Elephant rumblings

Sit near an elephant herd for a while, and you may hear a low rumble. At such a low frequency, many often think it may be lions calling in the distance. But the guide says no, and you hear it again, unmistakably coming from the elephants. Could it be that elephants share the same stomach rumble as humans? Observing for longer you may notice a change of behaviour while a rumble is emitted…the raising of a head, flapping of ears or opening of a mouth…but what is the connection and what does it mean?

Not quite the loud trumpeting sound one would expect from an elephant, these rumbles are in fact one of the huge range of elephant communication pitches.With sounds varying from higher frequency roars, cries and trumpets, to low frequency rumbles, elephant communication is far more complex then you can imagine. To get a sense of the range, if we compare to humans, a typical human males voice in speech fluctuates around 110 hertz, a child around 300 hertz. With elephants, a typical male rumble averages at 12Hz! Frequencies of elephant calls can vary from 5Hz all the way through to over 10,000Hz. An average human can hear frequencies as low as 20Hz, so there is a lot that goes on that is simply outside our realm of hearing.

In addition to this, elephants also have a “pharyngeal pouch”. This unique structure, found at the base of the tongue is used as an emergency water store (you may have occasionally seen elephants insert their trunk into their mouth and withdraw water - elephants are able to store several litres of water in this pouch for use during extreme hot weather). In having to house the pharyngeal pouch, the loosely attached larynx is therefore housed lower then usual, enlarging the resonance chamber further and hence helping in the production of lower frequency calls.

As per the natural world, nothing is the way that it is without good cause. Research has shown that seismic energy (waves of energy that travel through the ground) transits at its most efficient between 10-40Hz – the exact same range as elephant’s rumblings. Elephants can thus communicate in sound waves through the ground and can detect these vibrations through special cells called “Pacinian corpuscles”. These have been found in both their trunks and also their feet, concentrated in the front and back dermal layer. Vibrations deform the Pacinian corpuscles, sending nerve signals to the brain. These signals can be picked up from individuals communicating over 10km away.

Whilst the extent of elephant communication has been well researched, questions still remain about how they manage to reach this extraordinary range of notes. There are two possible theories. One theory holds that the rumbles are made by the elephants’ vocal cords, which, like ours, consist of two flaps of flesh in the larynx. Much like a slit made in a blade of grass, the flaps vibrate and produce sound when air rushes through them. The longer and looser these flaps, the lower frequency of the sound. Elephants then use their mouths and long trunks to shape those sounds. The second theory is that elephants, like cats, are purring. Purring is not passive: each pulse of the purr is made by voluntary contraction of the muscles around the larynx. Muscles can contract only so fast, so purrs are low pitched. That’s why a kitten, whose vocal cords are so small that it can only squeak when it meows, can make a deep rumble when it purrs. When it comes to elephants though, experiments on a deceased elephant donated to science proved that air passing through the larynx is enough to make it rumble – no muscle control required – hence elephant purring is a mere fancy.

Certainly the massive size alone of elephants’ voice box (an elephant’s larynx is eight times larger than ours) and length of their vocal cords help produce such low sounds, but the extension of their resonating chamber in the form of a 2m long trunk makes a significant difference too. They also have the ability to achieve very different frequencies of rumble depending on factors such as how high or low its head is held, if its mouth is open or closed, and even the movement of their ears. Scientists have discovered that the muscles and bones that support the tongue and larynx in elephants are different from other mammals. In most animals, a series of nine bones (hyoid apparatus, a series of bones at the base of the tongue) connect the tongue directly to the skull, whereas elephants have only 5 bones that connect via muscles, tendons and ligaments. This looser arrangement allows for much greater movement of the larynx and thus can resonate lower frequency sounds.