publications

2026

1. Spontaneous Rhythmic and Tool-Assisted Drumming across Variable Tempo and Technique in a Captive Chimpanzee

   James Brooks, Vesta Eleuteri, Jelle Van Der Werff, and 1 more author

   Ethology, Jul 2026

   Abs DOI

   ABSTRACT Rhythmic drumming on percussive instruments is a common element of music across human cultures. Chimpanzees drum on the buttress roots of trees and on man-made objects, and often combine their drumming with long-distance pant-hoot vocalizations. Previous studies have suggested that chimpanzees select drumming substrates for their acoustic properties and that chimpanzee drumming shares core elements of human musicality (e.g., non-random timing, isochronous, metronome-like rhythm, and de-contextualized production in captivity). But to what extent can chimpanzees flexibly control their drumming rhythm across percussive media and techniques? Here, we report on a long-lasting drumming session by a captive chimpanzee named Toon, which was performed across multiple pant-hoot displays. Toon employed diverse action forms, including drumstick-on-drum tool-composite use. We find flexible (isochronous) rhythm production across drumming implements, techniques, and tempi. Further, we describe tool-composite transport and reuse, selectivity of percussive acoustic properties associated with different vocal elements, and variable use of the facial expression “play face” associated with faster and less variable rhythms, potentially indicating intrinsic enjoyment of such rhythms. Together, these findings provide evidence for key elements of human musicality in Toon’s drumming, supporting the hypothesis of shared evolutionary roots of human and chimpanzee drumming.

2. Modeling Human Synchronization to Rhythmic Patterns with Varying Statistical Regularities

   Dunia Giomo, Federico Mancinelli, Andrea Ravignani, and 1 more author

   Acta Psychologica, Jun 2026

   DOI
3. Sound Guides Object Size Choices in African Penguins through Pitch–Size Association

   Francesca Terranova, Francesca D’Orazio, Cristina Pilenga, and 3 more authors

   Annals of the New York Academy of Sciences, Jun 2026

   Abs DOI

   ABSTRACT The brain’s ability to associate information from different sensory modalities, known as cross-modal integration, is crucial for forming a coherent perception of objects and events. When such associations follow systematic and predictable patterns, they are referred to as cross-modal correspondences. Humans, for example, tend to associate large objects with low-pitched sounds and small objects with high-pitched sounds, a phenomenon known as pitch–size cross-modal correspondence. This phenomenon has been documented in several vertebrate species, yet direct experimental evidence in avian species remains comparatively limited. Here, we tested African penguins using a preferential choice paradigm in which individuals chose between two cubes of different sizes after hearing either a high- or low-pitched sound. Following passive exposure to congruent pitch–size pairings, penguins chose larger objects following low-pitched sounds and smaller objects following high-pitched sounds, indicating that auditory pitch guided their visual size choices. Given that individuals were pre-exposed to a limited set of pitch–size pairings, this effect may reflect either a preexisting bias consistent with cross-modal correspondences or the generalization of a learned association. Nevertheless, these findings demonstrate that penguins can integrate auditory and visual information to guide their behavior and generalize a systematic pitch–size relationship across sensory dimensions.

4. The Ontogeny of Vocal Rhythms in a Non-Human Primate

   Lia Laffi, Teresa Raimondi, Chiara De Gregorio, and 9 more authors

   Developmental Science, May 2026

   Abs DOI

   ABSTRACT Rhythm is a fundamental aspect of human behaviour, and musical rhythm provides one of its most elaborate instances. Unlike speech, this rhythmic behaviour is characterized by the production of temporal patterns structured around small-integer ratios, which emerge early in life and change systematically across development. Whether such developmental trajectories are uniquely human or reflect broader biological constraints remains an open question. Here, we adopt a comparative developmental approach to map the ontogeny of rhythmic structure in the vocalizations of a non-human primate, the singing lemur Indri indri . We recorded songs from individuals of different age classes and quantified temporal organization by measuring inter-onset intervals between successive note onsets. From these intervals, we computed rhythmic ratios between adjacent units and assessed their correspondence to small-integer values. We find that isochrony (1:1 ratios), a core feature of human rhythm, is present from the earliest stages of vocal production. Over development, indris produce an increasing diversity of rhythmic structures corresponding to simple numerical relationships between adjacent intervals. This similarity to humans contrasts with three key differences. First, in indri, binary ratios (1:2 and 2:1) emerge gradually. Second, rhythmic precision around small-integer ratios does not systematically increase with age. Third, developmental trajectories differ between males and females. Together, these findings reveal both shared and divergent developmental pathways of rhythm production in humans and non-human primates, suggesting that early-emerging temporal regularity (i.e., isochrony) may reflect conserved biological constraints, whereas later-developing aspects of rhythmic structure are shaped by species-specific developmental processes. , Summary A non-human primate produces temporally regular vocal rhythms from the earliest stages of vocal development Isochrony (1:1 timing), a core feature of human musical rhythm, is present across sexes and all developmental stages Similarly to humans, rhythmic complexity increases over development through the emergence of additional small-integer ratios between adjacent intervals Unlike humans, the precision of rhythmic regularity does not increase with age and follows sex-specific developmental trajectories

5. Extreme Rhythm Keeping in Long-Range Slow Click Communication of Sperm Whales

   Simone K. A. Videsen, Teresa Raimondi, Pernille M. Sørensen, and 8 more authors

   Annals of the New York Academy of Sciences, May 2026

   Abs DOI

   ABSTRACT Male sperm whales produce loud, low-frequency clicks at low repetition rates. By combining measurements of source properties with sound propagation modeling, we show that sperm whale slow clicks with source levels > 200 dB re 1 \textmu Pa (peak-peak) are the loudest communication signal of any mammal, and that such loud, low-frequency clicks in deep ocean waters have an estimated active space of up to 70 km. We show that these slow clicks are highly rhythmic at rates of 0.1-0.3 Hz, which is an order of magnitude slower than other rhythmic communication signals among mammals and birds. Thus, slow clicks may allow for timing information to be maintained over extreme distances, and we, therefore, propose that sperm whale slow click production is a low entropy, long-range communication signal that may offer honest advertisement through rhythm-keeping to distant receivers. We speculate that the production of such loud, rhythmic clicks at extremely slow rates may be achieved by the sperm whales using extrinsic echo information from the environment to maintain extreme isochrony.

