Ovis canadensis

Bighorn Sheep live only in remote, treeless mountain terrain. They use steep slopes and cliffs to escape from wolves, coyotes, and cougars. Many migrate seasonally, some moving a few hundred meters up or down a mountainside and others going 10-20 km from one mountain range to another. Some males make much longer migrations. Males and females live apart except during the mating season, when males vie for access to females. Larger size and age usually confer an advantage. The males rear up on their hind legs, kicking with their front legs and clashing their horns. Although Bighorn Sheep have heavily buttressed heads that absorb the shock of butting, these battles can result in death. Ewes usually give birth to one lamb, in May; twins are extremely rare. The lambs can follow their mothers within a day after birth, and nurse for 4-5 months. Bighorns eat seasonally available grasses and other vegetation, and cactus in the desert. They are attracted to natural salt licks, cattle licks, and piles of salt placed along highways for melting snow. In some places where bighorn populations went extinct, groups have been reintroduced, but many parts of their original range are no longer suitable. The species is declining in desert areas.

Links:
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The former range of the bighorn sheep extended from the Northern Rocky
Mountains of Canada south to the mainland of Mexico and Baja California
[22]. It is now found in relatively isolated pockets in the Coast and
Cascade ranges and the Sierra Nevada, and in the Rocky Mountains south
of the Peace River to Mexico [6].

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
16 Upper Missouri Basin and Broken Lands

AZ CA CO ID MT NM NV ND OR SD TX UT WA WY AB BC MEXICO

The bighorn sheep ranges widely in western Canada, western United States, and northern Mexico.

In Canada, the bighorn sheep (O. c. canadensis) is distributed throughout the Rocky Mountains in Alberta and British Columbia, south from the Peace River to the Canada-USA border. Two small populations also have been introduced to central British Columbia outside their normal distribution. Populations of a second subspecies, California bighorn sheep (O. c. californiana), are scattered through central British Columbia from north of Anahim lake, south along sections of the Chilcotin, Chilco and other western tributaries of the Fraser river south of William’s Lake and west to just north of Lillooet, and also south from around Kamloops along both sides of the Okanagan valley to the border with Washington State (USA) and as far west as Granby, British Columbia. Populations around Kamloops and Granby have been introduced, mostly into historically occupied habitat.

In the United States, the bighorn sheep is widely distributed from Montana and Idaho south through Wyoming and northern Utah, to Colorado and New Mexico. These bighorn herds comprise most of the traditional O. c. canadensis for which Thorne et al. (1985) estimated a population of greater than 19,000. To the south, desert bighorn (traditionally O. c. nelsoni, O. c. cremnobates, and O. c. mexicana) inhabit southern portions of California, Nevada, Utah and New Mexico, much of Arizona, and west Texas. Weaver (1985) estimated 16,000 desert bighorn in this area. However, there are few bighorn and few herds (mostly transplants to reintroduce bighorns in areas where they were extirpated) within the Chihuahuan desert of New Mexico and west Texas. To the west, bighorn occur in scattered populations in the Columbia plateau and Great Basin ranges of Washington, Oregon, southwest Idaho, and northern Nevada. These herds comprise most of the traditional O. c. californiana, for which Thorne et al. (1985) estimated greater than 2,800 animals. East of the Rocky Mountains, bighorn exist in scattered herds in badlands and river-breaks in eastern Montana, North and South Dakota, northeast Wyoming, Nebraska, and outside of historic range in southeast Colorado.

In Mexico, the bighorn sheep was originally distributed in the northern states of Nuevo Leon, Coahila, Chihuahua, Sonora, Baja California and Baja California Sur. Desert bighorn in Mexico is now restricted to three states: Mexican bighorn (O. c. mexicana) in northwestern Sonora and on Tiburon island in the Sea of Cortez; Peninsular bighorn (O. c. cremnobates) in the northern two thirds of Baja California; and Weems’ bighorn (O. c. weemsi) in the southern third of Baja California Sur.

Ovis canadensis is found in the Rocky Mountains from southern Canada to Colorado, and as a desert subspecies (O. c. nelsoni) from Nevada and California to west Texas and south into Mexico.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Range includes mountains and river breaks from southwestern Canada (southern British Columbia and southwestern Alberta) south through the Rocky Mountains, Sierra Nevada, and desert mountains of the southwestern United States to Baja California and the northwestern mainland of Mexico. Distribution is naturally fragmented in many areas due to discontinuity of habitat. Local extirpations and subsequent reintroductions from local or distant stocks have occurred in many parts of the range. For example, this species formerly ranged east to the badlands in western North Dakota and Black Hills of South Dakota; after extirpation there, individuals from non-native populations were introduced (Valdez and Krausman 1999).

Males 119-127kg; females 53-91 kg. Rams typically measure 160-180 cm from head to tail, while ewes are approximately 150 cm. Bighorn sheep have double-layered skulls shored with struts of bone for battle protection. They also have a broad, massive tendon linking skull and spine to help the head pivot and recoil from blows. Horns may way as much as 14 kg, which is the weight of all the bones in a ram's body. The horns of a female are much smaller and only slightly curved. The horns of a ram can tell much about him such as his age, health, and fighting history. The desert subspecies, Ovis canadensis nelsoni, is somewhat smaller and has flatter, wider-spreading horns. The pelage of Ovis canadensis is smooth and composed of an outer coat of brittle guard hairs and short, grey, crimped fleece underfur. The summer coat is a rich, glossy brown but it becomes quite faded by late winter.

Range mass: 53 to 127 kg.

