Much like humans, bears too are bothered by unidentified flying objects (UFOs), a new study has claimed.
If a UFO suddenly appeared in the sky, it's likely your heart would beat faster. The same is true for bears, the study said.
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 distance and over difficult terrain.
It had appeared as though the animals were taking these encounters in their stride. For instance, American black bears rarely seem to startle or run away when a UAV comes close.
But the new study reveals that despite the bears' calm demeanour when in the presence of UAVs, their heart rates soar, which is 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 from University of Minnesota.
"We had one bear increase its 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," the researcher explained.
The researchers fitted free-roaming American black bears living in northwestern Minnesota with Iridium satellite GPS collars and cardiac biologgers.
The collars sent the researchers an email with each bear's location every two minutes while the biologgers 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 effect 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 biologgers revealed 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.
The researchers said it would 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 ecotourists.
The findings were reported in the Cell Press journal Current Biology.
