Measures Of Song Complexity Research Articles

Experimentally elevated corticosterone increases song output and complexity in common mynas.

Vocalization is an important communication tool that can reflect many aspects of an individual's internal and external condition. This is especially true for birds. Previous research has shown that bird calls and songs change in response to a variety of potential stressors, although the extent and direction of the changes depend on the nature of the stressor and the environment. Circulating glucocorticoids, such as corticosterone, often increase in response to stressors and mediate some of the observed changes via alterations of the individual's physiological state. Acute elevations of corticosterone often occur as a physiological response to short-term stressors; however, the effects of this elevation on adult vocalizations have not been well documented. Here, we experimentally elevated corticosterone at two different levels using a noninvasive method and examined the effects on the vocal communication of male and female adult common mynas (Acridotheres tristis). Corticosterone elevation temporarily increased song output and some measures of song complexity, while call output decreased. These effects were dosage dependent (higher corticosterone levels had a stronger effect), most evident 40 min after ingestion, and some vocal changes were sex-specific. Future studies should investigate whether the changes in vocal performance due to elevated glucocorticoids have consequences for the birds' behavior, reproductive success, and survival.

Maturational changes in song sparrow song

Age‐related changes in the production of sexually selected assessment signals have been identified across a diverse range of taxa, and in some cases, these changes have been shown to affect receiver response to those signals. One important type of change occurs even after a signaler reaches breeding age, a phenomenon known as delayed maturation. Delayed maturation has been observed in the songs of several bird species, with potential fitness consequences for males as a byproduct of female choosiness or male competition. Here, we analyzed songs recorded across the first three years of life in a cohort of hand‐reared song sparrows Melospiza melodia to detect early‐life age‐related changes in song. We focused on three measures of song complexity, including within song type variation, the average number of notes and the number of unique note types for the most common variant of each song type, and five measures of song production patterns, including singing rate, time interval between songs within a bout of the same song type, time interval between bouts (i.e. when the song type changes), within‐song stereotypy and between‐song consistency. All measures of song complexity and most measures of song production patterns (excluding within‐song stereotypy) changed significantly within individuals as birds aged from one to two years as well as from one to three years (excluding within‐bout time interval), whereas no significant changes occurred from two to three years of age. Based on these features, a linear discriminant model could distinguish between the song of young (age 1) and older (age 2 and 3) adult males, providing support that song could serve as an indicator of age in this species. We discuss potential implications of these results for mate choice and male–male competition in song sparrows.

Early life nutritional stress affects song learning but not underlying neural circuitry in zebra finches.

Early life stress negatively impacts behavior and underlying neural circuitry across species. The present study investigated the effects of nutritional stress (NS), which increases parental foraging, on song quality in males, song preferences in females, and the size and number of cells in song and auditory regions of the zebra finch brain. We hypothesized that NS would decrease song quality in males and decrease preference for high quality song in females. Furthermore, we predicted that NS would reduce the size of song nuclei and decrease the number of cells in song and auditory regions. In males, NS decreased the number of syllable types (a measure of song complexity), decreased the number of high notes and flat notes, and increased the number of noisy notes, but had no effect on song rate or song length. In females, NS reduced preferences for high quality song. Despite these behavioral effects, there were no effects of NS on song and auditory nuclei, although there were effects of age and sex. These results suggest that NS affects behavior in both males and females, but these effects are not attributable to the number of cells or size of song and auditory regions. Such findings add to our understanding of the effects of early life stress on behavior and cognition. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Relationships between repertoire size and organization of song bouts in the Grey-crowned Warbler (Seicercus tephrocephalus)

The complexity of bird song could serve as an indicator of male quality. Repertoire size is a widely used measure of song complexity. However, little is known about the influence of repertoire size on the song sequencing patterns. At the same time, individual variability of song sequencing and its relation to repertoire size could be important for intraspecific communication. It is unlikely for an individual to count and compare full repertoires. Instead, they are more likely to rely on patterns of song performance. I analyzed the intraspecific variability in the song sequencing and its relation to the repertoire size in the Grey-crowned Warbler (Seicercus tephrocephalus). Advertising vocalization of males with larger repertoires turned out to be more determined and predictable than of the males with smaller repertoires. This pattern might reflect different learning abilities of males with different repertoire sizes. Learning abilities, in turn, might reflect male quality and/or age. However, these patterns could not be evaluated by analyzing short song sessions and it is very unlikely for other individuals to estimate them. However, these patterns influenced the other parameters of song organisation which could be estimated from short song sessions (such as versatility and song switching rate). Thus, for other individuals the latter may serve as an indicator of a male’s repertoire size.

