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There have long been reports of animals behaving strangely before large quakes, including an account of snakes, weasels and rats leaving home prior to an earthquake in Greece in 373BC. But there is still a lack of scientific evidence.  A new study in Japan investigates pet owners’ reports of cat and dog behaviour, and changes in dairy milk production, before the magnitude 9 earthquake in 2011.

The earthquake and tsunami in Japan on 11th March 2011 was devastating. After the quake, in December 2011 and January 2012, Japanese scientists Hiroyuki Yamauchi et al (2014) conducted an internet survey of pet owners. As well as obtaining demographic information about pets, they asked about any unusual behaviour exhibited in the minutes, hours and days prior to the earthquake. The checklist included things like howling and barking (for dogs), vocalizing (for cats), trembling, being restless, and escaping. 

The questionnaire was distributed nationally, and postal codes were used to say how far away the animal lived from the epicentre. 1,259 dog owners and 703 cat owners took part. 

In addition, the scientists took advantage of existing data about the amount of milk produced by dairy cows. The quantity of milk each cow provides every day is recorded automatically at milking facilities. 86 Holstein dairy cows were used in three different locations: Ibaraki prefecture (340km from the epicentre), and at Kanagawa and Shizuoka prefectures (further away). Milk production for each day from 1^st Jan 2011 until 31^stMarch 2011 was examined. 

The reasoning is that if cows are able to predict an earthquake, they will be stressed and make less milk. The analysis took account of the length of time since calving and the temperature and humidity, as these factors are known to affect milk yield. 

Animals might detect an earthquake ahead of people for several reasons, according to the researchers, including that cats and dogs have a wider hearing range and better scent detection than humans. They say, “possible candidate stimuli include changes in atmospheric pressure, changes in gravity, ground deformation (ground uplift and tilt changes), acoustic signals and vibrations due to the generation of micro cracks, ground water level changes, and emanations of gases and chemical substances.”

The geographical range of dogs and cats in this study was between 140km from the epicentre to 1950km away (cats) and 2350km away (dogs). The results showed that unexpected behaviours were reported by 18.7% of dog owners and 16.4% of cat owners. 

Of those who reported unusual behaviours in dogs, they were most commonly observed immediately prior to the earthquake, in the seconds and minutes before it hit (60% of cases). 16.7% said it happened from 1 to a few hours before. In cats with unusual behaviour, 44.6% showed it immediately prior and 30.4% in the few hours before the earthquake. Some owners reported changes 6 or more days before (6.3% of dogs and 2.9% of cats with unusual behaviour).

The most common reports were of dogs and cats being restless and wanting to be near the owner. In dogs, most unusual behaviours in the minutes and hours before the earthquake occurred closer to the epicentre. For cats the only effect of distance was 2-3 days before the earthquake.

In the immediate area of the quake there were many pre-shocks (including one of magnitude 7.3 on 9^th March). It is possible that cats and dogs were responding to these. However the timing of some unusual behaviours (within a few hours of the quake) is interesting.

The problem with reports after-the-fact is that people may have misremembered. This is where the data on milk yield comes in. In Kanagawa and Shizuoka Prefectures, further from the epicentre, there were no changes in milk production in the time leading up to the quake. However, in Ibaraki Prefecture, the cows produced significantly less milk on 11^thFebruary, and on the 5^th, 6^th, 7^th and 8^thMarch. 

The scientists say, “the facility in Ibaraki showed lowered milk production 6 days before the EQ [earthquake]. The decrease in milk yield continued for four days. This might be because Ibaraki was the closest of the three institutes to the epicentre. If so, milk yield might be useful as an EQ precursor. Furthermore, these decreases of milk-yields were probably not caused by fear responses to the EQ’s shaking, because no seismic swarms … occurred near the location of the institute in Ibaraki Prefecture from the 5 to 8 March 2011.”

These results suggest it might be possible for animals to detect an impending earthquake, but further research is needed to confirm this and to understand the mechanism by which it occurs.

Have you ever noticed unusual animal behaviour before an earthquake?