Neotropical wrens learn new duet rules as adults

Emotions and courtship help bonded pairs cooperate, but emotional agents are vulnerable to deceit

Coordinated pair bonds are common in birds and also occur in many other taxa. How do animals solve the social dilemmas they face in coordinating with a partner? We developed an evolutionary model to explore this question, based on observations that a) neuroendocrine feedback provides emotional bookkeeping which is thought to play a key role in vertebrate social bonds and b) these bonds are developed and maintained via courtship interactions that include low-stakes social dilemmas. Using agent-based simulation, we found that emotional bookkeeping and courtship sustained cooperation in the iterated prisoner's dilemma in noisy environments, especially when combined. However, when deceitful defection was possible at low cost, courtship often increased cooperation, whereas emotional bookkeeping decreased it.

Neural mechanisms for turn-taking in duetting plain-tailed wrens

Recent studies conducted in the natural habitats of songbirds have provided new insights into the neural mechanisms of turn-taking. For example, female and male plain-tailed wrens (Pheugopedius euophrys) sing a duet that is so precisely timed it sounds as if a single bird is singing. In this review, we discuss our studies examining the sensory and motor cues that pairs of wrens use to coordinate the rapid alternation of syllable production. Our studies included behavioral measurements of freely-behaving wrens in their natural habitat and neurophysiological experiments conducted in awake and anesthetized individuals at field sites in Ecuador. These studies show that each partner has a pattern-generating circuit in their brain that is linked via acoustic feedback between individuals. A similar control strategy has been described in another species of duetting songbird, white-browed sparrow-weavers (Plocepasser mahali). Interestingly, the combination of neurophysiological results from urethane-anesthetized and awake wrens suggest a role for inhibition in coordinating the timing of turn-taking. Finally, we highlight some of the unique challenges of conducting these experiments at remote field sites.

Developmental Plasticity in Primate Coordinated Song: Parallels and Divergences With Duetting Songbirds

Homeothermic animals (birds and mammals) are prime model systems for investigating the developmental plasticity and neural mechanisms of vocal duetting, a cooperative acoustic signal that prevails in family-living and pair-bonded species including humans. This review focuses on the nature of this trait and its nurturing during ontogeny and extending into adulthood. I begin by outlining the underpinning concepts of duet codes and pair-specific answering rules as used by birds to develop their learned coordinated song, driven by a complex interaction between self-generated and socially mediated auditory feedback. The more tractable avian model of duetting helps identify research gaps in singing primates that also use duetting as a type of intraspecific vocal interaction. Nevertheless, it has become clear that primate coordinated song—whether overlapping or antiphonal—is subject to some degree of vocal flexibility. This is reflected in the ability of lesser apes, titi monkeys, tarsiers, and lemurs to adjust the structure and timing of their calls through (1) social influence, (2) coordinated duetting both before and after mating, (3) the repair of vocal mistakes, (4) the production of heterosexual song early in life, (5) vocal accommodation in call rhythm, (6) conditioning, and (7) innovation. Furthermore, experimental work on the neural underpinnings of avian and mammalian antiphonal duets point to a hierarchical (cortico-subcortical) control mechanism that regulates, via inhibition, the temporal segregation of rapid vocal exchanges. I discuss some weaknesses in this growing field of research and highlight prospective avenues for future investigation.

The multi-dimensional nature of vocal learning

How learning affects vocalizations is a key question in the study of animal communication and human language. Parallel efforts in birds and humans have taught us much about how vocal learning works on a behavioural and neurobiological level. Subsequent efforts have revealed a variety of cases among mammals in which experience also has a major influence on vocal repertoires. Janik and Slater (Anim. Behav.60, 1-11. (doi:10.1006/anbe.2000.1410)) introduced the distinction between vocal usage and production learning, providing a general framework to categorize how different types of learning influence vocalizations. This idea was built on by Petkov and Jarvis (Front. Evol. Neurosci.4, 12. (doi:10.3389/fnevo.2012.00012)) to emphasize a more continuous distribution between limited and more complex vocal production learners. Yet, with more studies providing empirical data, the limits of the initial frameworks become apparent. We build on these frameworks to refine the categorization of vocal learning in light of advances made since their publication and widespread agreement that vocal learning is not a binary trait. We propose a novel classification system, based on the definitions by Janik and Slater, that deconstructs vocal learning into key dimensions to aid in understanding the mechanisms involved in this complex behaviour. We consider how vocalizations can change without learning, and a usage learning framework that considers context specificity and timing. We identify dimensions of vocal production learning, including the copying of auditory models (convergence/divergence on model sounds, accuracy of copying), the degree of change (type and breadth of learning) and timing (when learning takes place, the length of time it takes and how long it is retained). We consider grey areas of classification and current mechanistic understanding of these behaviours. Our framework identifies research needs and will help to inform neurobiological and evolutionary studies endeavouring to uncover the multi-dimensional nature of vocal learning. This article is part of the theme issue 'Vocal learning in animals and humans'.

