Song Variation Research Articles

Responses in adult pied flycatcher males depend on playback song similarity to local population

Abstract Song divergence driven by social learning has been proposed to be a key factor driving allopatric speciation in oscine birds. Songbirds often respond more to songs deriving from their local population, suggesting the potential for acoustic divergence across populations to shape both intra- and intersexual interactions. However, many of these studies were conducted on species with simple songs and, as a result, we know comparatively little about the emergence of population differences and song discrimination in species with complex songs. We addressed this question in the pied flycatcher (Ficedula hypoleuca) by calculating the dissimilarity of songs from two foreign populations as well as from our study site to the local centroid. We then conducted a paired-design playback experiment where both local and foreign songs were played simultaneously. We found that pied flycatcher males showed significantly stronger responses to those songs that sounded more similar to the local population. This suggests that despite the high complexity of the pied flycatcher song, individuals are still able to discriminate across populations. Our results support the hypothesis that learned song divergence can act as a mechanism for assortative mating and allopatric speciation.

Chickadees sing different songs in sympatry versus allopatry.

Character displacement theory predicts that closely-related co-occurring species should diverge in relevant traits to reduce costly interspecific interactions such as competition or hybridization. While many studies document character shifts in sympatry, few provide corresponding evidence that these shifts are driven by the costs of co-occurrence. Black-capped (Poecile atricapillus) and mountain chickadees (P. gambeli) are closely-related, ecologically similar, and broadly distributed songbirds with both allopatric and sympatric populations. In sympatry, both species appear to suffer costs of their co-occurrence: 1) both species are in worse body condition compared to allopatry and 2) hybridization sometimes yields sterile offspring. Here, we explored character displacement in the songs of black-capped and mountain chickadees by characterizing variation in male songs from sympatric and allopatric populations. We found that mountain chickadees sing differently in sympatry versus allopatry. Specifically, they produced more notes per song, were more likely to include an extra introductory note, and produced a smaller glissando in their first notes compared to all other populations. Combined with previous research on social dominance and maladaptive hybridization between black-capped and mountain chickadees, we posit that differences in sympatric mountain chickadee song are population-wide shifts to reduce aggression from dominant black-capped chickadees and/or prevent maladaptive hybridization.

Photoperiodism, testosterone and adult neurogenesis in canaries (Serinus canaria).

Domestic strains of canaries (Serinus canaria) variably respond to photoperiod changes and apparently stay in breeding state for extended periods. Fife Fancy canaries are supposed to be similar to the native species living at 27-39° north where photoperiod significantly changes across the year. Our birds showed reproductive cycles when exposed to light regimes mimicking the annual cycle of photoperiod. However after 6 months in short days (SD: 8L:16D), males developed large testes, as observed by X-ray tomography, and intense singing. Switching to long days (LD: 16L:8D) did not further increase song rate nor testes size but increased song duration, number of syllables per song, and trill occurrence frequency. No sign of regression was observed after 12 weeks in LD but return to SD produced a rapid decrease in testes size and singing activity below values in birds maintained throughout in SD. Fife Fancy thus does not seem to develop absolute but only relative refractoriness. The relatively high singing activity expressed by SD-photosensitive males does not seem to depend on high testosterone (T) concentrations. Singing did not correlate with plasma testosterone (T). Treatment with ATD + Flutamide only marginally decreased song rate and did not affect song quality nor song control nuclei volume. These birds are either supersensitive to low T levels or their reproductive physiology is activated by other mechanisms. Neurogenesis is increased by T and by LD but the function of new neurons incorporated in HVC is poorly understood. We developed a procedure based on X-ray focal irradiation to deplete neural progenitors adjacent to HVC and study the functional consequences. The decrease in neurogenesis increased the variability of T-induced songs in females and decreased their bandwidth. Neurogenesis in HVC thus plays a role in song production and X-ray focal irradiation represents an excellent tool to analyze adult neurogenesis.