Range length: 150 to 180 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger; ornamentation

Average basal metabolic rate: 114.674 W.

Length: 185 cm

Weight: 150000 grams

Sexual Dimorphism: Males are larger than females.

Length:
Range: 1.6-1.9 m males; 1.6-1.7 m females

Weight:
Range: 75-135 kg males; 48-85 kg females

Habitat Type: Terrestrial

Comments: Bighorn sheep occur in mesic to xeric, alpine to desert grasslands or shrub-steppe in mountains, foothills, or river canyons (Shackleton et al. 1999, Krausman et al. 1999). Many of these grasslands are fire-maintained (Geist 1971, Erickson 1972). Suitable escape terrain (cliffs, talus slopes, etc.) is an important feature of the habitat. In winter, Rocky Mountain Bighorns spend as much as 86% of their time within 100 meters of escape terrain (Oldemayer et al. 1971, Erickson 1972), and usually stay within 800 meters of escape terrain throughout the year (Pallister 1974). Mineral licks are more important in the range of Rocky Mountain Bighorn than in the range of "California" Bighorn, presumably because the soils in the range of the former are generally lower in mineral content (Van Dyke 1978). Distribution is correlated with low precipitation levels, especially in winter and spring. Elevation varies considerably, both geographically and seasonally, from as low as 450 meters to over 3,300 meters (Shackleton et al. 1999).

Winter ranges of northern populations are relatively snow-free because of light snow, steep south aspect, and/or high winds; bighorns generally avoid snow deeper than 30 centimeters (Stelfox 1975). The solar heat on south aspects also reduces cold stress on sheep (Shackleton et al. 1999).

In the north, bighorn sheep usually are not dependent on free-standing water, getting water instead from succulent vegetation in the summer and snow or ice in the winter (Van Dyke 1978). However, in some southwestern deserts they may be dependent on access to free water during summer (Turner 1979, Turner and Weaver 1980, Seegmiller and Ohmart 1981).

Bighorn Sheep - Peninsular Ranges

Habitat includes steep slopes and cliffs, rough and rocky topography, and sparse vegetation (Monson and Summner 1980), "with use of alluvial fans and washes, and valley floors depending on environmental conditions and dispersal requirements" (USFWS 2011; see also Monson and Sumner 1980 and USFWS 2000). Females about to give birth "seek secluded sites with shelter, unobstructed views, and steep terrain, ...while rams may be found in less steep or rugged terrain" (USFWS 2011). In the Peninsular Ranges, bighorn sheep generally stay elevationally below the pinyon pine-juniper and chararral vegetation zones (USFWS 2011). Vegetation of occupied habitat often includes Agave deserti (agave)-Fouquieria splendens (ocotillo), Opuntia spp. (cholla)-Cercidium floridum (palo verde), and Larrea tridentata (creosote)-Prosopis spp. (palo verde-mesquite). Bighorns use open areas and generally avoid areas where visibility is obstructed by thick vegetation.

Valley floors provide important linkages between adjacent mountainous regions and allow bighorn sheep access to resources (e.g., forage, water, lambing habitat) in neighboring areas; these lowlands also allow gene flow to occur between subpopulations (USFWS 2011). Bighorns may forage or access water on gentle terrain (e.g., alluvial fans and washes) but may travel quickly through valley floors to reach nearby mountains (Simmons, in Monson and Sumner 1980). Reproductive females may make heavy use of the food resources on alluvial fans and washes, and these areas can be important in summer and during droughts, when nutritious forage is scarce elsewhere (Andrew 1994).

North-facing slopes provide cooler refuges during the hottest weather, and south-facing slopes may be used on cold winter days (Andrew 1994).

In summer, bighorn sheep may congregate around water sources; most sheep stay wihtin 3-5 km of water (see USFWS 2011). They may abandon areas where no standing water exists. Above-average rainfall and cooler temperatures may allow bighorns to occupy habitats that may be abandoned during droughts (USFWS 2011).

Suitable habitat exists as a narrow north-south continuum from the San Jacinto Mountains all the way to the U.S.-Mexico border (Rubin et al. 2009).

Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae)

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."

More info for the terms: cover, shrub, shrubs

Escape terrain is an important habitat requirement for bighorn sheep.
Cliffs, rock rims, rock outcroppings, and bluffs with sparse cover of
trees or shrubs typify escape habitat, which provides both thermal and
hiding cover. While bighorn sheep are not always found in precipitous
mountain areas, ewes and lambs rely on these areas for escape cover,
especially during the lambing period [6,26,27].

Visibility is another important habitat component for bighorn sheep. It
allows for predator detection, visual communication, and efficient
foraging [4]. Bighorn sheep tend to forage in open areas with low
vegetation such as grasslands, shrublands, or mixes of these. They
avoid foraging on mild slopes with shrub or canopy cover in excess of 25
percent and shrubs 2 feet (60 cm) or higher. On steep slopes they have
been noted to travel through or bed in dense brush [26].

More info for the term: shrubs

Bighorn sheep occupy a variety of plant communities ranging from alpine
meadows, woodlands, mixed-grass prairie, shrub-bunchgrass, and dry
pinyon-juniper (Pinus-Juniperus spp.) [2,7,14,25,27]. They avoid dense
forests [6].

