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.

A wild discovery

With bad news emerging from Kruger Park this month that a pack of wild dogs was wiped out by Canine Distemper, Wild dogs here at Singita Sabi Sands have put smiles back on everyone’s faces with the discovery of a den site and at least seven new pups.

The excitement began with the sight of a heavily pregnant alpha female moving with the pack, followed days later by tracks and signs of just a few dogs at a time, indicating that perhaps the pack had found a den site nearby. Guides and trackers made exploratory walks in different areas to try to find the den site, but it was the dogs themselves that ended up leading us straight to their chosen spot.

In the days following the discovery of the den, (a hole in a termite mound shaded by a beautiful Scotia tree), a continued presence of different individuals guarding the entrance as well as clear signs that the alpha female had been nursing, kept guides and guests on the edges of their seats, hoping and wishing for the first glimpse of the pups.

At last the day came, and what a sight it was! Four tiny balls of fluff with white tails wobbled their way out the den entrance. Keen to explore, they slid and staggered their way down the termite mound and out into the sunshine. The alpha female seemed to have her hands full, continually picking up the braver individuals in her mouth and bringing them back closer to the den.

With a gestation of 69-73 days on average, pups are born black and white and only start to develop their tricolour tan in the second month. For the first ¾ weeks before they emerge, the alpha female stays at the den while the pack goes hunting. Puppies can be weaned as early as 5 weeks, and become dependant on meat disgorged by returning pack members. By 7 weeks, the puppies loose their rotund shape and assume adult conformation. By 8-10 weeks the pack abandon the den after which the youngsters gain most of their food directly from a kill. Aggression is rare within the pack, with peace and good-will maintained through ritualized begging, a technique all young canids employ to make adults regurgitate food for them.

The secret social lives of plants

Contrary to the long held idea that plants are un-communicative, recent research has made it clear that they do in fact conduct informative exchanges between themselves. Film fans might be reminded of the 2009 blockbuster Avatar. On the moon where the movie takes place, all the organisms are connected. They can communicate and collectively manage resources, thanks to “electrochemical communication between the roots of trees."

Tree of souls....Avatar

Although the general theory of plant communication is not new – plant scientists discovered it in the 1980’s – more accurate experimentation is now helping us understand more about how and why they communicate. And it is certainly more then mere gossip, but an important means of spreading news about danger.

The ability to no only react to danger but to warn others of it has been a controversial finding, suggesting that a brainless tree can not only send and receive messages, but interpret them as well. Despite the growing evidence that plants are capable of communication, many plant scientists still question whether this cross talk is biologically meaningful. No experiment has yet demonstrated that the signalling between neighbouring plants can benefit the emitting plant, prompting some researchers to suggest that “eavesdropping” is a more accurate description of what has been observed than “intentional” communication.

This diagram displays how plants communicate. It is not only hungry animals they have to be aware of, but insects too! Source: Logan Parsons, The Science Magazine

Back on on earth, scientists have revealed that plants communicate through the air, by releasing odorous chemicals called volatile organic chemicals (VOCs), and through the soil, by secreting soluble chemicals and transporting them along thread-like networks formed by soil fungi. It turns out almost every green plant that has been studied releases its own cocktail of these chemicals, and many species pick up and respond to the various messages. As an example, the smell of cut grass — a blend of alcohols, aldehydes, ketones and esters — may be pleasant to us but to other plants signals that danger is on the way. 

Wouter Van Hoven, a zoologist from Pretoria University found that when Acacias were nibbled on by antelope, they produce leaf tannin quantities that are lethal to the browsers, forcing them to move on, and in addition the acacias emit ethylene into the air, which warns other trees of the impending danger. Trees up to 50 yards away then react to this message and step up their own production of leaf tannin within just five to ten minutes. You don’t need to be a scientist to see this in action…next time you are watching giraffe, notice how they tend to feed in the opposite direction of the wind, avoiding the bitter leaves from trees that have been pre-warned and already upped their tannin levels! The defensive compound that gets emitted from the leaves is called Jasmonic acid, providing the name “Jasmonation” to the process of the tree’s talking to each other.