Ovis canadensis sierrae - Grinnell, 1912
Sierra Nevada Bighorn Sheep
Synonym(s): Ovis canadensis californiana Douglas, 1829
Taxonomic Status: Accepted
Unique Identifier: ELEMENT_GLOBAL.2.102472
Element Code: AMALE04015
Informal Taxonomy: Animals, Vertebrates - Mammals - Other Mammals
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Mammalia Artiodactyla Bovidae Ovis
Genus Size: C - Small genus (6-20 species)
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Concept Reference
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Concept Reference: Wehausen, J. D., V. C. Bleich, and R. R. Ramey, II. 2005. Correct nomenclature for Sierra Nevada bighorn sheep. California Fish and Game 91(3):216-218.
Concept Reference Code: A05WEH01NAUS
Name Used in Concept Reference: Ovis canadensis sierrae
Taxonomic Comments: This population formerly was included in Ovis canadensis californiana, but Wehausen and Ramey (2000) transferred the population at the type locality of californiana (Yakima Co., Washington) to O. c. canadensis, and transferred more southern populations to O. c. nelsoni. The Sierra Nevada bighorn population, however, appears to be a lineage distinct from O. c. nelsoni (Ramey 1995, Wehausen and Ramey 2000). Wehausen et al. (2005) reviewed the taxonomy of bighorn sheep in the Pacific states and determined that correct name for the Sierra Nevada population is Ovis canadensis sierrae Grinnell, 1912. USFWS (2008) also reviewed available taxonomic information and agreed that the Sierra Nevada population should be recognized as a distinct subspecies (Ovis canadensis sierrae).
Conservation Status
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NatureServe Status

Global Status: G4T2
Global Status Last Reviewed: 04Sep2013
Global Status Last Changed: 04Sep2013
Ranking Methodology Used: Ranked by calculator
Rounded Global Status: T2 - Imperiled
Reasons: Small range in the Sierra Nevada, California; five disjunct populations totaling a few hundred individuals; imminently threatened by mountain lion predation and disease.
Nation: United States
National Status: N2 (04Sep2013)

U.S. & Canada State/Province Status
United States California (S2), Idaho (S3), Utah (SNA)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (03Jan2000)
Comments on USESA: Listed Endangered as Ovis canadensis sierrae.
U.S. Fish & Wildlife Service Lead Region: R8 - California-Nevada

NatureServe Global Conservation Status Factors

Range Extent: 1000-5000 square km (about 400-2000 square miles)
Range Extent Comments: Sierra Nevada bighorn sheep inhabit portions of the southern Sierra Nevada along the eastern boundary of California in Tuolumne, Mono, Fresno, Inyo, and Tulare counties. Habitat occurs from the eastern base of the range at elevations as low as 4,790 feet (1,460 meters) and extends to above 14,100 feet (4,300 meters) in some areas(Wehausen 1980:3, 82, cited by USFWS 2008). Habitat is patchy, so the distribution is naturally fragmented (see USFWS 2008).

Historical range: eastern slope of the southern Sierra Nevada, and, for at least one subpopulation, a portion of the western slope, from Sonora Pass in Mono County south to Walker Pass in Kern County, a total distance of about 346 km (USFWS 1999). The extant range begins in the Lee Vining area in Mono County and extends south
to the Mount Langley area in Inyo County, a linear distance of approximately 110 miles (177 kilometers) (USFWS 2008).

Area of Occupancy: 126-500 4-km2 grid cells
Area of Occupancy Comments: Currently occupied habitat is about 980 square kilometers (USFWS 2008).

Number of Occurrences: 6 - 20
Number of Occurrences Comments: Of the 12 units encompassed by the critical habitat desognation, 7 are currently occupied (USFWS 2008); these can be regarded as distinct occurrences or subpopulations.

Population Size: 50 - 1000 individuals
Population Size Comments: Estimates of the Sierra Nevada bighorn sheep population in 2006 indicate that 350 to 400 individuals occur throughout the range; this is an increase from the 125 individuals estimated at the time of listing; current individual herd numbers in the different subpopulations range from 8 to 113 individuals (Wehausen and Stephenson 2006, cited by USFWS 2008). The number of reproductively active individuals would be smaller than these figures..

