The wolverine is one of the rarest mammals in North America, estimated to number between 250-300 animals in the western continental US. While little information exists on the current distribution of wolverines, they are generally believed to occur in high elevation alpine and subalpine habitats of western Montana, central and northern Idaho, northwestern Wyoming, north-central Washington and northeastern Oregon.
Wolverines occupy large home ranges, with males covering as much as 800 mi2 and female home ranges typically 200-300 mi2. Wolverines remain active throughout the winter, traveling extensively across their home ranges in search of carrion that is their primary winter food source. In late February, pregnant female wolverines choose areas with deep snow such as north-facing slopes to dig tunnels down to jumbled talus boulders and fallen logs, creating insulated and safe havens for their 1-3 young, called kits. They maintain these snow-based dens through approximately mid-May, and most wolverine ecologists believe that wolverines exhibit a dependence upon snow for denning and reproduction. The snowpack likely also serves other important functions including preservation of carcasses or cached meat. The loss of wolverine habitat from climate change has been predicted based on the modeled loss of spring (mid-May) snow due to temperature and precipitation changes.
The rugged and remote habitats of the wolverine were naturally inhospitable to people and these areas were historically largely undisturbed by humans in the winter months. However, many wolverine habitats on previously-undisturbed and unreachable public lands are now accessible to humans for winter activities thanks to the growing popularity of winter backcountry recreation combined with advanced snowmobile technology and other mechanized options such as tracked vehicles (cat-skiing) and helicopters.
Given the potentially vulnerable status of the species and lack of scientific information regarding impacts of winter recreation, Round River saw a need and interest to develop a scientifically-robust understanding of wolverine responses to winter recreation in order to provide insights into approaches to management that ensure both winter recreation and wolverine populations may be sustained.
Partnering with the USFS Rocky Mountain Research Station, multiple Forests, Idaho Department of Fish and Game and other government and non-government collaborators, Round River led a Wolverine – Winter Recreation Study beginning in 2010 with the objective of identifying and evaluating wolverine responses to winter recreation. Specifically, we sought to: 1) increase the science-based understanding of the effects of winter recreation on wolverine populations through examining wolverine behaviors, habitat use and reproductive efforts within landscapes supporting a diversity of winter recreation activities; and 2) provide science-based information to guide public land management for the sustainability of both winter recreation and wolverine.
In the process, we developed a uniquely collaborative research effort across federal and state agencies, non-government organizations, winter recreationists and local businesses. This collaborative approach has been critical not only to the success of data collection efforts but also to the creation of opportunities for collaborative and creative problem solving when research-based management actions are considered.
The potential effects of winter recreation on wolverine reproduction, behavior, habitat use and populations are unknown but there is concern regarding the effects of winter recreation on wolverine, particularly in areas favored by females for reproductive denning. Currently, there is little scientific foundation for management of winter recreation for wolverine persistence and accounts of wolverine responses to human disturbance are primarily anecdotal and conflicting. Given the potentially vulnerable status of the species, there is the need and interest to develop a scientifically robust understanding of wolverine responses to winter recreation that can provide insights into approaches to management that ensure both winter recreation and wolverine populations may be sustained.
Over 6 winters (2010 – 2015) and four study areas, we GPS collared 24 individual wolverines over 39 animal-years to collect >54,000 GPS locations, one of the largest GPS datasets collected on wolverines in the lower 48 states. These wolverines were exposed to a diversity of winter recreation activities across our study areas spanning >1.1 million ha in Idaho, Wyoming and Montana. Simultaneously, we monitored and sampled winter recreation, collecting 5,899 GPS tracks from backcountry winter recreationists representing >198,000 km of recreation activity, in the most intensive and extensive backcountry winter recreation monitoring effort that we know of to date. Backcountry winter recreation information was also collected through trail use counts and aerial-based recreation surveys, and the combination of data allowed us to create maps of backcountry winter recreation portraying the extent and relative intensity of motorized recreation and non-motorized recreation within wolverine home ranges.
We used resource selection functions to model habitat selection of male and female wolverines within their home ranges. We first modeled habitat selection for environmental covariates to understand male and female habitat use then incorporated winter recreation covariates. We assessed the potential for indirect habitat loss from winter recreation and tested for functional responses of wolverines to differing levels and types of recreation. Motorized recreation occurred at higher intensity across a larger footprint than non‐motorized recreation in most wolverine home ranges. Wolverines avoided areas of both motorized and non‐motorized winter recreation with off‐road recreation eliciting a stronger response than road‐based recreation. Female wolverines exhibited stronger avoidance of off‐road motorized recreation and experienced higher indirect habitat loss than male wolverines. Wolverines showed negative functional responses to the level of recreation exposure within the home range, with female wolverines showing the strongest functional response to motorized winter recreation. We suggest indirect habitat loss, particularly to females, could be of concern in areas with higher recreation levels. We speculate that the potential for backcountry winter recreation to affect wolverines may increase under climate change if reduced snowpack concentrates winter recreationists and wolverines in the remaining areas of persistent snow cover.
We continue to work alongside the Idaho Department of Fish and Game and the US Forest Service and recreation partners to reduce the impacts of backcountry winter recreation on wolverines and other wildlife particularly in areas predicted to have resilient snowpack into the future. Our approach is to use our knowledge of wolverine habitat use as an umbrella for conservation of high elevation species especially susceptible to climate change, through improved management of national forest lands.
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