'Creep' Of Baby Tortoises Survives First Winter Sleep At Edwards AFB

PALM DESERT, CA—The head-start Mojave Desert tortoise project at the Living Desert Zoo and Gardens, in a combined effort with other agencies across California, may dramatically increase the species' survival, according to a recent news release.

This spring, 70 young Mojave desert tortoises, born in captivity and raised in the Palm Desert Zoo's Head Start program, survived and thrived through their first winter.

The “creep” of juvenile tortoises (as a group of the reptiles is called) was released from the zoo in September and spent six months in a natural habitat at Edwards Air Force Base in Southern California. There, they burrowed homes and entered brumation—a deep, hibernation-like sleep through the winter, waking "bask in their burrows" under the April sun, a spokesperson for the Living Desert Zoo and Gardens said. This gives scientists hope that the breed will one day be removed from the critical endangered species list.

"Within 24 hours after their release last fall, the juveniles got their bearings, explored old burrows, and dug new ones where they would spend the winter," according to a recent news release. Both the successful exploration of their new digs and emergence after brumation are wins for the head-start program that raises them both indoors and outdoors.

Now that they're out and about, scientists are conducting health assessments and replacing the tortoises' radio transmitters so they can continue monitoring the "creep" and better understand the juvenile age class.

The program's experts track egg-carrying desert tortoises, monitor the adult females as they lay eggs in human care, and rear the hatchlings for one to two years, both indoors and outdoors.

James Danoff-Burg, Ph.D., director of Conservation at the Living Desert Zoo and Gardens, says that indoor rearing at The Living Desert "enables the tortoises to grow to three to five times the size they would at this stage in their native habitat, making them less vulnerable to predation."

"Our head-starting program is essential for maximizing the success of young tortoises as we release them into the wild," Danoff said.

"Mortality of juvenile desert tortoises is dramatic, often approaching 100% in areas where ravens are overpopulated due to humans providing them food via their open trash containers."

Within six months, the benefits of the head-start are clear, according to Danoff.

"We can get them to the approximate size of a two-and-a-half-year-old tortoise! Larger tortoises are much more resistant to raven and coyote predation than smaller ones, and our head-starting program ensures that not only normal juvenile mortality rates in the wild are reduced, but so is predation. Head-starting makes reintroductions of desert tortoises more successful," he said.

The tortoises are still monitored at their new homes, and intervention is necessary during times of environmental crisis, such as when an influx of predatory ants and fly larvae attacked the hatchlings. During this time, hatchlings were retrieved and brought to the Living Desert Zoo and Gardens for care.

"It is believed that Hurricane Hilary's historic arrival created extra moist conditions, leading to a breeding ground for these insects," the release said.

Sadly, not all of the hatchlings made it.

"The rescued hatchlings were reared indoors at The Living Desert for the first six months of their lives and, in April of 2024, will be transferred to the outdoor head-start where they will spend the next six months.

At approximately one year of age, the tortoises will be reintroduced into their permanent native habitat.

Experts say that once common throughout the Mojave and Sonoran deserts of California, Nevada, and Arizona, desert tortoise populations have declined by an estimated 90% in the last 20 years.

California's Mojave desert tortoise, federally protected in the United States since 1989, is categorized as Critically Endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species and faces threats including habitat loss and fragmentation, disease, human-subsidized predators, and climate change.

The U.S. Fish and Wildlife Service's evaluation of population trends from 2018 indicates the species is on a path to extinction under current conditions. However, with continued successful efforts to address the threats they face, there is hope the tortoise's limited numbers can be reversed. Learn more at www.thelivingdesert.org and www.sdwza.org.

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