Seismic or vibrational communication is a process of conveying information through mechanical (seismic) vibrations of the substrate. The substrate may be the earth, a plant stem or leaf, the surface of a body of water, a spider's web, a honeycomb, or any of the myriad types of soil substrates. Seismic cues are generally conveyed by surface Rayleigh or bending waves generated through vibrations on the substrate, or acoustical waves that couple with the substrate. Vibrational communication is an ancient sensory modality and it is widespread in the animal kingdom where it has evolved several times independently. It has been reported in mammals, birds, reptiles, amphibians, insects, arachnids, crustaceans and nematode worms. Vibrations and other communication channels are not necessarily mutually exclusive, but can be used in multi-modal communication.
Functions Communication requires a sender, a message, and a recipient, although neither the sender or receiver need be present or aware of the other's intent to communicate at the time of communication.
Intra-specific communication Vibrations can provide cues to conspecifics about specific behaviours being performed, predator warning and avoidance, herd or group maintenance, and courtship. The Middle East blind mole-rat (Spalax ehrenbergi) was the first mammal for which vibrational communication was documented. These fossorial rodents bang their head against the walls of their tunnels, which was initially interpreted as part of their tunnel building behaviour. It was eventually realised they generate temporally patterned vibrational signals for long-distance communication with neighbouring mole-rats. Footdrumming is used widely as a predator warning or defensive action. It is used primarily by fossorial or semi-fossorial rodents, but has also been recorded for spotted skunks (Spilogale putorius), deer (e.g. white-tailed deer Odocoileus virginianus), marsupials (e.g. tammar wallabies Macropus eugenii), rabbits (e.g. European rabbits Oryctolagus cuniculus) and elephant shrews (Macroscelididae). Banner-tailed kangaroo rats (Dipodomys spectabilis) footdrum in the presence of snakes as a form of individual defense and parental care. Several studies have indicated intentional use of ground vibrations as a means of intra-specific communication during courtship among the Cape mole-rat (Georychus capensis). Footdrumming has been reported to be involved in male-male competition where the dominant male indicates its resource holding potential by drumming, thus minimising physical contact with potential rivals. The Asian elephant (Elephas maximus) uses seismic communication in herd or group maintenance and many social insects use seismic vibrations to coordinate the behaviour of group members, for example in cooperative foraging. Other insects use vibrational communication to search for and attract mates, like North American treehoppers, Enchenopa binotata. Males of this species use their abdomen to send vibrations through their host plant's stem. Females perceive these signals and respond to them to initiate a duet.
Inter-specific communication The banner-tailed kangaroo rat, (Dipodomys spectabilis), produces several complex footdrumming patterns in a number of different contexts, one of which is when it encounters a snake. The footdrumming may alert nearby offspring but most likely conveys that the rat is too alert for a successful attack, thus preventing the snake's predatory pursuit. Vibrations caused by stampeding animals may be sensed by other species to alert them to danger, thereby increasing the size of the stampede and reducing the risk of danger to an individual.
Eavesdropping Some animals use eavesdropping to either catch their prey or to avoid being caught by predators. Some snakes are able to perceive and react to substrate-borne vibrations. The vibrations are transmitted through the lower jaw, which is often rested on the ground and is connected with the inner ear. They also detect vibrations directly with receptors on their body surface. Studies on horned desert vipers (Cerastes cerastes) showed they strongly rely on vibrational cues for capturing prey. Localisation of the prey is probably aided by the two halves of the lower jaw being independent. Vibrational cues can even indicate the life stage of prey thereby aiding optimal prey selection by predators, e.g. larval vibrations can be distinguished from those generated by pupae, or, adults from juveniles. Although some species can conceal or mask their movements, substrate-borne vibrations are generally more difficult to avoid producing than airborne vibrations. The common angle moth (Semiothisa aemulataria) caterpillar escapes predation by lowering itself to safety by a silk thread in response to substrate-borne vibrations produced by approaching predators.
Mimicry Several animals have learnt to capture prey species by mimicking the vibrational cues of their predators. Wood turtles (Clemmys insculpta), European herring gulls (Larus argentatus), and humans have learnt to vibrate the ground causing earthworms to rise to the surface where they can be easily caught. It is believed that deliberately produced surface vibrations mimic the seismic cues of moles moving through the ground to prey on the worms; the worms respond to these naturally produced vibrations by emerging from their burrows and fleeing across the surface. Other animals mimic the vibrational cues of prey, only to ambush the predator when it is lured towards the mimic. Assassin bugs (Stenolemus bituberus) hunt web-building spiders by invading the web and plucking the silk to generate vibrations that mimic prey of the spider. This lures the resident spider into striking range of the bug. Spiders from at least five different families routinely invade the webs of other spiders and lure them as prey with vibratory signals (e.g. Pholcus or 'daddy long-leg' spiders; salticid 'jumping' spiders from the genera Portia, Brettus, Cyrba and Gelotia). Portia fimbriata jumping spiders lure female Euryattus species by mimicking male courtship vibrations.
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