On the Trail of the Mojave's Elusive Desert Tortoise

Defenders’ renewable energy and wildlife policy associate, Pasha Feinberg, traveled in search of the mysterious Agassiz’s desert tortoise.  

I arrived in the heart of the Mojave Desert just in time to witness it in bloom. The golden and sage landscape lay peppered with the fuchsia, yellow, and purple bursts of cactus flowers. This breathtaking show of color and life in the middle of North America’s driest desert draws countless visitors each year, but although the display was stunning, I was in search of a less conspicuous desert denizen: Agassiz’s desert tortoise.

My journey began in my office in Washington, D.C., with a call to travel west and meet with officials at the Bureau of Land Management (BLM). These agency staff are charged with approving and overseeing much of the renewable energy infrastructure built in the Southwest and I was sent to discuss solar energy projects slotted for areas in the Mojave Desert—the only place in the world where these tortoises live. We discussed strategies to appropriately site renewable energy projects while still protecting important habitat for desert tortoises.

After discussing options with the BLM to ensure a better future for the desert tortoise, it was time to actually see some. Luckily, if the tortoises proved too elusive, I had an ace up my sleeve—I’d been granted access to the National Park Service’s Ivanpah Desert Tortoise Research Facility.

The Ivanpah Desert Tortoise Research Facility was built a stone’s throw from the Mojave National Preserve in prime desert tortoise habitat, a fact confirmed as I drove towards it and spied a basking tortoise! After carefully encouraging the tortoise off the road (you don’t want to pick up and scare tortoises, which may cause them to pee and lose precious water), I headed into the facility to learn more about these charismatic critters.

Diving Headfirst into Headstarting

The desert tortoise spends the vast majority of its long life—they can live up to 80 years!—in underground burrows, hibernating in the winter and avoiding the scorching desert sun in the summer. Although its brown and gray color helps it blend seamlessly into its environment when above ground, desert tortoises weren’t always so hard to find. A variety of factors have caused their numbers to decline, including habitat loss from development and agriculture, military training, grazing, roadkill, disease, and predation.

Even with the U.S. Fish and Wildlife Service’s listing the tortoise as a threatened species under the federal Endangered Species Act, threats persist and the tortoise population continues to decline. Exacerbating existing problems are increasing desert development, poorly sited energy projects, off-road vehicle use, and high juvenile mortality.

In an effort to bolster the wild population of desert tortoises, Professor Brian Todd from University of California, Davis and Drs. Tracey Tuberville and Kurt Buhlmann from the University of Georgia’s Savannah River Ecology Laboratory set up the Ivanpah Desert Tortoise Research Facility to provide a safe space for tortoises to grow before being released into the wild.

Exterior of the outdoor enclosures at Ivanpah

Upon entering the facility’s grounds, I immediately notice the four outdoor enclosures, complete with native Mojave vegetation, sprinklers, artificial burrows (with plenty of room for tortoises to dig their own), and an overhead net to keep out ravens.

Although adult desert tortoises have few natural predators, baby tortoises are easy prey and few survive past their first year. Ravens are a leading tortoise predator and human development in the Mojave provides the birds with plenty of food, water, and perches. Even though ravens have always been in the desert, because of this development, their numbers have skyrocketed in recent years.

“Juvenile tortoises are like raviolis to ravens,” explains Mark Peaden, a PhD student at UC Davis. Mark is conducting his dissertation research at the Ivanpah Desert Tortoise Research Facility and has generously agreed to show me around.

Along with his fellow researchers, Mark works at the facility with the dual purpose of “headstarting” tortoises and exploring their ecology. It’s in these outdoor enclosures, he explains, that most of the facility’s headstarting is conducted.

Juvenile headstarted tortoise

Headstarting is the process of protecting animals during particularly vulnerable life stages to increase the likelihood of their survival, usually by rearing them in captivity. Headstarted animals are later released, supplementing the populations in the wild. Even if we could remove all threats to the desert tortoise, the combination of high juvenile mortality and long time frame until sexual maturity (15 years or more) means that once a tortoise population has declined, unassisted recovery is a slow, difficult process. For desert tortoises, headstarting can help protect hatchlings and juveniles, which are particularly prone to predation, overheating, and dehydration.

