Reaction to conspecific degraded song by the wren Troglodytes troglodytes: Territorial response and choice of song post

We investigated the response of the wren Troglodytes troglodytes to playback of a territorial song degraded by long-range propagation. It appears that the wren is sensitive to this degradation since the territorial reaction is less intense with the degraded song than with the undegraded one. However, the degraded song is still considered by the receiver as a specific territorial aggressive signal. This differential response suggests that the male wren can use the degradation characteristics of the signal to adapt its territorial reaction. Indeed, in response to this stimulus, the receiver wren chooses a higher song post. By so doing, the bird improves both the propagation distance of the emitted song and the receiver's ability to hear the opponent's song. This behavioural change may correspond to a communication strategy, counteracting the environmental constraints on sound propagation. Therefore, in response to sound degradation during long-range propagation, birds may have developed behavioural adaptations complementary to the various adaptations concerning song structure and coding-decoding processes.     

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.     

Development of Tonal Quality in Birdsong: Further Evidence from Song Sparrows

Song sparrow (Melospiza melodia) songs are composed largely of pure-tone notes. Song sparrows raised in acoustic isolation (i.e. never hearing conspecific songs) tend to produce half of their notes with harmonic overtones, an atypical tonal structure, suggesting that exposure to pure tones is necessary for the development of normal tonal quality. The experiment presented here directly investigated the influence of early exposure to songs with different tonal qualities on subsequent production. Seven young song sparrow males were exposed to 16 normal, pure-tone song sparrow songs and 6 males were exposed to the same 16 song types with added harmonic overtones. Birds in both groups learned equally well, confirming an earlier finding that tonal quality does not influence selection of models during the sensitive period for song acquisition. Birds exposed exclusively to harmonic song models, however, produced over 85% of their learned notes in a pure-tone fashion, even though they had never heard pure-tone sounds. Thus, pure tones do not need to be experienced directly by song sparrows, but exposure to some features of species-typical song models appears to facilitate the reproduction of models in a pure-tone fashion.     

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.     

Solitary Song and its inhibition in some Estrildidae

Summary In the species studied song appears to have two functions; an epigamic function = Display Song, and a contact function = Solitary Song. Solitary Song appears to be common to all the species studied. Its utterance indicates that the bird is unpaired or separated from another individual with which it has formed a bond. InUraeginthus bengalus, U. angolensis, andAmandava amandava Solitary Song is also uttered by the hen in similar circumstances. InLonchura punctulata, A. amandava, andEuodice malabarica song is usually but not completely inhibited by the presence of a mate, in whose absence Solitary Song will be uttered even when other individuals of the same species are present. In the species studied of the generaEstrilda, Lagonosticta, andUraeginthus Solitary Song is inhibited by the continued close proximity of another bird even though this may be of the same sex or of a different species and may elicit aggressive or fleeing reactions; but conditions of close association with a bird other than a suitable mate would presumably only occur under captive conditions. There appears to be a distance factor controlling such inhibition. There is evidence of the inhibition of song due to the presence of a mate in other passerine species.     

Use of Song Amplitude for Ranging in Carolina Wrens,Thryothorus ludovicianus

Songbirds are well known to use the degradation of conspecific song to assess the distance of the singer (called ranging). Because a song's degradation accumulates progressively with propagation distance and thus is not under direct control of the singer, it potentially provides more reliable distance information than the amplitude of songs. However, song amplitude decreases progressively with distance and thus also provides information about the singer's distance, provided that interference from wind is low and that the sender does not alter broadcast volume. This study investigated whether or not Carolina wrens, Thryothorus ludovicianus, can use changes in amplitude of conspecific song as a relative cue for ranging. Twelve male subjects each received one playback consisting of two successive songs differing by 6 dB in amplitude. Half the subjects received playbacks with the louder song first and the other half received playbacks with the louder song second. Receivers that would use song amplitude for ranging would perceive the simulated rival either as approaching or retreating, depending on whether the louder song was played first or second. Subjects responded as if the rival was farther away in the simulated retreat than in the simulated approach, indicating that Carolina wrens can use differences in amplitude of successive songs for ranging. Apparently, the risk of inaccurate ranging by song amplitude is outweighed by the advantage of using multiple cues, including information from song amplitude, to assess a rival's distance.     

