PNW Pacific Northwest Research Station INSIDE Mapping Changes in Wolverine Distribution.... 2 Sleuthing for Habitat Clues................................... 3 The Importance of Spring Snow Cover............... 4 Implications of Global Climate Change............. 5 FINDINGS issue one hundred fourteen / july 2009 “Science affects the way we think together.” Lewis Thomas ON THE TRACK OF THE ELUSIVE WOLVERINE I N S U M M A R Y John Rohrer The wolverine is one of the rarest and least- known mammals in North America. A lack of understanding regarding its historical distribution in the contiguous United States and its broad-scale habitat needs has ham- pered conservation efforts. Using a suite of research methods, including the assemblage of historical data on wolverine occurrence, analyses of habitat factors, GIS mapping, radio-telemetry tracking, and genetic studies, researchers were able to address these information gaps. Their findings show that historically, wolver- ines occurred primarily in high-elevation areas of the major western mountain ranges and in the Great Lakes region, where spring Snow cover that lingers into May is a defining habitat feature for wolverines in the contiguous United States. snow cover persisted throughout the animals’ reproductive denning period. By the mid- 1900s, the wolverine’s range was dramatically "Picture a weasel—and most of us attacking humans. However, most of these diminished, owing probably to high levels can do that, for we have met stories are either misunderstandings of wolverine behavior or tall tales. Although of human-caused mortality and low or that little demon of destruction, there have undoubtedly been altercations nonexistent immigration rates. that small atom of insensate between wolverines and bears or wolves Today, wolverines survive in high-elevation courage, that symbol of slaughter, over potential food sources, wolverines pockets of northern Washington, northwestern sleeplessness, and tireless, incred- do not try to compete directly with these Montana, south-central Idaho, and north- ible activity—picture that scrap much larger predators—in fact, wolverines are primarily scavengers. Their long western Wyoming. Throughout the year, of demoniac fury, multiply that canine teeth and claws, a sense of smell wolverines stay within areas characterized mite some fifty times, and you so acute they can sniff out animals buried by persistent spring snow cover, even when have the likeness of a Wolverine." under 6 feet of snow, and muscular jaws dispersing to new locales, and avoid areas —Ernest Thompson Seton capable of breaking bone and tearing with warmer temperatures to prevent thermal apart even frozen flesh—likely earned stress. This narrowly defined “bioclimatic he wolverine has a near-mythical wolverines their scientific name: Gulo envelope” suggests the wolverine’s range reputation. Stories abound of gulo, meaning “gluttonous glutton.” will retreat northward in the face of climate wolverines chasing down or Related to weasels and otters, wolverines T change, but it also offers an empirical basis leaping on the backs of animals as large resemble small bears with bushy tails, and for initiating new conservation efforts. as moose, harassing bears and wolves over the musky odor they exude has elicited prey, ravaging hunters’ cabins, and even such nicknames as “skunk-bear.” The wolverine has long played its ecological role as scavenger, predator, and nutrient KEY FINDINGS recycler in boreal regions from Mongolia and Siberia to Scandinavia and North America. • Contrary to previous beliefs, the historical range of the wolverine in the West was But the wolverine’s unwarranted reputation as limited to discontinuous, high-elevation areas of the Rocky Mountains, Cascade a particularly fierce and dangerous carnivore, Range, and Sierra Nevada, primarily in areas of alpine habitat and snow cover and their propensity to raid traplines set for that persists until mid-May. marten and other valuable furbearers, steal food from cabins, and spray musk and urine • The historical wolverine population in California was genetically unique and on the remaining contents made human- highly isolated for millennia. wolverine conflicts inevitable. As a result, wolverines were persecuted during the • Wolverines were extirpated from their historical range in California, Colorado, settlement of the West, and by 1930, they and Utah by 1930. had been eliminated from most of their former range in the contiguous United States. • In the contiguous United States, wolverines currently occur only in northern The wolverine is one of the rarest and least- Washington, northwestern Montana, south-central Idaho, and northwestern known mammals in North America. Its sparse Wyoming. An ongoing field study in