Habitat Components for Desert Bighorn Sheep in the Harquahala Mountains, Arizona

Abstract

Desert bighorn sheep (Ovis canadensis mexicana) habitat was quantified in the Harquahala* Mountains, Arizona, in 1984. We compared measurements of perennial vegetation and topographic features on 300 plots in areas frequently used by bighorn sheep with measurements from 300 plots on an adjacent area not used by sheep. A 10-variable discriminant function model was 88.3% correct in differentiating areas used by sheep. Bighorn sheep habitat is farther from permanent water and bajadas (gentle slopes); has less large boulders, sheetrock, false-mesquite calliandra (Calliandra eriophylla), snakeweed (Gutierrezia spp.), needlegrass (Stipa spp.), and California jojoba (Simmondsia chinensis); and more basketgrass (Nolina texana), big galleta (Hilaria rigida), and propeller-bush (Janusia gracilus) than areas not used by sheep. J. WILDL. MANAGE. 50(3):504-508 It is important that managers understand habitat requirements of desert bighorn sheep, which have declined in numbers. Desert bighorn sheep do not thrive in the presence of livestock (Albrechtsen and Reese 1970, Wilson et al. 1980) or human activities (Bates and Workman 1983). The most important factors in wild ungulate management are conservation and use and development of adequate habitat (Scotter 1980). Habitat requirements of desert bighorn sheep are not well understood. However, the general characteristics of bighorn sheep habitat include forage, escape cover, bedding, lambing and rutting areas, thermal protection, and water (Ferrier and Bradley 1970, Shannon et al. 1975, Wilson et al. 1980, Tilton and Willard 1982). Desert bighorn sheep do not necessarily increase in direct proportion to the amount of available habitat because of variation in habitat quality (Holl 1982). We studied desert bighorn sheep movements and distribution patterns in the Harquahala Mountains of western Arizona from 1979 to 1984. To answer questions related to habitat selection we discovered that ?20% of the range was not used by sheep; the unused range visually appeared to have all the necessary habitat components important to sheep. Our objective in this study was to determine what specific habitat components were important to sheep. This study was funded by the U.S. Bur. Reclamation and the U.S. Fish and Wildl. Serv. M. R. and J. L. Cashman, T. L. Steel, D. W. Cramer, and D. R. and B. H. Smith assisted with the data collection. J. R. Alldredge and M. Trosset reviewed earlier drafts of the paper. Their efforts are appreciated. STUDY AREA The Harquahala Mountains, La Paz and Maricopa counties, are 147 km west of Phoenix and cover approximately 311 km2. Elevations range from 580 to 1,732 m. Topography varies from rolling hills to rugged cliffs. The northeast end of the range is bisected by Sunset Canyon and is not used by bighorn sheep. The sheep population is estimated at 35-50 individuals (Krausman 1985). Although the Harquahala Mountains are classified into 11 vegetative associations, there are only 2 basic vegetative formations: (1) the desertscrub formation, between 580 and 1,646 m, and (2) the chaparral formation, between 1,036 and 1,732 m (Lowe 1964:11). Average annual precipitation is 22 cm. Average seasonal temperatures range from 14 C in winter to 28 C in summer. Daily temperatures >45 C are