U.S. Fish & Wildlife Service

[Desert Adaptations] [Food] [Social Life] [Disturbances]
[Conservation Efforts] [Suggested Reading]

Desert Adaptations

The desert bighorn has become well adapted to living in the desert heat and cold and, unlike most mammals, their body temperature can safely fluctuate several degrees. During the heat of the day, bighorn often rest in the shade of trees and caves.

Cabeza Prieta NWR's bighorn and those further south in Mexico are typically found in small scattered bands adapted to a desert mountain environment with little or no permanent water. Some of the bighorn may go without visiting one of the refuge's water developments for weeks or months, sustaining their body moisture from food and from rainwater collected in temporary rock pools. They may have the ability to lose up to 30 percent of their body weight and still survive. After drinking water, they quickly recover from their dehydrated condition. Wildlife ecologists are just beginning to study the importance of this adaptive strategy, which has allowed these small bands to survive in areas too dry for many of their predators.

Desert bighorn are stocky, heavy-bodied sheep, similar in size to mule deer. Weights of mature rams range from 125 to 200 pounds, while ewes are somewhat smaller. Due to their unique padded hooves, bighorn are able to climb the steep, rocky terrain of the desert mountains with speed and agility. Bighorn rely on their keen eyesight to detect potential predators such as mountain lions, coyotes, and bobcats, and they use their climbing ability to escape.

Both sexes develop horns soon after birth, with horn growth continuing more or less throughout life. Older rams have impressive sets of curling horns measuring over three feet long with more than one foot of circumference at the base. Cabeza's bighorn often have a unique rusty color on their horns which is thought to be a result of rubbing against the elephant tree, another unique species found here. The ewes' horns are much smaller and lighter and do not tend to curl. The head and horns of an adult ram may weigh more than 30 pounds. Annual growth rings indicate the animal's age. Both rams and ewes use their horns as tools to break open cactus, which they consume, and for fighting.

Food

Bighorn feed on a wide variety of leaves, twigs, flowers, forbs, grasses, and cacti. On Cabeza a few plants that bighorn are known to forage are ironwood, paloverde, mormon tea, brittlebush, and big galleta.

Social Life

Rams battle to determine the dominant animal, which then gains possession of the ewes. Facing each other, rams charge head-on from distances of 20 feet or more, crashing their massive horns together with tremendous impact, until one or the other ceases.

Bighorns live in separate ram and ewe bands most of the year. They gather during the breeding season (usually July-October), but breeding may occur anytime in the desert due to suitable climatic conditions. Gestation lasts about 6 months, and the lambs are usually born in late winter.

Disturbances

In the late 1800s and early 1900s bighorn sheep populations rapidly declined. Domestic cattle and sheep, along with wild horses and burros, competed with bighorns, especially at waterholes. Domestic stock also introduced diseases to bighorn populations. Cabeza Prieta NWR's bighorn, like other Arizona bighorn, suffer from chronic sinusitis caused by a bot fly and the disease can be fatal. We are hopeful that some of the bands on the refuge are free of this disease.

Activities that influence bighorn sheep numbers include disturbance from a wide variety of sources: hunting and other recreational use of habitat, poaching, and habitat fragmentation and encroachment caused by roads, fences, mining, and military and recreational activities. Individual bands become isolated and eventually whole populations can be lost as usable habitat is increasingly intruded upon by humans.

Conservation Efforts

The Cabeza Prieta National Wildlife Refuge is one of several wildlife refuges preserving desert bighorn. Conservation is accomplished primarily through habitat protection and limiting disturbance and stress from all sources. Waterhole maintenance, active monitoring, and research are the management tools we use. These efforts on the refuge involve the Arizona Game and Fish Department, the Marines and Air Force, and the Arizona Desert Bighorn Sheep Society as well as individual conservationists. All have contributed to a desert bighorn sheep population we believe is similar to that originally found in the mountains of Cabeza Prieta NWR.

Suggested Reading

Aldo Leopold. "A Plea for Wilderness Hunting Grounds," Outdoor Life. November 1925.

Bill Hook and Raymond Lee, editors, Borrego, The Fall and Rise of Desert Bighorn Sheep in Arizona. The Arizona Desert Bighorn Sheep Society, Inc., 1987.

William T. Hornaday. Campfires on Desert and Lava (reprinted Tucson: University of Arizona Press, 1985).

Raymond M. Lee, editor. The Desert Bighorn Sheep in Arizona. Arizona Game and Fish Department, 1989.

Karl Lumholtz. New Trails in Mexico (reprinted Glorieta: Rio Grande Press, 1971).

Gale Monson and Lowell Sommer, editors. The Desert Bighorn, Its Life History, Ecology, and Management. University of Arizona Press, 1990.

Gary P. Nabhan, editor. Counting Sheep, 20 Ways of Seeing Desert Bighorn. University of Arizona Press, 1993.

Charles Sheldon. The Wilderness of Desert Bighorns and Seri Indians, from the Southwestern Journals of Charles Sheldon. The Arizona Desert Bighorn Sheep Society, Inc., 1979.