Song Output Research Articles

Bachelor and paired male rufous-and-white wrens use different singing strategies

To attract a breeding partner, males may behave differently when they are bachelors compared to when they are paired. Comparisons between groups of paired males versus groups of unpaired males in temperate-breeding animals have revealed such differences in signalling behaviour. Few studies, however, have explored how individual males alter their signalling behaviour with changes in pairing status, and very few investigations have explored paired versus unpaired male behaviour in tropical animals. During a 5-year study in Costa Rica, we analysed changes in the singing behaviour of male rufous-and-white wrens (Thryothorus rufalbus) when they were paired and when they were bachelors. We compared three aspects of male vocal behaviour: gross differences in song output, variation in repertoire use and differences in song structure. Males as bachelors had significantly higher song output and switched song types less frequently. Contrary to our expectation, bachelors sang significantly fewer song types from their repertoire compared to when those same males had a breeding partner. Songs sung by bachelor males were higher in syllabic diversity and had broader-bandwidth terminal syllables than the songs those males sang only when paired. Within song types, the fine structure of songs remained consistent across pairing status. Our results demonstrate that males change their singing behaviour with pairing status, delivering songs at a higher rate but with less variety when they are bachelors. Rufous-and-white wrens are renowned for their vocal duets, and we discuss the pattern of repertoire use in light of their duetting behaviour. These results enhance our understanding of how male behaviour varies with pairing status and the importance of vocal signalling behaviour in socially monogamous tropical animals.

Supplemental Feeding and Dawn Singing in Black-Capped Chickadees

Abstract. The dawn chorus is a collective behavior involving a network of birds signaling at the same time. Two hypotheses can explain the mechanisms of dawn singing. The “condition-dependent hypothesis” states that the dawn chorus consists of a “broadcast network” in which the signal is given in all directions but is not dependent on the singer's neighbors' chorus. The song output is condition dependent and can thus be limited by the amount of food to which a signaler has access to in its territory. On the other hand, the “social-dynamic hypothesis” states that during the chorus the birds are constantly interacting with their neighbors. Under this scenario, the dawn chorus consists of an “interactive network” and the song output is not dependent on the condition of the signaler but on the interaction with the neighbors. To determine which scenario best explains the mechanisms of the dawn chorus in the Black-capped Chickadee (Poecile atricapillus), we set up a supplemental-feeding experiment in a dyadic f...

Song competition changes the brain and behavior of a male songbird

Males should adjust their behavior and its neural substrates according to the quality of competition that they assess by eavesdropping on other males' courtship signals. In European starlings (Sturnus vulgaris), females base mate choice, in part, on aspects of male song associated with its length, which positively correlates with the males' reproductive success, immunocompetence, age and ability to repel competing males. To determine how variation in the quality of male courtship song affects the brain and behavior of incidental male receivers, we exposed adult male starlings to either long or short songs periodically over 7 days, followed by 1 day of no song. We found no difference between groups in the length (i.e. quality) of songs that subjects produced during the experiment. However, compared with males exposed to short songs, those exposed to long songs sang more songs, exhibited more non-singing activity and, by the end of the experiment, weighed less and had a 30% larger robust nucleus of the arcopallium (RA), a forebrain nucleus that translates pre-motor signals into the appropriate combination of respiratory and syringeal activity. The change in RA volume was not entirely due to variation in song output, suggesting, for the first time, the possibility of acoustically driven plasticity in this motor nucleus. We hypothesize that such neuroplasticity helps prepare the individual for future song output tailored to the prevailing competitive environment.

The rich get richer: song complexity predicts song element sharing and song output in song sparrows Melospiza melodia

Animal signals are often complex, raising the possibility that different aspects of a signal may convey different types of information. Birdsong, for example, may simultaneously advertise the singer's condition during early life (through song complexity), location of song learning (through local song structure) and current condition (through song output). Each of these aspects of song is behaviourally salient: females generally prefer complex over simple song, local over nonlocal song, and high over low rates of song output. We examined the degree to which these three components of song convey complementary versus redundant information, in eastern song sparrows, Melospiza melodia melodia. One measure of song complexity, syllable repertoire size, was positively related to syllable sharing with other birds in the local population. This finding suggests that these aspects convey somewhat redundant information and that local-sounding song may in part advertise song-learning ability. A second measure of song complexity, song repertoire size, was positively related to song output, despite the widely differing developmental timescales over which song complexity and output are thought to vary. Condition during early development may have carryover effects on adult condition; alternatively, complex singers may have most to gain from advertising this attractive signal. Finally, despite our finding that both syllable sharing and song output were related to song complexity, syllable sharing and song output were not themselves significantly correlated. Overall, the three ostensibly independent aspects of song investigated here appear to overlap substantially in the information they convey.

