There's been a drastic drop in desert tortoise numbers in the preserve

For the desert tortoise, an approximately 1-foot-long reptile found in desert valleys across California and the American Southwest, a full lifespan can be up to 80 years. So while the Mojave National Preserve recently marked its 30th birthday, many of the tortoises inhabiting the area were already well into middle age when the National Park Service began managing the land they call home.

In some ways, that makes the tortoises' plight all the more tragic: Increased human activity has increased their mortality numbers, partially due to vehicle collisions. It's the primary reason the preserve is spending more than $1 million to install "tortoise fencing" -- 2-foot-tall metal barriers to prevent the tortoises from trying to cross the park's busiest roads.

It's part of an ongoing effort to save the species, whose numbers have dropped drastically in the past four decades. They were added to the Endangered Species List in 1990 and are currently listed as "threatened," meaning they're likely to become endangered in the near future. (The list includes both endangered and threatened species.)

"For the preserve, now, we came up with an estimate of about 10,000 tortoises," says Neal Darby, wildlife biologist for Mojave National Preserve, equidistant between Death Valley and Joshua Tree national parks. "But boy, that's way below what it's been historically. Back in the 1970s, we had an estimate of maybe 200 to 250 roughly per square mile. Today, it's more like three."

That drastic drop in desert tortoise numbers is part of the reason the preserve is undertaking the fencing project. So far, the thigh-high barriers have been erected on both sides of a 5-mile stretch of road, totaling 10 miles of fencing. The preserve plans to install additional fencing in early 2025, eventually installing another 50 to 60 miles along the park's heaviest-used roads, through what Darby calls "prime tortoise habitat."

At $20 per foot, the new fencing project is costly, and more than the preserve could typically afford. However, the preserve secured funding by collaborating with local highway agencies and drawing from the federal 2022 Infrastructure Investment and Jobs Act, which allocated more than $500 billion for new infrastructure projects. The fences, installed in October 2024, mark the first time the park has tested the technology, making it an expensive trial. But Darby says it's also an essential one, as previous efforts to protect tortoises over the 18 years he's worked at the preserve haven't been successful.

"Since I got here, we've done a lot of focus on trying to alter driver behavior -- making people slow down, making them aware not just of tortoises, but all wildlife," he says. "We installed signage, there's educational outreach, increased law enforcement -- not just tortoises, but all wildlife. But for most part, that hasn't panned out so well. I'm sure we've reached some people, but most people don't pay attention."

The Mojave National Preserve spans 1.6 million acres, making it the largest national preserve outside Alaska. Over the past decade, annual visitor figures have nearly doubled, rising from 549,599 in 2013 to 1.18 million in 2023. This surge poses a serious risk to tortoises, whose slow movement and increased activity during the autumn mating season make them particularly vulnerable to vehicle strikes. Darby notes that at least a dozen tortoises are reported killed by cars each year, though this figure is likely an underestimate, as not all collisions are documented and scavengers can quickly remove roadkill remains.

In some years, the toll is far higher.

"Last year was terribly bad," he says. "We had over two dozen documented strikes last year."

While the loss of a few dozen tortoises may not seem alarming, it is one of several ways the species is suffering due to increased human presence. Predation by ravens is drastically up, and Darby says humans are to blame. Ravens are scavengers, he explains, and look for convenient food sources. Humans provide that by leaving trash and creating more roadkill. Increased visitation also increases the need for infrastructure favorable to raven nesting, like power poles and additional water sources.

"We've made the desert more hospitable for them, and they prey on juvenile tortoises," he says.

Other invasive species, such as wild burros, are also contributing to the tortoises' demise. Burro populations can grow by up to 20% a year, and their intense grazing can degrade desert tortoise habitats.

The pricey fencing is one of several strategies within the preserve to reverse the desert tortoise's population decline. The preserve has programs in place to remove ravens and wild burros, and tests various strategies to encourage birds to nest elsewhere.

Mojave National Preserve is also home to the Ivanpah Desert Tortoise Research Facility, where researchers can "head-start" tortoises by raising them past their vulnerable stage. The challenging part about that conservation strategy is that a tortoise can naturally live a really long time.

"When a tortoise hatches, it's maybe an inch long. But the shell is still very soft," Darby says. "And that stage can actually last up to 10 or more years."

That means it takes a decade of work to give one desert tortoise a chance at making it into adulthood -- so each mature tortoise saved from vehicle collisions can have a significant impact on the long-term population.

While the fences could slightly disrupt mating patterns, Darby believes the trade-off is necessary. Tortoises might need to find mates closer to home, but "reducing the road mortality that they experience is a greater need than their ability to find a mate across the road," he says.

Mojave National Preserve has just three employees on the team tasked with protecting the park's endangered species, and Darby estimates about 60 percent of his time is spent on tortoise-related work. That's because tortoises are enthusiastic burrowers while attempting to escape the desert heat, creating homes for countless other wildlife.

"They drive the ecosystem so that other species can persist in a desert environment," Darby says.

But there's another reason the park works so hard to protect tortoises: People like them. While visitors want to see iconic species like bighorn sheep and bears in other parks, in the desert, tortoises take the top spot.

"A lot of people love to see these animals," Darby says. "Knowing they're out there is a big thrill. Even still, I get a thrill when I see one today."