Defenders Magazine

Shell Shocked

Desert tortoises struggle to survive a host of challenges in the Mojave Desert

by Krista Schlyer

© David M. Barren/oxygengroup.com

At the ragged base of a yucca plant in the Mojave Desert, we find him resting upon the shaded sand of his well-placed burrow. He looks like any other gray-green desert rock, but with an intricate pattern of polygons etched into his back and legs. His legs and feet barely show beneath the edge of his shell, just enough to reveal the tough skin that covers them. And like all desert tortoises, and most native residents of this southern California desert, he melts into the muted landscape perfectly, as if he were a part of it from the beginning.

U.S. Geological Survey tortoise researcher Kristin Berry pulls him out from his burrow and he quickly stuffs himself tightly inside his shell.

"This is a choice spot to have for a tortoise because the plant provides extra shade," comments Berry as she wipes the dust from his carapace and examines a quirk in this tortoise's appearance. His scutes, the segments of his carapace, are slightly raised, rather than smooth like most of the wild tortoises here. This may indicate that the tortoise was raised as a pet and fed improperly—which can make for a dramatically different looking animal—and then dumped in the desert.

"They almost start to look like a different species," she says, carefully looking him over.

Being a captive-raised tortoise is no crime. But releasing a captive tortoise in the wild is—because it may be a threat to its wild brethren and to the long-term outlook for the species. Of tortoises that have lived in captivity, about 70 percent have a respiratory disease that has become an epidemic for wild tortoises in the Mojave. Captive tortoises can also be from different areas, and if they mix with native tortoises can alter the gene pool. Additionally, says Berry, captive tortoises can introduce new diseases, throw off the wild population's social order, and add further stress on tortoise food resources, which in many years are already scarce. The Mojave is a heartbreakingly spare environment, where plants and animals need every adaptive advantage they can muster—any added stress can mean the difference between life and death.

Berry, one of the country's leading experts on desert tortoises, will act as judge and jury for this tortoise. She has to decide whether he will stay here, or be taken to a tortoise adoption center, as is the policy with captive-raised tortoises.

Work with desert tortoises is full of difficult decisions and crushing uncertainties, and constant reminders of how unintended consequences of human actions can have devastating impacts on wild species.

This tortoise species ranges from Nevada south to Arizona and Southern California and into the state of Sonora in Mexico. But the Mojave population faces the most immediate threat. The U.S. Fish and Wildlife Service estimates 200,000 or more tortoises live here, but because population data are uncertain (the critter spends as much as 95 percent of its time underground, evading both the sun and researchers), management of the tortoise is not based on total numbers. Instead it is informed by population trends, which over the past 20 years have made one thing clear—tortoises are in trouble.

They were officially listed as threatened under the Endangered Species Act in 1990. Since then, studies in some areas have shown a 60 percent to 90 percent decline in populations, and the list of causes is so long it's hard to know where to begin addressing the problems.

"Unlike some endangered species, the tortoise is affected by a multitude of threats. Not just one or two, but 10 or 20," says William Boarman, now an independent researcher who used to work with the geological survey. "It's not like the brown pelican or bald eagle—get rid of DDT and they will have a good chance of recovery. There's no single thing like that for the tortoise."

In addition to disease, people have introduced exotic plants like Moroccan mustard and invasive annual grasses, which have displaced tortoise food sources and brought increased wildfire to the Mojave. If tortoises are not burned to death when fire rolls through, their major food sources are scoured clean. Human development in the desert has also brought cows, horses and sheep, which can crush tortoises and remove vegetation. And with humans come cars and off-road recreational vehicles, which run over tortoises and their burrows.

Roadkill, garbage and human water sources also subsidize predators that would normally have a hard time surviving in the desert. Raven populations, for example, are 1,000 percent above their numbers in the Mojave in the 1960s—and ravens prey on young tortoises whose shells are not yet hardened.

Habitat loss to homes, businesses and military use continues to cripple the tortoise. The current expansion of Fort Irwin, a U.S. Army base in Barstow, California, will claim 130,000 acres of prime tortoise habitat during the next few years, and will likely claim many tortoise lives as the creatures are moved to alternate and sometimes substandard locations.

Added to all these threats is the specter of climate change, which could have devastating impacts on the tortoise.

"It all makes for a very complex management situation because you can't just deal with the top one or two threats—both because you can't identify what those are and because even if you dealt with them there are so many more to consider," Boarman says.

Berry has an extensive research agenda covering many human impacts on the tortoise, but this plot we are visiting today centers on disease and climate change. She and her research assistant Jeremy Mack will be measuring temperatures and other characteristics of tortoise burrows and caves, to determine what types of cover sites provide the best protection. And they will be gathering data on how disease affects this population, with the hope of learning how the disease spreads, whether some tortoises are resistant and other information that may help in management of the species.