6. The Emergence of a Universal Rhythmic Feature: Simple Models Can Produce Categorical Rhythms

   Chloé Coissac, Laura Ferreri, Marco Gamba, and 2 more authors

   Annals of the New York Academy of Sciences, Apr 2026

   Abs DOI

   ABSTRACT Across musical cultures, rhythm consists of discrete categories of interval durations. Such rhythmic categories are also increasingly quantified in various nonhuman species’ displays. However, their evolutionary origins are still largely unknown. Complementing cross-species comparative work with computational modeling can help us understand the cognitive mechanisms underlying the emergence of this universal rhythmic feature and the minimum requirements for producing it. This study investigates whether minimal computational models can produce rhythmic categories. We compare two computational models: a single spiking neuron model representing a minimal neural system, and a model of cricket stridulation as a minimal synchronization mechanism. Both models transform a random temporal sequence into a more structured, isochronous rhythm; that is, randomly distributed temporal intervals get more similar in duration. An isochronous input sequence, in contrast, combined with the models’ intrinsic bias, has a more complex effect on the produced temporal patterns. At frequencies that closely relate to the models’ intrinsic frequency, the models produce stable temporal patterns with rhythmic categories. Our results show that rhythmic categories can emerge from simple mechanisms, likely shared across species, especially when multiple individually isochronous mechanisms interact. As such, we should expect to find categorical rhythms across an even larger range of animal displays.

7. Global and Local Deviance Effects in the Processing of Temporal Patterns

   Dunia Giomo, Romain Brasselet, Gianfranco Fortunato, and 1 more author

   Annals of the New York Academy of Sciences, Feb 2026

   Abs DOI

   ABSTRACT Perceptual and sensorimotor events are often experienced as temporal patterns, that is, identified as sequences based on their temporal features. While current timing models propose separate mechanisms supporting the processing of single intervals and temporal patterns, they leave partially unclear whether the latter entails the processing of both individual intervals and the overall structure of a pattern, or only one of these features. Here, we narrowed this question down by investigating how violations of regularity within the individual intervals of a temporal sequence (i.e., local violations) and in its overall structure (i.e., global violations) differentially affect its reproduction. We tested these violation effects in three experiments in which the sequences were experienced either in the visual or auditory domain and had either simple or complex structures. Results showed that the precision in reproducing simple visual and auditory patterns was primarily affected by local violations, whereas global violations mostly impacted the reproduction of visual patterns with complex structures. These detrimental effects were partially explained by rescaling and bias effects in the reproduced patterns. Overall, our findings indicate that the processing and reproduction of temporal patterns differentially weigh individual intervals and global structure, depending on sensory modality and, for visual patterns, on structural complexity. , Our experience of the world is inherently structured by temporal patterns. Yet a full understanding of how we process such patterns is still lacking. Across three finger-tapping experiments employing the local–global paradigm, we show that the processing and reproduction of temporal patterns rely on a differential weighting of their individual elements and overall structure. This weighting depends on both the structural complexity of the patterns and the sensory modality in which they are experienced.

8. Neonatal Auditory Input Affects Vocal Development in Harbour Seals

   Teresa Raimondi, Caroline E. Haas, Koen De Reus, and 3 more authors

   Philosophical Transactions B, Feb 2026

   Abs DOI

   Abstract Vocal individuality has important biological functions in mammals: at crucial stages of development, it ensures feeding and is a prerequisite for auditory-based mother–pup recognition. Is vocal individuality only shaped by maturation or also by the degree of conspecific acoustic input? Here, we test how the neonatal auditory environment shapes development and individualization of calls in harbour seal pups (Phoca vitulina). To simulate low- versus high-conspecific acoustic density, 18 pups heard playbacks of calls from either 2 or 30 conspecifics. We recorded calls before and after playback exposure and extracted 12 acoustic parameters. Supervised machine learning and discriminant function analyses showed greater individual distinctiveness in both groups after playback, indicating a developmental trend toward individualization. Notably, pups exposed to less-variable input showed higher individuality. Euclidean distances on call parameters showed that both groups diverged from the playback signals. Distances on within-pup and between-pups housed together revealed opposite trajectories in the two groups: after the exposure, less-variable auditory input determined steadier individual calls, while more-variable auditory input scattered calls across the acoustic space. Altogether, our findings indicate that auditory input modulates vocal development in pups, making harbour seals a promising model for unravelling how neonatal environment affects vocal plasticity in a non-human mammal. This article is part of the theme issue ‘Mechanisms of learning from social interaction’.

9. SEX in Bonobos: The Intensity of Sexual Stimulation Sharply Drops after Facial Mimicry

   Martina Francesconi, Alice Galotti, Yannick Jadoul, and 3 more authors

   Evolution and Human Behavior, Jan 2026

   DOI
10. Dancing Male Riflebirds Create a Dynamic Sensory Trajectory That Guides Female Choice

    Thomas MacGillavry, Yannick Jadoul, and Leonida Fusani

    Current Biology, Jan 2026

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11. Coastal Resident’s Perceptions and Attitudes of the Visual Impacts of Oyster Aquaculture Cultivation Methods along the Atlantic Coast of the US

    Kelsey M. Schultz, Steven B. Scyphers, A. Randall Hughes, and 3 more authors

    Ocean & Coastal Management, Jan 2026

    DOI
12. Local Specialists’ Experience and Skills in Animal Behaviour Studies: Insights from Wild Chimpanzee Field Assistants

