Are Mojave desert tortoises actually native to Southern Utah?

ST. GEORGE —  The Mojave desert tortoise is uniquely adapted to survive in the temperature extremes found in Washington County’s red desert, but some residents question: are they native to Southern Utah?

A wild desert tortoise pokes its head out of a burrow, date and location not specified | Photo courtesy of Jason Jones / Utah Division of Wildlife Resources, St. George News

The Mojave desert tortoise is federally protected, prompting habitat conservation, laws preventing the handling and ownership of wild tortoises and other protective measures.

While some say tortoises are not native to the area, Mike Schijf, a biologist with the Red Cliffs Desert Reserve, said there is “not really evidence” to support the claim that the reptiles have not inhabited the region prehistorically.

There have been multiple studies that have evaluated the genetic composition of Mojave desert tortoises from throughout their habitat, Schijf said, adding that he corresponded with genetic researchers from the University of Nevada in Reno on the subject.

The results of their studies reportedly found that there are no significant genetic differences between Upper Virgin River and Beaver Dam Slope tortoises, Schijf said. The Upper Virgin River recovery area includes tortoises in Red Cliffs Deserve Reserve, and Beaver Dam Slope includes a population near Highway 91 in the southwest corner of Washington County.

The sample of tortoises from the Beaver Dam Slope region included in the researcher’s final results was small, but Schijf said that it appears most individuals located east of Lake Mead belong to the same genetic cluster.

This file photo shows a tortoise that was found and rehabilitated by Red Cliffs Desert Reserve biologists after sustaining serious injuries and later released, location not specified, March 28, 2011 | Photo courtesy of Red Cliffs Desert Reserve, St. George News

Schijf said that the reserve “has no doubt that some tortoises were brought into this area from elsewhere” but added that there is also evidence of a native population.

Some of the reptiles located in the St. George area may have ancestors that were potentially brought in from other parts of the tortoises’ range, “as evidenced by admixture of these individuals with individuals further west” in the Central Mojave Desert.

But Schijf said if this was the case, it appears these reptiles bred with native tortoises already present in the region, which would lead to the current genetic mix seen in the area.

“The nuance in this explanation might not be as satisfying as some would like,” he said. “However, I feel confident that this is an accurate interpretation of the genetic data that has been collected.”

Ann McLuckie, a wildlife biologist with the Utah Division of Wildlife Resources, said that the idea that tortoises are not native to Washington County has been a local “urban legend for quite some time.”

“But basically, yes, we do know that tortoises are native in this area,” she said.

Referencing a 2018 study, which can be found on Nature Portfolio, McLuckie reiterated that the Upper Virgin River tortoises are genetically related to each other, are closely related to their nearest neighbors on the Beaver Dam Slope and are more distantly related to those on the opposite side of the range in California.

This is what would be expected of a native population, she added.

This file photo shows a Mojave desert tortoise in Snow Canyon State Park, Aug. 19, 2022 | Photo courtesy of Bret Berger, St. George News

Additionally, Upper Virgin River tortoises are “uniquely adapted to living on the northeastern edge of their range,” as these populations experience temperature extremes, McLuckie said.

Washington County is at the merging of three geographic provinces: the Colorado Plateau, the Great Basin Desert and the Mojave Desert. Tortoises are found at the edge of the Mojave Desert, but this isn’t the case where the desert ends to the north, McLuckie said.

Other unique plants and animals, such as the Gila monster, live throughout the Mojave Desert, many of which are also present in Southern Utah, so it would be “kind of odd” if tortoises weren’t, said Ammon Teare, outreach coordinator for Red Cliffs Desert Reserve.

The Mojave desert tortoises are found across a continuous range from California to Arizona, McLuckie said, adding that there isn’t a physical barrier that would have prevented tortoises from being present in Southern Utah.

Desert tortoise conservation

The Mojave Desert tortoise is listed as threatened under the Endangered Species Act due to ongoing threats, such as lost, degraded or fragmented habitat, wildfires, disease and road mortality, according to the United States Fish and Wildlife Service’s website.

This file photo shows “Bonnie,” a tortoise that lives at the Red Cliffs Desert Reserve’s office, St. George, Utah, Sept. 6, 2022 | Photo by Alysha Lundgren, St. George News

To protect the Mojave desert tortoise and other sensitive local species, 62,000 acres of land were set aside in 1996 to create the Red Cliffs Desert Reserve, which is still expanding with the recent addition of Zone 6, located west of the Bloomington area and south of Santa Clara.

The reptiles are a “really big part of the desert food web,” Teare said. When young, tortoises are vulnerable and serve as a nutrition source for predators like coyotes, ravens and snakes.

“If they were to all just to go extinct, at least in this area, who knows what effect that would have on the higher-order predators that rely on tortoises for their sustenance,” he said.

Additionally, tortoises dig burrows that are used by other animals. For instance, burrowing owls, which are considered a sensitive species, don’t typically build their own and utilize those created by tortoises for shade, shelter and to hide from predators, Schijf said.

To learn more about the Red Cliffs Desert Reserve, Mojave desert tortoise and other local species, visit the reserve’s website.

Copyright St. George News, LLC, 2022, all rights reserved.

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