Sierra Nevada Bighorns have a small population size and are said to be „one of the rarest mammalian taxa in North America“.

Names

English: Sierra Nevada Bighorn Sheep [2]

French: Mouflon Bighorn du Sierra Nevada [2]

German: Nevada Dickhornschaf [2] ((editor’s note: This name is misleading as it seems to refer to the state of Nevada, therefore it is advisable to proceed according to other languages and make it „Sierra Nevada Dickhornschaf“.))

Spanish: Carnero de Sierra Nevada [2]; ((editor’s note: Castello (2016), who is spaniard, prefers the term „Borrego“ for Bighorn, accordingly it should be „Borrego de Sierra Nevada.))

Other (putative) scientific names and synonyms: none known

„California Bighorn Sheep“ is not a synonym (see next entry) – but is still used as such, which causes confusion

For example Castello (2016) mentions the following states as regions, where Sierra Nevada Bighorns occur: British Columbia, Idaho, Nevada, Oregon, Washington, Utah – in fact the subspecies occurs only in California’s Sierra Nevada (see: „Distribution“).

Taxonomy

Ovis canadensis sierrae Grinnell, 1912 – California (Central and South Sierra Nevada) [16]

The taxonomy of North American mountain sheep has been revised by Wehausen and Ramey (2000). They designated the animals in the Sierra Nevada as O. c. californiana. Grinnell (1912) had assigned the subspecific epithet sierrae to animals from the Sierra Nevada and as it has been affirmed that sheep in the Sierra Nevada warrant subspecific recognition, judicious application of the rule of priority dictates they are again assigned to the subspecies sierrae (Wehausen et al. 2005). That nomenclature change ended the subspecies O. c. californiana. At the same time, all other wild sheep formerly designated as californiana were synoymized with O. C. canadensis or O. c. nelsoni. However, the name „California Bighorn“ incorrectly paired with the scientific name O. c. california, is still in use. [2]

Similar Subspecies

The Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae) is one of three currently recognised subspecies of Bighorn Sheep (Ovis canadensis). The other two are Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis) and Desert Bighorn Sheep (Ovis canadensis nelsoni).

Distinctions between subspecies: The Sierra Nevada Bighorn Sheep is considerably smaller than the Rocky Mountain Bighorn. Horns in Sierra Nevada Bighorns are shorter and less massive, and tend to have more flare. [1] Castello (2016) also writes that the pelage in Sierra Nevada Bighorns is „more grey than brown“, but the description of Damm and Franco (2014) is contradicting in stating that it is „varying from dark brown to greyish to pale almost whitish tan“. [2]

Distribution

by country / state: United States / California

distribution in detail: Sierra Nevada Bighorns occur within the Inyo and the Humboldt-Toiyabe National Forests. Some also live in the Sequoia/Kings Canyon National Park, Yosemite National Park, and the Sierra National Forests. [2]

Native Sheep live at Mt. Williamson, Mt. Baxter/Sawmill Canyon. Reintroductions of Sierra Nevada Bighorns from the Baxter population occurred at: Wheeler Ridge, Mono Basin (which includes the Lee Vining Canyon, Lundy Canyon, Mt. Warren and Mt. Gibbs), and Mt. Langley. [2]

Description

general appearance: like other Bighorn Sheep – stocky build with relatively short legs [2]

height at withers: 91 cm [2]

weight: about 100 kg (rams) – up to 145 kg; 63,5 kg (females) [2]

Colouration / pelage

pelage in general: The smooth coat consists of guard hairs and dense fleece, varying from dark brown to greyish to pale almost whitish tan. [2]

muzzle: white [2]

eye patch: white [2]

tail: short, dark [2]

rump patch: white [2]

belly: white [2]

legs: back side white [2]

Horns

Sierra Nevada Bighorn rams carry horns which are, compared to other Bighorn subspecies, notably wide and flaring, but relatively small. Brooming is thought to occur less frequently than in Rocky Mountain Bighorn sheep. The frontal horn surface is relatively smooth, without prominent lateral ridges. [2]

horn length, females: rarely exceed 30,5 cm [2]

Habitat

Sierra Nevada Bighorns are found on steep eastern slopes and high alpine habitat of southern and central regions of the Sierra Nevada where elevations are greatest: above 4.000 metres. They typically spend summers in the alpine (above 3.250 metres) and winters at the eastern base of the range as low as 1.450 metres. Some individuals of this subspecies may spend the entire year in alpine environment. [2]

Optimal Sierra Nevada Bighorn habitat is visually open and contains steep and generally rocky slopes. Forest and thick brush are usually avoided to the extent possible. Fire can play an important role in creating Bighorn habitat as well as making existing patches safer with regards to predators. [2]

