a Spectrogram of a typical thrush nightingale song (recorded in Poland) showing the characteristic song organisation of the species. The sub-parts (indicated by Greek characters and highlighting the ending “castanet” and “rattling” parts as introduced by Sorjonen 1983) are characterized by elements that always occur in the same sequence. The α-part is usually the most variable part between and within individual repertoires, while the last parts of the song (solid red arrow lines) are the most stable ones. In this study, song type categories are defined as the same combination of the last β element and the following Ψ1 (Castanet) and Ψ2 (Rattling, fast trill covering a wide frequency range), indicated by solid arrow lines underneath the spectrogram. b–g Spectrograms illustrating syllable renditions selected for the spectral cross-correlation analysis and their sequential position: b, c Poland; d, e Russia; f, g Tanzania. Highlighted syllables illustrate renditions selected for comparison of the same syllable type in two songs of the same type and from the same individual

a Spectrogram of a typical thrush nightingale song (recorded in Poland) showing the characteristic song organisation of the species. The sub-parts (indicated by Greek characters and highlighting the ending “castanet” and “rattling” parts as introduced by Sorjonen 1983) are characterized by elements that always occur in the same sequence. The α-part is usually the most variable part between and within individual repertoires, while the last parts of the song (solid red arrow lines) are the most stable ones. In this study, song type categories are defined as the same combination of the last β element and the following Ψ1 (Castanet) and Ψ2 (Rattling, fast trill covering a wide frequency range), indicated by solid arrow lines underneath the spectrogram. b–g Spectrograms illustrating syllable renditions selected for the spectral cross-correlation analysis and their sequential position: b, c Poland; d, e Russia; f, g Tanzania. Highlighted syllables illustrate renditions selected for comparison of the same syllable type in two songs of the same type and from the same individual

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The songs of migratory passerine birds have a key role in mate attraction and territory defence during the breeding season. Many species also sing on their wintering grounds, but the function of this behaviour remains unclear. One possible explanation, proposed by the song improvement hypothesis, is that the birds take advantage of this period to d...

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... The "song types" concept has been used in a number of studies of Thrush Nightingale song (Ivanitskii et al. 2017;Sorjonen 1987;Souriau et al. 2019). Following Grieβmann and Naguib (2002), we assigned different songs to the same type if they did not differ in more than two basic song components or their syntactical arrangement. ...
... All the three studied populations of the Thrush Nightingale belong to the same vocal dialect (Marova et al. 2015); therefore, joint wintering of individuals from these populations looks quite possible. As we have shown earlier, the Thrush Nightingale is an active winter singer (Souriau et al. 2019). Songs performed by Thrush Nightingales on their eastern Africa wintering ground exhibited a lower syllable consistency and higher element variability than the songs produced by individuals from breeding grounds. ...
Article
We present results of our long-term research on the song dynamics of the Thrush Nightingale (Luscinia luscinia) in the city of Moscow and the Moscow region. The research covered three populations located 50–100 km apart from each other and lasted for a total of 11 years. We present data on the between-year variability with respect to the frequency, time, and structural features of homologous elements in the song types observed in the three studied populations. We identified two types of dynamics in the vocal repertoire of the Thrush Nightingale. The first type included abrupt shifts, wherein some song types disappeared from the population repertoire and other song types appeared instead. The second type of dynamics involved gradual interannual changes in the fine structure of individual song types. We show that such changes occurred surprisingly synchronously, not only in the majority of males in a given population but also encompass large areas, and manifested themselves in parallel, even in distant populations. The behavioral mechanisms underlying the rapid transmission of vocal patterns between distant populations remain unexplored. As a possible explanation, we hypothesize the existence of vocal exchange between individuals in common wintering grounds.
... Because the total number of syllables per song did not differ between breeding and nonbreeding (Fig. 2f), the augmentation of the song repertoire for part C was not due to a more complex song during breeding, but rather to a tendency of males to sing more song types (Fig. 2e). In other species, song features change between different life-cycle stages, for instance, the number and length of repetitive elements [64,67,72,73] or the song repertoire size [74]. In black redstarts, although the reproductive context may be a major factor, the function of this increase in repertoire size of part C in response to the STI during spring needs further exploration. ...
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Background The connection between testosterone and territoriality in free-living songbirds has been well studied in a reproductive context, but less so outside the breeding season. To assess the effects of seasonal androgenic action on territorial behavior, we analyzed vocal and non-vocal territorial behavior in response to simulated territorial intrusions (STIs) during three life-cycle stages in free-living male black redstarts: breeding, molt and nonbreeding. Concurrently, we measured changes in circulating testosterone levels, as well as the mRNA expression of androgen and estrogen receptors and aromatase in the preoptic, hypothalamic and song control brain areas that are associated with social and vocal behaviors. Results Territorial behavior and estrogen receptor expression in hypothalamic areas did not differ between stages. But plasma testosterone was higher during breeding than during the other stages, similar to androgen receptor and aromatase expression in the preoptic area. The expression of androgen receptors in the song control nucleus HVC was lower during molt when birds do not sing or sing rarely, but similar between the breeding and the nonbreeding stage. Nevertheless, some song spectral features and the song repertoire differed between breeding and nonbreeding. Territorial behavior and song rate correlated with the expression of steroid receptors in hypothalamic areas, and in the song control nucleus lMAN. Conclusions Our results demonstrate seasonal modulation of song, circulating testosterone levels, and brain sensitivity to androgens, but a year-round persistency of territorial behavior and estrogen receptor expression in all life-cycle stages. This suggests that seasonal variations in circulating testosterone concentrations and brain sensitivity to androgens is widely uncoupled from territorial behavior and song activity but might still affect song pattern. Our study contributes to the understanding of the complex comparative neuroendocrinology of song birds in the wild.
... Accordingly, it is possible to use this method in the so-called song type species, where traditionally the diversity is described with the repertoire size of song types (and not syllable types) like in thrush nightingale Luscinia luscinia (Souriau et al., 2019). In these cases, the components of acoustic diversity can provide additional information on the within-and between-song type variation, thus open a way to test new, biologically relevant hypotheses. ...
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The study of the diversity of animal signals on within‐ and among‐species levels is the key to uncover mechanisms that shape the evolution of communication systems. However, the methods used to quantify acoustic diversity (like repertoire size) lack to grasp several aspects of acoustic diversity. Here, we propose a new framework for the study of animal communication, in which we decompose the acoustic diversity with the methodological toolbox from community ecology. We explore how different diversity estimates reflecting different aspects of acoustic diversity can be applied to characterise the complexity of acoustic signals. We propose that this approach can be used in a wide range of animal taxa to derive further insights about the function and evolution of communication systems beside of the traditional methods. To illustrate the use of our approach in a case study, we used the song of the collared flycatcher (Ficedula albicollis) as model system. Based on three frequency and time variables, we calculated three functional diversity indies (FRic, FEve, and FDiv) to characterise the distribution of song elements (syllables) in the acoustic parameter space. We aimed to uncover the interrelations of diversity indices, reveal the degree of among‐individual consistency, and investigate their relationships with certain aspects of individual quality (body condition, age, arrival date). We found that the diversity indices were largely independent from each other and showed different consistency patterns that were timescale dependent, indicating different signalling potential of individual‐specific attributes. We also found that FEve strongly related to the age of males. Our case study showed that decomposing the diversity into different components can reveal additional biologically meaningful aspects of birdsong.
Article
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).