The desert tortoise is an admirable reptile, living in extreme conditions that other species of his kind can't handle. He's also unique because he can dig underground to seek refuge from high heat and freezing temperatures. The desert tortoise population has declined 90 percent during the past three decades.
Built for Work, Not Beauty
The desert tortoise is a thick skinned fellow, with a scaly head. His flat, heavy front legs and very long nails help him dig his burrows. He's not a showy tortoise; his high shell ranges from dull yellow to dull brown and can be as short as 5 inches or as long as 15 inches. His weight varies widely, ranging from 24 pounds to more than 50 pounds. Males are generally larger than females.
An herbivore, the desert tortoise will eat what's available in his home range. As a rule, he'll dine on freshly fallen leaves and low-growing plants, including tree fruit and flowers, succulents, grasses, bark, stems, shrubs and woody vines. He takes advantage of the rainy season by drinking large amounts of water when it's available. This guy has learned to dig pits in the soil to catch rainwater and will wait near a pit if he thinks rain is on the way. An adult desert tortoise can live a year without access to water.
The southwestern United States and northwestern Mexico comprise the desert tortoise's home range, specifically, the Sonoran and Mojave deserts. His preferred habitat is rocky hillsides, desert washes, semi-arid grasslands and sandy canyon bottoms at elevations below 3,500 feet. He's able to live where ground temperatures reach 140 degrees Fahrenheit -- or even higher -- because he can burrow underground to escape the heat or to protect himself against freezing in his dormant stage. In fact, he spends at least 95 percent of his time in his burrows, which are 3 to 6 feet deep.
Filling Their Time
The desert tortoise is active spring through fall, spending November through February in his underground burrow. When the weather's cool enough, he'll spend his daylight hours foraging for food; when it's hot, he'll take care of dinner business during twilight. His burrow system can be quite extensive, sometimes extending 30 feet. Located under rocks or shrubs or in washes, he may use the same burrow over and over and often will share it with other tortoises. He's not particularly social and prefers the company of the opposite gender when spending time with another tortoise.
Mating time is any time the desert tortoise is above ground, but he's more active in late summer and early fall. Females lay eggs May through July, with the clutch size averaging three to five eggs and hatching after three or four months. A female may lay a second clutch of eggs later in the summer, which will hatch the next spring. It takes a long time for a female to reach sexual maturity. She can't breed until she's about 15 years old -- or even older. As well, the survival rate for hatchlings is very low; only about 2 to 3 percent of hatchlings make it to adulthood. Once a tortoise makes it to age 20, he's got a great chance of living at least another 30 years or more. The life expectancy of a desert tortoise that celebrates his 20th birthday jumps to 50 to 80 years.
Threats to the Tortoise
Despite his tough shell, the desert tortoise has predators. The mountain lion can crush his shell and other animals, such as coyote, badgers, bobcats, gray foxes, ravens and golden eagles, prey on eggs, hatchlings and juveniles. Humans haven't been helpful either, contributing to his habitat loss, as well as collecting the desert tortoise for the pet and food industry. California has strict laws against collecting or harming its state reptile.
- Defenders of Wildlife: Basic Facts About Desert Tortoises
- DesertUSA.com: Desert Tortoise
- Center for Biological Diversity: Desert Tortoise
- A-Z Animals: Desert Tortoise
- Animal Diversity Web: Gopherus agassizii (Californian) Desert Tortoise
- Endangered Species International: Threats to the Desert Tortoise