Duet structure provides information about pair identity in the red-crowned crane (Grus japonensis)

We studied the acoustic features of the endangered red-crowned crane (Grus japonensis), and, specifically, whether or not the duets carry information about a mating pair identity. The population of this species in the wild is only approximately 2,000 individuals. In 2003–2006, we recorded 343 duets from eight captive and two wild pairs. All of the duets contained an introduction, an unordered alternation of pair mate calls, followed by the main part, representing the regular sequence of syllables, containing 1–2 male and 1–4 female calls per syllable. We subdivided the syllables into five types, by the number of male and female calls per syllable, and analyzed the occurrence of the different syllable types in the duets of the ten pairs. The analysis showed the sustainable pair-specific use of particular syllable types through the years. The discriminant analysis standard procedure, based on seven frequency and temporal parameters of male and female calls, showed 97.7% correct assignment to the pair, which is significantly higher than random values. The high pair specificity of the duet acoustic structures provides the basis for call-based censuses. This would enable the monitoring of the red-crowned crane mating pairs in their natural habitat.     

Examination of pair-duet stability to promote long-term monitoring of the endangered red-crowned crane (<Emphasis Type="Italic">Grus japonensis</Emphasis>)

Acoustic-based monitoring has proved useful for many birds and seems promising for the endangered red-crowned crane. However, its validity in crane conservation is unclear in the absence of knowledge concerning the long-term stability of pair-specific duets. The red-crowned crane is monogamous and long-lived, with stable pair bonding both within and between years. Pair mates perform loud duets—a succession of male and female calls emitted with definite temporal coordination. We examined the stability of duets for five captive pairs over five years (2003–2007) on the basis of analysis of the syllables within the duets. MANOVA showed that the effect of pair identity on syllable characteristics was always stronger than the effect of the year of recording. Cross-validation of duets from 2004, 2005, 2006, and 2007 with discriminant analysis (DFA) functions derived, respectively, from pooled samples from 2003, 2003–2004, 2003–2005, and 2003–2006 resulted in comparably high percentages of correct classification into pairs. The pairs could be reliably identified by their duets and pair-specific differences in syllable characteristics were stable with time. These data suggest acoustic monitoring is a feasible alternative to more invasive methods of identification.     

Angry Birds Need Not Apply: A Perspective on the Flexible form and Multifunctionality of Avian Vocal Duets

Research into avian vocal duets has revealed much about the social interactions of mated pairs, including how communication signals mediate important components of fitness such as reproductive success and resource‐holding ability. Excellent reviews have been written on avian duets, but none have quantified the prevalence of different duet features and functions, or tested for potential links between structure and function. Here we have compiled a thorough list of studies at the species level and investigated whether there are trends in duet form, trends in duet function and matches between form and function. We have also provided recommendations for reporting of duet structure to help standardize future data collection and facilitate comparative analyses. We found that duet vocalizations are typically tightly coordinated (69% of 33 species), initiated by both partners (80% of 35 species), and have sex‐specific contributions (73% of 48 species). Duets vary substantially in structure both across and within species, and this flexibility in duet form may contribute to their use in multiple contexts. Among the well‐studied species (functions well supported by experimental evidence and studied post‐1983), duets are usually multifunctional, with functions including joint resource defence, signalling commitment, maintaining contact, ensuring reproductive synchrony and mate‐guarding. Levels of support for different hypotheses have changed over time as theory within the field developed, but overall, the best‐supported function of duets across avian species (81% of 26 species) has been joint resource defence. In all but one of these 26 species, duets are sometimes cooperative (meaning that duet participation benefits both duetting partners), and they often produce multiple benefits. We found associations between form and function, in that duets directed to non‐pair individuals have higher amplitude and are more likely to have sex‐specific notes than duets directed within the pair. We see the field moving away from labelling duets as representing ‘cooperation’ or ‘conflict’ and moving towards a general multifunctionality framework within which researchers test multiple hypotheses for duet function under the assumption that both duet form and function can vary moment to moment and that such flexibility can provide multiple benefits.     