Agonistic song rate positively correlates with male breeding success and avian malaria infection in Acrocephalus paludicola (Aquatic Warbler), a promiscuous songbird with female-only parental care

Abstract The link between male song and reproductive success has been explored at length in socially monogamous birds, but results were inconsistent and under-represented socially non-monogamous species with uniparental care. Here, we evaluated whether metrics of male song in Acrocephalus paludicola (Aquatic Warbler), a promiscuous songbird with female-only care and large repertoires, are associated with fitness- and quality-related traits. We showed that the number of 9-day-old nestlings fathered and probability of avian malaria infection increased with the rate of agonistic song, produced in male–male interactions, and that male-scaled mass index (proxy for energy reserves) positively correlated with the repertoire size. The male breeding success was not explained by repertoire size and song duty cycle. None of the song variables clearly explained the male return rate or change in the tarsus length (proxy for structural body size) and scaled mass index of the fathered chicks between days 2 and 9 post-hatch. No other relationships between the song characteristics and the inbreeding coefficient, scaled mass index, wing-length and Trypanosoma infection status of the males were supported, and Plasmodium infection was unrelated to the song duty cycle and repertoire size. We conclude that in male A. paludicola the repertoire size could be a signal of early developmental stress or current body condition, and the agonistic song rate could be shaped by sexual selection and signal to females a genetic makeup that enhances survival upon infection by Plasmodium.

Song and genetic divergence within a subspecies of white-crowned sparrow (Zonotrichia leucophrys nuttalli).

Animal culture evolves alongside genomes, and the two modes of inheritance-culture and genes-interact in myriad ways. For example, stable geographic variation in culture can act as a reproductive barrier, thereby facilitating genetic divergence between "cultural populations." White-crowned sparrows (Zonotrichia leucophrys) are a well-established model species for bird song learning and cultural evolution, as they have distinct, geographically discrete, and culturally transmitted song types (i.e., song dialects). In this study, we tested the hypothesis that divergence between culturally transmitted songs drives genetic divergence within Nuttall's white-crowned sparrows (Z. l. nuttalli). In accordance with sexual selection theory, we hypothesized that cultural divergence between mating signals both preceded and generated genetic divergence. We characterized the population structure and song variation in the subspecies and found two genetically differentiated populations whose boundary coincides with a major song boundary at Monterey Bay, California. We then conducted a song playback experiment that demonstrated males discriminate between songs based on their degree of divergence from their local dialect. These results support the idea that discrimination against non-local songs is driving genetic divergence between the northern and southern populations. Altogether, this study provides evidence that culturally transmitted bird songs can act as the foundation for speciation by sexual selection.

Body size shapes song in honeyeaters.

Birdsongs are among the most distinctive animal signals. Their evolution is thought to be shaped simultaneously by habitat structure and by the constraints of morphology. Habitat structure affects song transmission and detectability, thus influencing song (the acoustic adaptation hypothesis), while body size and beak size and shape necessarily constrain song characteristics (the morphological constraint hypothesis). Yet, support for the acoustic adaptation and morphological constraint hypotheses remains equivocal, and their simultaneous examination is infrequent. Using a phenotypically diverse Australasian bird clade, the honeyeaters (Aves: Meliphagidae), we compile a dataset consisting of song, environmental, and morphological variables for 163 species and jointly examine predictions of these two hypotheses. Overall, we find that body size constrains song frequency and pace in honeyeaters. Although habitat type and environmental temperature influence aspects of song, that influence is indirect, likely via effects of environmental variation on body size, with some evidence that elevation constrains the evolution of song peak frequency. Our results demonstrate that morphology has an overwhelming influence on birdsong, in support of the morphological constraint hypothesis, with the environment playing a secondary role generally via body size rather than habitat structure. These results suggest that changing body size (a consequence of both global effects such as climate change and local effects such as habitat transformation) will substantially influence the nature of birdsong.

