Song Sharing in Neighboring and Non-Neighboring Thrush Nightingales (Luscinia luscinia) and its Implications for Communication

In many passerines, males have repertoires of different songs of which some songs are often shared with other males. Sharing of song repertoires among males can provide insights into the context in which songs were acquired and on the role of song repertoires in inter- and intrasexual communication. Here we studied repertoire sharing in male territorial thrush nightingales ( Luscinia luscinia ). We compared male vocal repertoires of the basic song components, full songs, and the sequencing of songs in a bout. The results show that males differed significantly in the size of their song repertoires but not in the size of the repertoire of basic song components. Moreover, they shared almost all (80%) the repertoire of song components but only 30% of their song types. Neighboring males shared significantly more song types than did non-neighboring males but interestingly they did not share more basic song components than non-neighboring males. These results show that the repertoire of basic song components is under much less sexual selection than the size of song repertoires. Sharing of song repertoires among neighbors presumably results from repertoire conversion over time and from males returning to their territories in the following season. Repertoire sharing then can be an indicator of territory tenure and thus it can be important in repelling rivals and in female choice.     

Rufous‐capped Warblers Basileuterus rufifrons show seasonal,temporal and annual variation in song use

In the majority of songbird species, males have repertoires of multiple song types used for mate attraction and territory defence. The wood‐warblers (family Parulidae) are a diverse family of songbirds in which males of many migratory species use different song types or patterns of song delivery (known as ‘singing modes’) depending on context. The vocal behaviour of most tropical resident warblers remains undescribed, although these species differ ecologically and behaviourally from migratory species, and may therefore differ in their vocal behaviour. We test whether male Rufous‐capped Warblers Basileuterus rufifrons use distinct singing modes by examining song structure and context‐dependent variation in their songs. We recorded multiple song bouts from 50 male Warblers in a Costa Rican population over 3 years to describe seasonal, diel and annual variation in song structure and vocal behaviour. We found that Rufous‐capped Warbler songs are complex, with many syllable types shared both within and between males’ repertoires. Males varied their song output depending on context: they sang long songs at a high rate at dawn and during the breeding season, and shortened songs in the presence of a vocalizing female mate. Unlike many migratory species, Rufous‐capped Warblers do not appear to have different singing modes; they did not change the song variants used or the pattern of song delivery according to time of day, season or female vocal activity. Our research provides the first detailed vocal analysis of any Basileuterus warbler species, and enhances our understanding of the evolution of repertoire specialization in tropical resident songbirds.     

Age-related changes in song repertoire size and song type sharing in the Whinchat Saxicola rubetra

In many oscine passerines males’ songs, the repertoire size increases with age. At the same time it often remains unknown when and where males learn new songs. To infer the Whinchat Saxicola rubetra song learning strategy, we described and catalogued song-type repertoire, revealed age differences and examined song sharing strategies among neighbouring and distant males. We recorded song vocalizations of 40 males in a limited (104 ha) study plot during four years. Whinchats produce short and discrete songs with clear intersong pauses. In total 45 song types were allocated, the individual repertoire size averaged 23.5 ± 7.6 song types (range 9–34 song types). The males’ age significantly influenced the song-type repertoire size. The second calendar year (first breeding) males had a lower repertoire size than the older males. The majority of song types were shared by less than half of males in our sample. The Jaccard similarity indexes varied from 0.5 to 0.7. We could not find a relationship between males’ song sharing and geographic distances between their nests. We assume that Whinchat males learned new songs in the local population before territory establishment.     

Male singing behaviour and female presence in the territory in whitethroats Sylvia communis

Unmated male songbirds usually change their vocal behaviour when females enter their territories. Either the males court the females by changing the rate or pattern with which their normal long-ranging full songs are emitted, or they shift to special displays and long- or short-ranging vocalisations. In this study we quantified how female presence and behaviour affect the singing behaviour of male whitethroats. In the presence of a female the male frequently performed song flights, maybe to locate the female before it was courted, with sequences of diving-song displays. The courtship was interrupted by periods of perch songs. Female dscharp calls and short movements made the males initiate or resume courtship, whereas short horizontal jumps made the males intensify their courtship. Overall, the males changed their dual-function song activity in females' presence by emitting fewer perch songs and more flight songs. The quiet diving songs were only emitted during direct courtship of a female. The song types emitted immediately before, during, and after courtship are all highly variable, thus allowing for a quick assessment of the male's song repertoire. The courtship was also interrupted by periods of male woid calling, a call that is known to have a deterring effect on rival males. Bouts of woid calls were usually followed by song flights, again probably to locate the female that might have moved out of sight, or maybe to locate potential rival intruders. The latter was supported by an increased intrusion rate during female presence. Communicated by P. McGregor     

