If an unidentified flying object (UFO) suddenly appeared in the sky, it's likely your heart would beat faster, and 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.
Until now, researchers thought the animals were taking these encounters in stride.
But new study by researchers from the University of Minnesota shows that despite the bears' calm demeanour when in the presence of UAVs, their heart rates soar, a sign of acute stress.
"Some of the spikes in the heart rate of the bears were far beyond what we expected," said Mark Ditmer, post-doctoral researcher in the university's Department of Fisheries, Wildlife and Conservation Biology.
"We had one bear increase her heart rate by approximately 400 per cent - 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," said Ditmer.
The researchers fitted free-roaming American black bears living in northwestern Minnesota with Iridium satellite GPS collars and cardiac bio-loggers.
The collars sent the researchers an email with each bear's location every two minutes while the bio-loggers captured every heartbeat. Then Ditmer and his colleagues programmed a UAV to fly to the bear's most recent location.
In the end, the researchers were able to analyse their data very precisely to find out what hidden effects their UAV flights - which lasted only a brief five minutes due to battery life and other logistical constraints - might have had on the bears.
In 18 UAV flights taken in the vicinity of four different bears, individuals only twice showed any major change in their behaviour in response to the UAVs.
However, the bio-loggers showed consistently strong physiological responses. All of the bears in the study responded to UAV flights with elevated heart rates. Fortunately, the bears recovered very quickly.
"Without the use of the bio-logger, we would have concluded that bears only occasionally respond to UAVs," Ditmer said.
The researchers said it will now be important to consider the additional stress on wildlife from UAV flights when developing regulations and best scientific practices.
UAVs are growing in popularity for many uses in addition to research - for example, to discourage poachers and track down wildlife for eco-tourists, researchers said.
The study was published in the journal Current Biology.