Low frequency groans indicate larger and more dominant fallow deer (Dama dama) males

Sound symbolism in Japanese names: Machine learning approaches to gender classification

This study investigates the sound symbolic expressions of gender in Japanese names with machine learning algorithms. The main goal of this study is to explore how gender is expressed in the phonemes that make up Japanese names and whether systematic sound-meaning mappings, observed in Indo-European languages, extend to Japanese. In addition to this, this study compares the performance of machine learning algorithms. Random Forest and XGBoost algorithms are trained using the sounds of names and the typical gender of the referents as the dependent variable. Each algorithm is cross-validated using k-fold cross-validation (28 folds) and tested on samples not included in the training cycle. Both algorithms are shown to be reasonably accurate at classifying names into gender categories; however, the XGBoost model performs significantly better than the Random Forest algorithm. Feature importance scores reveal that certain sounds carry gender information. Namely, the voiced bilabial nasal /m/ and voiceless velar consonant /k/ were associated with femininity, and the high front vowel /i/ were associated with masculinity. The association observed for /i/ and /k/ stand contrary to typical patterns found in other languages, suggesting that Japanese is unique in the sound symbolic expression of gender. This study highlights the importance of considering cultural and linguistic nuances in sound symbolism research and underscores the advantage of XGBoost in capturing complex relationships within the data for improved classification accuracy. These findings contribute to the understanding of sound symbolism and gender associations in language.

"The song remains the same": not really! Vocal flexibility in the song of the indris

In studying communicative signals, we can think of flexibility as a necessary correlate of creativity. Flexibility enables animals to find practical solutions and appropriate behaviors in mutable situations. In this study, we aimed to quantify the degree of flexibility in the songs of indris (Indri indri), the only singing lemur, using three different metrics: Jaro Distance, normalized diversity, and entropy. We hypothesized that the degree and the co-variation of the flexibility of indris singing together would vary according to their status and sex. We found that dominant females were more flexible than dominant males when concatenating elements into strings (element concatenation). The number of different elements in a song contribution normalized by the contribution length (contribution diversity) of dominant individuals positively co-varied for seven duetting pairs. Non-dominant individuals were more variable in element concatenation than dominant individuals, and they were more diverse in phrase type than dominant females. Independently from sex and status, individual contributions did not differ in entropy (a measure of the predictability of contributions). These results corroborate previous findings regarding the dimorphism by sex and by status of individual contributions to songs. Thus, they shed light on the presence and expression of flexibility in the behavior of a non-human primate species. Indeed, they potentially show an effect of social features in shaping vocal flexibility, which underlies many communication systems, including human language. We speculate that this degree of flexibility may account for creativity.

Penguins perceive variations of source- and filter-related vocal parameters of species-specific vocalisations

Animal vocalisations encode a wide range of biological information about the age, sex, body size, and social status of the emitter. Moreover, vocalisations play a significant role in signalling the identity of the emitter to conspecifics. Recent studies have shown that, in the African penguin (Spheniscus demersus), acoustic cues to individual identity are encoded in the fundamental frequency (F0) and resonance frequencies (formants) of the vocal tract. However, although penguins are known to produce vocalisations where F0 and formants vary among individuals, it remains to be tested whether the receivers can perceive and use such information in the individual recognition process. In this study, using the Habituation-Dishabituation (HD) paradigm, we tested the hypothesis that penguins perceive and respond to a shift of ± 20% (corresponding to the natural inter-individual variation observed in ex-situ colonies) of F0 and formant dispersion (ΔF) of species-specific calls. We found that penguins were more likely to look rapidly and for longer at the source of the sound when F0 and formants of the calls were manipulated, indicating that they could perceive variations of these parameters in the vocal signals. Our findings provide the first experimental evidence that, in the African penguin, listeners can perceive changes in F0 and formants, which can be used by the receiver as potential cues for the individual discrimination of the emitter.

Encoding of Arousal and Physical Characteristics in Audible and Ultrasonic Vocalizations of Mongolian Gerbil Pups Testing Common Rules for Mammals

In mammals, common rules for the encoding of arousal and physical characteristics of the sender are suggested based on a similar vocal production apparatus. In this study, we want to investigate to what extent vocalizations of developing Mongolian gerbil pups fulfill these rules. We recorded vocalizations of 28 Mongolian gerbil pups in four developmental stages using a separation paradigm, suggested to induce different arousal levels. For low arousal, a pup was placed in an arena isolated from its siblings and parents; for high arousal, the pup was additionally stressed through the simulation of a predator. An unsupervised cluster analysis revealed three call types: ultrasonic (USV), audible vocalizations (ADV), and transitions between both (USV-ADV). The USV and USV-ADV rate showed an age-dependent decrease, contrasting an age-dependent increase for ADVs. Vocal correlates for the encoding of arousal were found for USVs and of physical characteristics for USVs and ADVs. However, the pattern of encoding these cues differed between call types and only partly confirmed the common rules suggested for mammals. Our results show that divergent encoding patterns do not only differ between species but also between call types within a species, indicating that coding rules can be shaped by socio-ecological factors or call type specific production mechanisms.

Variability in humpback whale songs reveals how individuals can be distinctive when sharing a complex vocal display

Individually distinctive acoustic signals in animal vocal communication are taxonomically widespread, however, the investigation of these signal types in marine mammals has focused only on a few species. Humpback whale songs are a stereotyped, hierarchically structured vocal display performed by males, and hence thought to be sexually selected. Within a population, whales conform to a common version of the song despite the song constantly evolving. While humpback songs have been studied extensively at the population level, individual level variation has been rarely described, with inconclusive results. Here, we quantified inter- and intra-individual variability at different levels in the song hierarchy using songs from 25 singers across two song types from the eastern Australian population song of 2002 (12 singers), and the revolutionary song introduced in 2003 (13 singers). Inter-individual variability was found heterogeneously across all hierarchical levels of the song structure. In addition, distinct and individually specific patterns of song production were consistently recorded across song levels, with clear structural differences between the two song types. These results suggest that within the constraints of song conformity, males can produce individually distinctive patterns that could function as an advertisement to females to convey individual qualities.

