Male Song Research Articles

Large scale analysis of gender bias and sexism in song lyrics

We employ Natural Language Processing techniques to analyse 377,808 English song lyrics from the “Two Million Song Database” corpus, focusing on the expression of sexism across five decades (1960–2010) and the measurement of gender biases. Using a sexism classifier, we identify sexist lyrics at a larger scale than previous studies using small samples of manually annotated popular songs. Furthermore, we reveal gender biases by measuring associations in word embeddings learned on song lyrics. We find sexist content to increase across time, especially from male artists and for popular songs appearing in Billboard charts. Songs are also shown to contain different language biases depending on the gender of the performer, with male solo artist songs containing more and stronger biases. This is the first large scale analysis of this type, giving insights into language usage in such an influential part of popular culture.

Manual Versus Semiautomated Bioacoustic Analysis Methods of Multiple Vocalizations in Tricolored Blackbird Colonies

Abstract Bioacoustic monitoring can reveal aspects of animal behavior because many species vocalize in association with certain behaviors. Despite this, bioacoustics remain infrequently used to monitor animal behavior because of lack of knowledge of how vocalizations relate to behavior and the challenge of efficiently analyzing the large acoustic data sets necessary to capture relevant behaviors. Vocalizations and associated behaviors have been previously established for the colonial tricolored blackbird Agelaius tricolor, but efficient analysis of the acoustic data remains a challenge. Previous work with tricolored blackbird acoustic data relied on manually listening to recordings, which is not practical on large scales. Using software to automatically detect vocalizations of interest has potential to reduce analysis time. However, automated detection is prone to errors often caused by faint vocalizations, overlapping calls, and background noise. Thus, incorporating components of manual and automated analysis of acoustic data sets remains essential. To address these challenges, we deployed autonomous recording units at three tricolored blackbird colonies in California from 2019 to 2021 and analyzed acoustic data using a manual and a semiautomated analysis method. Specifically, we used tricolored blackbird male song, male chorus, female song, hatchling call, nestling call, and fledgling call to determine the approximate timing of breeding stages and number of breeding attempts, or pulses, for each colony. We found that using a semiautomated approach was more time efficient than manual analysis, while using comparable numbers of recordings and obtaining equivalent information from the colonies. The odds of correct detections of vocalizations using the semiautomated method were generally lower for fainter vocalizations and colonies with high background noise. Overall, the semiautomated approach had tolerable rates of recall, precision, false positives, and false negatives. Our methodology adds to a growing body of literature addressing acoustic analyses, especially for colonial species and where questions of breeding phenology are important.

Strange Tunes—Acoustic Variation and Character Displacement in a Tarsier Hybrid Zone

Natural hybridization provides valuable insights into evolutionary processes, such as speciation and the forces driving or hindering it. Sulawesi tarsiers Tarsius dentatus and T. lariang hybridize within a limited area, suggesting selection against hybrids. Their species- and sex-specific duet songs might serve as a premating barrier in sympatry, especially if differences are strengthened by character displacement. Individuals of mixed origin might face disadvantages if they inherit intermediate song traits. To shed light on the processes shaping this hybrid zone, we analysed 55 duet songs from within and outside the zone. For females and males, we identified temporal and frequency-related parameters that differ between species. We inspected hybrid songs for intermediate characteristics and analysed purebred songs for character displacement in sympatry. Female hybrid songs (N = 2) were intermediate in four to five of six parameters; interpretation of male hybrid songs (N = 2) was inconclusive, because only two parameters were reliably quantifiable. There was no character displacement in female songs in sympatry (N = 11) compared with monospecific areas (N = 17). In male songs, interspecific differences in note rate were significantly larger within the hybrid zone (N = 8) compared with outside (N = 13). Intermediate song traits indicate inheritance and may disadvantage hybrids during mate choice. Character displacement in male songs is consistent with female mate choice, because females should opt for unmistakable signals to avoid costly hybridization. Our findings thus suggest that duet songs of T. lariang and T. dentatus play an important role in limiting this hybrid zone.

