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Singing is known to play significant roles in songbird communication. For a long time, singing was believed to be a male attribute, whereas rare episodes of female singing were seen as deviations. However, there has been more and more research on female vocals in recent times, suggesting this in no way to be a rare event. In this study, we investigated the vocalization of the black-hooded oriole (Oriolus xanthornus) in Nam Cat Tien National Park, southern Vietnam. We identified two singing variants significantly differing in both maximum frequency and frequency range, these parameters being higher in variant 2. Variant 1 appeared to be more often, being performed in various situations: spontaneous singing, territorial interactions, and duets. Variant 2 occurred only in duets or in territorial interactions where the bird focal pair also performed in duets. No syntax variation was found between the different singing variants. In addition, no variation was revealed in the syntax of variant 1 in the different situations (spontaneous singing and duets). In one observation, we reliably discovered that the male used variant 1, while the female used variant 2. Variant 1 is likely usually to be used by males, while variant 2 is typically used by females. We also identified two types of calls for this species. [ABSTRACT FROM AUTHOR]

Female song in birds is more widespread than previously thought, and studies across different species are critical for better understanding the entire evolutionary process of bird song. In this study, we recorded the songs of males and females in a duetting, montane bird species, the Elliot's laughingthrush Trochalopteron elliotii, across consecutive breeding seasons. We specifically focused on identifying the number and structure of different song types by males and females, and compared these acoustic structures between the sexes. Our findings revealed that both males and females sang sex‐specific solos. More specifically, females sang a single type of solo that varied significantly in the number of notes, whereas males produced three different solos composed of 2, 3, or 4 notes, respectively. Female solos exhibited significantly more notes and longer song duration compared to males. Male solos typically had a significantly higher maximum frequency for the entire song. No significant differences were observed in the duration of the first note, song rate, and other frequency characteristics between male and female solos. Furthermore, paired males and females coordinated their sex‐specific solos to form duets when challenged by conspecific territory intruders, both within and outside the breeding season. Sex‐specific solos suggested that male and female songs play different roles and may be subject to different selective pressures. Further research is necessary for elucidating the functions of male song, female song, and duets in this montane bird species. [ABSTRACT FROM AUTHOR]

Female song and male–female duetting have been detected mainly in tropical passerines, in which female singing serves a variety of functions that vary with social contexts. Females of numerous temperate passerine species also sing and engage in male–female duetting, but it is still unclear whether these vocalizations function in a similar manner to those of tropical species. To help address this knowledge gap, we used multiple field experimental approaches to investigate the function of female song and male–female duets in a colour-marked population of the plain laughingthrush, Pterorhinus davidi , a socially monogamous, pair-living, resident, temperate species. Baseline observations revealed that both unpaired males and females sing more than paired individuals, and both paired males and females sang more when they were apart, suggesting that females sing to attract potential mates and/or contact their partners. Playback experiments revealed that pair members coordinated their approach to the playback speakers and engaged in duetting, suggesting that duets play a significant role in joint territorial defence. Responses of focal birds to playback stimuli were not sex specific and joint territory defence was male dominated. Mate removal experiments found that both males and females sang more when their mate was experimentally removed, suggesting that females also use songs for contacting a missing mate within their territory. Simulated intrusions using live decoy experiments indicated that duets may also function in shared resource defence during the nonbreeding season. Our study highlights the importance of investigating the functions of female song and male–female duets in songbirds by using a combination of different field approaches to quantify the multifunctional nature of these vocalizations. • Female songs are multifunctional and employed across broad social contexts. • Female solos are used for contacting male partners and for mate attraction. • Male–female duetting functions primarily for defending shared resources. [ABSTRACT FROM AUTHOR]

Passive acoustic monitoring (PAM) – an approach that uses autonomous acoustic recording units (ARUs) – can provide insights into the behavior of cryptic or endangered species that produce loud calls. However, extracting useful information from PAM data often requires substantial human effort, along with effective estimates of the detection range of the acoustic units, which can be challenging to obtain. We studied the duetting behavior of pair-living red titi monkeys (Plecturocebus discolor) using PAM coupled with an open-source automated detection tool. Using data on spontaneous duetting by one titi pair, combined with recordings from two Song Meter SM2 ARUs placed within their home range, we estimated that the average source level of titi duets was ~105 dB re 20 μPa at 1 m with an attenuation rate of 8 dB per doubling of distance, and we determined that the detection radius for manual annotation of duets in audio recordings was at least 125 to 200 m, depending on the approach used. We also used a supervised template-based detection algorithm (binary point matching) to evaluate the efficacy of automated detection for titi duets in audio recordings using linear arrays of ARUs within a ~2 km2 area. We used seven titi duet templates and a set of “off-target” howler monkey (Alouatta seniculus) templates to reduce false positive results. For duets with a signal-to-noise (SNR) ratio > 10 dB (corresponding to a detection radius of ~125 m) our detection approach had a recall (the number of all duets that are correctly detected) of 1.0. Performance decreased when including duets with a lower SNR (recall = 0.71, precision = 0.75). The fact that multiple lines of evidence suggest an effective detection radius of 125 to 200 m for titi duets across upland terra firme and seasonally flooded forest lends support to our findings. We suggest that PAM studies of other cryptic but vocally active species would benefit from following similar experimental and analytic procedures to determine an ARU’s effective detection radius and to improve the performance of automated detection algorithms.

The evolution of human language is a topic that has received undiminished attention. Numerous hypotheses for the origin of human language have been proposed, including gestural communication found specifically among apes. This study advances the hypothesis that human evolution, including human language development, is three-pronged: prosocial, cognitive, and collaborative. Duetting and turn-taking in primates are used as pivotal examples of how bonding leads to joint action and collaboration. It points out that such vocal behavior itself may be a crucial precursor of language evolution in the sense that it is explicitly focused on a conspecific. Some current hypotheses have acknowledged duetting as an important perceptual and behavioral example of synchronicity. Some forms of synchronized behavior, as found in duetting, synchronized dance, or even shared song, were perhaps crucial evolutionary steps preceding the evolution of human language. Duetting signifies more than that, however, because it is an observable and significant cognitive investment that signals attention toward a partner. This study also advances the hypothesis that affect and cognition would have needed to precede any form of duetting or signs of affiliation such as grooming. Hence, this study, asking what duetting in primates signifies in evolutionary terms, takes a multidisciplinary and multimodal approach to suggest important affective and cognitive steps in the evolution of human language and speech, the chief of which is prosociality. Prosociality, as an attitude and awareness of another, be this as a friend or partner for whom one can do favors or whom one can help, is a model for collaboration and cooperation, and also increased cognition.