Ovine vocal individuality expression by ewes and lambs at a late (40 days) post-partum time point

Recognizing the identity of conspecifics is important for survival and social interactions. In sheep, vocal individuality enhances postnatal recognition and strengthens the mother-offspring bond. Although previous studies report vocal individuality in an early postnatal period (3-15 days of life), scarce information exists on whether individuality occurs at a later postnatal time point. The aim of the study was to identify whether individuality in acoustic cues is expressed in ewes' and their lambs' bleats at 40 days post-partum. Dairy ewes (N = 21) and their suckling offspring (n = 30) were isolated separately without hearing or seeing each other, and vocalizations were recorded. Different approaches for estimating individuality on 18 determined acoustic parameters were implemented. All parameters showed individuality, but higher individuality appeared in those related with source and spectral characteristics. A discriminant function analysis showed similar levels of individuality between ewes and lambs, but lower than that reported in an earlier postnatal time, suggesting that ewes and lambs do not need strong individualized cues at the examined time point. In both cases, jitter was the only common parameter, suggesting its importance. Distinctive cues were noted between siblings. Ewes displayed vocal individuality at their dry season (a later time point than suckling period), which was based on amplitude-related acoustic parameters.

Mathematical models of long term evolution of blue whale song types' frequencies

The linear decrease in the frequency of blue whale songs around the world is, to date, an unexplained phenomenon. We show it can be reproduced by a mathematical model considering two antagonistic behavioral trends: first, a bias towards conformity in the song, and second, a tendency to try and sing lower than the other whales. We check the robustness of our model by considering some more complex premises. First, different hierarchical relations between the singers are explored, adapting methods used in the flocking motion studies. Then a population-dependant simulation shows that even considering the gradual addition of new whales, the evolution is still globally linear. Finally, we show that intra-annual variations surging from different causes can be naturally incorporated into the model. We then conclude that, unlike other explanations, a cultural hypothesis seems compatible with the observed linearity of the blue whales's songs frequency shift.

Long duration advertisement calls of nesting male plainfin midshipman fish are honest indicators of size and condition

The plainfin midshipman fish (Porichthys notatus) has long served as a model organism for neuroethology research on acoustic communication and related social behaviors. Type I or "singing" males produce highly stereotyped, periodic advertisement calls that are the longest known uninterrupted vertebrate vocalizations, lasting up to two hours in duration. Despite the extensive literature on the acoustic behaviour of this species, it remains unclear whether reproductive males signal their quality via their highly energetic, multiharmonic advertisement calls. Here, we recorded the advertisement calls of 22 reproductive type I males at night in a controlled laboratory setting in which males were housed in artificial tanks maintained at a constant temperature (13.9+0.3°C). The duration of the advertisement calls from type I males was observed to increase from the first call of the night to the middle call after which call duration remained steady until the early morning hours and first light. A strong positive correlation was observed between loudness (SPL and maximum SPL) of the advertisement call and body size (mass and standard length; rs>0.8). In addition, an asymptotic relationship was observed between the harmonic frequencies (F0-F10) of the advertisement calls and male body condition, with harmonic frequencies initially increasing with body condition but then plateauing at higher body condition. Taken together, our results suggest that type I male advertisement calls provide reliable honest information about male quality regarding size and body condition. Such condition dependent information of calling males could potentially be used by receptive females to help facilitate mate choice decisions.

Behavioural and physiological plasticity in social hierarchies

Individuals occupying dominant and subordinate positions in social hierarchies exhibit divergent behaviours, physiology and neural functioning. Dominant animals express higher levels of dominance behaviours such as aggression, territorial defence and mate-guarding. Dominants also signal their status via auditory, visual or chemical cues. Moreover, dominant animals typically increase reproductive behaviours and show enhanced spatial and social cognition as well as elevated arousal. These biobehavioural changes increase energetic demands that are met via shifting both energy intake and metabolism and are supported by coordinated changes in physiological systems including the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes as well as altered gene expression and sensitivity of neural circuits that regulate these behaviours. Conversely, subordinate animals inhibit dominance and often reproductive behaviours and exhibit physiological changes adapted to socially stressful contexts. Phenotypic changes in both dominant and subordinate individuals may be beneficial in the short-term but lead to long-term challenges to health. Further, rapid changes in social ranks occur as dominant animals socially ascend or descend and are associated with dynamic modulations in the brain and periphery. In this paper, we provide a broad overview of how behavioural and phenotypic changes associated with social dominance and subordination are expressed in neural and physiological plasticity. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Movement of Free-Ranging Koalas in Response to Male Vocalisation Playbacks

Simple Summary

Conservation management is critical for threatened wildlife species and an effective conservation approach relies on good understanding of animal behaviour in natural habitat. Currently, koalas are listed as vulnerable to extinction in Australia with declining populations, but their social and breeding system remains unclear. Male koala vocalisations, known as bellows, are believed to be closely related to their breeding behaviour. Bellows incorporate callers’ body size information which can be perceived by other koalas. In this study, we tested the behavioural responses of 20 GPS-collared free ranging koalas to bellow recordings collected from small (<6 kg) and large (>8.5 kg) adult male koalas. We report evidence of intra-male competition, with adult males approaching bellow playbacks, particularly those from small-sized males. In contrast, juvenile males under three years of age showed avoidance of the playbacks. No patterns in the response of females were detected. Our results provide the strongest evidence yet that bellows are primarily a means by which males occupy and control habitat space during the breeding season. Future studies are required to see if female response to bellows depends on their reproductive status.