Summer ranges of bighorn sheep in southeastern Oregon vary from
subalpine meadows or grasslands to sagebrush (Artemisia spp.)/grasslands
or shrublands. Winter ranges are usually shrub/grasslands and
shrublands. Communities dominated by trees or tall shrubs such as aspen
(Populus spp.), cottonwood (Populus spp.), fir (Abies spp.), pine,
juniper, mountain-mahogany (Cercocarpus spp.), squaw apple (Peraphyllum
ramosissimum), and cherry (Prunus spp.) may occur throughout both summer
and winter ranges [26].

On two bighorn sheep winter ranges in the upper Yellowstone River
Valley, vegetation types in which bighorns were observed included
bluebunch wheatgrass (Pseudoroegneria spicata), needle-and-thread (Stipa
comata), and Idaho fescue (Festuca idahoensis) grasslands; sagebrush
(primarily A. tridentata) and black greasewood (Sarcobatus vermiculatus)
shrublands; open Douglas-fir (Pseudotsuga menziesii) woodland; and the
vegetation mosaics associated with cliffs and draws [14]. Bighorn sheep
range in Glacier National Park includes bunchgrass communities dominated
by bluebunch wheatgrass, Idaho fescue, rough fescue (F. scrabrella), and
Saskatoon serviceberry (Amelanchier alnifolia); and seral vegetation of
subalpine fir (Abies lasiocarpa) habitat types [24].

Other plant species common on bighorn sheep range include bitterbrush
(Purshia tridentata), mountain muhly (Muhlenbergia montana), russet
buffaloberry (Shepherdia canadensis), bearberry (Arctostaphylos
uva-ursi), blue grama (Bouteloua gracilis), rabbitbrush (Chrysothamnus
spp.), bluegrass (Poa spp.), buffalograss (Buchloe dactyloides), western
wheatgrass (Pascopyron smithii), and sedges (Carex spp.) [2,7,11,24,25].

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the term: shrub

K003 Silver fir - Douglas-fir forest
K004 Fir - hemlock forest
K005 Mixed conifer forest
K010 Ponderosa shrub forest
K011 Western pondersoa forest
K012 Douglas-fir forest
K015 Western spruce - fir forest
K016 Eastern ponderosa forest
K018 Pine - Douglas-fir forest
K019 Arizona pine forest
K020 Spruce - fir - Douglas-fir forest
K021 Southwestern spruce - fir forest
K022 Great Basin pine forest
K024 Juniper steppe woodland
K023 Juniper - pinyon woodland
K028 Mosaic of K002 and K026
K029 California mixed evergreen forest
K031 Oak - juniper woodlands
K032 Transition between K031 and K037
K035 Coastal sagebrush
K037 Mountain-mahogany - oak scrub
K038 Great Basin sagebrush
K039 Blackbrush
K040 Saltbush - greasewood
K041 Creosotebush
K042 Creosotebush - bursage
K047 Fescue - oatgrass
K050 Fescue - wheatgrass
K051 Wheatgrass - bluegrass
K053 Grama - galleta steppe
K054 Grama - tobosa prairie
K057 Galleta - three-awn shrubsteppe
K058 Grama - tobosa shrubsteppe
K059 Trans-Pecos shrub savanna
K052 Alpine meadows and barren
K063 Foothills prairie
K064 Grama - needlegrass - wheatgrass
K065 Grama - buffalograss
K066 Wheatgrass - needlegrass
K067 Wheatgrass - bluestem - needlegrass
K068 Wheatgrass - grama - buffalograss
K069 Bluestem - grama prairie
K070 Sandsage - bluestem prairie
K074 Bluestem prairie

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES23 Fir-spruce
FRES26 Lodgepole pine
FRES29 Sagebrush
FRES30 Desert shrub
FRES32 Texas savanna
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES37 Mountain meadows
FRES38 Plains grasslands
FRES39 Prairie
FRES40 Desert grasslands
FRES44 Alpine

Bighorn sheep inhabit remote mountain and desert regions. They are
restricted to semiopen, precipitous terrain with rocky slopes, ridges,
and cliffs or rugged canyons [6,26]. Forage, water, and escape terrain
are the most important components of bighorn sheep habitat [26].

Winter range - Generally, bighorn sheep have two distinct, separate
summer and winter ranges [6]. Most of the year is spent on the winter
range, where the elevation is typically below 10,826 feet (3,300 m).
The aspect is usually south or southwest. Rams often venture onto the
more open slopes, although rugged terrain is always nearby. Desert
bighorn sheep rarely stray far from the base of a mountain and usually
are found on eastern aspects, where they use dry gullies. During
severe weather, if snow becomes unusually deep or crusted, bighorn sheep
move to slightly higher elevations where wind and sunshine have cleared
the more exposed slopes and ridges [6].

Spring range - The spring range is generally characterized by the same
parameters as the winter range. However, bighorn sheep begin to respond
to local greenups along streambanks and valleys. Bighorn sheep use
areas around saltlicks heavily in the spring. Preferred lambing range
is in the most precipitous, inaccessible cliffs near forage, and
generally has a dry, southern exposure [6].

Summer range - In the summer, bighorn sheep are mostly found grazing on
grassland meadows and plateaus above timber. In early summer south and
southwestern exposures are most frequently utilized; however, in the
case of the desert bighorn sheep the eastern aspect is preferred. By
late summer the more northerly exposures are preferred [6]. Snow
accumulation seems to be the principal factor that triggers bighorn
sheep to move from summer to winter ranges [26].

