Story is courtesy of Cathy Raley & Keith Aubry of the Pacific Northwest Research Station (United States Department of Agriculture, Forest Service) in Olympia, Washington).

 

NORTH CASCADES WOLVERINE STUDY

The wolverine is one of the rarest mammals in North America.  Currently, wolverine populations in the contiguous U.S. are being evaluated by the U.S. Fish and Wildlife Service to determine if they should be listed under the Endangered Species Act. 

 

The northern Cascade Range in Washington was not only a focal area of wolverine occurrence historically, it also represents the southernmost extent of current wolverine range along the Pacific coast; however, wolverine distribution and ecology in this region is poorly understood.  Prior to our work, wolverines had never been studied in the field in this region, due to their low densities, the remoteness of their primary habitat (alpine meadows and subalpine forests with snow cover that persists into spring), heavy and frequent winter snowfalls, and limited access during all periods of the year into the unroaded wilderness areas where they occur.  Thus, the most effective way to obtain reliable data on wolverines in this challenging environment was to live-capture individuals and fit them with Argos satellite collars. 

 

We worked with Sirtrack® to customize Argos-compatible satellite collars for deployment on wolverines, which included tailoring the collar material and width to reduce potential irritation to the neck area as well as reducing the weight and size of the transmitter package to minimize potential interference with a wolverine’s daily activities (i.e., wolverines range over large areas, they are primarily scavengers but also hunt live prey, and females need to access small spaces as they locate their reproductive dens under fallen trees or boulders buried under the snowpack).

 

The resulting collar design we used for the majority of our 10-year study weighed 205 grams which is 2% of the average weight (8.8 kg) of female wolverines in our study area.  When operated continuously at a repetition rate of 60 seconds, the life of the satellite transmitter in a collar of this size is limited to 78 days.  Consequently, to enable us to monitor wolverine movements during as much of the year as possible, we programmed the transmitter to be on for 14 hours (0500-1900 PST) every other day which extended the transmitter life to 255 days. 

 

Wolverines are active day or night; however, in the initial years of our study when experimenting with different duty cycles, we discovered that we obtained more high-quality locations (Argos accuracy classes 3, 2, and 1) between 0600 and 1800 hours.  This pattern could reflect the limitation of satellite coverage in the steep mountain terrain of our study area, patterns of wolverine behavior, or both.  For example, wolverines may be less active during the night and potentially resting in a position that obstructs the ability of Argos satellites to pick up transmission signals from the collar’s antenna (see photo of a collar on a wolverine).

 

From 2006 thru 2015, we live-captured and monitored 14 individual wolverines and located the first wolverine reproductive dens ever documented for this region. The resident wolverines in our study population occupied an area of about 8,211 km2 extending from Manning Provincial Park in southern British Columbia south to the Wenatchee Lake area in Washington State.  We obtained almost 3,000 high-quality locations (Argos accuracy classes 3, 2, and 1) enabling us to calculate wolverine activity areas. Resident wolverines used large areas and male activity areas (1,149–2,992 km2 in extent) overlapped those of one of more females (293-1,969 km2 in extent). Using Argos satellite collars also enabled us to track two subadults that made long-distance movements well to the north of our study area (a female traveled >483km and a male >563km), suggesting that our study population may be connected with wolverines in the Coast Range of British Columbia. Because wolverines have large spatial requirements and are sensitive to anthropogenic influences, they are often considered an “umbrella” species. Thus, wolverines may be a valuable focal species for large-scale ecosystem management and planning, as well as an indicator of effective wilderness area management.