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 ; tactile ; acoustic ; chemical
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
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
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:
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 )
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 )
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
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.
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.
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:
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); sexual ; 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 bighorn sheep (Ovis canadensis)[6] is a species of sheep native to North America.[7] It is named for its large horns. A pair of horns might weigh up to 14 kg (30 lb);[8] the sheep typically weigh up to 143 kg (315 lb).[9] Recent genetic testing indicates three distinct subspecies of Ovis canadensis, one of which is endangered: O. c. sierrae.
Sheep originally crossed to North America over the Bering Land Bridge from Siberia; the population in North America peaked in the millions, and the bighorn sheep entered into the mythology of Native Americans. By 1900, the population had crashed to several thousand, due to diseases introduced through European livestock and overhunting.[10]
Ovis canadensis is one of two species of mountain sheep in North America; the other species being O. dalli, the Dall sheep. Wild sheep crossed the Bering land bridge from Siberia into Alaska during the Pleistocene (about 750,000 years ago) and subsequently spread through western North America as far south as Baja California and northwestern mainland Mexico.[11] Divergence from their closest Asian ancestor (snow sheep) occurred about 600,000 years ago.[12] In North America, wild sheep diverged into two extant species — Dall sheep, which occupy Alaska and northwestern Canada, and bighorn sheep, which range from southwestern Canada to Mexico.[13] However, the status of these species is questionable given that hybridization has occurred between them in their recent evolutionary history.[14]
In 1940, Ian McTaggart-Cowan split the species into seven subspecies, with the first three being mountain bighorns and the last four being desert bighorns:[11]
Badlands bighorn sheep (or Audubon's bighorn sheep), O. c. auduboni, occurred in North Dakota, South Dakota, Montana, Wyoming, and Nebraska. This subspecies has been extinct since 1925.Starting in 1993, Ramey and colleagues,[12][15] using DNA testing, have shown this division into seven subspecies is largely illusory. Most scientists currently recognize three subspecies of bighorn.[16][17] This taxonomy is supported by the most extensive genetics (microsatellite and mitochondrial DNA) study to date (2016) which found high divergence between Rocky Mountain and Sierra Nevada bighorn sheep, and that these two subspecies both diverged from desert bighorn prior to or during the Illinoian glaciation (about 315–94 thousand years ago).[18] Thus, the three subspecies of O. canadensis are:
In addition, two populations are currently considered endangered by the United States government:[1]
Bighorn sheep are named for the large, curved horns borne by the rams (males). Ewes (females) also have horns, but they are shorter with less curvature.[20] They range in color from light brown to grayish or dark, chocolate brown, with a white rump and lining on the backs of all four legs. Males typically weigh 58–143 kg (128–315 lb), are 90–105 cm (35–41 in) tall at the shoulder, and 1.6–1.85 m (63–73 in) long from the nose to the tail. Females are typically 34–91 kg (75–201 lb), 75–90 cm (30–35 in) tall, and 1.28–1.58 m (50–62 in) long.[9] Male bighorn sheep have large horn cores, enlarged cornual and frontal sinuses, and internal bony septa. These adaptations serve to protect the brain by absorbing the impact of clashes.[21] Bighorn sheep have preorbital glands on the anterior corner of each eye, inguinal glands in the groin, and pedal glands on each foot. Secretions from these glands may support dominance behaviors.[21]
Bighorns from the Rocky Mountains are relatively large, with males that occasionally exceed 230 kg (500 lb) and females that exceed 90 kg (200 lb). In contrast, Sierra Nevada bighorn males weigh up to only 90 kg (198 lb) and females to 60 kg (132 lb). Males' horns can weigh up to 14 kg (30 lb), as much as all the bones in the male's body.[8]
The Rocky Mountain and Sierra Nevada bighorn sheep occupy the cooler mountainous regions of Canada and the United States. In contrast, the desert bighorn sheep subspecies are indigenous to the hot desert ecosystems of the Southwestern United States and Mexico. Bighorn sheep generally inhabit alpine meadows, grassy mountain slopes, and foothill country near rugged, rocky cliffs and bluffs.[8] Since bighorn sheep cannot move through deep snow, they prefer drier slopes, where the annual snowfall is less than about 150 cm (60 in) per year.[8] A bighorn's winter range usually lies at lower elevations than its summer range.[22]
Bighorn sheep are highly susceptible to certain diseases carried by domestic sheep, such as psoroptic scabies[23] and pneumonia; additional mortality occurs as a result of accidents involving rock falls or falling off cliffs (a hazard of living in steep, rugged terrain). Bighorns are well adapted to climbing steep terrain, where they seek cover from predators. Predation primarily occurs with lambs, which are hunted by coyotes, bobcats, gray foxes, wolverines, jaguars, ocelots, lynxes, and golden eagles.[24]
Bighorn sheep of all ages are threatened by black bears, grizzly bears, wolves, and especially mountain lions, which are perhaps best equipped with the agility to prey on them in uneven, rocky habitats.[20][25][26] Fire suppression techniques may limit visibility through shrublands, and therefore increase cover and predation rates by mountain lions.[27] Bighorn sheep are considered good indicators of land health because the species is sensitive to many human-induced environmental problems. In addition to their aesthetic value, bighorn sheep are considered desirable game animals by hunters.
