Vibration and animal communication: A review

We know less about how large animals might produce vibration signals than how they might receive them. O'Connell et al. (1997) reported measurements of Rayleigh waves in the substrate that were propagated by elephant vocalizations and movements that might be important in long-range communication. Propagation of those signals was later quantified at distances up to 120 m (Arnason et al., 1998).

Initiation of substrate vibrations during courtship has also been reported recently in vertebrates. The veiled chameleon, Chamaeleo calyptratus, produces plant-borne vibrations that may be used in communication (Barnett et al., 1999). This is especially intriguing because Hartline (1971) noted thirty years ago that structures for hearing in chameleons and snakes were at least superficially similar, and thus chameleons might detect substrate vibrations (Barnett et al., 1999). Two species of frogs in the genus Leptodactylus produce substrate-borne vibrations, but in very different ways. The white-lipped frog, L. albilabris, produces Rayleigh waves as it sings a sexual advertisement call. This frog thumps its gular pouch against the soft soil where it lies and rapidly inflates its vocal sac (Lewis and Narins, 1985). Its Brazilian congener L. syphax has been observed drumming its forelimbs on granitic outcroppings, but this behavior is not produced simultaneously with either the advertisement or aggressive calls (Cardoso and Heyer, 1995).

Allopatric species of the genus Dipodomys footdrum in species-specific patterns (Randall, 1997). Banner-tailed kangaroo rats, Dipodomys spectabilis, produce individually distinct signatures in their foot-- drumming that remain constant over time (Randall, 1989) and that allow discrimination between neighbors and strangers (Randall, 1994). Although the airborne component of this footdrumming clearly does evoke a response when isolated and presented singly (Randall, 1994), Randall and Lewis (1997) have shown that these airborne signals are best for communication with distant neighbors while outside the burrow on windless nights. Substrate-borne vibration provides a channel for communication from inside the burrow to near neighbors on windy nights (Randall and Lewis, 1997).

Species-specific head drumming signals in the blind subterranean mole rat, Spalax ehrenbergi, may function as an isolating mechanism between species, as well as part of a long-range communication system within the species (Heth et al., 1987). Individuals in tubes separated by a space of one mm could hear and smell each other but did not initiate drumming signals. When the tubes were brought into contact, individuals began head drumming that resulted in duets in 72% of the pairs tested. It is suggested that sensory input and signal response are both in the form of vibration in this blind subterranean species that would have limited additional options for intraspecific communication (Rado et al., 1987).

We know more about production and response to vibration in arthropods. Some of the best-known studies of vibration and communication are Friedrich Barth's work with spiders (Barth, 1998). Spiders produce vibration ". . . by drumming with the pales and the abdomen, by stridulating, or by plucking threads of their own or other spiders' webs" (Barth, 1982). Information from vibration in their environments affects many aspects of spider ecology: prey-catching, ". . . courtship, territorial behavior, and social interactions in species sharing a common web" (Barth, 1982). We have long known about spiders' ability to locate prey through vibrations of the web, but Cupien-- nius salei, a spider that does not live on a web, is also capable of reciprocal signalling between mates at least one meter apart on banana or agave plants (Rovner and Barth, 1981). Through use of synthetic male vibrations, Schuch and Barth (1990) showed that frequency and temporal characteristics of the male's signal were of utmost importance in female recognition, while amplitude was not. Females even compensate for the well-known changes in temporal parameters of the vibration with changes in temperature (Shimizu and Barth, 1996).