Wildlife Discovery: The Desert Tortoise

The desert tortoise (Gopherus agassizii) is a species of tortoise native to the Mojave desert and Sonoran desert of the southwestern United States and northwestern Mexico. They can be located in the western Arizona, southeastern California, south Nevada, and the southwestern region of Utah. The species name agassizii is in honor of Swiss-American zoologist Jean Louis Rodolphe Agassiz. This tortoise may attain a length of 10 to 14 inches (25 to 36 cm), with males being slightly larger than females. Male tortoise’s plastron (lower shell) is concave compared to female tortoises. Males have larger tails than females do. Their shells are high-domed, and greenish-tan to dark brown in color. Desert tortoises can grow from 4–6”(10–15 cm) in height and weigh 8–15 lb (4–7 kg) when fully grown. The front limbs have sharp, claw-like scales and are flattened for digging. Back legs are skinnier and very long. The tortoise is able to live where ground temperature may exceed 140 degrees Fahrenheit (60 degrees Celsius) because of its ability to dig underground burrows and escape the heat. At least 95% of its life is spent in burrows. There, it is also protected from freezing winter weather while dormant, from November through February or March. With its burrow, this tortoise creates a subterranean environment that can be beneficial to other reptiles, mammals, birds and invertebrates. Scientists have divided the desert tortoise into two types: the Mojave and Sonoran Desert tortoises, with a possible third type in the Black Mountains of northwestern Arizona. They live in a different type of habitat, from sandy flats to rocky foothills. They have a strong proclivity in the Mojave desert for alluvial fans, washes and canyons where more suitable soils for den construction might be found. They range from near sea level to around 3,500 feet (1,100 m) in elevation. Tortoises show very strong site fidelity, and have well established home ranges where they know where their food, water and mineral resources are, and who their neighbors are. They also live to be 80–100 years old, although predation, disease and habitat loss have created significant challenges for the population at large. he desert tortoise is eats grass. Grasses form the bulk of its diet, but it also eats herbs, annual wildflowers, and new growth of cacti, as well as their fruit and flowers. Rocks and soil are also ingested, perhaps as a means of maintaining intestinal digestive bacteria as a source of supplementary calcium or other minerals. As with birds, stones may also function as gastroliths, enabling more efficient digestion of plant material in the stomach. Much of the tortoise’s water intake comes from moisture in the grasses and wildflowers they consume in the spring. A large urinary bladder can store over forty percent of the tortoise’s body weight in water, urea, uric acid and nitrogenous wastes. One defense mechanism the tortoise has when it is handled or molested is to empty its bladder. This can leave the tortoise in a very vulnerable condition in dry areas, and they should never be alarmed, handled or picked up in the wild unless they are in imminent danger (like in a road). Tortoises mate in the spring and in the fall. The female will lay a clutch of 3 - 5 hard-shelled-eggs (which are the size and shape of ping-pong balls), usually in June or July, and they hatch in August or September. Wild female tortoises can produce 2 or possibly 3 young ones a year. Their eggs incubate from 90 to 135 days. Tortoises reach sexual maturity at the age of 15. With a high mortality rate, their average life expectancy is between 50 to 80 years if they survive past 20 years of age. Ends