Water - Bighorn sheep obtain water from dew, streams, lakes, springs,
ponds, catchment tanks, troughs, guzzlers, and developed seeps or
springs [26]. Alkaline water is not suitable. Bighorn sheep spend most
of their time within 1 mile (1.6 km) of water but have been located as
far as 2 miles (3.2 km) from water. Water sources more than 0.3 mile
(0.5 km) from escape terrain or surrounded by tall dense vegetation are
avoided by bighorn sheep [26]. Desert bighorn sheep primarily utilize
ephemeral water sources. They may drink every day if water is nearby,
but may go without water for up to 14 days in the dry season. Since
water is one of the major limiting factors of desert bighorn sheep,
management agencies have installed cisterns and other water developments
in critical areas [6].

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This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

204 Black spruce
205 Mountain hemlock
206 Engelmann spruce - subalpine fir
208 Whitebark pine
210 Interior Douglas-fir
218 Lodgepole pine
220 Rocky Mountain juniper
230 Douglas-fir - western hemlock
237 Interior ponderosa pine
238 Western juniper
239 Pinyon - juniper

Habitat and Ecology

Systems

• Terrestrial

Ovis canadensis canadensis inhabits alpine meadows, grassy mountain slopes and foothill country in proximity to rugged, rocky cliffs and bluffs. Bighorn sheep require drier slopes where the annual snowfall is less than about sixty inches a year, since they cannot paw through deep snow to feed. The winter range usually lies between 2,500-5,000 feet in elevation, while the summer range is between 6,000-8,500 feet.

Range elevation: 800 to 2500 m.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: desert or dune ; chaparral ; mountains

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Populations other than those in low deserts typically migrate between an alpine or montane summer range and a lower elevation winter range (Shackleton et al. 1999). Some may occupy as many as five separate ranges during a year (Geist 1971). This vertical migration is probably a response to the increasing abundance of nutritious, new vegetative growth at higher elevations as spring and summer progress (Shackleton et al. 1999). The downward migration is motivated by snow accumulation in the high elevation summer ranges (Shackleton et al. 1999).

Bighorn Sheep - Peninsular Ranges

"This population...exhibits a metapopulation structure, and requires habitat necessary to accommodate movements of males (rams), and more rarely females (ewes), between ewe groups (subpopulations)" (USFWS 2011).

In the San Jacinto Mountains, fixed-kernel home range sizes averaged 25 square kilometers for males and 20 square kilometers for females (DeForge et al. 1997). Home range size depends on forage quantity and quality, season, sex, and age of the animal, and on the location of required resources such as water, forage, escape terrain, and lambing habitat (USFWS 2000). In many populations, home range size is smaller in summer thatn in winter, presumably because movement away from permanent water sources is more restricted in the hotter months (see sources cited in USFWS 2011).

"The gregarious and philopatric (faithful to natal home range) behaviors of ewes limit their dispersal and exploratory abilities relative to those of rams" (USFWS 2011). Young learn seasonal movement patterns from their mothers. Adult males are more vagile than females and young, and they often move among groups of females. Young maleseventually begin to follow older males and may adopt their traditional travel routes.

In the Peninsular Ranges, movement of radio-collared females between female groups is rare, although inter-group movement does occasionally occur (Rubin et al. 1998).

Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae)

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).

Comments: Diet is diverse and variable. Bighorn sheep are primarily grazers of grass and forbs, but the diet can also include significant amounts of shrubs (Miller and Gaud 1989, Krausman et al. 1999, Shackleton et al. 1999). Diet changes seasonally. Access to mineral lick may be important for Rocky Mountain and desert bighorns, especially in spring (Shackleton et al. 1999, Krausman et al. 1999).

More info for the term: forbs

Bighorn sheep primarily graze grasses and forbs, but eat other
vegetation depending on availability [6]. They prefer green forage and
move up- or downslope or to different aspects for more palatable forage.
Forage areas that provide a variety of aspects are preferable because
they provide green forage for longer periods [26].

Bighorn sheep eat sedges and a variety of grasses including bluegrasses
(Poa spp.), wheatgrasses, bromes, and fescues. Browse species include
sagebrush, willow (Salix spp.), rabbitbrush, curlleaf mountain-mahogany
(Cercocarpus ledifolius), winterfat (Kraschnennikovia lanata),
bitterbrush, and green ephedra (Ephedra spp.). Forbs include phlox
(Phlox spp.), cinquefoil (Potentilla spp.), twinflower (Linnaea
borealis), and clover (Trifolium spp.) [6,23].

Because of the dry climate, browse is the dominant food of the desert
bighorn sheep and includes desert holly (Atriplex hymenelytra),
honeysweet (Tidestromia oblongifolia), brittlebush or encelia (Encelia
spp.), hairy mountain-mahogany (C. breviforus), Wright silktassel
(Garrya wrightii), desert mallow (Sphaeralcea ambigua), Russian-thistle
(Salsola kali), false mesquite (Calliandra eriophylla), goatnut
(Simmondsia chinensis), white ratany (Krameria canescens), bursage
(Hyptis emoryi), mesquite (Prosopis glandulosa), catclaw (Acacia
greggii), ironwood (Olneya tesota), paloverde (Cercidium spp.),
pincushion (Mammillaria spp.), and saguaro (Carnegiea gigantea). Dry
grasses are eaten throughout the year and are an important food reserve,
especially near waterholes [6].

Bighorn sheep are mainly diurnal, feeding intermittently throughout the day. Ovis canadensis canadensis is largely a grazer, consuming grasses, sedges, and forbs, but it will take some browse when preferred food is scarce (especially in winter). Desert bighorns (O. c. nelsoni) eat a variety of desert plants and get most of their moisture from the vegetation, although they still visit water holes every several days.

