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.     

Alternative forms of song matching in song sparrows

Song matching, replying to a song with a similar song, occurs in many songbird species. Almost all investigations of song matching have been of type matching, where one bird's reply is unambiguously similar to the other's song (i.e. the same song type). In many populations, however, neighbours do not share song types, and therefore cannot type-match. We hypothesized that a bird lacking a true type match could still song-match a stimulus song with a song from his repertoire that was similar in some way the birds recognized. We tested this hypothesis in song sparrows, Melospiza melodia, in two playback experiments. We played the subject a stranger song that was similar to one or more of his songs, but a type match to none of them. In the first experiment, we used playback songs that began with two buzzes (‘double-buzz’ songs). In the second experiment, we used songs that began with a slow trill that increased in tempo ('speed-up' songs). Birds replied at rates significantly above chance with their own double-buzz, or speed-up song match to the respective types of playback. The results suggest that birds who do not share true song types, can still song-match each other. This broad-sense form of song matching may also occur in populations with low song type sharing. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Song matching in a long-lived,sedentary bird with a low song rate: The importance of song type,song duration and intrusion

Territorial songbirds often match the song features or singing patterns of rivals, commonly as an aggressive signal. Most studies of song matching have been on Northern Hemisphere species with short lifespans and high song rates, but vocal matching is predicted to be affected both by longevity and territorial stability. We studied song matching in males of the white-browed scrubwren, Sericornis frontalis, a long-lived, sedentary, territorial Australian songbird. We quantified natural song rate and diversity, and then conducted three playback experiments to test: (a) whether males match by song type; (b) how they respond physically and vocally to territorial intrusion; and (c) whether they match by song length, and use it as an agonistic signal. Males naturally had very low song rates, singing on average less than three times per hour, and moderate repertoires, with an estimated mean of 17.5 song types for individual males. Males did not engage in extended counter-singing bouts. The first experiment showed that males matched the song type of immediate neighbours almost 90% of the time, if that type was in their repertoire. The remaining experiments revealed that song-type matching was an aggressive signal; males responded more aggressively to, and were more likely to match, playback simulating a neighbour's territorial intrusion than song from their shared boundary. Males did not match songs by length, but they produced longer songs after simulated intrusion. Males also responded more aggressively to playback of longer songs that simulated intrusion, but less aggressively to longer songs from the territory boundary. Overall, we show that sedentary, long-lived songbirds with low song rates, can use song-type matching as an aggressive signal to communicate with neighbours and intruders. Song length had a different role in communication, possibly related to individual quality or territory ownership.     

Song learning in domesticated canaries in a restricted acoustic environment

Many songbirds learn their songs early in life from a song model. In the absence of such a model, they develop an improvised song that often lacks the species-typical song structure. Open-ended learners, such as the domesticated canary, are able to modify their songs in adulthood, although the mechanisms that guide and time the song-learning process are still not fully understood. In a previous study, we showed that male domesticated canaries lacking an adult song model in their first year substantially change their song repertoire and composition when exposed to normally reared conspecifics in their second year. Here, we investigate song development in descendants of canaries that were raised and kept as a peer group without a song model. Such males represent tutors with abnormal song characteristics. Interestingly, the F₁ generation developed quite normal song structure, and when brought into an environment with normally raised canaries in their second year, they did not modify their songs substantially. These results suggest that contact with an adult song model early in life is crucial for song crystallization, but also that song development is at least partly guided by innate rules. They also question the existing classification of canaries as open-ended learners.     

Fighting talk: complex song elicits more aggressive responses in a vocally complex songbird

Song complexity in many songbirds is a trait subject to sexual selection. It is often associated with male territorial defence. Empirical studies testing differential male responses to rival song in vocally complex songbirds have, however, been scarce. We conducted playback experiments of the endemic New Zealand Tui Prosthemadera novaeseelandiae to test the aggressive response of territorial male Tui to rival songs with differing complexity levels. Overall, complex songs evoked significantly stronger responses from territorial males than did simple songs. Following playback of complex songs, focal males approached the playback more closely and rapidly, and responded with songs of higher complexity than they did to playback of simple songs. This suggests males could both distinguish between different levels of complexity within the Tui repertoire, and perceive a more complex song as a greater territorial threat. Our study is one of the first to demonstrate strong aggressive responses to increased levels of song complexity in a songbird species with highly complex vocalizations.     

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.     

