Few animals represent the remoteness and majesty of desert wildlands as does the desert bighorn sheep. They typically inhabit rugged, steep canyons and mountain ranges; some of Arizona’s most inhospitable country. Biologists estimate that the state’s historic population may have numbered as many as 30,000.
Numbers declined severely over the last 150 years, due mostly to the mining and livestock activities of early settlers. Habitat fragmentation is another strong factor influencing population decline. The building of highways, fences and water delivery canals create barriers to sheep movement for food or water between various desert mountain ranges. By the 1940s, the estimated population had dropped to 750.
In 1939, the Kofa and Cabeza Prieta game ranges were set aside as game ranges to be managed primarily for bighorn sheep. Since becoming national wildlife refuges in 1974, the application of modern, science-based wildlife management methods has helped resurrect the bighorn sheep and today Arizona’s statewide wild sheep population is approximately 6,000 animals.
Life on the Rocks
A desert bighorn is remarkably well adapted for survival in arid habitats. Its body utilizes water to its maximum potential with little waste. Although highly dependent on water sources, some sheep have been documented as not drinking freestanding water for a period of several months, getting any necessary moisture from cacti or other food sources. If human influences such as mining or off-road vehicle use affect movements to or from a waterhole, bighorns will discontinue using that source. This puts more pressure on forage surrounding remaining waterholes and may lead to population declines.
Desert bighorn are also able to fluctuate their body temperature slightly without ill effects. Bighorns have a vast network of blood vessels on their undersides and in their horns that help them dissipate body heat, even on the hottest of days, as they majestically stand motionless on rock points or edges of cliffs allowing updrafts and breezes to flow over their bodies.
Their most important adaptation may be their ability to lose up to 30 percent of their body weight in water (more than a camel) and still survive. If water is available, they can rapidly replenish their dehydrated condition. On any given summer day, one can observe what looks like a thin bighorn near death come to water, drink upwards to five minutes, and walk away looking healthy and fat, not drinking again for a week or more. In severe drought conditions, water adequate to sustain survival is often insufficient to enable animals to thrive and reproduce. Lactating ewes struggling to sustain lambs are especially vulnerable to water stress.
A Wildlife Management Success Story
In 1958, the Arizona Game and Fish Department began a program to reintroduce bighorn into parts of their historic range, translocating the first group to Aravaipa Canyon in southeastern Arizona. Today, a healthy herd inhabits this unique, rugged canyon. Primary capture sites for transplants are the Kofa and Plomosa Mountains near Yuma and the Black Mountains near Kingman. Funding for these transplants comes from donations of the Arizona Desert Bighorn Sheep Society and the Foundation for North American Wild Sheep. Additionally, numerous waterhole improvement projects have been carried out through cooperation and funding from these and other conservation organizations. These projects also benefit many other types of wildlife as well.