Rhythm in dyadic interactions

This review paper discusses rhythmic interactions and distinguishes them from non-rhythmic interactions. We report on communicative behaviours in social and sexual contexts, as found in dyads of humans, non-human primates, non-primate mammals, birds, anurans and insects. We discuss observed instances of rhythm in dyadic interactions, identify knowledge gaps and propose suggestions for future research. We find that most studies on rhythmicity in interactive signals mainly focus on one modality (acoustic or visual) and we suggest more work should be performed on multimodal signals. Although the social functions of interactive rhythms have been fairly well described, developmental research on rhythms used to regulate social interactions is still lacking. Future work should also focus on identifying the exact timing mechanisms involved. Rhythmic signalling behaviours are widespread and critical in regulating social interactions across taxa, but many questions remain unexplored. A multidisciplinary, comparative cross-species approach may help provide answers. This article is part of the theme issue 'Synchrony and rhythm interaction: from the brain to behavioural ecology'.

A boldly comparative approach will strengthen co-evolutionary accounts of musicality's origins

Focus on the evolutionary origins of musicality has been neglected relative to attention on language, so these new proposals are welcome stimulants. We argue for a broad comparative approach to understanding how the elements of musicality evolved, and against the use of overly simplistic evolutionary accounts.

Neurophysiological coordination of duet singing

Coordination of behavior for cooperative performances often relies on linkages mediated by sensory cues exchanged between participants. How neurophysiological responses to sensory information affect motor programs to coordinate behavior between individuals is not known. We investigated how plain-tailed wrens (Pheugopedius euophrys) use acoustic feedback to coordinate extraordinary duet performances in which females and males rapidly take turns singing. We made simultaneous neurophysiological recordings in a song control area "HVC" in pairs of singing wrens at a field site in Ecuador. HVC is a premotor area that integrates auditory feedback and is necessary for song production. We found that spiking activity of HVC neurons in each sex increased for production of its own syllables. In contrast, hearing sensory feedback produced by the bird's partner decreased HVC activity during duet singing, potentially coordinating HVC premotor activity in each bird through inhibition. When birds sang alone, HVC neurons in females but not males were inhibited by hearing the partner bird. When birds were anesthetized with urethane, which antagonizes GABAergic (γ-aminobutyric acid) transmission, HVC neurons were excited rather than inhibited, suggesting a role for GABA in the coordination of duet singing. These data suggest that HVC integrates information across partners during duets and that rapid turn taking may be mediated, in part, by inhibition.

Breeding season length predicts duet coordination and consistency in Neotropical wrens (Troglodytidae)

Many animals produce coordinated signals, but few are more striking than the elaborate male-female vocal duets produced by some tropical songbirds. Yet, little is known about the factors driving the extreme levels of vocal coordination between mated pairs in these taxa. We examined evolutionary patterns of duet coordination and their potential evolutionary drivers in Neotropical wrens (Troglodytidae), a songbird family well known for highly coordinated duets. Across 23 wren species, we show that the degree of coordination and precision with which pairs combine their songs into duets varies by species. This includes some species that alternate their song phrases with exceptional coordination to produce rapidly alternating duets that are highly consistent across renditions. These highly coordinated, consistent duets evolved independently in multiple wren species. Duet coordination and consistency are greatest in species with especially long breeding seasons, but neither duet coordination nor consistency are correlated with clutch size, conspecific abundance or vegetation density. These results suggest that tightly coordinated duets play an important role in mediating breeding behaviour, possibly by signalling commitment or coalition of the pair to mates and other conspecifics.

Duet singing in plain-tailed wrens

A Quick guide to plain-tailed wrens, sonbirds of the Andes which sing duet songs that can be heard at distances of over 200 metres.