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Group living often requires maintaining dynamic and varied relationships with fellow group members, while simultaneously monitoring and interacting with external competitors. Group members in many social species vocalize together to produce duets or choruses—coordinated, often conspicuous vocal displays—that may play a role in these interactions. Compared with male–female duets, however, relatively little research exists on the function and adaptive significance of group choruses, which involve three or more individuals. Here we investigate chorusing behavior in the greater ani (Crotophaga major), a communally breeding cuckoo that nests in stable social groups of four to eight unrelated individuals. Groups may remain together for several years on the same nesting territory, and groups occasionally destroy each other's clutches in conflicts over high‐quality territories. We asked whether the raucous, highly stereotyped choruses performed by ani groups are primarily used for intra‐ or intergroup communication, and whether they contain information about the identity of the social group and the number of birds vocalizing. Behavioral observations and acoustic recordings from three breeding seasons revealed that choruses typically occurred during social interactions within the group (78% of choruses) or in response to a predator or extra‐group individual (17%) and only rarely in intergroup interactions (4%). Consistent with this finding, choruses did not reliably reflect the number of birds vocalizing, and we found only limited evidence for group‐specific acoustic signatures (driven by a single group whose choruses were highly distinct). These results suggest that group choruses play an important role in intra‐group signaling, potentially in contexts such as group formation, reinforcement of social bonds within the group, and/or collective decision‐making, and they motivate new research questions about the role of collective signaling in social evolution. [ABSTRACT FROM AUTHOR]

Duetting, in which 2 or more individuals call in coordinated unison, is common in birds, yet most research investigating the function of avian duets has focused only on oscine passerines. However, we have discovered that duetting occurs in 61 species (59%) in the family Rallidae (rails), one of the highest known rates in any bird clade, and that rail duets are also significantly associated with year-round territoriality and habitat type. We applied a comparative approach to study the occurrence of duetting relative to socio-ecological traits and call properties in 103 rail species, with the prediction that duetting rails produce low-frequency calls that spread well over short distances in densely vegetated habitats. Using a model correcting for phylogenetic signal, we found that duetting is the ancestral state in Rallidae, and that duetting rails show a trending effect for being sedentary and nonmigratory. Contrary to our predictions, there was no significant correlation between rail duetting and social bond length, breeding system, breeding latitude from the equator, or sexual dimorphism, as year-round territoriality and forest or heterogeneous habitats were the strongest predictors of duets. Despite the prevalence of duetting in Rallidae, few studies have tested duet functions such as territory defense in this family, and our comparative phylogenetic study lays the groundwork for future research, as little remains known about the behavioral ecology and vocal interactions of many rails. [ABSTRACT FROM AUTHOR]

In bush-crickets, males produce a calling song to announce their presence to females. Females ready to mate respond either by a phonotactic approach or signal their presence acoustically by establishing a kind of duet. This duetting behaviour is typical of phaneropterid bush-crickets, of which many species in Europe are flightless. In the long-winged genus Phaneroptera, the females also respond acoustically to the male calling song, which is quite similar in the three west European species in this genus. After acoustical contact, however, the behaviour of males and females of the three species differ markedly. In P. nana, males and females engage in a duet in which the female responds to each syllable of the male song (and he approaches her). In P. falcata, the female only responds to certain elements of the male song that are produced at long intervals. However, after her response the male does not change its song or its position, but often increases its singing activity (and the female approaches him). In P. sparsa the female only responds to particular, very complicated and soft elements of the male song, which are typically repeated at intervals of several to many minutes. After hearing the response, the male drastically changes its song by producing only the soft elements. These parts of the song contain syllables with a unique spectral composition and others that may threaten eavesdropping rivals. In this species both sexes probably move towards each other during mate localization. At present, we can only speculate about the adaptive nature of the different strategies.

Acoustic communication serves a crucial role in the social interactions of vocal animals. Duetting—the coordinated singing among pairs of animals—has evolved independently multiple times across diverse taxonomic groups including insects, frogs, birds, and mammals. A crucial first step for understanding how information is encoded and transferred in duets is through quantifying the acoustic repertoire, which can reveal differences and similarities on multiple levels of analysis and provides the groundwork necessary for further studies of the vocal communication patterns of the focal species. Investigating acoustic tradeoffs, such as the tradeoff between the rate of syllable repetition and note bandwidth, can also provide important insights into the evolution of duets, as these tradeoffs may represent the physical and mechanical limits on signal design. In addition, identifying which sex initiates the duet can provide insights into the function of the duets. We have three main goals in the current study: (1) provide a descriptive, fine-scale analysis of Gursky’s spectral tarsier (Tarsius spectrumgurskyae) duets; (2) use unsupervised approaches to investigate sex-specific note repertoires; and (3) test for evidence of acoustic tradeoffs in the rate of note repetition and bandwidth of tarsier duet contributions. We found that both sexes were equally likely to initiate the duets and that pairs differed substantially in the duration of their duets. Our unsupervised clustering analyses indicate that both sexes have highly graded note repertoires. We also found evidence for acoustic tradeoffs in both male and female duet contributions, but the relationship in females was much more pronounced. The prevalence of this tradeoff across diverse taxonomic groups including birds, bats, and primates indicates the constraints that limit the production of rapidly repeating broadband notes may be one of the few ‘universals’ in vocal communication. Future carefully designed playback studies that investigate the behavioral response, and therefore potential information transmitted in duets to conspecifics, will be highly informative.