Vocal Repertoire of Chimango Caracaras in Rural and Urban Habitats

ABSTRACT Acoustic communication, such as bird song, is vital in animal ecology, facilitating reproduction, feeding, defense, and more. Variation in bird song may result from adaptation to environmental features such as anthropogenic noise. The vocal repertoire of raptors is essentially unstudied, particularly in urban environments. The aim of this work was to describe and quantify the acoustic repertoire of Chimango Caracaras (Milvago chimango) in rural and urban areas in La Pampa Province, Argentina. I recorded 26 1-min sound samples at each of four breeding colonies (one rural and three urban) during the austral reproductive season of 2021–2022. I recorded 241 vocalizations corresponding to nine clearly distinct call types. Two types of calls made up 50.6% and 19.5% of the vocalizations and seven others made up <10.0% each. Three call types had trills (fast repetitive notes). Average percentage of call types differed significantly between the two habitats (P < 0.01), with more trills produced in rural habitats. Average calling rate was 6.6 ± 5.1 calls/min at rural colonies and 10.7 ± 10.7 at urban colonies. The number of different call types produced was 2.1 ± 1.6 types/min at rural colonies and 2.7 ± 1.8 at urban colonies. The greater calling rate of Chimango Caracaras in urban areas may represent an attempt to improve signal effectiveness among the anthropogenic acoustic clutter.

Intraspecific variation of three plumage-cryptic bulbul species

Bird songs and morphometry are frequently used to distinguish bird species which are plumage-cryptic, or to delineate boundaries of subspecies. Rubigula flaviventris, Pycnonotus finlaysoni and Brachypodius melanocephalos have each recognized subspecies along the Thai-Malay Peninsula, however the range-limit of the subspecies distribution is still ambiguous and genetic data from a previous own study suggests a revision of the subspecies distribution and the subspecies barriers is warranted. To analyze the subspecies boundaries based on potential song and morphometric traits, we recorded, measured, and analyzed song characters and morphometry of the three bulbuls along the Thai-Malay Peninsula. The geographic variation of songs and morphometry differs significantly for specific traits; however, we could not find any trait discontinuities that would be in accordance with previously documented phylogeographic divides. Instead trait variation was mostly clinal and followed a North-South gradient in line with Bergmann’s rule. Due to the lack of distinctiveness of any subspecific taxon, we conclude that shallow genetic divides on the Thai-Malay Peninsula are not indicative of potential species-level splits in the three species of our study.

Dziesmu virknes kāzu apdziedāšanās tradīcijas kontekstā: īpatnības un problemātika

Singing of mutual mocking songs in Latvian traditional culture is an ancient and highly cultivated custom. It can be found at clean-up days, traditional annual celebrations and family-related festivities. Of all the festivities, this tradition is most vividly manifested in weddings and has been preserved in some places until today. Singing usually takes place between two groups – boys and girls, unmarried girls and married women, guests and housemates, etc. During the wedding, the singing takes place mainly between the relatives of the groom and the bride. This custom, which permeates the entire wedding ritual, symbolically features a clash between the groom’s family and the bride’s family, which allows psychological tension to be discharged by reaching the catharsis. In particular, singing mocking songs effectively discharges the accumulated negative feelings in a socially permitted manner. The 12th volume of the academic edition “Latvian Folk Songs” (Latviešu tautasdziesmas) was published in the summer of this year. This volume continues, which was started in the previous volume by publishing wedding songs. This edition covers the wedding theme more completely than all the ones published so far, so the texts included in the 12th volume and those not included were selected as the sources for this study. A folk song is usually understood as a content-autonomous and structurally closed quatrain, but when working with song manuscripts, it turns out that they are not always complete texts in content and form or aesthetically perfect texts. Additionally, a fairly large number of songs consist of much more than four lines. If we look at the tradition of Latvian folk songs as a whole, it can be seen that, for various reasons, long songs and strings of songs have been significantly less studied; therefore, the article focuses on one of these phenomena – strings of songs. The article also focuses on the importance and development of the wedding mutual mocking song singing tradition over time and the variability and improvisational nature of the mocking songs. At the end of the article, attention is paid to the following problems of publishing strings of songs: lack of classification principles, volume limitations, including whether and how the mentioned reasons have influenced the inclusion of a string of songs in the 12th volume of “Latviešu tautasdziesmas”.

