Analysis of the data revealed that the birds took off for Florida several days in advance of a large, severe thunderstorm system that was advancing across the Great Plains.
A new study suggests that these warblers detected the severe weather and got the heck out of the way—an ability never before documented in birds. (Read "Birds Can 'See' Earth's Magnetic Field.")
The scientists theorize the birds were tipped off by infrasound—a type of low-frequency noise—produced by the storms. Although humans can't hear infrasound, birds can, and the destructive nature of these storms may make it advantageous for the birds to get out of the way despite the high-energy costs of flight.
"We were completely blown away by this behavior. It shows that the birds can do more than we give them credit for," said study co-author Gunnar Kramer, a population ecologist at the University of Minnesota in Minneapolis.
Kramer and his colleagues happened upon the discovery by accident, while studying migration patterns of golden-winged warblers. (Also see "The Case of the Golden-Winged Warbler.")
The songbird spends winters in Central and South America and migrates to the Great Lakes region and the Appalachians to breed and raise young.
To learn more details about this behavior, the team traveled to the Great Lakes and fitted some of the warblers with a small, lightweight geolocator that recorded their exact locations every few minutes, according to the study, published December 18 in the journal Current Biology.
In April 2014, the researchers tracked the birds to the Cumberland Mountains of eastern Tennessee to check on them. But when they arrived, the mountains were silent. Their warblers weren't there. (See National Geographic's backyard birds identifier.)
"We thought the birds were just hunkering down. It never occurred to me that they might have evacuated," Kramer said.
When the team checked on the warblers' locations via their geolocators, they discovered the birds were in Florida. One bird had even traveled to Cuba.
Several days later, however, the birds flew back to Tennessee, having mysteriously traveled more than 900 miles (1,500 kilometers) round-trip.
A chance look at a weather report gave scientists their hint—right around the time the birds left Tennessee, a severe weather system clobbered the Midwest, spawning 84 tornadoes that killed at least 35 people. (Related: "Pictures: Social Media Capture Tornado Destruction.")
However, the scientists emphasize in the study that it's unknown exactly why the birds veered from their migration route in April 2014, and that the storms' infrasound was a "probable cue" to escape.
To Jonathan Hagstrum, a geophysicist at the United States Geological Survey who studies bird migration, the new research supports the idea that birds use infrasound during migration. (Read about animal migrations.)
"These results show another way that birds can use low-frequency sound," said Hagstrum, who wasn't involved in the new study.
"They're not just using it to navigate, but to identify and avoid severe weather. It all fits in," he said.