Auditory system biophysics in a new species of false-leaf katydid (Tettigoniidae: Pseudophyllinae) supports a hypothesis of broadband ultrasound reception

The auditory system of the katydid is an established model system for studies of hearing, predator-prey interactions, and cochlea dynamics. The components peripheral to the ear substantially influence the hearing threshold, with an internal auditory trachea tuned to the calling song of conspecifics, and external pinnae capable of enhancing ultrasounds for predator detection. The trade-off between such auditory pathways has been subject to multiple discussions, but received little experimental validation. In the most ultrasonic katydids (Pseudophyllinae and Meconematinae), it has been suggested that the external auditory pathway is of greater importance than the internal one, but the biophysical properties of the pinnae and tracheae in such groups have not been compared. Here, we describe the bioacoustics of a new species of pseudophylline katydid, Eubliastes viridicorpus. This species is found to produce a pure tone two-syllable song at 23.4 kHz, similar to other members of the genus. Using micro-CT scanning and finite element modelling, we describe the biophysical tuning of the internal auditory tracheae, and use 3D printed model experiments to investigate external auditory pinnae resonances. By modelling the natural resonant frequencies of the ear, we provide evidence that the acoustic trachea of E. viridicorpus female is tuned to the male song frequency. Experiments on 3D printed models of the pinnae demonstrate that E. viridicorpus has an external auditory pathway capable of broadband ultrasound amplification, providing pressure gains across an effective frequency range of 20–200 kHz, which could also provide enhanced reception of the male song. The importance of pinnae in ultrasonic rainforest katydids is discussed.

Male song of the Aquatic Warbler, a promiscuous bird without paternal care, is more complex than previously thought

The Aquatic Warbler Acrocephalus paludicola is one of the rarest European passerines and is characterised by promiscuity, lack of pair-bonds and female-only parental care. This makes the species an important model for studying the function of avian courtship song. The song of the Aquatic Warbler consists of whistle and rattle phrases produced as discontinuous A-, B- and C-songs, which are built by a single rattle, a rattle and a whistle, and more than two phrases of both kinds, respectively. The A- and B-songs are thought to be aggressive signals in male-male interactions, while C-songs are thought to be important for female choice. Here, we analysed recordings of 40 individually marked males, and determined the phrase repertoire. The enumerated repertoire (males recorded for ≥ 10 min) ranged from 16 to 158 (mean 99), however, it did not capture the complete phrase repertoires. We then used models from species diversity ecology to estimate the actual phrase repertoire size, which ranged between 18 and 300 phrases (mean 155). The estimated repertoire was predicted by the number of C-songs. The rattle repertoire was larger than the whistle repertoire, and both positively correlated with the number of C-songs. Our study indicates that male Aquatic Warblers have highly complex phrase repertoires that vary widely in size. Their courtship song is flexible and efficient, enabling relative song complexity to be demonstrated in a short sample, thus facilitating both female attraction through the quick presentation of large phrase repertoires and rival deterrence through the production of many short and simple A- and B-songs.

Song overlapping and matching during low‐arousal singing and their relation to visual ornaments, parental care and breeding success in the great tit (Parus major)

AbstractEavesdropping on interactions between conspecific animals provides a low‐cost method for assessing other individuals. Asymmetries in territorial counter‐singing interactions in songbirds provide a rich source of information for eavesdroppers about differences between the singers. Yet, little is known about the relationship between interactive singing in a natural, low‐arousal context among territorial neighbours and individual traits of males. We used a microphone array to monitor natural counter‐singing interactions in great tits (Parus major) during nest building, at the onset of the breeding season. We quantified song overlapping and song matching for 30 pairs (dyads) of interacting males, singing at their nest, respectively. We then compared these behaviours to five traits for 28 males: body condition, plumage ornamentation, offspring provisioning behaviour, offspring weight and breeding site quality. We found no relationship between a male song overlapping or matching behaviour and any of the measured traits. Therefore, our results do not support the idea that short‐term asymmetries in low‐arousal long‐range singing interactions among neighbours reflect differences in these fitness‐related traits. Instead, our findings suggest that such singing asymmetries have less signal value in the absence of an immediate conflict but instead reflect short‐term motivational differences, as shown in previous investigations.