Food and feeding

Nutrition strongly influences: time of lambing, growth rates of lambs, age and sexual maturity, frequency of lambing, and lamb survival to adulthood. [2]

Mortality / predators

Major predator: Puma (Puma concolor) [2]

Breeding

In general Sierra Nevada Bighorn Sheep are said to have slow population growth rates [2], but probably not different compared to other Bighorn subspecies.

sexual maturity: females at two years of age at best [2]

rutting season: in fall [2]

lambing season: restricted to spring and early summer – and not like desert populations [2]

number of young: one [2]

Movements, home ranges and social organisation

Large areas that lack precipitous escape terrain, such as the Owens Valley, represent substantial barriers to movement. Even within the Sierra Nevada the habitat is patchy and the population structure is one of natural fragmentation (Bleich et al. 1990). This includes multiple independent female subpopulations. Rams travel to and between these subpopulations. [2]

Altitudinal migrations are also common in the high mountains of the Sierra Nevada. The sheep minimize their exposure to environmental extremes and maximize their nutrient intake by occupying lower elevations in winter and spring, and then following the plant growing season up the mountain (Wehausen 1980, 1983). [2]

Status

IUCN classifies the species Ovis canadensis as „least concern“. Date assessed: 30 June 2008 [6]

„Given its small population size and recent population declines Sierra Navada Bighorn Sheep are currently more deserving of conservation attention than any other group of Bighorn Sheep. Sierra Nevada Bighorn Sheep are currently one of the rarest mammalian taxa in North America.“ Wehausen and Ramey 2000. [2]

The total population of Bighorn Sheep in the Sierra Nevada prior to settlement is unknown, but it probably exceeded 1.000 individuals. Following the discovery of gold in 1849, unregulated market hunting and diseases introduced by domestic livestock led to localised extirpations and in the latter half of the 20th century Sierra Nevada Bighorns experienced a series of dramatic declines. By 1995 the total population numbered few more than 100 individuals. In 1999 the California Fish and Game Commission classified the mountain sheep of the Sierra Nevada as a California endangered species; a month later the U. S. Fish and Wildlife Service classified it as a federal endangered species and January 2000 adjudicated full endangered species status (U.S. Fish and Wildlife Service 2000). At that time there were about 125 adult Bighorn remaining in the Sierra Nevada. Wehausen estimated total populations as follows:

2006: exceeding 400;

2011: at least 480;

2012: over 500 [2]

Threats

Diseases contracted from domestic livestock have been a problem. With the recovery plan in place (see below), this seems to be under control now. Predation by Mountain Lion may currently be the greatest threat to sustainability of Sierra Nevada Bighorn populations. [2]

Sierra Nevada Bighorns apparently never suffered from habitat fragmentation and to this day (2011) their habitat remains intact. [2]

Conservation

In 2008, after the Sierra Nevada Bighorn recovery plan was finally published, an area of more than 162.000 ha was designated as critical habitat for the subspecies. [2]

Before Sierra Nevada Bighorns obtained federal endangered status, California state law protected mountain lions. Once protected under the federal Endangered species Act, federal law superseded state law. Subsequently, the California State Legislature passed a law that permitted the killing of Mountain Lions to protect Bighorn Sheep. [2]

Recreational Hunting

In 1878, State legislation provided temporary protection from hunting for all Bighorn Sheep (Ovis canadensis) in California. In 1883, that protection became permanent, a status that remains in force today (2014) for all Bighorn Sheep in the Sierra Nevada. [2]

Ecotourism

Sierra Nevada Bighorns can sometimes be seen in summer around Mono Pass in Yosemite National Park and at Rae Lakes in Sequoia National Park. [3]

Literature cited

[1] Castelló, José R., 2016: Bovids of the World – Antelopes, Gazelles, Cattle, Goats, Sheep, and Relatives. Princeton University Press

[2] Damm, Gerhard R. and Franco, Nicolás, 2014: The CIC Caprinae Atlas of the World – CIC International Council for Game and Wildlife Conservation, Budakeszi, Hungary in cooperation with Rowland Ward Publications RSA (Pty) Ltd., Johannesburg, South Africa

[3] Dinets, Vladimir, 2015: Peterson Field Guide to Finding Mammals in North America. Houghton Mifflin Harcourt Publishing Company

[16] Wilson, D. E. and Mittermeier, R. A. [eds], 2011: Handbook of the mammals of the world. Vol. 2. Hoofed mammals. Lynx Edicions, Barcelona.