The Dusk Chorus from an Owl Perspective: Eagle Owls Vocalize When Their White Throat Badge Contrasts Most

BackgroundAn impressive number of studies have investigated bird vocal displays, and many of them have tried to explain the widespread phenomenon of the so-called dawn and dusk chorus, the sunrise and sunset peaks in bird song output. As many as twelve non-exclusive hypotheses have been proposed to explain why twilight peaks in vocal display might be advantageous; but, even after more than two decades of study, the basis underlying the dusk and dawn chorus is still unclear. Moreover, to date, the majority of studies on this topic have focused on songbirds.Methodology/Principal FindingsWe investigate here a novel hypothesis on why nocturnal birds with patches of white feathers call at twilight. We propose that white plumage patches and the timing of visual signaling have co-evolved to maximize the effectiveness of social communication such as the dusk chorus. This hypothesis centers on the recent discovery that eagle owls can adopt specific forms of visual signaling and is supported by the observation that adult eagle owls possess a white throat badge that is only visible during vocal displays. By monitoring the calling of eagle owls at dusk, a peak time for bird call output, we found that white throat badges contrasted most with the surrounding background during the owls' twilight chorusing.Conclusions/SignificanceCrepuscular and nocturnal species appear to have evolved white patches that, shown in association with vocal displays, allow them to communicate in dark surroundings. The evolution of a white badge that operates jointly with call displays at dawn and dusk may be relevant to the eagle owls' social dynamics. Our explanation for the dusk chorus may possibly represent an overlooked but common pattern of signaling among crepuscular and nocturnal birds that combine patches of white feathers with twilight displays. Furthermore, our findings could be relevant to songbirds that breed in dark forest habitats and have contrasting white badges, as well as birds living in open habitats and showing contrasting bars.

The ability to perform physically challenging songs predicts age and size in male swamp sparrows, Melospiza georgiana

Selection should favour female preferences for reliable signals of male quality when such preferences result in benefits to females. Research on bird song suggests that, because song is costly to produce or sustain, females are obtaining accurate information about male quality through song preferences. Females have been shown to express mating preferences for three general categories of costly song features: song output, song complexity and geographical variation. A novel mechanism for the reliability of song is suggested by constraints on the ability to produce rapid, broadband trills (i.e. ‘vocal performance’). In several species of birds, females show a preference for superior vocal performance, supporting a key prediction of the hypothesis that vocal performance, like other features of song, may be a reliable indicator of male quality. In this study, I further test this hypothesis by investigating whether female swamp sparrows' preference for vocal performance is favoured by selection because it reliably reflects male quality. I found that vocal performance in male swamp sparrows was correlated with age and size, measured as mass. By preferring males with superior vocal performance, female swamp sparrows may obtain direct and indirect benefits by mating with older larger males. These results support the hypothesis that vocal performance in swamps sparrows is a reliable indicator of male quality.

Strategies for producing sequential behavior in Bengalese finches ( Lonchura striata var. domestica) examined by three types of test

Communication between auditory and vocal motor nuclei is essential for vocal learning. In songbirds, the nucleus interfacialis of the nidopallium (NIf) is part of a sensorimotor loop, along with auditory nucleus avalanche (Av) and song system nucleus HVC, that links the auditory and song systems. Most of the auditory information comes through this sensorimotor loop, with the projection from NIf to HVC representing the largest single source of auditory information to the song system. In addition to providing the majority of HVC’s auditory input, NIf is also the primary driver of spontaneous activity and premotor-like bursting during sleep in HVC. Like HVC and RA, two nuclei critical for song learning and production, NIf exhibits behavioral-state dependent auditory responses and strong motor bursts that precede song output. NIf also exhibits extended periods of fast gamma oscillations following vocal production. Based on the converging evidence from studies of physiology and functional connectivity it would be reasonable to expect NIf to play an important role in the learning, maintenance, and production of song. Surprisingly, however, lesions of NIf in adult zebra finches have no effect on song production or maintenance. Only the plastic song produced by juvenile zebra finches during the sensorimotor phase of song learning is affected by NIf lesions. In this review, we carefully examine what is known about NIf at the anatomical, physiological, and behavioral levels. We reexamine conclusions drawn from previous studies in the light of our current understanding of the song system, and establish what can be said with certainty about NIf’s involvement in song learning, maintenance, and production. Finally, we review recent theories of song learning integrating possible roles for NIf within these frameworks and suggest possible parallels between NIf and sensorimotor areas that form part of the neural circuitry for speech processing in humans.

