Mapping occupied habitat for forest carnivores in the American West and estimating their conservation status. (Habitat issues).

Abstract

Conservation concerns are escalating due to the small numbers, reduced range, and increasingly fragmented distribution of wide-ranging forest carnivores in the American West--specifically the lynx (Lynx canadensis), wolverine (Gulo gulo), and fisher (Mattes pennanti). Observation data from the U.S. Forest Service and state natural heritage programs were compiled and mapped. Occupied habitats and population centers for the three species were identified and population sizes estimated based upon recorded densities and distribution. The results indicate small, isolated populations well below what may be necessary for long-term viability.

Introduction

Some of the smaller forest carnivores of the American West--the lynx (Lynx canadensis), wolverine (Gulo gulo), and fisher (Mattes pennanti)--have not yet grabbed headlines like bears (Ursus spp.) and wolves (Canis lupus). Yet mounting concerns about their viability indicate that large carnivores are not the only species in jeopardy because of past and ongoing habitat loss and fragmentation, and excessive human-caused mortality. While these lesser known species were never persecuted like the wolf, grizzly bear (Ursus arctos), and other species that pose a risk to livestock, their conservation status is now suffering due to neglect.

Critical information about the habitat requirements and population sizes of these animals is lacking, leaving conservationists ill-informed at where and how to initiate conservation strategies. Existing range maps are too coarse to prioritize specific areas for protection, such as individual mountain ranges or watersheds. There are few published population estimates, and they are limited to specific study areas and fail to address the conservation status of each species throughout its range.

We can no longer take for granted the survival of wide-ranging, low-density forest carnivores. As we have done for the grizzly bear and the wolf, we should make conscious decisions about where in the western U.S. we will maintain and restore forest carnivores, and protect them and their habitat in these areas accordingly. The capacity of these areas to support forest carnivores should be assessed to ensure that sufficient habitat is protected to provide for their long-term survival and recovery. Given the forest carnivores' large ranges and low densities and the fragmented nature of suitable habitat that remains, a conservation strategy will likely require restoration and maintenance of a connected network of population centers across the western U.S. and Canada (e.g., McKelvey et al. 2000a). The objective of this paper is to identify occupied habitats and population centers for the lynx, wolverine, and fisher based on available presence/ absence data, and to estimate population sizes within these areas based upon recorded densities, as a first step toward devising a long-term conservation strategy for these species.

Mapping occupied habitat

To identify occupied habitats and population centers for the lynx, wolverine, and fisher, observation data from the U.S. Forest Service and the natural heritage programs of eight western states were gathered (Maj and Garton 1994; McKelvey et al. 2000b). These data were not collected through standardized survey techniques but include observations made by workers in the field, trapping records, and museum specimen records. State natural heritage programs maintain this data and attempt to filter out unreliable observations.

GIS software was used to highlight parcels of public lands where the observations were located. Private land was excluded from this analysis, because of the difficulty delineating borders around point locations on private lands. Administrative boundaries were convenient for this purpose on public lands, and though they have no biological basis they serve the purpose of delineating the large landscape features relevant to this scale of analysis. This methodology unfortunately excludes important areas of carnivore habitat on private lands, but the vast majority (>80%) of the carnivore observations occurred on public lands.

These areas were sorted by date to provide an approximation of current versus historic range. Observations made after 1990 were used to delineate current range while observations prior to 1990 denote historic range for the purpose of this analysis. Overlapping data for all three species revealed occupied habitat for all three species, and for various combinations of the three (Figure 1).

[FIGURE 1 OMITTED]

Estimating current population status

Population centers for each species were identified using observation data plus additional information found in scientific literature. Population numbers were estimated by multiplying the area occupied by a species (as determined by current observation data) by density estimates obtained from field studies in those or similar areas. For example, an analysis of wolverine observations in Idaho indicates three areas where sightings are concentrated: the Selkirk Mountains of northern Idaho, the Lochsa and Kelly Creek drainages in north-central Idaho, and the Sawtooth and Smoky Mountains in south-central Idaho (Groves 1988). Delineation of the specific clusters was subjective, but they account for 21%, 18%, and 22% of the 89 "probable" wolverine reports respectively. Each of these areas encompasses approximately 20,000 square kilometers of public lands, which comprises 90 to 100% of these areas. Copeland (1996) estimated one wolverine per 90 to 248 k[m.sup.2] within his study area in the Sawtooth Mountains, based upon his analysis of 1,050 relocations of 19 wolverines by ground and aerial telemetry. A conservative estimate of one wolverine per 200 k[m.sup.2] across each of these areas indicates three subpopulations of 100 wolverines each in Idaho (Figure 2). Delineation of potential subpopulations for each of the forest carnivores and estimating their numbers provides a starting point to assess the conservation status of these species relative to other imperiled species like grizzly bears and wolves.

