The strange behaviour of animals before earthquakes has often made it seem that nature might know of seismic movements before humans. However, scientists have now proved it with a study of toads in L'Aquila, Italy.
Vibrations in rocks beneath the Earth's crust before an earthquake release particles that react with groundwater once they reach the air.
The toads are so highly attuned to their habitat that changes in the chemistry of the environment cause them to leave days before the earthquake occurs.
The chemicals from the rocks convert air molecules into charged particles known as ions. Dr Friedemann Freund, a geophysicist from NASA who led the research with Dr Rachel Grant from the UK's Open University, said:
"Positive airborne ions are known in the medical community to cause headaches and nausea in humans and to increase the level of serotonin, a stress hormone, in the blood of animals."
Although weird animal behaviour has been observed before, the tales were merely anecdotal and not scientific.
Snakes emerging from hibernation in the middle of winter were seen a month before an earthquake in China in 1973.
The exodus of cold-blooded reptiles slithering out of their nest in sub-zero temperatures baffled scientists at the time.
Dogs have also been heard barking before tremors. In 2003, a Japanese scientist made headlines suggesting that their behaviour could be used to predict earthquakes, but his advice was shrugged off.
Andy Michael, a geophysicist at USGS told the National Geographic: "What we're faced with is a lot of anecdotes. Animals react to so many things — being hungry, defending their territories, mating, predators — so it's hard to have a controlled study to get that advanced warning signal."
However, the L’Aquila toads study were being investigated in detail before the 2009 earthquake in Italy.
Dr Grant was monitoring the toads as part of an Open University Phd.
"It was very dramatic. It went from 96 toads to almost zero over three days. After that, I was contacted by Nasa," she told the BBC
She added: "When you think of all of the many things that are happening to these rocks, it would be weird if the animals weren't affected in some way."
"Once we understand how all of these signals are connected, if we see four of five signals all pointing in [the same] direction, we can say, 'OK, something is about to happen'."
The team's findings are published in the International Journal of Environmental Research and Public Health.
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