Golden-winged warblers may be able to hear deadly storms thousands of kilometres away and flee to safer places, according to a new study.
The study conducted by researchers at the University of California, Berkeley, found that warblers apparently knew in advance that a storm that would spawn 84 confirmed tornadoes and kill at least 35 people last spring in Tennessee was coming.
The birds left the scene well before devastating supercell storms blew in.
The discovery was made by accident while researchers were testing whether the warblers, which weigh "less than two nickels," could carry geolocators on their backs.
The researchers found that warblers could carry geolocators on their backs. But they also discovered that with a big storm brewing, the birds took off from their breeding ground in the Cumberland Mountains of eastern Tennessee, where they had only just arrived, for an unplanned migratory event.
The warblers travelled 1,500 kilometres in 5 days to avoid the tornado-producing storms.
"The most curious finding is that the birds left long before the storm arrived," said Henry Streby of the University of California, Berkeley.
"At the same time that meteorologists on The Weather Channel were telling us this storm was headed in our direction, the birds were apparently already packing their bags and evacuating the area," Streby said.
The birds fled from their breeding territories more than 24 hours before the arrival of the storm, Streby said.
The researchers suspect that the birds did it by listening to infrasound associated with the severe weather, at a level well below the range of human hearing.
"Meteorologists and physicists have known for decades that tornadic storms make very strong infrasound that can travel thousands of kilometres from the storm," Streby said.
While the birds might pick up on some other cue, he added, the infrasound from severe storms travels at exactly the same frequency the birds are most sensitive to hearing.
The findings show that birds that follow annual migratory routes can also take off on unplanned trips at other times of the year when conditions require it.
That's probably good news for birds, as climate change is expected to produce storms that are both stronger and more frequent, researchers said.
"Our observation suggests [that] birds aren't just going to sit there and take it with regards to climate change, and maybe they will fare better than some have predicted," Streby said.
"On the other hand, this behaviour presumably costs the birds some serious energy and time they should be spending on reproducing," Streby said.
The study is published in the Cell Press journal Current Biology.