First-Year Common Nightingales (Luscinia megarhynchos) Have Smaller Song-Type Repertoire Sizes Than Older Males

Based on the assumptions that birdsong indicates male quality and that quality is related to age, one might expect older birds to signal their age. That is, in addition to actual body condition, at least some song features should vary with age, presumably towards more complexity. We investigated this issue by comparing repertoire sizes of free‐ranging common nightingale males in their first breeding season with those of older males. Nightingales are a good model species as they are open‐ended learners, where song acquisition is not confined to an early sensitive period of learning. Moreover, nightingales develop an extraordinarily large song‐type repertoire (approx. 180 different song types per male), and differences in repertoire size among males are pronounced. We analysed repertoire characteristics of the nocturnal song of nine nightingales in their first breeding season and compared them with the songs of nine older males. The repertoire size of older males was on average 53% larger than that of yearlings. When analysing two song categories of nightingales, whistle and non‐whistle songs separately, we found similar results. Our findings show marked differences in repertoire size between age categories, suggesting that this song feature may reflect a male's age. We discuss those mechanisms that may constrain the development of larger repertoires in first‐year males. Whether repertoire sizes are crucial for female mate choice or in vocal interactions among conspecific males remains open to further investigations.     

An Interactive Playback Experiment Shows Song Bout Size Discrimination in the Suboscine Vermilion Flycatcher (Pyrocephalus rubinus)

Many aspects of the social behaviour of birds are mediated by vocal displays, and variation in song output or song structure conveys different information to receivers. After nest construction begins, when vermilion flycatcher (Pyrocephalus rubinus) females are potentially fertile, males increase their song rate during the dawn chorus. A previous study failed to give evidence that males discriminate among song rates. However, males sing in sequences of songs (song bouts), and an increase in song rate may be achieved by increasing the number of bouts, the number of songs in each bout (bout size) or both. Studying a vermilion flycatcher population in Mexico City, we evaluated whether dawn song rate is related to song bout size or to number of bouts. Bout size correlated with song rate and differed among males. We hypothesized that longer bouts are more threatening signals than shorter ones and predicted a stronger response by males towards the former. We exposed each male to three playback treatments: (1) Long song bout (Long), in which we replied to the male with twice the number of songs he sang in the bout, (2) Short song bout (Short), in which we played half the number of songs sung by the male and (3) Control, this was the same as the Long treatment but we used songs from a related species, the tropical kingbird (Tyrannus melancholicus). Males responded with a higher proportion of calls near the speaker when exposed to the Long treatment than during the Short or Control treatments, indicating that they discriminate among song bouts differing in size, that they may perceive longer bouts as more threatening and that they use calls rather than songs to address threatening situations. Our results suggest that song bout size is a relevant song attribute that conveys information during intrasexual interactions.     

BIOACOUSTICS IN NEW ZEALAND AND JAPAN

Although it is highly recognisable, relatively little is known about the repertoire composition and singing behaviour of the Hermit Thrush (Catharus guttatus). To address this, we recorded spontaneously singing males in two eastern populations (Halifax, NS (n = 11) and Hancock County, ME (n = 7)) and analysed the recordings with respect to repertoire size, basic song type characteristics and song syntax. Males had song type repertoires of 7–12 song types, and no song type sharing between individuals was observed within or between populations. While frequency-related structural characteristics of the song types were the same between the populations, song type duration (especially that of the introductory note) differed significantly. The song types within each repertoire could be categorised into high and low song types based on introductory note frequency, and these song type categories also differed with respect to the amount and distribution of spectral energy. In both populations, males sang with immediate variety, never repeating the same song type consecutively, and preferentially used some song-type to song-type transitions more than others. In addition, we found correlational evidence of changes in singing behaviour (e.g., the relative use of low versus high song types) over the course of the breeding season. We discuss these findings in the context of other songbird research as well as their implications for future work examining how Hermit Thrush males utilise their songs in defending territories and attracting mates.     

