Seismic communication, also known as vibrational communication, is an act of communication through vibrations of the substrate (def.: an underlying substance or layer). This substrate could be the earth, a plant stalk or leaf, a spider’s web, honeycomb, body of water, or any number of substances. It is an ancient form of communication seen straight across the animal kingdom; it has been reported in mammals, birds, insects, amphibians, crustaceans, and worms.
This form of communicating can be used to speak within ones species, across species lines, and used in mimicry to fool the other guy. Who amongst us that have had rabbits as pets have not heard the thumping of one of those big feet when inadvertently startled poor old Mr. Fluffy Pants? Many animals will use this type of communication to warn others of their herd/family group of impending danger, to signal courtship, and/or to basically tell the other guy where you are at. Ba-da-dump…still right here, man! It is a more effective means of communication than vocalizing because it can be heard at greater distances.
Seismic communication is used within a species grouping. Deer will stamp their feet to alert the rest of the herd that there is a predator within their midst and beavers will slap the surface of the water when frightened to make sure that the collective knows to be wary. The Cape mole-rat uses foot drumming in male-male competition to say, “Hey, I have much more food stuffs than you and would make the far superior mate.” In this, they avoid any real fighting amongst themselves with the better drummer winning like some subterranean battle of the mole-rats bands.
It is used as an inter-specific communication. The vibrations of thousands of hooves stampeding will alert every animal on a plain to danger. This increases the number of animals running in said stampede and thus increases the individual’s chance of survival. The banner-tailed kangaroo rat will produce very complex foot drumming when confronted with a snake to both alert its offspring but also to let that snake know that it is alert so a successful attack is less likely.
An off-branch of inter-specific communication is mimicry. Several animals have adapted to use the vibrational signals of predators to attract prey. European herring gull, wood turtles, and humans have all learned that if they tap the ground in the right vibration, earthworms will rise to the surface to avoid the moles that they think are after them. Other animals will fool their prey into an ambush situation with the vibrations they make. Several types of spider will vibrate another’s web in a way that signals caught prey. So when that first spider comes out to what he thinks is his lunch, the table is turned and he becomes the lunch.
One of the more interesting animals that use seismic communication is elephants. I think that elephants are immensely interesting for a number of reasons but this in particular is pretty cool. Elephants live in very tight-knit family groups and must work together to survive. Because of this and their very high intelligence, they have a complex system of communication. Elephants use foot stomping to alert the herd to any perceived danger just like the rabbit and deer mentioned above but they can vocalize a low-frequency rumble. Although elephants have many different vocalizations ranging from trumpeting to snorts to cries, it is this low-frequency rumbling that carries the furthest distances. This is especially useful in areas of dense vegetation such as the jungle where much of the information can be lost in the foliage and over greater distances. A seismic message can travel 8-9.5 km as opposed to the 1.6 km that a vocalization through the air travels.
Dr. Caitlin O’Connell-Rodwell and her colleagues from the Stanford University School of Medicine have been studying elephant communication and have discovered a lot about it. This seismic energy best transmits between 10 and 40 Hz. When an elephant rumbles, this sound travels through both the air and the ground but this information does not make it to the receiver at the same time. Elephant sounds travel at approximately 309 metres per second through the air and 248-264 metres per second through the ground. This differential is provides the elephants with the information about how far away the caller is and they can react accordingly. This differential also pro
vided the herd with the directionality of the call and the herd will align themselves perpendicularly to the source to, presumably, to maximize the interaural time differences used for localization of these low-frequency rumbles.
And how do they hear these seismic messages? Through their feet and trunk. When they hear/feel this rumble, they will stand still and press their feet into the ground to receive as much information as they can. They have a pad of fat at the back of their foot that spreads out when they stand on it. In the front and the back of their feet they have layers of cells called Pacinian corpuscles that area extremely sensitive to vibration. These cells are found in their trunks as well which is why they are constantly touching things with. When a vibration disturbs these cells, it sends a nerve impulse to the brain and lets the elephant both hear and feel at the same time.
The next time you feel the rumble of a passing truck, remember that you too are an animal that interprets seismic vibrations. I don’t know about you but if I feel a deep rumble beneath my feet, I have a flight response take over my logical mind; it could be a thunderclap or an earthquake.
–Janice Willson
References:
https://youtu.be/iYM9oXftLIQ
https://news.nationalgeographic.com/news/2014/05/what-elephant-calls-mean/
https://phys.org/news/2005-05-scientists-unravel-secret-world-elephant.html
Photo source: African elephant herd, Ikiwaner; Elephant female and calf, Charles J Sharp; Elephant foot, Psych USD
