SEASONAL-VARIATION IN CALIFORNIA BIGHORN RAM (OVIS-CANADENSIS CALIFORNIANA) HABITAT USE AND GROUP-SIZE

Seasonal changes in bighorn sheep (Ovis canadensis) habitat use and so cial systems can create profound management challenges. We studied spr ing-summer distribution, habitat use, and group size of California big horn rams on Poker Jim Ridge, Oregon. Ram groups were observed during April-August 1990. Herd range was smaller in spring (24.4 km(2)) than summer (74.5 km(2)). Ram groups were closer to escape terrain ((P) und er bar < 0.001), farther from water ((P) under bar < 0.001), on gentle r slopes ((P) under bar = 0.01) and at higher elevations ((P) under ba r < 0.001) in spring. Distance to escape terrain and distance to water were significant main effects differentiating spring and summer habit at use ((P) under bar < 0.001). Ram group size varied by month ((P) un der bar < 0.001), with groups in Jury-August smaller than those in Apr il-June ((P) under bar < 0.01). Seasonal changes in ram distribution a ppeared to be associated with changing habitat conditions, particularl y water availability. Small group sizes in late summer probably reflec ted resource limitations, and occurred in spite of use of less secure habitats during this period. Managers of bighorn sheep populations sho uld consider the unique requirements of their populations under a vari ety of environmental conditions, and provide adequate protection to su stain seasonal shifts in distribution.