Plant Foods: leaves

Primary Diet: herbivore (Folivore )

Golden eagles (Aquila chrysaetos) occasionally threaten bighorn sheep
lambs, but are rarely successful in taking one. Bighorn sheep are an
incidental food item in the diet of grizzly or black bears (Ursus
arctos, U. americanus) and wolverines (Gulo gulo), and are generally
eaten only as carrion. Wolves (Canis lupus), coyotes (C. latrans),
mountain lions (Felis concolor), and bobcats (Lynx rufus) are other
predators of bighorn sheep [6,26]. The number of bighorn sheep taken by
predators is usually of little consequence to healthy populations.
Predators are most effective when locations of escape terrain or water
limit sheep movement and allow predators to concentrate hunting efforts
[26].

Bighorn sheep are hunted by humans. Hunting has traditionally been for
rams only and is further restricted by a 3/4 or full horn curl policy.
In the last few years most states and provinces have adopted more
stringent horn curl regulations. While the overall trend has been for
more restrictive hunting seasons, in some cases local situations have
dictated either sex or 1/2 curl ram seasons [6].

Bighorn sheep are important predators of grasses and shrubs in their native landscapes, they are also important sources of prey for large predators. Bighorn sheep are hosts for a number of parasites. Nematode lungworms, Protostrongylus stilesi and P. rushi, infect all bighorn sheep individuals and probably co-evolved with these sheep in North America. Most sheep do not experience any significant deleterious effects of lungworms.

Commensal/Parasitic Species:

• Protostrongylus stilesi
• P. rushi

The availability of escape territory in the form of rocky cliffs is important to bighorn sheep survival. If a sheep can reach a rocky outcrop or cliff, it is usually safe from the attack of wolves, coyotes, bears, Canada lynx, and mountain lions. Golden eagles (Aquila chrysaetos) may take some lambs.

Known Predators:

• wolves (Canis lupus)
• coyotes (Canis latrans)
• bears (Ursus)
• Canada lynx (Lynx canadensis)
• mountain lions (Puma concolor)
• Golden eagles (Aquila chrysaetos)

Ovis canadensis (bighorn sheep, wapiti, mule deer) is prey of:
Gulo gulo
Ursus arctos

Based on studies in:
USA: Montana (Tundra)

This list may not be complete but is based on published studies.

Ovis canadensis (bighorn sheep, wapiti, mule deer) preys on:
alpine vegetation

Based on studies in:
USA: Montana (Tundra)

This list may not be complete but is based on published studies.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

Comments: Estimated in Demarchi et al. (1999a).

10,000 - 100,000 individuals

Comments: In 1991, the total population was estimated to be 70,840: Rocky Mountain-37,969; California-9816; and Desert-23,055 (Valdez and Krausman 1999). In 1992, End. Sp. Tech Bull. (17(3-8):6) reported that desert populations in the U.S. declined to 1171 by 1979 and to fewer than 400 in the early 1990s, and that 1500-2500 still occur in Mexico.

More info for the term: polygamous

Breeding season - Bighorn sheep are polygamous. Ewes are monesterous.
Rams of most subspecies rut in November and December. However, desert
bighorn sheep may rut for up to 9 months, with rutting reaching a peak
in August and September [6].

Age at sexual maturity - The age at which ewes attain sexual maturity is
quite variable and is dependent mainly on their physical condition [6].
Most bighorn sheep become mature at 2.5 years of age. Large-bodied rams
may reach sexual maturity within 18 months, but smaller rams may take as
long as 36 months. Very old ewes generally do not breed [6].

Gestation and lambing - The gestation period is 5.5 to 6 months. The
majority of ewes give birth to one lamb per year. Lambing of northern
bighorn sheep occurs between late April and late June, with most lambs
born before the end of May. Desert bighorn sheep ewes give birth
throughout the year; however, the peak is from January to April [6].

Development of lambs - Bighorn sheep lambs are precocious and within a
day or so climb almost as well as their mothers. Within 2 weeks lambs
can eat grass. They are weaned between 1 and 7 months. By their second
spring bighorn sheep are totally independent of their mother. Ewes
reach their adult weight by 4 to 5 years of age, while rams do not
achieve maximum weight until they are 6 or 7 years old [6].

Life span - Mortality is high for bighorn sheep 1 to 2 years of age,
drops to a relatively low rate for 2 to 8 years of age, then increases
to a maximum for those older than 8 to 9 years. Bighorn sheep that live
past 8 or 9 years may live to 15 to 17 years of age, but 10 to 12
years is more common [6].

Bighorn sheep are territorial. By 4 years of age, individuals have
established home ranges that are utilized throughout their life span [6].

Gregarious, but for most of the year adult males live apart from females/young (Shackleton et al. 1999, Krausman et al. 1999). Among mature males, older males (up to an age of not more than 10 years) generally dominate younger males during the breeding season; males older than 10 years decline rapidly in condition. In western Arizona, January-June home range of adult females was 19-27 sq km (Seegmiller and Ohmart 1981). Male annual home range up to 37 sq km in Nevada (Leslie and Douglas 1979).

Carrying capacity for bighorn can be reduced through grazing by other ungulates (cattle, burros, etc.). In the Santa Catalina Mountains of southern Arizona, not limited by forage quantity or quality (Mazaika et al. 1992).

Contact with a stray domestic sheep is believed to have resulted in the death (through bacterial pneumonia) of entire reintroduced herd of 65 in Warner Mountains, California (California Department of Fish and Game 1990). In some areas, lungworm infections may predispose bighorn to respiratory infection by opportunistic bacteria; lungworm life cycle involves gastropod intermediate host.

