Desert Bighorn Sheep, Ovis canadensis
TAXONOMY & NOMENCLATURE
(McKenna, 1997)(Hall, 1981)(Valdez, 1999) (USFWS, 2000)(Young & Manville,
1960)(Ramey & Wehausen, 1993) (Shackleton, 1985) (Geist, 1971)(Boyce et al,
Describer (Date): Shaw (1804). The Canadian Sheep. Plate 610, the
description and the index in Naturalist’s miscellany (by G. Shaw and E.
Nodder), Vol 15. Nodder and Co., London
Artiodactyla* (Even-toed hoofed animals: includes pigs, sheep goats, cattle, deer)
Suborder: Ruminantia (chevrotain, mouse deer, pronghorn, deer, giraffes,
okapi, antelopes, goats,
ibexes, turs, markhors)
Family: Bovidae (buffalo, cattle, sheep, goats)
Sub-Family: Caprinae (goats, sheep)
Genus: Ovis (Sheep, mouflons, urial, argali, bighorn, thin horns snow
sheep, Dall's sheep)
Species: Ovis ammon (Argali)
Species: Ovis aries (Mouflon)
Species: Ovis canadensis (American bighorn)
Subspecies: Ovis c. auduboni - EXTINCT
Subspecies: Ovis c. canadensis (Rocky mountain bighorn)
Subspecies: Ovis c. californiana (California bighorn)
Subspecies: Ovis c. cremnobates (Peninsular bighorn) - DESERT
Subspecies: Ovis c. mexicana (Mexicana bighorn) - DESERT
Subspecies: Ovis c. nelsoni (Nelson bighorn) - DESERT POPULATION
Subspecies: Ovis c. weemsi (Weems bighorn) - DESERT POPULATION
Species: Ovis dalli (Dall sheep)
Species: Ovis nivicola (Siberian bighorn)
Species: Ovis vignei (Urial)
*New anatomical and DNA evidence on the relationship between Artiodactyla (even-toed ungulates) and Cetacea (whales and dolphins) recently led to a merging of the two orders into a new group, Cetartiodactyla (Montgelard, 1997; reviewed in Kulemzina, 2009). As of October 2012, experts had not agreed on whether to define Cetartiodactyla as an official taxonomic order that would replace Artiodactyla and Cetacea. Some continue to list sheep in the order Artiodactyla (Franklin, 2011) or use the term Cetartiodactyla without defining it as an order (IUCN, 2008).
- Linneus described the genus Ovis in his 1766 Taxonomy.
- Official description and naming did not occur until 1804 although an
American wild sheep was recorded by the Spanish explorer Coronado in
- No consensus exists concerning the number of subspecies of Ovis
canadensis. Early zoologists recognized many subspecies based
solely on morphology and geographic separation.
- A case has been made for a single species, as diverse races hybridize
in zoos, producing viable and fertile offspring (Young & Manville)
- Cowan’s definitive 1940 nomenclature of North American mountain sheep
recognizes 2 species: Thinhorn sheep (Ovis dalli) and Bighorn sheep
(Ovis canadensis). Seven subspecies of mountain sheep are listed:
auduboni, californiana, canadensis, cremnobates, mexicana, nelsoni,
- Genetic studies by Ramey and Wehausen (1993) indicate that major
revisions are needed to Cowan’s taxonomy. They synonymized nelsoni
and cremnobates adopting the oldest name for the sub-species, Ovis
- Subsequent genetic studies have not been able to established a
consensus on the number of sub-species. Mitochondrial DNA analysis by
Boyce et al (1999), indicate that the multiple ewe subpopulations
existing within the Peninsular area are basic genetic units.
- “Desert bighorn” is an arbitrary term used for the bighorns
inhabiting the arid, sparsely vegetated desert environment of the
extreme western and southwestern parts of the U.S. and northern Mexico
- (cremnobates, mexicana, nelsoni, and weemsi). These sheep are also
referred to by regional names: Arizona Bighorn, Mexican Bighorn.
- "Peninsular bighorn" has been used recently to refer to the
combined populations of cremnobates and nelsoni (a synonomy suggested
- “Mountain bighorn” is a common term for the northern subspecies:
canadensis and californiana. They also have regional common names:
Rocky Mountain Bighorn, California Bighorn
- All subspecies may be referred to as “Bighorns” or “Mountain
- The ancestors of bighorn sheep resided in the mountain and desert
regions of Eurasia from early Pleistocene.
- Crossing the Bering land bridge during the late Pleistocene (100,000
years ago), they spread to mountains of Europe, North Africa, Asia and
- First sheep into New World were believed to be similar to the argali of
the Asiatic steppes
- The old world sheep evolved into an incredible number of new and
distinct species as they adapted to a variety of habitats. (There are
some 36-40 races or subspecies of wild sheep today)
- True goats (Capra) are closest relatives. Unlike goats, sheep have
preorbital and inguinal glands and lack an odoriferous tail gland.
They have interdigital glands on all four feet.
DISTRIBUTION & HABITAT
( Hall, 1981) (Hansen, 1980) (Risenhoover & Bailey,1985) (Shackleton, 1997)
(Ostermann et al,2001)(USFWS,2000) (USGS website, 2002)
Historical Distribution: (Cowan's 1940 taxonomy). Records indicate
at least 97 populations of desert bighorn occurred in California at one point.
- Ovis c. canadensis (Rocky mountain bighorn) - British Columbia,
Montana, Wyoming, Colorado, New Mexico, Idaho, Nevada, Utah, Oregon,
- Ovis c. californiana (California bighorn) - British Columbia,
Washington, Oregon, Nevada,California
- Ovis c. nelsoni (Nelson bighorn) - California, Nevada, Utah,
- Ovis c. mexicana (Mexicana bighorn) - Arizona, New Mexico,
- Ovis c. cremnobates (Peninsular bighorn) - Upper Baja
- Ovis c. weemsi (Weems bighorn) - Lower Baja
Map: From Hall’s The Mammals of
North America, Volume II, 1981. Based on Cowan
- O. c. auduboni
- O. c. californiana
- O. c. canadensis
- O. c. cremnobates
- O. c. mexicana
- O. c. nelsoni
- O. c. weemsi
Current Distribution: (Shackleton, 1997). Today, 61 bighorn
populations remain (Toweill & Geist, 1999). The Recovery Plan for Bighorn
Sheep in the Peninsular Ranges, California (2000) indicates 8 ewe
subpopulations in Riverside, Imperial, and San Diego counties from the San
Jacinto Mountains to the Mexican border. Link to IUCN map.
- Ovis c. canadensis (Rocky Mountain bighorn) - Rocky mountains
from Colorado north into British Columbia
- Ovis c. californiana (California bighorn) - scattered
populations east of the Rocky Mountains from Central California to
central British Columbia
- Ovis c. cremnobates(Peninsular bighorn) - Upper Baja
- Ovis c. mexicana (Mexicana bighorn) - Western Sonora; extinct in
much of former range
- Ovis c. nelsoni (Nelson bighorn) - Central Baja to SW Colorado;
scattered populations to eastern Texas. Includes Ovis c.
- Ovis c. weemsi (Weems bighorn) - Extreme southern Baja
Maps: From Shackleton’s Wild Sheep and Goats and their Relatives,
IUCN/SSC Status Survey and Conservation Action Plan for the Caprinae, 1997
Ovis canadensis in the U.S.
Distribution of desert bighorn in Mexico
c. O.c. cremnobates
m. O.c. mexicana
w. O.c. weemsi
i. O.c. mexicana (introduced on Isla Tiburon)
- Desert, grasses and shrub mosaic, shrublands
- Important habitat requirements are topography (escape terrain),
visibility, water, and forage quality and quantity
- Terrain typically rough, rocky and broken by canyons and washes
- Depends on steep slopes for lambing and to escape predators
- Uses cliff overhangs to rest from the hot desert sun and dry
- Desert bighorn sheep avoid low visibility areas with dense vegetation
- Distribution of waterholes influences pattern of home range for some
desert bighorn subspecies
(Bighorn Institute website, 2002)
- Adult Body Weight: Male (ram) - 150-200 lbs., Female (ewe) - 100 -125
- Adult Body Length: 50 -62"
- Adult Shoulder Height: 32 - 40"
- Horns: Male horns become a full curl by 7-8 years of age and spread of
up to 33 inches (up to 30 lbs.) Female horns are smaller than the rams
and never exceed half a curl.
- Both sexes have horns that grow throughout their lives. Male horns are
massive, curling and diverging. Female horns are smaller, thin and
- Horns consist of a bony core with a permanent sheath of keratin.
