Bighorn sheep

Taxonomy and Subspecies

The bighorn sheep is one of two species of mountain sheep in North America, the other being the Dall sheep (Ovis dalli), and wild sheep ancestors crossed the Bering Land Bridge from Siberia into Alaska during the Pleistocene epoch roughly 750,000 years ago. Genetic studies indicate they diverged from their closest Asian ancestor, the snow sheep, about 600,000 years ago, and in North America they further diverged into the two extant species, though hybridization has occurred in their recent evolutionary history. Historically, up to seven subspecies were recognized based on geography and morphology, but modern genetic testing supports a simpler classification with most scientists now recognizing three primary subspecies. The Rocky Mountain bighorn sheep (Ovis canadensis canadensis) occupies the Rocky Mountains from Canada through the northwestern United States, while the Sierra Nevada bighorn sheep (Ovis canadensis sierrae) is a genetically distinct subspecies found only in California's Sierra Nevada. The desert bighorn sheep (Ovis canadensis nelsoni) inhabits the desert regions of the southwestern United States and northwestern Mexico, and within this subspecies, genetic lineages correspond to the formerly recognized Nelson's, Mexican, and Peninsular bighorn sheep.

In Canada, the Rocky Mountain bighorn sheep is the relevant subspecies, found from British Columbia to Alberta. The Rocky Mountain bighorn sheep is the provincial mammal of Alberta. The Sierra Nevada bighorn sheep is listed as endangered by the United States government. A distinct population segment of the desert bighorn sheep, the Peninsular bighorn, is also listed as endangered. The overall species is currently assessed as Least Concern on the IUCN Red List. Many populations remain precarious due to their high susceptibility to diseases introduced by domestic livestock.

Physical Description

Bighorn sheep are named for the impressive, spiralled horns borne by the rams, which are made of keratin and continue to grow throughout the animal's life, forming annual rings that can be used to estimate age. A mature ram's horns can measure over three feet in length and weigh up to 14 kilograms, which is as much as all the bones in its body combined, and these horns serve as both weapons and status symbols during dominance clashes. Ewes also have horns, but they are much shorter, slimmer, and only curve slightly, lacking the dramatic curl of the males', and this dimorphism is a key visual difference between the sexes. The sheep have a compact, muscular build covered in fur that ranges from light brown to a dark, chocolate brown, and they feature characteristic white markings on their muzzle, rump, belly, and the backs of all four legs.

Males are significantly larger than females, with a typical ram weighing between 58 and 143 kilograms, standing 90 to 105 centimetres at the shoulder, and measuring 1.6 to 1.85 metres long, while Rocky Mountain bighorns are the largest subspecies with males occasionally exceeding 230 kilograms. Ewes are smaller, typically weighing 34 to 91 kilograms and standing 75 to 90 centimetres tall, and Sierra Nevada bighorns are notably smaller with males weighing up to only 90 kilograms. Adaptations for their rugged lifestyle and combat include large horn cores, enlarged sinuses, and internal bony septa that help protect the brain from the impact of headbutting during the rut. They also possess several scent glands, including preorbital glands near the eyes, inguinal glands in the groin, and pedal glands on each foot, and secretions from these glands are thought to play a role in communication and dominance behaviours within the herd.

Habitat and Distribution

Bighorn sheep inhabit alpine meadows, grassy mountain slopes, and foothill country near rugged, rocky cliffs and bluffs. The Rocky Mountain and Sierra Nevada bighorn sheep occupy the cooler mountainous regions of Canada and the United States. Since bighorn sheep cannot move through deep snow, they prefer drier slopes where the annual snowfall is less than about 150 centimetres per year. A bighorn's winter range usually has lower elevations than its summer range. In contrast, the desert bighorn sheep subspecies are indigenous to the hot desert ecosystems of the Southwestern United States and Mexico.

Bighorn sheep were widespread throughout the western United States, Canada, and northern Mexico two hundred years ago. The population was estimated to be 150,000 to 200,000. Unregulated hunting, habitat destruction, overgrazing of rangelands, and diseases contracted from domestic livestock all contributed to the decline. The most drastic decline occurred from about 1870 through 1950. In Canada, bighorn sheep are found in the Rocky Mountains. Many state and federal agencies have actively pursued restoration since the 1940s, but most of the historical range remains unoccupied.

