Long-distance, low-frequency elephant communication.

The production, transmission, and reception of and the behavioral response to long-distance, low-frequency sound by elephants is reviewed. The structure of low-frequency calls generated by elephants is separated into the "source" and the "filter" roles played by the lungs, larynx and vocal track, the composition of the expired air and the ambient air temperature. Implications regarding the size, age, sex, sexual and physical status follow from the call structure and detection. Reception of the signal is discussed in terms of the characteristics of the elephant's ear with particular attention to the determination of the threshold of hearing and the ability to locate the source of low-frequency sounds. Factors which influence the transmission of near infrasound are related to atmospheric structure. The critical role played by the thermal stratification and vertical gradient and magnitude of the wind in determining both the range and the detection of a signal are discussed for open and closed elephant habitats. Infrasound plays a pervasive role in reproduction, resource utilization, avoidance of predation and other social interactions. Current and future technology can be expected to contribute to the detection and interpretation of elephant communication. This will aid in the understanding of behavior and in efforts to sustain the species.