This guy in Berry's hands—identified by the number of the transmitter on his back, 23—has the disease. He's tested positive for it twice. But that in itself will not decide his fate. In fact, many of the tortoises on this study plot are diseased—that was what originally drew Berry here.

Finishing her examination, Berry makes her verdict: "We're going to leave him for now. I'm not certain he's captive."

She puts him back where he was and we move on, looking for other tortoises. As we walk, Berry studies the colorful spring forage. Because of abundant winter rains, desert dandelion, pincushion and other wildflowers that tortoises eat are plentiful this year.

"They're finicky eaters," Berry says. "So they're very dependent on the annual forbs."

But the availability of these herbaceous flowering plants and the timing of their blooms is getting more and more uncertain because of global warming. "One of our concerns is that the food will be out and available before the tortoises are out of their winter burrows and ready to eat," Berry says.

This could be especially problematic for females, who often wait to feed until they have deposited their eggs, which could be many weeks after they emerge in spring.

In this way, climate change and disease may work together to the detriment of the tortoise. Warmer climate, more drought and the dearth of food plants at times when tortoises need them most will create stresses that will hinder the tortoises' ability to fight the disease.

From the other side of a nearby hill, Mack calls out.

"We found one!"

"Which one is it, Jeremy?" Berry asks.

"36!"

"This is good! We were worried about this one," Berry says as we quickly join Mack and the tortoise whose transmitter signal has been silent for about 8 months. He's still wearing the dysfunctional transmitter, but it looks like it's been chewed. If it was a domesticated dog that did the chewing, this guy is lucky to be alive. Unleashed dogs frequently maul tortoises and leave them for dead. We have seen one empty tortoise shell already today whose owner may have met that fate.

This tortoise looks like he's doing fine now, and acts nonplussed as Mack struggles to remove his broken transmitter. Then 36 gets a detailed health check. This entails noting whether his breathing and appearance are normal, whether he is alert, has parasites, any discharge or clogged nares (nostrils). Berry knows he has respiratory tract disease from previous tests, but she wants to see if he is showing clinical signs of the disease.

"Some of them look like a little kid that's got a terrible cold," Berry says. "Others can appear anorexic." Eventually, when the disease progresses, the tortoise's upper respiratory tract fills with mucus, the lining of the tract is destroyed and the tortoise becomes lethargic, anorexic and dies.

So far, the prodigal tortoise has few signs of the disease. It takes perhaps 45 minutes for his health check and transmitter refitting, after which Mack returns 36 to the mouth of his cave in the side of a low hill. As we are gathering our stuff to leave, the tortoise backs out of his hole and trots over toward us. He then stops, plants himself about five feet away and watches us pack up our things—as if making sure we vacate, pronto.

His curiosity and bravado have us all laughing out loud. And when we walk away his lively dark eyes follow us. After leaving 36 we stand for a moment on the hill in which he has made his home and look out over the desert.

"In the olden days, if you stood in a place like this you could see eight to 10 tortoises. Just looking out." Berry laments.

We see none now.

She laughs and explains that she is teasing Mack, who is in his twenties, about his youth. "By the olden days I mean the 1970s."

As luck would have it, I find the last tortoise of the day. Seeing her resting placidly in the shade of a creosote bush, a hard feeling settles upon me—this desert landscape seems less a habitat than a graveyard. Tortoises can live to be 100 years old. But most of the tortoises I've met today will not come close to that. The disease will likely kill most of them within a few years, and if that doesn't get them, drought and climate change, ravens, dogs, vehicles or habitat loss will.

But the fate of these individuals does not have to be the fate of the desert tortoise.

Because a sizeable population of tortoises currently remains, there is hope, Berry says. "I think we have tremendous opportunity to recover this species if we just put in the effort."

Most tortoise advocates agree, the 1994 tortoise recovery plan crafted by the U.S. Fish and Wildlife Service was a good start, but it was never fully implemented. In addition to a shortage of funding and difficulty prioritizing the myriad threats facing the tortoise, some of the obstacles to its implementation are political. Many challenges to tortoise survival are related to human development, ranching and recreation, and political will to act on these threats has been hard to muster. The recovery plan is currently under revision by the service and a new plan—one that aims to use scientific modeling to prioritize threats and management actions—is due out for public comment later this year.

After her health check Mack fits my tortoise with a transmitter, her mark of initiation into the study. Sadly, she is already showing several signs of disease—a dull shell, clogged nose, lethargy. The sickness will cut her life short. But she is now number 207—joining 36, 23 and other subjects in a study that may help to find a future for this quiet Mojave icon.

Learn more about the value of the Mojave Desert, see our 2007 report, Economic Oasis: Revealing the True Value of the Mojave Desert.

Krista Schlyer is a freelance writer and photographer who contributes regularly to Defenders. For more information on Defenders' work on behalf of desert tortoises, visit www.defenders.org/deserttortoise.