Abstract

Effective conservation strategies rely on knowledge of seasonal and social drivers of animal behaviour. Koalas are generally solitary and their social arrangement appears to rely on vocal and chemical signalling. Male koala vocalisations, known as bellows, are believed to be closely related to their breeding behaviour. Previous research suggests that oestrous female koalas use bellows to locate unique males to mate with, and that males can similarly use bellows to evaluate the physical attributes of their peers. We tested the behavioural responses of 20 free ranging koalas to bellow recordings collected from small (<6 kg) and large (>8.5 kg) adult male koalas. Individual koala movement was reported by hourly-uploaded GPS coordinates. We report evidence of intra-male competition, with adult males approaching bellow playbacks, particularly those from small-sized males. In contrast, males under three years of age were averse to the playbacks. No patterns in the response of females were detected. Our results provide the strongest evidence yet that bellows are primarily a means by which males occupy and control space during the breeding season. Future studies are required to see if female response to bellows depends on their reproductive status.

Rethinking the frequency code: a meta-analytic review of the role of acoustic body size in communicative phenomena

The widely cited frequency code hypothesis attempts to explain a diverse range of communicative phenomena through the acoustic projection of body size. The set of phenomena includes size sound symbolism (using /i/ to signal smallness in words such as teeny), intonational phonology (using rising contours to signal questions) and the indexing of social relations via vocal modulation, such as lowering one's voice pitch to signal dominance. Among other things, the frequency code is commonly interpreted to suggest that polite speech should be universally signalled via high pitch owing to the association of high pitch with small size and submissiveness. We present a cross-cultural meta-analysis of polite speech of 101 speakers from seven different languages. While we find evidence for cross-cultural variation, voice pitch is on average lower when speakers speak politely, contrary to what the frequency code predicts. We interpret our findings in the light of the fact that pitch has a multiplicity of possible communicative meanings. Cultural and contextual variation determines which specific meanings become manifest in a specific interactional context. We use the evidence from our meta-analysis to propose an updated view of the frequency code hypothesis that is based on the existence of many-to-many mappings between speech acoustics and communicative interpretations.

This article is part of the theme issue ‘Voice modulation: from origin and mechanism to social impact (Part I)’.

Honest signaling in mouse lemur vocalizations?

Animal vocalizations may provide information about a sender’s condition or motivational state and, hence, mediate social interactions. In this study, we examined whether vocalizations of gray mouse lemurs (Microcebus murinus) emitted in aggressive contexts (grunts, tsaks) co-vary with physical condition, which would underly and indicate honest signaling. We recorded calls from captive individuals that were subjected to a caloric restricted (CR) or ad libitum (AL) diet, assuming that individuals on an ad libitum dietary regime were in better condition. We analyzed 828 grunts produced by seven CR and nine AL individuals and 270 tsaks by eight CR and five AL individuals. Grunts consisted of two separate elements, with the 1st element having more energy in higher frequencies than the 2nd element. Body mass correlated negatively with acoustic features of grunts, and heavier individuals produced lower-frequency grunts. Acoustic features of grunts did not differ between sexes. Acoustic features of tsaks were predicted by neither body mass nor sex. However, tsaks produced by AL individuals were noisier than those of CR individuals. Hence, manipulation of body condition via dietary regimes affected acoustic features of calls given during aggression in different ways: acoustic features of grunts varied according to the rule of acoustic allometry, and can be considered as honest signals. Acoustic features of tsaks, however, varied according to motivational structural rules. Longitudinal studies are now indicated to examine whether intra-individual changes in body mass are also reflected in the acoustic structure of calls, allowing callers to signal more flexible variation in condition.

Roars, groans and moans: Anatomical correlates of vocal diversity in polygynous deer

Eurasian deer are characterized by the extraordinary diversity of their vocal repertoires. Male sexual calls range from roars with relatively low fundamental frequency (hereafter fo ) in red deer Cervus elaphus, to moans with extremely high fo in sika deer Cervus nippon, and almost infrasonic groans with exceptionally low fo in fallow deer Dama dama. Moreover, while both red and fallow males are capable of lowering their formant frequencies during their calls, sika males appear to lack this ability. Female contact calls are also characterized by relatively less pronounced, yet strong interspecific differences. The aim of this study is to examine the anatomical bases of these inter-specific and inter-sexual differences by identifying if the acoustic variation is reflected in corresponding anatomical variation. To do this, we investigated the vocal anatomy of male and female specimens of each of these three species. Across species and sexes, we find that the observed acoustic variability is indeed related to expected corresponding anatomical differences, based on the source-filter theory of vocal production. At the source level, low fo is associated with larger vocal folds, whereas high fo is associated with smaller vocal folds: sika deer have the smallest vocal folds and male fallow deer the largest. Red and sika deer vocal folds do not appear to be sexually dimorphic, while fallow deer exhibit strong sexual dimorphism (after correcting for body size differences). At the filter level, the variability in formants is related to the configuration of the vocal tract: in fallow and red deer, both sexes have evolved a permanently descended larynx (with a resting position of the larynx much lower in males than in females). Both sexes also have the potential for momentary, call-synchronous vocal tract elongation, again more pronounced in males than in females. In contrast, the resting position of the larynx is high in both sexes of sika deer and the potential for further active vocal tract elongation is virtually absent in both sexes. Anatomical evidence suggests an evolutionary reversal in larynx position within sika deer, that is, a secondary larynx ascent. Together, our observations confirm that the observed diversity of vocal behaviour in polygynous deer is supported by strong anatomical differences, highlighting the importance of anatomical specializations in shaping mammalian vocal repertoires. Sexual selection is discussed as a potential evolutionary driver of the observed vocal diversity and sexual dimorphisms.

Chest beats as an honest signal of body size in male mountain gorillas (Gorilla beringei beringei)

Acoustic signals that reliably indicate body size, which usually determines competitive ability, are of particular interest for understanding how animals assess rivals and choose mates. Whereas body size tends to be negatively associated with formant dispersion in animal vocalizations, non-vocal signals have received little attention. Among the most emblematic sounds in the animal kingdom is the chest beat of gorillas, a non-vocal signal that is thought to be important in intra and inter-sexual competition, yet it is unclear whether it reliably indicates body size. We examined the relationship among body size (back breadth), peak frequency, and three temporal characteristics of the chest beat: duration, number of beats and beat rate from sound recordings of wild adult male mountain gorillas. Using linear mixed models, we found that larger males had significantly lower peak frequencies than smaller ones, but we found no consistent relationship between body size and the temporal characteristics measured. Taken together with earlier findings of positive correlations among male body size, dominance rank and reproductive success, we conclude that the gorilla chest beat is an honest signal of competitive ability. These results emphasize the potential of non-vocal signals to convey important information in mammal communication.

