Statistical and Prosodic Cues for Song Segmentation Learning by Bengalese Finches (Lonchura striata var. domestica)

Juvenile songbirds learn their songs from adults. Birds do not simply learn songs verbatim but they sometimes learn parts of songs from multiple tutors and recombine these into one song sequence. How they segment a particular part and select that as a chunk and how these chunks are recombined are interesting questions to ask, because such segmentation and chunking is also considered to be a basic mechanism in human language acquisition. The song of the Bengalese finch has a complex syntax with variable note‐to‐note transition probabilities and could thus be suitable for the study of segmentation and chunking in birdsong. Thirty‐two male Bengalese finch chicks were reared in a large aviary where 11 adult tutors and 10 adult females were breeding freely. In this environment most male chicks learned songs from several tutors. The song note‐chunks that juveniles copied had higher transition probabilities and shorter silent intervals than did the boundaries of the chunks, suggesting that Bengalese finches segment songs using both statistical and prosodic cues. Thus, the Bengalese finch could prove to be an excellent model in which to study neural and behavioral mechanism for sound segmentation.     

Conspecific-only experience during development reduces the strength of heterospecific song discrimination in Zebra Finches (Taeniopygia guttata): a test of the optimal acceptance threshold hypothesis

Conspecifics during development provide the most reliable sensory cues for species recognition in parental bird species. The Zebra Finch (Taeniopygia guttata) is a sexually dimorphic model species used for investigations of the behavioural cues and neurobiological substrates of species recognition. Regarding acoustic conspecific cues, theory predicts that exposure to both con- and heterospecific vocalisations and other environmental sounds results in more accurate auditory species discrimination, because diverse vocal cues during development shift optimal conspecific acceptance thresholds to be more restrictive to yield fewer acceptance errors. We tested the behavioural preferences of female and male Zebra Finches raised in an outdoor environment (Control) and female and male Zebra Finches reared in an indoor colony with exposure to Zebra Finches only (Restricted), to playbacks of songs of Zebra Finches, Zebra Finches cross-fostered by Bengalese Finches (Lonchura striata var. domestica), and Bengalese Finches. Several behavioural measures revealed minimal sexual dimorphism in discrimination but showed that Control subjects preferred conspecifics’ songs over either the songs of cross-fostered Zebra Finches or Bengalese Finches. Restricted Zebra Finches in contrast did not discriminate behaviourally between the three song types. These results support the concept of a shift in the species acceptance threshold in the restricted treatment resulting in more acceptance errors. We discuss future work to test the role of exposure to diverse vocal cues of both con- and heterospecifics in the ontogeny of song perception in this important laboratory model species for social recognition research.     

Song preference of female Bengalese finches as measured by operant conditioning

Male songbirds approach females by using their songs. Knowing what females perceive and prefer in male songs is an important aspect of understanding courtship behavior. Male Bengalese finches (Lonchura striata var. domestica) sing complex sequence patterns with their own variety of elements. We tested female preference with phonologically different songs and sequentially different songs using an operant selection task. In the first experiment we presented the father’s song and an unfamiliar song that were phonologically different. Females clearly preferred the father’s song over a novel song. In the second experiment, we used the father’s song and its element order reversed song to test female preference for the difference in element sequence. In the third experiment, we presented different sequence complexity songs edited from the same unfamiliar song elements to test female preference for complex sequence. Females did not show a significant preference in either the second or third experiment. Results show that female Bengalese finches discriminated the difference in song elements, preferred familiar songs, and did not show preference for difference of sequence. This study did not support evidence that female Bengalese finches prefer a complex sequence. However, in future research, we should carefully investigate female preference for choosing mates in a natural context.     

Vorbildwahl in der Gesangsentwicklung beim Japanischen Mövchen (Loncbura striata var. domestica,Estrildidae)

Birds which must learn their species-specific song need a means for choosing the appropriate song model. As individual Bengalese Finch ♂♂ have distinctive songs and song elements it is possible to determine a juvenile's choice of song models from within a restricted population. The results suggest that after an early period of learning from several models, juveniles preferentially copy the song of their father.     

