Bighorn Sheep

Bighorn Sheep

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The scientific name for Desert Bighorn Sheep (Ovis canadensis Nelsoni) with a classification of a mammal and a life span of 6 to 8 years. The State Conservation Status is labeled as Priority Species and the Federal Conservation Status is Least Concern with Game Status and Game Type is Big Game.

Desert Bighorn Sheep prefers the rough and rocky habitat of mountains in Southern Nevada and the steep rocks protect against predators. These predators cannot navigate and climb up after the bighorn sheep. Desert Bighorn Sheep require freestanding water to get through the hot desert summers. The threats to the Bighorn Sheep are disease and Habitat Fragmentation which occur when parts of a habitat are destroyed thus leaving smaller unconnected areas occurring naturally, or majority of the time due to human activity.

Desert Bighorn Sheep are herbivores with a diet of mostly grasses but includes shrubs, cacti, acacia, and forbs and their diet depends on their geographic location and availability of vegetation. In the warmer months, they move down to the valleys. Mating season, called the “rut” occurs in the fall when rams (male sheep) will compete to mate with females thereafter later in the season rams will join females and female groups. In the winter bands of ewes (female bighorn sheep) may join and form large groups of up to 100 sheep. The horns of a ram are called “curls” and can weigh up to 30 pounds.

The scientific name for Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis) with the classification of a mammal and a life span of 9 to 12 years. The State Conservation Status is labeled as Priority Species and the Federal Conservation Status is Least Concern with Game Status and Game Type is Big Game.

The Rocky Mountain Bighorn Sheep is the largest species of wild sheep and bulkier and stockier in body size that the other subspecies found in Nevada. Rocky Mountain Bighorn Sheep males can weigh over 300 pounds and stand over three feet tall at the shoulder and the females are roughly half this size. They are gray/brown to dark brown in color with white patches on their rump, muzzle and back of legs. Winter coats are thick, double-layered and may be lighter in color. Bighorn sheep shed these heavy coats in the summer. With a wide set of eyes that provide a large angle of vision, along with sharp hearing and highly developed sense of smell and detection of danger at distances. The Rocky Mountain Bighorn Sheep specialized hooves and rough soles give them a natural grip making jumps and climbs up and down sharp cliff faces.

Rocky Mountain Bighorn Sheep habitat is grassy mountain slopes alpine meadows, foothills near rugged rocky cliff and bluffs. The threats to the Rocky Mountain Bighorn Sheep are disease and Habitat Fragmentation which occur when parts of a habitat are destroyed thus leaving smaller unconnected areas occurring naturally or majority of the time due to human activity and Habitat Loss.

Rocky Mountain Bighorn Sheep rams (males) will band together in the spring and summer, while ewes (female bighorn sheep) and their babies will form separate groups. During the winter, the separate groups will come together to form larger herds. Mating season, called the “rut” starts in fall, rams use their horns as weapons of battle to fight for dominance or female mating rights. Ewes will have on lamb during spring to early summer and walk soon after birth, and nurse up to six months. Males leave their mother’s group around two to four years of age, while the females stay with their herd for life. In “rut” rams face each other with their rear up on hind legs and pitch forward at speeds up to 40 mph and repeat until one animal concedes and walks away.

These sheep graze on grasses, sedges, and clover in warmer summer months and willow, holly, cactus, and sage in the cooler months fall and winter. They seek minerals at natural salt licks such as lakes to add nutrients to their diet, with their digestive system acting as a survival mechanism. The Rocky Mountain Desert Bighorn have a four-part stomach which allows sheep to gain important nutrients from hard, dry forage, and they eat large amounts of vegetation quickly and head to cliffs or ledges in which they lie down and rechew their cud and digest food away from possible predators. Bighorn Sheep can go without drinking water for months at a time because they get all the necessary liquids and electrolytes from the plants that they eat.

The Rocky Mountain Bighorn Sheep, studies finding indicate that when having to cross highways this action creates a high level of stress in the animals, which can reduce their resistance to disease, increasing sheep mortality, Bighorn Sheep are sensitive to human disturbance and humans can assist in protecting the sheep by maintaining distance when viewing them.

The scientific name for California Bighorn Sheep (Ovis canadensis californiana) with a classification of a mammal and a life span of 6 to 8 years. The state Conservation Status is labeled as Priority Species and the Federal Conservation Status is Least Concern with Game Status and Game Type is Big Game.

The California Bighorn Sheep look like Rocky Mountain Bighorn Sheep but have less blocky body and smaller horns, and like the Rocky Mountain Bighorn Sheep have a dark to medium rich brown head, neck and dorsal body with a short black tail and a white muzzle, rump, and ventral patches. Both sexes male and female have sturdy muscular bodies and strong necks that support horns that curve back in females and are much larger and curled around in males. The most consistent anatomical feature distinguishing the California ecotype from the Rocky Mountain ecotype is the presence of continuous black or brown dorsal stripe dividing the white rump patch to the tip of the tail.

