Desert tortoise
The southwestern United States is lucky to have a wide variety of animals throughout its desert region. One special and ecologically important animal that is found here is the desert tortoise. This land-loving prehistoric critter has worked its way into the hearts of the public and has gained a lot of attention due to its declining populations resulting from encroachment on its habitat, droughts, and exposure to bacteria that cause upper respiratory tract disease.
The desert tortoise is one of four North American tortoise species that are uniquely adapted to the different habitats in which they thrive. These four tortoise species are all members of the genus Gopherus, and it can be tricky to tell them apart. We have seen all four species here at the Desert Tortoise Conservation Center (DTCC)! Following are some characteristics and life history traits of each species.
Gopher tortoise Gopherus polyphemus:
The gopher tortoise is a master burrower found in the southeastern U.S. from southern Louisiana all the way up to the southern tip of South Carolina, as well as throughout Florida (except in the range of the Everglades). The gopher tortoise is found in shrubby, prairie-like areas with sandy soil, as well as in longleaf pine/scrub oak habitat. Gopher tortoises are known for their long deep burrows, with some burrows reaching up to 40 feet (12 meters) long. These amazing burrows serve to protect gopher tortoises and over 300 other animals such as snakes, skunks, lizards, and armadillos from predators and harsh weather conditions.
Texas tortoise Gopherus berlandieri:
The smallest of the four Gopherus species, the Texas tortoise is found in southern Texas and northeast Mexico. It can be found in a variety of habitats but is mostly found in dry scrub and grassland areas. Unlike its cousin the gopher tortoise, the Texas tortoise doesn’t dig its own long burrows but instead uses a burrow dug by another animal or digs a shallow burrow under small shrubby plants. The Texas tortoise population has declined because of the pet trade in recent years, but new laws in Texas will be giving the tortoise a chance to recover.
Bolson tortoise
Bolson tortoise Gopherus flavomarginatus:
The Bolson tortoise, also called the Mexican tortoise, is the largest of the four Gopherus species and is believed to be the rarest as well. It is found in a small region in north-central Mexico and only at an altitude of 3,300 to 4,300 feet in arid, sandy desert habitat characterized by the unique flora and fauna of that region. The significant declines in the populations of this species are attributed to cattle ranching, road construction, the pet trade, and even collection by locals as food. Recently, a biosphere reserve was established for the conservation of the Bolson tortoise and its habitat.
Desert tortoise Gopherus agassizii:
The desert tortoise that we know and love right here in the Mojave Desert is naturally found in northwest Mexico, southern California, southern Nevada, southern Utah, and throughout much of Arizona. The desert tortoise’s range spans two different deserts, the Sonoran and the Mojave. Scientists have determined that there are genetic differences between the tortoises found in those two locations. Like the gopher tortoise, the desert tortoise is an excellent burrow digger, and it uses burrows to escape the extreme temperatures of the desert, which range from above 120 degrees Fahrenheit in the summer to below freezing in winter. Burrows also help to protect the desert tortoise from predation by coyotes, ravens, and even mountain lions. Desert tortoises have been known to live up to 100 years in managed care. They can lay up to two clutches of eggs in a single year if resources like food and water are abundant. Unfortunately, desert tortoises are a threatened species, and populations are declining due to upper respiratory tract disease and human encroachment on their habitat.
So how do we tell the difference between these four animals if they are all lined up in front of us?! Well, Texas tortoises and desert tortoises show one small characteristic on their carapace (top shell) that is different from the others and from each other. Texas tortoises are small and have a slightly different head structure from the others, while Bolson tortoises are big and do not show sexual dimorphism (you can’t tell males from females externally). Finally, gopher tortoises sometimes have a darker and slightly different-shaped carapace than the others. Not very definitive, is it?! That’s why we rely on genetic testing to be certain which species we have here at the DTCC!
Daniel Essary is a research associate at the San Diego Zoo’ Desert Tortoise Conservation Center. Read his previous post, Desert Tortoises: Unexpected Nests.
Thanks for a wonderfully informative blog, Daniel! Very captivating and easy to read!
It must take years of practise before you can even start to identify the different tortoises! I don’t think I’d be able to do that. Is that why the tortoises at the SDZ are numbered, so that you can recognise which is which? Mind you, when I was there 2 years ago I only ever saw number 3!
Local folks in Richmond have at least two “desert” tortoises which have bred numerous times. The local vet who cares for them has gone to great lengths to incubate the eggs in hopes of getting some of them to hatch. They have driven hundreds of miles to help rescue and raise other desert tortoises in need of aid. This couple has devoted several parts of their acreage to caring for some endangered Southwestern animals, and they are active with one of the local humane societies. Tours of their home and property have been used as a major fundraiser for animals in need. It is fun to watch the interaction between the tortoises, albeit in somewhat “slow” motion. If I remember correctly their tortoises are from Texas or New Mexico desert. They are large, not small so from your description of the difference it sounds like they are Desert rather than Texas Tortoises. I have not seen them for several years, so can’t recall in detail their individual characteristics. They are very interesting animals that have a special room in which they “hibernate” for the colder months.
Margaret,
Sounds like your friends are great tortoise rescuers, but for other people thinking about doing this, please keep in mind that desert tortoises are a threatened species so it is against the law to transport them across state lines without federal and state permits, even if they were legally obtained as pets. Also, tortoises that belong in the desert that are moved to other locations tend to show deformities in their shells over time due to the humidity – they are adapted to live in very dry environments. Conversely, tortoises that belong in humid conditions do not generally fair very well in the desert because they cannot handle the lack of humidity, and this results in deformities and dehydration, which may affect their health. Tortoises are tough critters, but sensitive in many ways so anyone who keeps them in captivity must be diligent about tending to their specific environmental requirements.
Thank you for a great article that is full of pertinent information and not ‘dumbed down’ like some public articles on tortoises. I work with torts in the western Mojave and I support outreach and education (it’s the only hope!) and hope you are able to get the message out far and wide!
I have been in Florida on a Photographic trip. I have found a very active population of Florida Tortoises. I was able to photograph many individuals. The Florida tortoises are able to move 3 to 4 times faster than the Mojave Desert Tortoises that are in my backyard. On a house size lot I have counted 6 burrows per lot that are active with many tortoises eating everyday. They are very easy to see. I question how the tortoises got on a island but they are doing quite well until someone decides to build on the lot. I would say there are at least 10 lots with active burrows. Many of the lots are up for sale but the area is quite well off and the lots would be in the $350,000 to $500,000 price range a little pricy for a private person to set up a reserve.
Hello there desert tortoise lovers,
I have not checked in for some time but wanted to see if you all had created a healthy and safe food list
yet. I have been looking for some specific plants such as Janusia gracilis (a vine) and am having trouble finding it as well as a large variety of the plants I know are safe.
Do you all have any reputable seed sites or nurseries you can recommend for Arizona? I’ll drive wherever I need to but am located in the Phoenix metro area.
I know you all had been working on creating a comprehensive plant list last year when I had written in.
Thank you for all of your hard work! I really appreciate all the information.
Liz
Desert Tortoise Team responds: We have a list but it’s not yet complete. We will send it to you directly and we’ll keep working on it!