The Neuroethology of Vocal Communication in Songbirds: Production and Perception of a Call Repertoire

A model of marmoset monkey vocal turn-taking

Vocal turn-taking has been described in a diversity of species. Yet, a model that is able to capture the various processes underlying this social behaviour across species has not been developed. To this end, here we recorded a large and diverse dataset of marmoset monkey vocal behaviour in social contexts comprising one, two and three callers and developed a model to determine the keystone factors that affect the dynamics of these natural communicative interactions. Notably, marmoset turn-taking did not abide by coupled-oscillator dynamics, but rather call timing was overwhelmingly stochastic in these exchanges. Our features-based model revealed four key factors that encapsulate the majority of patterns evident in the behaviour, ranging from internal processes, such as particular states of the individual driving increased calling, to social context-driven suppression of calling. These findings indicate that marmoset vocal turn-taking is affected by a broader suite of mechanisms than previously considered and that our model provides a predictive framework with which to further explicate this natural behaviour at both the behavioural and neurobiological levels, and for direct comparisons with the analogous behaviour in other species.

A perspective on neuroethology: what the past teaches us about the future of neuroethology

For 100 years, the Journal of Comparative Physiology-A has significantly supported research in the field of neuroethology. The celebration of the journal's centennial is a great time point to appreciate the recent progress in neuroethology and to discuss possible avenues of the field. Animal behavior is the main source of inspiration for neuroethologists. This is illustrated by the huge diversity of investigated behaviors and species. To explain behavior at a mechanistic level, neuroethologists combine neuroscientific approaches with sophisticated behavioral analysis. The rapid technological progress in neuroscience makes neuroethology a highly dynamic and exciting field of research. To summarize the recent scientific progress in neuroethology, I went through all abstracts of the last six International Congresses for Neuroethology (ICNs 2010-2022) and categorized them based on the sensory modalities, experimental model species, and research topics. This highlights the diversity of neuroethology and gives us a perspective on the field's scientific future. At the end, I highlight three research topics that may, among others, influence the future of neuroethology. I hope that sharing my roots may inspire other scientists to follow neuroethological approaches.

Lesions to Caudomedial Nidopallium Impair Individual Vocal Recognition in the Zebra Finch

Many social animals can recognize other individuals by their vocalizations. This requires a memory system capable of mapping incoming acoustic signals to one of many known individuals. Using the zebra finch, a social songbird that uses songs and distance calls to communicate individual identity (Elie and Theunissen, 2018), we tested the role of two cortical-like brain regions in a vocal recognition task. We found that the rostral region of the Cadomedial Nidopallium (NCM), a secondary auditory region of the avian pallium, was necessary for maintaining auditory memories for conspecific vocalizations in both male and female birds, whereas HVC (used as a proper name), a premotor areas that gates auditory input into the vocal motor and song learning pathways in male birds (Roberts and Mooney, 2013), was not. Both NCM and HVC have previously been implicated for processing the tutor song in the context of song learning (Sakata and Yazaki-Sugiyama, 2020). Our results suggest that NCM might not only store songs as templates for future vocal imitation but also songs and calls for perceptual discrimination of vocalizers in both male and female birds. NCM could therefore operate as a site for auditory memories for vocalizations used in various facets of communication. We also observed that new auditory memories could be acquired without intact HVC or NCM but that for these new memories NCM lesions caused deficits in either memory capacity or auditory discrimination. These results suggest that the high-capacity memory functions of the avian pallial auditory system depend on NCM.SIGNIFICANCE STATEMENT Many aspects of vocal communication require the formation of auditory memories. Voice recognition, for example, requires a memory for vocalizers to identify acoustical features. In both birds and primates, the locus and neural correlates of these high-level memories remain poorly described. Previous work suggests that this memory formation is mediated by high-level sensory areas, not traditional memory areas such as the hippocampus. Using lesion experiments, we show that one secondary auditory brain region in songbirds that had previously been implicated in storing song memories for vocal imitation is also implicated in storing vocal memories for individual recognition. The role of the neural circuits in this region in interpreting the meaning of communication calls should be investigated in the future.