The California Bighorn Sheep is found in the slopes of the Sierra Nevada and prefers rugged, rocky cliffs and bluffs and open areas with vegetation and grasses. They often move across their range as the seasons change. The threats to the California Bighorn Sheep are disease and Habitat Fragmentation which occur when parts of a habitat are destroyed thus leaving smaller unconnected areas occurring naturally, or majority of the time due to human activity.

California Bighorn Sheep are herbivores that spend their time grazing on sedges, grasses, and sagebrush. Mating season called the “rut” starts in fall and rams (male Bighorn Sheep) will compete to mate with females. Ewes (Female Bighorn Sheep) will have one lamb during spring to early summer. All the Bighorn Sheep have a four-part stomach that enables them to eat large portions rapidly before retreating to cliffs or ledges where they can thoroughly rechew and digest their food safe from predators.

Bighorn Sheep Classification System
  • Class I (Two-Year Old Ram)
  • Class II (Three-Year Old Ram)
  • Class III (Six-To Eight-Year-Old Ram)
  • Class IV (Nine Plus Year Old Ram)
Diseases of the Bighorn Sheep & Rocky Mountain Bighorn Sheep & California Bighorn Sheep

1) Bacteria Mycoplasma Ovipneumoniae is a threat to all Bighorn Sheep, Rocky Mountain Bighorn Sheep, and California Bighorn Sheep and can initial outbreaks of pneumonia that lead to high rates of mortality in the Bighorn Sheep and can initial outbreaks of pneumonia that lead to high rates of mortality in the Bighorn Sheep herds across the west. This pathogen initiates a cascade of events that can cause severe outbreaks of pneumonia with high rates of mortality in Bighorn Sheep herds. After an initial outbreak, some Bighorn ma chronically shed the bacteria and cause yearly outbreaks in lambs. Yearly lamb mortality can result in little to no recruitment and the population may eventually die out or at least fail to recover. NDOW has expended significant time and effort to study this disease and improve its management. This includes understanding how different strains vary across the landscape and how the strains interact with herds and environmental factors to cause disease, including understanding improvement of herds performance post outbreak response to the question of why some herds recover and others do not.

NDOW is doing ambitious test and removal project with many non-profit organizations to remove
chronic shedders from the population to eliminate the disease and recover the population. NDOW
continues to track the spread of the disease and respond to wandering Bighorn and domestic sheep that
have potential to transmit the disease to new herds. NDOW ask for the public assistance in reporting
observations of coughing or sick or dead Bighorn Sheep in the Bighorn range.

2) Sinus Tumor of Bighorn Sheep are a contagious tumor that grows in the sinuses of bighorn sheep. Tumors grow from the lining of the sinuses in the forehead, horns and above the teeth. These tumors are found in all 3 subspecies of bighorn sheep in Nevada with no risk to human health. NDOW’s wildlife health program is conducting surveillance of hunter harvested animals to learn where sinus tumor occurs and how it affects the sheep herds. These tumors cannot typically be seen from the outside of the head and the tumors destroy bone, produces thickened sinus lining, gelatinous tissue and mucus and pus. This disease is important because it may cause skull and horn Deformities and impairs respiratory function and may contribute to respiratory disease that is inevitably a threat to bighorn herds.

Groups Assisting NDOW with Sinus Tumors of Bighorn Sheep
Taxidermist to participate by sending over the remaining portion of the skull to NDOW after the cap has been removed for mounting and will pay the taxidermist per head. Sample collection does not interfere with taxidermy.

Ewe Hunters may donate your ewe skull for research if they are not doing a mount, leaving the head when the hunters are checking in their ewe. If the hunters are doing a mount, then they can ask for the assistance of the taxidermist to freeze portion of the head that is normally discarded.

Ram Hunters should ask taxidermist to please freeze the portion of the head that would normally be disregarded.

3) Sinusitis is inflammation of the sinuses. It is caused by bacterial infection secondary to damage caused by the migration of bot fly larvae (Oestrus ovis) through the sinus lining. When the damage is severe it can lead to weakening of the bone which can cause breakage of horns. Sheep may run from place to place and keep their head near the ground to avoid or stamp their feet or shake their head to try and prevent the bot fly from laying eggs in their nose. Sheep may also stand in a circle with their heads toward the center to avoid the fly.

4) Contagious ecthyma known as orf, is a viral disease of sheep and goats that results in crusting sores around the mouth. It is especially severe in lambs and the pain from the sores can prevent them from nursing normally, leading to poor nutrition and growth. In adults the disease manifests usually for a few weeks until they can mount an immune response and the sores resolve. Orf is a zoonotic disease (animal to human transmission) that can cause painful sores at the point of contact, usually the hands. To avoid contracting the disease it is best to wear gloves when handling your harvest, especially if you notice sores around the mouth and nose.