Acoustic signals are ubiquitous across mammalian taxa. They serve a myriad of functions related to the formation and maintenance of social bonds and can provide conspecifics information about caller condition, motivation and identity. Disentangling the relative importance of evolutionary mechanisms that shape vocal variation is difficult, and little is known about heritability of mammalian vocalizations. Duetting––coordinated vocalizations within male and female pairs––arose independently at least four times across the Primate Order. Primate duets contain individual‐ or pair‐level signatures, but the mechanisms that shape this variation remain unclear. Here, we test for evidence of heritability in two call types (pulses and chirps) from the duets of captive coppery titi monkeys (Plecturocebus cupreus). We extracted four features––note rate, duration, minimum and maximum fundamental frequency––from spectrograms of pulses and chirps, and estimated heritability of the features. We also tested whether features varied with sex or body weight. We found evidence for moderate heritability in one of the features examined (chirp note rate), whereas inter‐individual variance was the most important source of variance for the rest of the features. We did not find evidence for sex differences in any of the features, but we did find that body weight and fundamental frequency of chirp elements covaried. Kin recognition has been invoked as a possible explanation for heritability or kin signatures in mammalian vocalizations. Although the function of primate duets remains a topic of debate, the presence of moderate heritability in titi monkey chirp elements indicates duets may serve a kin recognition function. [ABSTRACT FROM AUTHOR]

Birds have a diverse acoustic communication system, with species-specific repertoires facilitating more complex behaviors in terms of both within- and between-pair communications. Certain song types are produced for specific functions, such as aggressive encounters. In addition, song matching behaviors, whereby neighboring individuals match song types, can be used in aggressive interactions as a sophisticated acoustic behavior. In this study, we examined the functions of song types, in a duet context, of male yellow-breasted boubous (Laniarius atroflavus), an Afromontane bush-shrike with a vocal sexual dimorphism. We aimed at assessing whether, structurally, certain song types elicited a heightened reaction than others and also whether song matching affected response behavior. A dual speaker playback procedure was performed for 18 pairs of boubous, each pair being exposed to duets with three different male song types. We found differences in response toward the different duet types but these differences resulted from the amount at which males matched different song types. Pairs responded stronger when a focal male matched the playback type, and matching was significantly more often found in cases where the rarest type of male song was used. We found no sex differences in terms of response strength to playback type. Our results indicate a two-level way of coding aggression toward intruding pairs. The yellow-breasted boubous utilize their repertoires, linking matching with structure in order to show aggression in terms of territory defense and sexual conflict. This study also confirms joint territorial defense as a main function of duets in this species. The diverse song repertoires of birds, in terms of size and organization, facilitate both within- and between-pair communication. Using playback experiments, we showed that males and females of a duetting Afromontane bush-shrike jointly defend territories. The small and shared repertoire of male songs is important for conflict resolution. Our results indicate a two-level way of coding aggression toward territory intruders. Both, song type used and matching a male intruders song type, shape the response strength. [ABSTRACT FROM AUTHOR]

Abstract Duets in breeding pairs may reflect a situation of conflict, whereby an individual answers its partner's song as a form of unilateral acoustic mate guarding or, alternatively, it may reflect cooperation, when individuals share in territory defense or safeguard the partnership. The degree of coordination between the sexes when responding to solo versus paired intruders may elucidate the function of songs in duets. We examined this issue in a study with rufous horneros (Furnarius rufus), a duetting, socially monogamous Neotropical species with low levels of extrapair paternity. We exposed social pairs during the nonbreeding season to playbacks of duets, male solos, female solos, and control heterospecific songs. Partners approached all conspecific stimuli together and responded by singing quickly, at higher rates and by coordinating ~80% of their songs into duets. For both sexes, most response variables (seven of nine) did not vary across conspecific treatments. These results suggest that partners duet and coordinate behaviors to cooperatively defend common territories. However, females spent more time in territorial vigilance, and partners were highly coordinated (correlated responses) in response to duets and female solos in comparison with male solos. This indicates that female intrusions (paired or solo) might be more threatening than male intrusions in the nonbreeding season, especially for territorial females, and that females are less cooperative with their partners in territory defense against male intruders.

Songbird vocalizations serve diverse functions including territory defence against neighbouring conspecific animals. In tropical and south-temperate regions, it is commonplace for both female and male songbirds to sing solo songs and coordinated vocal duets to defend their territories. The Área de Conservación Guanacaste in Costa Rica is the site of an ambitious conservation effort to protect and regrow tropical dry forests; it consists of a mosaic of regenerating and mature forest patches, presenting a special opportunity to study the effect of different numbers of neighbours on male and female wrens living in these fragmented forests. We analyzed recordings of Rufous-and-white Wrens (Thryophilus rufalbus) over a 17-year period, focusing on vocal behaviour and variation in the number of territorial neighbours within the fragmented landscape in the conservation area, and on diel and seasonal variation in female and male song. We hypothesized that the number of conspecific neighbours would influence vocal behaviours, including female and male solo song rate, duet responsiveness rate, repertoire use, and song-switching rate. For females, we found that wrens change song-types more often in areas with more neighbours, whereas the other aspects of female vocal behaviour did not vary with the number of neighbours. For males, we found no aspect of vocal behaviour that varied with the number of neighbours. For both sexes, we found variation in vocal behaviours with time of day and time of year, in keeping with previous research. Our results underscore the idea that we must explore female and male birds independently, because the sexes may respond differently to external factors. We did not find strong links between wren vocal behaviour and variation in the number of neighbours, yet we encourage further behavioural studies on vocal behaviour of birds with varying numbers of neighbours in fragmented landscapes. [ABSTRACT FROM AUTHOR]