Geographical Variation in Duet Songs of Sulawesi Tarsiers: Evidence for New Cryptic Species in South and Southeast Sulawesi

Geographic populations of Sulawesi tarsiers differ conspicuously in the acoustic structure of the loud duet calls produced by mated pairs. There is evidence that the differences in call features relate to species differentiation. Duet calls can thus be used as a tool to identify cryptic species and for their monitoring in the field. We recorded duets from various geographically isolated populations of Tarsius tarsier in south and southeast Sulawesi to survey the species identity of the tarsiers in these regions. We compared their calls with the duet calls of the Manado tarsier (= Tarsius spectrum), Tarsius dianae, and the Togian Island tarsier. In addition, we recorded and analyzed the duet call of the tarsier from Peleng Island, Tarsius pelengensis. Qualitative characteristics of duet songs of both sexes, analysis of frequency and temporal parameters, and multivariate statistics show 4 distinct vocal forms that predict the existence of 4 new species. These are found on Selayar Island, on the south mainland (Bantimurung), on the southeast mainland (Puwato), and on the Islands of Kabaena and Buton. Our analysis of the call of the Peleng tarsier revealed striking similarities with the call of Tarsius dianae. Further morphological analyses are needed to support the proposed new species in south and southeast Sulawesi and to clarify the taxonomic affinity between the central Sulawesi tarsier species Tarsius pelengensis and T. dianae.     

Context, Structural Variability and Distinctiveness of California Towhee (Pipilo crissalis) Vocal Duets

Avian vocal duets occur when paired birds produce temporally and structurally coordinated vocalizations. Duets are given by members of many species from taxonomically distinct lineages and show great variety in form that often reflects function. By describing the structure of vocal duets we can learn about the diversity of communication signals present in nature and also gain insight into the evolution and operation of those signals. This study quantified the usage patterns and acoustic structure of California towhee duet vocalizations, and tested the distinctiveness of duets among different pairs. California towhee duets consist of a 'squeal' vocalization that is highly unlike the species-typical call note or male advertizement song. California towhees duet an average of three times per hour during the breeding season, and all duets are accompanied by an approach response that brings duetting partners into close spatial proximity. Males and females produce duet contributions with the same syllabic structure. Individual birds produce highly variable squeal vocalizations that are distinctive enough to signal identity. California towhee duet characteristics indicate that the squeal vocalization has evolved separately from other vocal traits in this species and was promoted by natural selection as a duet-specific vocalization. Duet usage patterns and structure suggest that these communication signals function in a cooperative context.     

Breeding season length predicts duet coordination and consistency in Neotropical wrens (Troglodytidae)

Many animals produce coordinated signals, but few are more striking than the elaborate male–female vocal duets produced by some tropical songbirds. Yet, little is known about the factors driving the extreme levels of vocal coordination between mated pairs in these taxa. We examined evolutionary patterns of duet coordination and their potential evolutionary drivers in Neotropical wrens (Troglodytidae), a songbird family well known for highly coordinated duets. Across 23 wren species, we show that the degree of coordination and precision with which pairs combine their songs into duets varies by species. This includes some species that alternate their song phrases with exceptional coordination to produce rapidly alternating duets that are highly consistent across renditions. These highly coordinated, consistent duets evolved independently in multiple wren species. Duet coordination and consistency are greatest in species with especially long breeding seasons, but neither duet coordination nor consistency are correlated with clutch size, conspecific abundance or vegetation density. These results suggest that tightly coordinated duets play an important role in mediating breeding behaviour, possibly by signalling commitment or coalition of the pair to mates and other conspecifics.     

The Responses of Duetting Antbirds to Stereo Duet Playback Provide Support for the Joint Territory Defence Hypothesis

In multiple animal taxa, including many birds and primates, members of mated pairs produce coordinated acoustic displays known as duets. By observing the behaviour of territorial animals as they respond to playback‐simulated duets of rivals, we can gain insight into the behavioural significance of vocal duets. Playback experiments, however, have been conducted across a very narrow range of duetting animals. Furthermore, many studies have been conducted with single‐speaker playback, whereas stereo‐speaker playback offers more spatially realistic simulation of duets. Moreover, by evaluating the reactions of animals to separate loudspeakers broadcasting male and female duet contributions, we can study the interactions of both males and females with same‐sex vs. opposite‐sex rivals. We used a paired experimental design to broadcast duet stimuli through a single‐speaker and a stereo‐speaker apparatus to 30 pairs of duetting barred antshrikes Thamnophilus doliatus in Costa Rica. Our goals were (1) to evaluate whether territorial antbirds respond more aggressively to male vs. female duet components and (2) to assess aggressive responses of antbirds towards single‐speaker vs. stereo‐speaker playback. Neither males nor females differentiated between the loudspeaker simulating the male vs. female duet contribution during stereo‐speaker playback trials. Barred antshrikes displayed significantly stronger responses to stereo‐speaker playback compared with single‐speaker playback. Males displayed stronger playback responses than females with closer, quicker and more vocal responses. These results provide evidence for a joint resource defence function of antbird duets given that pairs responded together with equivalent intensity to male and female simulated intruders. This is the first study to show that although duetting is an aggressive territorial signal, birds do not necessarily respond to sex‐specific components of duets. Our results support the idea that spatially realistic stereo presentation of duet stimuli is critical for experimental duet research.     