Rutting vocal display in male impala (Aepyceros melampus) and overlap with alarm context

BACKGROUND

The rutting vocal display of male impala Aepyceros melampus is unique for its complexity among ruminants. This study investigates bouts of rutting calls produced towards potential mates and rival males by free-ranging male impala in Namibia. In particular, a comparison of male rutting and alarm snorts is conducted, inspired by earlier findings of mate guarding by using alarm snorts in male topi Damaliscus lunatus.

RESULTS

Rutting male impala produced 4-38 (13.5 ± 6.5) rutting calls per bout. We analyzed 201 bouts, containing in total 2709 rutting calls of five types: continuous roars produced within a single exhalation-inhalation cycle; interrupted roars including few exhalation-inhalation cycles; pant-roars distinctive by a pant-phase with rapidly alternating inhalations and exhalations; usual snorts lacking any roar part; and roar-snorts starting with a short roar part. Bouts mostly started and ended with usual snorts. Continuous roars were the shortest roars. The average duration of the exhalatory phase was longest in the continuous roars and shortest in the pant-roars. The average fundamental frequency (49.7-51.4 Hz) did not differ between roar types. Vocal tract length, calculated by using measurements of the first four vocal tract resonances (formants), ranged within 381-382 mm in all roar types. In the studied male impala, rutting snorts within bouts of rutting calls were longer and had higher values of the upper quartile in the call spectra than alarm snorts produced towards potential danger.

CONCLUSIONS

Additional inhalations during the emission of the interrupted and pant-roars prolong their duration compared to the continuous roars but do not affect the fundamental frequency or the degree of larynx retraction while roaring. Alarm snorts are separated from one another by large intervals, whereas the intervals between rutting snorts within bouts are short. Sometimes, rutting snorts alternate with roars, whereas alarm snorts do not. Therefore, it is not the acoustic structure of individual snorts but the temporal sequence and the occasional association with another call type that defines snorts as either rutting or alarm snorts. The rutting snorts of male impala may function to attract the attention of receptive females and delay their departure from a male's harem or territory.

Territorial calls of the bat Hipposideros armiger may encode multiple types of information: body mass, dominance rank and individual identity

In highly vocal species, territorial aggression is often accompanied using vocalizations. These vocalizations can play a critical role in determining the outcome of male-male agonistic interactions. For this, vocalizations of contestants must contain information that is indicative of each competitor's fighting ability as well as its identity, and also contestants must be able to perceive information about the physical attributes, quality and identity of the vocalizer. Here, we used adult male Great Himalayan leaf-nosed bats (Hipposideros armiger) to test whether territorial calls encoded honest information about a caller's physical attributes, quality and individual identity. We did this by exploring the relationships between territorial calls and two potential indices of fighting ability: body mass and dominance rank. Using synchronized audio-video recording, we monitored bat territorial calls and dominance rank of 16 adult male H. armiger in the laboratory. Additionally, habituation-dishabituation playback experiments were performed to test for vocal discrimination. Results showed that body mass was negatively related to minimum frequency and positively related to syllable duration. Dominance score was also negatively related to minimum frequency and positively related to peak frequency. Furthermore, a discriminant function analysis suggested that territorial calls encode an individual signature. Therefore, our data show that males have the ability to utilize this vocal individual signature to discriminate between vocalizing males. In short, territorial calls of male H. armiger contain information about body mass, dominance rank and individual identity, and contestants are probably capable of perceiving this information and may use it to make appropriate decisions during agonistic interactions.

Social Behaviour of Horses in Response to Vocalisations of Predators

We tested the hypothesis that social defensive responses to the vocalisation of a predator still exist in horses. The recordings of a grey wolf, an Arabian leopard and a golden jackal were played to 20 Konik polski and Arabian mares. Durations of grazing, standing still, standing alert and the number of steps in walk and trot/canter were measured. In one-minute scans, the distances of the focal horse from the reference horse (DIST-RH) and from the nearest loudspeaker (DIST-LS) were approximated. The vocalisation of a leopard aroused the Arabians more than the Koniks (less grazing, stand-still and walk, more stand-alert and trotting/cantering). Koniks showed more relaxed behaviours to the leopard vocalisation (more grazing, stand-still and walk), but high alertness to the wolf playback (stand-alert, trotting/cantering). Spatial formation of the herd of Koniks showed tight grouping (lower DIST-RH) and maintaining distance from the potential threat (DIST-LS) in response to the wolf howling, while the Arabians approached the loudspeakers in linear herd formation when the leopard growls were played. Adult horses responded to potential predation by changing spatial group formations. This ability to apply a social strategy may be one of the explanations for the least number of horses among all hunted farm animal species.

Semantic Associations Dominate Over Perceptual Associations in Vowel-Size Iconicity

We tested the influence of perceptual features on semantic associations between the acoustic characteristics of vowels and the notion of size. To this end, we designed an experiment in which we manipulated size on two dissociable levels: the physical size of the pictures presented during the experiment (perceptual level) and the implied size of the objects depicted in the pictures (semantic level). Participants performed an Implicit Association Test in which the pictures of small objects were larger than those of large objects - that is, the actual size ratio on the semantic level was inverted on the perceptual level. Our results suggest that participants matched visual and acoustic stimuli in accordance with the content of the pictures (i.e., the inferred size of the depicted object), whereas directly perceivable features (i.e., the physical size of the picture) had only a marginal influence on participants' performance. Moreover, as the experiment has been conducted at two different sites (Japan and Germany), the results also suggest that the participants' cultural background or mother tongue had only a negligible influence on the effect. Our results, therefore, support the assumption that associations across sensory modalities can be motivated by the semantic interpretation of presemantic stimuli.

