Home ranges of female mountain sheep, Ovis canadensis nelsoni: effects of precipitation in a desert ecosystem

We compared sizes of home ranges and other ecological variables for female mountain sheep (Ovis canadensis nelsoni) inhabiting climatologically distinct areas in the Mojave Desert, California, USA. We also examined the relationship between size of home range and body size and age of mountain sheep. The pattern of precipitation was uni-modal in the more xeric Panamint Range, and bimodal at Old Dad Peak. Density of female sheep was about four times greater at Old Dad Peak than in the Panamint Range; Old Dad Peak also had more shrubs and perennial grasses than the Panamint Range. Home ranges and core areas were nearly twice as large in the Panamint Range than at Old Dad Peak, and females at Old Dad Peak were consistently nearer water. We detected no relationships between size of body or age and size of home-ranges for female mountain sheep. Females at Old Dad Peak foraged predominantly on perennial grasses and forbs, whereas those in the more xeric Panamint Range consumed mostly shrubs, perennial forbs, and succulents. In general, quality of forage was higher at Old Dad Peak than in the Panamint Range. Fecal nitrogen did not differ between areas in spring, but was higher in the Panamint Range during summer and autumn. We conclude that mountain sheep from the Panamint Range had larger home ranges because of lower availability and quality of forage, ostensibly a consequence of that precipitation regime. Use of cacti by mountain sheep in the Panamint Range likely enhanced the ability of females to increase the area in which they foraged in that depauperate and xeric environment. We hypothesize that pattern and amount of precipitation, and subsequent productivity of plants, affect the distribution of mountain sheep, and ultimately probabilities of persistence for populations of these mountain ungulates.