Duetting in the Titi monkey Callicebus cupreus: structure,pair specificity and development of duets

Duets from a total of 6 female and 6 male titi monkeys (Callicebus cupreus) were analysed in order to provide an in-depth analysis of the duet structure, to investigate whether duets are pair specific and to examine whether duets of newly formed pairs differ from those of established pairs. Callicebus duets are composed of alternately uttered male and female contributions. Duets were pair specific as a result of a summation of individual attributes of the two mates rather than due to unidirectional or reciprocal song adaptation by mates. The two examined newly formed pairs produced species-typical duets from the first day on, but their duets showed greater variability in sequence durations than those of established pairs.     

Duets in Yellow-Naped Amazons: Variation in Syntax, Note Composition and Phonology at Different Levels of Social Organization

Complex vocal signals composed of multiple notes are used by many species. Such signals may vary in a number of features such as the rules that govern note order and timing (syntax), the relative number and types of different notes (note composition), and the acoustic structure of notes (phonology). Previous research examining male song in songbirds typically has shown greater conservation of syntax than phonology. Here we investigated whether these patterns of variation are also found in the duets of parrots. We examined geographic variation in the pair duets of yellow-naped amazons, Amazona auropalliata , at five sites within one vocal dialect. We also examined variation at several levels of social organization, including within pairs, among pairs and among sites, to assess where variability was greatest. Variation was highest at the within-pair level, although variation was also present at all other levels and for all of the duet factors. We hypothesize that variation at the among-site level allows duets to indicate site membership, while variation at the within-pair level allows pairs to change their duet to match their current social or physical environment. Syntax and phonology are also more conserved than note composition for all levels of social organization. This pattern may result because note composition is less important in duet function than syntax or phonology, or because development of syntax and phonology is more heavily influenced by genetic templates.     

The Mechanics of Duetting in a New Zealand Endemic, the Kokako (Callaeas cinerea wilsoni): Song at a Snail's Pace

New Zealand's endemic, duetting kokako (Callaeas cinerea wilsoni) produce one of the longest known bird songs (ca 30 s) and duets that differ strikingly from those of most duetters in their unusual length and non‐repetitive structure, long pauses between component phrases, and the great flexibility in sex roles. Here we present a structural analysis of the vocalizations of 17 kokako pairs collected during natural song bouts and in response to conspecific playback, to gain insight into the functional role of this extraordinary vocal behavior. Males tend to sing a greater proportion of the duet than females. Like many duetting species, kokako have a moderately sized repertoire of phrases (mean repertoire size =18) and pair members tend to sing antiphonally rather than in unison. Sharing of phrase types is high among neighboring kokako ( = 86%) and repertoires are not sex specific, as is typical of some but not all duetting species. Timing characteristics, broad sharing of phrase types, and countersinging behavior strongly suggest that kokako duets play an important role in territory defense. Additionally, differences in pairs’ sex role and phrase sequence flexibility suggest that these aspects of duet performance may reflect pair‐bond length or commitment, and require a time investment by pair members.     

VOCAL AND OTHER BEHAVIOUR OF KENYAN BLACK-COLLARED BARBETS LYBIUS TORQUATUS

We describe 12 visual and six acoustical displays of Black-collared Barbets, all associated with interactions of these sexually monomorphic barbets in greeting ceremonies and in antiphonal duets. Certain of the displays, e. g., bill directing, smooth posture and chatter calls largely are associated with multiple-barbet interactions and greeting ceremonies involving more than two barbets, and seem to represent purely agonistic displays. Other displays, most notably the bobbing and floating flight displays, and the tyaw call, are associated with preduet greeting ceremonies involving the presumed pair. In every case duets were performed by a presumed pair, following a greeting ceremony and visual displays accompany the duetting, which usually becomes precisely synchronized after the initial few notes. Four to 17 notes of each of two types, a usually lower pitched, short and mainly double type A note that introduces most duets, and a higher pitched, usually single, clear type B note that often terminates the duet. Variation in the notes and in their tempos within duets suggests no clearly defined temporal indicators for achieving, maintaining, and concluding the duets. The A and B notes cannot yet be assigned to one or other sex and similarity in form and development of the notes, from notes of greeting ceremonies, suggests the possibility that under some circumstances a bird of one sex may be able to deliver notes of either type. The duets are delivered from singing posts within the group's (or pair's) territory and usually only one duet is uttered from a site before the birds shift to another singing post. The duetting is compared with that of other barbets and appears to be among the best synchronized and most precise in the family. Comparisons with non-barbet duetting species are difficult because of the special habits and ecology of the barbets and uncertainty as to the sexual rôle of the duetters.     

