Acoustic structure and information content of trumpets in female Asian elephants (Elephas maximus)

Abstract

Most studies on elephant vocal communication have focused on the low-frequency rumble, with less effort on other vocalization types such as the most characteristic elephant call, the trumpet. Yet, a better and more complete understanding of the elephant vocal system requires investigating other vocalization types and their functioning in more detail as well. We recorded adult female Asian elephants (Elephas maximus) at a private facility in Nepal and analyzed 206 trumpets from six individuals regarding their frequency, temporal and contour shape, and related acoustic parameters of the fundamental frequency. We also tested for information content regarding individuality and context. Finally, we recorded the occurrence of non-linear phenomena such as bifurcation, biphonation, subharmonics and deterministic chaos. We documented a mean fundamental frequency ± SD of 474 ± 70 Hz and a mean duration ± SD of 1.38 ± 1.46 s (Nindiv. = 6, Ncalls = 206). Our study reveals that the contour of the fundamental frequency of trumpets encodes information about individuality, but we found no evidence for trumpet subtypes in greeting versus disturbance contexts. Non-linear phenomena prevailed and varied in abundance among individuals, suggesting that irregularities in trumpets might enhance the potential for individual recognition. We propose that trumpets in adult female Asian elephants serve to convey an individual’s identity as well as to signal arousal and excitement to conspecifics.

Sound Visualization Demonstrates Velopharyngeal Coupling and Complex Spectral Variability in Asian Elephants

“…The lower formants and concentration of energy in the lower harmonics have further been shown in the nasal calls of sheep [ 42 ], goitered gazelles [ 39 ], Saiga antelopes [ 40 ] and red deer [ 41 ], and in the previous study using the acoustic camera on African elephants [ 23 ]. Interestingly, trumpets are clearly uttered through the nose but are comparably as loud as the roars and exhibit high energy in upper harmonics (Beeck, unpublished data, [ 15 , 16 ]). This was suggested to be caused by the alternative sound production mechanisms, including the formation of a shockwave [ 80 ].…”

“…Since we were primarily interested in the sound production of the calls before their acoustic variation relevant to the behavioral context, we aimed at recording as many vocalizations as possible, rather than balancing the observational settings across the individuals. We established contexts in which the individual elephants can be stimulated to vocalize during a previous study period at the same site in February to March 2018, where we had yet collected acoustic and behavioral data, but no acoustic camera data [ 15 , 67 ]. The recording contexts included four settings: separation-reunion experiments at the corrals; vocalizations on the handler’s verbal cue; the elephants bathing at the river; and opportunistic observational recordings between call solicitations.…”

“…In addition, single captive individuals of African elephants and one Asian elephant proved capable of adding novel sounds to their repertoire through vocal production learning, a capability whose functional value in their interspecific communication remains unknown [ 12 , 13 ]. The trunk is used not only to produce the iconic high-frequency trumpet, where the exact sound source is not yet localized, but also squeaks, idiosyncratic high-frequency sounds, throbbing sounds, snorts and blows (Beeck, unpublished data, [ 14 , 15 , 16 ]). By vibrating their massive vocal folds, the elephants produce tonal rumbles [ 17 ] with fundamental frequencies reaching into the infrasonic range (<20 Hz), but with energy present in higher harmonics up to about 1000 Hz [ 18 , 19 ].…”

Singing more, singing harsher: occurrence of nonlinear phenomena in a primate’ song

“…Previous research provided various explanations for the occurrence of NLP in animal vocalizations. A broad of evidence shows that the emergence of nonlinearities in mammalian vocalizations may reflect the emotional state of the emitter, e.g., stress or arousal (Blumstein and Récapet 2009 ; Blesdoe and Blumstein 2014 ; Fuchs et al 2021 ; Marx et al 2021 ; Massenet et al 2022 ). Such sounds are indeed often associated with aversive states, such as rage, pain, and fear in animals, including humans (Anikin 2020 ; Marx et al 2021 ).…”