You might want to be careful about who you call a birdbrain. Some of our feathered friends exhibit powers of perception that put humans to shame.
Scientists said on Thursday that little songbirds known as golden-winged warblers fled their nesting grounds in Tennessee up to two days before the arrival of a fierce storm system that unleashed 84 tornadoes in southern U.S. states in April.
The researchers said the birds were apparently alerted to the danger by sounds at frequencies below the range of human hearing.
The storm killed 35 people, wrecked many homes, toppled trees and tossed vehicles around like toys, but the warblers were already long gone, flying up to 1,500 km (930 miles) to avoid the storm and reaching points as far away as Florida and Cuba, the researchers said.
Local weather conditions were normal when the birds took flight from their breeding ground in the Cumberland Mountains of eastern Tennessee, with no significant changes in factors like barometric pressure, temperature or wind speeds. And the storm, already spawning tornadoes, was still hundreds of miles away.
"This suggests that these birds can detect severe weather at great distances," said wildlife biologist David Andersen of the U.S. Geological Survey and the University of Minnesota, one of the researchers in the study published in the journal Current Biology.
"We hypothesize that the birds were detecting infrasound from tornadoes that were already occurring when the storm was still quite distant from our study site," Andersen added.
Infrasound is below the normal limits of human hearing, but some animals can hear it.
The warblers came right back home after the storm passed, said fellow researcher Henry Streby, an ecologist from the University of California, Berkeley.
The researchers, who were already studying the migratory patterns of the warblers, tracked their evacuation using transmitters that had been placed on a small number of the birds.
Golden-winged warblers boast gray plumage marked by patches of yellow on the head and wings. They weigh about nine grams (0.30 ounces), and have a wingspan of about 19 cm (7.5 inches).
The warblers spend winters in Central America and northern South America before migrating back to the Appalachian Mountain region of the southern United States and the Great Lakes region of the United States and Canada to breed.