Song characterization in the spectacled warbler (Sylvia conspicillata): a circum-Mediterranean species with a complex song structure

The spectacled warbler (Sylvia conspicillata) is a small passerine with a patchy distribution throughout the circum-Mediterranean region, including the North Atlantic archipelagos of Madeira, Canary Islands and Cape Verde. Here we characterize the species song structure on the island of Fuerteventura, quantifying repertoire size, inter- and intra-individual spectrographic variation, to determine whether acoustic variation occurred within an island population. Male song display was organized in song bouts of a variable number of song phrases, which in turn were made up of 4–69 syllables. We classified syllable types to derive a measure of repertoire size (number of different syllables) per song bout, and then used rarefaction methods to calculate the estimated repertoire size for our population of males. Three categories of song bout length were considered in analyses: short song bouts of 10 phrases, average bouts of 19 phrases and long bouts of ≥ 29 phrases. The observed and estimated repertoire size per male (between 43 and 126 syllables per male) increased with song bout duration, although the relationship was not significant for the estimated values. To test whether songs could be individually specific, we measured 11 spectrotemporal parameters of the song. A discriminant analysis using these variables performed poorly in classifying songs to the individuals that uttered them, but we found less variation in the individual than in the population for three out of the 11 variables. These individually specific variables, involving the first or the most common syllable of the song, the trill, were the duration of the first syllable of the phrase, the duration and the dominant frequency of the trill syllable. Our study emphasizes the complexity of spectacled warbler songs, in which males continuously add novel syllables over the entire song bout. This complexity appears to be determined by individual innovation capabilities rather than by the behaviour of copying neighbour repertoires, since songs of close birds were not more similar than songs from far-away territories.     

Syllable repertoire and the size of the song control system in captive canaries (Serinus canaria)

In songbirds, there is considerable interest in relationships between song structure and the size of the song control system in the forebrain. In male canaries, earlier studies have reported that repertoire size increased with age, and positive correlations were obtained between repertoire size and the volume of song control nuclei such as high vocal center (HVC). Here we investigate whether age has an effect upon both the song structure and the morphology of two song control nuclei [HVC and robustus archistriatalis (RA)] that are important in song production. We recorded songs from an aviary population of 1- and 2-year-old male domesticated canaries. We found that repertoire size, number of sexually attractive (sexy) syllables, and size of song nuclei did not differ between 1- and 2-year-old males. Neither did we find significant correlations between syllable repertoire size and the size of the song control nuclei. However, HVC size was positively correlated with the proportion of sexy syllables in the repertoires of 2-year-old males. Some older males may enhance vocal performance by modifying the control of syllables rather than by increasing repertoire size or neural space.     

Neighbour recognition in two sister songbird species with a simple and complex repertoire – a playback study

The ability of individuals to recognize others based on vocalizations has been proven in many species of birds. However, we are still far from understanding important aspects of the discrimination process. For example, it is still not fully understood whether, and why, repertoire size hinders discrimination between individuals. Further, the strategies and vocal cues used for discrimination between individuals are largely unexplored. In this study, we tested the ability of chiffchaffs Phylloscopus collybita and willow warblers Phylloscopus trochilus, two closely related species with different repertoire sizes and song organization, to differentiate between their neighbours on the basis of a single song of a neighbouring male. We did playback experiments within the ‘dear enemy’ paradigm in which we tested resident males with a single song of a neighbour broadcast from the correct and opposite, incorrect territory border. Both species displayed a strong ability to discriminate between their neighbours representing further evidence that repertoire size per se has no negative impact on individual recognition in songbirds. Using a single song for playback allowed us to speculate about the nature of the possible cues used by males for recognition. Individual recognition in both species is most likely based on the modulation of syllables or on general voice characteristics. We suggest that specific changes in song organization, for example the tendency of individuals to insert a distinct phrase at the beginning of each song, may facilitate individual recognition and compensate for increased repertoire size in willow warblers.     

