American Scientist May-June issue, pp. 278-287 Charif, R.A. 1993. The sounds of silence. Payne, K. and Langbauer, W.R. 1992. Langbauer, W.R., K.B Payne, R.A. Charif, L. Rapaport, and F. Osborn.
African elephants respond to distant playbacks of low-frequency conspecific calls.
Payne, K. 1991. A Change of Tune. Langbauer, W.R., K.B Payne, R.A. Charif, and E.M. Thomas. Responses of captive African elephants to playback of low-frequency calls. Payne, K. 1989.