the North Cascades has confirmed the populations and secretive habits make finding existence of a resident population in Washington. and observing the animal tricky at best. Past • Correlations between reproductive denning sites and telemetry data from efforts to map their historical range in the throughout the wolverine’s circumboreal range indicate that the distribution of contiguous United States produced sketchy spring snow cover defines Gulo gulo’s bioclimatic envelope. In addition, genetic and often contradictory results. Similarly, analyses indicate that these areas also serve as the species’ primary pathways the habitat conditions that affect wolverine for dispersal. distribution and abundance were poorly understood. This lack of information became critical when petitioners sought in 1994, and again in 2000, to list Gulo gulo under the research wildlife biologist Keith Aubry at ecology in the contiguous United States. Endangered Species Act. In rejecting both the Pacific Northwest Research Station in Among other findings, these studies provided petitions, federal officials concluded that Olympia, Washington, in collaboration with the first reliable and comprehensive maps of there simply wasn’t enough known about Kevin McKelvey, Jeff Copeland, and Mike the wolverine’s past and present distribution the wolverine to determine whether it was Schwartz at the Rocky Mountain Research in the “lower 48,” and revealed specific endangered or not. In 2004, a program of Station in Missoula, Montana, and others environmental factors that support the research on the wolverine was begun by to increase our understanding of wolverine species’ survival. MAPPING CHANGES IN WOLVERINE DISTRIBUTION any previous range maps for the were available from trappers and other wolverine basically ‘connected the early pioneers who had killed or captured Purpose of PNW Science Findings ‘‘ dots’ among geographic locations wolverines, and from the USBS biologists who M To provide scientific information to people associated with museum specimens or charted furbearer populations during the late who make and influence decisions about encounters with wolverines,” Aubry says, 1800s and early 1900s. In all, the researchers managing land. “but for a wide-ranging carnivore that may compiled 729 reliable records of wolverine make long-distance movements to places occurrence dating from 1827 to 2005. PNW Science Findings is published where they don’t actually reside, such range monthly by: The next step was to organize the records in maps can be very misleading.” To identify Pacific Northwest Research Station space and time. The records were grouped the areas that were occupied by wolverines USDA Forest Service into three major periods: historical (1827 to historically, Aubry’s team tracked down P.O. Box 3890 1960), recent (1961 to 1994), and current Portland, Oregon 97208 specimen records, photos, and written (1995 to 2005). Mapping the geographic accounts of wolverines being killed or Send new subscriptions and change of locations associated with the records showed captured. They searched in 114 museums address information to: that wolverines once traversed terrain in and combed through the published and [email protected] 24 states, spanning parts of the western unpublished literature, the archives of state mountains, northern Great Plains, and and federal resource management agencies, Rhonda Mazza, editor; [email protected] Great Lakes region, as well as the upper and the archives of the U.S. Biological Survey Keith Routman, layout; [email protected] Midwest and Northeast. However, as previous (USBS) at the Smithsonian Institution in researchers had suspected, the new data Washington, DC. showed that, by the mid-1900s, Gulo gulo’s United States Forest Fewer than 100 museum specimens exist range in the contiguous United States had Department Service from the lower 48, but numerous reports shrunk dramatically. of Agriculture Science Findings is online at: http://www.fs.fed.us/pnw/ The site also includes Science Update—scientific knowledge for pressing decisions about controversial natural resource and environmental issues. 2 SLEUTHING FOR HABITAT CLUES o home in on the environmental features that determine the wolverine’s distribution, the team employed three broad- T scale habitat maps: one that depicts potential natural vegeta- tion types in the contiguous United States (i.e., those that would occur in the absence of major human or natural disturbances), another that maps the climatic conditions associated with ecosys- tem function (i.e., “climatic life zones”), and a third that shows the geographic extent of spring snow cover based on satellite imagery. When the team overlaid their historical wolverine records on these maps, a fresh interpretation