Vocal Creativity in Elephant Sound Production

Abstract

How do elephants achieve their enormous vocal flexibility when communicating, imitating or creating idiosyncratic sounds? The mechanisms that underpin this trait combine motoric abilities with vocal learning processes. We demonstrate the unusual production techniques used by five African savanna elephants to create idiosyncratic sounds, which they learn to produce on cue by positive reinforcement training. The elephants generate these sounds by applying nasal tissue vibration via an ingressive airflow at the trunk tip, or by contracting defined superficial muscles at the trunk base. While the production mechanisms of the individuals performing the same sound categories are similar, they do vary in fine-tuning, revealing that each individual has its own specific sound-producing strategy. This plasticity reflects the creative and cognitive abilities associated with ‘vocal’ learning processes. The fact that these sounds were reinforced and cue-stimulated suggests that social feedback and positive reinforcement can facilitate vocal creativity and vocal learning behavior in elephants. Revealing the mechanism and the capacity for vocal learning and sound creativity is fundamental to understanding the eloquence within the elephants’ communication system. This also helps to understand the evolution of human language and of open-ended vocal systems, which build upon similar cognitive processes.

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uttered through the nose but are comparably as loud as the roars and exhibit high energy in upper harmonics (Beeck, unpublished data, [ 15 , 16 ]).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 ].…”

“…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 ].…”

“…During arousal, rumbles often occur in combination with loud roars with a F0 of approximately 200 Hz (in Asian elephants in this current study) [ 11 ]. The roars are suggested to be produced laryngeally and the acoustic camera recordings revealed that the African elephants emit their roars orally [ 16 ]. In African elephants, rumbles were found to vary gradually [ 6 , 53 ] (but see [ 54 , 55 ]), but to encode perceptional discrete information [ 52 , 56 , 57 ].…”