Field Propagation Experiments of Male African Savanna Elephant Rumbles: A Focus on the Transmission of Formant Frequencies.

African savanna elephants live in dynamic fission⁻fusion societies and exhibit a sophisticated vocal communication system. Their most frequent call-type is the 'rumble', with a fundamental frequency (which refers to the lowest vocal fold vibration rate when producing a vocalization) near or in the infrasonic range. Rumbles are used in a wide variety of behavioral contexts, for short- and long-distance communication, and convey contextual and physical information. For example, maturity (age and size) is encoded in male rumbles by formant frequencies (the resonance frequencies of the vocal tract), having the most informative power. As sound propagates, however, its spectral and temporal structures degrade progressively. Our study used manipulated and resynthesized male social rumbles to simulate large and small individuals (based on different formant values) to quantify whether this phenotypic information efficiently transmits over long distances. To examine transmission efficiency and the potential influences of ecological factors, we broadcasted and re-recorded rumbles at distances of up to 1.5 km in two different habitats at the Addo Elephant National Park, South Africa. Our results show that rumbles were affected by spectral⁻temporal degradation over distance. Interestingly and unlike previous findings, the transmission of formants was better than that of the fundamental frequency. Our findings demonstrate the importance of formant frequencies for the efficiency of rumble propagation and the transmission of information content in a savanna elephant's natural habitat

Multimodal communication and audience directedness in the greeting behaviour of semi-captive African savannah elephants

This research was funded by the Austrian Science Fund (FWF) [AW0126211] and the European Union’s 8th Framework Programme, Horizon 2020 [802719].Many species communicate by combining signals into multimodal combinations. Elephants live in multi-level societies where individuals regularly separate and reunite. Upon reunion, elephants often engage in elaborate greeting rituals, where they use vocalisations and body acts produced with different body parts and of various sensory modalities (e.g., audible, tactile). However, whether these body acts represent communicative gestures and whether elephants combine vocalisations and gestures during greeting is still unknown. Here we use separation-reunion events to explore the greeting behaviour of semi-captive elephants (Loxodonta africana). We investigate whether elephants use silent-visual, audible, and tactile gestures directing them at their audience based on their state of visual attention and how they combine these gestures with vocalisations during greeting. We show that elephants select gesture modality appropriately according to their audience’s visual attention, suggesting evidence of first-order intentional communicative use. We further show that elephants integrate vocalisations and gestures into different combinations and orders. The most frequent combination consists of rumble vocalisations with ear-flapping gestures, used most often between females. By showing that a species evolutionarily distant to our own primate lineage shows sensitivity to their audience’s visual attention in their gesturing and combines gestures with vocalisations, our study advances our understanding of the emergence of first-order intentionality and multimodal communication across taxa.Peer reviewe

Visualizing sound emission of elephant vocalizations: evidence for two rumble production types

Recent comparative data reveal that formant frequencies are cues to body size in animals, due to a close relationship between formant frequency spacing, vocal tract length and overall body size. Accordingly, intriguing morphological adaptations to elongate the vocal tract in order to lower formants occur in several species, with the size exaggeration hypothesis being proposed to justify most of these observations. While the elephant trunk is strongly implicated to account for the low formants of elephant rumbles, it is unknown whether elephants emit these vocalizations exclusively through the trunk, or whether the mouth is also involved in rumble production. In this study we used a sound visualization method (an acoustic camera) to record rumbles of five captive African elephants during spatial separation and subsequent bonding situations. Our results showed that the female elephants in our analysis produced two distinct types of rumble vocalizations based on vocal path differences: a nasally- and an orally-emitted rumble. Interestingly, nasal rumbles predominated during contact calling, whereas oral rumbles were mainly produced in bonding situations. In addition, nasal and oral rumbles varied considerably in their acoustic structure. In particular, the values of the first two formants reflected the estimated lengths of the vocal paths, corresponding to a vocal tract length of around 2 meters for nasal, and around 0.7 meters for oral rumbles. These results suggest that African elephants may be switching vocal paths to actively vary vocal tract length (with considerable variation in formants) according to context, and call for further research investigating the function of formant modulation in elephant vocalizations. Furthermore, by confirming the use of the elephant trunk in long distance rumble production, our findings provide an explanation for the extremely low formants in these calls, and may also indicate that formant lowering functions to increase call propagation distances in this species'

What Pinnipeds Have to Say about Human Speech, Music, and the Evolution of Rhythm

Research on the evolution of human speech and music benefits from hypotheses and data generated in a number of disciplines. The purpose of this article is to illustrate the high relevance of pinniped research for the study of speech, musical rhythm, and their origins, bridging and complementing current research on primates and birds. We briefly discuss speech, vocal learning, and rhythm from an evolutionary and comparative perspective. We review the current state of the art on pinniped communication and behavior relevant to the evolution of human speech and music, showing interesting parallels to hypotheses on rhythmic behavior in early hominids. We suggest future research directions in terms of species to test and empirical data needed

