Date of Award


Document Type


Degree Name

Master of Science (MS)




The bighorn sheep (Oyis canadensis califomiana) in the North Dakota Badlands were studied in an effort to obtain baseline ecological data and examine the effects of human disturbance (primarily oil development) on their ranges, habitat use, movements and reproductive performance. The study was conducted from May and April, 1992 and 1993, respectively, through December of each year. Additionally, the summer of 1994 was used to complete habitat classification in the field.

Eight bighorn ewes were captured by helicopter and net-gun in each of 2 primary study areas (one highly impacted by oil development and the other less impacted) and fitted with radio collars and ear tags. The radioed ewes were tracked and visually observed at least once a week - more frequently during the lambing season. As time permitted, the demographics and reproductive performance of 7 other free-ranging groups of bighorns were also monitored.

The sheep did not occupy different ranges during different times of the year and no seasonal migration occurred. There was a high degree of home range fidelity and bighorns in the primary study areas still occupied the same ranges animals did more than 20 years ago. The non-vegetated habitat, associated with escape terrain, was preferred (P < 0.05) for bedding in all seasons. Grass habitats were generally avoided for bedding in all seasons, except plateau tops in the fall. Trec/Shrub habitats were avoided (P < 0.05) for all activities in all seasons.

Within their ranges, sheep used some areas more heavily than others. These areas were always associated with escape terrain. Nearly 60% of their activity occurred on approximately 33% of their range, and 88% of their activity occurred within 100 m of escape terrain. Ewes with lambs were nervous, wary, and quick to flee. They were even more closely associated with the escape terrain.

While production was high for some groups, lamb survival (recruitment) was low for most and non-existent for others. Predation and disease appeared to be major factors. Survival of sheep older than 4 months was high, with most mortality (rams) a result of the hurting season.

While there was no significant difference in lamb recruitment between the 2 primary study areas (P < 0.05). there were differences when ail areas were combined and categorized by level of disturbance. The recruitment of lambs was significantly higher (P < 0.05) in areas with low levels of human disturbance than it was in areas with moderate or high levels.