Quantitative analysis of vocalisation types in male common cuckoos' "gowk" call complex

Acoustic communication of animals often contains two types of vocalizations: loud sounds for long-range and soft sounds for short-range signalling. Brood parasitic common cuckoos (Cuculus canorus) are suitable study objects for research on acoustic signalling as they have a simple acoustic repertoire, of which the loud territorial advertisement calls of males, the "cu-coo", is the most famous type. Although a distinct group of soft calls has also been reported in early naturalists' works, no systematic studies compared them acoustically. Even the classification of these soft calls is lacking. Here we surveyed these neglected types of calls, and evaluated them through bioacustic analyses. Specifically, we compared the following soft calls: single gowk, guo, and the series of gowk calls. The advertisement call ("cu-coo") was used as the referent for these comparisons. As the male's gowk series call most typically contains 3-5 elements with decreasing volume (disappearing at the end), we compared the first two elements of this call. Our analyses revealed great acoustic similarities between three call types (gowk series call 1st note, gowk series call 2nd note, and single gowk call), and the distinctiveness of the other call type (guo) from this group. Structurally the gowk cannot be regarded as a separate call from a male's gowk series call, and the only difference is that the series call contains a set of the gowk calls. Our classification of cuckoo calls offers the possibility for further research into their functional importance and communicative role in male-male or female-male social contexts.

A small vocal repertoire during the breeding season expresses complex behavioral motivations and individual signature in the common coot

Background

Although acoustic communication plays an essential role in the social interactions of Rallidae, our knowledge of how Rallidae encode diverse types of information using simple vocalizations is limited. We recorded and examined the vocalizations of a common coot (Fulica atra) population during the breeding season to test the hypotheses that 1) different call types can be emitted under different behavioral contexts, and 2) variation in the vocal structure of a single call type may be influenced both by behavioral motivations and individual signature. We measured a total of 61 recordings of 30 adults while noting the behavioral activities in which individuals were engaged. We compared several acoustic parameters of the same call type emitted under different behavioral activities to determine how frequency and temporal parameters changed depending on behavioral motivations and individual differences.

Results

We found that adult common coots had a small vocal repertoire, including 4 types of call, composed of a single syllable that was used during 9 types of behaviors. The 4 calls significantly differed in both frequency and temporal parameters and can be clearly distinguished by discriminant function analysis. Minimum frequency of fundamental frequency (F0min) and duration of syllable (T) contributed the most to acoustic divergence between calls. Call a was the most commonly used (in 8 of the 9 behaviors detected), and maximum frequency of fundamental frequency (F0max) and interval of syllables (TI) contributed the most to variation in call a. Duration of syllable (T) in a single call a can vary with different behavioral motivations after individual vocal signature being controlled.

Conclusions

These results demonstrate that several call types of a small repertoire, and a single call with function-related changes in the temporal parameter in common coots could potentially indicate various behavioral motivations and individual signature. This study advances our knowledge of how Rallidae use “simple” vocal systems to express diverse motivations and provides new models for future studies on the role of vocalization in avian communication and behavior.

Contextual variations in calls of two nonoscine birds: the blue petrel Halobaena caerulea and the Antarctic prion Pachyptila desolata

Bird vocalizations are critical cues in social interactions as they convey temporary information varying with the social context, for example, the signaler motivation when facing a rival or a potential mate. To date, literature mainly focused on learning birds. Burrowing petrels (Procellariidae) are nonlearning birds with a limited vocal repertoire. Bachelor males communicate with conspecifics with a single call emitted in three situations: in the absence of a certain auditory (spontaneous calls), toward females (female-directed calls), and toward males (male-directed calls). We first hypothesized that, although the call structure is preserved, temporal and spectral parameters vary between the three call types of bachelor males, translating different motivations (Motivation Hypothesis). To go further, we hypothesized that acoustic variations in male-directed calls indicate the signaler’s aggressive motivation and, therefore, the variations are similar whether calls are produced by breeder or bachelor males (Breeding Status Hypothesis). We tested the two hypotheses performing field playback experiments on two petrel species: the blue petrel (Halobaena caerulea) and the Antarctic prion (Pachyptila desolata). Despite the obvious call stereotypy, we observed temporal variations and frequency shifts when males react to a female or a male, which may translate the sexual or aggressive motivation of the signaler. Furthermore, the similarity of variations in male-directed calls of both breeder and bachelor males suggests the aggressive motivation. So far, vocal plasticity in nonlearning birds has been greatly underestimated. Here, we highlighted the expression of different motivations through vocal variations and the ability to produce frequency variations in species with genetically coded vocalizations.

