DESCRIPTION: L=up to 14" (35.5cm). Overall brown to gray above (carapace), yellowish below (plastron). Males have concave plastron to fit better over the rounded carapace of the female (females have flat pastron).
NATURAL HISTORY: Herbivorous, augmenting their diet with Prickly Pear fruit when available. Crepuscular, becoming more nocturnal when temperatures are higher. Most active during monsoon summer months (July to October). The sonoran subspecies tends to be solitary. They live up to 40 years in the wild. Growth rate is depends on the quantity and quality of food eaten. Age may be estimated by counting the annual rings on the scutes (section of carapace). They become sexually mature at about 13 years of age (when carapace is about 7" [18cm] long). Males fight each other for access to females. Females can store sperm for at least two years to fertilize their eggs that they lay.

Desert Tortoises have many adaptations to their desert habitat. They avoid temperature stress by being most active in the morning and early evening during the monsoon summer months -- times when temperature (and water) stress are less. When not active, they seek shelter in burrows or rock crevices where temperatures are more favorable (and humidity is higher). To further reduce water stress, they store and conserve water. They obtain much of their water requirements from their herbivorous diet, but will drink huge quantities of water when available (e.g., after a rain). They can store water in their large urinary bladders (up to 40% of their body weight in water and urinary waste). This water in their urinary bladders can then be extracted when needed (unlike humans who cannot extract water out of their urinary bladders). This is one reason why you should not handle wild desert tortoises -- they often void the precious water out of their urinary bladder when handled. To conserve water, they excrete their nitrogenous wastes in the form uric acid which contains very little water compared to the urea we eliminate. Also, during winter and summer, they hibernate and estivate, thus reducing their water (and energy) needs even more. See adaptations for more general information on desert adaptations.

Desert Tortoises are a protected species in Arizona. If you come across an individual, please resist the urge to pick it up; it is illegal to collect, transport, sell, or export (not to mention kill) Desert Tortoises in Arizona without authorization from the Arizona Game and Fish Dept.