If an unidentified flying object suddenly appeared in the sky, it's likely your heart would beat faster.
Now, researchers have found that the same is true for bears.
The UFOs in this case are actually unmanned aerial vehicles (UAVs), which have become increasingly valuable to wildlife researchers, allowing them to observe animals, including endangered species, in their natural settings from long distances and over difficult terrain. It had appeared as though the animals were taking these encounters in stride. For instance, American black bears rarely seem to startle or run away when a UAV comes near. But the new study reveals that despite the bears' calm demeanor when in the presence of UAVs, their heart rates soar, a sign of acute stress.