Bighorn sheep (Ovis canadensis) once were ubiquitous in large areas, including lands now contained in the national parks of the Intermountain and Colorado Plateau regions of the United States. Due to catastrophic declines in the late 1800s and early 1900s, most extant populations now occur as small, isolated groups with a highly fragmented distribution. Three different subspecies of bighorn sheep were extirpated from 14 of 18 areas that are now managed by the National Park Service. We describe an eight‐year plan to restore bighorn sheep to currently suitable historic habitats in the national parks within a six‐state intermountain region of the western United States, 1991–1998. A seven‐point program was recommended for each park unit that included: (1) survey the existing populations; (2) conduct a GIS‐based habitat assessment to identify suitable habitat; (3) convene scientific advisory panels to review results of habitat assessment; (4) convene interagency panels to discuss metapopulation management and to plan the restoration(s); (5) draft interagency restoration and management plans; (6) conduct translocation(s); and (7) monitor the populations. We evaluated 38,781 km2 of area; 32% (12,329 km2) was potential habitat for bighorn sheep. The scientific advisory panels and the GIS modeling recommended bighorn restoration on 73 sites within these areas. By 1996, 36 of these sites (2,647 km2 or 22% of the entire suitable area) were inhabited by bighorn sheep. By 1999, the translocated animals increased 25%, and restoration efforts will continue in many of the remaining sites.
Translocation of bighorn sheep (Ovis canadensis) is time, labor, and cost intensive and, therefore, high levels of success are desirable. We tested a widely used habitat suitability model against translocation success and then modified it to include additional factors which improved its usefulness in predicting appropriate translocation sites. The modified Smith habitat suitability model for bighorn sheep was 64% accurate in predicting success or failure of 32 translocations of bighorn sheep into the Rocky Mountains, Colorado Plateau desert, and prairie‐badlands of six states. We had sheep location data for 13 populations, and the modified habitat model predicted the areas used by bighorn sheep with greater than 90% accuracy in eight populations, greater than 55% accuracy in four populations, and less than 55% accuracy in one population. Translocations were more successful when sheep were placed into discrete habitat patches containing a high proportion of lambing period habitat (>10% of suitable habitat, p = 0.05), where animals had a migratory tendency ( p = 0.02), no contact with domestic sheep ( p = 0.02), or greater distance to domestic sheep (>23 km, p = 0.02). Rate of population growth was best predicted by area of lambing period habitat, potential area of winter range, and distance to domestic sheep. We retested the model using these refined criteria and the refined model then predicted success or failure of these 32 translocated populations with 82% accuracy.
Restoration of Bighorn Sheep Metapopulations In and Near 15 National Parks fills a critical gap in the understanding and solution to restoring a severely fragmented vertebrate to large areas of the western United States. The program described in these pages represents a truly unique interagency and interdisciplinary effort. Many individuals and groups were involved and deserve credit.
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