Earlier this year, researchers from Duke University went to Gabon to monitor that country’s dwindling elephant population. They took along three drones, which they planned to use to count the elephants, follow their herds, and map their migrations.

Only things didn’t exactly go as planned.

The elephants noticed the drones, which hovered anywhere from 25 feet to 300 feet above them. And it wasn’t just that the elephants noticed them; in many cases, the elephants were clearly agitated. Some of them took off running. In at least one case, an elephant used her trunk to hurl mud in the drone’s direction. “She had her baby with her,” said Missy Cummings, the director of Duke’s Robotics Lab.

The elephants reacted so strongly, the researchers believe, because drones, it turns out, sound a lot like bees. And elephants do not like bees. At all.

“Animals as powerful as the African elephant can go largely untroubled by predators,” my colleague Ed Yong wrote back in 2009, “Their bulk alone protects them from all but the most ambitious of lion prides. But these defenses do nothing against the African bees, which can sting them in their eyes, behind their ears and inside their trunks.”

For the researchers at Duke, the next step is to test just how similar bees buzzing and drones droning actually are. (The team used 3DR’s Iris+ model for their work in Gabon.)

“We’re doing a frequency analysis of the sound of these small drones, so we can figure out how similar they are, and what can be done to mitigate the negative consequences,” Cummings told me.  

Her team is also looking at the possibility of using different kinds of drones—perhaps smaller or larger devices that make softer or louder sounds, or emit different frequencies. The hope is that such devices may be less likely to “annoy the elephants,” she said.