In desert, can survive 10 or more days in summer without drinking; may meet water needs in part by eating barrel cacti (Warrick and Krausman 1989).

PREDATION: Probably live in groups primarily to reduce predation (Shackleton et al. 1999). Coyotes may be a significant predator on young in some areas, killing up to 80% of the year's lambs (Hebert and Harrison 1988, Harper 1984, Hass 1989). Cougars can be important predators as well (Harrison and Hebert 1988, Krausman et al. 1999), and can have significant impacts on remnant or transplant herds (Krausman et al. 1999). Direct losses to predation are not generally as important as the fact that predation has forced females and young to use less productive habitats in and near escape terrain (Festa-Bianchet 1988, Demarchi et al. 1999a).

Bighorn sheep are very alert and have remarkable eyesight that allows them to judge distances accurately in jumping and locating footholds. They often watch other animals moving at distances of up to a mile away. Bighorn sheep probably also use chemical cues, as do most mammals, to distinguish reproductive states and may use visual cues to assess dominance among males. Bighorn sheep are less vocal than domestic sheep. The lambs bleat, and ewes respond with a gutteral "ba." At other times of the year, adults utter throaty rumbles or "blow" in fright. During the rut, the rams frequently snort loudly.

Communication Channels: visual ; acoustic ; chemical

Perception Channels: visual ; acoustic

Comments: During the day, feeding alternates with rest-rumination periods. Daily activity may vary seasonally; often feeding peaks in early morning and at dusk. In winter, feeding periods are longer.

Longevity depends on population status. In declining or stable populations, most sheep live over 10 years, with a maximum of 19 years. However in an expanding population with heavy reproduction, average life span is only 6 to 7 years. Females have been known to live up to 19 years and males to 14 but attaining these ages is rare. Even in areas where no hunting occurs, females rarely make it past 15 and males rarely live beyond 12. Juvenile mortality is variable and can be quite high, from 20 to 80%, averaging 5 to 30%. Between the ages of 2 and 6 there is relatively low mortality.

Range lifespan
Status: wild: 19 (high) years.

Typical lifespan
Status: wild: 6 to 15 years.

Maximum longevity: 20.6 years (captivity) Observations: Young females have an over 90% survival in the wild, though an increased mortality with age has been reported for both males and females after about 8 years of age (Loison et al. 1999). It has been reported that these animals live up to 24 years in captivity (David Macdonald 1985), which could be overestimated. Record longevity in captivity is 20.6 years (Richard Weigl 2005).

Bighorn sheep are perhaps best known for the head-to-head combat between males. Horn size is a symbol of rank, and the mass of the horns (as much as 14 kg) is used to a male's best advantage as he smashes into an opponent at speeds of 20 miles per hour. Combat has been observed to last for as long as 25.5 hours (with approximately 5 clashes an hour) until one of the males conceded. Males do not defend territories but rather engage in battles over mating access to a particular female. Male dominance status is determined by age as well as horn size, and homosexual activity often occurs in groups of males with the dominant animal behaving like a courting male and the subordinate playing the role of an estrous female. Ewes are seasonally polyoestrous and will accept several rams, often frequently, when in oestrus. Because of intense competition between males for females and the dominance hierarchy based on age and size (including the size of the horns), males do not usually mate until they are seven years old. Younger males will mate sooner if dominant rams in their group are killed.

Mating System: polygynous

Rutting season is in the autumn and early winter, and births take place in the spring. Mating for the desert bighorn, however, can last from July to December. Gestation lasts from 150-180 days, after which usually one, rarely two, young are born. Newborns are precocial and are able to follow their mothers at a good pace over the rocky terrain after the first week. Within a few weeks of birth, offspring form bands of their own, seeking out their mothers only to suckle occasionally. They are completely weaned by 4 to 6 months of age. Ovis canadensis females have been mated when 10 to 11 months old in captivity, but they generally do not breed until their second or third year in the wild.

Breeding interval: Bighorn sheep breed once yearly.

Breeding season: Mating occurs from July to December, with most activity concentrated in the fall rut.

Range number of offspring: 1 to 2.

Average number of offspring: 1.36.

Range gestation period: 5 to 6 months.

Range weaning age: 4 to 6 months.

Range time to independence: 4 to 6 months.

Range age at sexual or reproductive maturity (female): 1 (low) years.

Average age at sexual or reproductive maturity (female): 2-3 years.

Range age at sexual or reproductive maturity (male): 7 (high) years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average birth mass: 4400 g.

Average number of offspring: 1.

Female bighorn sheep seek out protected areas to give birth to their lambs. They nurse the young for 4 to 5 months, with the lambs increasing from about 4 kg at birth to 25 to 35 kg at weaning (males generally weighing more). Lambs are capable of walking and following their mothers on precipitous terrain soon after birth. Males do not participate in parental care.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female); post-independence association with parents; extended period of juvenile learning

The timing of the mating season varies throughout the range. Bighorns in southwestern deserts have an extended season encompassing several months (Krausman et al. 1999), but the season is relatively later and shorter elsewhere, generally November in the northern part of the range (Shackleton et al. 1999), November-December in some southern California mountains (DeForge (1980). Gestation lasts about 175 days (Geist 1971, Shackleton et al. 1999). Lambing generally peaks in March in desert populations (Rubin et al. 2000), May (occasionally April or June) in the remainder of range (Krausman et al. 1999, Shackleton et al. 1999). Litter size is 1, rarely 2 (Geist 1971, Turner and Hansen 1980).Young are weaned in 4-6 months. Females first breed usually in second year in south, third year in north; occasionally in first year in some areas (Krausman et al. 1999, Shackleton et al. 1999); fecundity generally declines only slightly after eight years of age (Caughley 1977).

In the mating season, mature males battle over access to females through vigorous head butting contests, but during most of the rest of the year they live amiably in small bands apart from the females.

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There is 1 barcode sequence available from BOLD and GenBank.   Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen.  Other sequences that do not yet meet barcode criteria may also be available.

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 4
Species With Barcodes: 1

Information on state- and province-level protection status of animals in the
United States and Canada is available at NatureServe, although recent changes
in status may not be included.

Nelson's Peninsular and Sierra Nevada bighorn sheep are listed as endangered [28].

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 1996
  Lower Risk/conservation dependent

Several populations may be threatened with eventual extinction, bighorn numbers are only one-tenth the population that existed when western settlers first began exploiting the Rockies. Their main threats are unregulated or illegal hunting, introduced diseases, competition from livestock, and continual human encroachment on their habitat. The subspecies O. c. auduboni of the Black Hills and adjacent areas has already become extinct. Bighorn sheep are incompatible with domestic sheep because they are susceptible to diseases of domestic livestock, including pneumonia, which is periodically responsible for large die-offs in bighorn sheep populations. Hunting has been prohibited or controlled since the early 1900's, but much illegal poaching still occurs. Hunting for trophies is particularly damaging to the cohesiveness of bighorn groups because it eliminates the dominant, breeding males. Recovery of numbers has been slow for these animals and their future is threatened unless further conservation measures are implemented. California bighorn sheep (O. c. californicus) are considered endangered under the U.S. Endangered Species Act.

US Federal List: endangered

CITES: appendix ii; no special status

IUCN Red List of Threatened Species: least concern

"#The Ovis canadensis weemsi, Weems' Bighorn Sheep, is Critically Endangered; Peninsula Bighorn Sheep, Ovis canadensis cremnobates, is an Endangered subspecies; the Mexican Bighorn Sheep, Ovis canadensis mexicana, is Vulnerable."

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Still widespread in western North America from Canada to Mexico, although populations are much smaller than in the past. In some areas threatened by habitat changes resulting from fire suppression, interactions with feral and domestic livestock, and human encroachment; protected in some areas through adequate management.

Population

Population Trend

Global Short Term Trend: Relatively stable (=10% change)

Comments: Recent trends seem more or less stable; some increases are apparently offset by local dieoffs. Some sources conclude that numbers of Rocky Mountain bighorn sheep are increasing, whereas others cite declines due to habitat loss and disease (Risenhoover et al. 1988). Population on east slope of Sierra Nevada has increased in recent decades due to reintroduction program (California Department of Fish and Game 1990). (California and Baja California) has declined (California Department of Fish and Game 1990). A die-off occurred in Canyonlands National Park/Glen Canyon NRA and vicinity in the 1980s (Park Science, Summer 1993). Penisular range population declined between 1971 and 1991 in the United States, but is relatively stable in Mexico (USFWS 1998).

Global Long Term Trend: Decline of 50-70%

Comments: Long-term trend is a great decline: from approximately 150,000-200,000 before 1800 (Seton's 1929 estimate of 2 million or more is considered an order of magnitude too high, Demarchi 1976, Valdez and Krausman 1999) to very few thousand at the turn of the century. Numbers are not available for the total population at this time, but in 1915, there were only 1775-3400 Rocky Mountain Bighorns in Canada (Miller 1916). Protection from hunting and some habitat protection helped populations over the next few decades, but devastating dieoffs occurred as more and more domestic sheep (and their exotic diseases) were introduced onto western ranges in the early 1900s (Goodson 1982). The number of domestic sheep in 11 western states increased to approximately 28 million in 1920 and remained high until 1945 (Goodson 1982). After 1945, however, domestic sheep numbers declined and this allowed an energetic program of reintroductions and habitat enhancement to begin to turn the trend around. By 1960, populations in the contiguous United States had increased to 15,200-18,000 (Buechner 1960). Since 1960, populations of Rocky Mountain and California Bighorns have generally increased: 1975-30,667; 1983-37,035; 1993-48915 (Gilchrist (1998). In 1991, the total population (Rocky Mountain, California, and Desert Bighorns) was estimated to be 70,840 (Valdez and Krausman 1999).

Degree of Threat: High

Comments: Initial large declines were primarily the result of competition with domestic stock (e.g., cattle, sheep, burros), diseases and parasites introduced by domestic sheep, overhunting, and habitat loss (Cowan 1940; Buechner 1960; Sugden 1961; Stelfox 1971; Goodson 1982, Boyce et al. 1990, Valdez and Krausman 1999).

DOMESTIC STOCK: In Idaho, introduced bighorns avoided cattle and were more sensitive to cattle presence than were established populations, based on previous studies (Bissonette and Steinkamp 1996). Decline of desert populations has been attributed destruction of habitat and competition with domestic livestock and other native and domestic species (e.g., may be limited through resource competition with burros; Seegmiller and Ohmart 1981).

