Desert Bighorn Sheep

Desert Bighorn Sheep, Ovis canadensis nelsoni

Desert Bighorn Sheep, Ovis canadensis nelsoni. Sheep photographed within the confines of the Arizona-Sonora Desert Museum, Tucson, Arizona, February, 2022.

Desert Bighorn Sheep, Ovis canadensis nelsoni. Captive animal within the confines of the Living Desert Zoo and Gardens, Palm Desert, California, March 2011. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California. New for 2023.

The Desert Bighorn Sheep, Ovis canadensis nelsoni, is a member of the Bovidae family of Cloven-hoofed, Ruminant Mammals. The Bovidae family consists of one hundred forty extant and three hundred extinct species. Designation of subfamilies within the Bovidae family has been controversial and many experts disagree about whether the family is monophyletic or not. Three subspecies of Bighorn Sheep are found in North America: the Desert Bighorn Sheep, Ovis canadensis nelsoni, the Rocky Mountain Bighorn Sheep, Ovis canadensis canadensis, and the Sierra Nevada Bighorn Sheep, Ovis canadensis sierrae. Unlike other subspecies, the Desert Bighorn Sheep have adapted to hot, dry climates. The Desert Bighorn Sheep is known in Mexico as Borrego Cimarrón Del Desierto.

Desert Bighorn Sheep have longer legs, lighter coats, and smaller bodies than their Rocky Mountain Bighorn Sheep cousins. They have muscular bodies with chocolate brown fur and white fur around their muzzle, rump, and belly. Males (rams) have large curved horns, while females (ewes) have short horns with only slight curvature. The horns of an adult rams can weigh up to 13.6 kg (30 pounds). Their outer hooves are modified toenails that are shaped to snag any slight protrusion, while a soft inner pad provides grip that conforms to each variable surface. They are a sexually dimorphic species with males weighing greater than 136 kg (300 pounds) and females weighing greater than 86.2 kg (190 pounds). Adults typically stand at 76.2 cm (2 feet 6 inches) to 99.1 cm (3 feet 3 inches) tall at the shoulders.

The breeding season for Desert Bighorn Sheep is from August through December while rut occurs from August through the early fall. During this time, the bachelor herds that form during the winter and spring break up, and males search for females while keeping a sharp eye out for each other. Large-horned, older males do much of the breeding, though younger males will breed opportunistically. Males breed with several females, however, they are not territorial nor do they form harems, but rather are serial polygynists. Competition for mates is fierce and males will square up with each other, charge, and bash their heads together. Fortunately, their thick skull helps to cushion their brains from the impact. Females typically first breed at two and one-half years of age and give birth from February to early April after a gestation period of about 6 months or 180 days. Females typically give birth to one lamb per year and are fiercely protective of their young, using their sharp hooves for defense. Lambs can walk shortly after being born and stay with the herd where they learn where to find food and water from their mother and the other ewes. A typical herd consists of eight to ten individuals, but sometimes herds of one hundred individuals are observed. Young males also stay with the main herd but eventually split off into bachelor herds when they are a few years old. They have life spans of between ten and fourteen years. 

Desert Bighorn Sheep are highly adapted for desert climates and can go for extended periods without drinking. They are generalist herbivores and eat a variety of desert plants including shrubs, grasses, brome, fescue, clover phlox, cinquefoil, and cacti. Their diet supplies a significant portion of their water needs but in addition, they will drink water from potholes in rocks and seasonal streams. Desert Bighorn Sheep are exceptional climbers and can maneuver through steep, rocky canyons to find resources. Their agility also helps them escape predators such as bobcats, coyotes, gray foxes, and mountain lions.

Desert Bighorn Sheep inhabit a wide range that includes the mountains of eastern California, much of Nevada, northwest Arizona, southern Utah, the Sonoran Desert including the northern portions of Sonora, Chihuahua, Cohauila and Nuevo León, all of Baja California and Baja California Sur within the Baja Peninsula, and Tiburon Island. They prefer rugged and open habitats with grasses and forbs for grazing. This includes rocky slopes and cliffs, canyons, and washes. 

By the late 1800’s Bighorn Sheep had disappeared or declined in many areas due to diseases introduced by domestic livestock and overhunting by early colonizers. Currently, Bighorn Sheep are considered to be of Least Concern, however, the Peninsular Desert Bighorn Sheep population is federally endangered. The IUCN currently includes all Bighorn Sheep species under the same listing so the exact status of this subspecies is unclear. However, according to the Bureau of Land Management and the U.S Forest Service, the Desert Bighorn Sheep is considered sensitive to extinction.