Drones most likely look like UFOs to wildlife, and new research suggests these flying devices can be as scary to animals as little green men would be to us.

Unmanned aerial vehicles (UAVs) are often used to study wild animals and track endangered species, but a recent study revealed the presence of the objects caused bears' heart rates to soar, Cell Press reported.

"Some of the spikes in the heart rate of the bears were far beyond what we expected," said Mark Ditmer of the University of Minnesota, St. Paul. "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."

To make their findings, a team of researchers fitted free-roaming American black bears living in northwestern Minnesota with Iridium satellite GPS collars and cardiac biologgers The collars sent out a GPS locations for each bear every two minutes biologgers documented every heartbeat. The researchers then sent a UAV to fly to the bear's most recent location to observe the effect it would have on the animal.

In 18 UAV flights made near four different individual bears, the animals rarely were observed to change their behavior in the presence of the drone, but did display significantly elevated heart rates.

"UAVs hold tremendous potential for scientific research and as tools for conservation," Ditmer said. "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."

In the future, the researchers plan to study whether or not the bears can get used to the presence of a drone over time, and if so how long that would take.

The findings were published in a recent edition of the journal Current Biology.