Song Frequency Research Articles

さえずり頻度の時間的変異を考慮したヨタカの効率的な生息調査法

さえずり頻度の時間的変異を考慮したヨタカの効率的な生息調査法

Do birds vocalize at higher pitch in noise, or is it a matter of measurement?

Studies have found that some birds use vocalizations with higher minimum frequency in noisy areas. Minimum frequency is often measured by visual inspection of spectrograms (“by-eye practice” (BEP)), which is prone to bias, e.g., if low-frequency components are masked by noise. We tested for this bias by comparing measurements of minimum frequency obtained with the BEP for the same set of red-winged blackbird vocalizations (songs and two call types “checks” and “cheers”) played back under ambient, medium, and high noise conditions using a dual playback experiment where both vocalizations and noise were introduced. We compared BEP measurements to those obtained from power spectrum analyses using a preset amplitude threshold (“threshold method” (TM)). The BEP was biased when measuring the minimum frequencies of songs and checks, which are masked by noise, but not when measuring cheers, which are higher pitched and thus not masked. Measures using the TM were not affected by noise, but this method may fail to identify the vocalizations’ lowest frequency if noise necessitates a low (i.e., conservative) threshold. Using the BEP, we also found a bias toward shorter-duration measurements for songs in increasing noise, and for checks, a bias toward increased measures of an energy distribution parameter (Freq5%), likely in correlation with increased measured minimum frequency. Measures taken from the unmasked cheers were similar regardless of the technique used. We discuss limitations of each approach and encourage the use of the TM, as studies using the BEP may lead to spurious results. Noise from human activities is ubiquitous. Researchers have found that some birds vocalize at higher frequency (pitch) in noise, hypothesizing that this may improve signal detection in low-frequency noise. Noise may also hinder detection of signal components by researchers using the most common measurement technique (the BEP), which may be mistaken for increasing frequency. To examine this bias, we conducted a dual playback experiment, in which we broadcast the same vocalizations at three background noise levels. We found that BEP measures of minimum frequency increased with increasing noise even though the vocalizations did not change. We recommend the TM which yielded similar measures across noise levels, although it excluded some lower-frequency elements included by the BEP. We encourage researchers to use the TM over the BEP and to validate their methods across noise levels of interest.

The effect of aircraft noise on bird song

In general, it has been found that birds respond to exposure of anthropogenic noise by singing at a higher frequency range. This is presumably the result of an attempt by the birds to reduce the masking effect of the low rumble of urban noise. In sharp contrast, we report that chiffchaffs reduce song frequency at airports where noise levels are intermittent rather than constant, but at a much higher amplitude level. In addition, we show experimentally that airport birds respond more aggressively to playback of airport songs than the control songs, while a nearby control population does not discriminate between airport and control songs. Potential explanations for these results will be discussed.

Does the Song of the WrenTroglodytes troglodytesChange with Different Environmental Sounds?

Abstract. Birds inhabiting urban areas have to deal with high levels of ambient noise. Some species show a certain song flexibility that enables them to reduce noise interferences in their communications. This vocal adjustment usually implies an increase in the minimum frequencies of songs. Since urban noise is mainly made up of low frequencies (about 2.5–3.5 kHz), song of species that sing at higher frequencies could be less susceptible to being masked by anthropogenic noise. This study explores whether such species also show any kind of adjustment to noisy environments. For this purpose, the spectral and temporal parameters (note duration, maximum and minimum frequency and diversity) of the song of the European Wren Troglodytes troglodytes were analysed in three different environments (urban, periurban and rural). To evaluate the impact of noise on the vocalizations, a specific acoustic descriptor of song variability was developed. Song variability increased along the urban noise gradient from rural to ...

Stay tuned: active amplification tunes tree cricket ears to track temperature-dependent song frequency.

Tree cricket males produce tonal songs, used for mate attraction and male-male interactions. Active mechanics tunes hearing to conspecific song frequency. However, tree cricket song frequency increases with temperature, presenting a problem for tuned listeners. We show that the actively amplified frequency increases with temperature, thus shifting mechanical and neuronal auditory tuning to maintain a match with conspecific song frequency. Active auditory processes are known from several taxa, but their adaptive function has rarely been demonstrated. We show that tree crickets harness active processes to ensure that auditory tuning remains matched to conspecific song frequency, despite changing environmental conditions and signal characteristics. Adaptive tuning allows tree crickets to selectively detect potential mates or rivals over large distances and is likely to bestow a strong selective advantage by reducing mate-finding effort and facilitating intermale interactions.

