Creating Safe Passage for Desert Tortoises

Desert Tortoise crossing roadway. Photo: NPS/Brad Sutton

Mojave Desert tortoises live in one of the harshest environments in North America—the southwestern United States. They survive in areas where ground temperatures can exceed 140 degrees by burrowing into the sand, emerging only rarely to feed on desert grasses, flowers, and cacti. Desert Tortoises typically have 50-year life spans in the wild, with many individuals reaching 80 years and above, but in recent years, more and more of these lives are being cut short.

Prior to the 20th Century, the Mojave Desert was teeming with these desert dinosaurs. Tortoises have lived in the area for millions of years, even before it was a desert. Some locations were previously estimated to have as many as 1,000 individuals per square kilometer, but over the last 100 years, Desert Tortoise populations have crashed by 90% as roads, cities, and renewable energy developments have bloomed across the desert. Despite conservation efforts dating to the 1970s, and the species listing under the Endangered Species Act in 1989, Desert Tortoise populations have continued to decline.

Center for Large Landscape Conservation Road Ecologist Elizabeth Fairbank

“Though they spend much of their time in their burrows, when tortoises do emerge to find food, water, or mates, they are at great risk of being struck by vehicles, especially as juveniles,” says Fairbank, a member of the Corridors & Crossings team at the Center for Large Landscape Conservation. “Desert Tortoises are particularly vulnerable to oncoming vehicles as they move slowly and, especially when they are young and only a couple inches in diameter, are very hard for motorists to see.”

In 2011, the US Fish and Wildlife Service (USFWS) developed a revised recovery plan for the Desert Tortoise that identified road- and highway-related mortality as a critical issue for the species recovery. More than 60,000 miles of roads and highways have been constructed across the Desert Tortoise’s range, and over 13,000 tortoises are killed on roads each year.

The Race to Save the Mojave Desert Tortoise

Fairbank and her colleagues at the Center are now working with the USFWS to bring together private and public partners to explore options for creating safe passage for Desert Tortoises.

“If we continue to kill tortoises on roads and fragment their habitat at the rate we are now, they will cease to exist in the very near future,” says Fairbank.

Roads also restrict the movement of tortoises indirectly, limiting their access to suitable habitat that they need to survive and reproduce. Noxious weeds that reduce habitat and forage quality and increase fire risk spread out from roads, while trash and road-related infrastructure attract ravens that prey on young tortoises.

Desert Tortoise
Desert Tortoise (Gopherus agassizii). Photo: USFWS

Scientists have found that installing fencing and wildlife underpasses (culverts) along roadways can be effective for reducing roadway mortality and improving connectivity for the species. The fencing keeps tortoises from crossing in high-risk areas and guides them to use the underpasses instead. The implementation of these measures has also been identified as a priority by the US Fish and Wildlife Service. But several challenges remain.

Desert tortoise habitat spans four states—California, Utah, Arizona, and Nevada—and numerous jurisdictions, including private lands, state lands, tribal lands, and federal public lands. States often have different policies and standards for implementing roadway mitigation measures that create challenges for collaboration. Land managers, such as National Park supervisors, are often reluctant to install fencing because it can impact the views for park visitors, while transportation managers face many policy, technical, and funding challenges in implementing conservation measures. In addition, fencing and underpasses are expensive to install and maintain, leading to disagreements about who should shoulder the bulk of the funding and workload.

The Center and Partners Tackle Road Impacts on Tortoise

To help navigate these issues, the USFWS partnered with the Center for Large Landscape Conservation and Western Transportation Institute to organize activities that can enable interagency efforts to mitigate roadway impacts on Desert Tortoise.

“We know that one of the most important things that we can do for Desert Tortoise recovery is to address the issues they face with regard to transportation infrastructure. One of the biggest obstacles to doing so has been lack of a coordinated, range-wide approach,” explains Fairbank. “What we need is wildlife, transportation, and land management agencies to come together and agree on standard policies and practices that can be implemented consistently across the four-state range.”

Workshop Summary Report

In late March of 2021, the Center for Large Landscape Conservation and the USFWS hosted a virtual Desert Tortoise Transportation Ecology Workshop, bringing together representatives from state and federal transportation and wildlife agencies, land management agencies, non-profit organizations, and universities who are working on tortoise and transportation issues. Participants shared challenges as well as ideas for technical solutions, best management practices, and other recommendations that could be implemented throughout the tortoise’s range.

On the final day of the workshop, participants began to set up the framework for an interagency and interdisciplinary Task Force that will begin working on solutions to prioritize, fund, and implement effective mitigation measures to protect the Desert Tortoise from the impacts of roads. The Center and USFWS subsequently co-authored a workshop summary report to support collaborative action to improve the desert tortoise’s chance of long-term recovery.

“This Task Force will be a game-changer for Desert Tortoise,” says Fairbank. “By bringing all of the right people to the table, we have a real chance at implementing policies and on-the-ground conservation measures across Mojave Desert Tortoise range that will give them a fighting chance at recovery and will provide huge benefits for a whole suite of species across the Mojave ecosystem.”

Learn more about the Center’s Corridors & Crossings program

The Center for Large Landscape Conservation and USFWS have partnered with Clark County Nevada’s Desert Conservation Program and University of Nevada-Las Vegas film students to create The Road to Recovery, a short documentary chronicling Mojave Desert Tortoise transportation ecology issues:

The Road to Recovery Documentary from Ahmad on Vimeo.

Photo, above post – Courtesy of Marcel Huijser


Stay informed

Join our email list for news and updates.