Analysis and Classification of Sounds Produced by Asian Elephants (\u3ci\u3eElephas Maximus\u3c/i\u3e)

Relatively little is known about the vocal repertoire of Asian elephants (Elephas maximus), and a categorization of basic call types and modifications of these call types by quantitative acoustic parameters is needed to examine acoustic variability within and among call types, to examine individuality, to determine communicative function of calls via playback, to compare species and populations, and to develop rigorous call recognition algorithms for monitoring populations. This study defines an acoustic repertoire of Asian elephants based on acoustic parameters, compares repertoire usage among groups and individuals, and validates structural distinction among call types through comparison of manual and automated classification methods. Recordings were made of captive elephants at the Oregon Zoo in Portland, OR, USA, and of domesticated elephants in Thailand. Acoustic and behavioral data were collected in a variety of social contexts and environmental noise conditions. Calls were classified using perceptual aural cues plus visual inspection of spectrograms, then acoustic features were measured, then automated classification was run. The final repertoire was defined by six basic call types (Bark, Roar, Rumble, Bark, Squeal, Squeal, and Trumpet), five call combinations and modifications with these basic calls forming their constituent parts (Roar-Rumble, Squeal-Squeak, Squeak train, Squeak-Bark, and Trumpet-Roar), and the Blow. Given the consistency of classifications results for calls from geographically and socially disparate subject groups, it seems possible that automated call detection algorithms could be developed for acoustic monitoring of Asian elephants