Nesting Behaviour and Reproductive Success of Sprague’s Pipit (<i>Anthus spragueii</i>) and Vesper Sparrow (<i>Pooecetes gramineus</i>) during Pipeline Construction

Industrial activity occurs in the breeding habitat of several species at risk, including the federally threatened Sprague’s Pipit (Anthus spragueii). To evaluate whether oil pipeline construction reduces the productivity of this species, we examined (a) noise levels in relation to distance from the pipeline right-of-way (ROW), (b) the extent to which noise and song frequencies overlapped, (c) the distribution of Sprague’s Pipit nests relative to the ROW, and (d) Sprague’s Pipit reproductive success during exposure to pipeline construction and clean-up activity. We also examined the songs, nest locations, and reproductive success of the Vesper Sparrow (Pooecetes gramineus) for comparison. Study plots (400 × 400 m, n = 30) were established in grassland adjacent to the pipeline ROW or 600 m away from the ROW in similar habitat. Mean maximum noise levels during pipeline activity included frequencies that overlapped the song range of both species and were louder than the recommended 49 dB threshold up to 250 m from the ROW. Sprague’s Pipit nests were evenly distributed across close and distant plots, whereas Vesper Sparrow nests were more abundant within 50 m of the ROW. Sprague’s Pipit daily nest survival rate and the number of young surviving to day 8 both increased with increasing distance from the ROW; and Vesper Sparrow daily nest survival decreased slightly with exposure to pipeline activities. Our findings validate the restricted activity period and indicate that the recommended setback distance of 350 m is a reasonable guideline for pipeline projects.

No Effect of Body Size on the Frequency of Calling and Courtship Song in the Two-Spotted Cricket, Gryllus bimaculatus.

The relationship between body size and vocalization parameters has been studied in many animal species. In insect species, however, the effect of body size on song frequency has remained unclear. Here we analyzed the effect of body size on the frequency spectra of mating songs produced by the two-spotted cricket, Gryllus bimaculatus. We recorded the calling songs and courtship songs of male crickets of different body sizes. The calling songs contained a frequency component that peaked at 5.7 kHz. On the other hand, courtship songs contained two frequency components that peaked at 5.8 and 14.7 kHz. The dominant frequency of each component in both the calling and courtship songs was constant regardless of body size. The size of the harp and mirror regions in the cricket forewings, which are the acoustic sources of the songs, correlated positively with body size. These findings suggest that the frequency contents of both the calling and courtship songs of the cricket are unaffected by whole body, harp, or mirror size.

Insularization effects on acoustic signals of 2 suboscine Amazonian birds

Environmental change may alter the communication systems of birds by imposing shifts in their acoustic signals. In tropical forests, vocally active species usually avoid overlapping signals in acoustic space by calling within narrow frequency ranges, whereas in forest islands a less saturated acoustic space may allow variation in acoustic signals. Some signals are also adapted to optimize its propagation in the prevailing habitat. Despite a growing understanding of what drives acoustic variation, it is unclear if human-induced insularization of natural landscapes can unleash alterations in avian communication systems. We investigated the variability of acoustic signal properties in 2 suboscines birds (Lipaugus vociferans and Tyranneutes virescens) in islands within an artificial lake created by the damming of the Uatuma River, in Brazilian Amazonia. We tested if signal variability was related to variation in acoustic community proxies (island area and isolation), and vegetation structure by surveying 13 variable-sized forest sites and 2 mainland continuous forest sites. Bandwidth variation in L. vociferans songs was related to island area and isolation (N = 67 inds), but these relationships were not observed in T. virescens songs (N = 69 inds). Additionally, the lowest and peak frequencies of songs of both species were higher in islands with greater tree basal area. In both species, temporal properties of songs were not associated with variation in island characteristics. Our study suggests that land-use changes may lead to alterations in particular traits of acoustic signals for species for which songs are innate.