Neighbour–stranger discrimination in an African wood dove inhabiting equatorial rainforest

We investigated within- and between-individual song variation and song-based neighbour-stranger discrimination in a non-learning bird species, the blue-headed wood-dove (Turtur brehmeri), which inhabits lowland rainforests of West and Central Africa. We found that songs of this species are individually specific and have a high potential for use in individual recognition based on the time–frequency pattern of note distribution within song phrases. To test whether these differences affect behaviour, we conducted playback experiments with 19 territorial males. Each male was tested twice, once with the songs of a familiar neighbour and once with the songs of an unfamiliar stranger. We observed that males responded more aggressively to playback of a stranger’s songs: they quickly approached close to the speaker and spent more time near it. However, no significant differences between treatments were observed in the vocal responses. In addition, we explored whether responses differed based on the song frequency of the focal male and/or that of the simulated intruder (i.e., playback), as this song parameter is inversely related to body size and could potentially affect males’ decisions to respond to other birds. Song frequency parameters (of either the focal male or the simulated intruder) had no effect on the approaching response during playback. However, we found that the pattern of response after playback was significantly affected by the song frequency of the focal male: males with lower-frequency songs stayed closer to the simulated intruder for a longer period of time without singing, while males with higher-frequency songs returned more quickly to their initial song posts and resumed singing. Together, these results depict a consistently strong response to strangers during and after playback that is dependent on a male’s self-assessment rather than assessment of a rival’s strength based on his song frequency. This work provides the first experimental evidence that doves (Columbidae) can use songs for neighbour-stranger discrimination and respond according to a “dear enemy” scheme that keeps the cost of territory defence at a reasonable level.

Atypical song of Blackcap Sylvia atricapilla

The song of the Eurasian Blackcap Sylvia atricapilla consists of two distinct parts: an initial chattering of different harsh notes followed by a louder, fluting warble. However, some enigmatic individuals present an atypical version of their song characterised by a remarkable simplification of the traditional rich fluting warble. This study documents the unprecedented observation in the Iberian Peninsula of an atypical singer in Els Ports Natural Park (Catalonia, NE Spain). This bird exhibited distinct behavior including perching high in trees and intense morning singing, in addition to the atypical song marked by the substitution of the rich fluting warble by a monotonous series of approximately 15 similar notes. In a meticulous analysis of atypical Blackcap recordings on the online portal xeno-canto, we identified 12 cases of similar atypical singers distributed across Europe. We compared the vocal patterns of these atypical singers with the well-known Blackcap song variant leiern and concluded that there are important differences. People participating in common bird censuses should be aware of this variability in Eurasian Blackcap songs and the occurrence of atypical singers to avoid misidentification. The description and reporting of such observations will help improve knowledge of the complex subject of bird vocalisations.

Fin whale song evolution in the North Atlantic.

Animal songs can change within and between populations as the result of different evolutionary processes. When these processes include cultural transmission, the social learning of information or behaviours from conspecifics, songs can undergo rapid evolutions because cultural novelties can emerge more frequently than genetic mutations. Understanding these song variations over large temporal and spatial scales can provide insights into the patterns, drivers and limits of song evolution that can ultimately inform on the species' capacity to adapt to rapidly changing acoustic environments. Here, we analysed changes in fin whale (Balaenoptera physalus) songs recorded over two decades across the central and eastern North Atlantic Ocean. We document a rapid replacement of song INIs (inter-note intervals) over just four singing seasons, that co-occurred with hybrid songs (with both INIs), and a clear geographic gradient in the occurrence of different song INIs during the transition period. We also found gradual changes in INIs and note frequencies over more than a decade with fin whales adopting song changes. These results provide evidence of vocal learning in fin whales and reveal patterns of song evolution that raise questions on the limits of song variation in this species.

