Within the last 12 years several large land mammals have been found to produce infrasound, including elephants, (Payne et al., 1986), rhinoceros, (von Muggenthaler et al., 1991), and okapi, (von Muggenthaler, 1992; Lindsey, Green, and Bennet, 1999). Other animals may also use infrasound, and low frequency vocalizations may be an important component of large animals� signals.

Payne et al. (1986) found that Asian elephants communicate both at sonic and infrasonic frequencies. The infrasonic signals ranged in frequency from 14 to 24 hertz with decibel ranges between 70 and 100 dB. African elephants also produce infrasound (Poole et al., 1988) in the range between 14-35 hertz with decibel levels up to 90 dB, and can perceive the calls of other elephants at distances up to 4 kilometers (Langbauer et al., 1991). Male African elephants have been shown to walk silently for more that 1.5 km toward a loudspeaker playing the female elephant�s distinctive, low frequency estrous call (Langbauer et al., 1991).

The long wavelengths of infrasound mean that these low frequency signals are only reflected by very large objects. Therefore, there is little attenuation of infrasonic signals due to scattering by objects in the environment, making infrasound ideal for the long distant communication (Pye and Langbauer, 1998) of elephants.

Infrasound is useful for communicating in dense forest as well and for long-distance communication on the open savanna. Sounds above 1 kHz attenuate much more quickly in forest than would be expected by the inverse-square law (Eyring, 1946; Dneprovskaya et al., 1963). Low frequency sounds (below 100 Hz), however, show little excess attenuation in forest environments (e.g., Marten and Marler, 1977; Marten et al., 1977; Wiley and Richards, 1978). The okapi, a rainforest giraffid, produces infrasonic calls at around 14Hz that are likely used to maintain mother/infant contact (Lindsey et al., 1999). Okapi infants spend their days hidden in a nest while their mother browses in the forest.

Giraffes are found in the African savannah from the scrub and grasslands of the Sahara almost to Capetown, not including the Central African rain forest. Their range seems to be closely linked to the presence of acacias (Pellew, 1984). Giraffes inhabit large roaming areas, and those of giraffe cows can extend up to 43 square miles. Immature males tend to range even further than either the sexually mature bull or cows (Pellew, 1984). Roaming areas of individual giraffes overlap considerably, and loose congregations of several animals, particularly females, are common. These congregations, however, are often not stable and individual animals may leave the herd, and others join it. Giraffes appear to recognize each other "personally", and to be in visual contact with one another over large distances (Pellew, 1984).

The authors noticed two giraffe behaviors that are very similar to behaviors seen in okapi. Giraffes produce a behavior where the head and neck starts at about chest level, is thrown back over the body and curled upwards until the nose is straight up in the air. The behavior was termed a neck stretch. A similar behavior was also observed but involved only the head in which the chin is lowered and quickly raised so that the nose is pointing straight up into the air. This behavior was called a head throw.