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The ability to vary the characteristics of one's voice is a critical feature of human communication. Understanding whether and how animals change their calls will provide insights into the evolution of language. We asked to what extent the vocalizations of penguins, a phylogenetically distant species from those capable of explicit vocal learning, are flexible and responsive to their social environment. Using a principal components (PCs) analysis, we reduced 14 vocal parameters of penguin's contact calls to four PCs, each comprising highly correlated parameters and which can be categorized as fundamental frequency, formant frequency, frequency modulation, and amplitude modulation rate and duration. We compared how these differed between individuals with varying degrees of social interactions: same-colony versus different-colony, same colony over 3 years and partners versus non-partners. Our analyses indicate that the more penguins experience each other's calls, the more similar their calls become over time, that vocal convergence requires a long time and relative stability in colony membership, and that partners' unique social bond may affect vocal convergence differently than non-partners. Our results suggest that this implicit form of vocal plasticity is perhaps more widespread across the animal kingdom than previously thought and may be a fundamental capacity of vertebrate vocalization.

Recursive procedures that allow placing a vocal signal inside another of similar kind provide a neuro-computational blueprint for syntax and phonology in spoken language and human song. There are, however, no known vocal patterns among nonhuman primates arranged in self-embedded combinations that evince vocal recursion or potential insipient forms and neuro-procedures thereof, suggesting a neuro-cognitive transformation exclusive to humans. Here, we uncover that wild flanged male orangutan long calls show two hierarchical strata, wherein rhythmically isochronous call sequences are nested within self-similar isochronous call sequences. Remarkably, three unrelated recursive motifs occurred simultaneously in long calls, refuting that motifs resulted from three parallel linear procedures or that motifs were simple anatomical artifacts of bodily constrains. Findings represent a case of recursive hominid vocal production in the absence syntax, semantics, phonology or music. Second-order combinatorics, ‘sequences within sequences’, involving hierarchically organized and cyclically structured vocal sounds in ancient hominids may have preluded the evolution of recursion in modern language-able humans.

Strepsirrhine vocalisations are extraordinarily diverse and cross-species comparisons are needed to explore how this variability evolved. We contributed to the investigation of primate acoustic diversity by comparing the vocal repertoire of two sympatric lemur species, Propithecus diadema and Indri indri. These diurnal species belong to the same taxonomic family and have similar activity patterns but different social structures. These features make them excellent candidates for an investigation of the phylogenetic, environmental, and social influence on primate vocal behavior. We recorded 3 P. diadema groups in 2014 and 2016. From 1,872 recordings we selected and assigned 3814 calls to 9 a priori call types, on the basis of their acoustic structure. We implemented a reproducible technique performing an acoustic feature extraction relying on frequency bins, t-SNE data reduction, and a hard-clustering analysis. We first quantified the vocal repertoire of P. diadema, finding consistent results for the 9 putatively identified call types. When comparing this repertoire with a previously published repertoire of I. indri, we found highly species-specific repertoires, with only 2% of the calls misclassified by species identity. The loud calls of the two species were very distinct, while the low-frequency calls were more similar. Our results pinpoint the role of phylogenetic history, social and environmental features on the evolution of communicative systems and contribute to a deeper understanding of the evolutionary roots of primate vocal differentiation. We conclude by arguing that standardized and reproducible techniques, like the one we employed, allow robust comparisons and should be prioritized in the future.

