Unregulated harvesting, habitat destruction, overgrazing of rangelands, and diseases contracted from domestic livestock all contributed to drastic declines, the most drastic occurring from about 1870 through 1950.
Bighorn exist mostly in small, isolated populations within their former vast range.
Thorne et al. Restoration of bighorn sheep has been pursued actively by many state and federal agencies since the 1940's, although these efforts have met with only limited success, and most of the historical range of bighorns remains unoccupied. Human encroachments near bighorn populations are severe enough in some areas that the peninsular population of desert bighorns in California has been proposed for federal threatened status. Factors contributing to the success of 115 transplants of bighorn sheep that occurred over the past five decades in six Rocky Mountain states are also reviewed. Information on the status and restoration of bighorns in the National Park Service units came from published accounts, university theses, unpublished park records, and a questionnaire mailed to state wildlife agencies and land managers in Colorado, Montana, North and South Dakota, Wyoming, and Utah.