The common toad may be ugly, warty and squat, but it is blessed with an extraordinary gift. It has an uncanny ability to predict earthquakes several days before they occur, according to a remarkable study that documents for the first time an extraordinary "supersense" in wild animals.
Scientists studying a colony of breeding toads living in an Italian lake found that they suddenly disappeared en masse five days before a magnitude 6.3 earthquake struck the town of L'Aquila in central Italy in the early hours of 6 April 2009. Most remarkably, L'Aquila is 74km (46 miles) from the lake.
The researchers behind the observations believe there is no explanation other than the fact that the toads must have been able to detect some changes in their environment which led them to believe that violent tremors were imminent. Within days of the earthquake, the toads had returned to their breeding pool to continue spawning.
Anecdotal reports of animals behaving strangely before an earthquake are not unusual, but most cannot be properly assessed scientifically because they rely on eyewitness accounts after the event. In this case, however, the scientists were monitoring the toads long before the earthquake happened.
"Our study is one of the first to document animal behaviour before, during and after an earthquake. Our findings suggest that toads are able to detect pre-seismic cues such as the release of gases and charged particles, and use these as a form of earthquake early warning system," said Rachel Grant of the Open University in Milton Keynes.
"We looked at the weather and other possible causes of the sudden disappearance of the toads, but nothing seemed to fit. There didn't seem to be any other reason for it except that they had somehow managed to sense that an earthquake was going to happen," Dr Grant said.
The lake where the toads were breeding was being monitored nightly by Dr Grant and her Italian colleagues, who were studying the effect of moonlight on amphibian behaviour. Males of the common toad, bufo bufo, collect in large groups of up to 100 individuals to mate with passing females.
One night, Dr Grant found that the number of males had fallen dramatically, which she thought may be due to cold weather. However, for the next five nights, she failed to find a single toad, which was unprecedented.
"They could have gone back up into the high ground around the lake or they could have dug into the mud – we don't know," she said.
Russian scientists suggested that the toads may have been able to detect the release of radioactive radon gas from the ground, or the presence of charged particles in the ionosphere of the night sky, Dr Grant said. If so, it may be an evolved ability to protect the slow-moving animals from the frequent mud slides caused by earthquakes, she added.
"There could be more evolutionary pressure on them to develop an effective early seismic escape response," she said.
The study is published in the Journal of Zoology.
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