Sexual Segregation in Sierra Nevada Bighorn Sheep, Ovis canadensis sierrae: Ramifications for Conservation

Abstract

We studied sexual segregation in an endangered alpine ungulate, Sierra Nevada bighorn sheep (Ovis canadensis sierrae) in the Sierra Nevada, California, U.S.A., during winter 2005–2006. We tested hypotheses for sexual segregation to better understand that phenomenon and to obtain information critical for the conservation of these rare mammals. Females foraged in larger groups that were closer to escape terrain than did males. Areas used by males had higher biomass of vegetation and were less open than areas used by females. Males foraged more efficiently in larger groups, whereas females foraged more efficiently when close to escape terrain. Females exhibited a higher bite rate than did males. Males traveled farther per day and in more open terrain than did females. Sexes of bighorn sheep also differed in their dietary niches. Those niches differed most where sexes of bighorn sheep overlapped more in spatial distribution, and differed less where spatial separation was more pronounced. These outcomes are most parsimoniously explained by the gastrocentric and predation hypotheses. In addition, sexes of bighorn sheep behaved as if they were separate species by exhibiting avoidance on one niche axis (space) when there was overlap on another axis (diet). Management and conservation plans must consider the disparate requirements of males and females to help assure the viability of these endangered mountain ungulates.