Vocal production, affect expression, and communicative function in African elephant rumble vocalizations.

Abstract

African elephant rumbles are harmonically rich vocalizations with clear formant structure. The low-frequency, high amplitude nature of rumbles is consistent with the observed large vocal production anatomy. Examination of formant locations and inter-formant dispersion implicates the trunk in addition to the oral cavity in rumble production. Adult female African elephants express affect intensity in ways similar to other mammals. When interacting with social superiors, subordinate rumbles exhibited increased and more variable fundamental frequencies, and increased amplitudes and durations, compared to periods of social calm. Filter features did not change across behavioral contexts. Acoustic responses originally related solely to affect may come to serve communicative functions. During dyadic approaches by adult females, rumbles resembling the “fear response” of subordinates (i.e., those with increased durations and more variable fundamental frequencies) increased the likelihood of friendly social interaction, and these signals were produced by both subordinate and dominant animals. Two top-ranking females were co-dominant and competed for alpha status. When interacting with each other, they produced rumbles with decreased fundamental frequencies, increased amplitudes and durations, and a decrease in inter-formant dispersion. This acoustic response is not generally consistent with the expression of affect but may signal large body size to social competitors.