For thousands of years the large, jet black raven has been one of the most common birds found in all regions of the Northern Hemisphere. With the ability to show cognitive thought, problem solving skills, and imitation, ravens are considered to be highly intelligent creatures. This intelligence, along with their omnivorous diet has led to their populations growing tremendously. For the majority of the world, large populations of ravens are not a big issue. On the contrary, they are helpful as these birds eat road kill and  pests like mosquitoes. However, in some areas where raven populations have increased by the thousands over short periods of time, they have been wrecking havoc on the biodiversity of ecosystems.

The Mojave Desert stretches for 47,877 sq mi through southeastern California, southern Nevada, and parts of Utah and Arizona. As the driest desert in North America, it has become famous as the only home of Joshua Trees. The Mojave is also home to the desert tortoise, which if able to reach full maturity can live for 80 years. Because the desert tortoise has a low reproductive rate, grows slowly, and is a favorite snack to predators like ravens they are listed as a vulnerable species on the endangered species list. Their slow growth rate means the their protective shells can remain soft for up to 10 years. As they slowly move through the desert they become easy targets for the large populations of ravens. Conservationists sadly find caches of empty desert tortoise shells under raven nests with holes pecked into them. Over the span of a 4 years research mission, one group of researchers found over 250 tortoise carcasses under a single raven nest.

Conservationists have been testing out methods to protect the desert tortoise from ravens for many years now. Two biologists, Tim Shields and Mercy Vaughn have spent the last 4 years designing a system to reduce the rate at which ravens are preying on the desert tortoises. Vaughn recalls that, “Surveys conducted in 1994 turned up 250 tortoises per square mile in some areas. Now, there’s maybe one or two.” The idea that Shields and Vaughn came up with is to attack the predator much like how an exterminator attacks an insect infestation by going after the raven eggs. Reduction methods of hunting and minimizing landfill trash have been minimally effective. But if eggs found in nests are not able to hatch, the problem stops before it even begins.

Much like how an exterminator will spray an insecticide on eggs, preventing them from hatching, Shields and Vaughn set out to spray an oil over raven eggs. The oil would cause the eggs to suffocate so the embryo inside doesn’t develop. This has a two fold effect of reducing the population as well as encouraging the problem solving adult ravens to relocate to a new nest site. If a raven sees that it’s eggs are continually not coming to maturity they will stop laying in that nest and find a safer environment. The question for Shields and Vaughn was how to spray the nests in a safe and efficient manner. The solution, a tool that had been successfully used to gather data on other bird species, a drone.

Shields custom built a drone to have not only a high resolution camera, but to be able to oil the eggs found in trees, on power line towers, and along the edges of cliffs. All of these nesting sites are areas that a human would not be able to reliably reach, so a drone is a perfect tool for the job. The camera allows the operator to get a clear image of what is in the nest. It is important that data is collected on how many eggs are oiled to give researchers a way to predict population evolution. Once the nest is counted and catalogued, the operator uses the camera to precisely aim the sprayer. A layer of oil is sprayed over the eggs, a method that has been long considered a humane way of reducing an invasive species.

In a paper detailing Shield’s and Vaughn’s research they describe how they first used the drone and other data to establish a population count and nest location. The paper then goes on to state, “To implement the model’s results in afield-practical way and manage reproduction with minimal disturbance, we developed novel technology, a Remote Fluid Application System (RFAS). The RFAS applies the egg addling technique of egg oiling to high (usually out of reach) nesting situations. We tested these tools in the Mojave Desert, CA, where the raven is a heavily human-subsidized predator. We mounted our RFAS on telescoping poles and unmanned aerial vehicles (UAVs; drones) and found that we were able to aerially, and precisely, spray-oil eggs high in trees or cliffs/rock faces, halting 100% (n=46) of raven nesting events.”

Without the drones, egg oiling would have to be done by hand. This is the preferred method used in controlling Canadian geese nests that are made on the ground. For raven nests, that is far too impractical. Shields says that being able to quickly spray the eggs is critical if they are to save the desert tortoise population. There is a small window of opportunity during the nesting season, the second trimester, for oiling to be effective. “If ravens figure out earlier than that their eggs are rotten, they are likely to eat them and nest someplace else,” Vaughn said. “If we wait longer than that to treat their eggs, chances are that we’ll have a baby raven in the nest.” The goal is to reduce the number of raven hatchlings while encouraging the adults to move on. Fitting in treatments for all the nesting sites throughout the Mojave Desert would not be possible without the use of the drone.

Previous Drone News: