Desert Tortoise
© Dan Fillipi

Desert Tortoise

Basic Facts

No other tortoise in North America shares the extreme conditions faced by the Gopherus agassizzi, or Agassiz’s desert tortoise. 

Agassiz’s desert tortoises have a high domed shell, which is usually brown in adults and dark tan in younger adults. Their powerful limbs are equipped with claws to dig underground burrows, which provide refuge from extreme heat and cold, and their front limbs are protected with a covering of thick scales that help deter would-be predators. 

Diet

The diet of this desert tortoise somewhat depends on its location within the species’ range as well as past rainfall events. An Agassiz’s desert tortoise may eat a variety of vegetation, including annual wildflowers and grasses, perennial new growth of selected shrubs and grasses, and cacti and their flowers. 

Population

As recently as 2011, this denizen of the Mojave Desert, was believed to be the same species of tortoise found in the Sonoran Desert, now identified as Gopherus morafkai. The discovery of their distinction greatly diminished the perceived abundance of Agassiz’s desert tortoise population.  

In some areas, the number of Agassiz’s desert tortoises has decreased by 90 percent due primarily to human activity. These declines appear to have been most severe and widespread in the western Mojave Desert. Recent studies indicate Agassiz’s desert tortoise populations are often highly-fragmented throughout much of their range and occur in patchy distributions; their adult populations commonly numbering in the single digits per square mile. 

Habitat and Range

Agassiz’s desert tortoises occur throughout the Mojave and Colorado Deserts of California, as well as in Nevada, Utah and portions of Arizona. 

Most desert tortoises live in habitats typical of valley bottoms that include plant communities like creosote bush scrub, often preferring streambanks in desert washes where the soil is more suitable for construction of their burrows. The species has, however, also been recorded in rocky and steeper slope areas, as well as in saltbush scrub, Joshua tree woodland and blackbrush scrub.

Behavior

Agassiz’s desert tortoises can live where ground temperatures may exceed 140 degrees Fahrenheit. This is due to their ability to dig underground burrows three to six feet deep to escape the heat of summer and the cold of winter. They are one of the most elusive inhabitants of the desert, spending up to 98 percent of their time underground. 

Agassiz’s desert tortoises forage throughout the year, with higher activity levels common in the spring and again in the fall. During the hottest, driest periods of the year, these tortoises remain largely inactive to conserve the water already stored in their bodies. From November through February, Agassiz’s desert tortoises enter a torpid state, similar to hibernation, where they remain in their underground burrows to escape the cold winter temperatures.

Much of these tortoises’ water intake comes from moisture in the grasses and wildflowers they consume. To get the most out of the rain that falls so infrequently in their habitat, desert tortoises dig basins in the soil to catch rainwater. They remember where these basins are and often return to them when rain appears imminent.

Reproduction

Females in general do not successfully reproduce until they are 13 to 20 years old. When hatchlings emerge from eggs they are approximately 2 inches long.  It is estimated that only about 2 percent of hatchlings survive to become adults.

Mating Season: Late summer to early fall

Gestation: 10-12 months

Clutch size: 4-6 eggs

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