Horns of a Bighorn Sheep
Bighorn sheep rams start growing their horns at birth and continue to grow their horns throughout their lifespan until the animal dies. Older rams have massive horns that can grow over three feet long with a more than one-foot circumference at the base. Females or ewes also have horns, but they are short with only a slight curvature to a sharp point within the first four years of life. Both rams and ewes using their horns as tools for eating and fighting. Males, called rams have large horns that curl around their faces by eight years of age. These horns can weigh up to 30 pounds. Within each horn there is a living core that provides a continuous flow of blood beneath the hard sheath. The horns are made of keratin, which is the same material that fingernails and hooves are made of. As the bighorn rams age and go through the summer and winter a growth ring is created. For each year that passes a ring is reflected in a ram’s horn and is often referred to as “growth rings” or “annuli rings”. The ring is created when the animal is under stress, which is usually caused by rutting or mating rituals in which they are not thinking about feeding and maintaining their nutrition, but only trying to breed the opposite sex. For Desert Bighorn sheep the ring is created in the summer; for the Rocky Mountain Bighorns, the ring is created in the winter. Counting rings is the best way to age a bighorn ram. The most important thing to look for when aging a bighorn ram is the four-year ring.

Habitat Threats and Habitat Conservation
In the end an increasing amount of traditional winter and spring habitat of Bighorn Sheep is being alienated and/or developed for residential, agricultural, and industrial purposes. These conflicting land uses have been and will be inevitable, because low elevation Bighorn Sheep habitat is often some of the most desirable for human development. For the Bighorn Sheep, the capability of the habitat has been diminished by permanent factors such as land alienation, highways, subdivision, and open-pit mines. The suitable habitat at present is capable habitat within the historic distribution because of forest access roads, forest succession, competition with livestock, and human disturbance. In addition to the direct loss of habitat, forest fire succession and forest succession. There are population threats such as disease transmission habitat effects from urban and agricultural development, weed invasion, fire suppression, increased predation, range depletion and forage competition with livestock and wild ungulates and harassment by humans and dogs, and high levels of parasites. Due to their higher moisture regimes, encroachment has been even greater on spring and fall transition range. The loss of transition ranges forces Bighorn Sheep to arrive on winter ranges earlier and leave later. Overused winter ranges cause nutritional stress and can increase parasite especially lungworm infection rates leading to increased lung damage. High levels of lungworm infection can cause high mortality in Bighorn Lambs causing damage to the lung tissue.

Next there is harassment of wildlife by the presence of humans, whether in the form of wildlife viewing stands, aerial censuses, snowmobiles, helicopters, vehicles, or domestic dogs can add undue stress to the Bighorn Sheep. Predation is a possible limiting factor for Bighorn populations with carnivore and raptor species can prey on Bighorn Sheep such as Black Bear, Bobcats, Wolves, Golden Eagles, Coyotes. A large amount of domestic sheep and the free ranging of large numbers of horses on these ranges result in damage to fragile low elevation. Impacts from cattle grazing include reduced forage supply, abandonment of ranges, decreased distance to escape terrain and altered habitat use patterns and
depletion of range condition and trampling and fouling of watering holes. Plants may not support a second grazing by cattle if they are to support Bighorn Sheep the following winter and spring. While grazing lands can benefit from judicious management of cattle, it must be carefully managed to ensure Bighorns have the appropriate forage available at the critical time of year on the critical preferred habitats.

Livestock ranching is the primary threat to Bighorn Sheep through disease transmission, range depletion and resource competition. Industrial developments such as forestry, mining and hydro-electric developments can result in habitat loss and displacement, disturbance, interference with seasonal movements along established secure corridors and increase in animal exposure to predation. Helicopter activity associated with seismic work, forestry and recreation can disturb and displace the sheep. Impacts from recreation are terrain vehicles, rock climbing, golf, include habitat loss, disturbance, and foraging efficiency reduction. The resulting chronic stress can lead poor health, reduced growth and reduced reproductive fitness. Chronic disturbance can work together with other habitat and animal factors and lead to immuno-compromised individuals or populations and result in outbreak of disease. Sheep habituated to human disturbance may be susceptible to increased highway mortality, harassment by people and dogs and dependency on artificial food sources that may be temporarily available. Forest encroachment and fire suppression are reducing suitable habitat by replacing grass, forbs, and shrubs and forest succession can interfere with seasonal movement patterns and grazing behavior and as the density of trees increases, the visibility decreases, increasing predation by carnivores relying on stealth
and it alters the fire ecology and competition for forage from elk and mule deer on low elevation winter ranges may be substantial and when resources are scarce, Bighorn Sheep ewes may postpone first reproduction or reduce maternal care resulting in decreased lamb survival. The introduction and spread of invasive species on grasslands are a great concern because they replace nutritious native forage species with inedible or non nutritious plants.

Hunting seasons are permitted, and the Bighorn Sheep are normally harvested under a general open season and quotas, administrative guidelines limited entry hunting are used to regulate hunting in some areas, limited ewe and lamb hunting are provided where sheep numbers are approaching or have exceeded carrying capacity. Hunting can be an important management tool for Bighorn Sheep herds due to the potential for dramatic cyclical die offs associated with exceeding the carrying capacity of ranges. The goal for Bighorn Sheep should be maintaining and enhancing Bighorn Sheep populations and habitats.

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