Automated bioacoustics: methods in ecology and conservation and their potential for animal welfare monitoring

Vocalizations carry emotional, physiological and individual information. This suggests that they may serve as potentially useful indicators for inferring animal welfare. At the same time, automated methods for analysing and classifying sound have developed rapidly, particularly in the fields of ecology, conservation and sound scene classification. These methods are already used to automatically classify animal vocalizations, for example, in identifying animal species and estimating numbers of individuals. Despite this potential, they have not yet found widespread application in animal welfare monitoring. In this review, we first discuss current trends in sound analysis for ecology, conservation and sound classification. Following this, we detail the vocalizations produced by three of the most important farm livestock species: chickens ( Gallus gallus domesticus), pigs ( Sus scrofa domesticus) and cattle ( Bos taurus). Finally, we describe how these methods can be applied to monitor animal welfare with new potential for developing automated methods for large-scale farming.

Contiguity-based sound iconicity: The meaning of words resonates with phonetic properties of their immediate verbal contexts

We tested the hypothesis that phonosemantic iconicity--i.e., a motivated resonance of sound and meaning--might not only be found on the level of individual words or entire texts, but also in word combinations such that the meaning of a target word is iconically expressed, or highlighted, in the phonetic properties of its immediate verbal context. To this end, we extracted single lines from German poems that all include a word designating high or low dominance, such as large or small, strong or weak, etc. Based on insights from previous studies, we expected to find more vowels with a relatively short distance between the first two formants (low formant dispersion) in the immediate context of words expressing high physical or social dominance than in the context of words expressing low dominance. Our findings support this hypothesis, suggesting that neighboring words can form iconic dyads in which the meaning of one word is sound-iconically reflected in the phonetic properties of adjacent words. The construct of a contiguity-based phono-semantic iconicity opens many venues for future research well beyond lines extracted from poems.

Vocal tract modelling in fallow deer: are male groans nasalized?

Males of several species of deer have a descended and mobile larynx, resulting in an unusually long vocal tract, which can be further extended by lowering the larynx during call production. Formant frequencies are lowered as the vocal tract is extended, as predicted when approximating the vocal tract as a uniform quarter wavelength resonator. However, formant frequencies in polygynous deer follow uneven distribution patterns, indicating that the vocal tract configuration may in fact be rather complex. We CT-scanned the head and neck region of two adult male fallow deer specimens with artificially extended vocal tracts and measured the cross-sectional areas of the supra-laryngeal vocal tract along the oral and nasal tracts. The CT data were then used to predict the resonances produced by three possible configurations, including the oral vocal tract only, the nasal vocal tract only, or combining the two. We found that the area functions from the combined oral and nasal vocal tracts produced resonances more closely matching the formant pattern and scaling observed in fallow deer groans than those predicted by the area functions of the oral vocal tract only or of the nasal vocal tract only. This indicates that the nasal and oral vocal tracts are both simultaneously involved in the production of a non-human mammal vocalization, and suggests that the potential for nasalization in putative oral loud calls should be carefully considered.

Re-emergence of the leaf clip gesture during an alpha takeover affects variation in male chimpanzee loud calls

Loud calls are used by many species as long-distance signals for group defense, mate attraction, and inter- and intragroup spacing. Chimpanzee loud calls, or pant hoots, are used in a variety of contexts including group coordination and during male contests. Here, we observed an alpha male takeover in wild chimpanzees (Pan troglodytes verus) during which the leaf clipping gesture re-emerged after disappearing for almost two years in this community. Leaf clipping only occurred in males and was observed almost exclusively prior to pant hoot vocalizations, as has been observed in other chimpanzee communities of the Taï forest in Côte d'Ivoire. Consequently, we hypothesized that leaf clipping may be important for male-male competition by affecting variation in the acoustic properties of male chimpanzee loud calls. We therefore investigated whether pant hoots preceded by leaf clipping differed acoustically from those without, while also testing the influence of social context on pant hoot variation, namely male dominance rank and hierarchy instability, i.e., before, during and after the alpha takeover. We found that pant hoots preceded by leaf clipping were longer, contained more call elements and drum beats, and lower fundamental and peak frequencies. Moreover, during the alpha takeover pant hoots were shorter, contained fewer drum beats and higher fundamental frequencies. Additionally, pant hoot and aggression rates were also highest during the alpha takeover with leaf clipping more likely to occur on days when pant hooting rates were high. Overall social rank had limited effects on pant hoot variation. We suggest that elevated arousal and aggression during the alpha takeover triggered the re-emergence of leaf clipping and the associated acoustic changes in pant hoots. Further research should focus on the potential mechanisms by which leaf clipping is connected to variation in pant hoots and cross-population comparisons of the behaviour.

Female harbor seal (Phoca vitulina) behavioral response to playbacks of underwater male acoustic advertisement displays

During the breeding season, male harbor seals (Phoca vitulina) make underwater acoustic displays using vocalizations known as roars. These roars have been shown to function in territory establishment in some breeding areas and have been hypothesized to be important for female choice, but the function of these sounds remains unresolved. This study consisted of a series of playback experiments in which captive female harbor seals were exposed to recordings of male roars to determine if females respond to recordings of male vocalizations and whether or not they respond differently to roars from categories with different acoustic characteristics. The categories included roars with characteristics of dominant males (longest duration, lowest frequency), subordinate males (shortest duration, highest frequency), combinations of call parameters from dominant and subordinate males (long duration, high frequency and short duration, low frequency), and control playbacks of water noise and water noise with tonal signals in the same frequency range as male signals. Results indicate that overall females have a significantly higher level of response to playbacks that imitate male vocalizations when compared to control playbacks of water noise. Specifically, there was a higher level of response to playbacks representing dominant male vocalization when compared to the control playbacks. For most individuals, there was a greater response to playbacks representing dominant male vocalizations compared to playbacks representing subordinate male vocalizations; however, there was no statistical difference between those two playback types. Additionally, there was no difference between the playbacks of call parameter combinations and the controls. Investigating female preference for male harbor seal vocalizations is a critical step in understanding the harbor seal mating system and further studies expanding on this captive study will help shed light on this important issue.

