African Elephants Respond to Distant Playbacks of Low-frequency Conspecific Calls

We conducted 58 playback experiments with free-ranging African elephants in Etosha National Park, Namibia, to estimate the distance over which some of their low-frequency calls are audible to other elephants. We broadcast pre-recorded elephant calls to elephants that were 1.2 and 2.0 km from the speaker while making simultaneous video and audio recordings of their behavior. In order to reduce the risk of habituation, we used a variety of call types as stimuli. Elephants responded to playbacks at both 1.2 and 2.0 km, with a full response consisting of the elephant vocalizing, lifting and spreading its ears, remaining motionless in this position ('freezing'), moving the head from side to side ('scanning') and, in the case of males responding to female estrous calls, orienting to and finally walking 1 km or more towards the loudspeaker. We analyzed our data quantitatively for three of these responses. The occurrence of each behavior increased substantially immediately after playbacks. Owing to limitations of the loudspeaker, we were only able to broadcast calls at half the sound pressure level (i.e. —6dB) of the strongest calls we have recorded. Since sound at the frequencies of these calls is predicted to suffer from little, if any, attenuation in excess of that caused by spherical spreading, we estimate these calls to be audible to elephants at least 4 km from the source (twice the distance over which we documented responses). These results are consistent with the hypothesis that the very low-frequency calls of elephants function in communication between individuals and groups of elephants separated by distances of several kilometers.