A small quadcopter was attacked and destroyed by a bald eagle in Michigan, and the story got hot on social media thanks to a humorous official response to the drone-downing, though there may be something important for remote pilots to learn from this terrible tale of tenacious talons: specifically, what might have provoked the bird to flip the drone.
A local media account based on a news release issued by the state agency responsible for the drone on August 13 was shared more than 200,000 times on social media within 30 hours of publication, with another 100,000 added to that total by August 17. The Michigan Department of the Environment, Great Lakes, and Energy (the acronym EGLE is pronounced "eagle," as luck would have it), the agency responsible for the drone, had a lighthearted take on the loss of a DJI Phantom 4 Advanced (valued by state officials at $950, presumably just the cost of replacing an airframe), indulging in the suggestion that the eagle was provoked by hunger, territoriality, or spelling. No harm had come to humans. Or, most likely, to the eagle.
The EGLE team reached no definitive conclusion about what might have motivated the “brazen eagle vs. EGLE onslaught” near Escanaba, Michigan. “The attack could have been a territorial squabble with the electronic foe, or just a hungry eagle. Or maybe it did not like its name being misspelled,” the department supposed in the news release. “EGLE’s drone team is considering steps to reduce the possibility of a repeat attack, including possibly using ‘skins’ or other designs on the aircraft to make them look less like seagulls.”
One experienced public safety operator (who is employed by the federal government and declined to be named on the record) posited another possible theory: The system used to detect close-range obstacles may have irritated the eagle, and the manual for that model does mention (on page 27) the use of ultrasonic sensors for obstacle detection, though no details are provided on the operating frequency.
Several large bird species have been known to attack drones, and the motive has never been clarified by scientific study. A widely cited 2004 paper by Robert Beason of the U.S. Department of Agriculture’s National Wildlife Research Center in Sandusky, Ohio, cites previous studies on various species that found most do not appear to react to sounds in the ultrasonic frequency range. The 2004 research paper, presented at a conference addressing wildlife problems including airport infestation by certain birds, was examining what kinds of synthetic stimuli might be most effective at keeping birds away from airports and farms, where their presence can be destructive. (Bird strikes are a well-known and persistent problem for aviation writ large.)
“No species of bird has shown sensitivity to ultrasonic frequencies (>20 kHz),” Beason wrote. “Sensitivity to frequencies below 20 Hz (infrasound) has not received much attention; however, pigeons and a few other species have shown behavioral and psychological responses to these low frequencies.”
Sound may yet be useful for deterring birds, and the DJI Phantom 4 Advanced that was struck down in midflight and sent “to the bottom of Lake Michigan,” as reported, was certainly producing sound audible to human ears, principally the propeller noise sometimes described as a sound similar to a swarm of bees. Notwithstanding the findings that Beason reported in 2004, there are a variety of products marketed to airport managers and agricultural customers that use a range of sounds, including ultrasonic frequencies, to drive birds away from airports and crops.
There is even a drone that is purpose-built for this mission, the AeroDrone Avian Scout, which is produced in Australia, home of the wedge-tailed eagle, that continent’s largest bird of prey. There is anecdotal evidence that the avian response to synthetic sound can be hard to predict, and deterrence is not the only possible outcome. A federal UAS pilot reports that Skydio drones, when flown within proximity of some number of turkey vultures, have caused a “dystopian Alfred Hitchcock scene” that human observers believed to have been provoked by ultrasonic emissions from the aircraft.
King, who was identified by state officials as the remote pilot in command of the ill-fated flight, searched fruitlessly with the help of witnesses who saw the eagle attack, though they were surprised to learn from King that the object of that attack was inanimate, according to the August 13 news release. Flight data transmitted from the aircraft pinpointed the impact of the eagle in space and time. Forward speed was almost instantly arrested, and the drone transmitted its terminal data packet 3.5 seconds later, presumably at the same time or an instant before it hit the water. Days later, EGLE Unmanned Aircraft Systems Coordinator Arthur Ostaszewski paddled a kayak to the scene and mucked around in turgid water for a few hours but found no sign of the downed EGLE drone.
State officials spent some time planting their tongues firmly in their cheeks before issuing a press release announcing that “an airborne attack on a drone” by a local eagle had taken place, “tearing off a propeller and sending the aircraft to the bottom of Lake Michigan.” (You have to read a few more paragraphs to get to the detail that the water was four feet deep.) Telemetry data tells a harrowing tale of an innocent drone flying 162 feet above the water at 22 mph, when suddenly a stream of warnings including “excessive spin” and something about a missing propeller fill the final 3.5 seconds of the data log, 27 warnings in all.
It should surprise no one that a bald eagle is capable of quickly dispatching the most popular drone in history (DJI’s Phantom was among the first mass-produced, ready-to-fly drones, and has sold in huge numbers around the world). Dutch police showed the world how badly outmatched a rogue Phantom might be if a police eagle engaged it. (Who among us can resist watching that video one more time?) The Dutch attack eagles also became social media darlings, probably because watching bad things happen to innocent drones never gets old, no matter how you feel about the technology. They are robots. Watching them get destroyed can be quite funny.
Sadly, the Dutch eagle experiment was over and done in a year. The eagles were fired (or retired) because they just didn’t do what they were told. (The U.S. Air Force may still be looking into training falcons to take down drones; falcons have more history when it comes to working with humans and may have greater respect for the chain of command than eagles do.)
It is possible that the Dutch police eagles took to attacking drones so readily because the obstacle avoidance systems were engaged, and they could hear it, and be disturbed by what eagles and other large raptors may perceive as unpleasant noise pollution. Generally, obstacle detection should be on during flights. It’s a good default option that reduces the likelihood of collision. Perhaps not everywhere, however.
Pilots flying over Michigan’s Upper Peninsula, along the shores of Lake Michigan, well clear of trees and 150 feet from shore, might consider turning the obstacle avoidance system “off,” whatever “skin” their drone is in. In any case, spotting an eagle in the air is a good reason to land any small, unmanned aircraft as soon as practicable.
According to the release, there are 849 active bald eagle nesting sites in Michigan, an environmental success story considering that there were just 76 nesting sites in the 1970s, but possibly a bit of a disaster for drone pilots who need to survey the shoreline to monitor erosion. There is a safety case to consider the risk noted by an unnamed spokesperson for the Michigan Department of Natural Resources (which reportedly declined to prosecute the offending eagle), according to the same press release:
"Nature is a cruel and unforgiving mistress."