Sheaths grow from the base
- Mountain bighorns have by far the biggest horns. Longest horn length
recorded measured 52 inches with a basal circumference of 18 inches
(Horn tips are often broken, splintered or broomed)
- Clark (1940) reports a weight of 44 lbs (upper skull and horn) for a
Canadian Rocky ram
- Growth rings (annuli) are formed in the fall and are associated with
hormone and diet changes. First visible annulus is 2.5 years. Fourth
year is the first heavy, dark ring.
Other Physical Characteristics
- Smooth outer coat of brittle guard hairs and short, gray, crimped
- Fur is a pale brown, paler in appearance than other bighorn sheep
- The summer coat is a rich, glossy brown but can fade by late winter
- Female fur is often lighter than the males
- Whitish patch on rump
- Molting usually occurs in June and July. Molting progresses from
posterior region with chest the last to shed.
- Compact and muscular body
- Climbing, cloven hooves providing amazing jumping ability
- Acute eyesight
BEHAVIOR & ECOLOGY
(Hansen, 1980)(Shackleton,1985 USFWS, 2000)(Valdez, 1999)
- Largely determined by availability of food and water (rain dependent)
- Predominantly diurnal but also may be active on moonlit nights
- Alternate between feeding and rest-rumination bouts
- Feeding bouts generally occur at dusk and dawn
- Some areas used repeatedly as bedding sites by groups
- Can move over level ground at 30 mph and up mountain slopes at 15 mph
- Matrilineal (based on female associations)
- Gregarious and faithful to natal home range. "Home range
groups" or "ewe groups" tend to be related females and
- Young learn from older sheep their home range, escape terrain, water
sources and lambing habitat. Familiarity with range is an advantage in
- Rams are not as tied to a specific group - they tend to range, moving
between "ewe groups"
- Linear dominance orders among ewes
- Rams with larger horns and body size dominate both males and females
- Playing between lambs is highest during spring when food is available
and lambs are young
- Threat jumps, clashes, and mounting are the most frequent social
patterns used by lambs associated as play
- “Clashing” of rams’ horns during rutting season to determine /
- Male horn size is a symbol of rank. Head-to-head combat between rams
may occur during mating season.
- During the rut, bighorn rams will snort loudly. The lambs bleat, and
the ewes respond with a guttural "ba."
- Adult males utter a growl or gutteral
Interspecies Interaction (Bighorn Institute website, 2002)(USFW, 2000)
- Scent mark spread by rubbing eye glands on trees and rocks
- Natural predators include: mountain lions, wolves, bobcats, coyotes and
- Mule deer are the primary competitor for resources
- Known to become alarmed and startled by a flock birds or other sudden
- Unnatural competitors include: cattle, horses, domestic goats and
- Urbanization and human disturbance (habitat fragmentation, recreation
- Disease caused by domestic livestock
DIET & FEEDING
(Bighorn Institute website, 2002)(Hanson,1980)(Turner, 1973)(Valdez, 1999)
- Desert bighorn sheep are opportunistic herbivores and ruminants. Turner
(1973) documented 43 species of plants in diet.
- Diet consists of shrubs, forbs, cacti, grasses (favorites include:
acacia or catclaw, encelia, sweetbush, and krameria).
- Low terrain and washes provide high quality forage (productive soils)
and water during summer months and reproductive season
- Sheep are ruminants with a 4 chambered stomach that can digest most of
the cellulose in vegetation with the aid of bacteria and protozoans.
- Forage quality influences daily and seasonal patterns. When forage
digestibility is low, bighorn spends most of its time ruminating.
- Daily food intake of captive bighorn sheep is estimated at 3 lbs (1.5
kg) plant material.
- Desert bighorn sheep will be found 3-5 kilometers from water sources
during the summer months. Can go without drinking for 5 to 15 days
- Efficient digestive system is able to utilize dry, abrasive forage
REPRODUCTION & DEVELOPMENT
(Turner & Hansen, 1980)( Shackleton, 1984)( USFWS, 2000) (Thompson &
- Estrus cycle averages 28 days and female is receptive for 48 hours.
- Females are estimated to produce lambs between the ages of 2 to 16.
- Males have been documented as breeding successfully as young as 6
months of age. (Turner & Hansen, 1980. Larger rams would control
this in the wild.
- Rams routinely check estrus status of ewes by flehmen (urine-testing),
and they can stimulate females to urinate by licking the vulva.