Intra‐specific variance in sperm morphometry: a comparison between wild and domesticated Zebra Finches Taeniopygia guttata

The Zebra Finch Taeniopygia guttata is a model bird species for the experimental study of behavioural and evolutionary concepts in captivity and especially sexual selection. The validity of sexual selection studies of domesticated birds is of long‐standing concern as little is known about the influence of domestication on sexually selected traits. Most domesticated Zebra Finch populations are maintained under a strict breeding regime to avoid potential inbreeding. However, these breeding regimes may interfere with the processes of sexual selection and influence the evolution of sexually selected traits because they may limit or prohibit active mate choice. Here, we investigated the potential impact of a monogamous breeding scheme in a domesticated population in which active mate choice is largely inhibited, on the evolution of sperm morphometry as a sexually selected trait. We compared sperm morphometric traits (total sperm length and length of sperm head, midpiece and flagellum), and the variance thereof, between a domesticated and two wild Zebra Finch populations. Although we found significant differences between the three populations for certain sperm traits (head length, midpiece length), which may be of importance in postcopulatory sexual selection, overall, variance in sperm morphometry did not differ between the domesticated and the wild Zebra Finch populations. Our results validate the use of domesticated Zebra Finches for further studies of postcopulatory sexual selection and sperm competition.     

Imitation and Invention in Song Learning in Nightingales (Luscinia megarhynchos B., Turdidae)

Song learning in oscine birds is often defined solely as a process of song imitation; nonetheless, not all songs produced by laboratory‐tutored birds are imitations of the model songs. If song learning were strictly a process of imitation, these non‐imitated songs (inventions) would be expected to contain no learned attributes. To determine whether species‐typical song attributes can be learned in the absence of imitation, we compared the imitations and inventions of laboratory‐tutored nightingales (Luscinia megarhynchos B.) with the songs of wild nightingales and the songs of laboratory‐reared, untutored nightingales. The species‐typical song attribute measured was stereotypy. We quantified stereotypy by four variables: (1) percentage of notes shared between two renditions of the same song type (2) difference in repetition rates of the same trill in two renditions of the same song type (3) acoustic similarity of the same note in two renditions of the same song type, and (4) acoustic similarity of the same note repeated within a trill. Wild songs and imitated songs were significantly more stereotypical than the songs of untutored birds for all measures. For the percentage of notes shared (1), and the acoustic similarity of notes in two renditions of the same song type (3), invented songs did not differ from the songs of untutored birds, suggesting that imitation is necessary for the acquisition of these song characteristics. However, invented songs were significantly more stereotypical than the songs of untutored birds for measures of stereotypy related to trills (2 and 4), and neither imitated nor invented songs differed significantly from the songs of wild birds in terms of trill rate stereotypy (2). Thus, it appears that the process of learning to produce trills may differ from the process of learning non‐repetitive song components: increased stereotypy in trills occurs even when the trills themselves are not copied from song models. Strict imitation does not fully account for the acquisition of some learned song attributes.     

Song Learning in Bengalese Finches: a Comparison with Zebra Finches

Male Bengalese finches, Lonchura striata var. domestica, learn their song from an adult male conspecific with whom they can interact at 35 to 70 days of age and normally-raised males fail to reproduce song which they have only heard before or after this time. Birds which have been raised by their mother alone and those which have been deprived of a song tutor during the learning phase produce abnormal songs with indistinct elements and little or no phrase structure; this is typical of males which fail to hear adult song during their development. These songs are unstable and are replaced by normal songs, if there is an opportunity to learn from an adult male conspecific. Presumably, this flexibility in the time when young males learn acts as a safeguard to ensure that normal conspecific song is produced. These results bear striking similarity to those on zebra finch song development. Differences between the two species, especially in the learning of call notes by female zebra finches, are discussed.     

