The sub-20 hertz conversation
In the expansive savannas of Kajiado County, parts of the Amboseli ecosystem, elephants carry on conversations inaudible to human ears. They are masters of infrasound, producing powerful, low-frequency "rumbles" with most of their energy concentrated between 14 and 35 Hertz (Hz). The lower limit of human hearing is around 20 Hz. These sounds are not faint whispers; an elephant's rumble can reach 117 decibels, a volume comparable to a construction site or an ambulance siren. This immense power allows the calls to travel up to 10 kilometers under ideal atmospheric conditions.
The sound originates in the larynx, the largest known among mammals, which contains vocal folds about eight times the size of a human's. Much like a person speaking or singing, elephants produce sound by passing air from the lungs over these folds, causing them to vibrate. The sheer size of the vocal folds naturally results in a very low-frequency sound. Different rumbles serve distinct purposes and have been identified by researchers in nearby Amboseli National Park. There is a "greeting rumble" for reuniting family members, a "contact call" from separated individuals, and a specific "musth rumble" emitted by males during their reproductive period.
A world felt and heard
Elephant communication involves sound waves traveling through the air. The low-frequency rumbles also transmit powerful vibrations through the ground as seismic waves. Elephants are uniquely adapted to detect this subterranean information. Their feet contain large cushion pads with cartilaginous nodes and concentrations of specialized nerve endings called Pacinian corpuscles. These corpuscles, which are extremely sensitive to pressure and vibration, are densely packed in the dermis layer of the toes and heel.
When seismic waves travel through the ground, they are detected by these receptors in the feet. The signals are then believed to travel up through the elephant's massive leg and shoulder bones to the middle ear, a process known as bone conduction. This gives the elephant a physical sensation of calls from distant herds. They can distinguish between familiar and unfamiliar alarm calls and even orient themselves toward the source of the vibration. Locomotion, like a mock charge, can produce seismic waves that travel up to 32 kilometers, while vocalizations can travel 16 kilometers through the ground. This dual-channel communication system, acoustic and seismic, allows elephants to stay connected across the vast landscapes of Kajiado.