Machine learning reveals that climate, geography, and cultural drift all predict bird song variation in coastal Zonotrichia leucophrys

Abstract Previous work has demonstrated that there is extensive variation in the songs of White-crowned Sparrow (Zonotrichia leucophrys) throughout the species range, including between neighboring (and genetically distinct) subspecies Z. l. nuttalli and Z. l. pugetensis. Using a machine learning approach to bioacoustic analysis, we demonstrate that variation in song is correlated with year of recording (representing cultural drift), geographic distance, and climatic differences, but the response is subspecies- and season-specific. Automated machine learning methods of bird song annotation can process large datasets more efficiently, allowing us to examine 1,913 recordings across ~60 years. We utilize a recently published artificial neural network to automatically annotate White-crowned Sparrow vocalizations. By analyzing differences in syllable usage and composition, we recapitulate the known pattern where Z. l. nuttalli and Z. l. pugetensis have significantly different songs. Our results are consistent with the interpretation that these differences are caused by the changes in characteristics of syllables in the White-crowned Sparrow repertoire. This supports the hypothesis that the evolution of vocalization behavior is affected by the environment, in addition to population structure.

Layers of Folkloric Variation: Computational Explorations of Poetic and Narrative Text Corpora

Variation is a core feature of folklore that plays a part in configuring the processes of folkloric communication, transmission and creativity. Computational analysis of large folklore collections offers new outlooks on the study of variation. The article explores the nature of folkloric variation on the basis of folk song and fairy tale text corpora from the Estonian Folklore Archives. Our enquiry into regional variation in Estonian folk song showed different patterns of geographic variation for metre, repertoire and language. To investigate further the possibilities to disassemble the components of variation we turned to a smaller corpus of fairy tale texts from the distinct Seto language community. The results of stylometric analysis of fairy tales collected within the close language community as a rule found that word usage patterns in stories told by the same storytellers were closer to each other than stories with the same content (i.e. tale types). However, other factors, such as collectors’ individual styles, recording time, length of text, and storyteller’s place of origin contributed notably to similarity as per stylometric scores. The study has shown that the individual features and aspects of such a complex phenomenon as folklore can follow its own variation patterns. Computational analysis of the variation in large text corpora helps us get a better understanding of the functioning of variation, and the processes of folkloric creation. However, the layers of folkloric variation are not that easy to disassemble, one must be aware of the biases in text corpora and keep in mind the effect of the linguistic variation on the results.

Higher-order dialectic variation and syntactic convergence in the complex warble song of budgerigars.

Dialectic signatures in animal acoustic signals are key in the identification of and association with group members. Complex vocal sequences may also convey information about behavioral state, and may thus vary according to social environment. Some bird species, such as psittaciforms, learn and modify their complex acoustic signals throughout their lives. However, the structure and function of vocal sequences in open-ended vocal learners remains understudied. Here, we examined vocal sequence variation in the warble song of budgerigars, and how these change upon contact between social groups. Budgerigars are open-ended vocal learners which exhibit fission-fusion flock dynamics in the wild. We found that two captive colonies of budgerigars exhibited colony-specific differences in the syntactic structure of their vocal sequences. Individuals from the two colonies differed in the propensity to repeat certain note types, forming repetitive motifs which served as higher-order signatures of colony identity. When the two groups were brought into contact, their vocal sequences converged, and these colony-specific repetitive patterns disappeared, with males from both erstwhile colonies now producing similar sequences with similar syntactic structure. We present data suggesting that the higher-order temporal arrangement of notes/vocal units is modified throughout life by social learning as groups of birds continually associate and dissociate. Our study sheds light on the importance of examining signal structure at multiple levels of organization, and the potential for psittaciform birds as model systems to examine the influence of learning and social environment on acoustic signals.

Integrative revision of species limits in the genus Schiffornis (Aves: Tityridae) reveals cryptic diversity in the Neotropics

Abstract Accurate species delimitation is essential for many biological subdisciplines. Nonetheless, current species diversity remains incompletely documented even in well-studied groups such as birds. Here, we take an integrative approach to examine species limits in the genus Schiffornis, a widespread group of dull-plumaged, whistle-voiced suboscine passerines of Neotropical humid-forest understory, currently considered to comprise seven species. We measured geographic variation in song, morphology, and mitochondrial and genome-wide nuclear markers to resolve the taxonomy of the genus. We show that Schiffornis comprises 13 separately evolving population lineages, of which most qualify as species taxa under all species definitions. These include a cryptic new species, several species splits, and the resurrection of a morphologically undifferentiated, but vocally and genetically distinct, taxon that was synonymized nearly a century ago in the Schiffornis turdina complex. We also found several hitherto unnoticed contact zones between diverging lineages and a leapfrog pattern of geographic song variation in the S. turdina complex, and we highlight potential avenues of further research of this genus.