Individual and Geographic Variation in Non-Harmonic Phases of Male Capercaillie (Tetrao urogallus) Song

Individually distinct acoustic signals, produced mainly as tonal and harmonic sounds, have been recorded in many species; however, non-tonal 'noisy' signals have received little attention or have not been studied in detail. The capercaillies (Tetrao urogallus) produce complex courtship songs composed of non-tonal noisy signals in four discrete phases. We analyzed recordings from 24 captive male capercaillies in breeding centres in the Czech Republic, Poland, and Germany, and songs from wild males in Sweden, Norway, Finland, and Estonia to test whether a non-harmonic song can encode individual-specific information. We also analyzed the intra-population variation of the male song from three separate areas: Carpathian (Polish and Czech Beskid), Sumava, and Boreal (boreal range of species distribution). Temporal and frequency characteristics can reliably distinguish capercaillies at the individual level (91.7%). DFA model testing geographic variation assigned 91% of songs to the correct area (Carpathian, Sumava, Boreal). The cluster analysis revealed that males from the Boreal area formed a distinct cluster. Our analysis shows clear geographical patterns among our study males and may provide a valuable marker for identifying inter-population dynamics and could help to characterize the evolutionary histories of wood grouse. We discuss the potential use of this marker as a non-invasive monitoring tool for captive and free-roaming capercaillies.

Female preferences for high vocal effort in singing mice

Abstract Although vocalizations are essential to mammalian sociosexual behaviours, little is known about female preferences for male vocal displays in non-model mammalian species. Here, we characterized female preferences for the advertisement songs of male Alston’s singing mice (Scotinomys teguina). We developed procedures for inducing oestrus, using vaginal perforation as a morphological indicator of oestrus. We then broadcasted ‘high-effort’ and ‘low-effort’ songs recorded from wild-caught males to virgin laboratory-reared females, using a two-choice experiment. Our results indicate that females spent more time investigating speakers playing high-effort songs; surprisingly, this phonotactic response is independent of oestrus status. In wild singing mice, acoustic characteristics of high-effort male songs positively correlate with body condition. Our data suggest that females could use acoustic cues to select mates in good condition, thus providing preliminary support for adaptive mate choice hypotheses. More generally, our results support the hypothesis that elaborate Scotinomys song may be shaped by female choice.

Evolution of female song and duetting in the chaffinch (Fringilla) species complex

Female song is ancestral to songbirds and shows considerable phylogenetic signal, but its presence also appears to be labile and correlated with life‐history and ecology. While previous studies have examined the evolution of female song across species‐rich families, here we studied female song in island populations of a recently diverged species‐complex, the chaffinches (genus Fringilla). We show this behaviour has recently evolved in these populations, and probably on two independent occasions. In F. teydea, female song is performed in loose duets with males, while in F. coelebs, female song is produced solo. Populations with singing females showed year‐round territoriality and were found in regions with low seasonality – both factors previously connected with high rates of female singing. To determine the relative saliency of female songs to conspecifics, and the degree to which they instigate territorial defence behaviours, we performed a series of speaker playback experiments. In F. c. canariensis, female song could induce comparable responses to male song, whilst duetting F. teydea playback produced similar responses to solo songs, and therefore may relate to within‐pair communication instead. Our results suggest female song can be a highly labile trait that can evolve over short evolutionary timescales.

Male‐specific nocturnal song functions similarly to day song in a diurnal bird species

AbstractHistorically, birdsong research has been biased towards song of male birds at dawn and during the day, even though some diurnal birds sing at night. To address this gap, we studied how song in the willie wagtail, Rhipidura leucophrys—a diurnal species with prolific male‐specific nocturnal song during the breeding season—varies with time of day, breeding status and simulated intrusions. We recorded male nocturnal and dawn song over three breeding seasons and examined how this related to fertile and non‐fertile breeding stages of females. To test whether song functions for territory defence, we simulated territorial intrusion experimentally in both sexes with daytime and nighttime playback of male and female song. To test whether nocturnal song could function for mate guarding or post‐pairing mate attraction, we describe the mating system of willie wagtails using molecular genetic methods. We showed that both nocturnal and day song of male willie wagtails has roles in mate attraction and territory defence, while day song by females functioned primarily for territorial defence. Males increased song behaviour during fertile periods of resident females, suggesting possible roles in mate stimulation and mate guarding. Males and females responded similarly to simulated daytime intrusions and no differences were seen in male responses dependent on the time of day. We found 10%–14% of offspring were fathered by extra‐pair males, suggesting song may also function for mate guarding and post‐pairing mate attraction. In a species with small repertoires and simple songs like the willie wagtail, differences between males in overall song output achieved through nocturnal singing may be important in mate attraction and territory defence.