[FIGURE 2 OMITTED]

Results

Occupied habitat for all three forest carnivores occurs throughout northern and central Idaho, northwestern Montana, portions of the Greater Yellowstone Ecosystem, Washington (northeastern corner, North Cascades), and Oregon (South Cascades). Lynx presence diminishes to the south, notwithstanding recent progress restoring lynx to the southern Rockies. Fishers are rarely observed south or east of the Bitterroot Range along the Idaho/Montana border, although populations persist in Cascades of southwestern Oregon, and in both the northern and southern Sierra Nevada Range. Wolverine range appears to have decreased over recent decades as follows. Known to historically occupy the Cascades of the Northwest and south into the southern Sierra Nevada, current sightings throughout this western extent of their range are rare. In Washington and Oregon, there have been only seven verifiable sightings since 1986, and despite an extensive helicopter survey in the Cascades, current wolverine presence is confirmed only in the North Cascades of Washington (K. Aubry personal communication). There has not been a verified wolverine observation in the Sierra Range since before 1990 (Zielinski, personal communication).

Population estimates indicate current numbers of all three species may be well below what is needed to ensure their long-term viability, if you consider that a minimum effective population size of 500 individuals may be necessary (Soule 1987), and that just a fraction of the individuals within these carnivore populations are actively breeding and thus count toward the effective population size (Ruggiero et al. 1994). The fisher appears to be the most imperiled of the three in the West, with an estimated total population of perhaps 600 animals, including populations that may be functionally isolated in the southern Sierra, northern Sierra, southwestern Oregon, and portions of Greater Yellowstone (Figure 3). The wolverine is more widespread than the fisher, but its low densities coupled with recent declines in the Sierra and Northwest are cause for concern. Population estimates for both the fisher and the wolverine are less than estimated numbers of lynx (Figure 4) and grizzly bear across the western U.S., both of which are listed as threatened species under the federal Endangered Species Act.

[FIGURES 3-4 OMITTED]

Discussion

This analysis provides a coarse but useful first step toward identifying occupied habitat for the lynx, wolverine, and fisher, toward assessing their conservation status across the American West and prioritizing areas for their protection. Observation data are inherently biased by observer effort and reliability, and by imperfect reporting and organization of observations. These data should be refined with more careful screening and supplemented with new information regarding the conservation status and distribution of these species. Additional data from Canada are needed to develop a comprehensive, range-wide conservation assessment and strategy for the forest carnivores. Despite these limitations, this analysis provides an initial step toward the design and implementation of a forest carnivore conservation strategy that encompasses occupied habitat within the western U.S. for one or more of these species.

Acknowledgements

I am grateful to the U.S. Forest Service Rocky Mountain Research Station for compiling and providing me with its lynx distribution data, and to the natural heritage programs of California, Colorado, Idaho, Montana, Oregon, Utah, Washington, and Wyoming for providing forest carnivore observation data free of charge. Thanks also to the Ecology Center in Missoula, Montana for some GIS assistance, to Defenders of Wildlife for providing a venue to share this analysis, and to Stephen Kendrot (USDA Wildlife Services) for a helpful review.

Literature cited

Copeland, J. 1996. Biology of the wolverine in central Idaho. MS Thesis, University of Idaho, Moscow, Idaho, May 1996.

Groves, C.R. 1988. Distribution of the wolverine in Idaho as determined by mail questionnaire. Northwest Science 62(4): 181-5.

Maj, Mary and E.O. Garton. 1994. Fisher, lynx, wolverine; summary of distribution information. Pp 169-175 in L.F. Ruggiero, K.B. Aubry, S.W. Buskirk, L.J. Lyon, and W.J. Zielinski, eds. The scientific basis for conserving forest carnivores: American marten, fisher, lynx, and wolverine in the western United States. U.S. Dept. of Agriculture, Forest Service, Gen. Tech. Rep. RM-254.

McKelvey, K.S., K.B. Aubry, J.K. Agee, S.W. Buskirk, L.F. Ruggiero, and G.M. Koehler. 2000a. Lynx conservation in an ecosystem management context. Chapter 15 in Ruggiero, L.F., K.B. Aubry, S.W. Buskirk, G.M. Koehler, C.J. Krebs, K.S. McKelvey, and J.R. Squires, eds. Ecology and conservation of lynx in the United States. U.S. Dept. of Agriculture, Forest Service Rocky Mountain Research Station, Missoula, Montana; published by University Press of Colorado, Boulder, Colorado.

McKelvey, K.S., K. B. Aubry, and Y.K. Ortega. 2000b. History and distribution of lynx in the contiguous United States. Chapter 8 in Ruggiero, L.E, K.B. Aubry, S.W. Buskirk, G.M. Koehler, C.J. Krebs, K.S. McKelvey, and J.R. Squires, eds. Ecology and conservation of lynx in the United States. U.S. Dept. of Agriculture, Forest Service Rocky Mountain Research Station, Missoula, Montana; published by University Press of Colorado, Boulder, Colorado.

Ruggiero, L.F., K.B. Aubry, S.W. Buskirk, L.J. Lyon, and W.J. Zielinski, eds. 1994. The scientific basis for conserving forest carnivores: American marten, fisher, lynx, and wolverine in the western United States. Gen Tech Rep RM-254, Fort Collins, Colorado, U.S. Dept. of Agriculture, Forest Service, Rocky Mountain Forest and Range Exp. Stat, 184 pp.

Soule, M.E. 1987. Viable populations for conservation. Cambridge University Press, Cambridge, England.

David L. Gaillard
Predator Conservation Alliance, P.O. Box 6733, Bozeman, MT 59771; (406)
587-3389; [e-mail]; www.predatorconservation.
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