    Adrian Soldati, Pawel Fedurek, Vesta Eleuteri, and 10 more authors

    Proceedings of the Royal Society B: Biological Sciences, Jan 2026

    Abs DOI

    Abstract The study of wild animal behaviour and cognition has greatly benefited from the foundational work of local specialists (LSs), particularly field assistants. In primate research, long-term studies rely on accurate identification and tracking of individuals—a skill often honed by LSs and passed on to international specialists (ISs). Despite growing recognition in publications, LSs’ scientific contributions often remain undervalued. Here, we show that LSs at the Budongo Conservation Field Station (Uganda) reliably extract acoustic information (caller identity, sex and age, call components and production context) from long-distance pant hoot calls produced by wild chimpanzees. Importantly, LSs significantly outperform ISs at identifying individuals (LS accuracy = 50% (95% confidence interval (CI): 45–56%); IS accuracy = 8% (95% CI: 5–11%)), an important skill for recognizing and locating individuals in dense forests. LSs’ performance was positively associated with duration of working experience. Given the limited field time of ISs (typically 1–2 years), LSs’ expertise and longer commitment (mean 16.75 years) represent an essential yet underacknowledged scientific resource. Our study highlights LSs’ critical role in ethological research—not only enhancing skills and data quality, but also potentially helping address both ethical (e.g. community involvement) and environmental (e.g. travel carbon footprint) challenges linked to fieldwork in remote locations.

2025

1. Hidden Assumptions of Integer Ratio Analyses in Bioacoustics and Music

   Yannick Jadoul, Tommaso Tufarelli, Chloé Coissac, and 2 more authors

   Annals of the New York Academy of Sciences, Nov 2025

   Abs DOI

   Abstract Rhythm is ubiquitous in human culture and in nature, but hard to capture in all its complexity. A key dimension of rhythm, integer ratio categories occur when the relationship between temporal intervals can be expressed as small-integer ratios. Recent work has found integer ratio categories in most human musical cultures and some animal species’ vocalizations or behavioral displays. But biological systems are noisy, and empirically measured intervals rarely form an exact small-integer ratio. Here, we mathematically assess whether a leading integer ratio analysis method makes valid statistical and biological assumptions. In particular, we (1) make the temporal properties of empirical ratios explicit, both in general and for the typical use in the literature; (2) show how the choice of ratio formula affects the probability distribution of rhythm ratios and ensuing statistical results; (3) guide the reader to carefully consider the assumptions and null hypotheses of the statistical analysis; and (4) present a comprehensive methodology to statistically test integer ratios for any null hypothesis of choice. Our observations have implications for both past and future research in music cognition and animal behavior: They suggest how to interpret past findings and provide tools to choose the correct null hypotheses in future empirical work.

2. Dancing Male Riflebirds Create a Dynamic Sensory Trajectory That Guides Female Choice

   Thomas MacGillavry, Yannick Jadoul, and Leonida Fusani

   Current Biology, Nov 2025

   DOI
3. Testing Hypotheses on the Major/Minor Dichotomy: Movement, Consonance/Dissonance, and (the Lack of) Cross-Species Evidence. Comment on “the Major-Minor Mode Dichotomy in Music Perception” by Giulio Carraturo, Victor Pando-Naude, Marco Costa, Peter Vuust, Leonardo Bonetti, Elvira Brattico

   Nicola Di Stefano and Andrea Ravignani

   Physics of Life Reviews, Sep 2025

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4. A Harbor Seal (Phoca Vitulina) Shows Extensive Respiratory Control in Sound Production

   Diandra Duengen, Yannick Jadoul, and Andrea Ravignani

   BMC Ecology and Evolution, Sep 2025

   Abs DOI

   Abstract The duration of animal vocalizations varies between and within species. Which mammals can learn to control this duration? Such respiratory production learning is a scarcely studied subcomponent of vocal learning. Here, we test the hypothesis that harbor seals ( Phoca vitulina ) are capable of respiratory production learning by testing whether a harbor seal can be trained to i) actively control its vocalization’s duration in two directions (short and long), and ii) exceed the pre-experimental vocalization’s duration (min = 0.202 s, max = 2.621 s). The seal learned to produce uninterrupted vocalizations spanning more than two orders of magnitude in duration, from 79 ms to 9.23 s. Our findings demonstrate a remarkable level of respiratory control in a harbor seal: this respiratory production learning encompasses an extensive range of sound durations and arises at a young age. Producing durations that span such a magnitude is hardly reported in the non-human animal literature; this capacity may be orthogonal to other vocal learning modules and should be tested in more species, both vocal production learners and non-learners.

5. Humans Can Find Rhythm in Randomly Timed Sounds

   Jelle Van Der Werff, Tommaso Tufarelli, Laura Verga, and 1 more author

   Royal Society Open Science, Aug 2025

   Abs DOI

   Humans are keen pattern-seekers and take advantage of regularities present in their environment. In the temporal domain, we may call these patterns rhythms, but what is rhythm? Definitions vary, but all presuppose a categorical distinction between rhythm and randomness. Here, we challenge this view and show that two types of random sound sequences—classically considered arrhythmic by experimenters—differ in the amount of regularity humans reconstruct from them. When asked to synchronize to randomly timed sounds, participants leverage statistics to estimate the underlying tempo of the sequence, similar to linear statistical estimators. Theoretically, our results challenge current definitions of rhythm by showing that rhythmicity and randomness are instances of a continuum. Methodologically, our data and mathematical model show that a common method for creating random timing, namely the jittering of event onsets, introduces an undesirable regularity that humans readily exploit. New experiments should aim to maximize temporal randomness, and past experiments’ outcomes require reconsideration.

6. Investigating Intentionality in Elephant Gestural Communication

   Vesta Eleuteri, Lucy Bates, Yvonne Nyaradzo Masarira, and 3 more authors

   Royal Society Open Science, Jul 2025

   Abs DOI

   A crucial feature of language is the ability to communicate cognitive goals to a specific audience, i.e. goal-directed intentionality. Core criteria for this ability include (i) audience directedness: signalling in the presence of an attentive audience, (ii) persistence: continuing signalling until goals are met, and (iii) elaboration: using new signals following communicative failure. While intentional use has been demonstrated in individual gestures in some non-primates, primates—in particular apes—show this ability across many gestures. But is goal-directed intentionality across many gestures restricted to primates? We explored whether savannah elephants use many gestures with goal-directed intentionality. We presented semi-captive elephants with desired and non-desired items, recording their communicative attempts when an experimenter met, partially met or failed to meet their goal of getting the desired item. Elephants used 38 gesture types almost exclusively when a visually attentive experimenter was present, demonstrating audience directedness. They persisted in gesturing more when their goal was partially as compared with fully met but showed no difference in persistence when the goal was met or not met. Elephants elaborated their gesturing when their goal was not met. We find goal-directed intentionality across many elephant gestures and reveal that elephants, like apes, assess the communicative effectiveness of their gesturing.

