A recent study by scientists of the Indian Institute of Science (IISc), Bengaluru has revealed fresh insights into the behaviour of Asian elephants (Elephas maximus). Their findings show that Asian elephants modulate their vocalisations when disturbed.
The paper titled ‘Asian elephants modulate their vocalisations when disturbed’, which was published in February 2020 in the international peer reviewed journal Animal Behaviour , also makes a distinction between low-frequency rumbles and high-frequency trumpets, and suggests that Asian elephants modulate both high- and low-frequency calls when disturbed.
The other key findings of the paper authored by Nachiketha Sharma, Vijay Prakash, Shiro Kohshima and Raman Sukumar states that the duration of trumpets decrease and that of rumbles increase when Asian elephants are disturbed.
Rumbles, trumpets
“To understand disturbance-induced communication in free-ranging Asian elephants, we compared two call types, ‘rumbles’ (low-frequency calls) and ‘trumpets’ (high-frequency calls), produced in disturbed [by humans or other animals] and undisturbed [social interaction] states,” Nachiketha Sharma, the lead author of the paper states.
The observations in the paper indicate that these disturbance-induced modulations, especially modulated rumbles, could be an adaptive acoustic mechanism and may serve the functional role of alerting conspecifics (members of the same species) to imminent danger.
The study was situated in the protected areas of Bandipur National Park and adjoining areas of the Mudamalai National Park in south India. Surveys were conducted from August 2016 to February 2019 to locate groups of free-ranging Asian elephants in various microhabitats such as woodlands, swamps, salt licks, and grassland sand along water pools, canals and rivers.
Followed, recorded
“Elephants were followed and their calls were recorded for as long as it was possible. The maximum time spent continuously following elephants to observe their behaviour and record vocalisations was about three hours; the minimum observation time for inclusion in our dataset was set at 15 minutes,” Mr. Sharma said.
During the study, the researchers described the disturbed state for elephants as “detection of a disturber by smell, vision, hearing or a combination of multimodal cues” and a “disturber” was defined as “any subject other than elephant conspecifics, including humans and other heterospecifics such as deer, birds or predators”.
The team recorded more than 1,000 different calls. For this study, the authors analysed 59 rumbles and 84 trumpets.
“The mean pitch of these calls were analysed on the basis of the undisturbed situation to another situation where elephants were distributed, and the results indicate that the elephants actively modulate both rumbles and trumpets when disturbed,” the study found.
First of its kind
While considerable research on elephant vocalisation have been conducted in the case of African elephants, the study reveals the first of its kind results on vocalisations when it comes to Asian elephants, particularly during disturbance. Of late, studies on behavioural aspects of Asian elephants, including their response to stress and deaths, have resulted in fascinating insights into the large mammals.
“Further studies should address whether Asian elephants assign specific calls to particular types of disturbances, whether there are age- and sex-related differences during disturbance-associated vocalisations,” Mr. Sharma added.