Temporal coordination of duets consists of nonrandom overlap, alternation or association between rhythms of acoustic elements. Since duet coordination presumably requires high attentiveness between signallers, the coalition quality hypothesis suggests it may indicate the ability or motivation of partners to engage cooperatively in aggressive interactions against intruders. To test this hypothesis, we monitored behavioural as well as vocal responses in a playback experiment conducted with a polyphonal duetting bird, the rufous hornero, Furnarius rufus. We used three categories of treatments in the experiment, which totalled six treatments: duet playbacks that varied in phrase overlap and coordination of temporal rhythms; nonoverlapped (consecutive) solos; and a control heterospecific song. We predicted that birds would respond more strongly to playbacks of coordinated duets than to uncoordinated duets, and also to playbacks of uncoordinated duets than to nonoverlapping male and female solo songs. Coordinated duets (degree of phrase overlap) provoked the weakest response across conspecific stimuli, whereas the responses to uncoordinated duets and nonoverlapped solos were similar. However, partners produced more highly coordinated duets (degree of phrase overlap) in response to coordinated duets (association of phrase rhythms), when compared to all other stimuli. These results suggest that territorial pairs not only perceive but also alter their degree of temporal coordination of duets during territorial interactions. In addition, partners seem to behave cautiously and with more coordinated duets when responding to paired intruders that produce coordinated duets. Our results partially support the coalition quality hypothesis, suggesting that duet coordination may indicate the ability of partners to cooperatively engage in aggressive interactions. • Rufous horneros were exposed to playbacks of duets varying in temporal coordination. • Coordinated duets provoked the weakest response from birds. • However, partners increased duet coordination in response to coordinated duets. • Results suggest that highly coordinated duets may be intimidating to individual birds. [ABSTRACT FROM AUTHOR]

Among the five loon species (Gaviidae), Red-throated Loon (Gavia stellata) is the oldest lineage and is the most divergent in morphology and vocalizations. We substantially expand earlier description of calls for a nesting pair and non-breeding birds on Haida Gwaii, British Columbia, Canada. Three major calls used by the nesting pair (Quack, Wail, Plesiosaur) were all low frequency (700-3000 Hz) with multiple harmonics, calls that were also used by non-breeding birds without territories that overnight on freshwater lakes. Call duetting in the Wail and Plesiosaur, as well as sexually dimorphic frequencies and structure within the duets, typically occur in territorial display or pair interactions. The nesting pair used several calls audible only at short distances (Coo, Extended Coo, Staccato, Soft Raack) that were low frequency (200-1200 Hz), graded in behavioural intensity and that resulted in chick responses, including feeding or return to nest. A high amplitude Loud Raack was used by the female and is associated with flight incentives for pre-fledged chicks. Vocalizations of chicks, usually feeding solicitations to the adults, develop from simple chirps in the first week following hatch to more complex calls resembling the Wail and the Plesiosaur calls just prior to fledging. Although the majority of our acoustical descriptions are limited to a single nesting pair where sexes could be differentiated, these represent the first quantification of sound frequency, harmonic structure, and duration, most often associated with context-specific responses, and are suggestive of syntactical content to the vocal repertoire of this basal taxon. [ABSTRACT FROM AUTHOR]

Duets in breeding pairs may reflect a situation of conflict, whereby an individual answers its partner's song as a form of unilateral acoustic mate guarding or, alternatively, it may reflect cooperation, when individuals share in territory defense or safeguard the partnership. The degree of coordination between the sexes when responding to solo versus paired intruders may elucidate the function of songs in duets. We examined this issue in a study with rufous horneros (Furnarius rufus), a duetting, socially monogamous Neotropical species with low levels of extrapair paternity. We exposed social pairs during the nonbreeding season to playbacks of duets, male solos, female solos, and control heterospecific songs. Partners approached all conspecific stimuli together and responded by singing quickly, at higher rates and by coordinating ~80% of their songs into duets. For both sexes, most response variables (seven of nine) did not vary across conspecific treatments. These results suggest that partners duet and coordinate behaviors to cooperatively defend common territories. However, females spent more time in territorial vigilance, and partners were highly coordinated (correlated responses) in response to duets and female solos in comparison with male solos. This indicates that female intrusions (paired or solo) might be more threatening than male intrusions in the nonbreeding season, especially for territorial females, and that females are less cooperative with their partners in territory defense against male intruders. [ABSTRACT FROM AUTHOR]

Chrysoperla duellii sp. nov. is discovered, associated with coniferous vegetation, in the Kyrgyz Republic in central Asia, co-occurring with two other cryptic species of the Chrysoperla carnea-group. It is distinguished by its courtship duetting song, which exhibits a uniquely complex multi-volleyed temporal and tonal structure but is nevertheless noticeably convergent on the species-specific song of another conifer-associated member of the carnea-group, C. downesi (Smith), from North America. The song of C. duellii also shows some superficial similarity to those of European/north African C. mediterranea (Hölzel) and southern Californian C. calocedrii Henry et al., both of which, like C. duellii, prefer conifers and exhibit dark-green adult body pigmentation. The new species is herein formally described as Chrysoperla duellii Henry, Taylor and Johnson and is shown to be diagnosable by song and morphology from all other known members of the Chrysoperla carnea-group. Results of restriction site-associated DNA sequencing (RADseq) of C. duellii and five other carnea-group species strongly reject the hypothesis that similar songs and dark-green body colour among the four conifer-associated species are due to common ancestry, instead supporting independent, parallel acquisition of such features. [ABSTRACT FROM AUTHOR]

• Avian song ontogeny is an important model system for language learning. • Most past work has focused on song learning in species where only males sing. • We review literature and propose future studies on song learning in duetting species. • Duetting species could provide an important model for understanding vocal learning. Avian song learning has a rich history of study and has become the preeminent system for understanding the ontogeny of vocal communication in animals. Song learning in birds has many parallels with human language learning, ranging from the neural mechanisms involved to the importance of social factors in shaping signal acquisition. While much has been learned about the process of song learning, virtually all of the research done to date has focused on temperate species, where often only one sex (the male) sings. Duetting species, in which both males and females learn to sing and learn to combine their songs into temporally coordinated joint displays, could provide many insights into the processes by which vocal learning takes place. Here we highlight three key features of song learning—neuroendocrine control mechanisms, timing and life history stages of song acquisition, and the role of social factors in song selection and use—that have been elucidated from species where only males sing, and compare these with duetting species. We summarize what is known about song learning in duetting species and then provide several suggestions for fruitful directions for future research. We suggest that focusing research efforts on duetting species could significantly advance our understanding of vocal learning in birds and further cement the importance of avian species as models for understanding human conversations and the processes of vocal learning more broadly. [ABSTRACT FROM AUTHOR]

