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Desert tortoises may be two separate species


MOJAVE DESERT • The desert tortoise may consist of two different species which are separated by the Colorado River, according to a scientific paper published Tuesday.

According to the paper published in the open access journal ZooKeys, significant genetic differences exist between tortoises that typically live northwest of the Colorado River and those that live southeast of the Colorado River. The tortoises that live in the California Mojave Desert are referred to as Mojave desert tortoises, while those that live in the Sonoran Desert in Arizona and Mexico are referred to as Sonoran desert tortoises.

Along with the genetic differences between the tortoises, there are also some physical and behavioral differences, said Mickey Quillman, chief of resources for the Barstow Bureau of Land Management office. Sonoran tortoises normally have taller shells, often live in rockier climates and have different reproductive patterns. Mojave tortoises sometimes lay more than one clutch of eggs a year while Sonoran tortoises usually only lay one clutch of eggs each year, said Quillman.

According to the study, the designation of a new species would result in the loss of 70 percent of the home range for the Mojave tortoise, because much of the current desert tortoise habitat is in Arizona and Mexico.

Quillman said if a new species was designated, the BLM’s plans to conserve the species would not change.

“Overall, the conservation efforts will have to remain the same,” said Quillman. “We have to remain judicious in protecting our desert tortoise population.”

Quillman said that if a new species was designated, the BLM would have to be careful not to translocate tortoises too far away from where they were originally found — moving tortoises less than 20 miles away compared to 50 miles away. He said the BLM is already being careful to keep tortoises close to the same area.

“We want to keep the same genetic population close to where it was found,” said Quillman.
Ileene Anderson — biologist for wildlife conservationist group Center for Biological Diversity — said the potential designation of two separate species of tortoises means that there should be more federal protection designated for both types.

“This study has important conservation implications for tortoises on both sides of the Colorado River,” said Anderson. “Because tortoises in California and Arizona are now confirmed to be separate species, protecting them on only one side of the river is clearly not enough.”

For more information on the tortoise study, visit

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