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NATURAL HISTORY

DESERT TORTOISE } Gopherus agassizii
FAMILY: Testudinidae

DESCRIPTION: The desert tortoise is terrestrial, with an oblong, domed shell and round, elephantine hind legs. Males may be slightly larger than females; average lengths range between six and 14.6 inches. The tortoise has flattened forelegs that are heavily scaled and specifically adapted for burrowing. Toes are not webbed, females have longer nails than males, and front and hind feet are roughly same size. Generally, the head is small and rounded in front, with reddish-tan coloring; the eyes have distinctive greenish-yellow irises.

HABITAT: The desert tortoise lives in valleys, flat areas, and dry alluvial fans and washes. In the Mojave and Colorado deserts, tortoises are generally found below 4,000 feet in Joshua tree-Mohave yucca communities, creosote bush-saltbush scrub habitats, and some ocotillo-creosote habitats. They may live in a variety of soil types, including those of sand dunes, rocky hillsides, washes, sandy soils, and desert pavements.

RANGE: Tortoises living in southern California, southern Nevada, southwestern Utah, and extreme northern Arizona comprise the Mojave population of desert tortoise. The Sonoran population is located in the lower elevations of Arizona but is not currently protected under the Endangered Species Act.

MIGRATION: The desert tortoise is nonmigratory.

BREEDING: Breeding may occur any time after March, when tortoises emerge from hibernation, until the beginning of hibernation in October, but most breeding takes place in spring.

LIFE CYCLE: Between May and July, females dig nests at or near their burrows or beneath nearby shrubs and deposit from one to 14 ping-pong-ball-sized eggs. After incubating for 70 to 120 days, the hatchlings emerge, and their internal yolk sacs continue to provide nourishment after hatching. Females do not care for their young; typically, only one to five of every 100 hatchlings reach adulthood. While adult tortoises hibernate in winter, tortoises less than two or three years old are active throughout the year. They may live to be 80 to 100.

FEEDING: Desert grasses and spring wildflowers are tortoises’ primary nutritional source. In summer, dry grass stems and cactus pads are main sources of sustenance. Tortoises may eat some nonnative plants and very rarely may eat insects and carrion. Desert tortoises obtain most water from moist spring foods; they may go many years without drinking.

THREATS: Road construction, housing developments, energy developments, and conversion of native habitats for agricultural purposes have destroyed desert tortoise habitat. Diseases, including the Upper Respiratory Tract Disease and a shell-deforming disease, have decimated populations across the Mojave Desert, while grazing and off-road vehicle use continue to degrade habitat.

POPULATION TREND:    Since the early 1970s, biologists have noted that desert tortoise populations were declining in the United States. Remaining populations continue to decline.

Photo © Robin Silver