Lucky break documents warbler tornado warning

A freak of luck has let researchers document warblers fleeing their territories before temperatures, air pressure or other obvious weather signs foretold the arrival of a tornado-spawning storm.

Henry Streby of the University of California, Berkeley and colleagues had fitted lightweight but frustratingly simple data-collecting devices on tiny golden-winged warblers (Vermivora chrysoptera) in 2013 to see where the birds wintered. The devices were too simple to transmit data, so the team had to catch the same warblers in 2014 to recover any information.

Just as the team was assembling for data catching, a storm triggering 84 tornadoes slashed through the southeastern United States in April, killing at least 35 people and causing extensive property damage. The warblers apparently sensed it coming.

Five data-carrying  birds had just returned to their Tennessee breeding grounds after flying hundreds of kilometers. Yet the warblers left again for storm-dodging trips that added up to 1,500 more kilometers to the distance they had just flown. One bird even flew to Cuba and back to evade the storm. What tipped off the birds may have been the infrasound — sounds lower than the normal limit of human hearing — of the approaching storm, which can radiate more 1,000 kilometers, the researchers report December 18 in Current Biology.