The desert tortoise (Gopherus agassizii) in California’s Mojave Desert has been listed on the Federal Endangered Species List since 1990 due to rapid population declines. This decline correlates with a significant increase in the raven population.
According to a press release from the Marine Corps Logistics Base Barstow, California, the rise in ravens is partly attributed to power lines installed across the desert. These structures provide nesting sites for the predatory birds, shielding them from predation. On Marine Corps Logistics Base Barstow, the decline of Mojave desert tortoises is directly linked to the growing raven population, as stated by the U.S. Marines. Cody Leslie, a natural resource specialist for the base, explained that surveys show fewer juvenile tortoises as raven numbers surge. He noted a direct correlation: while tortoise populations decrease, ravens have increased by as much as 1,500 percent. Ravens have been documented attacking and eating desert tortoise hatchlings and adults in the Mojave Desert. Leslie reported that ravens are now targeting healthy adult tortoises, killing them by accessing through shell points, describing the attacks as gruesome. Researchers conducted a study using dummy adult tortoises equipped with cameras to capture raven attack methods. Footage revealed that 43 percent of the adult-sized dummies were attacked by ravens. Base researchers observed that while adult breeding tortoises exist, no juveniles or hatchlings have been found recently. They attribute this to an out-of-control raven population. To mitigate this, the Marines employ a technique called egg oiling, using drones and manual methods to oil raven eggs. This process suffocates the fetus, preventing development, and the ravens continue incubating the infertile eggs throughout the breeding season without re-breeding. Leslie stated that over time, this reduces breeding raven numbers. A 2009 Raven Environmental Assessment confirmed that the method does not harm the overall raven population but helps control numbers in critical Mojave Desert tortoise habitat.