Old and young female voices: effects of body weight, condition and social discomfort on the vocal aging in red deer hinds (Cervus elaphus)

In female terrestrial mammals, vocal aging has only been studied in humans and pandas. In cervids displaying convergent sex dimorphism of vocal apparatus with humans, vocal aging is only investigated in males. This cross-sectional study examined acoustic variables of nasal (closed-mouth) and oral (open-mouth) contact calls of 32 farmed Iberian red deer hinds (Cervus elaphus hispanicus) aged of 4-18 years and their relationships with caller´s age, weight, social discomfort score (bites of other hinds on hind pelt) and body condition score (fat reserves). Decrease of fundamental frequency was associated with age in both oral and nasal calls, but more prominently in the nasal calls. An increase in call duration, peak frequency and power quartiles was associated with a higher degree of bites due to social aggression. Weight and body condition weakly influenced acoustic traits. We discuss that vocal aging of hinds parallels that of vocal aging in human females.

Sound iconicity of abstract concepts: Place of articulation is implicitly associated with abstract concepts of size and social dominance

The concept of sound iconicity implies that phonemes are intrinsically associated with non-acoustic phenomena, such as emotional expression, object size or shape, or other perceptual features. In this respect, sound iconicity is related to other forms of cross-modal associations in which stimuli from different sensory modalities are associated with each other due to the implicitly perceived correspondence of their primal features. One prominent example is the association between vowels, categorized according to their place of articulation, and size, with back vowels being associated with bigness and front vowels with smallness. However, to date the relative influence of perceptual and conceptual cognitive processing on this association is not clear. To bridge this gap, three experiments were conducted in which associations between nonsense words and pictures of animals or emotional body postures were tested. In these experiments participants had to infer the relation between visual stimuli and the notion of size from the content of the pictures, while directly perceivable features did not support–or even contradicted–the predicted association. Results show that implicit associations between articulatory-acoustic characteristics of phonemes and pictures are mainly influenced by semantic features, i.e., the content of a picture, whereas the influence of perceivable features, i.e., size or shape, is overridden. This suggests that abstract semantic concepts can function as an interface between different sensory modalities, facilitating cross-modal associations.

Generalized structural equations improve sexual-selection analyses

Sexual selection is an intense evolutionary force, which operates through competition for the access to breeding resources. There are many cases where male copulatory success is highly asymmetric, and few males are able to sire most females. Two main hypotheses were proposed to explain this asymmetry: "female choice" and "male dominance". The literature reports contrasting results. This variability may reflect actual differences among studied populations, but it may also be generated by methodological differences and statistical shortcomings in data analysis. A review of the statistical methods used so far in lek studies, shows a prevalence of Linear Models (LM) and Generalized Linear Models (GLM) which may be affected by problems in inferring cause-effect relationships; multi-collinearity among explanatory variables and erroneous handling of non-normal and non-continuous distributions of the response variable. In lek breeding, selective pressure is maximal, because large numbers of males and females congregate in small arenas. We used a dataset on lekking fallow deer (Dama dama), to contrast the methods and procedures employed so far, and we propose a novel approach based on Generalized Structural Equations Models (GSEMs). GSEMs combine the power and flexibility of both SEM and GLM in a unified modeling framework. We showed that LMs fail to identify several important predictors of male copulatory success and yields very imprecise parameter estimates. Minor variations in data transformation yield wide changes in results and the method appears unreliable. GLMs improved the analysis, but GSEMs provided better results, because the use of latent variables decreases the impact of measurement errors. Using GSEMs, we were able to test contrasting hypotheses and calculate both direct and indirect effects, and we reached a high precision of the estimates, which implies a high predictive ability. In synthesis, we recommend the use of GSEMs in studies on lekking behaviour, and we provide guidelines to implement these models.

Acoustic correlates of body size and individual identity in banded penguins

Animal vocalisations play a role in individual recognition and mate choice. In nesting penguins, acoustic variation in vocalisations originates from distinctiveness in the morphology of the vocal apparatus. Using the source-filter theory approach, we investigated vocal individuality cues and correlates of body size and mass in the ecstatic display songs the Humboldt and Magellanic penguins. We demonstrate that both fundamental frequency (f0) and formants (F1-F4) are essential vocal features to discriminate among individuals. However, we show that only duration and f0 are honest indicators of the body size and mass, respectively. We did not find any effect of body dimension on formants, formant dispersion nor estimated vocal tract length of the emitters. Overall, our findings provide the first evidence that the resonant frequencies of the vocal tract do not correlate with body size in penguins. Our results add important information to a growing body of literature on the role of the different vocal parameters in conveying biologically meaningful information in bird vocalisations.

Persistent Females and Compliant Males Coordinate Alarm Calling in Diana Monkeys

Sexual dimorphisms in animal vocal behavior have been successfully explained by sexual selection theory (e.g., mammals [1-5]; birds [6, 7]; anurans [8, 9]), but this does not usually include alarm calls, which are thought to be the product of kin or individual selection (e.g., [10, 11]). Here, we present the results of playback experiments with wild Diana monkeys, a species with highly dimorphic predator-specific alarms, to investigate the communication strategies of males and females during predator encounters. First, we simulated predator presence by broadcasting vocalizations of their main predators, leopards or eagles. We found that males only produced predator-specific alarms after the females had produced theirs, in response to which the females ceased alarm calling. In a second experiment, we created congruent and incongruent situations, so that the calls of a predator were followed by playbacks of male or female alarms with a matching or mismatching referent. For congruent conditions, results were the same as in the first experiment. For incongruent conditions, however, the males always gave predator-specific alarms that referentially matched the females' calls, regardless of the previously displayed predator. In contrast, females always gave predator-specific alarms that matched the predator type, regardless of their own male's subsequent calls. Moreover, the females persistently continued to alarm call until their own male produced calls with the matching referent. Results show that males and females attend to the informational content of each other's alarm calls but prioritize them differently relative to an experienced external event, a likely reflection of different underlying selection pressures.

