Elephants will respond to signals transmitted through the earth without a sound whispering through the air. This has been shown by a team of scientists working at a waterhole in Etosha, Namibia, where they seismically transmitted a recording of a distress call to herds of wild elephants. The elephants showed defensive behaviour, clustering together and turning at a 90-degree angle to the source of the seismic signal before leaving the waterhole much faster than they would otherwise.
The findings were recently published in the journal Behavioural Ecology and Sociobiology. Although it has long been suspected that elephants 'hear' seismic signals, the paper is the first to scientifically document that elephants hear and respond to impulses transmitted through the ground.
Insects, amphibians, reptiles and small mammals have all been shown to use seismic messages to communicate, but this is the first example published about large mammals. The researchers used an alarm call recorded several years previously when a breeding herd at the same waterhole encountered lions.
The recorded call was transformed into vibrations in the ground by special buried equipment, while a microphone checked that no audible noise was created. The same distress call, when played audibly over loudspeakers to herds at the waterhole, had caused a swift retreat.
The elephants' reaction to the seismic message was similar, but not as extreme. Debate is still ongoing as to how elephants receive seismic signals, but possibly the signal travels through the elephants via their toe bones to their middle ear, where one of the bones is able to receive seismic information.
Other means of receiving ground vibrations could include special nerves in the elephant's feet (which have yet to be described by scientists) or by using some of the many nerves in the trunk when the trunk is placed on the ground.
The scientists performing the study, led by ecologist Caitlin O'Connell-Rodwell, have experimentally determined that elephants might be able to receive seismic signals created by other elephants from up to 2km away. Other studies have said that depending on soil types, elephants could theoretically intercept seismic messages from up to 16km away.