Song variation in a Neotropical mountain passerine, the Brown-capped Redstart (Myioborus brunniceps), is predicted by geographic isolation and environmental factors

Song variation in a Neotropical mountain passerine, the Brown-capped Redstart (Myioborus brunniceps), is predicted by geographic isolation and environmental factors

Local Features of Ballads in Northeast Siberia: Plots of ‘The Mother-in-Law Held Captive by Her Son-in-Law’ and ‘Prince Volkonsky and the Gatekeeper’

This article aims to clarify the characteristics of the ballad genre among other works in Northeast Siberia (in Yakutia and a separate settlement in the Magadan region). It examines the local features of ballad song variants recorded from long-time residents of Northeast Yakutia. The source materials used are texts published in the collections “Folklore of Russian Ustye” (1986) and “Russian Epic Poetry of Siberia and the Far East” (1991). The article presents ballad songs of Russian settlers from the lower reaches of the Indigirka River and the Kolyma River basin. Recordings by D. I. Melikov and V. G. Bogoraz are also utilized. The study is conducted using descriptive and comparative methods, as well as some techniques of lexical-semantic analysis. The work continues the research related to specifying the repertoire, genre, and stylistic features that constitute the uniqueness of epic poetry in Northeast Yakutia recorded in the 19th-20th centuries. The specifics of their dissemination are characterized. The first recordings made in the 19th century are compared with ballad texts documented in the 20th century. Special attention is given to the ballad song “The Mother-in-Law Held Captive by Her Son-in-Law.” It is noted that this folklore specimen reflects certain historical realities related to the area where the song was circulated. It is reported that ballad texts were lost by the 1970s.

Isochronous singing in 3 crested gibbon species (Nomascus spp.).

The search for common characteristics between the musical abilities of humans and other animal species is still taking its first steps. One of the most promising aspects from a comparative point of view is the analysis of rhythmic components, which are crucial features of human communicative performance but also well-identifiable patterns in the vocal displays of other species. Therefore, the study of rhythm is becoming essential to understand the mechanisms of singing behavior and the evolution of human communication. Recent findings provided evidence that particular rhythmic structures occur in human music and some singing animal species, such as birds and rock hyraxes, but only 2 species of nonhuman primates have been investigated so far (Indri indri and Hylobates lar). Therefore, our study aims to consistently broaden the list of species studied regarding the presence of rhythmic categories. We investigated the temporal organization in the singing of 3 species of crested gibbons (Nomascus gabriellae, Nomascus leucogenys, and Nomascus siki) and found that the most prominent rhythmic category was isochrony. Moreover, we found slight variation in songs' tempo among species, with N. gabriellae and N. siki singing with a temporal pattern involving a gradually increasing tempo (a musical accelerando), and N. leucogenys with a more regular pattern. Here, we show how the prominence of a peak at the isochrony establishes itself as a shared characteristic in the small apes considered so far.

Evolutionary and Ecological Processes Underlying Geographic Variation in Innate Bird Songs.

AbstractEcological and evolutionary processes underlying spatial variation in signals involved in mate recognition and reproductive isolation are crucial to understanding the causes of population divergence and speciation. Here, to test hypotheses concerning the causes of song divergence, we examine how songs of two sister species of Atlantic Forest suboscine birds with innate songs, the Pyriglena fire-eye antbirds, vary across their ranges. Specifically, we evaluated the influence of isolation by distance and introgressive hybridization, as well as morphological and environmental variation, on geographic variation in male songs. Analyses based on 496 male vocalizations from 63 locations across a 2,200-km latitudinal transect revealed clinal changes in the structure of songs and showed that introgressive hybridization increases both the variability and the homogenization of songs in the contact zone between the two species. We also found that isolation by distance, morphological constraints, the environment, and genetic introgression independently predicted song variation across geographic space. Our study shows the importance of an integrative approach that investigates the roles of distinct ecological and evolutionary processes that influence acoustic signal evolution.