The evolution of acoustic size exaggeration in terrestrial mammals

Recent studies have revealed that some mammals possess adaptations that enable them to produce vocal signals with much lower fundamental frequency (F0) and formant frequency spacing (ΔF) than expected for their size. Although these adaptations are assumed to reflect selection pressures for males to lower frequency components and exaggerate body size in reproductive contexts, this hypothesis has not been tested across a broad range of species. Here we show that male terrestrial mammals produce vocal signals with lower ΔF (but not F0) than expected for their size in mating systems with greater sexual size dimorphism. We also reveal that males produce calls with higher than expected F0 and ΔF in species with increased sperm competition. This investigation confirms that sexual selection favours the use of ΔF as an acoustic size exaggerator and supports the notion of an evolutionary trade-off between pre-copulatory signalling displays and sperm production.

The Role of Grunt Calls in the Social Dominance Hierarchy of the White-Lipped Peccary (Mammalia, Tayassuidae)

Grunt-like calls are present in the vocal repertoire of many group-living mammals and seem to facilitate social interactions between lower and higher-ranking members. The white-lipped peccary (Tayassu pecari) lives in stable hierarchical mixed-sex groups and like non-human primates, usually emits grunt-like calls following aggressive interactions, mainly during feeding contexts. We investigated the possible functions of peccaries’ grunt-like calls and their relationship to the individuals’ social rank, identity, and sexual dimorphism. We observed that low-ranking individuals emitted grunt-like calls more often than high-ranking ones, and that the alpha male never emitted this vocalization. Moreover, the mean minimum frequency of grunt-like calls decreased as the peccary’s rank increased. The findings revealed differences among individual grunts, but the low accuracy of cross-validation (16%) suggests that individual recognition in peccaries may be less important than an honest signal of individual social status. In addition, the absence of differences in the acoustic parameters of grunt-like calls between males and females points to the lack of sexual dimorphism in this species. We verified that after hearing grunt calls, dominant opponents were more likely to cease attacking a victim, or at least delay the continuation of conflict, probably decreasing the severity of agonistic interactions. Our findings are particularly important to improve the current understanding of the role of grunt-like calls in herd-living mammals with linear dominant hierarchies, and strongly suggest that they are involved in the maintenance of herd social stability and cohesion.

A Chinese alligator in heliox: formant frequencies in a crocodilian

Crocodilians are among the most vocal non-avian reptiles. Adults of both sexes produce loud vocalizations known as ‘bellows’ year round, with the highest rate during the mating season. Although the specific function of these vocalizations remains unclear, they may advertise the caller's body size, because relative size differences strongly affect courtship and territorial behaviour in crocodilians. In mammals and birds, a common mechanism for producing honest acoustic signals of body size is via formant frequencies (vocal tract resonances). To our knowledge, formants have to date never been documented in any non-avian reptile, and formants do not seem to play a role in the vocalizations of anurans. We tested for formants in crocodilian vocalizations by using playbacks to induce a female Chinese alligator (Alligator sinensis) to bellow in an airtight chamber. During vocalizations, the animal inhaled either normal air or a helium/oxygen mixture (heliox) in which the velocity of sound is increased. Although heliox allows normal respiration, it alters the formant distribution of the sound spectrum. An acoustic analysis of the calls showed that the source signal components remained constant under both conditions, but an upward shift of high-energy frequency bands was observed in heliox. We conclude that these frequency bands represent formants. We suggest that crocodilian vocalizations could thus provide an acoustic indication of body size via formants. Because birds and crocodilians share a common ancestor with all dinosaurs, a better understanding of their vocal production systems may also provide insight into the communication of extinct Archosaurians.

Highlighted Article: Frequency peaks in bellows of a Chinese alligator breathing a helium–oxygen mixture instead of air shift to significantly higher frequencies, showing that crocodilian vocalizations contain vocal resonance frequencies or ‘formants’.

Honest signaling in domestic piglets (Sus scrofa domesticus): vocal allometry and the information content of grunt calls

The information conveyed in acoustic signals is a central topic in mammal vocal communication research. Body size is one form of information that can be encoded in calls. Acoustic allometry aims to identify the specific acoustic correlates of body size within the vocalizations of a given species, and formants are often a useful acoustic cue in this context. We conducted a longitudinal investigation of acoustic allometry in domestic piglets (Sus scrofa domesticus), asking whether formants of grunt vocalizations provide information concerning the caller's body size over time. On four occasions, we recorded grunts from 20 kunekune piglets, measured their vocal tract length by means of radiographs (X-rays) and weighed them. Controlling for effects of age and sex, we found that body weight strongly predicts vocal tract length, which in turn determines formant frequencies. We conclude that grunt formant frequencies could allow domestic pigs to assess a signaler's body size as it grows. Further research using playback experiments is needed to determine the perceptual role of formants in domestic pig communication.

Evidence of biphonation and source–filter interactions in the bugles of male North American wapiti (Cervus canadensis)

With an average male body mass of 320 kg, the wapiti, Cervus canadensis, is the largest extant species of Old World deer (Cervinae). Despite this large body size, male wapiti produce whistle-like sexual calls called bugles characterised by an extremely high fundamental frequency. Investigations of the biometry and physiology of the male wapiti's relatively large larynx have so far failed to account for the production of such a high fundamental frequency. Our examination of spectrograms of male bugles suggested that the complex harmonic structure is best explained by a dual-source model (biphonation), with one source oscillating at a mean of 145 Hz (F0) and the other oscillating independently at an average of 1426 Hz (G0). A combination of anatomical investigations and acoustical modelling indicated that the F0 of male bugles is consistent with the vocal fold dimensions reported in this species, whereas the secondary, much higher source at G0 is more consistent with an aerodynamic whistle produced as air flows rapidly through a narrow supraglottic constriction. We also report a possible interaction between the higher frequency G0 and vocal tract resonances, as G0 transiently locks onto individual formants as the vocal tract is extended. We speculate that male wapiti have evolved such a dual-source phonation to advertise body size at close range (with a relatively low-frequency F0 providing a dense spectrum to highlight size-related information contained in formants) while simultaneously advertising their presence over greater distances using the very high-amplitude G0 whistle component.