PARASITES AND DISEASE: Psoroptic scabies from domestic sheep devastated bighorn populations in the first half of the twentieth century (Boyce et al. 1990). The Peninsula ranges population (California and Baja California) has declined due to disease-caused low survival rate of juveniles (California Department of Fish and Game 1990). Many dieoffs (greater than 50% mortality over a few months) of herds have been reported over the last century; these are poorly understood, but seem to result from stress, which interacts with endemic lungworm infestations and lowers the animals' resistance to organisms such as PASTEURELLA bacteria. The animals subsequently die from acute bronchopneumonia (Ryder et al. 1992, Dunbar 1992, Schwantje 1988). See Bunch et al. (1999) for a general account of diseases and parasites affecting Bighorn Sheep.

HABITAT LOSS AND DEGRADATION: Loss and degredation of habitat, especially key winter forage sites, is a key threat (Valdez and Krausman 1999, Shackleton 1999, Krausman et al. 1999). Habitat degradation can occur through overgrazing by domestic stock, competition with exotic ungulates (e.g. Aoudad or Barbary, AMMOTRAGUS LERVIA), excessive off-road vehicle use, spread of rangeland weeds, and the usurpation of water sources (Simpson 1980, Valdez and Krausman 1999, Krausman et al. 1999). Fire suppression and resulting vegetation succession (encroachment of tall dense shrubland and forest) has been a major cause of habitat loss in Colorado and British Columbia (Davidson 1991, Cannings et al. 1999, Wakelyn 1987; see also Etchberger et al. [1989] for similar conclusion on the importance of fire in Santa Catalina Mountains, Arizona). Fragmentation of habitat reduces or eliminates genetic interchange among populations (Ramey 2000) and reduces the probability of recolonization following local extirpation; both these effects are especially of concern in small populations (fewer than 100 individuals), which are especially vulnerable to extirpation (Berger 1990).

OTHER: The social behavior and predator evasion strategy may have contributed to their decline (Miller and Gaud 1989). Feral honey bees may interfere with sheep attempting to drink at artificial water sources (guzzlers) in desert environments (Boyce et al. 2003).

Bighorn Sheep - Peninsular Ranges

Threatened in the United States by habitat loss, degradation, and fragmentation resulting from urban and commercial development (including proposed and approved renewable energy projects), invasive non-native plants (e.g., tamarisk), fire suppression (allows development of unsuitable thick vegetation), increased fire frequency (in some areas this facilitates invasion by non-native plants), and off-highway vehicle (OHV) activity; disease (in some instances contracted directly or indirectly from introduced domestic livestock); low recruitment (still a problem despite a recent increase in the bighorn sheep population); nonadaptive behavioral responses associated with residential and commercial development; high predation rates (by mountain lions and others) coinciding with low bighorn sheep population numbers in some areas; effects of non-native (e.g., ornamental) toxic plants; and climate change, particularly the ongoing and predicted trend toward warmer and drier conditions (USFWS 1998, 2011). Populations in Mexico are regarded as not very threatened (USFWS 1998).

Responses of bighorn sheep to human activity range from cautious curiosity to immediate flight or abandonment of habitat, as well as disruption of normal social patterns and resource use (USFWS 2011). Responses depend on the type of activity, an animal's previous experience with humans, size or composition of the bighorn sheep group, location of the sheep relative to elevation of the activity, distance to escape terrain, and distance to the activity (USFWS 2000).

The apparent extirpation of a subpopulation near the United States-Mexico border (Recovery Region 9) in the 1980s may have been caused construction of Interstate 8 in the mid-1960s, railroad activity, livestock grazing, poaching, and fire suppression (Rubin et al. 1998).

Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae)

"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).

Major Threats

Conservation Actions

Preserve Selection and Design Considerations: In the southwestern U.S., Berger (1990) found that populations with fewer than 50 individuals are not viable; all such populations went extinct within 50 years.

Management Requirements: See Douglas and Leslie (1999) for a general discussion of Bighorn Sheep management; and see Smith and Krausman (1988) for a discussion of management of desert populations.

Management needs for the Rocky Mountain population: identification of seasonal ranges and migration corridors and identification of factors limiting range expansion; improvement of ranges by vegetation manipulation (burning, clearing); protection of ranges from human encroachment; avoiding contact between bighorn and domestic livestock Risenhoover et al. 1988). Smith et al. (1991) presented a habitat evaluation procedure for the Rocky Mountain population.

See California Department of Fish and Game (1990) for brief comments on management activities relating to Peninsular Range (California) population; recovery of this population with require compatible grazing programs by BLM, USFS, and private landowners.

Management Research Needs: Research into habitat requirements is important, and much work remains to be done in assessing habitat suitability and capability, and modeling habitat on a landscape scale. Continued studies of diseases are vital, as is research into population and metapopulation dynamics and population genetics (Douglas and Leslie 1999).

Global Protection: Many to very many (13 to >40) occurrences appropriately protected and managed

Comments: Protected in many National Parks; many reserves have been established specifically for the species.

USFWS (2008) designated as critical habitat for subspecies sierrae approximately 417,577 acres (168,992 hectares) in Tuolumne, Mono, Fresno, Inyo, and Tulare counties, California.

Needs: Protect habitat from domestic livestock damage; protect populations from excessive hunting. Desert populations exhibit more movement between isolated patches of habitat than previously thought; consequently corridors between traditional habitats should be given conservation consideration (Bleich et al. 1990).

There are no known negative effects of bighorn sheep on humans.

Native Americans and early settlers prized bighorn meat as the most palatable of American big-game species. Native Americans also used the horns to fashion large ceremonial spoons and handles for utensils. The horns have also been popular for many centuries as trophies. Bighorn sheep may serve as an attraction for ecotourism ventures in parts of western North America.

Positive Impacts: food ; body parts are source of valuable material; ecotourism