Arizona has two species of desert tortoise, the Sonoran Desert Tortoise, Gopherus morafkai and
the Mojave Desert Tortoise, Gopherus agassizii. Although similar in many ways, the two species differ geographically (their ranges are split by the Colorado River), and also by habitat, behavior, and genetics.
Photo by George Andrejko.
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Desert tortoise handling guidelines
The desert tortoise is an herbivorous and completely terrestrial turtle with a brown, high-domed shell and stout, elephantine legs. One of four members of the Testudinidae family in North America, the desert tortoise inhabits the desert ecosystems of the southwestern United States and northern Mexico.
The desert tortoise has many remarkable behaviors and traits that make it well-suited for life in the desert. Because the desert tortoise is ectothermic, it controls its body temperature by using a burrow. The burrow shelters the tortoise from the extreme heat or cold of the desert. It provides a constant climate that keeps the tortoise cool when the weather is hot, and shelters it from freezing temperatures during hibernation in the winter.
A desert tortoise may spend up to 95 percent of its life in burrows, only emerging to feed, bask, and breed when the weather allows, mostly during the monsoon season. In fact, it will get most of its food for the entire year during this period. It eats the leaves, stems, and flowers of many species of desert plants. Surprisingly, it is able to digest many species of plants that are indigestible to other animals with help from bacteria that reside in its digestive system.
A desert tortoise emerges from its burrow
Another adaption that makes the desert tortoise suited for desert-life is the ability to acquire almost all of its water from the plants that it eats. Because desert tortoise live in an arid climate where most of the rainfall occurs during the monsoons, it is able to store water in its bladder for use during drought. It can go over a year without drinking. One of its defense mechanisms when handled or disturbed is to release the contents of its bladder, which can deplete its water supply and can cause harm or death during a drought. For this reason, if you find a desert tortoise, do not pick it up.
As an adult, it has very few natural predators because of its thick, scaly skin and hard shell. In the Sonoran desert, mountain lions are the main predators of adult desert tortoises. Worse than predation, however, is the pressure the species is under from development, the construction of roads, and other human activities that degrade its habitat and cause mortality.
Adult desert tortoises are generally solitary animals. Individuals of the same sex will fight each other when they cross paths in the wild. Males, who are especially combative, have enlarged gular scutes, which are two large scales that grow outward from the front of the plastron, just under the head and neck of the tortoise. They use the gular scutes to ram and flip other males. A flipped male will usually right itself after the defeat, but if it cannot, it will die.
The male desert tortoise on the left was flipped over during a battle with the other male.
This type of defeat can determine territorial and mating disputes.
At 12-20 years of age, tortoises start to breed. They will breed during the summer after the onset of the monsoon season, typically from late June through July. Females will lay on average 3-12 eggs in a nest near or inside the entrance of a burrow. Sonoran desert tortoises only lay one clutch of eggs per year, whereas tortoises in the Mojave desert usually lay two clutches of eggs per year. Hatchlings emerge towards the end of the rainy season in September or October. A hatchling desert tortoise is small (2-3 inches in length) and soft-shelled. It has many predators, including raptors, ravens, coyotes, foxes, and bobcats.
Hatchling desert tortoise
The Mojave desert tortoise inhabits the area north and west of the Colorado River and is listed as threatened under the Endangered Species Act. The Sonoran desert tortoise is found south and east of the Colorado River, in the central and western parts of Arizona and into northwestern Mexico.
Each species favors different habitats because they have evolved separately across a large range. The Mojave desert tortoise inhabits Mojave Desertscrub, where it is generally found in the flat inter-montane basins. The Sonoran desert tortoise, found in Sonoran Desertscrub and Semidesert Grassland, prefers rocky slopes and bajadas.
Primary threats to survival of the desert tortoise are related to loss and degradation of the species’ habitat, through drought, wildfire, habitat destruction and fragmentation, and invasion of exotic plant and wildlife species. Other impacts to the species include removal of individuals from the wild, vandalism, mortality from vehicles, irresponsible off-highway vehicle (OHV) use, release of captive tortoises into the wild, and disease.