Context Even though habitat use is essential information for conservation management strategies, studying it in elusive and scarce forest species has proven challenging. Passive acoustic monitoring allows collecting accurate presence-absence data even for species that typically exhibit low detectability. It further provides tools for long-term and cost-effective biodiversity monitoring, and may also be used to infer population estimates at the landscape level. Objectives We aimed to demonstrate the application of passive acoustic monitoring to the problem of detecting elusive species, especially in forests, using the Eurasian pygmy owl as a model species. We explored its habitat selection, and estimated occupancy and density at the landscape level in the managed boreal forest. Methods We conducted a wide-scale autonomous recording units (ARUs) survey, involving 292 sites in a single season, in a study area covering approx. 370 km2 in south-western Finland. We clustered the detections into territories of males to infer population size by also taking into account the size of home ranges derived from GPS-tags data. Since we were simultaneously monitoring the occupancy of a network of nest boxes and previously estimated the abundance of natural cavities, we could also estimate the proportion of pygmy owls nesting in natural cavities. Results Increasing availability of mature forests was consistently the most critical habitat variable both for calling and nesting sites, increasing occupancy probability of the pygmy owls in a landscape dominated by managed forests. The proportion of sites showing occupancy by the pygmy owls was 20.9%, corresponding to an estimate of ca. Six territorial males/100 km2. Conclusion Our results confirmed that the pygmy owl can be considered a species of mature and old forests, and we provide the first data-based estimate of the total density of territorial males of this species. Passive acoustic monitoring proved to be an efficient method in detecting the presence of pygmy owls, and may overcome weaknesses of other methods, such as nest box surveys, in order to quantify population numbers.

Nonlinear phenomena (NLP) in animal vocalizations arise from irregularities in the oscillation of the vocal folds. Various hypotheses have been put forward to explain the occurrence of NLP, from adaptive to physiological ones. Non-human primates often display NLP in their vocalizations, yet the meaning of these features is still unclear. We present here the first study of NLP occurrence in the song of a singing primate: the indri (Indri indri). We found that the more an individual sings, the higher the likelihood of emitting NLP. Our results show that NLP occurrence in indri depends on phonation, i.e., the cumulative duration of all the units emitted by an individual. Furthermore, NLP occurrence depends on the timing of the signal and increases as the singing progresses. Our findings suggest that indris may be subjected to physiological constraints during the singing process which may limit the production of harmonic sounds because of the fatigue needed to perform loud and long calls. However, indris may still benefit from emitting NLP by strengthening the loudness of their signals for better advertising their presence to the neighboring conspecific groups.

In humans, individuals’ social setting determines which and how language is acquired. Social seclusion experiments show that sociality also guides vocal development in songbirds and marmoset monkeys, but absence of similar great ape data has been interpreted as support to saltational notions for language origin, even if such laboratorial protocols are unethical with great apes. Here we characterize the repertoire entropy of orangutan individuals and show that in the wild, different degrees of sociality across populations are associated with different ‘vocal personalities’ in the form of distinct regimes of alarm call variants. In high-density populations, individuals are vocally more original and acoustically unpredictable but new call variants are short lived, whereas individuals in low-density populations are more conformative and acoustically consistent but also exhibit more complex call repertoires. Findings provide non-invasive evidence that sociality predicts vocal phenotype in a wild great ape. They prove false hypotheses that discredit great apes as having hardwired vocal development programmes and non-plastic vocal behaviour. Social settings mould vocal output in hominids besides humans.

Here, we investigated the possible linkages among geophagy, soil characteristics, and gut mycobiome of indri (Indri indri), an endangered lemur species able to survive only in wild conditions. The soil eaten by indri resulted in enriched secondary oxide-hydroxides and clays, together with a high concentration of specific essential micronutrients. This could partially explain the role of the soil in detoxification and as a nutrient supply. Besides, we found that soil subject to geophagy and indris’ faeces shared about 8.9% of the fungal OTUs. Also, several genera (e.g. Fusarium, Aspergillus and Penicillium) commonly associated with soil and plant material were found in both geophagic soil and indri samples. On the contrary, some taxa with pathogenic potentials, such as Cryptococcus, were only found in indri samples. Further, many saprotrophs and plant-associated fungal taxa were detected in the indri faeces. These fungal species may be involved in the digestion processes of leaves and could have a beneficial role in their health. In conclusion, we found an intimate connection between gut mycobiome and soil, highlighting, once again, the potential consequent impacts on the wider habitat.