Bighorn sheep graze on grasses and browse shrubs, particularly in fall and winter, and seek minerals at natural salt licks.[25] Females tend to forage and walk, possibly to avoid predators and protect lambs,[28] while males tend to eat and then rest and ruminate, which lends to more effective digestion and greater increase in body size.[28]
Bighorn sheep live in large herds, and do not typically follow a single leader ram, unlike the mouflon, the ancestor of the domestic sheep, which has a strict dominance hierarchy. Prior to the mating season or "rut", the rams attempt to establish a dominance hierarchy to determine access to ewes for mating. During the prerut period, most of the characteristic horn clashing occurs between rams, although this behavior may occur to a limited extent throughout the year.[29] Bighorn sheep exhibit agonistic behavior: two competitors walk away from each other and then turn to face each other before jumping and lunging into headbutts.[30] Rams' horns can frequently exhibit damage from repeated clashes.[25] Females exhibit a stable, nonlinear hierarchy that correlates with age.[31] Females may fight for high social status when they are integrated into the hierarchy at one to two years of age.[31]
Rocky Mountain bighorn rams employ at least three different courting strategies.[32] The most common and successful is the tending strategy, in which a ram follows and defends an estrous ewe.[32] Tending takes considerable strength and vigilance, and ewes are most receptive to tending males, presumably feeling they are the most fit. Another tactic is coursing, which is when rams fight for an already tended ewe.[32] Ewes typically avoid coursing males, so the strategy is not effective. Rams also employ a blocking strategy. They prevent a ewe from accessing tending areas before she even goes into estrus.[32]
Bighorn ewes have a six-month gestation. In temperate climates, the peak of the rut occurs in November with one, or rarely two, lambs being born in May. Most births occur in the first two weeks of the lambing period. Pregnant ewes of the Rocky Mountains migrate to alpine areas in spring, presumably to give birth in areas safer from predation,[33] but are away from areas with good quality forage.[33] Lambs born earlier in the season are more likely to survive than lambs born later.[34] Lambs born late may not have access to sufficient milk, as their mothers are lactating at a time when food quality is lower.[34] Newborn lambs weigh from 3.6 to 4.5 kg (8 to 10 lb) and can walk within hours. The lambs are then weaned when they reach four to six months old. The lifespan of ewes is typically 10–14 years, and 9–12 years for rams.[20]
Many bighorn sheep populations in the United States experience regular outbreaks of infectious pneumonia,[35][36][37][38] which likely result from the introduction of bacterial pathogens (in particular, Mycoplasma ovipneumoniae,[39][40] and some strains of Mannheimia haemolytica)[41] carried asymptomatically in domestic sheep.[42] Once introduced, pathogens can transmit rapidly through a bighorn population, resulting in all-age die-offs that sometimes kill up to 90% of the population. In the years following pathogen introduction, bighorn populations frequently experience multiple years of lamb pneumonia outbreaks. These outbreaks can severely limit recruitment and likely play a powerful role in slowing population growth.[38]
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Two hundred years ago, bighorn sheep were widespread throughout the western United States, Canada, and northern Mexico. The population was estimated to be 150,000 to 200,000.[43][44] Unregulated hunting, habitat destruction, overgrazing of rangelands, and diseases contracted from domestic livestock all contributed to the decline, the most drastic occurring from about 1870 through 1950.[45]
In 1936, the Arizona Boy Scouts mounted a statewide campaign to save the bighorn sheep. The scouts first became interested in the sheep through the efforts of Major Frederick Russell Burnham.[46] Burnham observed that fewer than 150 of these sheep still lived in the Arizona mountains. The National Wildlife Federation, the Izaak Walton League, and the National Audubon Society also joined the effort.[47] On January 18, 1939, over 600,000 hectares (1,500,000 acres) of land were set aside to create the Kofa National Wildlife Refuge and the Cabeza Prieta National Wildlife Refuge.[47]