Changes in vocal parameters with social context in humpback whales: considering the effect of bystanders

Abstract

Many theories and communication models developed from terrestrial studies focus on a simple dyadic exchange between a sender and receiver. During social interactions, the “frequency code” hypothesis suggests that frequency characteristics of vocal signals can simultaneously encode for static signaler attributes (size or sex) and dynamic information, such as motivation or emotional state. However, the additional presence of a bystander may result in a change of signaling behavior if the costs and benefits associated with the presence of this bystander are different from that of a simple dyad. In this study, two common humpback whale social calls (“wops” and “grumbles”) were tested for differences related to group social behavior and the presence of bystanders. “Wop” parameters were stable with group social behavior, but were emitted at lower (14 dB) levels in the presence of a nearby singing whale compared to when a singing whale was not in the area. “Grumbles” were emitted at lower (30–39 Hz) fundamental frequencies in affiliative compared to non-affiliative groups and, in the presence of a nearby singing whale, were also emitted at lower (14 dB) levels. Vocal rates did not significantly change. The results suggest that, in humpbacks, the frequency in certain sound types relates to the social behavior of the vocalizing group, implying a frequency code system. The presence of a nearby audible bystander (a singing whale) had no effect on this frequency code, but by reducing their acoustic level, the signal-to-noise ratio at the singer would have been below 0, making it difficult for the singer to audibly detect the group.

Significance statement

The frequency, duration, and amplitude parameters of humpback whale social vocalizations were tested between different social contexts: group social behavior (affiliating versus non-affiliating), the presence of a nearby singing whale, and the presence of a nearby non-singing group. “Grumbles” (commonly heard low-frequency unmodulated sounds) frequencies were lower in affiliating groups compared to non-affiliating groups, suggesting a change in group motivation (such as levels of aggression). “Wop” (another common sound type) structure (frequency and duration) was similar in affiliating and non-affiliating groups. In the presence of an audible bystander (a singing whale), both sound types were emitted at similar rates, but much lower amplitudes (14 dB), vastly reducing the detectability of these sounds by the singer. This suggests that these groups were acoustically avoiding the singing whale. They did not, however, acoustically respond to the presence of a nearby non-singing group.

Structural Classification of Wild Boar (Sus scrofa) Vocalizations

Determining whether a species' vocal communication system is graded or discrete requires definition of its vocal repertoire. In this context, research on domestic pig (Sus scrofa domesticus) vocalizations, for example, has led to significant advances in our understanding of communicative functions. Despite their close relation to domestic pigs, little is known about wild boar (Sus scrofa) vocalizations. The few existing studies, conducted in the 1970s, relied on visual inspections of spectrograms to quantify acoustic parameters and lacked statistical analysis. Here, we use objective signal processing techniques and advanced statistical approaches to classify 616 calls recorded from semi‐free ranging animals. Based on four spectral and temporal acoustic parameters—quartile Q25, duration, spectral flux, and spectral flatness—extracted from a multivariate analysis, we refine and extend the conclusions drawn from previous work and present a statistically validated classification of the wild boar vocal repertoire into four call types: grunts, grunt‐squeals, squeals, and trumpets. While the majority of calls could be sorted into these categories using objective criteria, we also found evidence supporting a graded interpretation of some wild boar vocalizations as acoustically continuous, with the extremes representing discrete call types. The use of objective criteria based on modern techniques and statistics in respect to acoustic continuity advances our understanding of vocal variation. Integrating our findings with recent studies on domestic pig vocal behavior and emotions, we emphasize the importance of grunt‐squeals for acoustic approaches to animal welfare and underline the need of further research investigating the role of domestication on animal vocal communication.

Age related decline in female lar gibbon great call performance suggests that call features correlate with physical condition

BACKGROUND

White-handed gibbons (Hylobates lar) are small Asian apes known for living in stable territories and producing loud, elaborate vocalizations (songs), often in well-coordinated male/female duets. The female great call, the most conspicuous phrase of the repertoire, has been hypothesized to function in intra-sexual territorial defense. We therefore predicted that characteristics of the great call would correlate with a caller's physical condition, and thus might honestly reflect resource holding potential (RHP). Because measurement of RHP is virtually impossible for wild animals, we used age as a proxy, hypothesizing that great call climaxes are difficult to produce and maintain over time, and that older adults will therefore perform lower quality great calls than young adults. To test this we analyzed the great call climaxes of 15 wild lar gibbon females at Khao Yai National Park, Thailand and 2 captive females at Leo Conservation Center, Greenwich, CT.

RESULTS

Findings show that call climaxes correlate with female age, as young animals (n = 8, mean age: 12.9 years) produced climaxes with a higher frequency range (delta F0), maximum F0 frequency and duty cycle than old animals (n = 9, mean age: 29.6 years). A permuted discriminant function analysis also correctly classified calls by age group. During long song bouts the maximum F0 frequency of great call climaxes' also decreased. Additional data support the hypothesis that short high notes, associated with rapid inhalation as an individual catches its breath, reflect increased caller effort. Older females produced more high notes than younger females, but the difference only approached statistical significance, suggesting that calling effort may be similar across different ages. Finally, for the first time in this species, we measured peak intensity of calls in captive females. They were capable of producing climaxes in excess of 100 dB at close range (2.7 m).

CONCLUSIONS

Age and within-bout differences in the lar gibbon great call climax suggest that call features correlate with physical condition and thus the call may have evolved as an honest signal in the context of intra-sexual territorial defense and possibly also in male mate choice via sexual selection, although further testing of these hypotheses is necessary.