Desert Tortoise
gopherus agassizii
The desert tortoise, Gopherus agassizii, is a vegetarian and can even eat some species of cacti. It is often found in association with creosote bush. They can live to 50 years old or more, and grow to over a foot in length. The growth lines on the shields (bumps) on the carapace (back shell) can help experts determine the tortoise's age. They hibernate in winter in ground burrows.
Tortoises are land-dwelling, while turtles are water-dependent. The desert tortoise can go for long periods without drinking water, but it does need to drink occasionally. It stores water in its bladder, and if handled, often expels that water. Thus, unless the tortoise can replace the water quickly, handling one can be a death sentence to it and should be avoided. The tortoise in the picture is drinking rainwater from a puddle.
Because they live in isolated populations, are somewhat slow breeders (once per year, max. 9 eggs, of which few survive), and reach sexual maturity around 8 - 15 years old, desert tortoise populations can easily become threatened or extinct.

Tortoises can be tracked and their movements recorded by attaching a transponder and antenna to each tortoise's shell with epoxy. Information gained through this research allows scientists to estimate populations, deduce which habitats are the best, and create plans for protection of this federally-listed threatened species.
References:

Merlin, Pinau (1999). A Field Guide to Desert Holes. Arizona-Sonora Desert Museum Press, Tucson, AZ.

Stebbins, Robert C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin Company, New York, NY.

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