Can Animals Detect Earthquakes?

Over at the always-excellent Discover magazine blog 80 Beats, a fascinating post from a couple of days ago on a topic that has fascinated natural historians for several thousand years now: can animals’ strange behavior provide forewarning that an earthquake is about to strike?

I’ve been reporting a story about earthquake prediction for Parade magazine lately, and spent a day talking with some of the nation’s leading seismologists at Caltech. I came away with a renewed appreciation for the difficulty of the scientists working toward that holy grail of earthquake research, figuring out how to predict the behavior of faults that lie invisible deep beneath the surface of the earth (and which may be fundamentally chaotic in their nature anyway).

All the more intriguing, then, to hear that biologist Rachel Grant, while studying the mating behavior of toads in Italy, may have stumbled upon the first scientific evidence of animals being able to foresee what seismologists could not:

Her team was studying common toads in Italy in April 2009 when the amphibians began to disappear from the study site. This didn’t make much sense to her, the toads abandoning a breeding site in the midst of breeding season. So the researchers tracked them. They found that 96 percent of males — who vastly outnumber females at breeding spots — abandoned the site, 46 miles (74 kilometers) from the quake’s epicenter, five days before it struck on April 6, 2009. The number of toads at the site fell to zero three days before the quake. Grant says her initial reaction to the mass toad dispersal was annoyance—their flight was holding up her research. However, when they began to return the day after the earthquake, things began to make more sense.

It’s an amazing story, a seemingly irrefutable case of cause and effect. But I’m still not buying it. Here’s why.

As geologist Susan Hough explains in her delightful book Explaining the Unexplainable, scientists have been trying to chase down the link between earthquakes and animal behavior for years now. The most intriguing potential link turned up during the Maoist era in China, after the Haicheng region was struck with a series of earthquakes. Concerned that a really big one might be on the way, the authorities enlisted the peasantry in a mass effort to look for clues. Sure enough, reports began trickling in of strange behavior: “Records indicate that snakes and frogs reportedly came out of the ground, something snakes and frogs are not supposed to do during the winter hibernation season,” Hough writes.

The big quake did come, a magnitude 7.3 tremblor that struck Haicheng on February 4, 1975. Because many had been warned that a quake was on its way, fatalities were low.

In China, the successful forecast was taken as a great victory for the People’s Seismology, but from a modern perspective it doesn’t quite hold up. For one thing, along with the reports of strange reptilian behavior there were also numerous small quakes that are a more traditional indicator that a bigger quake might happen.  Hough writes:

The ground was not exactly crawling with snakes, but there were almost one hundred documented snake sightings in the Haicheng region in the month prior to the earthquake. How does one account for this? The simplest explanation is that they were disturbed by foreshock activity, including shocks too small for humans to feel. Or perhaps the reported sightings reflected only a sort of mass hysteria on the part of those doing the sightings. There is no question that the mind is capable of extraordinary invention, if suitably primed. But neither explanation sits entirely well. The number of reports… did not track either the earthquake activity or the sense of urgency among local people and officials. Either explanation could be right; the truth is, we just don’t know.

Personally, I think that Hough is being excessively even-handed in her reluctance to discount both theories. Both seem to be clearly incorrect. A snake that crawls out of its hole a full month before an earthquake, in the dead of winter, is simply doing a terrible job. And while reptiles may be able to sense vibrations in the earth that humans cannot, I doubt that they are more sensitive than seismometers.

I don’t think it was  a case of mass hysteria, either. Not exactly. But if you ask a broad population of people to look for something — especially if you are the Communist Chinese government at the height of the Cultural Revolution — a certain number of them will find it. Back in the mid-’90s, I traveled to Vietnam to do a story about field biologists working on the Laotian border. They wanted to know what birds were indigenous to the area, so they gave one of the local Vietnamese biologists a list of potential species and asked him to check off the ones he saw. A month later, when he turned in his list, they found that he had checked off every single species. In his mind, the best possible accounting of the bird population was one which showed the maximum number of species. I imagine something similar might have happened in Haicheng: asked to report anomalous behavior, the peasants reported anomalous behavior.

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