Sound production of Asian elephant high-frequency vocalisations

Anatomical and cognitive adaptations to overcome morph-mechanical constraints of the vocal folds increase vocal diversity across taxa. The Asian elephants´ vocal repertoire ranges from infrasonic rumbles (F0 ~ 20 Hz) to higher pitched trumpets (F0 340-540 Hz) and species-specific squeaks (F0 300-2300 Hz). While rumbles are congruent with vocal fold vibration in large sized mammals, trumpets and squeaks were hypothesised to be emitted by the trunk without current knowledge of the sound source. We use an acoustic camera to visualise nasal trumpet but oral squeak emission and an event of simultaneous oral and nasal emission (biphonation) in a captive group of female Asian elephants. By combining these findings with acoustic, behavioural and morphological data we suggest that trumpets are produced by vibration of nasal cartilages, but squeaks by vibration of the tensely closed lips. Our data further suggests that context or vocal production learning might be involved in squeak sound productio

Sound production of Asian elephant high-frequency vocalisations

Anatomical and cognitive adaptations to overcome morph-mechanical constraints of the vocal folds increase vocal diversity across taxa. The Asian elephants´ vocal repertoire ranges from infrasonic rumbles (F0 ~ 20 Hz) to higher pitched trumpets (F0 340-540 Hz) and species-specific squeaks (F0 300-2300 Hz). While rumbles are congruent with vocal fold vibration in large sized mammals, trumpets and squeaks were hypothesised to be emitted by the trunk without current knowledge of the sound source. We use an acoustic camera to visualise nasal trumpet but oral squeak emission and an event of simultaneous oral and nasal emission (biphonation) in a captive group of female Asian elephants. By combining these findings with acoustic, behavioural and morphological data we suggest that trumpets are produced by vibration of nasal cartilages, but squeaks by vibration of the tensely closed lips. Our data further suggests that context or vocal production learning might be involved in squeak sound productio

Sexual dimorphism in African elephant social rumbles

<div><p>This study used the source and filter theory approach to analyse sex differences in the acoustic features of African elephant (<i>Loxodonta africana</i>) low-frequency rumbles produced in social contexts (‘social rumbles’). Permuted discriminant function analysis revealed that rumbles contain sufficient acoustic information to predict the sex of a vocalizing individual. Features primarily related to the vocalizer’s size, i.e. fundamental frequency variables and vocal tract resonant frequencies, differed significantly between the sexes. Yet, controlling for age and size effects, our results indicate that the pronounced sexual size dimorphism in African elephants <i>is partly</i>, <i>but not exclusively</i>, <i>responsible for</i> sexual differences in social rumbles. This provides a scientific foundation for future work investigating the perceptual and functional relevance of specific acoustic characteristics in African elephant vocal sexual communication.</p></div

Study sites, sex, age and number of calls for each study subject.

<p>Study sites, sex, age and number of calls for each study subject.</p

Comparison of a female (left, Chikwenya) and a male (right, Mike) African elephant.

<p>The spectrogram and power spectra below the photograph provide an example of a social rumble of each sex, indicating formant positions (rumbles uttered first by Chikwenya, followed by Mike).</p

Field Propagation Experiments of Male African Savanna Elephant Rumbles: A Focus on the Transmission of Formant Frequencies

African savanna elephants live in dynamic fission&ndash;fusion societies and exhibit a sophisticated vocal communication system. Their most frequent call-type is the &lsquo;rumble&rsquo;, with a fundamental frequency (which refers to the lowest vocal fold vibration rate when producing a vocalization) near or in the infrasonic range. Rumbles are used in a wide variety of behavioral contexts, for short- and long-distance communication, and convey contextual and physical information. For example, maturity (age and size) is encoded in male rumbles by formant frequencies (the resonance frequencies of the vocal tract), having the most informative power. As sound propagates, however, its spectral and temporal structures degrade progressively. Our study used manipulated and resynthesized male social rumbles to simulate large and small individuals (based on different formant values) to quantify whether this phenotypic information efficiently transmits over long distances. To examine transmission efficiency and the potential influences of ecological factors, we broadcasted and re-recorded rumbles at distances of up to 1.5 km in two different habitats at the Addo Elephant National Park, South Africa. Our results show that rumbles were affected by spectral&ndash;temporal degradation over distance. Interestingly and unlike previous findings, the transmission of formants was better than that of the fundamental frequency. Our findings demonstrate the importance of formant frequencies for the efficiency of rumble propagation and the transmission of information content in a savanna elephant&rsquo;s natural habitat