International audience; In human and nonhuman primates eye-to-eye contact (EEC), a face-to-face communication component, can promote emotional/attentional engagement and prolong affiliative interactions. Owing to its direct impact on fitness, the reproductive context is perhaps the most critical context for investigating EEC's importance. However, the presence of this phenomenon around mating and its functions in primates is still understudied. In this work, we investigated whether EEC was present during copulations and influenced the copula duration and postcopulation grooming occurrence in the wild gelada, Theropithecus gelada, an Old World monkey species. We found that the previous presence of the male ‘look-at’ triggered the female ‘look-at’. Moreover, copulations were most likely to last longer in the presence of EEC. In addition, the occurrence of postcopulation grooming between partners, most frequently initiated by females, increased when copulations included EEC. Females' engagement in EEC with the male may be a form of continuation of female precopulatory proceptivity and facilitate males' copulatory activity. By prolonging sexual contacts, EEC may also increase the chances of ejaculation. By grooming their partners after mating, female geladas may attempt to reduce male arousal and prolong the social interaction with them, possibly strengthening their social bond. These results provide the first quantitative evidence that EEC is an effective mechanism for prolonging mating interactions and enhancing postmating affiliation in a Papionini species. On a broader perspective, the presence of EEC in an Old World monkey species suggests that EEC may have been favoured by natural selection to promote reproductive advantages during human evolution.

The stability of individual acoustic features is fundamental in social species, and more importantly in monogamous and territorial species, showing long-term fidelity both to the partner and the breeding site. In this study, the stability over time of two discrete vocal types was investigated in the African penguin (Spheniscus demersus), a monogamous and territorial seabird. Contact calls and ecstatic display songs were recorded from an ex situ colony in 2017 and in 2020. For each vocalisation, we measured 14 spectral and temporal acoustic parameters related to both source and filter components. Two separate leave-one-out cross-validated Discriminant Function Analyses (DFA) were then performed, generating the discriminant functions from the vocalisations collected in 2017 to classify those recorded in 2020. The DFA correctly classified 62% of the contact calls (10 subjects) and 80.9% of the ecstatic display songs (seven subjects) according to the correct emitter, showing that acoustic cues to individuality encoded in both vocal types remained unchanged over four consecutive breeding seasons. We suggest that, in this monogamous and territorial bird species, individual acoustic stability could be selected for to identify groupmates and neighbours over the years and to help couples to reunite in consecutive breeding seasons, increasing individual fitness.

Vocal and gestural sequences of several primates have been found to conform to two general principles of information compression: the compensation between the duration of a construct and that of its components (Menzerath-Altmann law) and an inverse relationship between signal duration and its occurrence (Zipf's law of abbreviation). Even though Zipf's law of brevity has been proposed as a universal in animal communication, evidence on non-human primate vocal behavior conformity to linguistic laws is still debated, and information on strepsirrhine primates is lacking. We analyzed the vocal behavior of the unique singing lemur species (Indri indri) to assess whether the song of the species shows evidence for compression. As roars have a chaotic structure that impedes the recognition of each individual utterance, and long notes are usually given by males, we focused on the core part of the song (i.e., the descending phrases, composed of two-six units). Our results indicate that indris' songs conform to Zipf's and Menzerath-Altmann linguistic laws. Indeed, shorter phrases are more likely to be included in the song, and units' duration decrease at the increase of the size of the phrases. We also found that, despite a sexual dimorphism in the duration of both units and phrases, these laws characterize sequences of both males and females. Overall, we provide the first evidence for a trade-off between signal duration and occurrence in the vocal behavior of a strepsirrhine species, suggesting that selective pressures for vocal compression are more ancestral than previously assumed within primates.

In animal vocal communication, the development of adult-like vocalization is fundamental to interact appropriately with conspecifics. However, the factors that guide ontogenetic changes in the acoustic features remain poorly understood. In contrast with a historical view of nonhuman primate vocal production as substantially innate, recent research suggests that inheritance and physiological modification can only explain some of the developmental changes in call structure during growth. A particular case of acoustic communication is the indris’ singing behavior, a peculiar case among Strepsirrhine primates. Thanks to a decade of intense data collection, this work provides the first long-term quantitative analysis on song development in a singing primate. To understand the ontogeny of such a complex vocal output, we investigated juvenile and sub-adult indris’ vocal behavior, and we found that young individuals started participating in the chorus years earlier than previously reported. Our results indicated that spectro-temporal song parameters underwent essential changes during growth. In particular, the age and sex of the emitter influenced the indris’ vocal activity. We found that frequency parameters showed consistent changes across the sexes, but the temporal features showed different developmental trajectories for males and females. Given the low level of morphological sexual dimorphism and the marked differences in vocal behavior, we hypothesize that factors like social influences and auditory feedback may affect songs’ features, resulting in high vocal flexibility in juvenile indris. This trait may be pivotal in a species that engages in choruses with rapid vocal turn-taking.