7. Accelerando and Crescendo in African Penguin Ecstatic Display Songs

   Taylor A. Hersh, Yannick Jadoul, Marco Gamba, and 2 more authors

   Annals of the New York Academy of Sciences, Jul 2025

   Abs DOI

   Abstract Many species produce rhythmic sound sequences. Some purportedly speed up their vocalizations throughout a display, reminiscent of—but not necessarily equivalent to— accelerando in human music. This phenomenon has been frequently reported but rarely quantified, which limits our ability to understand its mechanism, function, and evolution. Here, we use a suite of rhythm analyses to quantify temporal and acoustic features in the ecstatic display songs of male African penguins ( Spheniscus demersus ). We show that songs get faster (i.e., accelerando) and louder (i.e., crescendo) as they progress. The accelerando occurs because the intersyllable silences, not the syllables themselves, predictably shorten over time. This rhythmicity is maintained even when individuals take audible breaths. Individuals also show plasticity: when they start with a slow tempo, they speed up more strongly than when they start with a fast tempo. We hypothesize that this well-timed accelerando may stem from arousal-based mechanisms, biomechanical constraints, or more complex rhythmic control. Future work should test the mechanisms behind this intra-individual rhythmic variation since nonpasserine birds are thought to have limited vocal plasticity. By integrating a rich empirical dataset with cutting-edge rhythm analyses, we establish the necessary foundation to determine how such features evolved and their role(s) across communication systems.

8. Chimpanzee Drumming Shows Rhythmicity and Subspecies Variation

   Vesta Eleuteri, Jelle Van Der Werff, Wytse Wilhelm, and 18 more authors

   Current Biology, May 2025

   DOI
9. Singing out of Tune: Sexual and Developmental Differences in the Occurrence of Nonlinear Phenomena in Primate Songs

   Chiara De Gregorio, Daria Valente, Walter Cristiano, and 8 more authors

   Philosophical Transactions of the Royal Society B: Biological Sciences, Apr 2025

   Abs DOI

   Animal vocalizations contain a varying degree of nonlinear phenomena (NLP) caused by irregular or chaotic vocal organ dynamics. Several hypotheses have been proposed to explain NLP presence, from unintentional by-products of poor vocal technique to having a functional communicative role. We aimed to disentangle the role of sex, age and physiological constraints in the occurrence of NLP in the songs of the lemur Indri indri , which are complex harmonic vocal displays organized in phrases. Age and sex affected the presence and type of NLP in songs. In particular, the proportion of the phenomena considered decreased with age, except for subharmonics. Subharmonics potentially mediate the perception of lower pitch, making signallers appear larger. Subharmonics and frequency jumps occurred in lower-pitched notes than regular units, while chaos and sidebands occurred in higher-pitched units. This suggests that different types of NLP can be associated with different vocal constraints. Finally, indris might present short-term vocal fatigue, with units occurring in the last position of a phrase having the highest probability of containing NLP. The presence of NLP in indris might result from proximate causes, such as physiological constraints, and ultimate causes, such as evolutionary pressures, which shaped the communicative role of NLP. This article is part of the theme issue ‘Nonlinear phenomena in vertebrate vocalizations: mechanisms and communicative functions’.

10. An Evolutionary Model of Rhythmic Accelerando in Animal Vocal Signalling

    Yannick Jadoul, Taylor A. Hersh, Elias Fernández Domingos, and 3 more authors

    PLOS Computational Biology, Apr 2025

    Abs DOI

    Animal acoustic communication contains many structural features. Among these, temporal structure, or rhythmicity, is increasingly tested empirically and modelled quantitatively. Accelerando is a rhythmic structure which consists of temporal intervals increasing in rate over a sequence. Why this particular vocal behaviour is widespread in many different animal lineages, and how it evolved, is so far unknown. Here, we use evolutionary game theory and computer simulations to link two rhythmic aspects of animal communication, acceleration and overlap: We test whether rhythmic accelerando could evolve under a pressure for acoustic overlap in time. Our models show that higher acceleration values result in a higher payoff, driven by the higher relative overlap between sequences. The addition of a cost to the payoff matrix models a physiological disadvantage to high acceleration rates and introduces a divergence between an individual’s incentive and the overall payoff of the population. Analysis of the invasion dynamics of acceleration strategies shows a stable, non-invadable range of strategies for moderate acceleration levels. Our computational simulations confirm these results: A simple selective pressure to maximise the expected overlap, while minimising the associated physiological cost, causes an initially isochronous population to evolve towards producing increasingly accelerating sequences until a population-wide equilibrium of rhythmic accelerando is reached. These results are robust to a broad range of parameter values. Overall, our analyses show that if overlap is beneficial, emergent evolutionary dynamics allow a population to gradually start producing accelerating sequences and reach a stable state of moderate acceleration. Finally, our modelling results closely match empirical data recorded from an avian species showing rhythmic accelerando, the African penguin. This shows the productive interplay between theoretical and empirical biology.

