Bighorn Sheep Habitat Studies, Population Dynamics & Population Modeling

The U.S. Geological Survey conducted a three-year study from 2000 to 2003 to investigate the causes of decline in the bighorn sheep population of Bighorn Canyon National Recreation Area, the Pryor Mountain Wild Horse Range, and surrounding state and U.S. Forest Service land. The study included radio-collaring 30 adult rams and ewes (~1/3 of the herd) with mortality sensors to monitor adult mortalities and population range. Ewes were tracked during the lambing season to determine pregnancy and lambing rates. Population range and dynamics were also estimated through aerial and boat surveys. Habitat assessments, including the evaluation of nutrient concentrations in key forage species, were conducted to determine why the population was not using areas previously modeled as suitable or acceptable habitat. Habitat suitability models were created and conducted using different methodologies. Recommendations for management included conducting habitat treatments (e.g., burning or clearing) to increase horizontal visibility, continuing radio-tracking and monitoring, encouraging dispersal to the northern end of Bighorn Lake through habitat improvement or translocation, and supplementing sheep diets with selenium blocks. Since the conclusion of the study, park staff monitor the remaining collared sheep on a weekly basis. Multiple habitat treatments, including fire and mechanical thinning, have been conducted to improve habitat, based on recommendations from the study.