Tortoise, desert

Gopherus agassizii

phylum: Chordata

class: Reptilia

order: Testudines

family: Testudinidae

status: Vulnerable, IUCN Threatened, ESA

range: Mexico, USA (Arizona, California, Nevada, Utah)

Description and biology

The desert tortoise has an oblong, domed, brown carapace (pronounced KAR-a-pace), or top shell, that measures between 7.5 and 15 inches (19 and 38 centimeters) long. Its head is narrow and scaly, and its tail is short. The tortoise has armored front legs, which it uses for digging, and large, powerful rear legs. Males of the species are much larger than females.

The desert tortoise's diet consists primarily of plants that contain a high level of water. In its desert habitat, the tortoise drinks from depressions that it often scrapes out itself to catch rainwater. The desert tortoise is active mainly in the spring. In summer, it is active when rains provide moisture and food.

During courtship, males often hiss and butt females. After mating, a female desert tortoise lays two to seven hard- shelled eggs in early summer. She covers the eggs with only a thin layer of sand, allowing the sun's heat to incubate (develop)

them. The eggs hatch after three to four months. The young tortoises have soft shells that begin to harden after about five years.

Desert tortoises do not reach sexual maturity until they are 15 to 20 years of age, but can live as long as 100 years.

Habitat and current distribution

The desert tortoise is found in the Mojave and Sonoran Deserts in the southwestern United States and Mexico. Although this range is wide, the tortoise population is scattered and isolated throughout it. Biologists (people who study living organisms) believe the total desert tortoise population to be only around 100,000.

To the north and west of the Grand Canyon, desert tortoises inhabit valleys and tracts where creosote bushes (evergreen resinous desert shrub) and yucca plants grow. To the south and east of the Grand Canyon, isolated populations of tortoises inhabit steep, rocky slopes of mountain ranges where paloverde trees (small bushy trees with sharp spines) and cacti grow. Biologists are unsure of the tortoise's habitat in Mexico.

History and conservation measures

The desert tortoise was once found at lower elevations throughout the Mojave and Sonoran Deserts. Recently, however, its numbers have declined in most areas. Many factors have led to this decline. These tortoises have been illegally hunted for food or for sale as pets. Their habitat has been lost or destroyed as farms and cities have been built, roads have been constructed, mining explorations have been undertaken, and toxic and radioactive waste dumps have been established. Livestock from nearby ranches and farms have trampled their food sources, and off-road vehicles have further destroyed what remains of the animal's fragile habitat.

The desert tortoise is California's official state reptile. At present, there are two reserves in California providing protected habitats for the tortoise: the Desert Tortoise Research Natural Area and the Chuckwalla Bench Area of Critical Environmental Concern. A small reserve in Utah provides a protected habitat for a few desert tortoises.

A federal plan to save the desert tortoise was developed in 1995. However, due to a lack of money and arguments between conservationists (people protecting the natural world) and people who use the desert for recreational purposes, this plan has yet to be set in motion.