Revised checklist of Cicadidae (Insecta: Hemiptera) of Mindanao, Philippines, with descriptions of a new genus and nine new species

ABSTRACT This paper provides a revised faunal checklist for the subfamilies, tribes, subtribes, genera and species of the family Cicadidae (Insecta: Hemiptera) from Mindanao, Philippines, comprising 31 species belonging to 19 genera. A new genus, Neopurana Lee and Marshall gen. nov., and nine new species, Platypleura bella Lee and A. Mohagan sp. nov., Platypleura minima Lee and Marshall sp. nov., Chremistica flavialata Lee and Marshall sp. nov., Oncotympana obesa Lee and Marshall sp. nov., Neopurana bouptera Lee and Marshall sp. nov., Purana mindanaoensis Lee and Marshall sp. nov., Mogannia tenebrosa Lee and Marshall sp. nov., Philipsalta exilis Lee and Marshall sp. nov. and Philipsalta lata Lee and Marshall sp. nov., are described. Platypleura transitiva Lee, 2021 is newly added to the list of cicadas from Mindanao. Male calling songs are illustrated and described for all new species. Information on the geographic distributions of the 31 Mindanao species is provided. http://www.zoobank.org/urn:lsid:zoobank.org:pub:AA69FCBE-81ED-4B41-90D6-0D32EBE887CA

Four decades later: The highly conserved repertoire of song types in chaffinch (Fringilla coelebs)

The long-term stability of culturally transmitted traits like bird song has attracted much attention from researchers; however, it remains insufficiently studied up to the present time. This study investigates, by using spectrographic analysis, whether the repertoire of song types recorded at the same locality is persistent at short terms (of four years) and at long terms (of 38 years) in a migratory European continental population of chaffinches. The population song type repertoires recorded in 1978 and 1982 were only slightly different, thus indicating the high repertoire persistence within a few years. There were more differences between repertoires recorded in 1982 and 2020. In total, eight of the 29 song types (28 %) identified in 1982 were not found in 2020, and 5 of the 26 song types (19 %) discovered in 2020 were completely new compared to 1982. All the other song types recorded in 2020 were similar to those recorded in 1982. The frequency of use of these song types in 1982 and 2020 was also similar. By 2020, mainly those song types had disappeared from the population repertoire, which in 1982 were performed by a limited number of males. These data suggest a high long-term persistence of repertoire of song types in male song of a migratory continental population. This long-term stability of the population repertoire was maintained despite significant changes in the habitat structure caused by a massive expansion of bark beetles in 2010–2014.

Sex Differences in the Neural Song Circuit and Its Relationship to Song Acoustic Complexity in House Wrens (Troglodytes aedon).

The song circuit in passerine birds is an outstanding model system for understanding the relationship between brain morphology and behavior, in part due to varying degrees of sex differences in structure and function across species. House wrens (Troglodytes aedon) offer a unique opportunity to advance our understanding of this relationship. Intermediate sex differences in song rate and complexity exist in this species compared to other passerines, and, among individual females, song complexity varies dramatically. Acoustic complexity in wild house wrens was quantified using a new machine learning approach. Volume, cell number, cell density, and neuron soma size were then measured for three song circuit regions, Area X, HVC (used as a proper name), and the robust nucleus of the arcopallium (RA), and one control region, the nucleus rotundus (Rt). For each song control area, males had a larger volume with more cells, larger somas, and lower cell density. Male songs had greater acoustic complexity than female songs, but these distributions overlapped. In females, increased acoustic complexity was correlated with larger volumes of and more cells in Area X and RA, as well as larger soma size in RA. In males, song complexity was unrelated to morphology, although our methods may underestimate male song complexity. This is the first study to identify song control regions in house wrens and one of few examining individual variation in both sexes. Parallels between morphology and the striking variability in female song in this species provide a new model for understanding relationships between neural structure and function.

Divergence of a speciation trait through artificial selection: Insights into constraints, by-product effects and sexual isolation.

Speciation and sexual isolation often occur when divergent female mating preferences target male secondary sexual traits. Despite the importance of such male signals, little is known about their evolvability and genetic linkage to other traits during speciation. To answer these questions, we imposed divergent artificial selection for 10 non-overlapping generations on the Inter-Pulse-Interval (IPI) of male courtship songs; which has been previously shown to be a major species recognition trait for females in the Drosophila athabasca species complex. Focusing on one of the species, Drosophila mahican (previously known as EA race), we examined IPI's: (1) rate of divergence, (2) response to selection in different directions, (3) genetic architecture of divergence and (4) by-product effects on other traits that have diverged in the species complex. We found rapid and consistent response for higher IPI but less response to lower IPI; implying asymmetrical constraints. Genetic divergence in IPI differed from natural species in X versus autosome contribution and in dominance, suggesting that evolution may take different paths. Finally, selection on IPI did not alter other components of male songs, or other ecological traits, and did not cause divergence in female preferences, as evidenced by lack of sexual isolation. This suggests that divergence of male courtship song IPI is unconstrained by genetic linkage with other traits in this system. This lack of linkage between male signals and other traits implies that female preferences or ecological selection can co-opt and mould specific male signals for species recognition free of genetic constraints from other traits.

