On a crisp spring morning in 2016, biologists Tim Shields and Bill Boarman hiked into a remote area of California’s Mojave Desert to put an idea they had to the test. The arid Mojave touches four states, although the bulk of it lies in California. It boasts the world-record high temperature of 134 degrees Fahrenheit, and much of the sparse terrain is dotted with brush, cacti and, in some areas, Joshua trees. Bighorn sheep, coyotes, jack rabbits, rattlesnakes and scorpions traverse the landscape. Water is scarce, especially at lower elevations, and many animals have adapted to survive on less than four inches of average annual rainfall. The desert tortoise, for example, can survive up to a year without fresh water just by eating plants and reusing water stored in its bladder.
In this extreme landscape, Shields and Boarman set up lifelike, 3D-printed replicas of juvenile desert tortoises, dubbed Techno-Torts, and aimed motion-activated cameras at them. The researchers hoped the fake reptiles would lure ravens, which feed on baby tortoises. The scientists left, and when they returned to check the cameras, they found the birds had swooped in for the prey but left disappointed. With the footage they captured, the two researchers gathered valuable information on how ravens approach and attack desert tortoises.
Shields, who has over 35 years of fieldwork under his belt, formed a company called Hardshell Labs just a year earlier as a way to develop and deploy new wildlife conservation technologies that would help save the threatened desert tortoise. Since then, Shields and his associates have collaborated with the U.S. Fish and Wildlife Service to collect data using hundreds of Techno-Torts in key habitat areas.
The result was an astonishing new study on the impact of raven predation on tortoises. Conducted by Fish and Wildlife biologist Kerry Holcomb, it was published November 2021 and made available online a year later in Human-Wildlife Interactions. According to Holcomb, between birth and age 10, raven predation diminishes the number of juvenile tortoises by approximately 42 percent each year if any part of their core use area is within roughly 1,600 feet of an active raven nest and the local raven population consists of about six birds per square mile, a density that is frequently observed in the western Mojave. That bird count is vastly higher than the number of ravens the land could normally support. The animals are bolstered by human food and water supplies, and nesting in such structures as electrical utility towers and billboards. About another 15 percent of juvenile tortoises die from other causes.
Holcomb explains that, under these conditions, if 4,000 tortoises were born in a given year, after ten years only one of the hatchlings would have survived. According to Holcomb, multiyear studies have established that without ravens, 429 hatchlings out of 4,000 would have survived in that same time period. “Tortoises start to reproduce at about age 13,” says Shields. “Significant losses at an early age due to raven predation are taking a heavy toll on the overall population.”
“When raven eggs hatch, the adults go into overdrive because they have babies to raise,” says Shields. “You have these predatory vacuum cleaners scooping up everything, and it’s not just baby tortoises—its lizards, mammals, snakes, insects and the young of other birds. They just go out and start killing everything, and if baby tortoises are around, they’re really easy to nail.”
During one four-year period in the 1980s, an alarming 250 tortoise shells were found under a single raven nest.
Only a handful of biologists have the experience to work on raven and tortoise interactions, and fieldwork is costly. Boarman has spent three decades studying this problem. “Techno-Torts can sit out there for two to four weeks. I’ve even had them out four to five months,” he says. “We can record a lot of activity over that time. We would need 200 biologists, each working 12-hour shifts for 60 days, to obtain similar data.”
It’s extremely rare for anyone to witness a real-time raven attack on a tortoise. “Prior to this we were doing forensic biology,” says Shields. “We were coming to the scene of the crime and trying to discern its nature from the remains of actual tortoises.” With Techno-Torts, biologists can study video of ravens during an actual attack.
“It’s hard to study juvenile tortoise mortality if you can’t find them or if they’ve all been eaten,” says Roy Averill-Murray, desert tortoise recovery coordinator for Fish and Wildlife. “Having a proxy with the Techno-Torts is allowing us to measure predation rates relative to the number of ravens.”
Shields and his team are researching ways to use the technology to change the behavior of predatory ravens. They are testing “weaponized” Techno-Torts that, when attacked, emit a noxious, nonlethal spray that causes unpleasant sensations in the birds. “If this allows us to trick them into thinking that tortoises are yucky and not to be messed with, that would be awesome,” says Averill-Murray.
Tortoises have lived in the Southwest for 20 million to 30 million years, but they are now in danger of extinction. According to Boarman, tortoise numbers in some areas have dropped by 90 percent in the last 40 years.
The portion of the Mojave situated between Los Angeles and Las Vegas has been severely affected. Between 1950 and 2020, the population of the Las Vegas metropolitan area grew from 35,000 to nearly 2.7 million. Today, Riverside County, which cuts through the southern portion of the Mojave, is the fastest-growing county in California. Its population increased around 12 percent between 2010 to 2021. Loss of habitat, introduction of disease, poaching and increased vehicle strikes have devastated tortoise populations. Climate change has affected tortoises as well by raising temperatures, lowering rainfall and reducing edible vegetation. Invasive plants with lower nutritional value are crowding out preferred native plants. On top of all that, ravens are aggressively hunting juvenile tortoises.
According to Boarman, the number of ravens in the Mojave Desert has increased by 1,000 percent since the 1960s. During the same period, the birds increased 1,400 percent in the Sonoran Desert, which lies southeast of the Mojave and extends into Mexico. In California’s Central Valley, the increase was a whopping 7,600 percent, largely because of agricultural activities that support ravens. While raven predation on tortoises is not an issue in the Central Valley, some of those ravens have migrated into the Mojave Desert and feed on tortoises.
With all this in mind, a petition has been filed by concerned citizens and scientific organizations asking Fish and Wildlife to raise the tortoise’s status from threatened to endangered. They hope a decision will be made sooner rather than later. “We’re in a chess match with one of the smartest birds on the planet,” says Shields. “They learn, communicate, problem-solve, play and even use simple tools. They’re really impressive.”
Bolstered by the data obtained using Techno-Torts, the objective now is to use the birds’ intelligence against them. In a test, Hardshell Labs successfully dissuaded ravens from raiding a California pistachio orchard. The birds love the highly nutritious nuts and can quickly destroy a harvest. Researchers used drones and lasers to flush ravens from portions of the orchard, denying them a valuable food source and reducing crop losses by 95 percent. They now want to incorporate artificial intelligence software into fully autonomous lasers that will repeat this success. According to Boarman, these innovative techniques can be used to teach ravens to stay away from high-quality resource sites like landfills, compost facilities and agricultural areas where food and water are readily available. “Without access to subsidies, the current raven population cannot sustain itself anywhere near the current level,” says Boarman.
Shields’ company is also implementing drones to spray oil on raven eggs. The eggs don’t hatch, but the adults continue to care for them, effectively halting reproduction for a year. Researchers hope continued reproductive failure will cause ravens to abandon their nests and leave the area.
Together, these new technologies could help mitigate raven predation on tortoises, but Holcomb is quick to point out that the objective is not to eliminate ravens. The goal is to humanely provide juvenile tortoises with relief from the current rate of predation while still maintaining a stable, low-density raven population.
In September 2022, the Fish and Wildlife Service announced that the Hardshell Labs team was awarded the Theodore Roosevelt Genius Prize for “promoting nonlethal human-wildlife conflict management.” “It’s a great honor,” says Shields. “If we can demonstrate success in helping the desert tortoise, we expect these techniques to be used much more widely in conservation. There could be no more satisfying feeling for someone who loves the tortoise and respects the raven.”