Shifting song frequencies in response to anthropogenic noise: a meta-analysis on birds and anurans

Anthropogenic noise has been shown to alter the transmission environment and distort acoustic signals, prompting vocalizing species to use compensatory mechanisms. Through a meta-analysis we investigated the relative importance of biological and contextual factors predisposing species to shift their singing/calling frequencies in response to anthropogenic noise. We gathered data from 36 studies, synthesizing information on more than 160 experiments and 60 bird and anuran species. To estimate the breadth of frequency shift, we calculated a standardized effect size using Hedges’ g. We fitted a multilevel linear mixed-effect model on g as the dependent variable weighted by its inverse variance, with typical frequency, body mass, experimental condition, and noise source type as independent terms. Our results reveal broader shifts in smaller bird species when compared with bigger species, an effect that was emphasized in the low-frequency component of the song spectrum. Birds increased their dominant frequencies when confronted to anthropogenic noise, whereas anurans were less prone to such shifts. Human-altered acoustic environments can be considered a novel selective force impelling change to the communication patterns of many vocalizing species.

秩父山地におけるヨタカのさえずり頻度の季節変化

秩父山地におけるヨタカのさえずり頻度の季節変化

Urban-associated drivers of song variation along a rural–urban gradient

Most studies demonstrating associations between avian song and urbanization have tested noise as the primary driver, but alternative explanations remain largely unexplored. In particular, urban-associated changes in vegetation, density of conspecifics, and morphology also may promote changes in song. In this study, we 1) identified relationships between urbanization and song characteristics and 2) evaluated the extent to which altered song was explained by variation in noise level, vegetation, social context, and morphology of individual birds. We monitored the territories and recorded songs of northern cardinals (Cardinalis cardinalis) within forest stands in central Ohio that varied with surrounding urbanization. As landscapes surrounding forests urbanized, songs were longer, sung at faster rates, and comprised of higher-frequency notes. Noise best predicted minimum song frequency, with individuals singing at higher frequencies in environments with higher levels of background noise. However, temporal attributes of song (e.g., syllable rate, length) were best explained by conspecific densities, which are substantially greater in urban than rural landscapes. Morphology and vegetation did not predict any song attributes tested. These findings show that although anthropogenic noise may shape urban-associated changes in song, other features of the urban environment may be more important contributors to patterns in song variation.

No phenotypic signature of acoustic competition in songs of a tropical cricket assemblage

Efficient acoustic communication in multispecies assemblages is challenging due to the presence of heterospecific signals. Masking interference and signal confusion of similarly structured signals can impose fitness costs and, thus, drive evolutionary processes that shape acoustic signals to reduce their overlap in signal space. Although the partitioning of signal space has been frequently studied in frog and bird communities, this topic has received much less attention with reference to insects that communicate acoustically. In this study, we examined the role of acoustic competition in a tropical cricket community and tested the following hypotheses: 1) cosignaling species are expected to exhibit more dissimilar calling songs as compared with species that are spatially and/or temporally separated and 2) species signaling with similar song frequencies, who are thereby subject to energetic masking, are more likely to differ in the temporal domain of their calling songs. Using non-metric multidimensional scaling and pairwise comparison methods to measure acoustic dissimilarity, we found no evidence for either hypothesis: the acoustic signals of species pairs that cosignaled or used similar calling frequencies did not significantly differ from those of species that were spatially/temporally segregated or had large song frequency differences. In conclusion, for the acoustically communicating cricket community investigated, no supportive evidence for the partitioning hypothesis and the widespread belief that acoustic competition has led to divergent selection pressures on signal structure to avoid masking interference was found. Instead, we argue that selection pressures on sensory/neuronal mechanisms seem to more strongly drive reliable communication.

Dynamics of Cricket Sound Production

The clever designs of natural transducers are a great source of inspiration for man-made systems. At small length scales, there are many transducers in nature that we are now beginning to understand and learn from. Here, we present an example of such a transducer that is used by field crickets to produce their characteristic song. This transducer uses two distinct components—a file of discrete teeth and a plectrum that engages intermittently to produce a series of impulses forming the loading, and an approximately triangular membrane, called the harp, that acts as a resonator and vibrates in response to the impulse-train loading. The file-and-plectrum act as a frequency multiplier taking the low wing beat frequency as the input and converting it into an impulse-train of sufficiently high frequency close to the resonant frequency of the harp. The forced vibration response results in beats producing the characteristic sound of the cricket song. With careful measurements of the harp geometry and experimental measurements of its mechanical properties (Young's modulus determined from nanoindentation tests), we construct a finite element (FE) model of the harp and carry out modal analysis to determine its natural frequency. We fine tune the model with appropriate elastic boundary conditions to match the natural frequency of the harp of a particular species—Gryllus bimaculatus. We model impulsive loading based on a loading scheme reported in literature and predict the transient response of the harp. We show that the harp indeed produces beats and its frequency content matches closely that of the recorded song. Subsequently, we use our FE model to show that the natural design is quite robust to perturbations in the file. The characteristic song frequency produced is unaffected by variations in the spacing of file-teeth and even by larger gaps. Based on the understanding of how this natural transducer works, one can design and fabricate efficient microscale acoustic devices such as microelectromechanical systems (MEMS) loudspeakers.