Evidence of repertoire sharing and stability despite a high turnover rate in a duetting neotropical wren

In songbirds, the spatial pattern of song sharing among individuals is influenced by the song learning and dispersal strategies within each species. In birds where females and males sing and create joint acoustic displays (duets), the processes defining the patterns of song sharing become more complex as there might be different selection pressures shaping the behaviour of each sex. To provide further insight into the vocal development and the dispersal strategy of duetting tropical species, we investigated the patterns of individual and pair repertoire sharing, as well as the stability of these repertoires, in a colour-marked population of riverside wrens, Cantorchilus semibadius, located in the Osa Peninsula, Costa Rica. Using data collected over a five-year period, we found considerable variation in the sharing levels of phrase and duet type repertoires among neighbouring individuals coupled with a general decline of repertoire sharing as distance increased between birds’ territories. These results are consistent with a pattern predicted in age-restricted learners that establish preferentially near their tutors. Furthermore, we found no evidence of individuals changing their phrase type repertoires over time, including after remating events. Duet type repertoires were also stable when pairs remained together. However, we observed a surprisingly high turnover rate. When individuals remated, even though the majority of the previous duet type repertoire remained, several new duet types were included. Taken together, our findings suggest that riverside wrens might create their individual repertoires by copying their same-sex parent and neighbouring individuals before dispersal. Additionally, we speculate that even though birds were able to create new duet types after changing partners, a substantial portion of their duet type repertoire might also be copied from their parents and neighbouring pairs during the initial critical period of song learning.     

鸟类鸣唱曲目与复杂性

鸟类的鸣唱是研究性选择和动物声音通讯的良好素材,一般认为鸟类的鸣唱曲目是性选择的结果.本文综述了鸣唱曲目和鸣唱复杂性的实验和理论成果,阐述二者的相关性,曲目和复杂鸣唱产生的解剖学基础及其得以进化形成的功能性原因.曲目和鸣唱的复杂性源于鸟类发声器官特定结构的复杂性和神经系统的协调作用,鸣唱的表现形式同时受多种因子影响,可根据改变的生境进行适应性调节.曲目和多种鸣唱型存在的必要性还在于其功能的多样性,鸟类借助于多种鸣唱型之间的转换,传达了有利于繁殖的多种信息.     

Song organisation and patterns of variation in the serin (Serinus serinus)

This article describes the organisation of song in the serin (Serinus serinus) and analyses its variation among individuals. Serins have a repertoire of about 50 complex syllables that are sung at a very fast rate and in a very stereotyped order, forming discrete songs. Songs are high pitched for the serin’s body size. Song organisation is circular, with a limited number of starting points. Songs can stop at any point in their cycling. Within songs there are trilled sections and fast, non-repeated sections that account for the greatest part of songs. These two modes of singing also differ in average inter-element intervals and probably in their respiratory kinematics. Bird repertoire size was measured and the difficulties of measuring it in this species are discussed. Repertoires are individually specific and have a variable amount of syllable sharing with other birds. We found evidence for geographical variation in the composition of repertoires. Considering our current knowledge of song in carduelines, the stereotyped and circular nature of serin song appear to be unique within this group of birds. Received: 30 May 2000 / Received in revised from: 14 August 2000 / Accepted: 12 September 2000     

Using Shannon entropy on measuring the individual variability in the Rufous-bellied thrush Turdus rufiventris vocal communication

We applied the information theory concepts to notes repertoire characteristics combined with temporal parameters of the Rufous-bellied thrush Turdus rufiventris song, using this particular case to test a new method of analysing quantitatively complex animal communication systems. Like most Turdus thrushes, Rufous-bellied thrushes are remarkable for their long, varied and melodious songs. For the analysis of the species repertoire, we used recordings of 44 individuals from 24 localities covering its full geographical range. We measured the repertoire size, note duration and rhythm (frequency of note utterance), and combined these parameters with the Shannon entropy values calculated for each individual. Although individuals maintain species-specific recognition capacity, we find a large variation between their song parameters and show that the information theory can be useful to analyse large and varied animal vocal repertoires. We are introducing two new parameters, temporal average entropy (E(t)) and utterance frequency average entropy (E(f)), for measuring such communication systems.     