Rapid evolution of a novel song and an increase in repertoire size in an island population of an Australian songbird

Cultural innovations are commonly noted in animals, but times of development of novel traits are usually unknown. We report here a novel song type arising in a bird population on an offshore island of Western Australia where the time of colonization of the island by the Western Gerygone Gerygone fusca is known. On the mainland, a single song type is widespread. On Rottnest Island, many individuals sing a different type of song and a number possess a repertoire of two song types: the standard song shared with the mainland and the novel song type not found on the neighbouring mainland. The novel song type found on Rottnest is so different in its syntactical structure that one could easily mistake it for that of a new species. The characteristic song of mainland birds is irregular in the frequencies at which the notes within a song are delivered. The novel song on Rottnest has a highly structured syntax with notes delivered at a strict and repeated sequence of frequencies resulting in a rhythmic musical sound. The species is known to have colonized Rottnest in about 1955. The new song type apparently developed rapidly by cultural evolution in the last 50 years.     

Interspecific Response to Playback of Bird Song

Responses to bird song have usually only been studied at the intraspecific level. I experimentally tested whether playback of the song of the black wheatear Oenanthe leucura in an area in S Spain resulted in responses from conspecifics as well as heterospecific birds by comparing the numbers of individuals singing before and after playback. The number of singing male black wheatears increased considerably, but also the number of singing males of five other passerine species increased significantly. The heterospecific response to playback may be due (1) to interspecific territoriality, (2) to black wheatear song signalling the absence of predators, or (3) to heterospecifics confusing the species-identity of the singer. The second alternative is considered more likely, since an ecologically wide array of species increased their song rate following playback. The conspicuous dawn (and dusk) chorus of bird song may be augmented by social facilitation due to the singing of conspecifics as well as heterospecifics.     

Song complexity is associated with habitat quality in an upland passerine

Understanding the influence of intrinsic (genetic and morphological) and extrinsic (geographical, environmental and social) factors on the performance and spatial differentiation of sexual signals, such as bird song, can help identify behavioural indicators of individual quality, habitat degradation and social environment. We used the Iberian Bluethroat Luscinia svecica azuricollis, a migratory bird that breeds in fragmented landscapes dominated by shrublands, as a case study to: (1) assess how a set of acoustic indicators of song performance are driven by intrinsic and extrinsic factors; and (2) contrast deterministic (adaptations to the environmental context and morphological constraints) vs. stochastic (differentiation by geographical isolation) explanations for song differentiation patterns. We explored acoustic indicators of song performance (spectral, temporal and song complexity) in relation to parameters related to genetic structure, body size, habitat type, habitat quality (assessed through a spatially explicit modelling approach) and social context (population abundance and songbird community composition). Then, we explored the contribution of genetic, geographical and environmental dissimilarity to song diversification across space. Our results highlight an association of song spectral variables with genetic structure and a significant connection between song complexity and duration with habitat quality. We found no relationship between social features and acoustic variables, or between song differentiation and genetic or geographical distances. There was, however, a correlation between song differentiation and environmental dissimilarity. We recommend the consideration of song complexity as an indicator of habitat quality.     

