A new study suggests that the tiny golden-winged warbler can sense deadly storms hundreds of miles away and fly to safer grounds.
The study conducted by the researchers at the University of California (UC), Berkeley, gives evidence that a flock of warblers flew away from their nesting grounds in Tennessee a few days before the weather forecast confirmed the arrival of a deadly storm that produced 84 tornadoes, which killed more than 30 people.
Henry Streby, a National Science Foundation postdoctoral research fellow and visiting scholar at UC Berkeley who is also the lead author of the study, suggests that meteorologists predicted that the deadly storm may come but when they were sure about the storm the warblers had already sensed it and left.
Streby suggests that the birds left Tennessee over 24 hours prior to the onset of the devastating storm. The researchers believe that the tiny birds listened to the "infrasound" that accompanies severe weather, sounds which are outside the hearing capacity of humans. Infrasound is low-frequency sound that is lower than 20 Hz frequency, the "normal" limit of human hearing.
"Meteorologists and physicists have known for decades that tornadic storms make very strong infrasound that can travel thousands of kilometers from the storm," explains Streby.
Streby suggests that birds may have also picked up other clues about the storm, but the infrasound that is produced from storms usually travels at a frequency which the birds can hear.
The researchers discovered the birds' ability by accident. Streby explains that he and his colleagues fitted tiny geolocators on 20 warblers to track the winter migration pattern of the birds. The focus of the study was to find out if it is possible to outfit such sensors on birds as small as the warblers.
The study found that the sensors worked without affecting the flying abilities of the birds. The researchers collected the geolocators from five birds and the rest got lost. The study found that the birds fled in late April, which is the breeding season for them. The researchers found that the birds had flown a few hundred miles and one of them also managed to fly to Cuba.
Initial analysis of the geolocators made Streby and his team assume that there was something wrong with the devices as data did not match with the regular migratory pattern of the warblers. Even though the travel distance for the birds was similar to their regular migration distance, the path they took and the time of the year they flew did not match with previous records. Moreover, data from all five geolocators reflected similar migration patterns.
The researchers then realized that the weird migration of the warblers occurred around the same time as the arrival of the storm. The study suggests that the birds heard the storm coming and fled earlier than the regular migration time to be safe from the storm, which may have killed them.
The study suggests that even though the warblers are able to save their lives from severe storms, the flight may still drain a lot of energy from the birds, which they could use for reproducing during the breeding season.
The study has been published in the journal Current Biology.