Diet and birdsong: short‐term nutritional enrichment improves songs of adult Bengalese finch males

Song is a notable sexual signal of birds, and serves as an honest indicator of male quality. Condition dependence of birdsong has been well examined from the viewpoint of the developmental stress hypothesis, which posits that complex songs assure fitness because learned acoustic features of songs are especially susceptible to early‐life stress that young birds experience in song learning periods. The effect of early stress on song phenotypes should be crucial, especially in age‐limited song learners which sing stereotyped songs throughout life. However, little attention has been paid to non‐learned song features that can change plastically even in adulthood of age‐limited song‐learners. Although it has been shown that food availability affects song rate in wild songbirds, there is limited evidence of the link between favorable nutritional conditions and song phenotypes other than song rate. Under the prediction that singing behavior reflects an individual's recent life history, we kept adult Bengalese finch males under high‐nutrition or normal diet for a short term, and examined changes in body mass and songs. We found that birds on a high‐nutrition diet showed higher song output (e.g. song rate and length) compared with those of the control group, while changes in body mass were moderate. In addition, note repertoire became more consistent and temporal structures got faster in both nutrition and control groups, which indicates that songs were subject to other factors than nutrition. Considering that female estrildid finches, including Bengalese and zebra finches, show a preference toward complex songs as well as longer songs and higher song rate, it is plausible that different aspects of singing behavior signal different male qualities, and provide multifaceted clues to females that choose mates.     

Age‐dependent song changes in a closed‐ended vocal learner: elevation of song performance after song crystallization

Birdsong is a sexual signal that serves as an indicator of male quality. There is already abundant evidence that song elaboration reflects early life‐history because early developmental stress affects neural development of song control systems, and leaves irreversible adverse effects on song phenotypes. Especially in closed‐ended vocal learners, song features crystallized early in life are less subject to changes in adulthood. This is why less attention has been paid to lifelong song changes in closed‐ended learners. However, in the eyes of female birds that gain benefits from choosing mates based on male songs, not only past but also current conditions encoded in songs would be meaningful, given that even crystallized songs in closed‐ended learners would not be identical in the long term. In this study, we examine within‐individual song changes in the Java sparrow Lonchura oryzivora, with the aim of shedding light on the relationship between song and long‐term life history. Specifically, we compared song length, tempo, and song complexity measures between the point just after song crystallization and around 1 yr later, and also compared those traits between fathers and sons to clarify the effect of vocal learning. While it is not surprising that song complexity did not differ depending on age or between fathers and sons, we found that song length and tempo increased with age. Follow‐up analyses have revealed that frequency bandwidth and peak frequency of song notes also elevated with age. Our results show that song performance related to motor skills can be improved even after song crystallization. We also suggest that song performance in closed‐ended vocal learners gives a reliable clue for mate choice by reflecting male quality with aging.     

Phonology and Geographic Song Discrimination in Song Sparrows

We investigated whether song sparrows discriminate foreign from local songs using specific phonologic markers, a mechanism of geographic discrimination previously described for some other songbirds. Song sparrows from Linesville, Pennsylvania (PA) respond more strongly to local songs than to songs from Millbrook, New York (NY). We identify 61 note categories in PA and NY songs, of which 13 are unique to PA, 17 are unique to NY, and 31 are shared. The most common note category in PA song, ‘buzz BO5’, is present in 89% of PA songs and only in 8% of NY songs; this difference in percentage representation is the largest we found for any note category. Substituting this potential PA marker into NY songs, however, did not make those songs more salient to PA sparrows; instead, PA males tested with territorial playback responded significantly less aggressively to NY/PA hybrid songs than to NY songs. A series of control experiments showed that song sparrows do not detect substitution of PA notes into PA songs or of NY notes into NY songs. The results weigh against the hypothesis that geographic discrimination in song sparrows is accomplished simply by recognition of a small number of phonologic markers.     

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

Birdsong 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.     

