Arizona-Sonora Desert Museum Digital Library

Distinguishing Features

The desert bighorn is a heavy-bodied, gray-brown, deer-sized animal with a large white rump patch. Both males and females have horns, but the males' are much larger, growing into a curled spiral shape over the course of several years.

Habitat

Bighorn sheep are found in rugged, rocky desert mountain ranges and some canyons. They prefer precipitous slopes and cliffs where they can be safe from predators.

Feeding

• Diet: These hooved animals are herbivores. Bighorn sheep eat many different grasses as well as mesquite leaves and beans, desert lavender, fairy duster, desert ironwood, palo verde, globe-mallow, cactus fruits and agave.

• Behavior: Bighorn sheep feed early in the mornings and again late in the afternoons. A sheep sometimes kicks the top off a barrel cactus to reach the succulent inside, or butts its horns against a saguaro to get at the tender flesh.

Life History

Bighorn sheep live in and around the most inaccessible steep canyon walls and rugged terrain. Their defense is to retreat to these hard-to-reach spots where predators cannot follow.

Bighorn feed with their herds early in the morning, bedding down to rest near each other in shallow caves or thick brush, while they chew their cuds. Activity resumes in the late afternoon. Breeding occurs during August and September. Rams butt heads to establish dominance and the right to breed, and the cracking sound of their butting heads can be heard a mile away.

The ewes move off alone to drop their lambs in February, rejoining the group about a week later with the new lamb. Lambs imprint on the spot where they were born, and try to return there when they are ready to give birth.

Both males and females have horns. The ewe's horns are narrow and only grow about 12 inches (30 cm) long (about a half curl). The male's horns are broad and massive and eventually curl in nearly a full spiral. The ram's horns may weigh as much as 40 pounds (18 kg)!

The Sonoran Desert is home to 4 species of hooved animals — javelina, mule deer, pronghorn, and bighorn sheep. Hooves are specialized claws or toenails, adaptations for running to escape predators. Hooved animals, also called ungulates, are usually herbivores that socialize in herds or bands. Living in a group benefits all the individuals, since there are many sets of eyes watching for predators.

Javelina are common throughout the Sonoran Desert region. Any area with sufficient prickly pear and other cacti can be home to a herd of javelina. They usually provide plenty of evidence of their presence, such as chewed prickly pear pads, rooted-up areas around plants, and many trails and bed grounds.

Our other three hooved desert animals are ruminants (even-toed, cud-chewing animals). Mule deer inhabit the lower foothills and brushy canyons in the desert, while white-tailed deer live at the higher elevations in the mountains. Mule deer depend mainly on good hearing and eyesight, camouflage, and running for defense. Their large (9 inch; 23 cm) ears move continually, checking antennae-like for any sounds of danger. The main predator of deer is the mountain lion.

Pronghorn populations are not large anywhere in Arizona. The Sonoran pronghorn is listed as endangered, but herds in a few places — the Buenos Aires Wildlife Refuge is one — are doing well.

Bighorn sheep numbers have also declined due to human encroachment and competition with domestic sheep and wild burros, but reintroduced populations are increasing in numbers. The construction of artificial waterholes in some areas has helped maintain bighorn herds.

Bighorn: Adapted for Desert Living

Bighorn sheep inhabit some of the driest mountain ranges in Arizona — they are superbly adapted to life in these arid environments. During winter months when dew is available and plants contain more moisture, the sheep can last for several months without drinking free water. In the intense heat of summer when most green plants have dried up, they seek out barrel cactus, chain fruit cholla fruits, and other cactus fruits for their water content. They avoid the sun by resting in the shade or in caves and shallow overhangs, but they can withstand body temperatures of up to 107°F (42°C)! (Normal body temperature for bighorn sheep is 101 to 102°F; 38 to 39°C.) Enlarged stomach compartments can store water to last for several days, allowing the sheep to go two or three days without a drink. They can then drink up to 20 percent of their body weight (up to 2 gallons; 7.5 liters) in just a few minutes at a waterhole.