Resource: Bighorn Sheep

Print Background Essay

The long-term success of all living things depends on their ability to adapt to their environment. Any trait or characteristic that promotes survival and is believed to have evolved under specific environmental pressures is considered to be an adaptation. Desert bighorn sheep have evolved several physical and behavioral adaptations that help them survive the high summer temperatures, snowy winters, and rugged terrain of the mountain ranges of the Southwest's deserts.

With a compact, muscular body and sharp-edged hooves, desert bighorns are adept at jumping and climbing. They can run up to 30 miles per hour on level ground and scramble up steep slopes at approximately half that speed. With their excellent eyesight, desert bighorns can spot coyotes, mountain lions, and other predators from up to a mile away. Their fur protects them from both rocks and the Sun: an outer coat of hair guards against abrasion, and a short fleece undercoat helps regulate temperature.

Male bighorns, called rams, possess large, fully curled horns. The female ewes have much smaller horns that do not curl. While the horns are used by both sexes as tools to break up cacti, rams also use their horns against one another to establish dominance within a herd during the breeding, or rutting, season.

Desert bighorn behaviors, as well as some of their features, have been influenced by their environment. During the heat of the day, desert bighorns rest in the shade of trees, caves, and rock overhangs. They cool their bodies by panting—a behavior commonly associated with dogs—or perspiring through sweat glands located throughout their bodies. Desert bighorns feed at night on grasses, shrubs, and cacti. Like cows, they are ruminants. They have a four-chambered stomach that can digest dry and coarse material. They get moisture from vegetation, yet they also rely on water holes or rock pools that form naturally from rainfall. In summer, they can go for a week or more without drinking if water is scarce, because when they do drink, they can take in up to 20 percent of their body weight in water.

While the population of desert bighorns in North America is estimated to have reached several tens of thousands prior to European colonization, there has been a steep decline caused by hunting, disease, and habitat loss from activities related to mining and livestock grazing. Today, conservation measures, such as habitat protection, waterhole maintenance, and reintroduction programs, have helped the population rebound. Nearly 20,000 desert bighorns now reside mostly in Arizona, Nevada, California, and Utah.

To learn more about desert conditions and inhabitants, check out Desert Biome.

To learn about other animals that inhabit the southwest desert, check out Bats of the Southwest, Burrowing Owl, Horned Lizard, and Tarantulas.

To learn more about how animals adapt to better survive in their environment, check out Kratts' Creatures.

Print Questions for Discussion

• Describe some of the adaptations that bighorn sheep have that protect them in a desert climate.
• Can you think of other climates or conditions in which these same adaptations would be useful?
• How do the horns of bighorn sheep help this species survive in its environment?
• Why do you think bighorn sheep are not found in other environments, for example, New England woodlands or Florida swamps?