Seasonal variation in California bighorn ram (Ovis canadensis californiana) habitat use and group size

Abstract

Seasonal changes in bighorn sheep (Ovis canadensis) habitat use and social systems can create profound management challenges. We studied spring-summer distribution, habitat use, and group size of California bighorn rams on Poker Jim Ridge, Oregon. Ram groups were observed during April-August 1990. Herd range was smaller in spring (24.4 km2) than summer (74.5 km2). Ram groups were closer to escape terrain (P< 0.001), farther from water (P < 0.001), on gentler slopes (P = 0.01) and at higher elevations (P < 0.001) in spring. Distance to escape terrain and distance to water were significant main effects differentiating spring and summer habitat use (P < 0.001). Rain group size varied by month (P < 0.001), with groups in July-August smaller than those in April-June (P < 0.01). Seasonal changes in ram distribution appeared to be associated with changing habitat conditions, particularly water availability. Small group sizes in late summer probably reflected resource limitations, and occurred in spite of use of less secure habitats during this period. Managers of bighorn sheep populations should consider the unique requirements of their populations under a variety of environmental conditions, and provide adequate protection to sustain seasonal shifts in distributionPayer and Coblentz "Seasonal variation in California bighorn ram (Ovis canadensis californiana) habitat use and group size." Northwest Science. 1997; 71(4): 281-28