Elephants are social animals that live in family units of related females and their offspring. The families cover vast age ranges and the members interact with other elephant families. Elephants have the ability to produce and detect near-infrasonic, low frequency, high amplitude vocalisations. The acoustic and seismic waves produced are subject to less attenuation and can travel for much greater distances. .
2.0 Hearing Sensitivity in Elephant.
The first studies on the ability of Asian elephants to produce infrasonic calls found that calls in the range of frequency of 14-24Hz were common (Payne et al, 1986). The recordings taken at 5m from captive elephants had sound pressure levels of 85-90dB. These low-frequency sounds were inaudible to the experimenters. Rumbles in the audible range coincided with a 'fluttering' of the skin where the nasal passage joins the skull, and was also observed to occur when rumbles were produced in the infrasonic range. This was used as a tool to identify which elephant produced the recorded infrasonic call. .
Further playback experiments were conducted to determine the hearing range over which elephants can detect low-frequency calls. Langbauer et al, (1991) used playback calls of elephants at distances of 1.2km and 2.0km and determined the behavioral response of elephant families. Behavioral responses were analyzed vocalizing, "freezing," listening and moving towards the signal source. Positive behavioral responses were observed at both distances indicating that the signal was received at these distances. The responses at 2.0km were less pronounced which may indicate that the elephants were less interested in distant calls. The authors propose that it is possible that the hearing range of elephants could be as much as 4km, as the audio equipment used in the study could only transmit sound at half the decibel level of previously recorded elephant vocalizations.
