How low frequency sound gives some animals a peek into the future...
Have you ever been caught out by the Great British weather? Leaving the house under clear skies, only to be caught short without an umbrella by the sudden torrential downpour hours later? Well, it might be time you got yourself an elephant.
Scientists in Namibia have recently discovered that the world’s favourite pachyderm may be able to predict the weather. The African elephant undertakes vast seasonal migrations, yet the factors that drive these movements are relatively unknown. However, by using a GPS system to track the movements of nine individuals, Garstang and his colleagues believe they have the answer.
Across a time period of seven years, the elephants would repeatedly begin their extensive migration a few days before the end of the dry season. In several instances these movements mirrored those of herds in other locations, suggesting this was not a random occurrence. This implies these animals were moving in response to an environmental signal – but what? Seasonal changes in vegetation do occur; plant cover and type would vary according to the strength of sunlight, the acidity of the soil, and numerous other factors. But these variables are complex and differ largely between regions, and therefore this does not explain the simultaneous migration of multiple individuals. It was also hypothesised that the onset of rain would, naturally, signify the beginning of the wet season. However, elephant movements occurred well in advance – days or even weeks – of any rainfall in that region. Could it be that these elephants were giving Michael Fish a run for his money by making a forecast?
Well - unbelievably – yes. Determined by satellite precipitation observations, the timing and location of rain events were compared with the elephants’ behaviour, and demonstrated that significant changes in movement patterns were observed prior to a downpour. In fact, the predictive ability of the elephant is so finely tuned that their movements were often triggered by rainstorms up to 300km away. So how do these magnificent beasts acquire such powers of fortune telling? Are they psychic? Or are they just avid listeners to the BBC weather report?
The explanation lies with something known as ‘infrasonic sound’. Sometimes referred to as low frequency sound, this is a term used to describe sound characterised by frequencies below 20 Hz (Hertz) or cycles per second, which is below the normal limit of human hearing. However, it is proven that elephants – amongst other species – are able to detect such frequencies. Natural phenomena such as thunderstorms produce infrasonic signals that can travel great distances, therefore it could be this rain-system-generated infrasound that is the trigger for the movements of savannah elephants.
Don’t despair if you don’t have Dumbo nearby to help choose your outfit in the morning. The ability to predict – or rather, detect – oncoming natural disasters such as storms and earthquakes has been demonstrated by other creatures as well. Animals have been known to react to infrasonic waves travelling through the earth, using them as a tell-tale warning sign of impending danger. A good example of this is the Indian Ocean tsunami that devastated the shores of Indonesia. Hours before any visual warning signs, animals were reported to flee the area. In Sri Lanka’s wildlife park Yala, which is home to buffalo, monkeys, big cats and – you guessed it – elephants, there were no reported animal casualties, yet only 30 of the parks 250 tourist vehicles returned. Similarly, history is littered with reports of animals behaving oddly in the lead up to a natural disaster; giraffes, hippos, tigers, pigeons, even cassowaries—can hear infrasound waves. A recent study testing the responses of cats and dogs prior to earthquakes found that the majority became agitated many hours before the event. The research, carried out in Western Piedmont, Italy, showed that many household pets would give “early warnings” by either pacing or barking out alarm signals. Interestingly, these early warnings coincided with the arrival of p-signal waves associated with infrasound emission.
However, our knowledge of these unusual behaviours are still in their infancy. Whilst seismic events are known to bring about strange behaviours in animals, it is still uncertain as to whether it is indeed infrasound that triggers it. It could also be a result of electromagnetic waves, or simply the intense vibrations from deep underground. Rayleigh waves – waves that spread out from the epicentre of an earthquake at ten times the speed of sound – also go unnoticed by us, but are detected by birds, insects and other species of mammal. But even the heaviest of rainfalls wouldn’t be sufficient to produce such vibrations. In the case of the Namibian elephants, it seems that infrasound is the most likely explanation.
So, how is it that so many mammals possess this superior knowledge, when us humans are successfully hoodwinked by blue skies? It turns out we do feel intrasound – the problem is, we don’t know what it is we’re experiencing. Some people report being spooked or even begin to believe in divine intervention; intrasound has been proved to provoke feelings of fear or awe, and may cause us to believe we have experienced something supernatural. So the next time you see a ghost, you might want to pick up an umbrella.