Since 2011, researchers have been bringing female desert tortoises into the facility to nest. After the females lay their eggs, they are equipped with radio transmitters and carefully returned to their desert burrows. Each year, the facility gets about 90 eggs, which are left to naturally incubate in the enclosures’ burrows. Once the eggs hatch, some hatchlings are released back into the wild with radio transmitters while others are reared in the protected pens, allowing researchers to compare and assess how well the program is working.

So far, it’s working well: The headstarted tortoises have much higher survivorship than their released siblings, and reliable water sources boost their growth. What is perhaps even more encouraging is that these early advantages seem to continue throughout their lives: when the researchers checked in on headstarted tortoises after they were released into the wild, they were still larger than their siblings who were released immediately after hatching.

This program provides a much-needed leg up from the conditions in the wild, but even the tortoises reared in the enclosures take five and a half years to grow large enough to be safe from ravens. The scientists at the research facility wanted to do better, and thus, the tortoise spa was born.

A Day at the Spa

In the outdoor pens, just like in the wild, baby tortoises find small, preexisting burrows and hunker down for the winter. However, the researchers realized that if they raised baby tortoises indoors for a few months they could create an environment where the hatchlings could feed and grow rather than hibernating.

Juvenile tortoise getting the “spa treatment” enjoys lunchtime

Their tortoise “spa” consists of six large, black tubs nestled inside the walls of the facility, each of which is directly below a set of heat lamps. A few dozen lucky hatchlings are brought inside after birth to see whether their growth can be further accelerated over the headstarted tortoises in the outdoor pens. There isn’t too much to see as the tubs have many places for a baby tortoise to hide, but Mark’s done me a favor and delayed tortoise lunchtime.

Into each tub, Mark adds a plate of leafy greens. It looks like your average salad but it is actually a carefully tailored mix to ensure that the juvenile tortoises get the right amount of nutrition without overdoing it. (Since desert tortoises rarely pee, it’s hard for them to get rid of extra nutrients!) Before I knew it, tiny heads had popped out of unseen hideaways and the juvenile tortoises plodded over to chow down.

Baby Huey, on the left, spent nine months in the tortoise spa as compared to the tortoise on the right, his sibling, who was reared in the outdoor pens (both are two years old in this picture)

The nine-month-old tortoises seem pretty small to my untrained eyes (and pretty adorable), but they’re actually the size of three- to four-year-old tortoises grown in less cushy environs. In fact, Mark takes me back outside and introduces me to Baby Huey, one of the first tortoises who received the spa treatment—a full nine months of living and growing inside. Baby Huey is just two years old and already big enough to be a tough lunch for any raven. Clearly indoor rearing is working, with reliable food, water, and warmth drastically accelerating the hatchlings’ growth.

When Did the Tortoise Cross the Road?

The researchers’ headstarting efforts have led to new discoveries about how juvenile tortoises—notoriously hard to find in the wild—are using their habitat and what causes their mortality. In conjunction with this work, the scientists at the research facility are tracking tortoise movements in the Mojave. This data sheds light on how tortoises are moving across a landscape, how they interact with roads, and how mitigation fencing (fencing constructed to keep tortoises off the road) affects their behavior, survival, and habitat.

Understanding how tortoises move across their landscape may seem academic, but it has real conservation implications: if researchers can determine when tortoises are most likely to be outside their burrows or crossing roads, resources can be more efficiently utilized to increase targeted enforcement of speed limits and road closures (in areas where off-road vehicle use is prohibited) to those times and places where tortoises are most active. Additionally, juvenile tortoises’ behaviors are relatively poorly studied, so knowing what their preferred plant species are and where they are likely to live can help inform whether a location is important habitat and needs to be protected, even if the tortoises can’t be found during surveys (especially because juveniles are so elusive).

The research being done at the Ivanpah Desert Tortoise Research Facility informs Defenders’ work to save this incredible species. Headstarting is a promising tool to be used in conjunction with habitat protection and restoration: While headstarted tortoises are helping to increase wild tortoise populations, we are also working to translate scientific findings into enforceable policies to address the ongoing threats to desert tortoises and promote the recovery of the species. Defenders works with the solar energy industry, land managers, and federal and state agencies to improve land management practices and direct renewable energy development to places where projects won’t cause significant harm to the tortoises, while requiring developers to mitigate for unavoidable impacts.

For millions of years, before the rise of the Sierra Nevada Mountains turned the Mojave into an arid landscape, desert tortoises have roamed this area; Defenders is working to ensure that they’ll still be here for the future.

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Can’t get enough of the desert tortoise? Check out this slideshow of Pasha’s trip.

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