Multiple song features are related to paternal effort in common nightingales.

BackgroundSexual ornamentation may be related to the degree of paternal care and the ‘good-parent’ model predicts that male secondary characters honestly advertise paternal investment. In most birds, males are involved in bringing up the young and successful reproduction highly depends on male contribution during breeding. In passerines, male song is indicative of male attributes and for few species it has been shown that song features also signal paternal investment to females. Males of nightingales Luscinia megarhynchos are famous for their elaborate singing but so far there is only little knowledge on the role of male song in intersexual communication, and it is unknown whether male song predicts male parenting abilities.ResultsUsing RFID technology to record male feeding visits to the nest, we found that nightingale males substantially contribute to chick feeding. Also, we analyzed male nocturnal song with focus on song features that have been shown to signal male quality before. We found that several song features, namely measures of song complexity and song sequencing, were correlated with male feeding rates. Moreover, the combination of these song features had strong predictive power for male contribution to nestling feeding.ConclusionsSince male nightingales are involved in chick rearing, paternal investment might be a crucial variable for female mate choice in this species. Females may assess future paternal care on the basis of song features identified in our study and thus these features may have evolved to signal direct benefits to females. Additionally we underline the importance of multiple acoustic cues for female mating decisions especially in species with complex song such as the nightingale.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0390-5) contains supplementary material, which is available to authorized users.

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.

Comparative Analyses of Song Complexity and Song-Control Nuclei in Fourteen Oscine Species

Most studies on the relationship between measures of song behavior and the sizes of song control nuclei have focused on one or two oscine species, and often show inconsistent results. To address this issue, we first measured four variables for song complexity, i.e., song repertoire size, syllable repertoire size, the mean number of syllables per phrase (MNS) and the number of syllables in the longest phrase (NSLP), and the sizes of three song control nuclei, i.e., HVC, RA (the robust nucleus of the arcopallium), and Area X in 14 oscine species from eight families. To tackle the problem of statistical non-independence that probably existed among the closely related species, we reconstructed the phylogeny of the species studied using mitochondrial cytochrome b DNA sequences from GenBank. By using the methods adopted in most previous reports, we tested the relationship between song complexity and the sizes of the song control nuclei. We found that: 1) the absolute sizes of RA and Area X, but not of HVC, were positively correlated to the three measures of song complexity, but that only the residual size of RA in regard to telencephalon size was significantly correlated to the song measures; 2) independent contrasts analysis showed RA and Area X to be significantly associated with NSLP. Our results indicated that the relationship between song behavior and its neural structures varied among song nuclei, suggesting that each song control nucleus may play a different role in song behavior.

Estimating the complexity of bird song by using capture-recapture approaches from community ecology

Repertoire size, the number of unique song or syllable types in the repertoire, is a widely used measure of song complexity in birds, but it is difficult to calculate this exactly in species with large repertoires. A new method of repertoire size estimation applies species richness estimation procedures from community ecology, but such capture-recapture approaches have not been much tested. Here, we establish standardized sampling schemes and estimation procedures using capture-recapture models for syllable repertoires from 18 bird species, and suggest how these may be used to tackle problems of repertoire estimation. Different models, with different assumptions regarding the heterogeneity of the use of syllable types, performed best for different species with different song organizations. For most species, models assuming heterogeneous probability of occurrence of syllables (so-called detection probability) were selected due to the presence of both rare and frequent syllables. Capture-recapture estimates of syllable repertoire size from our small sample did not differ significantly from previous estimates using larger samples of count data. However, the enumeration of syllables in 15 songs yielded significantly lower estimates than previous reports. Hence, heterogeneity in detection probability of syllables should be addressed when estimating repertoire size. This is neglected using simple enumeration procedures, but is taken into account when repertoire size is estimated by appropriate capture-recapture models adjusted for species-specific song organization characteristics. We suggest that such approaches, in combination with standardized sampling, should be applied in species with potentially large repertoire size. On the other hand, in species with small repertoire size and homogenous syllable usage, enumerations may be satisfactory. Although researchers often use repertoire size as a measure of song complexity, listeners to songs are unlikely to count entire repertoires and they may rely on other cues, such as syllable detection probability.

