Vocalizations of wild Asian elephants (Elephas maximus): Structural classification and social context

Abstract

Elephants use vocalizations for both long and short distance communication. Whereas the acoustic repertoire of the African elephant (Loxodonta africana) has been extensively studied in its savannah habitat, very little is known about the structure and social context of the vocalizations of the Asian elephant (Elephas maximus), which is mostly found in forests. In this study, the vocal repertoire of wild Asian elephants in southern India was examined. The calls could be classified into four mutually exclusive categories, namely, trumpets, chirps, roars, and rumbles, based on quantitative analyses of their spectral and temporal features. One of the call types, the rumble, exhibited high structural diversity, particularly in the direction and extent of frequency modulation of calls. Juveniles produced three of the four call types, including trumpets, roars, and rumbles, in the context of play and distress. Adults produced trumpets and roars in the context of disturbance, aggression, and play. Chirps were typically produced in situations of confusion and alarm. Rumbles were used for contact calling within and among herds, by matriarchs to assemble the herd, in close-range social interactions, and during disturbance and aggression. Spectral and temporal features of the four call types were similar between Asian and African elephants.

Wild Asian elephants distinguish aggressive tiger and leopard growls according to perceived danger

“…All elephant encounters shown in this rsbl.royalsocietypublishing.org Biol Lett 9: 20130518 and grunts (likelihood ratio x 2 1 ¼ 11:193; p , 0.001). Both trumpets and grunts are used by elephants in instances of alarm, disturbance and interspecific aggression [11]. After hearing an angry leopard maintaining its position rather than fleeing, some elephants exhibited conflicted behaviour as evidenced by their investigative circling, kicking dirt and even kicking a battery box powering the playback-trigger device.…”

“…Elephant vocalizations that were recorded on video were categorized as trumpets and grunts (see electronic supplementary material) based on previous literature showing spectrograms and descriptions of dominant frequencies and durations [10,11]. Elephant grunts [13] have also been characterized as 'roars' [11].…”

“…Tigers are known to opportunistically prey on elephant calves, whereas there is no mention, either in the literature or anecdotally, of elephants being a part of leopards' diets [7][8][9]. Elephants themselves produce guttural growls while communicating with conspecifics [10,11] and may possess a broad, low-frequency acoustical-assessment ability useful for differentiating similar growls of other species. Therefore, we predicted that elephants would discriminate the acoustically distinct growls of tigers and leopards and would display stronger antipredator behaviour to the more dangerous tiger-growl playbacks.…”

Surveillance and Tracking of Elephants Using Vocal Spectral Information

“…Elephant call signal frequency varies from 5 Hz to 10,000 Hz which includes harmonics also. Out of the 258 measurable calls described by [8], close to 30% are trumpets, 22% are roars, 26% are "chirps" (squeaks) and 22% are rumbles. …”

“…Some of the practical issues include the difficulty of acquiring continuous data from forest environments and identifying elephant signals within recordings are resolved. Asian elephant calls can be categorized in to 4 basic types they are Trumpet, Roar, Chirp, and Rumble [8]. The call type and its frequency range used by elephants are given in Table 1.…”