Confronting ‘heavy hit’ of drought, 51 desert tortoises released in Southern Nevada

Desert tortoise numbers in Southern Nevada are on a steady decline, a trend wildlife managers hope to counter with the release of 51 juvenile desert tortoises into the wild.

Last week, Clark County’s Desert Conservation Program in coordination with the U.S. Geological Survey released one of the largest batches of the federally protected species in years.

Dozens of volunteers combed the Boulder City Conservation Easement — a county-managed habitat established in 1995— determined to find areas that would give the threatened tortoises the best shot at survival.

After two years of extreme drought in Southern Nevada, biologists hope the young tortoises live long enough to replace the dozens of tortoises lost during recent bone-dry summers. 

Scott Cambrin, the senior biologist for the county’s conservation program, said he and his team have tracked up to 45 desert tortoises every year for nearly a decade through sensors in a process called “telemetry.” During drought years, data on survival rates of the tortoises is grim.

“Most years, their survival is like upwards of 95 percent. But when we hit drought years, like last year, it can be a heavy hit,” Cambrin said. “During this last insane two-year drought, I think we lost close to half of our telemetry tortoises during that time.”

The U.S. Fish and Wildlife Service estimates that between 2004 and 2014, the desert tortoise population fell by more than one-third. 

The number of tortoises in the wild today is a bit of a mystery — an unfortunate byproduct of the global COVID-19 pandemic. Until recently, data collection and field work scheduled for 2020 needed for population analysis were postponed due to the pandemic, according to the agency.

Desert tortoises in Southern Nevada are at the highest risk of local extinction, according to a federal review by the wildlife agency.  An analysis of a dozen tortoise habitats in the southwest found that the Mojave Desert’s Eldorado Valley — southwest of Boulder City — had the steepest negative trend of desert tortoises in the region.

Volunteer Daleesa Cole, a senior studying biology at the University of Portland, places desert tortoise under desert shrub. (Photo: Jeniffer Solis)

Volunteer Daleesa Cole, a senior studying biology at the University of Portland, examines desert tortoise before releasing into the wild. (Photo: Jeniffer Solis)

Desert tortoises being assigned to volunteers for release. (Photo: Jeniffer Solis)

Habitat degradation, wildfires, more severe weather patterns that accompany climate change, and predation of their eggs and hatchlings have prevented the recovery of desert tortoises, say biologists.

In his work as an independent contractor, biologist Robert Smith said he’s often called in by developers who need to remove the threatened tortoises from construction sites around the valley.

Most of the 51 juvenile desert tortoises released in the Boulder City Conservation Easement last week were pulled from development sites near Las Vegas, Smith said.

“They may not have been there when they cleared it, but they’ll wander in, because it’s part of their actual home range,” Cambrin said. “I mean, we’re moving out. All those exterior sites? That was all desert for the longest time, and so we’re moving out into these habitats.”

Reaching even further into the desert in recent years are large-scale solar energy facilities and electrical transmission corridors.

On the opposite side of the Boulder City Conservation Easement— the desert tortoises’ new home — are miles of solar panels by developer SunPower. 

Solar farms are becoming a common sight in Southern Nevada. More than 18,000 acres of desert tortoise habitat have been replaced by utility-scale solar energy in the eastern Mojave, according to the USFWS.

Two years ago, federal wildlife biologists relocated nearly 150 desert tortoises from a 3,000 acre solar farm under construction near Pahrump. Less than three weeks later, about 30 of those tortoises were killed by desperate badgers impacted by drought, according to wildlife managers.

During the construction of the massive Gemini solar project by Primergy Solar, about 30 miles northwest of Las Vegas last year, biologists removed another 167 tortoises for relocation.

In fact, solar energy development is the second-ranked threat in the Boulder City Conservation Easement, according to the USFWS federal review.

Wildlife managers in Nevada are now working with solar companies to regrow native vegetation and reintroduce desert tortoises to habitat they’ll need to share with solar farms. There is limited data on whether solar farms can actually function as a stable habitat for desert tortoises, and it’s unknown for now, the USFWS admits. 

“Gemini just recently released all of their tortoises back onto the site. They had over 60, but that’s because they removed them all and kept them in captivity until they could put them back,” said Cambrin, the senior biologist for the county’s conservation program.

Overall, desert tortoises do not coexist well with human development. Tortoises are essentially absent from habitat within half a mile of areas with even minimal development, including agriculture, energy, pipelines, transmission lines, and roads.

Cambrin said the tortoises released last week are still years away from reaching sexual maturity. For now, the slow-growing desert tortoises will spend most of their time underground in egg-shaped burrows they’ll dig at the base of desert shrubs.

Biologists with the U.S Geological Survey raised the juvenile tortoises in captivity until they were large enough to avoid being eaten, while their shells were still soft and penetrable.

Encroaching urban development has placed opportunistic predators, like coyotes and ravens, closer to desert tortoise habitats. During drought years, coyotes’ preferred prey of black-haired jackrabbits are more scarce, putting tortoises next on the menu.

Before the tortoises are released into the wild, volunteers soak them in shallow water, giving the reptiles one last opportunity to store water in their bladder for the dry weeks ahead. The extra hydration will also give the tortoise the fuel they need to find their next meal of desert herbs, wildflowers, and cactus pads.

“It’s supposed to be a wet winter, but we don’t know that for certain. We had an insane drought the last two years, so every little bit helps,” Cambrin said.