Cultural transmission and its possible effect on urban acoustic adaptation of the great tit Parus major

Urban great tits (Parus major) sing with a higher minimum frequency than their forest conspecifics. Cultural processes may account at least in part for the song divergence in city birds as great tits learn their repertoire from conspecifics and switch to high pitch song types in presence of background noise. However, in small cities, this process of cultural divergence could be constrained because it is likely that these birds have a greater exchange of song types with the outside. We tested this prediction by recording great tit songs in a small city (Toledo, central Spain) and in a nearby forest. We found that background noise and the peak and the maximum frequency of songs were higher in the city but the minimum frequency did not differ. The pause length was also longer in forest birds. Seventy percent of the song types were shared between Toledo and the nearby forest. These results suggest that the small size of Toledo allows a homogenized cultural wealth, preventing the development of a high pitch song as observed in larger cities.

“The Times They Were A-Changin’”: A Database-Driven Approach to the Evolution of Musical Syntax in Popular Music from the 1960s

The goal of this research is to investigate the pitch structures of popular music in the 1960s through a large corpus study in order to identify any consistent changes in harmonic and tonal syntax. More specifically, two studies based on the Billboard DataSet (Burgoyne, Wild & Fujinaga, 2011; Burgoyne, 2011), a new corpus presenting transcriptions for more than 700 songs, is presented. The first study looks at the incidence of multi-tonic songs throughout the decade, while the second study focuses on the incidence of flat-side harmonies (e.g. bIII, bVI, and bVII) over the same period of time. While no difference was observed in the frequency of multi-tonic songs, the study showed a significant increase in the incidence of flat-side harmonies during the second half of the decade.

Evolution of leaf warbler songs (Aves: Phylloscopidae).

Songs in passerine birds are important for territory defense and mating. Speciation rates in oscine passerines are so high, due to cultural evolution, that this bird lineage makes up half of the extant bird species. Leaf warblers are a speciose Old-World passerine family of limited morphological differentiation, so that songs are even more important for species delimitation. We took 16 sonographic traits from song recordings of 80 leaf warbler taxa and correlated them with 15 potentially explanatory variables, pairwise, and in linear models. Based on a well-resolved molecular phylogeny of the same taxa, all pairwise correlations were corrected for relatedness with phylogenetically independent contrasts and phylogenetic generalized linear models were used. We found a phylogenetic signal for most song traits, but a strong one only for the duration of the longest and of the shortest element, which are presumably inherited instead of learned. Body size of a leaf warbler species is a constraint on song frequencies independent of phylogeny. At least in this study, habitat density had only marginal impact on song features, which even disappeared through phylogenetic correction. Maybe most leaf warblers avoid the deterioration through sound propagation in dense vegetation by singing from exposed perches. Latitudinal (and longitudinal) extension of the breeding ranges was correlated with most song features, especially verse duration (longer polewards and westwards) and complexity (lower polewards). Climate niche or expansion history might explain these correlations. The number of different element types per verse decreases with elevation, possibly due to fewer resources and congeneric species at higher elevations.

Singing in the city: high song frequencies are no guarantee for urban success in birds

Urbanization involves dramatic environmental alterations, which can limit survival and reproduction of organisms and contribute to loss of biodiversity. One such alteration is anthropogenic noise, which biases natural ambient noise spectra toward low frequencies where it may interfere with acoustic communication among birds. Because vocalizing at higher frequencies could prevent masking by noise, it has been hypothesized that species with higher song frequencies should be less affected by urbanization. Indeed, evidence is accumulating that urban birds often vocalize at higher frequency than nonurban birds. However, the extent to which singing frequency affects their success in cities is less clear. We tested this hypothesis with a comprehensive phylogenetic Bayesian analysis comparing song frequency of songbirds from 5 continents with 4 measures of success in urbanized environments. Tolerance to urbanization was not associated with dominant or minimum song frequencies, regardless of the metric used to quantify urban success and the intensity of the urban alterations. Although song frequency was related to habitat preferences and body size of the species, none of these factors explained the lack of association with urban success. Singing high may be beneficial for signal perception under noisy conditions, but these high frequencies are apparently no guarantee for the success of bird species in urbanized environments.