Female preferences between incipient species of Drosophila athabasca reveal divergent closed functions, epistasis, and segregation of veiled preference alleles.

Theoretical models typically assume that speciation is driven by divergence in female preference functions for secondary sexual traits. However, little is known about how these functions diverge between incipient species. This study used song playback experiments and mate choice tests to characterize female preference functions for divergent male courtship songs between two incipient species of Drosophila athabasca complex; D. athabasca (WN) and Drosophila mahican (EA). The study focused on two male song parameters: pulses per burst (PPB) and inter-pulse interval (IPI). Preference functions for PPB were open-ended and lacked species-specificity. In contrast, preference functions for IPI revealed a closed shape, with peak preferences highly divergent between species. Thus, females imposed divergent and ongoing sexual selection on male IPI. Further work demonstrated variation in peak preferences and choosiness for IPI across genetic lines, while F1 hybrid females varied extensively in their mating preferences across different heterospecific line crosses. Finally, F2 female genotypes with foreign single-copy chromosome substitutions showed little to no change in preferences until three or four chromosomes were combined: indicating strong dominance epistasis. These results suggest "veiled" or hidden segregating female preference alleles for male speciation phenotypes. This may explain the rapid speciation observed in this species complex.

Decoupling of sexual signals and their underlying morphology facilitates rapid phenotypic diversification.

How novel phenotypes evolve is challenging to imagine because traits are often underlain by numerous integrated phenotypic components, and changes to any one form can disrupt the function of the entire module. Yet novel phenotypes do emerge, and research on adaptive phenotypic evolution suggests that complex traits can diverge while either maintaining existing form-function relationships or through innovations that alter form-function relationships. How these alternate routes contribute to sexual signal evolution is poorly understood, despite the role of sexual signals in generating biodiversity. In Hawaiian populations of the Pacific field cricket, male song attracts both female crickets and a deadly acoustically orienting parasitoid fly. In response to this conflict between natural and sexual selection, male crickets have evolved altered wing morphologies multiple times, resulting in loss and dramatic alteration of sexual signals. More recently, we and others have observed a radical increase in sexual signal variation and the underlying morphological structures that produce song. We conducted the first combined analysis of form (wing morphology), function (emergent signal), and receiver responses to characterize novel variation, test alternative hypotheses about form-function relationships (Form-Function Continuity vs. Form-Function Decoupling), and investigate underlying mechanistic changes and fitness consequences of novel signals. We identified three sound-producing male morphs (one previously undescribed, named "rattling") and found that relationships between morphology and signals have been rewired (Form-Function Decoupling), rapidly and repeatedly, through the gain, loss, and alteration of morphological structures, facilitating the production of signals that exist in novel phenotypic space. By integrating across a hierarchy of phenotypes, we uncovered divergent morphs with unique solutions to the challenge of attracting mates while evading fatal parasitism.

Loss of complex female song but not duetting in the ancestors of Carolina wrens

AbstractFemale singing and coordinated male–female duetting are often but not always found in the same species. Both behaviors are more common in tropical than temperate songbirds, but few studies have differentiated between the factors selecting for each. Here we investigate the evolution of female vocal complexity and male–female vocal coordination in Carolina wrens (Thryothorus ludovicianus), one of the few non‐tropical members of a songbird family (Troglodytidae) that is well known for producing coordinated male–female duets. Female Carolina wrens are not known to sing; rather, they produce relatively simple, sex‐specific chatters, often during territorial encounters. We analyzed field recordings to show that females coordinate these chatters with male songs at rates similar to those observed in some tropical duetting wren species. We then used phylogenetic comparative methods to show that the evolutionary ancestors of Carolina wrens had female songs that were more acoustically complex than the vocalizations of current females, suggesting past selection against female vocal complexity. Levels of vocal coordination with males, in contrast, have changed relatively little from those of tropical ancestors. Our results suggest that these two aspects of female behavior, acoustic complexity and vocal coordination with males, have evolved independently and have different functions in communication.