11. Discrimination between the Facial Gestures of Vocalising and Non-Vocalising Lemurs and Small Apes Using Deep Learning

    Filippo Carugati, Olivier Friard, Elisa Protopapa, and 12 more authors

    Ecological Informatics, Mar 2025

    DOI
12. Rhythmic Analysis in Animal Communication, Speech, and Music: The Normalized Pairwise Variability Index Is a Summary Statistic of Rhythm Ratios

    Yannick Jadoul, Francesca D’Orazio, Vesta Eleuteri, and 5 more authors

    Vibration, Mar 2025

    Abs DOI

    Rhythm is fundamental in many physical and biological systems. Rhythm is relevant to a broad range of phenomena across different fields, including animal bioacoustics, speech sciences, and music cognition. As a result, the interest in developing consistent quantitative measures for cross-disciplinary rhythmic analysis is growing. Two quantitative measures that can be directly applied to any temporal structure are the normalized pairwise variability index (nPVI) and rhythm ratios (rk). The nPVI summarizes the overall isochrony of a sequence, i.e., how regularly spaced a sequence’s events are, as a single value. Meanwhile, rk quantifies ratios between a sequence’s adjacent intervals and is often used for identifying rhythmic categories. Here, we show that these two rhythmic measures are fundamentally connected: the nPVI is a summary static of the rk values of a temporal sequence. This result offers a deeper understanding of how these measures are applied. It also opens the door for creating novel, custom measures to quantify rhythmic patterns based on a sequence’s rk distribution and compare rhythmic patterns across different domains. The explicit connection between nPVI and rk is one further step towards a common quantitative toolkit for rhythm research across disciplines.

13. Rhythmic Categories in Horse Gait Kinematics

    Lia Laffi, Félix Bigand, Christian Peham, and 3 more authors

    Journal of Anatomy, Mar 2025

    Abs DOI

    Abstract Anecdotally, horses’ gaits sound rhythmic. Are they really? In this study, we quantified the motor rhythmicity of horses across three different gaits (walk, trot, and canter). For the first time, we adopted quantitative tools from bioacoustics and music cognition to quantify locomotor rhythmicity. Specifically, we tested whether kinematics data contained rhythmic categories; these occur when adjacent temporal intervals are categorically, rather than randomly, distributed. We extracted the motion cycle duration (t k ) of two ipsilateral hooves from motion data of 13 ridden horses and calculated the ratios from two successive t k values. We tested whether these ratios significantly fell within rhythmic categories and quantified how close they were to small-integer ratios, a rhythmic feature also present in animal vocalizations and human music. We found a strong isochronous pattern—a 1:1 rhythmic ratio, corresponding to the ticking of a clock—in the motion of single limbs for all gaits. We also analyzed the interlimb coordination of the two ipsilateral hooves’ impacts to identify differences associated with the biomechanical patterns of the three gaits. We found an interlimb 1:1 rhythmic pattern for trot and 1:3 and 3:1 rhythmic categories for walk and canter. Our findings are a first step toward quantifying rhythmicity in horse locomotion and potentially the resulting rhythmic sounds, with possible implications as tools to detect gait irregularities. Overall, we show that rhythmic categories are a valuable tool for gait kinematic analysis and that they can be used to quantify temporal patterns in the motor domain.

14. The Rhythm of Horse Gaits

    Lia Laffi, Teresa Raimondi, Carola Ferrante, and 5 more authors

    Annals of the New York Academy of Sciences, Jan 2025

    Abs DOI

    Abstract What makes animal gaits so audibly rhythmic? To answer this question, we recorded the footfall sound of 19 horses and quantified the rhythmic differences in the temporal structure of three natural gaits: walk, trot, and canter. Our analyses show that each gait displays a strikingly specific rhythmic pattern and that all gaits are organized according to small-integer ratios, those found when adjacent temporal intervals are related by a mathematically simple relationship of integer numbers. Walk and trot exhibit an isochronous structure (1:1)—similar to a ticking clock—while canter is characterized by three small-integer ratios (1:1, 1:2, 2:1). While walk and trot both show isochrony, trot has a slower tempo and is more precise and accurate, like a metronome. Our results quantitatively discriminate horse gaits based on rhythm, revealing striking commonalities with human music and some animal communicative signals. Gait and vocal rhythmicity share key features, and the former likely predates the latter; we suggest this supports gait-based hypotheses for the evolution of rhythm. Specifically, the perception of locomotor rhythmicity may have evolved in different species under pressure for predator recognition and mate selection; it may have been later exapted for rhythmic vocal communication.

15. Selectivity in Buttress Drumming Tree Properties among Chimpanzees ( \emphPan\emph Troglodytes Schweinfurthii ) of the Waibira Community in Budongo Forest, Uganda

