Tortoise Decoys

Tim Shields has been studying desert tortoises for more than 35 years. In that time, he watched their population in California’s Mojave Desert plummet by more than 90 percent. He was finding fewer and fewer young tortoises in the area. More often, Shields found only their empty shells. Most had been pecked open by hungry ravens. 

Tim Shields has studied desert tortoises for more than 35 years. In that time, their population in California’s Mojave Desert dropped by more than 90 percent. Shields was finding fewer and fewer young tortoises in the area. More often, he found only their empty shells. Hungry ravens had pecked most of them open. 

For Shields’s idea to work, the decoy shells needed to be convincing enough to trick ravens into believing they were real. Shields and his colleague, biologist William Boarman, teamed up with a high school student in Shields’s hometown of Haines, Alaska, to develop the first prototypes, or testable models, of the decoys. The student, Eli White, knew how to use a 3-D printer—a device that builds up layers of a material to manufacture solid objects. With this technology, White showed that it was possible to create the complex shape of a tortoise shell out of plastic.

Shields and Boarman showed these prototypes to Autodesk, a design company in California, which offered to help refine the design. To make the 3-D printed models even more realistic, the company scanned the shells of real baby tortoises. 

Soon it was time to put their decoys to the test. Shields and Boarman placed the shells throughout the desert and set up cameras nearby. Then they waited to see how ravens would respond. The team was able to collect valuable data about when, where, and how ravens tend to attack.

For Shields’s idea to work, the decoy shells needed to look true to life. The ravens had to believe they were real. Shields and fellow biologist William Boarman worked with a high school student in Shields’s hometown of Haines, Alaska. They developed the first prototypes, or testable models, of the decoys. The student was Eli White. He knew how to use a 3-D printer. This device builds up layers of a material to form solid objects. With this technology, White created the complex shape of a tortoise shell out of plastic. He showed that the idea was possible.

Shields and Boarman showed these prototypes to Autodesk, a design company in California. Autodesk offered to help improve the design. The company scanned the shells of real baby tortoises. This made the 3-D printed models even more realistic.

Soon it was time to test their decoys. Shields and Boarman placed the shells all over the desert. They set up cameras nearby. Then they waited to see the ravens’ reaction. The team collected useful data about when, where, and how ravens tend to attack.

After five years of testing different shell shapes, colors, and locations, the group was ready to move on to the final stage of the plan. Engineers added sensors and machinery to the fake shells. When attacked, these “techno-torts” released an explosive spray of methyl anthranilate (ME-thul an-THRA-nuh-layt). This nontoxic fluid smells and tastes like artificial grape. While it doesn’t harm the birds, they find it highly irritating. 

This past spring, the techno-torts were finally put into action. Boarman recalls one raven caught on video hammering on a weaponized shell with its beak. “Suddenly, the spray came out just like it’s supposed to,” he says. “The raven was so scared. It was the perfect reaction!”

For five years, the group tested different shell shapes, colors, and locations. Then they were ready to move on to the plan’s final stage. Engineers added sensors and machinery to the fake shells. When these “techno-torts” were attacked, they shot out a spray of methyl anthranilate (ME-thul an-THRA-nuh-layt). This nontoxic liquid smells and tastes like artificial grape. It doesn’t harm the birds, but they really dislike it. 

This past spring, the techno-torts finally went into action. Boarman recalls one raven that was caught on video. It was hammering on an armed shell with its beak. “Suddenly, the spray came out just like it’s supposed to,” he says. “The raven was so scared. It was the perfect reaction!”

Shields and Boarman want the ravens to learn that pecking a desert tortoise equals a face full of nasty spray. This negative experience will hopefully train the birds to leave real reptiles alone. But it can be extremely difficult to alter animals’ behavior, particularly ones as smart as ravens. Right now, “we know that ravens fly away when sprayed,” says Shields. “But we don’t know what they’ll do a month from now.” Will the birds start to avoid the shells along with the live tortoises that look like them? Or will they figure out the scientists’ trick?

The team plans to continue modifying the techno-torts’ design based on how the birds respond. Shields and Boarman are hopeful that ravens will decide that tortoises—both fake and real—aren’t worth eating. “We don’t know what the ravens are thinking,” says Shields. “But our videos show very surprised animals who will probably think twice the next time around.”

Shields and Boarman want the ravens to learn a lesson. Pecking a desert tortoise means a face full of nasty spray. They hope this negative experience will train the birds to leave real reptiles alone. But it can be extremely difficult to change animals’ behavior. And ravens are very smart. Right now, “we know that ravens fly away when sprayed,” says Shields. “But we don’t know what they’ll do a month from now.” Live tortoises look like the shells. So will the birds start to avoid the shells and the live tortoises? Or will they figure out the scientists’ trick?

The team will watch how the birds respond. Based on that, they’ll keep adjusting the techno-torts’ design. Shields and Boarman want ravens to decide that tortoises aren’t worth eating, whether they’re fake or real. “We don’t know what the ravens are thinking,” says Shields. “But our videos show very surprised animals who will probably think twice the next time around.”