Sex differences in the telencephalic song control circuitry in Bengalese finches (Lonchura striata var. domestica)

Bengalese finches, Lonchura striata, are extremely sexually dimorphic in their singing behavior; males sing complex songs, whereas females do not sing at all. This study describes the developmental differentiation of the brain song system in Bengalese finches. Nissl staining was used to measure the volumes of four telencephalic song nuclei: Area X, HVC, the robust nucleus of the arcopallium (RA), and the lateral portion of the magnocellular nucleus of the anterior nidopallium (LMAN). In juveniles (circa 35 days old), Area X and the HVC were well developed in males, while they were absent or not discernable in females. The RA was much larger in males but barely discernable in females. In males, the volumes of Area X and the RA increased further into adulthood, but that of the HVC remained unchanged. The LMAN volume was greater in juveniles than in adults, and there was no difference in the LMAN volume between the sexes. The overall tendency was similar to that described in zebra finches, except for the volume of the RA, where the degree of sexual dimorphism is larger and the timing of differentiation occurs earlier in Bengalese finches. Motor learning of the song continues until day 90 in zebra finches, but up to day 120 in Bengalese finches. Earlier neural differentiation and a longer learning period in Bengalese finches compared with zebra finches may be related to the more elaborate song structures of Bengalese finches.     

The Influence of Song Mode on Responses of Male American Redstarts

Male American redstarts (Setophaga ruticilla) exhibit two modes of singing: repeat and serial mode. Repeat mode consists of repetitions of a single song type, usually one possessing an accented terminal note. Serial mode is constituted by a series of different songs with unaccented terminal notes, sung in a versatile sequence. Different authors have observed that males discriminate between these two modes. In the experiments reported in this paper, we tested whether males use accented terminal notes, song versatility or both to discriminate between the two song modes. We observed that males responded more intensively to the accented song. The accented note seems a very important song characteristic for evoking male American redstart responses. In contrast, males did not show any difference in their response to single and varied serial songs.     

Limited Inter‐Annual Song Variation in the Serin (Serinus serinus)

Patterns of song plasticity in passerine birds beyond the first year are poorly studied. In general, songbirds are divided into two categories: open‐ended learners and closed‐ended learners, depending on the pattern of age‐related vocal plasticity. However, recent work based on longitudinal studies revealed a broader range of flexibility of song changes in adulthood. Serins sing very complex songs with large repertoires which are delivered in a very rigid way with little structural modification. However, there is little information on how serin song changes with age. We studied vocal plasticity in wild adult serins by recording male song over 2 years. The analyses show that male songs have only limited variation between years, with no increase in repertoire size and relatively small changes in their structural characteristics. Syllable production was very consistent within and between years with very little structural variation. New syllables represented only 8% of the repertoire, and they appeared to emerge from fusion or splitting of pre‐existing syllables. We conclude that serin song while structurally complex has a very limited age‐related plasticity after the first year. We hypothesise that this structural stability is a consequence of selection for performance consistency.     

Song learning in montane white-crowned sparrows: from whom and when

White-crowned sparrow, Zonotrichia leucophrys, adults and nestlings were colour-banded and songs of mature progeny recorded to determine whether songs were learned from fathers, age peers or adults other than fathers. Four out of 17 sons and daughters sang the same song types as their fathers, indicating that transmission of song from fathers to their young (vertical transmission) is not the norm. Since juveniles do not sing full (‘crystallized’) songs until they are older, transmission from juvenile to juvenile (horizontal) is unlikely on the breeding grounds but may occur if siblings migrate together and hear each other's song on the wintering grounds. The usual mode of transmission is via other adults (oblique). Birds learn one or two songs prior to or during migration, and upon settling on the breeding area the following year may utter only one theme, that which matches the neighbours' songs during matched countersinging bouts. A bird's song dialect is thus not necessarily an indicator of its birthplace. One wild and one laboratory-reared bird sang songs of a Lincoln sparrow, Melospiza lincolnii, and a strawberry finch, Amandava amandava, respectively. These data and data from field playback studies lend support to the notion that interspecific terrioriality may lead to acquisition of alien song for use in matched countersinging during territorial encounters with allospecific neighbours.     

