.org/wp-content/uploads/2011/02/NorthCascadesWolverineStudy_Final-Progress-Report2012-2016.pdf [Accessed 03/2021].