Arizona has two native species of 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 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 it 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
Adaption to desert life
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 and can go more than 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. The species is under increasing pressure from landscape development, the construction of roads and other human activities.
Adult desert tortoises are generally solitary animals and individuals of the same sex will fight each other when they cross paths in the wild. Males can be especially combative and have enlarged gular scutes, 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 will die if it cannot.
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.
Tortoises start breeding between 12 to 20 years old and will do so during the summer after the onset of the monsoon season, typically from late June through July. Females will lay on average three to 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 tortoise inhabits Mojave desertscrub, where it is generally found in the flat inter-montane basins. The Sonoran tortoise, found in Sonoran desertscrub and semi-desert 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 re-emerge 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
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(B)(1), a person may possess, transport or give away a desert tortoise or the progeny of desert tortoises legally held prior to April 28, 1989, or obtained through a Department authorized adoption program, without a special license. An individual who receives a desert tortoise that is given away under this rule is also exempt from the special license requirements. Possession limit is one desert tortoise per person. An individual shall not propagate captive desert tortoises or export a desert tortoise from this state unless authorized in writing by the Department.
Per Commission Order 43 possession limit is one tortoise per person per household.
Desert tortoise poster [pdf]