Increased syllable rate during aggressive singing in a bird with complex and fast song

Sexual signals can comprise traits with multiple functions, and species with extreme phenotypes offer an opportunity to link function with signal evolution. This is the case in the serin Serinus serinus, a songbird with extremely fast syllable rate compared to related finches, and high sound frequency for its body size. Previous work on receiver responses showed that playback of artificially increased syllable rate is avoided and inhibits vocal responses, suggesting it is perceived as aggressive, while, on the contrary, higher sound frequency appears preferred by females. We tested whether senders also change these traits during aggressive singing, with a field playback experiment. Serin males responding aggressively by approaching the playback loudspeaker also increased syllable rate, while males responding less aggressively did not change syllable rate. Together with work on receiver responses, this suggests that aggressive signalling may have been an important selective pressure for the evolution of extremely fast syllable rate in this species. It is noteworthy that aggressive male serins still increase syllable rate, despite of their already elevated natural syllable rate. We found no changes in sound frequency when singing aggressively, which agrees with previous work that instead showed a female preference for high song frequency. We conclude that the evolution of extreme traits in serin song is best explained by multiple functions.

Song characteristics track bill morphology along a gradient of urbanization in house finches (Haemorhous mexicanus).

IntroductionUrbanization can considerably impact animal ecology, evolution, and behavior. Among the new conditions that animals experience in cities is anthropogenic noise, which can limit the sound space available for animals to communicate using acoustic signals. Some urban bird species increase their song frequencies so that they can be heard above low-frequency background city noise. However, the ability to make such song modifications may be constrained by several morphological factors, including bill gape, size, and shape, thereby limiting the degree to which certain species can vocally adapt to urban settings. We examined the relationship between song characteristics and bill morphology in a species (the house finch, Haemorhous mexicanus) where both vocal performance and bill size are known to differ between city and rural animals.ResultsWe found that bills were longer and narrower in more disturbed, urban areas. We observed an increase in minimum song frequency of urban birds, and we also found that the upper frequency limit of songs decreased in direct relation to bill morphology.ConclusionsThese findings are consistent with the hypothesis that birds with longer beaks and therefore longer vocal tracts sing songs with lower maximum frequencies because longer tubes have lower-frequency resonances. Thus, for the first time, we reveal dual constraints (one biotic, one abiotic) on the song frequency range of urban animals. Urban foraging pressures may additionally interact with the acoustic environment to shape bill traits and vocal performance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-014-0083-8) contains supplementary material, which is available to authorized users.

Song structure, not high‐frequency song content, determines high‐frequency auditory sensitivity in nine species of New World sparrows (Passeriformes: Emberizidae)

Summary The evolution of vocal signals can be constrained by a host of factors including habitat effects on sound propagation, morphology of sound‐producing structures and phylogenetic relationships among species. Here, we asked whether auditory sensitivity over a broad range of frequencies correlates with the spectral content of conspecific vocalizations, or whether it is constrained by the overall structure of vocalizations, habitat effects on sound propagation or relatedness among species. We studied nine New World sparrows (Passeriformes: Emberizidae) including three open‐habitat species, three scrub‐like habitat species and three forest species. For each habitat, one species had pure‐trilled songs, another had tonal songs and another had complex songs with tones, trills and amplitude‐modulated buzzes. As predicted by the acoustic adaptation hypothesis, song spectral properties (specifically frequency and entropy) had the highest values in open‐habitat species and the lowest values in forest species. Based on our results from song analyses, and the sender–receiver matching hypothesis, we predicted that open‐habitat species would be more sensitive to high‐frequency sounds compared to forest species. Contrary to this prediction, habitat and high‐frequency song content had little effect on audiogram shape. Song type, however, had a strong effect, with species that produce complex songs showing higher sensitivity to high‐frequency sounds than all other species. Our results suggest that the use of song frequency by receivers depends on song structure and not necessarily on song spectral content. Therefore, our current understanding of how signal‐processing mechanisms should match signal properties appears to be too simple. When thinking about the evolution of signal‐processing mechanisms, the multidimensionality of signals, and how the different dimensions can interact, should be considered.