Tuned in to communication sounds: Neuronal sensitivity in the túngara frog midbrain to frequency modulated signals

For complex communication signals, it is often difficult to identify the information-bearing elements and their parameters necessary to elicit functional behavior. Consequently, it may be difficult to design stimuli that test how neurons contribute to communicative processing. For túngara frogs (Physalaemus pustulosus), however, previous behavioral testing with numerous stimuli showed that a particular frequency modulated (FM) transition in the male call is required to elicit phonotaxis and vocal responses. Modeled on such behavioral experiments, we used awake in vivo recordings of single units in the midbrain to determine if their excitation was biased to behaviorally important FM parameters. Comparisons of stimulus driven action potentials revealed greatest excitation to the behaviorally important FM transition: a downward FM sweep or step that crosses ~600 Hz. Previous studies using long-duration acoustic exposure found immediate early gene expression in many midbrain neurons to be most sensitive to similar FM. However, those data could not determine if FM coding was accomplished by the population and/or individual neurons. Our data suggest both coding schemes could operate, as 1) individual neurons are more sensitive to the behaviorally significant FM transition and 2) when single unit recordings are analytically combined across cells, the combined code can produce high stimulus discrimination (FM vs. noise driven excitation), approaching that found in behavioral discrimination of call vs. noise.

Vocal Learning and Behaviors in Birds and Human Bilinguals: Parallels, Divergences and Directions for Research

Comparisons between the communication systems of humans and animals are instrumental in contextualizing speech and language into an evolutionary and biological framework and for illuminating mechanisms of human communication. As a complement to previous work that compares developmental vocal learning and use among humans and songbirds, in this article we highlight phenomena associated with vocal learning subsequent to the development of primary vocalizations (i.e., the primary language (L1) in humans and the primary song (S1) in songbirds). By framing avian “second-song” (S2) learning and use within the human second-language (L2) context, we lay the groundwork for a scientifically-rich dialogue between disciplines. We begin by summarizing basic birdsong research, focusing on how songs are learned and on constraints on learning. We then consider commonalities in vocal learning across humans and birds, in particular the timing and neural mechanisms of learning, variability of input, and variability of outcomes. For S2 and L2 learning outcomes, we address the respective roles of age, entrenchment, and social interactions. We proceed to orient current and future birdsong inquiry around foundational features of human bilingualism: L1 effects on the L2, L1 attrition, and L1<–>L2 switching. Throughout, we highlight characteristics that are shared across species as well as the need for caution in interpreting birdsong research. Thus, from multiple instructive perspectives, our interdisciplinary dialogue sheds light on biological and experiential principles of L2 acquisition that are informed by birdsong research, and leverages well-studied characteristics of bilingualism in order to clarify, contextualize, and further explore S2 learning and use in songbirds.

The singing question: re-conceptualizing birdsong

Birdsong has been the subject of broad research from a variety of sub-disciplines and has taught us much about the evolution, function, and mechanisms driving animal communication and cognition. Typically, birdsong refers to the specialized vocalizations produced by oscines. Historically, much of the research on birdsong was conducted in north temperate regions (specifically in Europe and North America) leading to multiple biases. Due to these historic biases these vocalizations are generally considered to be highly sexually dimorphic, heavily shaped by sexual selection and essential for courtship and territoriality. Song is also typically defined as a learned trait shaped by cultural evolution. Together, this framework focuses research specifically on males, particularly during the north temperate breeding season - reflecting and thereby reinforcing this framework. The physiological underpinnings of song often emphasize the role of the hypothalamic-pituitary-gonadal axis (associated with breeding changes) and the song control system (underlying vocal learning). Over the years there has been great debate over which features of song are essential to the definition of birdsong, which features apply broadly to contexts outside males in the north temperate region, and over the importance of having a definition at all. Importantly, the definitions we use can both guide and limit the progress of research. Here, we describe the history of these definitions, and how these definitions have directed and restricted research to focus on male song in sexually selected contexts. Additionally, we highlight the gaps in our scientific knowledge, especially with respect to the function and physiological mechanisms underlying song in females and in winter, as well as in non-seasonally breeding species. Furthermore, we highlight the problems with using complexity and learning as dichotomous variables to categorize songs and calls. Across species, no one characteristic of song - sexual dimorphism, seasonality, complexity, sexual selection, learning - consistently delineates song from other songbird vocal communication. We provide recommendations for next steps to build an inclusive information framework that will allow researchers to explore nuances in animal communication and promote comparative research. Specifically, we recommend that researchers should operationalize the axis of variation most relevant to their study/species by identifying their specific question and the variable(s) of focus (e.g. seasonality). Researchers should also identify the axis (axes) of variation (e.g. degree of control by testosterone) most relevant to their study and use language consistent with the question and axis (axes) of variation (e.g. control by testosterone in the seasonal vocal production of birds).