    Wytse Wilhelm, Vesta Eleuteri, Kathelijne Koops, and 3 more authors

    American Journal of Primatology, Jan 2025

    Abs DOI

    ABSTRACT Wild chimpanzees drum on tree buttresses during dominance displays and travel, generating low-frequency sounds that are audible over distances of more than 1 km. Western chimpanzees ( Pan troglodytes verus ) in the Nimba Mountains of Guinea selectively choose trees and buttresses when drumming, potentially based on their resonant properties, suggesting that these chimpanzees are optimizing their drumming signals. We investigated whether male eastern chimpanzees ( Pan troglodytes schweinfurthii ) from the Waibira community in the Budongo Forest, Uganda, also show preferences in tree and buttress choice, exploring whether selectivity is a species-wide feature. We tested chimpanzee preferences for tree species and diameter, number of buttresses, and buttress area and width, by comparing trees and buttresses used in drumming bouts with nearby unused trees and buttresses. Waibira chimpanzees drummed preferentially on two tree species: the tropical hardwood Cynometra alexandrii and the softwood Chrysophyllum albidum . Chimpanzees selected trees with a larger diameter over nearby trees with a smaller diameter, and buttresses were more likely to be used for drumming if they had a larger area or larger width. These results suggest that chimpanzees in the Waibira community select trees and buttresses based on physical properties, most likely related to acoustically relevant characteristics. These findings support the argument that buttress drumming is a goal-directed behavior and contributes to our understanding of chimpanzees’ use and optimization of their long-distance acoustic signals. , Abstract (French) Les chimpanzés sauvages tambourinent sur les contreforts des arbres lors des démonstrations de dominance et des déplacements, générant des sons de basse fréquence audibles sur des distances de plus d’un kilomètre. Les chimpanzés de l’Ouest ( Pan troglodytes verus ) des Monts Nimba en Guinée choisissent sélectivement les arbres et les contreforts lorsqu’ils tambourinent, potentiellement en fonction de leurs propriétés de résonance (Fitzgerald et al., 2022), ce qui suggère que ces chimpanzés optimisent leur tambourinage. Nous avons cherché à savoir si les chimpanzés mâles de l’Est ( Pan troglodytes schweinfurthii ) de la communauté Waibira, de la forêt de Budongo, en Ouganda, montraient également des préférences dans le choix des arbres et des contreforts, afin d’explorer si la sélectivité est une caractéristique de l’espèce en general. Nous avons testé les préférences des chimpanzés pour les espèces d’arbres et leur diamètre, le nombre de contreforts, et la surface et la largeur des contreforts, en comparant les arbres et les contreforts utilisés lors des séances de tambourinage avec les arbres non utilisés à proximité et les contreforts. Les chimpanzés de Waibira tambourinent de préférence sur deux espèces d’arbres: le feuillu tropical Cynometra alexandrii et le résineux Chrysophyllum albidum . Les chimpanzés ont choisi des arbres de plus grand diamètre plutôt que des arbres voisins de plus petit diamètre, et les contreforts étaient plus susceptibles d’être utilisés pour le tambourinage s’ils avaient une plus grande surface ou une plus grande largeur. Ces résultats suggèrent que les chimpanzés de la communauté de Waibira sélectionnent les arbres et les contreforts en fonction de leurs propriétés physiques, très probablement liées à des caractéristiques acoustiques pertinentes. Ces résultats contribuent à notre compréhension de l’utilisation et de l’optimisation par les chimpanzés de leurs signaux acoustiques à longue distance. , Summary Waibira chimpanzees in the Budongo Forest, Uganda, drummed preferentially on the buttress roots of two tree species: the tropical hardwood Cynometra alexandrii and the softwood Chrysophyllum albidum . Waibira chimpanzees selected trees with a larger diameter over nearby trees with a smaller diameter, and buttresses were more likely to be used for drumming if they had a larger area or larger width. Chimpanzees across Africa select trees and buttresses based on physical characteristics likely to optimize acoustic resonance.

2024

1. Testing Rhythmic Abilities in Developmental Dyslexia

   Marina Rossi, Eline A. Smit, Jelle Van Der Werff, and 2 more authors

   Music Perception: An Interdisciplinary Journal, Dec 2024

   Abs DOI

   Rhythm processing deficits in developmental dyslexia (DD) span across different rhythmic subcomponents and are difficult to capture using one experimental paradigm. How are dyslexic deficits related to motor periodicity, i.e., the execution of repetitive actions while internally generating rhythm? The present experiment investigated rhythm production in DD by means of unprompted tapping paradigm, testing the hypothesis that the ability to internally generate rhythmic patterns may be impaired. The tasks involved tapping of isochronous sequences at a comfortable and a fast tempo and tapping of a free rhythm. Forty adolescents diagnosed with DD (with or without comorbid dyscalculia) participated, along with thirty typically developing control participants. A background questionnaire gathered information about participants’ prior music training. The data show that both dyslexic groups tapped faster than the typically developing participants at the comfortable tempo. We found no statistical differences between groups in fast isochronous tapping or in the free rhythm production tasks, irrespective of music training or the presence of dyscalculia. All participants favored regular rhythms when tapping a free rhythm, with a notable preference for isochrony. These results have theoretical and clinical implications for rhythm deficit hypotheses of DD.

2. Vocal Usage Learning and Vocal Comprehension Learning in Harbor Seals

   Diandra Duengen, Yannick Jadoul, and Andrea Ravignani

   BMC Neuroscience, Oct 2024

   Abs DOI

   Abstract Background Which mammals show vocal learning abilities, e.g., can learn new sounds, or learn to use sounds in new contexts? Vocal usage and comprehension learning are submodules of vocal learning. Specifically, vocal usage learning is the ability to learn to use a vocalization in a new context; vocal comprehension learning is the ability to comprehend a vocalization in a new context. Among mammals, harbor seals ( Phoca vitulina ) are good candidates to investigate vocal learning. Here, we test whether harbor seals are capable of vocal usage and comprehension learning. Results We trained two harbor seals to (i) switch contexts from a visual to an auditory cue. In particular, the seals first produced two vocalization types in response to two hand signs; they then transitioned to producing these two vocalization types upon the presentation of two distinct sets of playbacks of their own vocalizations. We then (ii) exposed the seals to a combination of trained and novel vocalization stimuli. In a final experiment, (iii) we broadcasted only novel vocalizations of the two vocalization types to test whether seals could generalize from the trained set of stimuli to only novel items of a given vocal category. Both seals learned all tasks and took ≤ 16 sessions to succeed across all experiments. In particular, the seals showed contextual learning through switching the context from former visual to novel auditory cues, vocal matching and generalization. Finally, by responding to the played-back vocalizations with distinct vocalizations, the animals showed vocal comprehension learning. Conclusions It has been suggested that harbor seals are vocal learners; however, to date, these observations had not been confirmed in controlled experiments. Here, through three experiments, we could show that harbor seals are capable of both vocal usage and comprehension learning.