Individual Signature in Canary Songs: Contribution of Multiple Levels of Song Structure

Through variations in features, both within and between individuals, songs of male passerines provide information on the identity of the singer. In domesticated canaries (Serinus canaria), these variations remain, for a large part, to be investigated. This led us to question whether individual identity might be coded at one or more hierarchical levels of song organization, i.e. in acoustic parameters, in the syllable repertoire and in the delivery order of syllables. A song as a whole had numerous individual distinctive acoustic features. However, the structure of its individual signature appeared to be complex. A repertoire combined syllables never sung by other individuals with those shared by other birds. But, most of the individual‐specific syllables that accounted for 16% of a repertoire did not recur frequently. Variation in sequences of multiple syllable types appeared to reflect the individual identity of a male canary. Nearly all sequences larger than three syllable types were specific to the individual that produced them. Some of these occurred recurrently in songs and differed in their acoustic structure between individuals. Focusing upon recurrent sequences might allow vocal recognition of an individual without requiring the knowledge of its full repertoire. However, acoustic parameters and repertoire composition might also serve as additional cues to limit confusion between individuals.     

Variation in the volume of zebra finch song control nuclei is heritable: developmental and evolutionary implications.

In many songbird species, females prefer males that sing a larger repertoire of syllables. Males with more elaborate songs have a larger high vocal centre (HVC) nucleus, the highest structure in the song production pathway. HVC size is thus a potential target of sexual selection. Here we provide evidence that the size of the HVC and other song production nuclei are heritable across individual males within a species. In contrast, we find that heritabilities of other nuclei in a song-learning pathway are lower, suggesting that variation in the sizes of these structures is more closely tied to developmental and environmental differences between individuals. We find that evolvability, a statistical measure that predicts response to selection, is higher for the HVC and its target for song production, the robustus archistriatalis (RA), than for all other brain volumes measured. This suggests that selection based on the functions of these two structures would result in rapid major shifts in their anatomy. We also show that the size of each song control nucleus is significantly correlated with the song related nuclei to which it is monosynaptically connected. Finally, we find that the volume of the telencephalon is larger in males than in females. These findings begin to join theoretical analyses of the role of female choice in the evolution of bird song to neurobiological mechanisms by which the evolutionary changes in behaviour are expressed.     

Repertoire size,auditory templates,and selective vocal learning in songbirds

When vocal variability, here measured by song repertoire size, increases in songbirds, it may become increasingly difficult to encode genetically all the information which is required to ensure the learning of only conspecific songs. Marsh wrens (Cistothorus palustris) have sizeable song repertoires, and while no vocal mimicry is evident in the field, males will readily learn heterospecific songs in the laboratory. These data, together with data from the literature, support the proposed relationship between increased repertoire sizes and reduced specificity of the innate auditory template which guides vocal learning.     

Acoustic Monitoring Reveals Congruent Patterns of Territorial Singing Behaviour in Male and Female Tropical Wrens

Many animals defend territories against conspecific individuals using acoustic signals. In birds, male vocalizations are known to play a critical role in territory defence. Territorial acoustic signals in females have been poorly studied, perhaps because female song is uncommon in north‐temperate ecosystems. In this study, we compare male vs. female territorial singing behaviour in Neotropical rufous‐and‐white wrens Thryothorus rufalbus, a species where both sexes produce solo songs and often coordinate their songs in vocal duets. We recorded free‐living birds in Costa Rica using an eight‐microphone Acoustic Location System capable of passively triangulating the position of animals based on their vocalizations. We recorded 17 pairs of birds for 2–4 consecutive mornings and calculated the territory of each individual as a 95% fixed kernel estimate around their song posts. We compared territories calculated around male vs. female song posts, including separate analyses of solo vs. duet song posts. These spatial analyses of singing behaviour reveal that males and females use similarly sized territories with more than 60% overlap between breeding partners. Territories calculated based on solo vs. duet song posts were of similar size and similar degrees of overlap. Solos and duets were performed at similar distances from the nest for both sexes. Overall, male and female rufous‐and‐white wrens exhibit very similar spatial territorial singing behaviour, demonstrating congruent patterns of male and female territoriality.