Seasonal rewiring of the songbird brain: an in vivo MRI study

The song control system (SCS) of songbirds displays a remarkable plasticity in species where song output changes seasonally. The mechanisms underlying this plasticity are barely understood and research has primarily been focused on the song nuclei themselves, largely neglecting their interconnections and connections with other brain regions. We investigated seasonal changes in the entire brain, including the song nuclei and their connections, of nine male starlings (Sturnus vulgaris). At two times of the year, during the breeding (April) and nonbreeding (July) seasons, we measured in the same subjects cellular attributes of brain regions using in vivo high-resolution diffusion tensor imaging (DTI) at 7 T. An increased fractional anisotropy in the HVC-RA pathway that correlates with an increase in axonal density (and myelination) was found during the breeding season, confirming multiple previous histological reports. Other parts of the SCS, namely the occipitomesencephalic axonal pathway, which contains fiber tracts important for song production, showed increased fractional anisotropy due to myelination during the breeding season and the connection between HVC and Area X showed an increase in axonal connectivity. Beyond the SCS we discerned fractional anisotropy changes that correlate with myelination changes in the optic chiasm and axonal organization changes in an interhemispheric connection, the posterior commissure. These results demonstrate an unexpectedly broad plasticity in the connectivity of the avian brain that might be involved in preparing subjects for the competitive and demanding behavioral tasks that are associated with successful reproduction.

Do male plumage and song characteristics influence female off-territory forays and paternity in the hooded warbler?

Extra-pair fertilizations are common in many socially monogamous species, and paternity studies have indicated that females may use male vocal performance and plumage ornaments as cues to assess male quality. Female off-territory forays may represent a key component of female choice and male extra-pair mating success, and female foray behaviour is expected to be strongly influ- enced by indictors of male quality. In this study, we examined how male song and ornamentation affect how often females left their territories, which males they visited and extra-pair paternity in a socially monogamous passer- ine, the hooded warbler (Wilsonia citrina). We radiotracked 17 females during the fertile period and quantified male vocal performance (song output and rate) and plumage characteristics (size of the black melanin hood and colour of the black hood, yellow cheeks and breast areas). We obtained blood samples and determined paternity at 35 nests including those of 14 females that we radiotracked. Eleven (65%) of the 17 females forayed off-territory, whilst fertile and female foray rate was positively correlated with the number of extra-pair young in the nest. Females that left their territories more frequently were paired with males that sang at a low rate. In addition, extra-pair mates had higher song rates than the social mates they cuckolded (5.3 songs/ min vs. 4.4 songs/min). Female off-territory forays or extra- pair paternity were not significantly related to male plumage characteristics. Our results indicate that a high song rate influences both the foray behaviour of a male's social mate and the likelihood that he will sire extra-pair offspring with neighbouring females.

Reproductive strategy and singing activity: blue tit and great tit compared

The costs and benefits of bird song are likely to vary among species, and different singing patterns may reflect differences in reproductive strategies. We compared temporal patterns of singing activity in two songbird species, the blue tit (Cyanistes caeruleus) and the great tit (Parus major). The two species live side by side year round, and they have similar breeding ecology and similar rates of extra-pair paternity. However, they differ in two aspects of reproductive strategy that may have an influence on song output: blue tits are facultatively polygynous and have a fairly short breeding season with almost no second broods, whereas great tits are socially monogamous but more commonly raise second broods. We found that great tit males continued singing at high levels during the egg-laying and incubation periods, while monogamously paired blue tit males strongly reduced singing activity after the first days of egg-laying by their female. Since males of both species sang much more intensely shortly before sunrise than after sunrise, at midday or in the evening, this difference was most conspicuous at dawn. No differences in singing activity were found within species when testing for male age. We suggest that in contrast to blue tits, great tit males continued singing after egg-laying to defend the territory and to encourage the female for a possible second brood.