3. Singing in the Rain! Climate Constraints on the Occurrence of Indri’s Song

   Valeria Ferrario, Teresa Raimondi, Chiara De Gregorio, and 10 more authors

   American Journal of Primatology, Oct 2024

   Abs DOI

   Abstract The study of how animals adapt their behaviors depending on weather variables has gained particular significance in the context of climate change. This exploration offers insights into endangered species’ potential threats and provides information on the direction to take in conservation activities. In this context, noninvasive, cost-effective, and potentially long-term monitoring systems, such as Passive Acoustic Monitoring (PAM), become particularly appropriate. Our study investigates the relationship between weather variables and the vocal behavior of Indri indri , the sole singing lemur species, within Madagascar’s Maromizaha New Protected Area. Using PAM, we explore the factors shaping the vocalization patterns of this primate species in response to some environmental factors in their natural habitat. Analysis of an extensive audio data set collected across different years revealed the differential influence of temperature and precipitation on Indri indri vocal activity. We found that rainfall negatively influenced the emission of the vocalizations while warmer temperatures correlated with a greater emission of songs. The various environmental factors we considered also affected the timing of vocal emissions, showing the same pattern. Furthermore, our study confirms, once again, the strength of PAM as a valuable tool for studying vocal animal communication quickly, giving us information about long-term behavioral patterns that would be difficult to get in other ways. This research gives us further valuable information about how indris use vocalizations in their environment and how they adjust to environmental changes. , Research highlights Indri indri , the only singing lemur, emits songs daily, a behavior strictly linked to intergroup territory spacing. We explored the influence of weather conditions on indris’ songs in the Maromizaha New Protected Area using Passive Acoustic Monitoring (PAM) and an automated detection algorithm. Indris adjusted their singing behavior based on weather conditions: rain and low temperatures are associated with decreased frequency. Rain determined delayed song emission in the morning. This suggests this behavior’s plasticity is linked to energetic costs. Our study widens the knowledge of the behavior of an endangered species of nonhuman primates. It also showcases the strength of PAM in the conservation and behavioral study of different species.

4. Chicks Produce Consonant, Sometimes Jazzy, Sounds

   Gianmarco Maldarelli, Andrea Dissegna, Andrea Ravignani, and 1 more author

   Biology Letters, Sep 2024

   Abs DOI

   Several animal species prefer consonant over dissonant sounds, a building block of musical scales and harmony. Could consonance and dissonance be linked, beyond music, to the emotional valence of vocalizations? We extracted the fundamental frequency from calls of young chickens with either positive or negative emotional valence, i.e. contact, brood and food calls. For each call, we calculated the frequency ratio between the maximum and the minimum values of the fundamental frequency, and we investigated which frequency ratios occurred with higher probability. We found that, for all call types, the most frequent ratios matched perfect consonance, like an arpeggio in pop music. These music-like intervals, based on the auditory frequency resolution of chicks, cannot be miscategorized into contiguous dissonant intervals. When we analysed frequency ratio distributions at a finer-grained level, we found some dissonant ratios in the contact calls produced during distress only, thus sounding a bit jazzy. Complementing the empirical data, our computational simulations suggest that physiological constraints can only partly explain both consonances and dissonances in chicks’ phonation. Our data add to the mounting evidence that the building blocks of human musical traits can be found in several species, even phylogenetically distant from us.

5. Vocal Tract Dynamics Shape the Formant Structure of Conditioned Vocalizations in a Harbor Seal

   Maria Goncharova, Yannick Jadoul, Colleen Reichmuth, and 2 more authors

   Annals of the New York Academy of Sciences, Aug 2024

   Abs DOI

   Abstract Formants, or resonance frequencies of the upper vocal tract, are an essential part of acoustic communication. Articulatory gestures—such as jaw, tongue, lip, and soft palate movements—shape formant structure in human vocalizations, but little is known about how nonhuman mammals use those gestures to modify formant frequencies. Here, we report a case study with an adult male harbor seal trained to produce an arbitrary vocalization composed of multiple repetitions of the sound wa . We analyzed jaw movements frame-by-frame and matched them to the tracked formant modulation in the corresponding vocalizations. We found that the jaw opening angle was strongly correlated with the first (F1) and, to a lesser degree, with the second formant (F2). F2 variation was better explained by the jaw angle opening when the seal was lying on his back rather than on the belly, which might derive from soft tissue displacement due to gravity. These results show that harbor seals share some common articulatory traits with humans, where the F1 depends more on the jaw position than F2. We propose further in vivo investigations of seals to further test the role of the tongue on formant modulation in mammalian sound production.

6. Isochronous Singing in 3 Crested Gibbon Species ( \emphNomascus Spp.)

   Chiara De Gregorio, Teresa Raimondi, Valeria Bevilacqua, and 8 more authors

   Current Zoology, Jul 2024

   Abs DOI

   Abstract The search for common characteristics between the musical abilities of humans and other animal species is still taking its first steps. One of the most promising aspects from a comparative point of view is the analysis of rhythmic components, which are crucial features of human communicative performance but also well-identifiable patterns in the vocal displays of other species. Therefore, the study of rhythm is becoming essential to understand the mechanisms of singing behavior and the evolution of human communication. Recent findings provided evidence that particular rhythmic structures occur in human music and some singing animal species, such as birds and rock hyraxes, but only 2 species of nonhuman primates have been investigated so far (Indri indri and Hylobates lar). Therefore, our study aims to consistently broaden the list of species studied regarding the presence of rhythmic categories. We investigated the temporal organization in the singing of 3 species of crested gibbons (Nomascus gabriellae, Nomascus leucogenys, and Nomascus siki) and found that the most prominent rhythmic category was isochrony. Moreover, we found slight variation in songs’ tempo among species, with N. gabriellae and N. siki singing with a temporal pattern involving a gradually increasing tempo (a musical accelerando), and N. leucogenys with a more regular pattern. Here, we show how the prominence of a peak at the isochrony establishes itself as a shared characteristic in the small apes considered so far.

7. Isochrony as Ancestral Condition to Call and Song in a Primate

   Chiara De Gregorio, Marco Maiolini, Teresa Raimondi, and 7 more authors

   Annals of the New York Academy of Sciences, Jul 2024

   Abs DOI

   Abstract Animal songs differ from calls in function and structure, and have comparative and translational value, showing similarities to human music. Rhythm in music is often distributed in quantized classes of intervals known as rhythmic categories. These classes have been found in the songs of a few nonhuman species but never in their calls. Are rhythmic categories song-specific, as in human music, or can they transcend the song–call boundary? We analyze the vocal displays of one of the few mammals producing both songs and call sequences: Indri indri . We test whether rhythmic categories (a) are conserved across songs produced in different contexts, (b) exist in call sequences, and (c) differ between songs and call sequences. We show that rhythmic categories occur across vocal displays. Vocalization type and function modulate deployment of categories. We find isochrony (1:1 ratio, like the rhythm of a ticking clock) in all song types, but only advertisement songs show three rhythmic categories (1:1, 1:2, 2:1 ratios). Like songs, some call types are also isochronous. Isochrony is the backbone of most indri vocalizations, unlike human speech, where it is rare. In indri, isochrony underlies both songs and hierarchy-less call sequences and might be ancestral to both.