Norepinephrine in the avian auditory cortex enhances developmental song learning

Sensory learning during critical periods in development has lasting effects on behavior. Neuromodulators like dopamine and norepinephrine (NE) have been implicated in various forms of sensory learning, but little is known about their contribution to sensory learning during critical periods. Songbirds like the zebra finch communicate with each other using vocal signals (e.g., songs) that are learned during a critical period in development, and the first crucial step in song learning is memorizing the sound of an adult conspecific's (tutor's) song. Here, we analyzed the extent to which NE modulates the auditory learning of a tutor's song and the fidelity of song imitation. Specifically, we paired infusions of NE or vehicle into the caudomedial nidopallium (NCM) with brief epochs of song tutoring. We analyzed the effect of NE in juvenile zebra finches that had or had not previously been exposed to song. Regardless of previous exposure to song, juveniles that received NE infusions into NCM during song tutoring produced songs that were more acoustically similar to the tutor song and that incorporated more elements of the tutor song than juveniles with control infusions. These data support the notion that NE can regulate the formation of sensory memories that shape the development of vocal behaviors that are used throughout an organism's life.NEW & NOTEWORTHY Although norepinephrine (NE) has been implicated in various forms of sensory learning, little is known about its contribution to sensory learning during critical periods in development. We reveal that pairing infusions of NE into the avian secondary auditory cortex with brief epochs of song tutoring significantly enhances auditory learning during the critical period for vocal learning. These data highlight the lasting impact of NE on sensory systems, cognition, and behavior.

High-capacity auditory memory for vocal communication in a social songbird

Effective vocal communication often requires the listener to recognize the identity of a vocalizer, and this recognition is dependent on the listener's ability to form auditory memories. We tested the memory capacity of a social songbird, the zebra finch, for vocalizer identities using conditioning experiments and found that male and female zebra finches can remember a large number of vocalizers (mean, 42) based solely on the individual signatures found in their songs and distance calls. These memories were formed within a few trials, were generalized to previously unheard renditions, and were maintained for up to a month. A fast and high-capacity auditory memory for vocalizer identity has not been demonstrated previously in any nonhuman animals and is an important component of vocal communication in social species.

Manipulations of sensory experiences during development reveal mechanisms underlying vocal learning biases in zebra finches

Biological predispositions in learning can bias and constrain the cultural evolution of social and communicative behaviors (e.g., speech and birdsong), and lead to the emergence of behavioral and cultural "universals." For example, surveys of laboratory and wild populations of zebra finches (Taeniopygia guttata) document consistent patterning of vocal elements ("syllables") with respect to their acoustic properties (e.g., duration, mean frequency). Furthermore, such universal patterns are also produced by birds that are experimentally tutored with songs containing randomly sequenced syllables ("tutored birds"). Despite extensive demonstrations of learning biases, much remains to be uncovered about the nature of biological predispositions that bias song learning and production in songbirds. Here, we examined the degree to which "innate" auditory templates and/or biases in vocal motor production contribute to vocal learning biases and production in zebra finches. Such contributions can be revealed by examining acoustic patterns in the songs of birds raised without sensory exposure to song ("untutored birds") or of birds that are unable to hear from early in development ("early-deafened birds"). We observed that untutored zebra finches and early-deafened zebra finches produce songs with positional variation in some acoustic features (e.g., mean frequency) that resemble universal patterns observed in tutored birds. Similar to tutored birds, early-deafened birds also produced song motifs with alternation in acoustic features across adjacent syllables. That universal acoustic patterns are observed in the songs of both untutored and early-deafened birds highlights the contribution motor production biases to the emergence of universals in culturally transmitted behaviors.