Joshua Tree National Park

Joshua Tree National Park

Species Spotlight: Desert Tortoise

October 7, 2010, 10:12 am

As you amble through the Joshua Tree forest or any low-lying area of the Mojave, the rustling of leaves or snapping of twigs might get your attention. And if you look carefully, you may be lucky enough to see your unwitting companion whose well-camouflaged cover has been blown by its determined forward motion. This scowling Desert tortoise (Gopherus agassizii) is small enough to fit in a boot box, but its size belies its age. It could be more than 100 years old and is likely in the neighborhood where it’s lived all its life.

Description: Adults range in size from 9 to 15 inches in length and sport a clay-brown shell with blackish-blue growth ridges arranged in boxy rings at the top and rounded fringe along the bottom of the shell.

Park habitat: Desert Tortoises live in low-lying and forested areas from extreme southwestern Utah and southern Nevada south through southeastern California, western and southern Arizona, and most of Sonora to northern Sinaloa, Mexico. Since they’re cold blooded and the desert climate is so erratic, they spend almost 95 percent of their time underground where the temperature is more constant. During its lifetime of 50 to 100 years, a wild tortoise rarely moves more than a couple of miles from its birthplace and is intimately familiar with the resources within its territory.

Diet: Desert Tortoises much on cacti, grasses and weeds. They store water for long-term use in their bladder—picking up a tortoise will cause them to void their storage so touching them is only recommended in cases where the animal is in danger, say, crossing a busy road.

Threats: The Desert Tortoise has been trudging along for about 15 million years but now finds itself on the threatened species list. Among factors depressing its population are ravens, which thrive in the tortoise’s habitat and feed on hatchlings. Human development not only encroaches on critical habitat, but also attracts more ravens as they flourish in developed areas. The latest big threat to the animal is Upper Respiratory Tract Disease (URTD), caused by invasive turtle species recently introduced to their environments.

Interesting fact: After mating, a female may wait for up to eight years before laying fertile eggs—fertilization and egg laying are not determined by mating time, but rather by when the female senses that water and food are readily available.