SIERRA NEVADA BIGHORN SHEEP } Ovis canadensis sierrae
DESCRIPTION: Similar in appearance to other bighorn sheep, the Sierra Nevada bighorn is a large mammal with a white rump, ranging in body color from almost white to fairly dark brown. Adult males stand up to three feet tall and weigh up to 220 pounds; females weight up to about 140 pounds. Both sexes have permanent horns; males’ horns are massive and coiled, while females’ horns are smaller and uncoiled. The horns of this subspecies are more divergent as they coil out from the base than those of other species.
HABITAT: The Sierra Nevada bighorn sheep lives in open upland, montane, and alpine habitats with rocky areas along the eastern slope of the Sierra Nevada from about 4,000 feet to approximately 14,500 feet.
RANGE: The historical range of the Sierra Nevada bighorn included the eastern slope of the Sierra Nevada and, for at least one subpopulation, from Sonora Pass in Mono County south to Walker Pass in Kern County. Currently, five subpopulations occur at Lee Vining Canyon, Wheeler Crest, Mount Baxter, Mount Williamson, and Mount Langley in Mono and Inyo Counties. Three of these subpopulations have been reintroduced using sheep from the Mount Baxter subpopulation.
MIGRATION: During the summer, most sheep live at higher elevations in subalpine and alpine areas; to avoid deep snow and to find forage in the winter, the sheep occupy either high-elevation windswept ridges or migrate to lower-elevation sagebrush-steppe habitats.
BREEDING: Breeding generally takes place in November, with single and sometimes twin lambs being born between late April and early July on precipitous rocky slopes. Lambs are able to climb soon after birth and eat vegetation within two weeks. They are weaned at between one and seven months of age and are independent of their mothers by their second spring.
LIFE CYCLE: Both female and male lambs may attain sexual maturity during the second year of life. The average lifespan is nine to 11 years, though some rams have been known to live 12 to 14 years.
FEEDING: These sheep are primarily grazers, feeding on various plants such as grasses, browse, and herbaceous plants, depending on season and location.
THREATS: The biggest threat to the Sierra Nevada bighorn sheep is the transmission of disease from domestic sheep grazing in bighorn habitat. Other threats include predation, small population size, competition for forage, watershed degradation, poorly planned human recreation, and some developmen t.
POPULATION TREND: After increasing from 250 in 1978 to almost 300 in 1985, the total number of bighorn sheep in the Sierra Nevada declined by about 60 percent to just more than 100 in 1995. Since emergency listing in 1999, numbers have since increased; today there are more than 300 individuals.