'Bird has flown': Warblers predict tornadoes, escape before they hit, report shows
Tracking a population of golden-winged warblers, a research team
led by UC Berkeley ecologist Henry Streby revealed that birds in
the mountains of eastern Tennessee escape their breeding grounds
one or two days prior to the arrival of powerful storms.
A storm system which swept through the central and southern US in April caused up to 84 tornadoes and killed 35 people. The findings are published in the journal Current Biology.
“It is the first time we’ve documented this type of storm avoidance behavior in birds during breeding season,” Streby told UC Berkley news center.
“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 noted.
The warblers in the latest study flew up to 1,500km to avoid the
storm. They smartly returned home as soon as the disaster passed
and the picture cleared.
The birds, with their trademark gray plumage spiced up by patches of yellow on the head and wings, fled while the storm was about 900km away, before changes in atmospheric pressure and wind speed. It means that when meteorologists were only announcing that the storm was on its way, the birds were already "packing their bags and evacuating the area,” Streby explained.
There's currently a real need to study the golden-winged
warblers, their population only 5 percent of historic levels in
the Appalachians due to habitat loss and hybridization with other
The researchers were testing whether a tiny bird, weighing some 9 grams, could manage to carry a half-gram geolocator throughout the year. To obtain the tracking data, they had to retrieve as many geolocators as possible from the 20 birds that had been originally tagged. The study results come from five geolocators.
According to Streby, these warblers are the smallest bird species ever marked. The fact that any geolocators had returned at all was a great relief, he mentioned.
Studying the data on the geolocators, the researchers detected anomalies in the geographical locations for the birds from April 26 to May 2. It turned out that the birds changed course and flew back from their breeding grounds in Tennessee’s Cumberland Mountains to the Gulf coast. At first the scientists thought there was a mistake in the data. When they double-checked and realized it wasn't the case, they started looking for a better explanation.
Streby said the supercell storm came to mind simply because they also had to move to a hotel to wait it go away.
However, the wise birds had gone long before, when local weather conditions were still normal. This made the researchers wonder how they got their early alert.
Infrasound appeared to be the answer. Acoustic waves, which occur at frequencies below 20 hertz, fall into the infrasound range below the limits of human hearing, but birds and other animals can hear infrasound. Tornadoes are also known to produce powerful infrasound, so the ability of birds to forecast deadly storms could become extremely important.
“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,” Streby said. “It could come at a cost, though, since such actions place added energetic and reproductive stress on populations that are already struggling.”