Sonoran Desert National Park, Arizona, USA Photograph by David Olson   Southern North America: Southwestern United States into northwestern Mexico Deserts and Xeric Shrublands   86,100 square miles (223,000 square kilometers) -- nearly twice the size of Louisiana Relatively Stable/Intact

· Old Man of the Desert
· Special Features
· Did You Know?
· Wild Side
· Cause for Concern
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Old Man of the Desert

The Sonoran Desert is probably best known for the species that has become universally (though incorrectly) symbolic of all deserts, the saguaro cactus. This tall, slow-growing, armed cactus is the largest of all cacti and grows only in this ecoregion. A saguaro may reach 50 feet (15 m) in height during its potential lifespan of 200 years! This impressive cactus provides habitat for many animal species, including the cactus wren and Gila woodpecker.

Special Features

With an average rainfall of 4-12 inches (100-300 mm) each year, the Sonoran is home to a wide variety of cacti-cholla cactus, organ pipe cactus, and silver-dollar cactus, just to name a few. A remarkable plant found in this desert is the octillo, a tall, spindly plant that has adapted to the dry conditions of the desert by sprouting leaves five or six different times during the year, and then dropping them during the winter to avoid excessive moisture-loss. Its beautiful red cone-shaped flowers often bloom right after the first spring rain.

	The Gila monster is not really a monster, of course. But it is poisonous and probably got its reputation from being one of the only two venomous lizards in the world. It has grooved teeth with venom glands, different from the hollow fangs of venomous snakes. The Gila's orange-and-black warning coloration is a tip-off that it is dangerous.

Wild Side

Typical plants of the Sonoran Desert include the creosote, white bursage, jojoba, and small trees such as paloverde and ironwood. Hummingbirds and other nectar-eating birds are especially attracted to the red flowers of the octillo. These and other birds such as the black-tailed gnatcatcher and phainopepla are what make the Sonoran an exceptional area for birdwatchers. The roadrunner is a famous Sonoran inhabitant and can be seen running across the ground hunting scorpions, tarantulas, rattlesnakes, and lizards. Fifty-eight species of reptiles -- including six species of rattlesnake and the giant Gila monster, as well as the threatened desert tortoise -- can be found here. The tiger salamander, the world's largest land-dwelling salamander, survives the desert weather by burrowing underground during the dry season and emerging during wet times. Mammals of the Sonoran include the California leaf-nosed bat, ring-tailed cat, black-tailed jackrabbit, desert kangaroo rat, Bailey's pocket mouse, round-tailed ground squirrel, mountain lion, bighorn sheep, coyote, and pronghorn.

Cause for Concern

About 60 percent of the Sonoran Desert has been altered by agriculture, grazing, and the expansion of urban areas, specifically Phoenix and Tucson. Excessive groundwater pumping for irrigating crops and to support human developments harms the habitat, both above and below ground. Areas along rivers -- particularly the Salt, Gila, and Verde rivers -- are fragmented by water-diversion projects and dams. Introduced species such as the tamarisk tree and buffelgrass are taking over native plant areas. Additional threats include activity by off-road vehicles, road-building (which also leads to fragmentation), and the collection of reptiles, cacti, and ironwood for trade.

For more information on this ecoregion, go to the World Wildlife Fund Scientific Report.