Collective signalling occurs in diverse animal groups. A particularly well-studied form of this sophisticated communication behaviour is vocal duetting in birds, in which members of a mated pair coordinate their songs on short temporal scales. Many hypotheses have been proposed to explain the function of bird duets, but the experimental evidence for them is still somewhat conflicting. Studies on songbirds often provide support for the joint resource defence or mate-guarding hypotheses. We investigated these hypotheses for a nesting cuckoo, the white-browed coucal, Centropus superciliosus , by presenting territorial pairs with four types of playback treatment: male–female duets, female solos, male solos, and a heterospecific control. The observed birds reacted aggressively to the conspecific playback by approaching the playback loudspeaker and singing. Pairs responded with duets more often to duet playbacks than to playbacks of female and male solo song. Also, neither sex treated simulated unmated intruders (solo playback) as more threatening than mated intruders (duet playback). Taken together, these findings argue against the mate-guarding hypothesis and instead suggest that duetting in white-browed coucals functions primarily in joint territory defence. In almost all cases, males were the first sex to sing in response to playbacks and, overall, they sang more than females. This suggests that males take a primary role in territorial defence. However, females also responded strongly, especially to the simulation of mated or unmated female intruders, hinting at a sex-specific division of labour in territorial defence. Highlights • The function of collective signalling, such as vocal duetting, is often unclear. • We used playback and radiotelemetry to study duet function in white-browed coucals. • Birds responded strongly to simulated conspecific intruders. • Subjects sang many more duets in response to simulated pairs than solo intruders. • Duet function appears to be mainly linked to cooperative territorial defence. [ABSTRACT FROM AUTHOR]

In diverse animal taxa, breeding partners coordinate their vocalizations to produce vocal duets. One seldom-studied hypothesis for duets is the paternity guarding hypothesis, which states that male animals create duets to advertise their partner's mated status and minimize extrapair mating attempts between their partner and other males. We experimentally tested the paternity guarding hypothesis in rufous-and-white wrens, Thryophilus rufalbus , a neotropical duetting songbird. We designed a two-part playback experiment: males first experienced a simulated territorial intrusion by a rival male, and were then given opportunities to answer their female breeding partner's songs to create duets. We repeated this experiment during the female's fertile and nonfertile breeding stages. In support of predictions of the paternity guarding hypothesis, male wrens created more duets with their partner's songs during the fertile period compared to the nonfertile period. Additionally, male wrens appeared to physically guard their mates with greater intensity during the fertile period but did not increase their overall song rates, demonstrating that increased duetting rates during the fertile period were a result of a change in male duetting behaviour, rather than a change in song rate. Our study is among the first to experimentally test the paternity guarding hypothesis for duet function, and suggests that male rufous-and-white wrens use both vocal and physical behaviours to guard their paternity. Highlights • Socially monogamous animals may use vocal duets as a paternity guarding strategy. • We used playback to study duets and paternity guarding in a tropical songbird. • Males created more duets with their breeding partners when they were fertile. • Males also appeared to physically guard their mates during the fertile period. • Therefore, these tropical birds use vocal and physical behaviours to guard their mates. [ABSTRACT FROM AUTHOR]

Madagascar is a well-known hotspot of biodiversity. However, many Orthoptera, and especially the Tettigonioidea, belong to little-studied groups. Here we describe a new genus and species of bush-cricket reared from fieldcollected eggs. Paraplangia sinespeculo gen. nov., sp. nov. belongs to Phaneropterinae and shares diagnostic characteristics with members of the tribe Amblycoryphini and its African subtribe Plangiina stat. nov. Paraplangia, which has a chromosome number of 31 X0, differs from other African members of the tribe and subtribe such as Eurycorypha and Plangia, which both have 29 X0. In addition to morphology, we describe the male calling song, female acoustic response, and mating behavior. As calling song, the male produces two series of short syllables. At the end of the second series the female responds with signals of similar duration and spectral composition as the male sounds (peak about 8-9 kHz). To make future identification easier, a key to all genera of Phaneropterinae found in Madagascar is presented. [ABSTRACT FROM AUTHOR]

Chrysoperla shahrudensis sp. nov. is discovered in northern Iran, co-occurring with at least five other cryptic species of the Chrysoperla carnea-group. It is distinguished by the volley period and tonality of its courtship duetting song. Another Asian species from alpine meadows of northern Kyrgyzstan, previously C. ‘adamsi-K’ but here named Chrysoperla bolti sp. nov., has a song distinct from but convergent with both C. shahrudensis and North American Chrysoperla adamsi. Coordinated duets can be established in the laboratory between individuals of C. shahrudensis and recorded songs of either C. bolti or C. adamsi. Such functional song equivalence in distinct allopatric species suggests that repeated episodes of parallel speciation can drive the origin of cryptic species diversity in lacewings. Morphology, life history, and ecology of larvae and adults of C. shahrudensis and C. bolti are then formally described. Adding C. shahrudensis to a large mitochondrial DNA data set for ≈ 21 species shows it to be similar to neither C. adamsi nor C. bolti, further supporting independent, convergent evolution of song rather than song similarity due to relationship. Although C. bolti and C. shahrudensis are both from Asia and share some basic temporal song features, the two taxa are distinct, allopatric biological species. www.zoobank.org/urn:lsid:zoobank.org:pub:D9B7BDC9-6C09-468B-A6B-D378628EC557 [ABSTRACT FROM AUTHOR]

