Synopsis of conservation information on the desert tortoise

Prepared by Jeff Lovich, Ph.D.

Figure 1. These hatchling tortoises are equipped with small radio transmitters to monitor their movements. The tortoise on the left is essentially "xanthic." Xanthic animals lack most pigments except for those that produce yellowish coloration. Its sibling, on the right, has color more characteristic of desert tortoises in California. These tortoises are part of a study by Curtis Bjurlin of Utah State University who is conducting research on tortoise reproductive ecology at the Marine Corps Air Ground Combat Center near Twentynine Palms, California as part of his Master's degree. Photo by Kathie Meyer.

The desert tortoise has the widest latitudinal distribution of any of the North American tortoises ranging from southwestern Utah to northern Sinaloa State in Mexico, a range of 1,100 kilometers. Across this vast range the tortoise occupies a staggering diversity of plant communities from tropical deciduous thorn scrub in Mexico, across the Mojave and Sonoran Deserts, to the edge of the Great Basin Desert and the Colorado Plateau.

Despite the wide distribution of the desert tortoise, some biologists reported widespread population declines in portions of the Mojave and Sonoran Deserts in the 1980's. Although no one knows how many tortoises there were prior to the arrival of humans in the southwest, they were assumed to be plentiful by some, but not all, biologists. Recent archaeological evidence shows that they were an important source of food for some Native American tribes, while other tribes considered them to be sacred. However, widespread alteration of the desert by overgrazing, off-highway-vehicle use, military training activities and urban development placed pressures on tortoise populations far beyond those imposed by subsistence utilization by Native Americans. As a result, tortoise populations in the western Mojave Desert and southwestern Utah have experienced significant declines.

In recognition of the problem, the United States Fish and Wildlife Service listed the tortoise population on the Beaver Dam Slope in Utah as "Threatened" in 1980 under the authority of the U.S. Endangered Species Act. In April of 1990, all populations north and west of the Colorado River in the United States were listed as Threatened. Threatened species are those that are likely to become "Endangered" if actions are not taken to protect them, and Endangered species are considered likely to become "Extinct" if they are not protected. The desert tortoise is the state Reptile of California and is also protected by the state as a Threatened species.

Turtles, including tortoises, are characterized by a set of life history traits that make them slow to adapt to rapid changes in mortality and habitat alteration. Long life spans (in excess of 50 years), late maturity, and widely variable nest success are traits that allowed turtles to outlive the dinosaurs, but they are poorly adapted for life in the rapidly changing modern world. Increased mortality of young and adults can seriously tip the delicate balance required for turtles to survive. Increasing populations of native predators, such as ravens and coyotes prey on hatchling and young tortoises, while habitat destruction, highway mortality, and removal of adults for pets have all contributed to the decline of desert tortoises.

A more recent threat may be disease. Upper Respiratory Tract Disease (URTD) and shell diseases have also been implicated in the decline of some populations. URTD is caused by a mycoplasm, a simple organism like bacteria. The disease is characterized by discharges from the eyes and nose, wheezing and, in extreme cases, emaciation and death of the tortoise. People that release sick captive tortoises back into the wild may actually facilitate the spread of these diseases.

Numerous research projects have been, or are being, conducted that will assist state and federal land managers who are trying to encourage the protection and recovery of desert tortoise populations. Projects include investigations of reproductive ecology, surveys of population density, feeding ecology, competitive interactions from livestock for food plants, transmission of disease, and predator ecology.

Desert tortoises are protected by law and should never be removed from the wild. Captive tortoises can be legally adopted through the California Turtle and Tortoise Club or the San Diego Turtle and Tortoise Society.