- Rut (term designating the breeding period)occurs in late summer and
- Male will begin courtship when a female is in estrous with a series of
contact patterns (twist, nose, kick, chest push).
- Females courtship is exhibited by the rubbing their body and horns on
- Dominant males gain priority over females but subordinate males still
attempt to mount estrous females.
- A ewe in estrous will often be pursued by numerous rams
- Mating and lambing seasons of desert species are extended because of
unpredictability of rain and forage availability.
Gestation: Generally accepted as 6 months (171 - 185 days)
- Birth rates and lamb survival vary with the quality of food supply
- Rates vary significantly among ewe groups in the desert region from 8
lambs: 100 ewes to 100 lambs: 100 ewes
- Breeding and parturition periods of desert bighorns more lengthy than
northern species. (May be due to unpredictable food supply)
- Twinning is rare in all bighorn sheep
- As the ewes age, there is a decrease in their fertility
- Ewes select an isolated, sheltered site with unobstructed view to give
- Lambing season (greatest # of lamb births)is generally between February
- Usually single young are born, but twins have been recorded
- Neonates are precocial and often called “followers”.
- After a few weeks of not being seen, the mother rejoins the herd and
put the lamb in a community nursery with other lambs.
Infants (<1 year of age)
Weaning: Lambs are weaned by 6
months of age.
- Body weight in newborns is 8-10 lbs.
- Body length at birth: 420 mm (16.5 inches)
- Young lambs are a grayish coloration with soft hooves and a black-brown
Juveniles (1-2 years of age):
Subadults (2-3 years of age):
- Body weight is 41-50 kg (90 - 110 lbs.) (females) to 52-59 kg (115 -
- Body length is 690 mm (27 in.) (females) to 915 mm (36 in.) (males).
- Yearling ram horn is much like adult ewe horn but thicker at the base
- Female horns are 125-178 mm long, thin and sharp-pointed.
Young adults (4-5 years
- Body weight is 45.8 kg (101 lbs.)(females) to 69.4 kg (153 lbs.)
- Body length is 851 mm (33.5 in.) (females) to 991 mm (39 in.)(males).
Adults (>5 years of age):
- Body weight is 55.6 kg (122.5 lbs.) (females) to 64.9 kg (153 lbs.)
- Body length is 965 mm (38 in.) (females) to 977 mm (39in.)(males).
- Body weight is 57.2 kg (126 lbs.) (females) to 78.5 kg (173
- Body length is 876 mm (34.5 in.) (females) to 1010mm (39.75
- Ram adults have a large knob on the back of their head, often calloused
and without hair while younger rams often have no knob.
- Permanent dentition is in place after four years of age.
Longevity Many rams live 9-12 years and ewes may live 10-14 years.
- 1971 study of Desert Bighorn mortality in Arizona and southeastern
Nevada: Poaching 41%, road kills 20%, natural accidents 15%, drownings
12%, fence mortalities 12%.
- Precipitous 52% decline in 1988-89 in Arizona due to livestock viral
disease and nutritional stress
- Other documented threats in Arizona: automobile collisions,
coyote/mountain lion predation
DISEASES AND PATHOLOGY
(Allen, 1980)(Gildart, 1999)(USFWS, 2000)(Valdez & Krausman,
- Common disease problems: chronic sinusitis, pneumonia, psoroptic
- Multiple pathogens (contagious ecthyma virus, blue tongue, Pasteurella,
and parainfluenza-3 virus) have been found in declining populations.
- Improperly fitted radio collars have caused injury to osseous and
dermal tissues decreasing fitness
- Peninsular bighorn sheep and other southern California bighorn
populations have shown higher levels of pathogen exposure than other
species of bighorn sheep.
- Diseases introduced by domestic livestock - They devastated bighorn
populations in the mid and late 1900's.
(IUCN website, 2002) (USFWS, 2000)(Shackleton, 1997)(Rubin, 1998)
- IUCN status of Ovis canadensis(all subspecies): Low Risk /
- Ovis canadensis cremnobates - IUCN status: Endangered (Listed as
"rare" in 1971 by the California Fish and Game Commission.