Research on neighbor-stranger discrimination theory has revealed the significance of social context and biological traits affecting the mechanisms that drive social discrimination, such as the dear enemy or nasty neighbor effects (strangers or neighbors more threatening, respectively). Nevertheless, the effects of territory size and human activity on neighbor-stranger experiments have yet to be explored. By examining behavioral responses to spontaneous duets of neighbors and playbacks of strangers' duets, we tested whether rufous horneros (Furnarius rufus) in smaller territories show heightened aggression, responding more strongly to strangers and less to neighbors than those in larger territories. This could be expected because birds in larger territories might struggle to differentiate competitors due to limited interactions, hindering familiarity with neighbors. Meanwhile, birds in smaller territories are likely to treat neighbors as dear enemies due to the need to minimize territorial costs caused by presumed frequent intrusions or to protect limited resources. Contrary to predictions, rufous horneros responded more strongly to strangers than neighbors, regardless of owner territory sizes. This suggests that the presumed higher intruder frequency in smaller territories does not necessarily lead to adjusted dear enemy relationships. Yet, small territory holders exhibited heightened vocal responses to duets of unfamiliar intruders, indicating a stronger 'dear enemy' effect compared to birds with larger territories. We also tested whether dear enemy relationships would be heightened during weekends. This is linked to the difficulty urban birds might face in distinguishing neighbors from strangers during high human activity days (i.e., on weekdays), due to factors like noise masking intruder acoustic cues and heightened vigilance. Territorial owners exhibited consistent dear enemy behavior towards neighbors, regardless of our proxy for human activity. This underscores their ability in identifying competitor identities within urban settings. • Urban horneros treat strangers more aggressively than neighbors (dear enemy effect). • The dear enemy effect is unaffected by territory size of the territorial owners. • The dear enemy effect holds regardless of a weekly cycle of human disturbance. [ABSTRACT FROM AUTHOR]

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

Many animal species, including insects, are capable of acoustic duetting, a complex social behavior in which males and females tightly control the rate and timing of their courtship song syllables relative to each other. The mechanisms underlying duetting remain largely unknown across model systems. Most studies of duetting focus exclusively on acoustic interactions, but the use of multisensory cues should aid in coordinating behavior between individuals. To test this hypothesis, we develop Drosophila virilis as a new model for studies of duetting. By combining sensory manipulations, quantitative behavioral assays, and statistical modeling, we show that virilis females combine precisely timed auditory and tactile cues to drive song production and duetting. Tactile cues delivered to the abdomen and genitalia play the larger role in females, as even headless females continue to coordinate song production with courting males. These data, therefore, reveal a novel, non-acoustic, mechanism for acoustic duetting. Finally, our results indicate that female-duetting circuits are not sexually differentiated, as males can also produce ‘female-like’ duets in a context-dependent manner.

Most Northern Hemisphere stoneflies have species-specific mating signals that are generally thought to constitute a barrier against interspecific mating. We tested this hypothesis in two species of the genus Zwicknia that have only very recently been recognised as distinct species, and that were found to occur together in a stream in Lower Saxony, Germany. Analyses of molecular markers COI and 28 S in combination with wing length (distinguishing males of both species) and mating signals revealed no instance of hybridisation among 23 studied specimens. In addition, eleven further males identified on the basis of morphology alone all produced the expected species-specific signal. Females and males of both species were presented with played back conspecific and heterospecific signals and duetting sequences, and responded only to conspecific stimuli. This lends support to the hypothesis that the intersexual communication system functions as an important pre-mating barrier against gene flow, although post-mating isolation cannot be excluded. Interspecific mating did occur when a mixed pair was confined together in a small container. Males of both species were found to call in response to played back duetting sequences with stereotypic latencies that are clearly longer than the latencies in male-female duets. We interpret this as an indication of eavesdropping behaviour coupled with attempts to take over the perceived duet. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 969-980. [ABSTRACT FROM AUTHOR]

Pairs of duetting birds can sing coordinated duets with such precision that they are often mistaken for a single individual, yet little is known about how this impressive temporal synchronization is achieved. We experimentally examined duet coordination in male happy wrens, held briefly in captivity, by playing song phrases from their partner at different distances and tempos. Males were more likely to respond to songs played nearby, but did not vary their amplitude to compensate for their partner's simulated distance. Males modified their song rate to match the manipulated female playback tempo, indicating that they listen and respond to each female utterance. Each happy wren has a sex-specific repertoire of about 40 different song phrases and pairs combine particular phrases according to pair-specific duet ‘codes’, creating a further challenge for coordinating duets. We found that most males produced the appropriate phrase to reply to the female playback song in the absence of any other potential cues, sometimes delivering the correct song phrase type within 0.5 s of the start of the very first female playback heard. These experiments demonstrate rapid decision making and vocal production, indicative of sophisticated underlying cognitive processing, and provide a novel experimental technique to investigate the mechanisms controlling vocal duets. [ABSTRACT FROM AUTHOR]

Snapping Turtles (Chelydra serpentina) prey on and injure Trumpeter Swan (Cygnus buccinator) cygnets. Adult Trumpeter Swans stamp on and attack turtles, and this sometimes saves the lives of cygnets. Stamping behaviour, duetting, clamouring, and mobbing are directed at predators. The stamping behaviour may be derived from the water treading display. During the Pleistocene ice sheet maxima, all Trumpeter Swans east of the Rockies nested within the range of the Snapping Turtle. Snapping Turtle prédation may have selected for the stamping behaviour. [ABSTRACT FROM AUTHOR]

Avian vocal duets are joint displays where paired birds produce temporally and structurally coordinated vocalisations. Duets show great variety in form that can reflect different functions, such as mate guarding, mutual recognition, pair bond maintenance or territory defence. By describing the structure of duets and singing behaviour, we can investigate whether these signals are based on cooperation or conflict and which functions they might have. Here we describe the singing behaviour and song repertoire of the Crimson-breasted Shrike in the Kalahari Desert, and assess four main hypotheses proposed for the function of duets. We found that Crimson-breasted Shrikes have a sex-specific repertoire, and the individuality of males, females and pairs is expressed acoustically. Differences in vocal strategies between the sexes indicate male mate guarding as one possible function. Temporal coordination is high and duetters follow strict codes, suggesting that duetting could be a cooperative endeavour in this species. The observed duetting behaviour is also consistent with the predictions for mutual recognition because each bird has its individual vocal characteristics that are consistent over time. Our results provide no support for the hypothesis that duets serve pair bond maintenance in this species as no partner-directed adjustment of temporal coordination took place. [ABSTRACT FROM AUTHOR]