Early-life lessons of the courtship dance in a dance-duetting songbird, the Java sparrow

Vocal learners, such as songbirds, must practise singing in a developmentally sensitive period to master songs. Yet, knowledge remains limited about the development of visual displays in birds, even when courtship includes well-coordinated vocalizations (songs) and body motions. The Java sparrow (Lonchura oryzivora) is a species of songbird that exhibits a courtship duet dancing exchange between the sexes, with this behaviour driving mating success. In this study, juvenile male Java sparrows were observed in captivity, showing that they repeatedly practise the courtship dance in their early life. We called it 'practice', as juvenile birds frequently dance towards family members or other juveniles well before sexual maturation. Based on our observation that dance motor performance increased with age, we propose that the practice is needed for motor learning. In addition, it could also be important for establishing vocal-motional coordination or socialization. Older juveniles gradually became capable of singing and dancing simultaneously, and participated in duet dancing more often. We also found that repeated encounters with the same individual promote dance movement. Though our results do not show how much social experiences account for the development of dance communication, early-life dance practising might influence future reproductive success, like song practising does.

New insights from female bird song: towards an integrated approach to studying male and female communication roles

Historically, bird song has been regarded as a sex-specific signalling trait; males sing to attract females and females drive the evolution of signal exaggeration by preferring males with ever more complex songs. This view provides no functional role for female song. Historic geographical research biases generalized pronounced sex differences of phylogenetically derived northern temperate zone songbirds to all songbirds. However, we now know that female song is common and that both sexes probably sang in the ancestor of modern songbirds. This calls for research on adaptive explanations and mechanisms regulating female song, and a reassessment of questions and approaches to identify selection pressures driving song elaboration in both sexes and subsequent loss of female song in some clades. In this short review and perspective we highlight newly emerging questions and propose a research framework to investigate female song and song sex differences across species. We encourage experimental tests of mechanism, ontogeny, and function integrated with comparative evolutionary analyses. Moreover, we discuss the wider implications of female bird song research for our understanding of male and female communication roles.

Deceptive vocal duets and multimodal display in a songbird

Many group-living animals cooperatively signal to defend resources, but what stops deceptive signalling to competitors about coalition strength? Cooperative-signalling species include mated pairs of birds that sing duets to defend their territory. Individuals of these species sometimes sing 'pseudo-duets' by mimicking their partner's contribution, but it is unknown if these songs are deceptive, or why duets are normally reliable. We studied pseudo-duets in Australian magpie-larks, Grallina cyanoleuca, and tested whether multimodal signalling constrains deception. Magpie-larks give antiphonal duets coordinated with a visual display, with each sex typically choosing a different song type within the duet. Individuals produced pseudo-duets almost exclusively during nesting when partners were apart, but the two song types were used in sequence rather than antiphonally. Strikingly, birds hid and gave no visual displays, implying deceptive suppression of information. Acoustic playbacks showed that pseudo-duets provoked the same response from residents as true duets, regardless of whether they were sequential or antiphonal, and stronger response than that to true duets consisting of a single song type. By contrast, experiments with robot models showed that songs accompanied by movements of two birds prompted stronger responses than songs accompanied by movements of one bird, irrespective of the number of song types or singers. We conclude that magpie-larks used deceptive pseudo-duets when partners were apart, and suppressed the visual display to maintain the subterfuge. We suggest that the visual component of many species' duets provides the most reliable information about the number of signallers and may have evolved to maintain honesty in duet communication.

Early development of vocal interaction rules in a duetting songbird

Exchange of vocal signals is an important aspect of animal communication. Although birdsong is the premier model for understanding vocal development, the development of vocal interaction rules in birds and possible parallels to humans have been little studied. Many tropical songbirds engage in complex vocal interactions in the form of duets between mated pairs. In some species, duets show precise temporal coordination and follow rules (duet codes) governing which song type one bird uses to reply to each of the song types of its mate. We determined whether these duetting rules are acquired during early development in canebrake wrens. Results show that juveniles acquire a duet code by singing with a mated pair of adults and that juveniles gradually increase their fidelity to the code over time. Additionally, we found that juveniles exhibit poorer temporal coordination than adults and improve their coordination as time progresses. Human turn-taking, an analogous rule to temporal coordination, is learned during early development. We report that the ontogeny of vocal interaction rules in songbirds is analogous to that of human conversation rules.