Despite freezing temperatures, scores of snakes struck from their hibernation in the weeks before a major earthquake struck the 4th Chinese city of Haicheng on February 4, 1975. The behavior of the reptiles, along with other incidents, helped authorities convince the city to evacuate hours before the massive shaking.
For centuries, men have described unusual animal behavior just for seismic events: dogs barking incessantly, cows stopping their milk, frogs jumping out of ponds. A few researchers have tried to substantiate a link. In a 2013 study, German scientists videotaped red wood ants nesting along a fault line and found that they changed their usual routine for a shake, became active at night and became less active during the day. But most such attempts, according to a 2018, relied for the most part on anecdotal evidence and some observations Bulletin of the Seismological Society of America review that examined 180 previous studies.
Now researchers from the Max Planck Institute for Animal Behavior and the University of Konstanz, both in Germany, along with a multinational team of colleagues, say they have been able to accurately measure increased activity in a group of farm animals prior to seismic activity. Although a definitive link has not yet been proven, scientists say their findings are an important step forward in the search for one. “There are the old stories of Aristotle and Alexander von Humboldt who saw this behavior,” says co-author Martin Wikelski, executive director of the Max Planck Institute for Animal Behavior. ‘But only we can do continuous biology of the activities and nervousness of animals. The technical possibilities are finally there. ”
The researchers used highly sensitive instruments that detect accelerated movements – up to 48 every second – in each direction. In separate periods, totaling about four months in 2016 and 2017, they attached these biologists and GPS sensors to six cows, five sheep and two dogs living on a farm in an earthquake-prone area of northern Italy. A total of more than 18,000 tremors occurred during the study periods, with more seismic activity in the first – when a magnitude 6.6 earthquake and its aftermath hit the region. The work of the team was published in July in Ethology.
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The statistical analysis of the paper took into account the normal daily movements and interactions of the animals. It turned out that their activity increased significantly for magnitude 3.8 as larger earthquakes when housed together in a stable – but not when they were grazing. Wikelski says this difference can be linked to the increased stress that some animals feel in confined spaces. Analyzing the increased movements as a whole, the researchers argued, showed a clear signal of anticipatory behavior hours before tremors. “It’s kind of a system of mutual influence,” Wikelski says. ‘At first the cows freeze in place – until the dogs go crazy. And then the cows actually get even crazier. And then that reinforces the behavior of the sheep, etc. ‘
Wikelski says this observation is consistent with theory of collective behavior. That idea was pioneered in part by his Max Planck colleague Iain Couzin, whose laboratory reportedly found evidence that mammals, birds, insects and fish share information that collectively improves survival skills, such as navigating and predator prevention. This “swarm intelligence” can happen within or across species, Wikelski says. For example, “we have done a study on Galápagos marine iguanas, and we know that they actually listen to warnings of mocking birds about the Hawkas of Galápagos,” he adds. “These kinds of systems exist all over the place. We just haven’t really tuned in to them yet. ”
The researchers said the farm animals appeared from tremors anywhere from one to 20 hours ahead, and responded earlier when they were closer to the origin and later when they were further away. This finding, the authors argue, is consistent with a hypothesis that animals somehow feel a signal that is different on the outside. It implies that in the days before an earthquake, displacing tectonic plates push rocks along a fault line. This action causes the rocks to release minerals that drive ions into the air, according to a 2010 study. “The animals then respond to this new sensation,” the authors of a 2013 paper suggested.
Wendy Bohon, a geologist at the Incorporated Research Institutions for Seismology in Washington, DC, who was not involved in the new study, is skeptical about the idea of air ionization. Numerous geologists have tried unsuccessfully to find such a preliminary signal of impending earthquakes, she notes. Bohon admits that Wikelski and his co-authors did some “cool things” to investigate the possibility of animals predicting earthquakes. But she wonders if there were specimens in which the creatures showed unusual activity and that there was no earthquake or did not react before one happened. “My cat could act crazy before an earthquake,” she says. “But my cat also acts crazy when someone uses the opener.” To use the animals as prognosticators, it would be necessary to establish that they exhibited unusual behavior on my own in response to upcoming seismic events, Bohon says. ‘Otherwise,’ she adds, ‘it becomes the’ Boy Who Wolf Cried Wolf ‘. “
Heiko Woith, a geologist at GFZ German Research Center for Geosciences and a co-author of the 2018 review, praised the authors of the new study for measuring more than a single occasion of abnormal behavior. But he says the time frame was still too short. Woith also points out that many studies that claim to show prior earthquake signals often rely on insufficient data collection over time, making it impossible to determine whether a measurement signal was related to an earthquake or just noise.
Wikelski and his colleagues say that their simple study could not discern all potential stimuli to which the animals could respond. But they still claim it is a good first step towards more controlled studies in the future. The researchers are setting up a new project in Italy, such as one in Chile and another on the Russian Kamchatka Peninsula. They hope to test many more species to see if those animals are susceptible to earthquake activity. “We call it a biotreat yacht,” says Wikelski.
