table of contents Sierra Nevada Forest Plan Amendment – Part 4.3 4.3. Endangered, Threatened, and Proposed Species4.3. Species 4.3.1 Mammals4.3.1 Mammals 4.3.1.1. SIERRA NEVADA BIGHORN SHEEP (Ovis canadensis californiana) Life History Breeding takes place in the fall, generally in November (Cowan and Geist 1971). Single births are the norm for North American wild sheep, but twinning is known to occur (Wehausen 1980) Gestation is about 6 months (Cowan and Geist 1971). Lambing occurs between late April and early July, with most lambs born in May or June (Wehausen 1980, Wehausen 1996). Ewes with newborn lambs live solitarily for a short period before joining nursery groups that average about six sheep. Ewes and lambs frequently occupy steep terrain that provides a diversity of slopes and exposures for excape cover. Lambs are precocious, and within a day or so, climb almost as well as the ewes. Lambs are able to eat vegetation within 2 weeks of their birth and are weaned between 1 and 7 months of age. By their second spring, they are independent of their mothers. Female lambs stay with ewes indefinitely and may attain sexual maturity during the second year of life. Male lambs, depending upon physical condition, may also attain sexual maturity during the second year of life (Cowan and Geist 1971). Average lifespan is 9 to 11 years in both sexes, though some rams are known to have lived to 12 or 14 years old (Cowan and Geist 1971, Wehausen 1980). Habitat relationships Current and historical habitat of the Sierra Nevada bighorn sheep is almost entirely on public land managed by the Forest Service (FS), Bureau of Land Management (BLM), and National Park Service (NPS). The Sieran Nevada mountain range is located along the eastern boundary of California. Peaks vary in elevation from 6,000 to 8,000 feet in the north to over 14,000 feet in the south adjacent to the Owens Valley, and then drop rapidly in elevation at the southern extreme end of the range (Wehausen 1980). Sierra Nevada bighorn sheep inhabitat the alpine and subalpine zones during the summer, using open slopes where the land is rough, rocky, sparsely vegetated and characterized by steep slopes and canyons (Wehausen 1980, Sierra Nevada Advisory Group 1997). Most of these sheep live between 10,000 and 14,000 feet in elevation in summer months (John Wehausen pers comm. 1999). In winter, they occupy high, windswept ridges, or migrate to the lower elevation sagebrush-steppe habitat as low as 4,800 feet to escape deep winter snows and find more nutritiouis forage. Bighorn sheep exhibit a preference for south-facing slopes in the winter (Wehausen 1980). Lambing areas are on safe precipitous rocky slopes. They prefer open terrain where they are better able to see predators. For these reasons, forests and thick brush usually are avoided. Bighorn sheep are primarily diurnal, and their daily activity show some predictable patterns that consist of feeding and resting periods (Jones 1950). Bighorn sheep are primarily grazers; however, they may browse woody vegetation when it is growing and very nutritious. They are opportunistic feeders selecting the most nutritiouis diet from what is available. Plants consumed include varying mixtures of grasses, browse (shoots, twigs, and leaves of trees and shrubs), and herbaceous plants, depending on season and locations (Wehausen 1980). In a study of the Mount Baxter and Mount Williamson subpopulations, Wehausen (1980) found that grass, mainly Stipa speciosa (perennial needlegrass) is the primary diet item in winter. As spring green-up progresses, the bighorn sheep FEIS Volume 3, Chapter 3, part 4.3 – page 1 – Affected Environment and Environmental Consequences Sierra Nevada Forest Plan Amendment – Part 4.3 shift from grass to a more varied browse diet, which includes Ephedra viridis (Mormon tea), Eriogonum fasciculatum (California buckwheat), and Purshia species (bitterbrush). Sierra Nevada bighorn sheep are gregarious, with group size and composition varying with gender and from season to season. Spatial segregation of males and females occurs outside the mating season, with males more than 2 years old living apart from females and younger males for most of the year (Jones 1950, Geist 1971, Wehausen 1980). Ewes generally remain in the same band into which they were born (Cowan and Geist 1971). During the winter, Sierra Nevada bighorn sheep concentrate in those areas suitable for wintering, preferrably Great Basin habitat (sagebrush-steppe) at the very base of the eastern escarpment. Subpopulation size can number more than 100 sheep, including rams (this was observed at a time when the population size was larger than it is currently) (J.Wehausen, pers. comm. 1999). Diet. Bighorn sheep graze and browse on various plant species, but prefer green, succulent grasses and forbs (Zeiner and others 1990b). This species forages in open habitats, such as rocky barrens, meadows, and low, sparse brushlands (Zeiner and others 