Role of a telencephalic nucleus in the delayed song learning of socially isolated zebra finches

Male zebra finches normally learn their song from adult models during a restricted period of juvenile development. If song models are not available then, juveniles develop an isolate song which can be modified in adulthood. In this report we investigate the features of juvenile experience that underly the timing of song learning. Juvenile males raised in soundproof chambers or in visual isolation from conspecifics developed stable isolate song. However, whereas visual isolate song notes were similar to those of colony-reared males, soundproof chamber isolates included many phonologically abnormal notes in their songs. Despite having stable isolate songs, both groups copied new notes from tutors presented to them in adulthood (2.7 notes per bird for soundproof chamber isolates, 4.4 notes per bird for visual isolates). Old notes were often modified or eliminated. We infer that social interactions with live tutors are normally important for closing the sensitive period for song learning. Lesions of a forebrain nucleus (IMAN) had previously been shown to disrupt juvenile song learning, but not maintenance of adult song for up to 5 weeks after surgery. In this study, colony-reared adult males given bilateral lesions of IMAN retained all their song notes for up to 4–7.5 months after lesioning. However, similar lesions blocked all song note acquisition in adulthood by both visual and soundproof chamber isolates. Other work has shown that intact hearing is necessary for the maintenance of adult zebra finch song. We infer that auditory pathways used for song maintenance and acquisition differ: IMAN is necessary for auditorily guided song acquisition—whether by juveniles or adults—but not for adult auditorily guided song maintenance. © 1993 John Wiley & Sons, Inc.     

Differentiation of Mating Vocalizations in Birds: Acoustic Features in Mainland and Island Populations and Evidence of Habitat-Dependent Selection on Songs

Local environments can act as selective agents on some characteristics of birds’ songs, whereas other song traits may not reflect local genetic adaptation. Geographic variation in songs of two Australian bird species (red‐capped robins Petroica goodenovii, western gerygones Gerygone fusca) was studied to examine one component of the ‘habitat‐dependent selection’ hypothesis. This hypothesis suggests that: (1) the detailed spectral characteristics of male songs are an evolved response to local habitat conditions affecting signal propagation and detection and (2) parallel evolution of other fitness traits sets up the potential for assortative mating by female choice. To examine the first part of the hypothesis, I made comparisons among widespread mainland populations and an island population using two levels of analysis: a typological analysis of song morphology (phonology: notes, syllables, syntax, temporal pattern, repertoires) and a spectral analysis of acoustic characteristics of songs (mean frequency, Wiener entropy, frequency modulation) using an automated procedure of feature extraction (Sound Analysis Pro). Spectral analysis was also used to extract values of the same acoustic features from the background sound environment of each recorded population. The typological analysis revealed no differences among mainland populations of either species, but large differences between mainland songs and those on the island. In contrast, the spectral analysis revealed acoustic divergence among populations, both mainland and island. For both species, Wiener entropy of songs correlated negatively with that of the ambient sound environment, consistent with predictions of the habitat‐dependent selection hypothesis of environmental selection on signal design.     

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.     

On the learning of degraded and undegraded songs in the Carolina wren

Adult male Carolina wrens (Thyrothorus ludovicianus) are known to use degradation in the songs they hear to estimate their distance from a singing conspecific. They also sing songs that are structured to prevent degradation owing to acoustic features particular to specific habitats. Here we ask if acoustically isolated, naive young wrens use sound degradation as a cue in choosing songs to learn. All four isolated birds learned significantly more undegraded than degraded songs, showing that song degradation is perceived and used by naive birds. We suggest that the attention given to song degradation by young birds learning songs produces a proximate mechanism to explain the common occurrence of song sharing by territorial neighbours and supports the ranging hypothesis (Morton 1982). Sufficient evidence now exists to suggest that sound degradation, and the ability of birds to use it, should be taken into account in studies using responses to playback of bird song.     

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.     