Song and brain development in canaries raised under different conditions of acoustic and social isolation over two years

Early isolation experiments indicate that male songbirds learn their songs during an early sensitive period, although later work has shown that some open-ended learners modify songs in later years. Recent isolation experiments suggest that in some species song has a stronger genetic basis than previously thought. This study raised domestic canaries under different combinations of acoustic and social isolation and followed song development into the second year. Males raised alone in acoustic isolation developed songs with normal syllables, but larger repertoires and also produced syllables with lower repetition rates when compared to controls. The smallest repertoire occurred in males raised in a peer group. Isolate males had a smaller song control nucleus HVC than controls, but there was no effect on nucleus RA or on brain weight in general. In the second year, after introduction into a large normal colony, isolate and peer group males adjusted their syllable repertoire to normal size. In particular, the isolates reduced their repertoire even though the size of HVC showed a significant increase in volume. However, songs of isolate and peer group males still differ in repetition rate and number of single syllables in the common aviary. In contrast, control males showed low syllable turnover and no significant change in repertoire size. Nor did they show any significant change in the volumes of song control nuclei. It seems that complete isolation affects only some aspects of song and brain development, and later socialization corrects some but not all of these in the second year.     

Are bird song complexity and song sharing shaped by habitat structure? An information theory and statistical approach

In songbirds, song complexity and song sharing are features of prime importance for territorial defence and mate attraction. These aspects of song may be strongly influenced by changes in social environment caused by habitat fragmentation. We tested the hypothesis that habitat fragmentation induced by human activities influences song complexity and song sharing in the skylark, a songbird with a very large repertoire and whose population recently underwent a large decline. We applied powerful mathematical and statistical tools to assess and compare song complexity and song sharing patterns of syllables and sequences of syllables in two populations: a declining population in a fragmented habitat, in which breeding areas are separated from each other by unsuitable surroundings, and a stable population in a continuous habitat. Our results show that the structure of the habitat influences song sharing, but not song complexity. Neighbouring birds shared more syllables and sequences of syllables in the fragmented habitat than in the continuous one. Habitat fragmentation seems thus to have an effect on the composition of elements in songs, but not on the number and complexity of these elements, which may be a fixed feature of song peculiar to skylarks.     

Soft Song in Song Sparrows: Acoustic Structure and Implications for Signal Function

In many species of songbirds, males sometimes produce songs at distinctly lower amplitude than in normal singing. Depending on the species, these 'soft songs' may be sung in the context of female courtship, male–male aggression, or both. In song sparrows, males produce soft songs during aggressive interactions with other males, and the amount of soft song produced is the only singing behavior that can be used to reliably predict a subsequent attack by the singer. Although soft song is clearly an important signal in this species, little is known about the acoustic structure of soft song or about how that structure compares to the structure of normal 'broadcast song'. We recorded a large sample of soft songs and broadcast songs from 10 male song sparrows, and measured song amplitudes in the field while controlling the subject's distance to a calibrated microphone. We show that song sparrow males produce songs over a wide range of amplitudes, with soft songs in the range of 55–77 dB sound pressure level and broadcast songs in the range of 78–85 dB. We present evidence for two types of soft song: 'crystallized' soft songs that are broadcast repertoire song types sung at low amplitude, and 'warbled' soft songs that are not found in the broadcast repertoire. Although highly variable, warbled soft songs produced by individual birds could be grouped into song types based on spectrographic similarity. To our knowledge, a distinct repertoire of soft song types has not been previously reported for any songbird.     

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.     

Territory establishment,song learning strategies and survival in song sparrows

In most songbirds, the processes of song learning and territory establishment overlap in the early life and a young bird usually winds up with songs matching those of his territorial neighbors in his first breeding season. In the present study, we examined the relationships among the timing of territory establishment, the pattern of song learning and territorial success in a sedentary population of song sparrows (Melospiza melodia). Males in this population tend to learn their songs from their neighbors and consequently they show high song sharing with neighbors and use these shared songs preferentially in interactions with them. Males also show significant variation in the timing of territory establishment, ranging from their natal summer to the next spring. Using a three-year dataset, we found that the timing of territory establishment did not systematically affect the composition of the song repertoire of the tutee: early establishers and late establishers learned equally as much from their primary tutors and had a similar number of tutors and similar repertoire sizes, nor did timing of territory establishment affect subsequent survival on territory. Therefore, the song-learning program of song sparrows seems versatile enough to lead to high song sharing even for birds that establish territories relatively late.     

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.     

Stereotyped and non-stereotyped features of the temporal patterning of singing sessions in the ovenbird Seiurus auricapillus

Temporal patterning of recorded singing sessions of 26 different male ovenbirds Seiurus auricapillus (Fringillidae: Parulini) was analyzed computationally, in order to test whether differences among songs are potentially informative or merely reflect performance errors. Repeated songs within a singing session by a given male showed relatively little inter-individual variation in the duration of the song or in the number of units composing it, although these features varied substantially among individuals. On the other hand, within a session of singing by an individual male, the most variable and potentially informative aspect of temporal patterning was the relative placement of the peak amplitude within the song. These results support the hypothesis that diversity in the vocalization sessions of oscine passerines can be produced by other means than the use of a varied song repertoire, even in a species like the ovenbird that uses just one song type. Because variation among song was focused on a single feature, performance errors are an unlikely explanation, suggesting that the temporal patterning of singing sessions may play an informative role, such as the minimization of habituation on the part of receivers.     