Ecology and Diet

Bighorn sheep are herbivores with a diet that shifts with the seasons and habitat, primarily grazing on a variety of grasses and browsing on shrubs, particularly in the fall and winter, and they will visit natural salt licks to obtain essential minerals. Desert bighorn sheep are selective feeders, choosing the most nutritious forage available, which includes leaves of mesquite and catclaw, various grasses, herbaceous plants, and cacti like the barrel cactus that also provides crucial moisture in arid environments. Their foraging behaviour differs by sex, with females tending to walk and eat more continuously, possibly to better watch for predators and protect lambs, while males often eat and then rest to ruminate, which lends to more effective digestion and greater increase in body size. As they feed, bighorn sheep play an important ecological role by helping to shape plant communities and open up landscapes, which can create diverse vegetation structures that benefit other species, and their waste contributes to nutrient cycling, enriching soils in their arid and alpine habitats.

Bighorn sheep of all ages are threatened by mountain lions, wolves, and bears. Lambs are the most susceptible to predation, with potential predators including coyotes, bobcats, and golden eagles. Mountain lions are perhaps best equipped with the agility to prey on them in uneven, rocky habitats. Bighorn sheep are considered good indicators of land health because the species is sensitive to many human induced environmental problems. They are highly susceptible to certain diseases carried by domestic sheep, such as psoroptic scabies and pneumonia. Many bighorn sheep populations experience outbreaks of infectious pneumonia, which can kill up to 90 percent of a population.

Social Behaviour and Reproduction

Bighorn sheep are social animals that live in large herds and do not typically follow a single leader ram, unlike the mouflon, and herds are often segregated by sex for much of the year, with ewes, lambs, and young rams forming one group and mature rams forming another. The most famous aspect of their behaviour is the rut, or mating season, which peaks in November in temperate climates, and before this period, rams attempt to establish a dominance hierarchy through dramatic headbutting clashes to determine access to ewes for mating. These battles involve two competitors walking away from each other and then turning to face each other before jumping and lunging into headbutts, and this behaviour often results in the horn tips becoming broken or 'broomed' from the frequent sparring. Rams employ at least three different courting strategies, with the most common and successful being the 'tending' strategy where a ram follows and defends an estrous ewe, while other tactics include 'coursing' and 'blocking', which are generally less effective.

After a six-month gestation, ewes give birth to one lamb, or rarely two, usually in May, with most births occurring in the first two weeks of the lambing period and newborn lambs weighing from 3.6 to 4.5 kilograms and able to walk within hours. Pregnant ewes of the Rocky Mountains often migrate to alpine areas in spring to give birth in areas safer from predation, but this means they are away from areas with good quality forage during a critical time. Lambs born earlier in the season are more likely to survive than lambs born later, as those born late may not have access to sufficient milk since their mothers are lactating when food quality is lower, and the lambs are then weaned when they reach four to six months old. Ewes exhibit a stable, nonlinear hierarchy that correlates with age, and may fight for high social status when integrated into the hierarchy at one to two years of age, while the lifespan of bighorn sheep is typically 10 to 14 years for ewes and 9 to 12 years for rams, though this is heavily influenced by disease, predation, and accidents.

Conservation and Threats

Bighorn sheep populations experienced a catastrophic decline from about 1870 through 1950. The historical population was estimated to be 150,000 to 200,000. Unregulated hunting, habitat destruction, overgrazing of rangelands, and diseases contracted from domestic livestock all contributed to the decline. Bighorn sheep are highly susceptible to diseases carried by domestic sheep, such as psoroptic scabies and pneumonia. Many bighorn sheep populations experience regular outbreaks of infectious pneumonia. These outbreaks can kill up to 90 percent of the population and severely limit lamb recruitment for years.

In 1936, the Arizona Boy Scouts mounted a statewide campaign to save the bighorn sheep. The National Wildlife Federation, the Izaak Walton League, and the National Audubon Society also joined the effort. On January 18, 1939, over 600,000 hectares of land were set aside to create the Kofa National Wildlife Refuge and the Cabeza Prieta National Wildlife Refuge. Many state and federal agencies have actively pursued the restoration of bighorn sheep since the 1940s. However, these efforts have met with limited success, and most of the historical range of bighorns remains unoccupied. Hunting for male bighorn sheep is allowed, but heavily regulated, in Canada and the United States.

Cultural Significance

Bighorn sheep were among the most admired animals of the Apsaalooka (Crow) people. The Bighorn Mountain Range was central to the Apsaalooka tribal lands. In a legend, a man is saved by bighorn sheep and takes the name of their leader, Big Metal. The message is that the Apsaalooka people will survive only so long as the river winding out of the mountains is known as the Bighorn River. Bighorn sheep are hunted for their meat and horns. The Shoshone used the horns in making composite bows, as recorded by Lewis and Clark. Lewis and Clark recorded numerous sightings and sometimes used the name argalia for the animal.