A Patriotic Song and its Consequences: ‘Du danske Mand’ Through Hundred Years

From his starting point in the instrumental music of his native Funen, Nielsen aspired towards the world of great art music, placing himself in the continuation of the classical central European tradition. In the first decade of the new century, two of his songs became national treasures, landeplager – i.e. ‘all the rage’, or ‘hits’ as later generations would have called them. He composed the first one, Thou Danish Man (Du danske Mand), as an ironic song for a music hall show, and without knowledge of the text. Even so the song was received as a manifestation of the Danish national spirit, which continued to be the case as late as the mobilisation of public opinion against the German occupation of Denmark in the Second World War. From the composer’s point of view these songs showed first and foremost that he was able to reach a wider public, and they formed the background for the pedagogic project (not National but folkeligt , i.e. Popular, in spirit) that he developed for the rest of his life through his song output, running side by side with his ‘great’ works.

Eavesdropping and communication networks revealed through playback and an acoustic location system

Our understanding of animal communication is expanding from a dyadic framework of one signaler and one receiver to a broader communication network model, yet empirical studies of communication networks are scarce. To investigate whether territorial males eavesdrop on interactions occurring outside of their territory boundaries and to quantify the neighborhood-level effects of song contests, we simulated diurnal dyadic countersinging exchanges in the undefended spaces between established territories of black-capped chickadees (Poecile atricapillus). In each of 10 neighborhoods, we used stereo playback to simulate interactions between 2 unknown rivals. We simulated 2 types of song contests that differed only in the relative timing and patterning of the songs of the contestants; aggressive treatments contained frequency matching and song overlapping, whereas submissive treatments contained neither matching nor overlapping. We used a 16-microphone acoustic location system to record males in the neighborhood surrounding the playback apparatus. Territorial chickadees responded more intensely to the aggressive treatments than the submissive treatments. Neighborhood song output (number of songs produced by all individuals in the recording area) was twice as high after aggressive playback than after submissive playback. Males with territories bordering the playback apparatus had higher song output than males who were more than one territory removed from the playback apparatus. We did not find an influence of male dominance rank on playback responses. Our results reveal that territorial male chickadees eavesdrop on and respond to interactions occurring outside of their territory boundaries.

Long-term influence of simulated territorial intrusions on dawn and dusk singing in the Winter Wren: spring versus autumn

Males of many songbird species have peaks of singing activity at dawn and dusk. Singing during those twilight periods can function in territory proclamation, and males are suggested to adjust song output to the level of intruder pressure. We used song playback during the breeding season to simulate intrusions into territories of male Winter Wrens (Troglodytes troglodytes) shortly after dawn. We then compared male singing behaviour during the dawn and dusk chorus before and 1 day after the simulated intrusion. One day after the playback, male Wrens increased their song output before sunrise, which confirms our results from a previous study on dawn singing in autumn territories. At dusk, on the evening following the playback, males slightly increased song output after sunset, but singing activity at dusk was generally very low. We found no significant changes of song output after sunrise, before sunset, and between 2 days of control without playback. These results are consistent with the hypothesis that dawn and dusk singing is important for territory defence in spring. Unlike in autumn, however, increased singing in spring at dawn and dusk could also serve to defend other resources such as fertile mates or to strengthen the pair bond after a territorial challenge. In comparison with the results on autumnal singing, male Wrens started singing earlier at dawn during the breeding season, and they generally sang more songs at dawn and immediately after playback. The increase in absolute numbers of songs sung in the morning after playback seemed greater in spring than in autumn; however, the proportional increase relative to overall song output was similar in both seasons.

Josephine Lang: Her Life and Songs (review)

