Why did a tsunami that killed more than 150,000 people harm no more than a handful of animals?

Over the last few weeks, we have been bombarded with terrible images of chaos, destruction and death. The cost in human lives has been made brutally clear. Yet wildlife officials in Sri Lanka, where more than 30,000 people have been reported dead so far, insist that there have been no recorded animal deaths. Similar reports are appearing from other devastated areas and one cannot help but wonder: where were they all when disaster struck?

As anecdotal evidence emerges of unusual animal behaviour prior to the catastrophe, the debate over whether animals can sense impending disaster and flee from it has resurfaced with a vengeance.

The roots of this debate stretch back to ancient Greece. In 373BC, historians recorded that animals including rats, snakes and weasels deserted the Greek city of Helice en masse just days before it was destroyed by an earthquake and tsunami. Tales of animal behaviour that appears to anticipate disaster have surfaced across the centuries ever since.

In spite of this wealth of anecdotal evidence, however, the majority of the scientific community does not recognise a link between animal behaviour and earthquakes. The United States Geological Survey (USGS) says on its website:

"Changes in animal behavior cannot be used to predict earthquakes. Even though there have been documented cases of unusual animal behavior prior to earthquakes, a reproducible connection between a specific behaviour and the occurrence of an earthquake has not been made."

In the recent press coverage of the Indian Ocean tsunami disaster, Andy Michael, a geophysicist at USGS, was quoted as saying: "What we're faced with is a lot of anecdotes. Animals react to so many things – being hungry, defending their territories, mating, predators – so it's hard to have a controlled study to get that advanced warning signal."

True, but this did not stop the USGS from attempting an extensive series of these studies in the late 1970s. The trigger for this flurry of activity was what has probably become the most famous example of alleged animal activity prior to an earthquake in modern history.

On 4 February 1975, Chinese authorities successfully evacuated Haicheng, a city with one million people, just days before a 7.3- magnitude earthquake struck (the Indian Ocean tsunami was caused by an 8.9-magnitude earthquake). They claimed that their decision to evacuate was based in part on observations of animal behaviour.

The ensuing excitement at USGS was further boosted in 1977 when researchers found that 50% of local people surveyed after an earthquake in California had noticed unusual behaviour in their pets prior to the event. The impossible suddenly seemed possible.

But it was followed by disappointment. The California findings were not deemed to merit further action and it emerged that the Chinese had neglected to mention a rare series of smaller quakes that had occurred in the area before the big one. The USGS ceased all research into a possible link between animal behaviour and earthquakes in 1980.

China did not, and nor did Japan. Whether because of their susceptibility to earthquakes or a philosophy that embraces nature, these two countries have continued to research animal behaviour as a possible earthquake prediction tool. They have had false alarms, of course, but they have had successes too.

Continued research in the Far East led to the headline-grabbing news in September 2003 that a Japanese medical doctor had conducted a study which demonstrated that erratic behaviour in dogs could be used to forecast earthquakes.

The study was contentious – The Guardian was at pains to point out that it was "even being regarded with caution in Japan" – but its reporting here reflects the continued allure of believing that animals have some kind of sixth sense to warn them of impending danger, even in the absence of scientific evidence.

The USGS is correct in saying that "a reproducible connection between a specific behaviour and the occurrence of an earthquake has not been made". However, just because there is no way of explaining something does not mean that something does not exist. The Chinese have taken this view in their construction of a network of experimental stations to collect and analyse animal behaviour observations.

Where Western geologists and seismologists have been reluctant to entertain the notion of animal behaviour as a predictive tool, biologists and behaviourists have proposed various theories to explain how animals may sense earthquakes seemingly before they happen.

Rather than postulating the existence of a mysterious sixth sense, the majority of these theories draw on animals' highly evolved existing sensory apparatus to make their case. Remember too that animals respond to each other: the flight of one may trigger an exodus.

Earthquakes shake the ground and one of the most obvious ways in which animals could `predict' them is by picking up advance vibrations that are too small for us to feel. Many animals, ranging from rodents to elephants, are known to use shockwaves in communication.

Joyce Poole, Director of the Savanna Elephant Vocalization Project, has worked with African elephants for 25 years and says that research on acoustic and seismic communication indicates that elephants could easily pick up vibrations generated from an earthquake-tsunami. Fellow researcher Caitlin O'Connell-Rodwell describes how the soft skin on the undersides of elephant feet is comparable to the taut surface of a drum and is similarly sensitive to the tiniest vibration.

But even if they can pick up vibrations that warn them of impending danger, how do they know where to run? A Dutch ethologist, Paul Koene, explains that elephants instinctively head for higher ground when they feel threatened. This fits in well with anecdotes of Sri Lankan elephants breaking loose for the hills just before the tsunami hit.

An alternative theory that has gained acceptance in recent years is that animals pick up on magnetic field changes that occur near the epicentre of an earthquake. Many animals are known to use the earth's magnetic field to navigate, including pigeons and turtles.

A third hypothesis postulates that it is changes in electric charges that alert animals to a quake. Certain species of fish are known to be sensitive to variations in electric fields – the electric eel is the most obvious example – and researchers believe they may pick up on the electric charge variations in water that sometimes precede earthquakes.

On land, organisms may respond to changes in the polarity and concentration of atmospheric ions, or charged particles. This could allow animals to detect the air-ionising effects of radon gas, which is sometimes released from the ground before an earthquake.

A piezoelectric effect has also been invoked: changes in the pressure exerted on crystals like quartz result in electrical charging of the crystals' surfaces. This is believed to generate enough electrical energy to drive the creation of airborne ions before, during and after an earthquake. Animals may anticipate earthquakes much as they sense oncoming thunderstorms.

That organisms should respond to vibrations, magnetism or electrical charges does not exhaust the range of theories that advocates of an earthquake-animal behaviour link have put forward.

More controversial hypotheses include the idea that animals react to ultrasound emitted by fracturing rock before an earthquake occurs. This theory has been heavily criticised by geologists who claim that no such sound is emitted.

Yet the most contentious argument of all remains the idea that animals do indeed possess a sixth sense, something fundamentally different to the five senses that we currently recognise. Perhaps animals perceive and respond to stimuli that science at present simply cannot measure.

Here we enter the realm of biologists like Rupert Sheldrake, who try to explain mysteries such as why dogs sometimes seem to anticipate the arrival of their owner, even in the apparent absence of any physical signals.

Critics will be inclined to make short thrift of the sixth sense theory in its most literal form and will point out the lack of scientific evidence to support it. Nevertheless, and here we return to the essence of the problem, critics and advocates alike suffer from the problem of how to conduct controlled experiments to test the earthquake-animal behaviour hypothesis.

Everyone agrees that there is an abundance of anecdotes detailing unusual animal behaviour prior to earthquakes and no one denies that amazingly few creatures appear to have died in the wake of the recent tsunami. Yet neither believers nor sceptics can realistically confirm or deny a direct link between animal behaviour and an impending disaster.

As scientists, we instinctively question and search for evidence. Perhaps this is a case where we should follow the East in their simple acceptance of a natural phenomenon. This does not mean that we should cease studying how animals may `predict' earthquakes; it means that we should use their abilities, even if we do not understand them, to save human lives where we can.

The Anthropological Survey of India's plan to immediately document the animal-based warning systems that enabled all five aboriginal tribes inhabiting the badly-hit Andaman and Nicobar islands to escape unscathed is a step in the right direction.

Sonja van Renssen

Informant: Sylviane


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Januar 2005

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