The Rocky Mountain bighorn sheep is the provincial mammal of Alberta and the state animal of Colorado. It is incorporated into the symbol for the Colorado Division of Parks and Wildlife. The desert bighorn sheep is the state mammal of Nevada. The bighorn sheep was featured in the children's book Buford the Little Bighorn by Bill Peet. The bighorn sheep was also featured in a series of prints by artist Andy Warhol in his 1983 Endangered Species portfolio. Bighorn sheep serve as a source of ecotourism, as tourists come to see them in their native habitat. The Bighorn River and Little Bighorn River retain their names on maps of western North America.

Questions about Bighorn sheep

Where can you see bighorn sheep in Canada?

In Canada, bighorn sheep are primarily found in the Rocky Mountains of Alberta and British Columbia, inhabiting alpine meadows, grassy slopes, and rugged cliffs in these regions. Specific locations include national parks like Banff and Jasper, as well as provincial parks and wildlife management areas where they seek escape terrain from predators. The Wilder Institute's Calgary Zoo also houses a herd for public education, and sightings by the public are more common during seasonal movements to lower elevations in winter when snow cover in the high country becomes too deep for them to move through effectively. Their very specific habitat requirements mean they are often associated with steep, rocky landscapes that offer both forage and security.

Why are bighorn sheep horns so big?

The massive, curled horns of male bighorn sheep serve two primary functions related to survival and reproduction within their social structure. First, they are used as weapons and shields during dramatic headbutting clashes with rival rams, especially before the mating season to establish dominance and breeding rights through a hierarchy. Second, horn size is a visual indicator of a ram's age, health, and status within the herd, influencing social interactions and mating success. The horns are made of keratin and grow throughout the ram's life, forming annual rings, and their structure, including enlarged sinuses and internal bony septa, helps absorb the impact of collisions to protect the brain from injury during these intense combats.

What is the main threat to bighorn sheep populations?

The most severe ongoing threat to bighorn sheep is infectious disease, particularly pneumonia, transmitted from domestic sheep and goats, as bighorns have little resistance to pathogens like Mycoplasma ovipneumoniae. These bacteria can be carried asymptomatically by domestic livestock, and contact can trigger outbreaks that kill up to 90 percent of a herd and cause years of poor lamb survival due to subsequent pneumonia outbreaks in young animals. Other major threats include habitat loss and fragmentation from human development and major highways, historical overhunting, and predation, while climate change also poses a risk by affecting the availability of critical water and forage in their often arid or seasonally variable habitats. The species' sensitivity to these human-induced problems makes them a key indicator of land health.

How do desert bighorn sheep survive without much water?

Desert bighorn sheep are remarkably adapted to arid environments through a combination of physiological efficiency and learned behaviours that conserve moisture. They obtain most of their water from natural sources like springs, seeps, and potholes in bedrock that collect rainwater, and they are also efficient at extracting moisture from the plants they eat, such as succulent cacti including the barrel cactus. Their kidneys are highly efficient at conserving water, producing very concentrated urine, and they reduce water loss by resting in the shade during the hottest parts of the day to minimize exertion and evaporation. Conservation efforts in some areas sometimes include installing man-made water catchments called guzzlers or drinkers to supplement these natural sources in extremely dry periods or fragmented habitats.

Are bighorn sheep endangered?

The bighorn sheep species as a whole is classified as Least Concern on the IUCN Red List. However, specific subspecies and populations are endangered. The Sierra Nevada bighorn sheep is listed as endangered by the United States government. A distinct population segment of the desert bighorn sheep, the Peninsular bighorn, is also listed as endangered. In Canada, bighorn sheep are considered a species of special concern in British Columbia. Many populations remain precarious due to disease and habitat issues.

What do bighorn sheep eat?

Bighorn sheep are herbivores with a varied diet that changes with habitat and season, primarily grazing on grasses and browsing on shrubs, forbs, and herbaceous plants, particularly in fall and winter. Desert bighorn sheep are selective feeders, consuming the most nutritious forage available, including leaves of mesquite trees and catclaw, various grasses, herbaceous plants, and cacti such as barrel cactus, which also provides essential moisture in dry environments. In mountain habitats like the Rockies, they feed on available grasses and shrubs on alpine meadows and slopes, and they also seek out natural mineral licks to obtain necessary nutrients. Their foraging helps shape plant communities, opens landscapes for other species, and contributes to nutrient cycling in their ecosystems through their waste.

Sources: Wikipedia and current public reporting, checked by the Your Space Hamilton desk. Last updated 2026-10-23.