The complexity of primates’ singing behavior has long gathered the attention of researchers interested in understanding the selective pressures underpinning the evolution of language. Among these pressures, a link between territoriality, pair-living, and singing displays has been suggested. Historically, singing primates have been found in a few taxa that are not closely related to each other, and, in the last years, their phylogeny has dramatically changed. Hence, we aimed at understanding if the dogmatic association between territorial behavior and a monogamous social structure still holds in the light of current research. Moreover, singing behavior has often been considered a whole, but animals can perform different singing forms depending on how many individuals call simultaneously. Currently, it is unclear to which extent these singing forms are widespread among these primate groups. Given that there is no unique definition for a song, solo, duet, and chorus, we envisioned some of the most used descriptions. We then formulated some new definitions that we followed in our review of the presence/absence of these different forms of song organization among singing primates’ taxa. In particular, we suggested that tarsier species that are typically considered non-singers may indeed sing, and we pointed out that non-duetting gibbons may perform duet interactions. We found that, besides duets, chorusing behavior and solo songs are essential features of primates’ communication, but their study is still in a descriptive phase. Moreover, while territorial behavior seems to be conserved in these singing taxa, we highlighted that the monogamous social structure is not the rule. Pair-living plus multi- females groups displaying singing behavior are common too. We suggest that ending to consider these taxa as uniform in their sociality and vocal behavior might be a significant turning point to unravel the different selective pressures that influenced the emergence and organization of such peculiar vocal behavior.

The ability to vary the characteristics of one's voice is a critical feature of human communication. Understanding whether and how animals change their calls will provide insights into the evolution of language. We asked to what extent the vocalizations of penguins, a phylogenetically distant species from those capable of explicit vocal learning, are flexible and responsive to their social environment. Using a principal components (PCs) analysis, we reduced 14 vocal parameters of penguin's contact calls to four PCs, each comprising highly correlated parameters and which can be categorized as fundamental frequency, formant frequency, frequency modulation, and amplitude modulation rate and duration. We compared how these differed between individuals with varying degrees of social interactions: same-colony versus different-colony, same colony over 3 years and partners versus non-partners. Our analyses indicate that the more penguins experience each other's calls, the more similar their calls become over time, that vocal convergence requires a long time and relative stability in colony membership, and that partners' unique social bond may affect vocal convergence differently than non-partners. Our results suggest that this implicit form of vocal plasticity is perhaps more widespread across the animal kingdom than previously thought and may be a fundamental capacity of vertebrate vocalization.

In mammals, olfactory communication plays an essential role in territorial and mating dynamics. Scent depositions in various species, including lemurs, can be placed via marking or overmarking (marking over previous depositions). We focused on the role that marking and overmarking play in territorial defence and intrasexual competition. We investigated these aspects in diademed sifaka (Propithecus diadema) in the primary rainforest of Maromizaha (eastern Madagascar). We collected scent marking data for five groups from April to November 2018 and from May to December 2019. We aimed to understand whether the lemurs deposited scent marks homogeneously across the home range and whether sex, rank, and occurrence of intergroup encounters affected the lemur’s deposition rate. We also asked whether males overmarked adult females more often than other depositions, and the marking and overmarking rates changed between the migration and non-migration seasons. We found that scent marking was performed higher in peripheral and overlapping areas than in the home range central areas. In addition, males had higher scent marking rates, but intergroup encounters did not affect deposition rates. Males showed higher rates of overmarking and primarily targeted dominant females’ depositions, particularly during the “migration” season (including premating and mating seasons). Our findings suggest a border-marking strategy in Propithecus diadema. More frequent scent marking in the “migration” season suggests intrasexual competition in males. Our results suggest that marking is associated with territorial and resource defence, suggesting that it plays a role in monopolizing females using a mate-guarding strategy and may also serve for males’ self-advertisement to females and subordinate depositors.