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‐type sharing in a population of Song Sparrows in the eastern United States

Male Song Sparrows (Melospiza melodia) sometimes interact with neighboring territory owners by song‐type matching or repertoire matching. In some Song Sparrow populations, levels of song sharing are high and most neighbors can interact by matching, but levels of song sharing are much lower in other populations, limiting the degree to which males can match their neighbors. One explanation for variation in sharing levels is that the importance of song‐type and repertoire matching, and therefore the extent of song sharing, varies geographically in North America, being greater in western populations than eastern populations. However, to date, two studies of eastern populations have provided conflicting evidence concerning levels of song sharing by Song Sparrows. Thus, we measured sharing of whole songs and introductory phrases of songs between males with adjacent territories in another population of Song Sparrows in the eastern United States (North Carolina), near the eastern and southern limits of the species’ breeding range. Males (N = 17) in our study shared an average of only 8.7% of their song types with neighbors, and more than half of neighbor pairs shared no whole songs. Sharing of introductory phrases was more common (mean = 22.8%). The level of whole song sharing in our study is the second lowest yet reported for any Song Sparrow population, supporting the hypothesis that sharing is generally lower in eastern than in western populations.     

Causes of the latitudinal gradient in birdsong complexity assessed from geographical variation within two Himalayan warbler species

Aspects of birdsong complexity, such as the number of distinct notes in a song, commonly increase along latitudinal gradients, a pattern for which at least 10 explanations have been suggested. In two Himalayan warblers, songs are more complex in the northwest than in the southeast. In Grey‐hooded Warbler Phylloscopus xanthoschistos, high complexity results from increased note diversity within song types, sung across a higher bandwidth. In Blyth's Leaf Warbler Phylloscopus reguloides, high complexity is a consequence of increased variation between song types. The hypothesis with strongest support is that songs evolved to be more complex in species‐poor, demonstrably less noisy environments. We consider geographical variation to be an outcome of sexual selection favouring complexity across environments, where detection of the signal varies. Sexual selection favouring complexity may be resolved in different ways, because complexity has multiple features (repertoire size, song switching, etc.). We argue this has led to the great diversity in song that we have documented among five Phylloscopus species.     

Song learning by prairie warblers: When,where, and from whom

Songbirds of many species acquire their songs by imitating the songs of conspecific singers. Conclusive evidence of such imitation comes from controlled laboratory studies, but such studies do not reveal when and where songbirds learn their songs under natural conditions. To determine the timing and location of song learning in a population of prairie warblers, we compared the songs of yearling prairie warblers of known hatching location to the songs of other birds in the yearlings' natal and first breeding areas. The comparisons yielded a likely model song (and model singer) for each of the song types used by the focal yearlings. We supplemented our findings from the song comparisons with inferences drawn from an analysis of local geographic variation in songs. This analysis revealed that shared song types showed no tendency to be geographically clustered within the study area. Taken together, our data suggest that prairie warblers learn their songs during the hatch year, at locations somewhat distant (mean distance 1,437 m) from their natal site, most likely as birds wander about during the post-fledging period.     

Territory tenure in song sparrows is related to song sharing with neighbours, but not to repertoire size

Song repertoires may be a product of sexual selection and several studies have reported correlations of repertoire size and reproductive success in male songbirds. This hypothesis and the reported correlations, however, are not sufficient to explain the observation that most species have small song repertoire sizes (usually fewer than 10, often fewer than five song types). We examined a second important aspect of a male's song repertoire, the extent to which he shares songs with his neighbours. Song sharing has not been measured in previous studies and it may be partially confounded with repertoire size. We hypothesized that in song sparrows, Melospiza melodia, song sharing rather than repertoire size per se is crucial for male territorial success. Our longitudinal study of 45 song sparrows followed from their first year on territory showed that the number of songs a bird shares with his neighbourhood group is a better predictor of lifetime territory tenure than is his repertoire size. We also found that song sharing increases with repertoire size up to but not beyond eight to nine song types, which are the most common repertoire sizes in the population (range in our sample 5-13). This partial confound of song sharing and repertoire size may account for some earlier findings of territory tenure-repertoire size correlations in this species and other species having small- or medium-sized repertoires. Copyright 2000 The Association for the Study of Animal Behaviour.