Restoration of bighorn sheep has been pursued actively by many state and federal agencies since the 1940s, although these efforts have met with only limited success, and most of the historical range of bighorns remains unoccupied.[45] Hunting for male bighorn sheep is allowed, but heavily regulated, in Canada and the United States.[1]
Bighorn sheep were among the most admired animals of the Apsaalooka (Crow) people, and what is today called the Bighorn Mountain Range was central to the Apsaalooka tribal lands. In the Bighorn Canyon National Recreation Area book, storyteller Old Coyote describes a legend related to the bighorn sheep. A man possessed by evil spirits attempts to kill his heir by pushing the young man over a cliff, but the victim is saved by getting caught in trees. Rescued by bighorn sheep, the man takes the name of their leader, Big Metal. The other sheep grant him power, wisdom, sharp eyes, sure-footedness, keen ears, great strength, and a strong heart. Big Metal returns to his people with the message that the Apsaalooka people will survive only so long as the river winding out of the mountains is known as the Bighorn River.[48]
Bighorn sheep are hunted for their meat and horns, which are used in ceremonies, as food, and as hunting trophies. They also serve as a source of ecotourism, as tourists come to see the bighorn sheep in their native habitat.[49]
The Rocky Mountain bighorn sheep is the provincial mammal of Alberta and the state animal of Colorado and as such is incorporated into the symbol for the Colorado Division of Parks and Wildlife.[50] The Desert bighorn sheep is the state mammal of Nevada.[51]
The Bighorn sheep was featured in the children's book Buford the Little Bighorn (1967) by Bill Peet. The Bighorn sheep named Buford has a huge pair of horns in the Spring, Summer, Fall and Winter, similar to Rudolph the Red-Nosed Reindeer.
Bighorn sheep were once known by the scientific identification "argali" or "argalia" due to assumption that they were the same animal as the Asiatic argali (Ovis ammon).[52] Lewis and Clark recorded numerous sightings of O. canadensis in the journals of their exploration—sometimes using the name argalia. In addition, they recorded the use of bighorn sheep horns by the Shoshone in making composite bows.[53] William Clark's Track Map produced after the expedition in 1814 indicated a tributary of the Yellowstone River named Argalia Creek and a tributary of the Missouri River named Argalia River, both in what is today Montana. Neither of these tributaries retained these names, however. The Bighorn River, another tributary of the Yellowstone, and its tributary stream, the Little Bighorn River, were both indicated on Clark's map and did retain their names, the latter being the namesake of the Battle of the Little Bighorn.[54]
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This article incorporates public domain material from Draft recovery plan for the Sierra Nevada Bighorn Sheep (PDF). United States Fish and Wildlife Service. This article incorporates public domain material from Description of Bighorn Sheep at Yellowstone Park. National Park Service. This article incorporates public domain material from Singer, Francis (1995). "Bighorn Sheep in the Rocky Mountain National Parks" (PDF). In Stohlgren, T.J. (ed.). The Interior West. In: Our Living Resources: A report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems. Washington, D.C.: U.S. Geological Survey. Archived from the original (PDF) on 2007-10-31. The bighorn sheep (Ovis canadensis) is a species of sheep native to North America. It is named for its large horns. A pair of horns might weigh up to 14 kg (30 lb); the sheep typically weigh up to 143 kg (315 lb). Recent genetic testing indicates three distinct subspecies of Ovis canadensis, one of which is endangered: O. c. sierrae.
Sheep originally crossed to North America over the Bering Land Bridge from Siberia; the population in North America peaked in the millions, and the bighorn sheep entered into the mythology of Native Americans. By 1900, the population had crashed to several thousand, due to diseases introduced through European livestock and overhunting.