The Role of Song Phonology and Syntax in Vocal Learning Preferences in the Song Sparrow,Melospiza melodia

Are young songbirds ready to learn virtually any song, or are they predisposed to learn songs of their own species? To explore this question tests were conducted on the equipotentiality of auditory song learning stimuli in the song sparrow. 23 males reared as nestlings were exposed to tape recordings of their own and other species songs in early life and subsequent song production was analyzed for imitations. Birds exposed to natural song sparrow songs, including their fathers', and equal numbers of swamp sparrow songs, strongly preferred conspecific songs. They neither favored nor eschewed paternal songs despite having had access to them for 6–10 days as nestlings. In three other experiments synthetic songs were used in which some properties were held constant and others were systematically varied. Birds were exposed to 1–4 segmented songs varying in phrase order, tempo and syllable number, each synthesized in two versions, one from conspecific and the other from heterospecific (swamp sparrow) song syllables. With one-segmented songs (alien syntax) subjects favored conspecific over heterospecific syllable songs. Heterospecific syllables were rendered more acceptable by incorporation into two-segmented trilled songs (more song sparrow-like syntax). Heterogeneous summation of phonological and syntactical cues appeared to occur. There was also evidence of interaction between phonology and syntax. When another phrase type, the note complex, was added, in three- and four-segmented songs, a preference for conspecific syllables reappeared. Heterospecific syllables may be more readily accepted as a trilled sequence than without repetition, as in a note-complex. When phrase structure within four-segmented songs was varied, birds favored patterns most like normal conspecific song. We conclude that there are innate learning preferences in the song sparrow, based on note and syllabic structure (phonology and syllabic syntax), and temporal organization of phrases (segmental syntax), differing from those of the closely related swamp sparrow, Melospiza georgiana, in which song syntax plays no role in learning preferences.     

Sex Differences in the Song of <Emphasis Type="Italic">Indri indri</Emphasis>

In some primate species, males and females within a social group emit loud calls in a coordinated manner or chorus. Indri indri emits a very conspicuous loud call that elicits the loud calls of neighboring groups. Previous investigations have hypothesized that the main functions of the indri chorus are related to territorial announcement, intergroup avoidance, and group cohesion. We investigated sex differences in indri song. We recorded and analysed songs given by 10 different groups over 160 d. Overall singing duration did not vary between the sexes. However, males emitted significantly fewer but longer notes. Adult males and females of each group participated in the song with sex-specific repertoires. Females had a song repertoire of 8 note types; males shared all of their 6 notes with females. Apart from the initial roars, in all note types shared by both sexes, male notes were significantly longer than female ones, whereas variations in frequency parameters differed according to the note type. These findings suggest that indri song may provide cues to conspecifics, such as group size and sex composition, which could influence interactions between groups.     

Is the Tonal Quality of Birdsong Learned? Evidence from Song Sparrows

Song sparrow (Melospiza melodia) songs are composed largely of pure-tonal sounds. This paper investigates the role that learning plays in the development of the tonal structure of song sparrow songs, as well as the role that tonal quality plays in determining the suitability of songs as models for learning. 20 birds were trained with both normal pure-tonal songs and modified songs that included harmonic overtones. The harmonic-modified songs were obtained from birds singing in a helium atmosphere, the result of which is to perturb vocal tract resonances and thus alter a song's tonal quality. Subjects learned equally well from normal and harmonic models. Birds that learned material from harmonic models reproduced some of this material with harmonic overtones, but the majority of notes learned from harmonic models were subsequently reproduced as pure-tonal copies. Thus, the tonal structure of songs does not influence young song sparrows in their selection of song models, but there is a strong tendency to reproduce songs in a pure-tonal fashion, even if learned from harmonic models.