Research on gut microbiome may help with increasing our understanding of primate health with species’ ecology, evolution, and behavior. Microbiome-related information has the potential to clarify ecology issues, providing knowledge in support of wild primates’ conservation and their associated habitats. Indri (Indri indri) is the largest extant living lemur of Madagascar able to survive only in wild conditions. This species is classified as “critically endangered” by the IUCN Red List of Threatened Species, representing one of the world’s 25 most endangered primates. Indris diet is mainly folivorous, but these primates frequently and voluntarily engage in geophagy. Here, we investigated the possible linkages among geophagy, soil characteristics, and gut microbiome and mycobiome of indri (Indri indri). In these works, we explored the chemical composition of soil eaten by indri, which resulted rich in secondary oxide-hydroxides and clays, together with a high concentration of specific essential micronutrients. This could partially explain the role of the soil in detoxification and as a nutrient supply. Then, we explored the gut microbiome composition of 18 indris belonging to 5 different family groups. The most represented phyla were Proteobacteria 40.1 ± 9.5%, Bacteroidetes 28.7 ± 2.8%, and Synergistetes 16.7 ± 4.5%. Besides, we found that soil subject to geophagy and indris’ faeces shared about 8.9% of the fungal OTUs. Also, several genera (e.g. Fusarium, Aspergillus and Penicillium) were found in both geophagic soil and indri samples. In conclusion, the intimate connection between gut mycobiome and soil, demonstrated that fungal species may be involved in the digestion processes of leaves and could have a beneficial role in their health. Altogether, the data presented in our works, provide a baseline for outlining some possible drivers responsible for the gut microbiome and mycobiome diversity in indris, thus laying the foundations for developing further strategies involved in indris’ conservation.

[Correction Notice: An Erratum for this article was reported online in Journal of Comparative Psychology on May 9 2019 (see record 2019-25503-001). In the article "Embracing in a Female-Bonded Monkey Species (Theropithecus gelada)" by Virginia Pallante, Pier Francesco Ferrari, Marco Gamba, and Elisabetta Palagi (Journal of Comparative Psychology, Advance online publication. March 25, 2019. http://dx.doi.org/10.1037/ com0000173), the title incorrectly read "Embracing in a Female-Bonded Monkey Specie (Theropithecus gelada)" All versions of this article have been corrected.] In several primate species, including humans, embracing predicts the level of affiliation between subjects. To explore the functional meaning of embracing, we selected Theropithecus gelada as a model species. The basic level of the gelada society is the 1-male unit, and the integrity of the group is maintained by the strong bonds between females. In our study group, we observed 3 different kinds of embracing: the frontal and side embraces involving a face-to-face and chest-to-chest interaction and the posterior embrace that consists in putting the arms around conspecifics' back and posing a cheek on it. We verified that the quality of relationships between subjects predicts the type of embracing. Frontal and side embraces were more frequent between females sharing strong bonds. Posterior embracing was randomly distributed. We found a high level of female embracing among the mothers during the first months of lactation. This may improve female cohesiveness against males, thus reducing the risk of infanticide, which is particularly high in geladas. Embracing seems also to act as an ice-breaker favoring grooming. Female embracing could be an affiliative strategy that has evolved to maintain group integrity and high social cohesion among females, especially mothers. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Female primates can emit vocalizations associated with mating that can function as honest signals of fertility. Here, we investigated the role of mating calls and visual signals in female geladas (Theropithecus gelada). Because females have a central role in the gelada society and seem to solicit sexual interactions, we answered whether they emit vocalizations in conjunction with gazing to increase mating success probability. Before and during copulations, females can emit pre-copulation calls and copulation calls. For the first time, we identified a new female vocalization emitted at the final stage of copulations (end-copulation call), possibly marking the occurrence of ejaculation. We found that longer pre-copulation call sequences were followed by both prolonged copulations and the presence of end-copulation calls, thus suggesting that females use pre-copulation calls to ensure successful copula completion. Moreover, we found that different combinations of female vocal types and gazing had different effects on male vocal behavior and motivation to complete the copula. The analysis of the vocal and visual signals revealed a complex inter-sexual multimodal chattering with the leading role of females in the signal exchange. Such chattering, led by females, modulates male sexual arousal, thus increasing the probability of the copula success.