8. Addressing Constraints to Shellfish Aquaculture through Quantifying Public Perceptions and Attitudes along the Atlantic Coast of the US

   Kelsey M. Schultz, Steven B. Scyphers, A. Randall Hughes, and 3 more authors

   Ocean & Coastal Management, Jul 2024

   DOI
9. Delineating the Field of Language Evolution Research: A Quantitative Analysis of Peer-Review Patterns at the Joint Conference on Language Evolution (JCoLE 2022)

   Stefan Hartmann, Sławomir Wacewicz, Andrea Ravignani, and 4 more authors

   Interaction Studies. Social Behaviour and Communication in Biological and Artificial Systems, Jun 2024

   Abs DOI

   Abstract Research on language evolution is an established subject area yet permeated by terminological controversies about which topics should be considered pertinent to the field and which not. By consequence, scholars focusing on language evolution struggle in providing precise demarcations of the discipline, where even the very central notions of evolution and language are elusive. We aimed at providing a data-driven characterisation of language evolution as a field of research by relying on quantitative analysis of data drawn from 697 reviews on 255 submissions from the Joint Conference on Language Evolution 2022 (Kanazawa, Japan). Our results delineate a field characterized by a core of main research topics such as iconicity, sign language, multimodality. Despite being explored within the framework of language evolution research, only very recently these topics became popular in linguistics. As a result, language evolution has the potential to emerge as a forefront of linguistic research, bringing innovation to the study of language. We also see the emergence of more recent topics like rhythm, music, and vocal learning. Furthermore, the community identifies cognitive science, primatology, archaeology, palaeoanthropology, and genetics as key areas, encouraging empirical rather than theoretical work. With new themes, models, and methodologies emerging, our results depict an intrinsically multidisciplinary and evolving research field, likely adapting as language itself.

10. Multimodal Communication and Audience Directedness in the Greeting Behaviour of Semi-Captive African Savannah Elephants

    Vesta Eleuteri, Lucy Bates, Jake Rendle-Worthington, and 2 more authors

    Communications Biology, May 2024

    Abs DOI

    Abstract 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.

11. Globally, Songs and Instrumental Melodies Are Slower and Higher and Use More Stable Pitches than Speech: A Registered Report

    Yuto Ozaki, Adam Tierney, Peter Q. Pfordresher, and 72 more authors

    Science Advances, May 2024

    Abs DOI

    Both music and language are found in all known human societies, yet no studies have compared similarities and differences between song, speech, and instrumental music on a global scale. In this Registered Report, we analyzed two global datasets: (i) 300 annotated audio recordings representing matched sets of traditional songs, recited lyrics, conversational speech, and instrumental melodies from our 75 coauthors speaking 55 languages; and (ii) 418 previously published adult-directed song and speech recordings from 209 individuals speaking 16 languages. Of our six preregistered predictions, five were strongly supported: Relative to speech, songs use (i) higher pitch, (ii) slower temporal rate, and (iii) more stable pitches, while both songs and speech used similar (iv) pitch interval size and (v) timbral brightness. Exploratory analyses suggest that features vary along a “musi-linguistic” continuum when including instrumental melodies and recited lyrics. Our study provides strong empirical evidence of cross-cultural regularities in music and speech. , Global collaboration by 75 researchers finds acoustic relationships between speech, song, and instrumental music across cultures.

12. Who You Live with and What You Duet for: A Review of the Function of Primate Duets in Relation to Their Social Organization

    Chiara De Gregorio, Daria Valente, Valeria Ferrario, and 6 more authors

    Journal of Comparative Physiology A, Mar 2024

    Abs DOI

    Abstract Duets are one of the most fascinating displays in animal vocal communication, where two animals fine-tune the timing of their emissions to create a coordinated signal. Duetting behavior is widespread in the animal kingdom and is present in insects, birds, and mammals. Duets are essential to regulate activities within and between social units. Few studies assessed the functions of these vocal emissions experimentally, and for many species, there is still no consensus on what duets are used for. Here, we reviewed the literature on the function of duets in non-human primates, investigating a possible link between the social organization of the species and the function of its duetting behavior. In primates and birds, social conditions characterized by higher promiscuity might relate to the emergence of duetting behavior. We considered both quantitative and qualitative studies, which led us to hypothesize that the shift in the social organization from pair living to a mixed social organization might have led to the emergence of mate defense and mate guarding as critical functions of duetting behavior. Territory/resource ownership and defense functions are more critical in obligate pair-living species. Finally, we encourage future experimental research on this topic to allow the formulation of empirically testable predictions.

13. Thebeat: A Python Package for Working with Rhythms and Other Temporal Sequences

    J. Van Der Werff, Andrea Ravignani, and Yannick Jadoul

    Behavior Research Methods, Feb 2024

    Abs DOI

    Abstract thebeat is a Python package for working with temporal sequences and rhythms in the behavioral and cognitive sciences, as well as in bioacoustics. It provides functionality for creating experimental stimuli, and for visualizing and analyzing temporal data. Sequences, sounds, and experimental trials can be generated using single lines of code. thebeat contains functions for calculating common rhythmic measures, such as interval ratios, and for producing plots, such as circular histograms. thebeat saves researchers time when creating experiments, and provides the first steps in collecting widely accepted methods for use in timing research. thebeat is an open-source, on-going, and collaborative project, and can be extended for use in specialized subfields. thebeat integrates easily with the existing Python ecosystem, allowing one to combine our tested code with custom-made scripts. The package was specifically designed to be useful for both skilled and novice programmers. thebeat provides a foundation for working with temporal sequences onto which additional functionality can be built. This combination of specificity and plasticity should facilitate research in multiple research contexts and fields of study.

14. Harbour Seals Use Rhythmic Percussive Signalling in Interaction and Display

    Kinga Kocsis, Diandra Duengen, Yannick Jadoul, and 1 more author

    Animal Behaviour, Jan 2024

    DOI