MIAMI - Birds appear to be able to sense a coming storm and fly away before it hits, according to research out Thursday on golden-winged warblers in the United States.
These tiny, delicate birds weigh just nine grams, or about as much as a palmful of coins, and yet somehow they knew that a massive storm system -- including tornadoes and high winds -- was on its way one to two days in advance.
They fled their breeding grounds in the mountains of eastern Tennessee just before the storm system swept through the central and southern United States in late April 2014.
The storm caused at least 84 tornadoes and killed 35 people.
"It is the first time we've documented this type of storm avoidance behaviour in birds during breeding season," said ecologist Henry Streby at the University of California, Berkeley.
"We know that birds can alter their route to avoid things during regular migration, but it hadn't been shown until our study that they would leave once the migration is over and they'd established their breeding territory to escape severe weather," he said.
When the birds flew off, the storm was still hundreds of miles away, so there would have been few detectable changes in atmospheric pressure, temperature and wind speed.
"The warblers in our study flew at least 1,500 kilometers (932 miles) total to avoid a severe weather system. They then came right back home after the storm passed."
Scientists think that this sixth sense that birds possess has to do with their ability to hear sounds that humans cannot.
Birds and some other animals have been shown to hear infrasounds, which are acoustic waves that occur at frequencies below 20 hertz.
Events like winds blowing, ocean waves crashing and volcanoes erupting at faraway distances can create infrasounds that birds may be able to sense, even when the events themselves are thousands of kilometers away.
Tornadoes are also known to produce strong infrasound.
"There's growing research that shows that tornadoes are becoming more common and severe with climate change, so evasive actions like the ones the warbler took might become more necessary," said Streby.
The findings are published in the journal Current Biology.