1990b). Status The Mountain sheep (Ovis canadensis) is fairly uncommon in California and, until 1979, the California bighorn sheep (O. c. californiana), one of three subspecies found in California, only occurred in two herds totaling 195 animals in the southern Sierra Nevada (Mt. Baxter and Mt. Williamson) (Ziener and others 1990b, CDFG 1991). The Sierra Nevada distinct population segment was emergency listed as Federally Endangered effective April 20, 1999. A proposed rule to list the Sierra Nevada bighorn sheep as endangered was published concurrently with the emergency rule (FR/Vol. 64, No. 75, 19300-19308). The Final Rule was published in the Federal Register January 3, 2000 listing the California Bighorn Sheep as Endangered. It has been reintroduced into Inyo County of the Inyo National Forest (NF), and into the South Warner Wilderness in Modoc County of Modoc National Forest. In spite of the reintroduction of almost 300 animals, only 80-150 remain on Inyo NF. The Inyo herd has declined steadily since the harsh winter of 1994. This is primarily due to increased stress in the herd and as a result, increased predation by mountain lions. The Modoc NF herd of 50 animals was lost in 1988 to pneumonia. The bighorn sheep is found in a variety of habitats associated with rocky, steep slopes and canyons (Zeiner and others 1990b). The California bighorn sheep currently occurs on only one national forest affected by the Sierra Nevada Forest Plan Amendment Project, the Inyo National Forest (Timossi 1990, Forest Wildlife Biologists Pers. comm.). Based on an older analysis of the taxonomy of the bighorn sheep using morphometrics and genetics the Sierra Nevada population was not found to be a distinct population (Ramey 1993, Ramey 1995, Wehausen and Ramey 1993, Wehausen and Ramey, in review). However, this and other research (Ramey 1993) was reconsidered and found to support the taxonomic distinction of the Sierra Nevada bighorn sheep relative to sheep of other nearby regions. The result was that the Sierra Nevada bighorn sheep was recognized as a distinct vertebrate population segment for purposes of listing. (61 FR 4722). Historical and Current Distribution The historical range of the Sierra Nevada bighorn sheep includes the eastern slope of the Sierra Nevada, and, for at least one subpopulation, a portion of the westerns slope, from Sonora Pass in FEIS Volume 3, Chapter 3, part 4.3 – page 2 – Affected Environment and Environmental Consequences Sierra Nevada Forest Plan Amendment – Part 4.3 Mono County south to Walker Pass in Kern County, a total distance of about 215 miles (Jones 1950, Wehauser 1979, Wehauser 1980). By the turn of the century, about 10 out of 20 sub-populations survived. The number dropped to five subpopulations at mid-century, and down to two sub- populations in the 1970s, near Mount Baxter and Mount Williamson, in Inyo County (Wehauser 1979). Currently, five subpopulations of Sierra Nevada bighorn sheep occur, respectively at Lee Vining Canyon, Wheeler Crest, Mount Baxter, Mouint Williamson, and Mount Langley in Mono and Inyo Counties. The other major factor affecting the Sierra Nevada bighorn sheep is the juxtaposition of domestic sheep grazing allotments to bighorn sheep winter range and the resulting potential for disease transfer from chance encounters. Transfer of viruses, parasites, and bacteria from domestic sheep to bighorn sheep have devastated most of the free ranging bighorn herds within the State of California. Viruses, parasites, and bacteria can join together to weaken or kill bighorn sheep. Bacteria, primarily Pasteurella spp., have led to massive all-age die-offs of bighorn sheep in every state in the western United States (Martin and others 1996). Of the numerous pathogens affecting bighorn sheep, Pasteurella haemolytica by far the most important respiratory pathogen leading to pneumonia and death (Foreyt 1993). Pasteurella multicida can also be important in the pneumonia complex. In wild situations, domestic sheep and bighorn sheep associations almost always result in death of the bighorns but does not affect the domestics. The finding of a shared P. haemolytica by DNA fingerprinting between domestic sheep and bighorn sheep in a Nevada study indicates this bacteria was transmitted between the two species under field conditions (Hunter 1995). DNA fingerprint test during the winter of 1995 to 1996 in Hells Canyon during a huge bighorn die-off revealed that P.multocida was transmitted from a feral goat to two bighorn sheep (Rudolph and others 1998). This transmission resulted in the death of in excess of 260 bighorn sheep in an eight-week period. When bighorn sheep experience a pneumonia episode, all-age mortality normally occurs. Lambs that are born from surviving ewes generally experience low survival rates for approximately 3 to 5 years after the initial pneumonia outbreak (Foryt 1990, Coggins and Matthews 1992, Ward and others 1992, Foreyt 1995, Hunter 1995).