Asymmetric song recognition does not influence gene flow in an emergent songbird hybrid zone

Abstract Hybrid zones can be used to examine the mechanisms, like song recognition, that affect reproductive isolation and speciation. Song has mixed support as a driver of speciation; we did not find song to be associated with reproductive isolation in White-crowned Sparrow subspecies (Zonotrichia leucophrys pugetensis and Z. l. gambelii). We examined an emerging secondary contact zone in these subspecies by measuring song variation, song recognition, plumage, morphology, and mitochondrial DNA (mtDNA). Plumage and morphological characters provided evidence of hybridization in the contact zone, with some birds possessing intermediate phenotype and song characteristics, and some possessing discordant phenotype and mitochondrial haplotype. Playback experiments revealed asymmetric song recognition: male pugetensis displayed greater response to their own song than gambelii song, whereas gambelii did not discriminate significantly. If female choice operates similarly to male song discrimination, we predicted asymmetric gene flow, resulting in a greater number of hybrids with gambelii mtDNA. Contrary to our prediction, more gambelii and putative hybrids in the contact zone possessed pugetensis mtDNA haplotypes, possibly due to greater pugetensis abundance and female-biased dispersal.

Superb fairy-wrens with extreme exploration phenotypes respond more strongly to simulated territory intrusions

Individuals can exhibit strong consistencies in behaviours across time and contexts, referred to as animal personalities. Yet studies linking personality differences measured in captivity to ecologically relevant social behaviours in the wild are sparse and contradictory. Here, we used wild superb fairy-wrens, Malurus cyaneus , to investigate whether two personality traits measured in short-term captivity (exploration and aggressiveness) predicted aggressiveness in the wild (measured as territory defence). We first identified behavioural phenotypes within our study population by temporarily capturing adult birds to measure their (1) emergence, activity and sector visits in a novel environment (exploration) and (2) aggression in response to mirror image stimulation (aggressiveness). We later simulated two conspecific intrusions within their territory using playback of vocalizations (female or male chatter song) within their territory, in a pairwise design. Both exploration and breeding status (breeder/dominant versus helper/subordinate) influenced the birds’ response to the simulated intrusions. Dominant individuals and individuals with extreme exploration phenotypes (i.e. fast or slow explorers) responded more strongly to playback compared to helpers or those with intermediate exploration phenotypes, respectively. However, aggressiveness measured in short-term captivity (mirror response) did not correlate with our measure of aggressiveness in the wild (playback response during territory defence). The personality matching of breeding pairs (whether their partner had a matching or mismatching exploration phenotype) also influenced playback response, as pairs with mismatching exploration phenotypes responded more strongly to conspecific intruders than pairs with similar phenotypes. Our results support a growing number of studies showing the importance of animal personalities for response strategies and social behaviours. • We explored associations between personality traits in wild superb fairy-wrens. • Birds with extreme exploration phenotypes were more aggressive against conspecifics. • Aggressiveness in captivity did not correlate with aggressiveness in the wild. • Pairs with mismatching exploration phenotypes responded more strongly to intruders. • Our results support the validity of personality in fitness-related contexts.

Soft song provokes stronger aggressive responses than broadcast song in the Plain Laughingthrush (Pterorhinus davidi)

Many bird species produce low‐amplitude acoustic signals, known as soft songs, which are widely believed to function primarily in aggressive interactions. However, there are surprisingly few experimental studies that have examined whether soft songs are reliable signalling strategies for escalating aggressive interactions. Here, we investigate the functions of soft song in a colour‐marked population of the Plain Laughingthrush Pterorhinus davidi, using playback experiments combined with specimen‐based simulated territory intrusions. We found that playback of male soft song provoked quicker response and stronger aggressive intent by territorial pairs compared with playback of male broadcast song. Responses by territorial pairs to male soft song playback were significantly stronger compared with responses to broadcast song playback, with a greater number of flights over the speaker, more time spent within 1 m of the speaker and closer approaches to the speaker. Furthermore, closer approach with the production of soft song by focal males was the best predictor of aggressive intent in combined playback and specimen intrusion experiments. Our results suggest that male soft song is used as an aggressive signal in the Plain Laughingthrush, and represents the first evidence of such for a monogamous temperate duetting species.