The desert tortoise, and other North American tortoise species, can become infected with a disease called Upper Respiratory Tract Disease (URTD), caused by a bacterium. URTD causes cold-like symptoms in tortoises. A tortoise can become infected when it comes into contact with a sick tortoise. Once a tortoise is infected with this pathogen it will be a carrier for life. The symptoms may go away, but can reemerge if the tortoise is under stress. URTD has caused catastrophic die-offs in the Mojave tortoise population, resulting in part to their federal listing as threatened under the Endangered Species Act. Although URTD has been found in the Sonoran desert, it is not known what impact, if any, the disease may have on the Sonoran desert tortoise. It may be a naturally occurring pathogen in these populations, but there is some evidence that URTD was introduced into the Mojave desert tortoise through the release of sick captive tortoises into the wild.
The Arizona Game and Fish Department is coordinating with local, state and federal agencies and private landowners to conserve and manage the desert tortoise in Arizona. In 1985, these groups formed the Arizona Interagency Desert Tortoise Team (AIDTT), which is responsible for coordinating research and management of the desert tortoise in Arizona.
Department's current research on desert tortoises
- Desert tortoise microhabitat use
- Illegal collection of desert tortoises
- Desert tortoise landscape-level habitat modeling
- Desert tortoise occupancy modeling
The Mojave desert tortoise was listed as threatened by the United States Fish and Wildlife Service (USFWS) in 1990. Arizona law has prohibited removal of desert tortoises from the wild since 1988. The Sonoran desert tortoise is listed as a Candidate species by the USFWS. Lawfully obtained desert tortoises may be privately adopted, but desert tortoise adoption in Arizona is subject to specific rules.
Per Commission Rule R12-4-407.1, desert tortoises legally held prior to April 28, 1989, may be possessed, transported, and propagated without a special license. Possession limit is one desert tortoise per person. Progeny of lawfully held desert tortoises may, for 24 months from date of hatching, be held in captivity in excess of the stated limit. Before or upon reaching 24 months of age, such progeny must be disposed of by gift to another person or as directed by the Department. An individual who receives a desert tortoise that is given away under this rule is also exempt from the special license requirements. An individual shall not export a desert tortoise from this state unless authorized in writing by the Department.
How You Can Help
Keep wild tortoises wild
Removing a tortoise from the wild can severely affect local populations because they reproduce slowly in natural conditions. It is illegal to remove a tortoise from the wild. You can lawfully adopt a desert tortoise that has been displaced due to construction or raised in captivity through state-sanctioned adoption facilities.
Keep captive tortoises captive
Captive tortoises released into the wild can severely jeopardize local wild populations through the introduction of URTD, which has been implicated in large tortoise die-offs in California. Also, captive tortoises released into the wild can displace or disrupt areas already occupied by tortoises. It is illegal to release captive tortoises into the wild. If you have a captive tortoise that you can no longer care for, contact your regional tortoise adoption facility.
Do not breed captive tortoises
The Arizona Game and Fish Department receives hundreds of unwanted captive-born tortoises each year. The Department spends a considerable amount of effort and resources finding homes for tortoises. This takes away time for conservation efforts of wild tortoises. Tortoises hatched in captivity cannot be released into the wild. Once in captivity, tortoises must be cared for by humans for the rest of their life.
Participate in the Sponsor-a-Turtle program
The Arizona Game and Fish Department Turtles Project utilizes technical equipment such as radio-telemetry tags, GPS units, and disease sampling gear to monitor tortoise populations statewide. By donating to the Turtles Project, you will help project biologists purchase this gear so that they may continue to plan and implement conservation and management. Click here to download the Sponsor-a-Turtle program brochure.
Practice responsible OHV use
Using off-highway vehicles (OHVs) in unauthorized areas can result in loss and degradation of tortoise habitat. Please stay on roads and trails and do not trample vegetation.
Watch and enjoy, but avoid contact
If you observe a desert tortoise in the wild, it is best to let it continue on its way. Observing tortoises in the wild is an exciting experience, but human handling can be deadly for wild tortoises. Tortoises store water in their bladder during dry times of the year, and if disturbed, they will release the contents of their bladder and likely die from dehydration. The one exception to this rule is if a tortoise is in harm’s way trying to cross a road. If it is safe to do so, gently lift the tortoise high enough so its feet are just above the ground and transport the tortoise across the road in the direction it was heading. To find out what to do if you find a desert tortoise in your neighborhood, click here.