Extrapair paternity and the evolution of bird song

Bird song is usually considered to have evolved in the context of sexual selection. Because extrapair paternity is a major component of sexual selection, mating advantages at the social level for males that produce songs of high quality may be transformed into higher success in extrapair paternity. Therefore, males with longer and more complex songs should suffer less from extrapair paternity intraspecifically, whereas species with high rates of extrapair paternity, reflecting intense sperm competition, should produce more elaborate songs. Although some intraspecific studies demonstrated a negative link between features of songs and extrapair paternity in own nest, others failed to detect such a relationship. Contrary to expectation, a metaanalysis of all studies revealed no significant intraspecific evidence for songs being associated with extrapair paternity. In addition, in comparative analyses based on generalized least squares (GLS) models, we found that no measures of song complexity and temporal output were significantly related to extrapair paternity interspecifically, even when potentially confounding factors such as social mating system, life history, migration, habitat, or sexual dichromatism were held constant. Only plumage dichromatism was significantly related to extrapair paternity. The absence of both intra- and interspecific relationships between measures of song variability and extrapair paternity suggests that factors other than postmating sexual selection have been the important evolutionary forces shaping differences in song. Key words: bird song, evolution, extrapair paternity, generalized least squares, meta-analysis, repertoire size, sexual selection. [Behav Ecol 15:508–519 (2004)]

Song as an indicator of male parental effort in the sedge warbler.

Repertoire size has been found to be a sexually selected trait in a number of bird species, although the advantages of mating with a male who possesses a complex song remain unclear. We studied the potential role of song as an indicator of male parental effort in the sedge warbler Acrocephalus schoenobaenus. The male provisioning rate was used as a measure of male parental effort and was found to increase with nestling age and brood size. When controlling for chick age, brood size and other variables, we found a highly significant positive correlation between a measure of song complexity (repertoire size) and male parental effort. Both male parental effort and repertoire size were found to be positively correlated with chick weight when controlling for chick age. We found no correlation between a measure of song output (amount of song flighting) or territory size and parental effort. Repertoire size is known to be the most important cue in female choice amongst sedge warblers and we discuss the possible reasons for this. We suggest that, in choosing a male with a large repertoire, a female obtains not only indirect benefits but also direct benefits in the form of increased parental effort.

Song Similarity in Populations of Fox Sparrows: A Rejection of Naugler's and Smith's Conclusions

Naugler and Smith (1991) used data on song in Fox Sparrows (Passerella iliaca) to test hypotheses about the evolution of the structure of song in insular avian populations. Their conclusions are incorrect for a host of reasons. The authors appear to have misused or ignored information within the references they cite and they appear to have relied on second-party assessments (Miller 1982) of data within these references. It will become clear that the review process for this manuscript failed in its assessment of the manuscript's accuracy and its contribution to ornithology. Naugler and Smith presented two hypotheses concerning possible effects of insularity on song complexity: (1) The song complexity hypothesis predicts song in insular populations may become more complex than mainland populations due to weaker selective pressures resulting from reduced interspecific constraints (competitive release ?). (2) The founder effect hypothesis predicts song complexity may be less in insular than mainland populations if a develops during the founding of the population. A bottleneck would result in an incomplete sampling of mainland song complexity, thus, exposing future generations to a depauperate species specific auditory field from which to model song. Following the procedures for measuring song complexity presented by Miller (1982), Naugler and Smith generated statistics for four measures of song complexity from their study population of migratory Fox Sparrows on Bon Portage Island, Nova Scotia. These were: (1) size of song repertoire (number of structurally distinct song units sung by an individual), (2) number of syllables/song, (3) number of syllable types/song, and (4) syllable diversity [number of different syllables (syllable types) in a song/total number of syllables in a song]. They then tested the two hypotheses by comparing their statistics with what they assumed to be similar statistics they or Miller (1982) generated from two other non-isolated Fox Sparrow populations reported on by Martin (1977, 1979) and Blacquiere (1979). In brief, these comparisons led them to conclude that song complexity was less in the Bon Portage population and that this condition resulted from a bottleneck ef-