PhD candidate finds his field of dreams studying Galapagos tortoises

After earning his undergraduate degree in biology from the University of Minnesota, Charles Lehnen was about to apply to medical school when he began having second thoughts.

“I felt like I was just checking another box on my to-do list,” he recalled.

His then girlfriend, Jilla Nadimi, asked him, “What do you want to do with your life?”

“Actually,” he responded, “I’d like to go to the Galapagos Islands and study giant tortoises.”

Nadimi was shocked but supportive. She was working on elections for the City of Minneapolis but was craving a change.

Soon after that discussion, the couple sold their belongings, bought some backpacks and moved to the Galapagos archipelago off the coast of Ecuador.

“It felt like it was the place I was supposed to be,” recalled Lehnen, who as a kid was obsessed with tortoises. He had a stuffed turtle collection and loved to hunt for insects.

Now, a little more than a decade later, he’s about to receive his PhD in integrative and evolutionary biology from the USC Dornsife College of Letters, Arts and Sciences.

A model PhD candidate at USC Dornsife

Lehnen’s research on rewilding Galapagos tortoises to the islands has earned praise from key mentors at USC Dornsife.

“He’s done important and fascinating work,” says Professor of Biological Sciences and Anthropology Craig Stanford, who has conducted extensive field research on wild great apes, monkeys and reptiles.

Cameron Egan, associate professor (teaching) of biological sciences and director of undergraduate studies for the department, nominated Lehnen for an outstanding teaching assistant (TA) of the year award, which Lehnen won. Only three TAs throughout the entire university win the award each year. As a TA in Egan’s “Ecology and Biodiversity” (BISC404) course, Lehnen designed the lab.

“His expertise, dedication and initiative have been nothing short of essential to the success of this course and the enrichment of our ecological course offerings at USC,” Egan said.

Challenging field work on the Galapagos islands

Lehnen’s research while at USC Dornsife involved several three-week field studies on Santa Fe Island, a small land mass in the middle of the Galapagos Archipelago. He and his team — in conjunction with the Galapagos Conservancy and the Galapagos National Park Directorate — researched the effects of introducing tortoises from a lineage similar to that of another, extinct lineage of the cold-blooded herbivores, which can grow to weigh hundreds of pounds.

Giant tortoises once played a central role in shaping the island’s ecosystems, and the researchers hoped bringing them back would rebalance the ecosystem. For example, just this February, after more than 180 years of absence, giant tortoises returned to Floreana Island, and Lehnen’s studies help researchers predict the impacts of this reintroduction.

Lehnen says the field work is very challenging. Santa Fe Island is treeless and rocky, with almost no flat ground. It’s also home to spiders, snakes and giant venomous centipedes. And rats — lots of rats.

During each trip to Santa Fe Island, Lehnen and his three or four assistants were virtually cut off from the world save for a satellite internet connection at camp. Many days, the humidity rose to about 90% and temperatures exceeded 90 F.

There is no electricity and no fresh water, so each time a boat dropped them off, Lehnen and his team had to drag about four dozen, 5-gallon jugs up a steep hill to camp.

“It’s extremely challenging to live there — physically but also mentally,” Lehnen said. “I’ve learned how to guide people through the process.”

Galapagos island research mixes high- and low-tech

Lehnen employs sophisticated technology in his field research, including drones to detect minute changes in vegetation and machine learning to classify drone imagery. AI also is used to analyze images from camera traps set up around the island.

Lehnen and his team also perform low-tech tasks such as sampling the tortoises toenails and shells. By analyzing isotopes from these samples, they’re able to monitor the animals’ diets. They also study the interactions between the tortoises and the island’s iguanas.

The payoff for such research, Lehnen said, has been priceless.

“Throughout the world, it’s becoming more common to translocate organisms to different areas through reintroduction,” he said. “Can we develop standards for measuring the impacts? I see this as the future of conservation.”

A harrowing survival story of his own

In fall 2025, the unimaginable happened to Lehnen and Nadimi. The two were walking home from campus, about a block from home, when they were hit in the crosswalk by a car. They had been discussing dinner plans.

Nadimi rolled onto the car and smashed through the windshield.

Lehnen was flung at least 15 feet and landed in an intersection.

Nadimi had to be cut out of the windshield. It took doctors 16 hours to pluck glass fragments out of her. She suffered serious bruising and muscle atrophy and still is undergoing physical therapy. She may also require surgery.

Lehnen suffered severe back fractures that required emergency spinal surgeries.

“Doctors told me if I had tried to stand up and put weight on my spine, my spinal cord would have snapped and I would have been paralyzed at best,” he said. “They told me I came inches if not centimeters from death.”

He spent nearly a week in the hospital and underwent two weeks of inpatient rehab. He then spent months receiving at-home nursing and therapy followed by outpatient physical therapy that continues.

As a testament to his dedication, Lehnen was in the classroom this past semester despite the seriousness of his injuries, supporting students without missing a beat, Egan notes.

Nadimi also is graduating this spring with a master’s degree in public administration from the USC Sol Price School of Public Policy.

The couple are getting married in December. Lehnen’s goal is to have recovered enough to be able to dance at his wedding.

Value in USC’s interdisciplinary opportunities

After the wedding and honeymoon, when he completely heals, Lehnen plans to get back to field work. He is applying for post-doctorate jobs with the goal of someday becoming a professor.

Lehnen said he appreciates the interdisciplinary nature of earning a PhD at USC Dornsife. He took many courses in the geospatial program and computer science and machine learning classes at the USC Viterbi School of Engineering.

“I’ve worked with engineers, geographers, computer scientists and more,” he said. “They’ve given me a totally different perspective on my studies.”

And how did Lehnen spend spring break in this, his final year? Helping a fellow professor teach an ecology course on the Colorado Plateau, Utah, and in the Mojave Desert.

The course was on how to properly handle lizards.

“That’s what I do for fun,” Lehnen says.