Overall Threat Impact: High
Overall Threat Impact Comments: "Factors limiting Sierra Nevada bighorn sheep recovery include disease, predation, low population numbers and limited distribution, availability of open habitat, and potential further loss of genetic diversity due to small population sizes and inadequate migration between them. Since the vast majority of Sierra Nevada bighorn sheep habitat is publicly-owned land, loss of habitat has not been a limiting factor. However, management of bighorn sheep habitat (e.g., fire suppression) can result in habitat alterations and loss of key dispersal corridors connecting herds, which could be limiting factors." [Source: USFWS 2007]

Existing subpopulations are very small and are imminently threatened by mountain lion predation (USFWS 1999, 2000), which may need to be managed in some areas. As the numbers of Sierra Nevada bighorn sheep increase with recovery, the need for mountain lion control specifically for the benefit of Sierra Nevada bighorn sheep should be reduced and eventually eliminated (USFWS 2008). Continued suppression of fires in Sierra Nevada bighorn sheep range is a threat as habitat succession alters the abundance of suitable bighorn sheep habitat and increases bighorn sheep vulnerability to mountain lion predation (see USFWS 2008).

Although die-offs of bighorn sheep due to disease have occurred unrelated to domestic sheep (Miller et al. 1991: 534-540, cited by USFWS 2008)), a major contributing factor responsible for the decline of Sierra Nevada bighorn sheep populations over the years is thought to be the introduction of diseases by domestic livestock. Clifford et al. (2007:18, cited by USFWS 2008) indicated concern regarding the probability of a respiratory disease case occurring from disease transmission between domestic sheep and Sierra Nevada bighorn sheep, especially in the northern part of bighorn sheep range. Domestic grazing allotments within the vicinity of Sierra Nevada bighorn sheep habitat should be reviewed and activities should be modified as necessary to prevent competition and contact between the domestic livestock (sheep and goats) and bighorn sheep.

Domestic livestock (sheep, goats, cattle) grazing practices that result in overgrazing or allow for contact between domestic sheep, domestic goats, and Sierra Nevada bighorn sheep is a threat. Domestic livestock could compete with Sierra Nevada bighorn sheep for forage at some level in designated critical habitat units (USFWS 2008).

Some population units require special management considerations or protection to address impacts from development activities, including road construction and maintenance within Sierra Nevada bighorn sheep habitat (USFWS 2008).

Patented mining claims occur within habitat used by the Sierra Nevada bighorn sheep, but the area of the claims is small. Mining activities and associated facilities threaten bighorn sheep by causing the loss of vegetation structure required for foraging activities; the destruction of habitats used for escape, bedding, lambing, or connectivity between ranges; and the disturbance due to ongoing mining activities. Disturbance could modify bighorn sheep behavior or cause them to flee an area (USFWS 2008).

It remains unclear how significantly Sierra Nevada bighorn sheep may be affected by human disturbance. Increases in human uses of bighorn sheep habitat, including recreational activities such as rock and ice climbing, mountaineering, ski touring, hiking, camping, pack station establishment, snowmobiling, and off-road vehicle use may cause detrimental disturbance to Sierra Nevada bighorn sheep in some areas (USFWS 2008). Impacts to the habitat could occur through trampling and reduced vegetation structure due to grazing by pack animals (USFWS 2008).

Management actions to protect Sierra Nevada bighorn sheep habitat from catastrophic, naturally occurring events may be necessary. Events such as wildfires and avalanches could temporarily destroy large areas that provide summer or winter foraging habitat (USFWS 2008).

Short-term Trend: Increase of >10%
Short-term Trend Comments: Total population size declined from 250 to 100 between 1978 and around 2000, while the number of disjunct populations increased from two to five (through reintroduction) (USFWS 1999, 2000). Snce then, the population has increased by about 200% (USFWS 2008).

Long-term Trend: Decline of 30-50%
Long-term Trend Comments: Based on current occupancy of 7 of the 12 critical habitat units (an admittently crude measure of long-term decline), the decline would be around 42 percent.

