Wolverine conservation in Yellowstone National Park: Final report

Murphy, K; Wilmot, J; Copeland, J; Tyers, D; Squires, J; Inman, R; Packila, M; McWhirter, D

Abstract We documented wolverine distribution and population characteristics from 2005 to 2009 in Yellowstone National Park and its neighboring wilderness areas along the park’s east, northeast, and south boundaries by capturing and monitoring radiomarked individuals, and conducting surveys for their tracks during winter. We captured four individuals and collaboratively monitored three others, including two immigrants, that were previously marked by Wildlife Conservation Society biologists in the western portion of the Yellowstone ecosystem. Wolverines in our study area selected habitats above 2,450 meters (8,000 ft), that is, in the Hudsonian (boreal) life zone, but did not use alpine habitats extensively. Live-trapping, telemetry data, and surveys for tracks indicated that wolverine numbers and distribution were more limited than expected, despite the fact that two contemporary models estimated an extensive coverage of wolverine habitat in the area. Wolverines occurred in the Absaroka-Beartooth Wilderness along the north boundary of the park, and at the southeast corner (Thorofare region) and the adjoining Washakie and Teton Wilderness areas. When conducting helicopter-based surveys for tracks during winter, we did not detect any wolverines in the park interior, including the portion of the Gallatin Range inside the park; the Washburn and Snake River Ranges; the Central and Madison Plateaus; and the Bechler region. We also did not detect resident wolverines in the North Absaroka Wilderness and the adjoining areas along the east boundary, including the upper Lamar River. Surveys for ungulates in this area during the winter did not indicate that the availability of carrion significantly limited wolverine numbers and distribution, although our anecdotal observations suggested that winter food might be limited in the heavily forested portions of interior Yellowstone. Wolverine home ranges did not overlap, and radio-marked individuals did not make extra-home range movements to forage in the major ungulate winter ranges in and near our study area, including the Pelican and Hayden Valleys, and the northern winter range. Our limited demographic data suggested that reproductive rates of wolverines were low, that home ranges were large, and that rates of survival were similar to estimates for other populations in the conterminous United States. The dynamics and distribution of our population appeared to be strongly linked to ingress from well-established populations in other parts of the ecosystem, rather than to recruitment of offspring born to our resident females. We developed and tested a reliable method to rapidly assess wolverine distribution over large areas using helicopter-based searches for tracks during the winter. We were highly successful in finding tracks of resident, radio-marked wolverines during both preliminary tests (searches in 10 x 10 km survey [grid] cells) on a Wildlife Conservation Society study site, and when applying our refined technique to wolverines on our study area. This survey method can be broadly applied to the incised terrain typical of the Rocky Mountains as a first step in assessing wolverine populations, provided that surveys are adequately replicated. We recommend that biologists continue to investigate the factors that limit the growth of wolverine populations, particularly in areas such as ours where models suggest that suitable habitat is abundant.