Reviewed by: Josephine Lang: Her Life and Songs Marie Sumner Lott Josephine Lang: Her Life and Songs. By Harald Krebs and Sharon Krebs. Oxford: Oxford University Press, 2007. [xiii, 308 p. ISBN-10: 0195173635; ISBN-13: 9780195173635. $45.] Music examples, illustrations, bibliographic references, appendices, index, compact disc. This latest book on the life and works of composer, singer, and pianist Josephine Lang contributes to a growing body of scholarship devoted to increasing awareness and appreciation of nearly forgotten artists. It will probably not surprise readers of Notes to hear that this woman composer, well known and revered in her time, has been written out of musical history since the onset of the twentieth century. This omission is slowly being corrected by the husband and wife team of Harald Krebs and Sharon Krebs, two formidable individual [End Page 278] researchers and performers, who accomplish together a significant feat in Josephine Lang: Her Life and Songs. The book is the result of several years of ongoing involvement with the documents of Lang's career, including her musical autographs, surviving letters between Lang and her colleagues and family members, published songs and piano pieces, and printed biographical studies from Lang's own time to the present. The study revisits the facts of Lang's life and career, adding some details that had previously been overlooked or suppressed, and provides many insightful commentaries on her artistic output. Illustrated throughout with copious music examples, the analysis provides a lively and engaging discussion of the composer's music. The authors also provide several essential tools for future investigators of Lang's music beyond their own text. An essential component of any reassessment of a marginalized composer is access to scores. Some of Lang's works were published in modern editions as part of the Women Composers Series edited by Judith Tick (Da Capo Press, 1982). To supplement this collection, many of the music examples in Josephine Lang provide full-length songs, and several other works are available online on a companion Web site hosted by the Württembergische Landesbibliothek Stuttgart (http://www .wlb-stuttgart.de/referate/musik/lang.html, accessed 22 August 2007). Unfortunately, whenever the site is mentioned in the book, an errant "%7Ewww/" is included in the address. (I found that omitting this typo led me to the correct site.) The Web site includes PDFs of nineteenth-century printed editions of several songs and a painstakingly detailed database of Lang's autographs. Harald Krebs has also edited a collection of songs by Lang forthcoming from Hildegard Publishing Company (Bryn Mawr, PA); when this collection is published, the majority of the songs discussed in the text will be easily available. The only other tool that one might request before launching into an investigation of an unknown composer and her works is a selection of well-performed recorded examples of the music, and by including a compact disc of thirty of Lang's songs discussed in the main text the Krebs provide just that. The captivating performances on the compact disc are a welcome addition to the discussion, even more helpful in this context, as they are rendered by the authors themselves (Sharon singing with Harald at the piano), lending special credence to their insights into Lang's works. Thus, the authors have created an entire collection of resources, appropriately packaged together, to allow the reader a comfortable entry into Lang's creative world. Having provided all the requisite tools, the authors advise the reader to keep in mind Lang's oft-repeated phrase, "my songs are my diary," and leap into the task at hand. The Krebs structure their work chronologically around Lang's biography, telling the story of her travails as a middle-class woman of weak constitution and pervasive bad luck and illustrating her emotional responses to her life with evidence from her song output. Chapter 1, "The Beginning of Josephine Lang's Compositional Career," covers her earliest musical experiences with her musician parents up to her first documented songs and her influential meeting with Felix Mendelssohn in 1830. From an early age, Lang's gift and charm led to some fame in her hometown of Munich. She performed in salons and for...

Digit ratios, secondary sexual characters and condition in barn swallows Hirundo rustica

The second and fourth digit length ratio (2D:4D) is sexually dimorphic in many vertebrates. This ratio has been suggested to provide an estimate of steroid levels encountered during prenatal development, which may have organizational consequences for physiology and behavior of adults. However, recent studies showed that the relation between digit ratio and steroids seems inconsistent and may vary among species and populations. We tested the hypothesis that digit ratios would be correlated with the expression of secondary sexual characters, using the barn swallow (Hirundo rustica) as a model system. This was done by testing whether variation in 2D:4D ratio was correlated with tail length and features of song, which are important secondary sexual characters positively correlated with circulating steroid concentration in adult birds. Furthermore, we examined the prediction that male and female digit ratios would correlate with body mass in an antagonistic way. There was no significant sexual dimorphism in digit ratio, which may be due to low levels of sexual selection in this population. Adult right 2D:4D ratio was negatively linked to tail length but not to male song output. Moreover, right 2D:4D ratio was negatively correlated with body mass in male and positively in females. These results are consistent with high digit ratios reflecting low levels of testosterone in this bird species. Key words: bird song, digit ratio, Hirundo rustica, morphology, secondary sexual characters. [Behav Ecol]

Inferring performance in the songs of dark-eyed juncos (Junco hyemalis)

Within bird species, songs differ in their attractiveness to females or effectiveness in male–male interactions. Some songs are more difficult to sing than others, and receivers may use a singer's performance of difficult songs as a means for evaluating the quality of the singer. The concept of song performance aims at quantifying how physiologically demanding are different songs. Using variation between song types of dark-eyed juncos, Junco hyemalis, we show that some song traits trade off with costly aspects of song output—short intervals between syllables or loud sound amplitude—suggesting that those traits are difficult to sing. First, after controlling for other traits, long syllables require longer intervals for recovery. This supports the idea that a measure of “respiratory performance” could be based on the relative lengths of syllables and intervals. Second, some syllable traits trade off strongly with sound amplitude, suggesting that these traits may be difficult to sing at high amplitudes. The ratio of frequency bandwidth and trill rate has been used to infer performance in other bird species, but we found no evidence that frequency bandwidth trades off with any aspect of song output in the junco. The negative association of bandwidth with trill rate may instead be a passive consequence of syllable length, with longer syllables randomly accumulating frequency modulation. We conclude that bird receivers may best evaluate how well a song is performed if they integrate multiple cues and discuss how researchers may similarly devise measures of song performance.