The origin of language is one of the most significant evolutionary milestones of life on Earth, but one of the most persevering scientific unknowns. Two decades ago, game theorists and mathematicians predicted that the first words and grammar emerged as a response to transmission errors and information loss in language's precursor system, however, empirical proof is lacking. Here, we assessed information loss in proto-consonants and proto-vowels in human pre-linguistic ancestors as proxied by orangutan consonant-like and vowel-like calls that compose syllable-like combinations. We played back and re-recorded calls at increasing distances across a structurally complex habitat (i.e. adverse to sound transmission). Consonant-like and vowel-like calls degraded acoustically over distance, but no information loss was detected regarding three distinct classes of information ( viz. individual ID, context and population ID). Our results refute prevailing mathematical predictions and herald a turning point in language evolution theory and heuristics. Namely, explaining how the vocal–verbal continuum was crossed in the hominid family will benefit from future mathematical and computational models that, in order to enjoy empirical validity and superior explanatory power, will be informed by great ape behaviour and repertoire.

In humans, individuals' social setting determines which and how language is acquired. Social seclusion experiments show that sociality also guides vocal development in songbirds and marmoset monkeys, but absence of similar great ape data has been interpreted as support to saltational notions for language origin, even if such laboratorial protocols are unethical with great apes. Here we characterize the repertoire entropy of orangutan individuals and show that in the wild, different degrees of sociality across populations are associated with different 'vocal personalities' in the form of distinct regimes of alarm call variants. In high-density populations, individuals are vocally more original and acoustically unpredictable but new call variants are short lived, whereas individuals in low-density populations are more conformative and acoustically consistent but also exhibit more complex call repertoires. Findings provide non-invasive evidence that sociality predicts vocal phenotype in a wild great ape. They prove false hypotheses that discredit great apes as having hardwired vocal development programmes and non-plastic vocal behaviour. Social settings mould vocal output in hominids besides humans.

Animal communication has long been thought to be subject to pressures and constraints associated with social relationships. However, our understanding of how the nature and quality of social relationships relates to the use and evolution of communication is limited by a lack of directly comparable methods across multiple levels of analysis. Here, we analysed observational data from 111 wild groups belonging to 26 non-human primate species, to test how vocal communication relates to dominance style (the strictness with which a dominance hierarchy is enforced, ranging from 'despotic' to 'tolerant'). At the individual-level, we found that dominant individuals who were more tolerant vocalized at a higher rate than their despotic counterparts. This indicates that tolerance within a relationship may place pressure on the dominant partner to communicate more during social interactions. At the species-level, however, despotic species exhibited a larger repertoire of hierarchy-related vocalizations than their tolerant counterparts. Findings suggest primate signals are used and evolve in tandem with the nature of interactions that characterize individuals' social relationships. Publisher PDF

Understanding local community attitudes toward wildlife is critical for making context-sensitive conservation planning and management decisions that may facilitate better human–wildlife coexistence. We conducted questionnaire-based interviews with local households in Qinglong Village of Mayanghe National Nature Reserve (MNNR) in China from March to August 2015. We used a mixed analysis technique based on a theoretical framework of categorical variables to explain attitudes to investigate the key factors that influenced local attitudes toward Endangered François’ langurs (Trachypithecus francoisi). We found that 53% (40, N = 75) of interviewees liked François’ langurs presence around the village, 27% did not, and 20% were neutral. Respondents with favorable attitudes to langurs associated them mainly with tangible benefits from local tourism and their positive aesthetic and emotional values. Respondents with negative attitudes to langurs associated them with tangible costs such as crop feeding and the destruction of their houses. Over half (N = 9) of respondents with neutral attitudes associated langurs with various cost and benefit trade-offs. Overall, local people tended to have slightly negative perceptions of the langurs’ impacts at the household level, while they had very positive perceptions of their impacts at the community level. Ordinal logistic regression models revealed that age, gender, and impact perceptions were significantly associated with local residents’ attitudes toward the langurs at the household and community levels. We suggest that such socioeconomic monitoring efforts should be periodically conducted in protected areas such as MNNR, especially in the context of rapid economic and infrastructure development.

