AN ELEPHANT DICTIONARY?
We believe that very complex information is communicated acoustically, including emotive state, physical characteristics, intention, and perhaps reference to abstract concepts. In addition, the 'rumble' class of vocalization carries information about familial relationship, if not individual identification. On these pages we will explore some of the categories of calls produced by forest elephants and the broad context in which they are used, but an actual 'dictionary' of meanings is still far off.
Elephant vocalizations, or calls, are sometimes quite powerful (90 to 117 dB Sound Pressure Level, which is equivalent to heavy truck traffic or a construction site). Such deep vocalizations are relatively rare in the animal kingdom. Because low-frequency sound attenuates very little with distance, elephants’ powerful infrasonic calls enable them to stay in contact as they move separately over large areas of savannah or forest. Playback experiments demonstrated that free-ranging savannah elephants respond to one another’s calls over at least two and probably four kilometers during daylight hours.
It will be difficult indeed, if not impossible, to perform similar playback experiments on forest elephants because the forests are mostly trackless. We have estimated the potential communication distance by using an acoustic array to locate where the elphant was calling from and then measuring how fast the sounds attenuate with distance. In the forest, elephants can probably communicate up to 7 km away from each other!
The repertoire of elephant calls appears to be similar in all three species, but has been best studied in savannah elephants. Based on behavioral context, there are dozens of call types: of these, the majority are made by females and function in group coordination or reproduction. The social system of elephants is characterized by repeated 'fission' and 'fusion' of variously related groups of individuals organized around adult females. Powerful, low-frequency contact calls enable females to identify one another acoustically and thus coordinate with subgroups foraging separately – sometimes miles apart. This type of acoustic coordination might be particularly critical in forest elephants as subgroups move through the dense rainforest, out of sight of one another.
New research has demonstrated that elephants can actually speak with two voices! They can either talk through their mouths or from the end of their trunks –the resulting rumbles are different and might be used for different types of communication. Although elephants produce sounds in much the same way as we do, using their vocal folds to generate the source (fundamental) frequency and then modifying the sound’s structure by ‘filtering’ it with the shape of their mouth cavity and the nasal passages, that nasal passage is something else when it comes to an elephant! The trunk gives elephants an extra six feet of ‘filter’ to use if they want to. The ‘filter’ lets an animal concentrate sound energy in different parts of the call structure and the longer the filter, the lower in frequency (tone) those areas of concentration can be. Scientists speculate that nasal rumbles may be particularly important for long distance communication.
Much of the information on this page comes from Katy Payne's chapter in Animal Social Complexity, edited by F.B.M. de Waal and P.L. Tyack (2003).
Langbauer, Jr., W.R., Payne, K., Charif, R., Rappaport, E. and Osborn, F. 1991. African elephants respond to distant playbacks of low-frequency conspecific calls. Journal of Experimental Biology, 157: 35-46.
McComb, K., Moss, C.J., Sayialel, S. and Baker, L. 2000. Unusually extensive networks of vocal recognition in African elephants. Animal Behaviour, 59: 1103-1109.
Payne, K., Langbauer, Jr., W.R., and Thomas, E. 1986. Infrasonic calls of the Asian elephant (Elephas maximus). Behavioral Ecology and Sociobiology, 18: 297-301.
Poole, J.H., Payne, K.B., Langbauer, Jr. W.R., and Moss, C.J. 1988. The social contexts of some very low frequency calls of African elephants. Behavioral Ecology and Sociobiology, 22: 385-392.
Poole, J.H. 1999. Signals and assessment in African elephants: Evidence from playback experiments. Animal Behaviour, 58: 185-193.