Other NatureServe Conservation Status Information

Distribution
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Global Range: (1000-5000 square km (about 400-2000 square miles)) Sierra Nevada bighorn sheep inhabit portions of the southern Sierra Nevada along the eastern boundary of California in Tuolumne, Mono, Fresno, Inyo, and Tulare counties. Habitat occurs from the eastern base of the range at elevations as low as 4,790 feet (1,460 meters) and extends to above 14,100 feet (4,300 meters) in some areas(Wehausen 1980:3, 82, cited by USFWS 2008). Habitat is patchy, so the distribution is naturally fragmented (see USFWS 2008).

Historical range: eastern slope of the southern Sierra Nevada, and, for at least one subpopulation, a portion of the western slope, from Sonora Pass in Mono County south to Walker Pass in Kern County, a total distance of about 346 km (USFWS 1999). The extant range begins in the Lee Vining area in Mono County and extends south
to the Mount Langley area in Inyo County, a linear distance of approximately 110 miles (177 kilometers) (USFWS 2008).

U.S. States and Canadian Provinces
Color legend for Distribution Map

U.S. & Canada State/Province Distribution
United States CA, ID, UTexotic

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
CA Fresno (06019), Inyo (06027), Modoc (06049)*, Mono (06051), Tulare (06107)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
18 Upper Pit (18020002)+*, Upper Kern (18030001)+, Upper King (18030010)+, Surprise Valley (18080001)+*, Crowley Lake (18090102)+, Owens Lake (18090103)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Habitat Type: Terrestrial
Non-Migrant: N
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: Seasonal migrations revolve primarily around avoidance of deep snow in winter.

Individuals tend to show a high level of philopatry to their seasonal home ranges, though long-distance dispersal to new areas sometimes occurs.

Maximum diameters of annual home ranges for females in the Mount Warren/Mount Gibbs, Wheeler, and Baxter herds ranged from 6.35 to 16.75 km); males from the Mount Warren/Mount Gibbs, Wheeler, and Sawmill herds ranged from 8.9 to 59.4 km (Sierra Nevada Bighorn Sheep Recovery Program 2004).

Terrestrial Habitat(s): Alpine, Bare rock/talus/scree, Cliff, Grassland/herbaceous, Shrubland/chaparral
Habitat Comments: Sierra Nevada bighorn sheep inhabit open areas where the land is rocky, sparsely vegetated, and characterized by steep slopes and canyons.. Habitats range from alpine to Great Basin sagebrush scrub. They prefer open ground and areas with good access to steep, rocky terrain (escape habitat) and so generally avoid forests, thick brush, and large expanses lacking precipitous escape terrain. In summer, most live at higher elevations (10,000-14,000 feet; 3,050-4,270 meters) in subalpine and alpine areas. Females occur largely in alpine environments, whereas males often are at somewhat lower elevations in subalpine habitats. In winter, they occupy high-elevation, windswept ridges if forage is available and tend to inhabit south-facing slopes where snow melts more readily, or they migrate to lower elevations in sagebrush-steppe areas to avoid deep snow and to find forage. Low-elevation winter ranges provide an important source of high quality forage early in the growing season. Reproductive female select steep, rugged slopes and canyons for lambing. Sources: McCullough and Schneegas (1966), Wehausen (1980), USFWS (2007, 2008).

USFWS (2008) determined that primary constituent elements (habitat features) for Sierra Nevada bighorn sheep include: (1) Non-forested habitats or forest openings within the Sierra Nevada from 4,000 feet (1,219 meters) to 14,500 feet (4,420 meters) in elevation with steep (greater than or equal to 60 percent slope), rocky slopes that provide for foraging, mating, lambing, predator avoidance, and bedding and that allow for seasonal elevational movements between these areas. (2) Presence of a variety of forage plants as indicated by the presence of grasses (e.g., Achnanthera spp.; Elymus spp.) and browse (e.g., Ribes spp.; Artemisia spp., Purshia spp.) in winter, and grasses, browse, sedges (e.g., Carex spp.) and forbs (e.g., Eriogonum spp.) in summer. (3) Presence of granite outcroppings containing minerals such as sodium, calcium, iron, and phosphorus that could be used as mineral licks in order to meet nutritional needs.