Female behavior involved in the expression of mate preferences often entails the production of cues that males may use to adjust their efforts and tactics, thus generating interactive back–and–forth reproductive dynamics. We investigated whether female duetting behavior in Enchenopa treehoppers (Hemiptera: Membracidae) offers cues about how attractive females find signaling males and whether males modify their signaling behavior accordingly. Playback experiments with females of 4 Enchenopa species showed that stimulus attractiveness influenced the likelihood, duration, and dominant frequency of female signals. A separate playback experiment with males of 1 of the 4 species showed that they modified their behavior according to the features of female duetting signals: Males were more likely to signal and to produce more signals when presented with longer female signals of intermediate frequency. Because the female signals evoking the greatest male response did not correspond to conspecific signals, we conclude that males have been selected to attend to cues indicating likely female receptivity but not species identity. We discuss the consequences of these findings for assortative mating and reproductive isolation. [ABSTRACT FROM PUBLISHER]

Vocal duetting occurs in diverse animal groups. Members of a mated pair may duet to communicate with each other or with other individuals. Many hypotheses have been proposed to explain the function of duets, and studies often provide support for the joint resource defence or mate-guarding hypotheses. We evaluated these hypotheses for the happy wren, Pheugopedius felix, using a two-speaker playback experiment. We observed the responses of happy wren pairs to playback of solo male, solo female and male/female duet songs, and compared these with heterospecific song control trials. Happy wrens responded aggressively to conspecific song playback by moving closer to their mate, approaching the playback speakers and increasing singing rates. Both sexes increased singing and especially duetting rates in response to conspecific playback. There were no differences in which sex initiated or terminated duets nor did birds vary the proportion of their partner’s songs answered across conspecific treatments. Furthermore, neither sex treated unmated intruders (solo playback) as more threatening than mated intruders (duet playback). Together, these results argue against the mate-guarding hypothesis and instead indicate that duetting in happy wrens functions primarily in cooperative territory defence. Overall, males sang more than females, moved closer to the speakers and were more likely to answer their partner’s songs, suggesting that males take a primary role in territorial defence. However, females also responded strongly, especially when female intruders were present (duet or female solo playback), which suggests a sex-specific division of labour in their territorial defence. [ABSTRACT FROM AUTHOR]

Female song is much more prevalent in tropical than in temperate songbirds but, we know surprisingly little about the evolutionary origins of this striking latitudinal difference. Here I reconstruct the evolution of female song in the New World blackbird family (Icteridae) and compare historical changes in this trait to changes in several other life-history characters: social mating system, nesting pattern, and migratory behavior. Reconstructions using both parsimony and maximum likelihood methods show that female song has been lost repeatedly in this clade and that tropical ancestors with frequent female song almost invariably were monogamous, had dispersed nest sites, and were nonmigratory. Losses of female song were not consistently associated with changes in any single life-history characteristic across the family, but rather appear to have occurred for different reasons in different lineages, including the evolution of migration in the oriole genus (Icterus), the evolution of brood parasitism in the cowbirds (Molothrus), and the evolution of polygynous, colonial breeding in the oropendolas (Psarocolius, Gymnostinops) and caciques (Cacicus). These results support previous suggestions that the prevalence of female song in the tropics is largely explained by the life-history traits associated with tropical habitats. [ABSTRACT FROM PUBLISHER]

Abstract: Wrens of the genus Thryothorus comprise over a third of the species diversity in the family Troglodytidae. In addition to this species diversity, these wrens vary in a number of behavioral characteristics, in particular in the presence and structure of vocal duets, which makes them an interesting target for comparative evolutionary ecological and behavioral study. However, no phylogenetic hypothesis for this group—which would provide a sound basis for comparative analysis—is currently available. While previous molecular phylogenetic work established conclusively that the type of this genus, Thryothorus ludovicianus (Latham), was not part of a monophyletic group with other Thryothorus, the exact limits of the genus could not be established due to limited taxon sampling. Here, we present molecular data from all but four currently recognized species of Thryothorus. These data confirm that Thryothorus is paraphyletic, and that the type T. ludovicianus does not form a monophyletic group with any other member of the genus. Based on analyses of our data, we resurrect two previously recognized wren genera, Pheugopedius and Thryophilus, and erect a new genus—Cantorchilus—to house the remaining ex-Thryothorus species. Our hypothesis of relationships will provide a firm basis for future behavioral and morphological analyses of these species. [Copyright &y& Elsevier]

The relationship between the form and function of coordinated acoustic signals is poorly understood. The coordination of signals by male and female birds to produce duets could be a cooperative display or a consequence of conflict between the sexes. Australian magpie-larks (Grallina cyanoleuca) produce antiphonal duets that function primarily in cooperative territorial defence. I investigate the form of these duets to determine the individual singing strategies of males and females and relate these to what is known about duet function, discussing the implications of variation in the form of duetting among other species. Male and female magpie-larks both initiate duets, and both sexes also frequently sing alone. Though males tend to initiate more vocalisations than females, both are equally likely to join their partners' songs to form duets. Consistent with the cooperative function of their duets, the similarity between the sexes in propensity to duet is maintained when duetting is less likely during the female fertile period, as well as when it is more likely during simulated intrusion. Male and female repertoires are similar, and partners combine their song types non-randomly and with considerable temporal precision to form duets. The interplay between partners that determines duet length and precision is consistent with both sexes benefitting from singing together. The role of duet repertoires and temporal precision in intra- and inter-pair interactions is poorly understood in magpie-larks and other duetting species, and requires further investigation. [ABSTRACT FROM AUTHOR]