Description of the acoustical interaction and synchronization between duetters of the Large-footed Finch (Pezopetes capitalis)

Duets are highly coordinated acoustical displays produced by two individuals. Studying the structure of duet songs and its causes is essential to understand the ecological role and evolution of this form of communication. Our goals in this study were to describe the structure of the duet of the Large-footed Finch, the temporal synchronization of each individual, and to test the effect of provoked (playback) duets. We recorded birds at Cerro de la Muerte, Costa Rica and simulated territory intrusions using playback trials. The duet of this species consisted of overlapping notes between both members of a mated pair, which were emitted either randomly or periodically. Temporal synchronization was similar between both individuals in a mated pair. Both partners adjust the silent intervals between notes in response to the duration of its partner’s note. The high frequency of the second part of the duet of this species decreased with time and the second individual, in duetting this part, not only synchronized its notes temporally with the first individual, but also synchronized the high frequency. The high frequency of the first note the second individual sung was a bit lower than the previous note sung by the first individual. Finally, birds responding to provoked duets produced duets with higher frequency and higher rate of notes compared to unprovoked duets. Our results provide information on the temporal and frequency synchronization in duets of an endemic emberizid and provide new information about a less reported vocal behaviour in bird duets, the acoustic frequency coordination.     

Duet function in the yellow-naped amazon, Amazona auropalliata: evidence from playbacks of duets and solos

The question of why animals participate in duets is an intriguing one, as many such displays appear to be more costly to produce than individual signals. Mated pairs of yellow-naped amazons, Amazona auropalliata, give duets on their nesting territories. We investigated the function of those duets with a playback experiment. We tested two hypotheses for the function of those duets: the joint territory defense hypothesis and the mate-guarding hypothesis, by presenting territorial pairs with three types of playback treatments: duets, male solos, and female solos. The joint territory defense hypothesis suggests that individuals engage in duets because they appear more threatening than solos and are thus more effective for the establishment, maintenance and/or defense of territories. It predicts that pairs will be coordinated in their response (pair members approach speakers and vocalize together) and will either respond more strongly (more calls and/or more movement) to duet treatments than to solo treatments, or respond equally to all treatments. Alternatively, the mate-guarding hypothesis suggests that individuals participate in duets because they allow them to acoustically guard their mate, and predicts uncoordinated responses by pairs, with weak responses to duet treatments and stronger responses by individuals to solos produced by the same sex. Yellow-naped amazon pairs responded to all treatments in an equivalently aggressive and coordinated manner by rapidly approaching speakers and vocalizing more. These responses generally support the joint territory defense hypothesis and further suggest that all intruders are viewed as a threat by resident pairs.     

Repertoire sharing by the individual and the pair: Insights into duet function and development in the plain wren Thryothorus modestus

Although both repertoire sharing and individual variation have been studied widely in male solo song, few studies have investigated these aspects of song in a species that performs complex duets. This study examined song repertoires of both males and females of the plain wren (canebrake subspecies, Thryothorus modestus zeledoni ), which performs antiphonal duets, and tested for patterns of repertoire sharing at the level of the individual and of the pair. We suggest that both males and females of the plain wren develop their phrase repertoires by direct imitation from other individuals of their sex, but that males, who may exist for a period as 'floaters' after dispersal, learn their songs from a wider pool of tutors than do females. In contrast to considerable individual repertoire sharing, whole duet types were very rarely shared between pairs, despite the potential for this to occur. This suggests that duet types are developed within the pair without reference to other pairs and the implications of this for duet functions are discussed.     

Plain wrens Cantorchilus modestus zeledoni adjust their singing tempo based on self and partner's cues to perform precisely coordinated duets

