Have you ever seen something flying low overhead and felt your heart race just that little bit faster? Well, it turns out that bears do, too. In fact, they are terrified of unidentified flying objects (UFOs) – specifically, unmanned aerial vehicles (UAVs), or drones.

The research was conducted by scientists from the University of Minnesota. Published in the journal Current Biology, the scientists fitted American black bears in northwestern Minnesota with GPS collars and cardiac biologgers. This gave them the bear’s location every two minutes, and also constantly updated the team on their heartbeat.

Knowing their location, the team then sent small drones flying over the locations that the bears were in. In total 18 flights were performed over four bears. On just two occasions, the bears showed a major change in their behavior. But on every single flight, the heart rate of the bears increased – sometimes dramatically, as much as four times.

"Some of the spikes in the heart rate of the bears were far beyond what we expected," said lead author Mark Ditmer of the University of Minnesota in a statement. "We had one bear increase her heart rate by approximately 400 percent – from 41 beats per minute to 162 beats per minute. Keep in mind this was the strongest response we saw, but it was shocking nonetheless."

Mark prepares to fly one of the drones. Jessie Tanner.

UAVs are being increasingly used by wildlife researchers to observe animals, such as endangered species in difficult-to-reach terrain. But this study suggests that the practice could be harming the animals. The fact that the animals do not show a major change in their behavior would suggest they don’t mind the drones in their vicinity, but the biologgers showed otherwise.

"Without the use of the biologger, we would have concluded that bears only occasionally respond to UAVs," said Ditmer. "UAVs hold tremendous potential for scientific research and as tools for conservation. However, until we know which species are tolerant of UAVs, at what distance animals react to the presence of UAVs, and whether or not individuals can habituate to their presence, we need to exercise caution when using them around wildlife."

The team’s next plan is to find out if captive bears can learn to get used to UAV flights. Until that can be deduced, observing animals with drones may not be that advisable.