Information content and acoustic structure of male African elephant social rumbles.

Angela S Stoeger,Anton Baotic

doi:10.1038/srep27585

Abstract

Until recently, the prevailing theory about male African elephants (Loxodonta africana) was that, once adult and sexually mature, males are solitary and targeted only at finding estrous females. While this is true during the state of ‘musth’ (a condition characterized by aggressive behavior and elevated androgen levels), ‘non-musth’ males exhibit a social system seemingly based on companionship, dominance and established hierarchies. Research on elephant vocal communication has so far focused on females, and very little is known about the acoustic structure and the information content of male vocalizations. Using the source and filter theory approach, we analyzed social rumbles of 10 male African elephants. Our results reveal that male rumbles encode information about individuality and maturity (age and size), with formant frequencies and absolute fundamental frequency values having the most informative power. This first comprehensive study on male elephant vocalizations gives important indications on their potential functional relevance for male-male and male-female communication. Our results suggest that, similar to the highly social females, future research on male elephant vocal behavior will reveal a complex communication system in which social knowledge, companionship, hierarchy, reproductive competition and the need to communicate over long distances play key roles.

Highlights

Acoustic structure and the information content of rumbles of non-musth male African elephants recorded in various social contexts
Body size and age are important correlates of reproductive success[22], and elephant rumbles are classical long-distance signals, male-male competition is likely to be related to the acoustic structure of male elephant vocal signals in general
We used permuted discriminant function analysis to examine differences in rumbles according to maturity of ten male African elephants that were categorized into two maturity groups (1) males with shoulder height above 3 meters and over 25 years, and (2) males with shoulder height below 3 meters and younger than 25 years (Table 1)

Summary

Introduction

Acoustic structure and the information content of rumbles of non-musth male African elephants recorded in various social contexts. The fundamental frequency, mainly determined by the mass of these vibrating vocal folds[32], is an important acoustic feature in elephants It generally decreases with age[33], which is a maturational effect, and has been shown to differ according to context and motivational state in adult female[34,35,36,37,38] and infant African elephants[9,10]. The aim of the current study was to determine whether male African elephant rumbles have the potential to convey information about maturity and individuality based on source and filter theory This approach provides the first important indications on their potential functional relevance for male-male and male-female communication apart from the context of musth

Objectives

Methods

Results

Conclusion