How Do Animals Predict Earthquakes?

Scientists speculate that changes in groundwater chemistry may be detectable by animals (h/t nc links):

Nasa geophysicist Friedemann Freund showed that, when rocks were under very high levels of stress - for example by the "gargantuan tectonic forces" just before an earthquake, they release charged particles.
These charged particles can flow out into the surrounding rocks, explained Dr Freund. And when they arrive at the Earth's surface they react with the air - converting air molecules into charged particles known as ions.
"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," said Dr Freund. They can also react with water, turning it into hydrogen peroxide.
This chemical chain of events could affect the organic material dissolved in the pond water - turning harmless organic material into substances that are toxic to aquatic animals.
It's a complicated mechanism and the scientists stress that it needs to be tested thoroughly.
But, Dr Grant says this is the first convincing possible mechanism for a "pre-earthquake cue" that aquatic, semi-aquatic and burrowing animals might be able to sense and respond to.

It sounds extremely preliminary, but is interesting nonetheless.