Johnson et al. (2007) used resource selection probability functions to identify important winter and summer habitat characteristics, and to generate predictive models of habitat use in unoccupied ranges. "Characteristics of topography and vegetation were significant in describing bighorn sheep winter habitat use, and only topographic characteristics were significant in describing summer habitat use. Habitat models were used to determine the amount of winter and summer range within each herd unit, the connectivity of seasonal ranges, areas at risk of contact with domestic sheep, and to simulate the effects of prescribed fire on bighorn sheep habitat."

Adult Food Habits: Herbivore
Immature Food Habits: Herbivore
Food Comments: These sheep are primarily grazers of grass, sedges, and forbs, but the diet can also include significant amounts of shrubs (USFWS 2008).
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Phenology Comments: Activity occurs throughout the year, primarily during daylight hours.
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: According to USFWS (2007), the following actions are needed immediately: 1. Protect existing herds through maximization of population growth and predator management. 2. Augmenting small herds through translocations; larger numbers of individuals are more likely to make adequate use of winter range essential for achieving positive population growth because they are able to be more vigilant to the presence of potential predators. 3. Preventing contact between Sierra Nevada bighorn sheep and domestic sheep or goats. Future actions include: 1. Reintroduce bighorn sheep to vacant herd units that are essential to recovery. 2. Monitor genetic variation of all herd units; take action to maintain variation if necessary. The recovery plan calls for development of a captive breeding contingency plan and separate implementation plans for: (1) bighorn sheep monitoring; (2) bighorn sheep translocation; (3) predator management; (4) genetic management; and (5) management of a disease outbreak.
Biological Research Needs: Additional investigations are needed to identify areas of conflict as situations arise where the increased presence of humans could be detrimental to the Sierra Nevada bighorn sheep or its habitat (USFWS 2008).
Population/Occurrence Delineation Not yet assessed
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Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 04Sep2013
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 22Aug2011
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Johnson, H., V. C. Bleich, and T. R. Stephenson. 2007. Habitat selection by mountain sheep and mule deer: a step toward understanding ecosystem health from the desert to the alpine. UC Davis Wildlife Helath Center, Department of Fish and Game Resource Assessment Program. Final report.

  • McCullough, D. R., and E. R. Schneegas. 1966. Winter observations on the Sierra Nevada bighorn sheep. California Fish and Game 52:68-84.

  • Ramey, R. R., II. 1995. Mitochondrial DNA variation, population structure, and evolution of mountain sheep in the south-western United States and Mexico. Molecular Ecology 4:429-439.

  • U.S. Fish and Wildlife Service (USFWS). 20 April 1999. Emergency rule to list the Sierra Nevada distinct population segment of California bighorn sheep as endangered. Federal Register 64(75):19300-19309.

  • U.S. Fish and Wildlife Service (USFWS). 2000. Final rule to list the Sierra Nevada distinct population segment of the California Bighorn Sheep as Endangered. Federal Register 65:20-30.

  • U.S. Fish and Wildlife Service (USFWS). 2007. Recovery plan for the Sierra Nevada bighorn sheep. USFWS, Sacramento, CA. xiv + 199 pp.

  • U.S. Fish and Wildlife Service (USFWS). 2008. Sierra Nevada bighorn sheep Ovis canadensis californiana (= Ovis canadensis sierrae) 5-year review: summary and evaluation. USFWS, Ventura Fish and Wildlife Office, Ventura, CA.

  • U.S. Fish and Wildlife Service (USFWS). 3 January 2000. Final rule to list the Sierra Nevada distinct population segment of the California bighorn sheep as endangered. Federal Register 65(1):20-30.

  • U.S. Fish and Wildlife Service (USFWS). 5 August 2008. Designation of critical habitat for the Sierra Nevada bighorn sheep (Ovis canadensis sierrae) and taxonomic revision. Federal Register 73(151):45534-45604.

  • Wehausen, J. D. 1980. Sierra Nevada bighorn sheep: history and population ecology. Ph.D. disseration, University of Michigan, Ann Arbor. 240 pp.

  • Wehausen, J. D., V. C. Bleich, and R. R. Ramey, II. 2005. Correct nomenclature for Sierra Nevada bighorn sheep. California Fish and Game 91(3):216-218.

  • Wehausen, J. D., and R. R. Ramey, II. 2000. Cranial morphometric and evolutionary relationships in the northern range of Ovis canadensis. Journal of Mammalogy 81:145-161.

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