We studied duet song and vocal duetting behavior in an endemic Taiwanese passerine, Steere’s liocichla ( Liocichla steerii). We found that the leading male song in duets was highly individualistic. Also, we found duetting behavior varied significantly across different habitat types. Females were more likely to answer male songs in densely vegetated, steep forest habitat compared to open agricultural habitat. These findings provide quantitative evidence for vocal individuality for a duet song and provide tentative support for the idea that females are duetting to reveal their location to their mates. [ABSTRACT FROM AUTHOR]

Duets are precisely coordinated acoustic displays, usually involving members of a mated pair. Studies investigating avian duet function often employ a single speaker playback system to compare response of focal pairs to simulated territorial intrusion by duetting and solo birds. It has recently been suggested that a 'stereo duet playback', in which male and female duet components are separated and broadcast through two different speakers, would provide a more realistic duet stimulus. We conduct the first comparison of a traditional single speaker versus a new stereo duet playback design and provide evidence that Australian magpie-larks, Grallina cyanoleuca, make significantly more flights towards duet playback presented in a more realistic stereo context. Male and female magpie-lark pairs did not split up and attack one 'intruder' each when presented with a stereo duet playback. Instead they moved towards the same speaker together as a united pair, showing a tendency to approach the speaker initiating the duet intrusion. Distance between the two speakers in a stereo duet design did not have a significant effect on the response variables measured. We conclude that magpie-larks can distinguish between use of a single speaker or stereo duet playback to broadcast a duet and suggest that cooperative defence against duetting intruders in magpie-larks is a result of joint territorial defence rather than intraspecific aggression against same-sex intruders. [ABSTRACT FROM AUTHOR]

We studied the duet of the Caribbean-slope subspecies of the Plain Wren (Thryothorus modestus zeledoni) in Costa Rica. It is one of the most complex duets to have been described. The duet proper consists of rapid, highly coordinated alternation of "A-phrases" from the female and "B-phrases" from the male. While the female initiates this section with her A-phrase, this cyclical part of the duet is almost invariably preceded by an introductory "I-phrase" from the male, so that it is the male that initiates the performance. Each male has a repertoire of I- and B-phrases, and each female has a repertoire of A-phrases. These are specifically associated with each other to form a repertoire of duet types. We hypothesize that the pattern of song organization in this species facilitates more coordinated and precise duetting. The presence of the three components means that a full duet requires the cooperation of both members of the pair, strongly suggesting that it represents a mutually beneficial signal. [ABSTRACT FROM AUTHOR]

The structure of male songs and the timing of female replies with respect to the male songs are described for four species of the palaearctic bushcricket genus Barbitistes (B. constrictus, B. ocskayi, B. serricauda, B. yersini). In a male song, 3 to 16 syllables form a chirp followed by a “trigger syllable” after a longer interval. The trigger syllable releases a female reply with a latency of 30 to 50 ms in all four species. In B. serricauda songs, there is no clearly separated trigger syllable. Instead, the first syllable of a chirp functions as a trigger syllable. Some B. serricauda males may produce a short female-type syllable just at the moment, when a female would reply. The possible function of such a syllable is acoustical mimicry. When comparing at least two song parameters, each species occupies a specific combination of values. According to the overlap of parameters a close phylogenetic relationship between B. constrictus and B. serricauda and between B. ocskayi and B. yersini is assumed. This interpretation is compared with a hypothesis based on morphological investigations. [ABSTRACT FROM AUTHOR]

• Duetting can be a cooperative form of calling or singing between female and male birds. • Female common cuckoos used bubbling calls for duetting with male conspecifics. • Male cuckoos used a 3-note variant of their typical 2-note "cu-coo" calls for duetting. • The male cuckoos' 3-note call had higher frequencies and faster speeds. • Cuckoos used duets for intersexual communication in the absence of formal pair bonding. Duetting is a coordinated form of acoustic communication with participants uttering calls or songs simultaneously and/or sequentially. Duetting is often observed in pair-bonded species, with mated females and males both contributing to the communal vocal output. We observed duetting between the sexes in the common cuckoo (Cuculus canorus), an obligate brood parasitic species without known pair formation. Specifically, female cuckoos use their sex-specific bubbling calls for duetting, while male cuckoos use a 3-note variant ("cu-cu-coo") of their typical and well-known 2-note ("cu-coo") territorial advertisement calls. The maximum frequency of the elements in the male's 3-note variants was higher relative to the 2-note calls, while durations of both the elements and the inter-element intervals were shorter. The vast majority (95 %) of the 3-note calling was detected together with the bubbling call, implying an intersexual duetting function, with the female calls preceding these male calls in 67 % of cases. The two call types in duetting followed each other rapidly (mean response time of females was 1.30 ± 0.71 SD s, and 0.76 ± 0.53 SD s in males), and typically overlapped with each other (95 %). Frequently (90 %), the male call was repeated 2–3 times, whereas the female call was repeated less frequently (9%). Our results are consistent with a main function of duetting in intersexual communication and coordination between female and male cuckoos. [ABSTRACT FROM AUTHOR]

Mate finding in the phaneropterid bushcricket Ancistrura nigrovittata is achieved by a duet, where the female replies with a short sound to the male song. In experiments with artificial song models we analysed the parameters necessary for eliciting a female response. A verse of the male song consists of a group of 5-9 syllabes which after an interval of about 400 ms is followed by a final syllable. The female response was shown to depend on two processes: (i) recognition of the syllable group as belonging to a conspecific male and (ii) perception of the final syllable as a trigger. Critical parameters for the recognition process are the duration of syllables and syllable pauses, as well as the number of syllables in a group. However, even with an optimal syllable group, the response probability still depends on the interval between the syllable group and the final syllable. The female only responds when the final syllable of the male song occurs within a 250 ms long time window begining approximately 250 ms after the end of the male's syllable group. Her reply consists of a single tick, which follows the male's final syllable with a latency of only 25 ms. [ABSTRACT FROM AUTHOR]