Item does not contain fulltext It is now widely accepted that the brunt of animal communication is conducted via several modalities, e.g. acoustic and visual, either simultaneously or sequentially. This is a laudable multimodal turn relative to traditional accounts of temporal aspects of animal communication which have focused on a single modality at a time. However, the fields that are currently contributing to the study of multimodal communication are highly varied, and still largely disconnected given their sole focus on a particular level of description or their particular concern with human or non-human animals. Here, we provide an integrative overview of converging findings that show how multimodal processes occurring at neural, bodily, as well as social interactional levels each contribute uniquely to the complex rhythms that characterize communication in human and non-human animals. Though we address findings for each of these levels independently, we conclude that the most important challenge in this field is to identify how processes at these different levels connect. This article is part of the theme issue 'Synchrony and rhythm interaction: from the brain to behavioural ecology'. 9 p.

An animal's ability to recognize another individual by matching their image to their voice suggests they form internal representations of other individuals. To what extent this ability, termed cross-modal individual recognition, extends to birds other than corvids is unknown. Here, we used an expectancy violation paradigm to determine whether a monogamous territorial seabird (Spheniscus demersus) can cross-modally recognize familiar conspecifics (partners or colony-mates). After pairs of penguins spent time together in an isolated area, one of the penguins was released from the area leaving the focal penguin alone. Subsequently, we played contact calls of the released penguin (congruent condition) or a different penguin (incongruent condition). After being paired with a colony-mate, focal penguins' response latency to the auditory stimulus was faster in the incongruent compared to congruent condition, indicating the mismatch violated their expectations. This behavioural pattern was not observed in focal penguins after being paired with their partner. We discuss these different results in the light of penguins’ natural behaviour and the evolution of social communication strategies. Our results suggest that cross-modal individual recognition extends to penguins and reveals, in contrast with previously thought, that social communication between members of this endangered species can also use visual cues.

The principle of acoustic allometry—the larger the animal, the lower its calls' fundamental frequency—is generally observed across terrestrial mammals. Moreover, according to the Acoustic Adaptation Hypothesis, open habitats favor the propagation of high-frequency calls compared to habitats with complex vegetational structures. We carried out playback experiments in which the calls of the Guizhou snub-nosed monkey (Rhinopithecus brelichi) were used as stimuli in sound attenuation and degradation experiments to test the hypothesis that propagation of Guizhou snub-nosed monkey calls is favored above vs through the forest floor vegetation. We found that low-pitched Guizhou snub-nosed monkey vocalizations suffered less attenuation than its high-pitched calls. Guizhou snub-nosed monkeys were observed emitting high-pitched calls from 1.5 to 5.0 m above the ground. The use of high-pitched calls from these heights coupled with the concomitant behavior of moving about above the understory may provide a signal for receivers which maximizes potential transmission and efficacy. Our results support the Acoustic Adaptation Hypothesis and suggest that by uncoupling its vocal output from its size, this monkey can produce a high-pitched call with a broad spectral bandwidth, thereby increasing both its saliency and the frequency range over which the animal may more effectively communicate in its natural habitat.

Summary What are the origins of musical rhythm? One approach to the biology and evolution of music consists in finding common musical traits across species. These similarities allow biomusicologists to infer when and how musical traits appeared in our species 1 . A parallel approach to the biology and evolution of music focuses on finding statistical universals in human music 2 . These include rhythmic features that appear above chance across musical cultures. One such universal is the production of categorical rhythms 3 , defined as those where temporal intervals between note onsets are distributed categorically rather than uniformly 2 , 4 , 5 . Prominent rhythm categories include those with intervals related by small integer ratios, such as 1:1 (isochrony) and 1:2, which translates as some notes being twice as long as their adjacent ones. In humans, universals are often defined in relation to the beat, a top-down cognitive process of inferring a temporal regularity from a complex musical scene 1 . Without assuming the presence of the beat in other animals, one can still investigate its downstream products, namely rhythmic categories with small integer ratios detected in recorded signals. Here we combine the comparative and statistical universals approaches, testing the hypothesis that rhythmic categories and small integer ratios should appear in species showing coordinated group singing 3 . We find that a lemur species displays, in its coordinated songs, the isochronous and 1:2 rhythm categories seen in human music, showing that such categories are not, among mammals, unique to humans 3 .