Regularity in speech rhythm as a social coalition signal

Regular rhythm facilitates audiomotor entrainment and synchronization in motor behavior and vocalizations between individuals. As rhythm entrainment between interacting agents is correlated with higher levels of cooperation and prosocial affiliative behavior, humans can potentially map regular speech rhythm onto higher cooperation and friendliness between interacting individuals. We tested this hypothesis at two rhythmic levels: pulse (recurrent acoustic events) and meter (hierarchical structuring of pulses based on their relative salience). We asked the listeners to make judgments of the hostile or collaborative attitude of two interacting agents who exhibit either regular or irregular pulse (Experiment 1) or meter (Experiment 2). The results confirmed a link between the perception of social affiliation and rhythmicity: evenly distributed pulses (vowel onsets) and consistent grouping of pulses into recurrent hierarchical patterns are more likely to be perceived as cooperation signals. People are more sensitive to regularity at the level of pulse than at the level of meter, and they are more confident when they associate cooperation with isochrony in pulse. The evolutionary origin of this faculty is possibly the need to transmit and perceive coalition information in social groups of human ancestors. We discuss the implications of these findings for the emergence of speech in humans.

Speech Rhythm Convergence as a Social Coalition Signal

Patterns of nonverbal and verbal behavior of interlocutors become more similar as communication progresses. Rhythm entrainment promotes prosocial behavior and signals social bonding and cooperation. Yet, it is unknown if the convergence of rhythm in human speech is perceived and is used to make pragmatic inferences regarding the cooperative urge of the interactors. We conducted two experiments to answer this question. For analytical purposes, we separate pulse (recurring acoustic events) and meter (hierarchical structuring of pulses based on their relative salience). We asked the listeners to make judgments on the hostile or collaborative attitude of interacting agents who exhibit different or similar pulse (Experiment 1) or meter (Experiment 2). The results suggest that rhythm convergence can be a marker of social cooperation at the level of pulse, but not at the level of meter. The mapping of rhythmic convergence onto social affiliation or opposition is important at the early stages of language acquisition. The evolutionary origin of this faculty is possibly the need to transmit and perceive coalition information in social groups of human ancestors. We suggest that this faculty could promote the emergence of the speech faculty in humans.

Combinatoriality in the vocal systems of nonhuman animals

A key challenge in the field of human language evolution is the identification of the selective conditions that gave rise to language's generative nature. Comparative data on nonhuman animals provides a powerful tool to investigate similarities and differences among nonhuman and human communication systems and to reveal convergent evolutionary mechanisms. In this article, we provide an overview of the current evidence for combinatorial structures found in the vocal system of diverse species. We show that considerable structural diversity exits across and within species in the forms of combinatorial structures used. Based on this we suggest that a fine-grained classification and differentiation of combinatoriality is a useful approach permitting systematic comparisons across animals. Specifically, this will help to identify factors that might promote the emergence of combinatoriality and, crucially, whether differences in combinatorial mechanisms might be driven by variations in social and ecological conditions or cognitive capacities. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Linguistics > Evolution of Language.

Individually specific call feature is not used to neighbour-stranger discrimination: the corncrake case

In various contexts, animals rely on acoustic signals to differentiate between conspecifics. Currently, studies examining vocal signatures use two main approaches. In the first approach, researchers search for acoustic characteristics that have the potential to be individual specific. This approach yields information on variation in signal parameters both within and between individuals and generates practical tools that can be used in population monitoring. In the second approach, playback experiments with natural calls are conducted to discern whether animals are capable of discriminating among the vocal signatures of different individuals. However, both approaches do not reveal the exact signal characteristics that are being used in the discrimination process. In this study, we tested whether an individual-specific call characteristic – namely the length of the intervals between successive maximal amplitude peaks within syllables (PPD) – is crucial in neighbour-stranger discrimination by males of the nocturnal and highly secretive bird species, the corncrake (Crex crex). We conducted paired playback experiments in which corncrakes (n = 47) were exposed to artificial calls with PPD characteristics of neighbour and stranger birds. These artificial calls differed only in PPD structure. The calls were broadcast from a speaker, and we recorded the birds' behavioural responses. Although corncrakes have previously been experimentally shown to discriminate between neighbours and strangers, we found no difference in the responses to the artificial calls representing neighbours versus strangers. This finding demonstrates that even if vocal signatures are individual specific within a species, it does not automatically mean that said signatures are being crucial in discrimination among individuals. At the same time, the birds' aggressive responses to the artificial calls indicated that the information transmitted by PPDs is important in species-specific call recognition and may be used by males and/or females to evaluate sender quality, similarly like sound frequency in some insect species.