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Feathered Forecasters? Tiny Birds Knew Killer Tornadoes Were Coming

Image: Gunnar Kramer displays one female and one male golden-winged warbler

Gunnar Kramer displays one female and one male golden-winged warbler. Henry Streby

A new study of migrating birds adds to signs that animals may make better meteorologists than humans do.

The latest evidence: A flock of birds flew away from its nesting site days before there were any signs of danger and well before forecasters predicted the arrival of a massive storm system that spawned 84 confirmed tornadoes and killed at least 35 people, researchers reported Thursday in Current Biology.

"Meteorologists were predicting that the storm might come our way," says the study's lead author, Henry Streby, a National Science Foundation postdoctoral research fellow and visiting scholar at the University of California, Berkeley. "But by the time they were saying they were sure it was coming, the birds had already figured it out and were gone."

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The golden-winged warblers normally spend winters in South America and fly up to Tennessee to nest, Streby says. They had been at their nesting site for just a couple of days before they turned around and headed south again.

The discovery was completely fortuitous. Researchers had been testing to see if a new kind of geolocator could be carried by the tiny birds. The geolocators fit like little backpacks on the birds' backs with harnesses attached around their legs.

The geolocators were a success and stayed on the warblers for a year, recording everywhere the birds went. When the researchers recaptured the birds and analyzed the location data they were stunned to discover that the warblers had taken off from their breeding grounds in the Cumberland Mountains of eastern Tennessee, where they had only just arrived, for an unplanned migration south taking them out of the path of the oncoming storm. All told, the warblers travelled 1,500 kilometers (932 miles) in five days to steer clear of the tornado-producing system.

Streby suspects that the birds were alerted by low-frequency sound waves sparked by the tornadic storm. Those waves would be right in the range birds can pick up, but undetectable by human ears.

"They might be able to hear the storms coming and make a decision to leave and come back rather than hunker down and try to survive the tornadoes," he says.

Image: Henry Streby with a male golden-winged warbler and the geolocator that the bird carried
Henry Streby with a male golden-winged warbler and the geolocator that the bird carried for more than 12 months, including during the evacuation migration. Gunnar Kramer

Some other sense involved?

Tornado expert John Allen isn't convinced that the birds are hearing the sounds of developing whirlwinds, but he says, "clearly they are sensing something we can't, and that's really interesting. Those warblers are predicting weather better than we are."

There's no doubt that the warblers took the warning seriously, whatever form it came in, says Allen, a postdoctoral researcher at Columbia University's International Research Institute for Climate and Society.

"The distances they traveled are amazing," he says. "They migrated to their nesting area and then two days later they have to fly out to another location. They went to the Gulf Coast and still got rain there. But it's not the rain that worries them, but the temperature differences. Little birds like the warblers have got to keep themselves warm."

The new findings are "incredibly exciting," says Dr. Erica Miller, an adjunct associate professor at the University of Pennsylvania School of Veterinary Medicine. "This is the first really sound data showing that, yes, animals can sense severe storm systems and will evade them. Certainly we have a sense of that from lots of anecdotal stories, like birdfeeders swarmed by birds the day before a big snowstorm comes."

Other evidence for Miller comes from back when she worked at a bird rescue.

"After a hurricane would come through we would brace ourselves in anticipation expecting to see birds thrown around by the storm," Miller says. "But we never saw that. We always wondered, where do the birds go? Somehow they are avoiding damage from the storm."

And it's not just birds that seem to have a sixth sense when it comes to dangerous weather.

"I am most familiar with birds, but I know from talking to my colleagues that even zoo animals will act differently when there is a storm coming," Miller says. "They may spend more time in their dens or more time pacing. They just know something is up."

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Just ask your horse

Horses, both wild and domesticated, seem to have the ability to avoid giving birth in stormy weather.

"We've actually investigated that, but haven't yet published the findings," says horse specialist Sue McDonnell, an adjunct professor of reproductive behavior at the University of Pennsylvania's New Bolton Center and founding head of Penn Vet's Equine Behavior Program. "We have a semi-feral herd that is out 24/7. And it turns out that they delay parturition, and then the first nice day after a bad stretch of weather in the spring we have a flurry of births."

Even domesticated horses being kept indoors will delay labor until stormy weather has passed, McDonnell says.

Though no one can say for sure how animals know a storm is brewing, "it's clear they are better forecasters than we humans are," Allen says.