Listed as "endangered" in 1998 by USFWS) The Latest
population estimate (excluding lambs) 334. (Rubin, 1998)
- Ovis canadensis mexicana - IUCN status: Vulnerable
- Ovis canadensis nelsoni - IUCN status: Low Risk
- Ovis canadensis weemsi - IUCN status: Critically Endangered
- Bighorn sheep subspecies in North America were estimated at 1.5 - 2
million during pre-columbian periods (Seton, 1929)
- By 1960, the population of bighorn sheep in North America dropped to
15,000 - 18,200 (Buchner, 1960)
- Major declines occurred from 1850's to early 1900's due to hunting
- In 1960 the total desert bighorn sheep population was estimated at
7,065 - 8,475
- In 1993 the overall desert bighorn sheep population increased to 18,965
- The California desert bighorn sheep subspecies were estimated in 1960
at 2,150 - 2,450, 1993 at 4,300 - 4,325
- The endangered Peninsular bighorn sheep, a population of desert bighorn
sheep was estimated in 1993 at 400 - 425 in California, and 780 -
1,170 in Baja California, Mexico
- March 18, 1998, the United States Peninsular Ranges population of
desert bighorn sheep was federally listed United States Fish and
Wildlife Service as an endangered species
- Census from Shackleton, 1997: O.c. cremnobates <2,500, O.c. mexicana
>2,000?, O.c. nelsoni 15,000? O.c. weemsi 500?
(Low Risk northern species: O.c. californiana 8,900 O.c. canadensis
- U.S. began preserving large parcels of wildlands as early as 1872 with
the establishment of Yellowstone. Animals in National Parks are
- Since 1976
- A genetic ID program has been initiated in Jaspar National Park to
deter trophy poaching.
- Management consists of establishing hunting quotas, regulating
harvests, habitat improvement, annual censuses, translocation of
animals and promoting research
- State wildlife agencies have reintroduced bighorns into many native
ranges as well as into areas where the animals did not naturally occur
- Many non-governmental conservation organizations are involved in
protecting bighorns. The Zoological Society of San Diego has had a
Conservation Program for the Peninsular Bighorn since 2000.
Threats to survival
- Populations of Sonora and Baja (cremnobates, nelsoni, mexicana, and
weemsi) have been greatly reduced due to widespread illegal hunting of
- Unpredictable epizootics (rapidly spreading disease affecting a large
number of animals throughout a wide range)
- Human disturbance. (Desert bighorn are highly intolerant of human
- Competition from domestic sheep, goats, feral burros for forage, water,
- Populations have a predominance of old indiviuals and insufficient lamb
recruitment (relationship between production and survival)
- Habitat loss, degradation, and fragmentation by urban and commercial
- Mountain lion, wolf predation coinciding with low population numbers
- Failure of populations to disperse into contiguous, suitable habitat
(caution / fear)
- Loss of genetic variation is always a danger when dealing with small
- Invasive plant species (e.g. tamarisk) compete with native plants
bighorns feed on.
- Introduced Barbary sheep could take over bighorn habitat.
- Fire suppression has created taller, denser vegetation. Reduced
visibility makes the bighorn more vulnerable.
- Drought - Limiting water & forage. Global warming may prove to be a
problem for the desert bighorns
(Gildart,1999) (USFWS, 2000)
ISIS captive population
- Require large enclosures with native vegetation, water source and a
variety of habitat types and topographic relief.
- Enclosure fencing at least 10 feet high and at least 2 feet underground
for predator control
- Males and females should be separated in nonbreeding season.
- Two captive populations of Peninsular bighorns: 1. The Bighorn
Institute, formed in 1982 to investigate bighorn population decline.
They established a captive breeding program in 1985. (more than 75
animals released to wild). 2. The Living Desert Museum is maintains a
small group of bighorns for educational purposes.
- The San Diego Wild Animal Park currently has two species of desert
bighorn sheep O.c. mexicana and O.c. nelsoni at the
Condor Ridge exhibit.
- In 1932 a Mexican sheep was brought to the San Diego Zoo after being
hand raised by a Mexican family. It joined a group of Rocky mountain
sheep that had been donated by the Canadian Department of Parks.
Important Web Resources:
USFWS Recovery Plan -- For bighorn sheep in the peninsular ranges of California
Coachella Valley Multiple Habitat Species Conservation Plan
IUCN Red List: Ovis canadensis
Oregon's Big Horn Sheep and Rocky Mountain Goat Management Plan (PDF)
United States Geological Survey
© 2002 San Diego Zoo Global. Last update 2002. Disclaimer: Although San Diego Zoo Global makes every attempt to provide accurate information, some of the facts provided may become outdated or replaced by new research findings. Questions and comments may be addressed to email@example.com.
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