Precise coordination appears to be an important signal in several duetting species. However, little attention has been directed to the proximate mechanisms that might drive this behavior. To perform highly coordinated duets, individuals can either have an intrinsic fixed singing tempo or modify their singing tempo based on cues in their own and their partner's songs. In this study I determined whether autogenous and/or heterogenous factors are associated with duet coordination in plain wrens Cantorchilus modestus zeledoni by analyzing recorded duets from 8 territorial pairs in the field. Previous research has determined that plain wrens perform highly coordinated antiphonal duets with almost no overlap. I found that to achieve such precise coordination individuals perform phrase‐by‐phrase modifications to the duration between two consecutive phrases (inter‐phrase interval) based on a) whether their song is answered, b) the phrase type used in the duet and c) the position of the inter‐phrase interval within the duet. Moreover, there are several sex differences in how individuals use these cues to modify their inter‐phrase intervals. Females produce longer inter‐phrase intervals when their mates do not answer a phrase, whereas males produce shorter inter‐phrase intervals when their mates do not answer. Females modify their inter‐phrase intervals based only on the phrase type their mates sing, whereas males modify their inter‐phrase intervals based on both the phrase that they sing and the phrase the females use to answer. Both males and females produce longer inter‐phrase intervals for longer phrase types sung by their partners, but males do so with more precision than do females. Finally both sexes increase their inter‐phrase intervals as the duet progresses. That precise coordination is achieved by a complex and dynamic process supports the idea that this behavior could signal pair bond strength.     

Song repertoire and duetting behaviour of the tropical boubou, Laniarius aethiopicus

Female song and the significance of duetting in birds remain puzzling, in part because of the limited number of species studied. We investigated duetting behaviour in the tropical boubou in West Africa. Birds produced a diverse song repertoire consisting of solos, duets and trios, with duets being the most conspicuous vocalization. We identified 12 distinct duet types in which tonal and broadband notes were combined by males and females in highly synchronized and temporally precise patterns. Molecular sexing and observations of colour-banded birds revealed that duets were initiated by both sexes, with strict sex-specific roles maintained within the duet. An equal number of duet types was initiated by males and females. Seven of 12 duets were terminated by the male. Male-initiated duets were also more common (89% of total) and were repeated more often, i.e. sung more frequently. Solo singing occurred when partners did not respond and was also used by unpaired birds. Trios were produced by subadult birds joining the duet of a resident pair. The wide variety of contexts in which duets were sung suggests that they serve several functions, including territorial defence and mutual mate guarding.     

Vocal negotiation over parental care? Acoustic communication at the nest predicts partners' incubation share

In species with biparental care, individuals adjust their workload to that of their partner to either compensate or match its investment. Communication within a pair might be crucial for achieving this adjustment. Zebra finches, Taeniopygia guttata, form life‐long monogamous pair bonds, in which partners are highly coordinated and both incubate the eggs. When relieving each other during incubation, partners perform a structured call duet at the nest. If this duet functions to coordinate incubation workload, disrupting the pair's usual nest‐relief pattern by delaying the male's return to the nest should affect the structure of the duet. Using domesticated birds breeding in a large aviary, we found that delaying the male's return induced shorter duets with higher call rates. In addition, we tracked the location of individuals with a transponder at the nest and the feeder, and showed that these accelerated duets were associated with an increased haste of the partners to take turns incubating and foraging. Females also spent less time incubating during their subsequent shift, and females' time off‐nest was best predicted by their mate's calling behaviour in the previous duet. Taken together, these results suggest that duets may function as ‘vocal negotiation’ over parental care.     

Duet Vocalizations among Different Populations of Sulawesi Tarsiers

A most conspicuous vocal behavior of Sulawesi tarsiers is the loud calls that males and females coordinate into duets. Differences in the acoustic structure of this display relate to specific differentiation in Tarsius spectrum and T. dianae. More recent studies on dueting behavior indicated the existence of a new species of tarsiers on the Togian Islands in Tomini Bay. I analyzed the duet calls of the Togian tarsier to assess the differences in acoustic structure of duet calls between this putative new species and T. spectrum or T. dianae. Discriminant function analysis revealed that Togian tarsiers, T. spectrum and T. dianae, are clearly separated by acoustic characteristics in songs. The degree of separation of the Togian tarsiers from the mainland species support them being a distinct species.     

Partners coordinate territorial defense against simulated intruders in a duetting ovenbird

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.     

MINUTES OF THE FORTY-SEVENTH ANNUAL GENERAL MEETING OF THE SOUTH AFRICAN ORNITHOLOGICAL SOCIETY HELD AT JOHANNESBURG AT 2.00 P.M. ON SATURDAY 19 JUNE 1976

Many duetting species are monomorphic and the suggestion has recently been made that duets may be female-led more often than has been supposed in the past. Observations were carried out on several marked individuals of two monomorphic duetting species, the Moho, Hypergerus atriceps, and Yellow-crowned Gonolek, Laniarius barbarus, in The Gambia. DNA analysis from blood samples revealed that in each case the male was the pair member that normally led the duet. It is suggested that duets of this sort may arise where it benefits a male to attract more than one female, but it is to the female's disadvantage that he should do so.