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In 2011, about three weeks before a magnitude-7 earthquake hit Peru, mammals and birds reportedly started clearing out of a national park in the Andes. You've probably heard stories like this before, about animals that seem to somehow sense an earthquake coming.

Unfortunately, a 2018 review of more than 700 of these reports found that most of them were just anecdotes or single observations; they couldn't really be backed up scientifically. So recently, different groups of researchers have been trying to get to the bottom of this claim for real. They've been trying to figure out if there really are changes in animal behavior before an earthquake—and what could possibly explain them.

Now, you might think, given the hundreds of times people have reported that animals were behaving oddly before an earthquake, there must be something to it. But the problem is, humans are pattern-finding machines and we're also prone to a psychological phenomenon known as hindsight bias where we think things that happened make sense after they happened but not beforehand. We kind of can't trust our memories.

So, instead of looking back after an earthquake happens and trying to remember what animals were doing, it's better to track animal behavior over a long period of time. That way, when an earthquake happens, we can use data to compare animal behavior before and after. And in a few cases, scientists have actually been able to do that.

For example, in 2014, researchers at a farm in Japan tracked the amount of milk a few dozen cows were making each day. Which might sound like a weird metric, but since most farm animals get milked at least once a day, it was an easy way to monitor their behavior. And the study found that, on average, cows produced less milk in the three weeks before an earthquake.

Authors could not explain why that was happening, but it wasn't the only study that measured a change in the behavior of farm animals before a quake. A couple years later, in Italy, researchers in a separate study mounted accelerometers on a farm's cows, sheep, and dogs to track their movements over a few months between 2016 and 2017. They basically put fitbits on them.

And the data showed that about five hours before a quake hit, the animals' activity patterns did change significantly. Not only that, but the closer they were to the earthquake, the earlier their behavior changed—possibly because whatever signals they were detecting were stronger. The results were interesting for two reasons:.

First, they suggested that it might be possible to set up some kind of early warning system for earthquakes using—of all things—farm animals in different locations. But second, they showed that it wasn't enough just to track a single species— a good prediction required data from multiple animals that captured how they interacted with each other. And soon, we're actually going to have a lot more data like that.

At the beginning of 2020, scientists from Germany and Russia launched a project called Icarus that tracks the movement of thousands of birds, mammals, and insects across the globe. Rather than just looking at what one animal or a small group of animals is doing, the idea behind Icarus is to use computer algorithms to analyze big patterns of movement. To do this, researchers plan to tag thousands of animals with small transmitters that regularly send information on their location, activity, and local weather conditions to an antenna mounted on the International Space Station.

It is an enormous project. And right now, it's still in its test phase, but the goal is that, by the end of 2020, researchers will be able to start gathering data and seeing how well it can be used to predict earthquakes and other natural events, like volcanic eruptions. All these findings are pretty exciting, and recent advances in things like artificial intelligence and satellite technology have made these sorts of studies easier.

But despite all of the evidence that at least some animals may be able to sense earthquakes well before they happen, we still don't know how they' re doing it. Some scientists hypothesize that animals might be sensing vibrations in the Earth from movements in the crust right before a quake, but there's no strong evidence for that. However, it's also possible that animals are picking up on other environmental events that are triggered by that movement in the crust.

For example, the air can become electrically charged as the squeezing and shifting of the Earth break chemical bonds in minerals, releasing charged atoms into the air. Some animals may be able to pick up on that change in the air itself. Those charged atoms can also dissolve into water, turning the water acidic.

And we know that, for instance, amphibians are super sensitive to changes in water chemistry because their skin is permeable. Which could explain why a whole bunch of toads fled their regular breeding pond five days before the 2009 earthquake in L'Aquila, Italy. Scientists who observed this behavior didn't measure the water acidity, so we don't know for sure.

But at least it's plausible. And as we learn more about how animals behave around earthquakes— and how they might detect the early signals of them— we may be able to better protect ourselves from the disasters they cause. Whether it's by setting up a network of farm animals or building sensors that mimic certain animals' abilities, perhaps we can learn from them how to predict earthquakes on our own.

To learn more about how scientists study earthquakes, you can watch our episode on earthquake science and the disaster that created it. And, as always, thank you for watching SciShow! [♪ OUTRO].