Reed bunting (Emberiza schoeniclus) males sing an 'all-clear' signal to their incubating females

AbstractWhile sexual functions of birdsong have been intensively investigated, non-sexual functions have received less attention. After pair formation males may sing to communicate with their established mates. Song aimed at incubating and feeding females could serve as an 'all-clear' signal, showing that there is no risk of predation and that it is safe for the female to exit the nest or to feed the young. Females should therefore preferentially leave nests when mates are singing nearby. Additionally, a vigilant male near the nest site could protect the brood from potential risks like predation and females could stay away longer for foraging. In this study, we investigated aspects of male singing activity of reed buntings (Emberiza schoeniclus) during incubation and feeding of nestlings after pair formation. Exits of incubating females from the nest occurred significantly more often than expected during male song output. When their mates were singing at high rates, females stayed away longer for incubation breaks. During the nestling period we found a high variation in male song output. Males that sang more fed their young significantly less. This suggests that time devoted to singing limits other activities such as feeding of offspring. Male reed buntings could choose different strategies for paternal investment: They either feed at high rates or they sing more to signal their vigilance. Another reason for this trade-off might be a conflict between paternal investment and territory defence or extrapair behaviour. However, even if male song after pairing has additional sexual functions, we suggest that non-sexually selected functions may be more common than expected.

Responses of a sub-oscine bird during playback: Effects of different song variants and breeding period

Vermilion flycatchers (Pyrocephalus rubinus) vary their song rate and song length across the breeding season. Males sing more and longer songs after nest construction than before. Here we explored the possibility that this variation is meaningful to territorial males. Using a playback approach, we tested several males with different variations in song output (i.e. variations in song length and song rate) in different periods of the breeding season (i.e. before and after the onset of nest construction). We found that males call more in response to playbacks of long and short songs before the onset of nest construction. However, after nest construction began they responded flying more when exposed to long songs than to short songs. These results show that vermilion flycatcher discriminates between different variants of song length, and suggest that males react to long songs as if they were more threatening signals than short songs, especially after the onset of nest construction. We did not find evidence of males discriminating between a high and a low song rate. We discuss some possible implications for song function in this sub-oscine species, and compare these findings with other results in oscine species.

Corn bunting (Miliaria calandra) males respond differently to alternating and overlapping playback of song

Interactive playback experiments were used to study the signal value to the corn bunting, Miliaria calandra, of alternating and overlapping singing. We subjected 15 males to two stimuli that differed in the temporal pattern of song playback (alternating or overlapping). We measured eight characteristics of the males’ response in two categories—song output and movements. Overlapping and alternating playback elicited a similar song response, characteristic of highly aroused males. Song response correlated positively with males’ singing activity before playback, irrespective of stimulus. There were significant differences between latency of approach to the loudspeaker and number of flights. Birds approached the loudspeaker more quickly and spent more time close to it when playback alternated with their songs. The results suggest overlapping song could be interpreted as a stronger threat but elicits a more cautious, rather than stronger, response than the alternating pattern. Males were found to shorten songs during the playback compared with songs sung before and after stimulation. The only predictor of degree of song shortening was song activity before the playback began. It should, therefore, be regarded as a signal which is related to escalated, close-distance counter-singing.

Early Rearing Conditions Affect the Development of Body Size and Song in Bengalese Finches

AbstractBirdsong is an acoustic ornament. According to indicator models, a trait must be costly to act as an honest signal, but the potential costs of elaborate songs are still poorly understood. The developmental stress hypothesis suggests that learned song characteristics could be an honest indicator of early developmental conditions because the brain structures associated with learning songs are susceptible to early developmental stress, which could thus affect song development. Unlike previous studies of developmental stress that examined the effect of a stress hormone or restricted nutrition, we observed Bengalese finches under semi‐natural breeding conditions in captivity to investigate the relationship between early rearing conditions (e.g., brood size and sex ratio) and the subsequent variation in body size and song among individuals. Our results suggest that the early rearing environment directly affects body size and song complexity, whereas song output is determined mainly by body size. These results support the developmental stress hypothesis. Moreover, our findings are the first to show that developmental condition affects not only the number of note types but also the syntactical complexity of the song.