A Potential Metric of the Attractiveness of Bird Song to Humans

The prevalence of passerines (mostly oscines, or songbirds) in international bird trade suggests that the possession or production of a song that is attractive or desirable to people may contribute to the likelihood of a species being traded. Testing this is difficult because we lack a general and readily available metric that quantifies attractiveness of bird song to humans. We propose and validate such a metric, based on the number of sound files lodged for a species on the Xeno‐Canto website ( www.xeno-canto.org ). Our hypothesis is that species with more attractive songs are likely to be recorded more often, and so be represented more often in this online bird sound resource, all else being equal. Using a sample of North American and European passerines, we show that song repertoire size and geographic range size are consistently related to the number of recordings on Xeno‐Canto. We use these results to derive a metric (the residuals of a model of the number of recordings in Xeno‐Canto as a function of geographic range size) that may identify songs that are attractive to humans. Bird species whose songs are known to have inspired classical music, including several well known for their songs (e.g. common nightingale, European blackbird), have higher values of the metric than those that have not been referenced in classical music. The metric may help explain which bird species are present in trade, and so contribute to studies of invasion and conservation biology.     

Why do songbirds sing intensively at dawn?

Among the ideas proposed to explain the existence of the dawn chorus in songbirds, the acoustic transmission hypothesis claims that birds sing most intensively at dawn because this is the time of the day when songs suffer least from environmentally induced degradation and hence propagate over the longest distances. In this article, we report on the first sound transmission experiment that directly tests this assumption using natural song from a typically forest-living dawn chorusing bird, the blackcap Sylvia atricapilla. Representative sound elements from the introductory twitter part and from the terminating motif part of the blackcap song were transmitted and re-recorded at three different times of the day: dawn, midmorning, and early afternoon. These recordings were then compared with respect to the following measures of sound degradation: signal-to-noise ratio (SNR), excess attenuation, blurring over song elements, and elongation of song elements by tails of echoes. As could be expected, both the background noise and the SNR varied considerably over the day. More surprisingly the excess attenuation decreased during the day, being lowest in the afternoon. There was no diurnal variation in blurring and elongation by echoes. The results may be explained by the diurnal variation in physical parameters such as temperature, relative humidity, and wind speed. The implications of this for different communication activities are discussed. Overall, the results show that dawn conditions in a temperate deciduous forest do not always constitute the best circumstances for long-range communication and therefore that the dawn chorus cannot be explained by the sound transmission hypothesis. Received in revised form: 24 September 2001 Electronic Publication     

Independent evolution of song structure and note structure in American wood warblers

This study addresses the issue of how evolutionary convergence within shared environments shapes some features of bird song while leaving others unaffected, using as an example the songs of 51 North American wood warblers (Parulinae). I combined published information on breeding habitats and evolutionary relationships to show that the structure of warbler songs is correlated with habitat, whereas the structure of the notes that comprise the songs is relatively unaffected by habitat and more closely related to phylogenetic history. The results confirm known relationships between bird song and habitat, including correlations between song frequency and the type and density of canopy foliage, and between the number and arrangement of notes in the song and foliage density and moisture. More importantly, the results suggest that individual notes and whole songs are to some extent functionally independent, because the configuration of notes shows more evidence of evolutionary constraint than does the way notes are assembled into songs.     

Song Amplitude of Rival Males Modulates the Territorial Behaviour of Great Tits During the Fertile Period of Their Mates

Bird song is a widely used model in the study of sexual selection. Variation in the expression of sexually selected traits is thought to reflect variation in male genetic and/or phenotypic quality. Vocal amplitude is a song parameter that has received little attention in the context of sexual selection, but there is some evidence that the intensity of bird song affects female preferences. Here, we tested whether the amplitude of broadcast song plays a role in male–male competition. We used song playback with varying song amplitude (within the natural amplitude range of the species) and a dummy bird taxidermy to simulate territorial intrusions in the great tit, Parus major, during the fertile period of the female and measured the response of the local male. The results show that playback amplitude significantly affected the subjects’ behaviour: after approaching to within 25 m around the loudspeaker, territorial males stayed longer within that perimeter after the playback of high‐amplitude songs compared with low‐amplitude songs. Our findings add to the small but growing body of evidence suggesting that vocal amplitude may be a sexually selected song trait.     

High Source Levels and Small Active Space of High-Pitched Song in Bowhead Whales (Balaena mysticetus)

The low-frequency, powerful vocalizations of blue and fin whales may potentially be detected by conspecifics across entire ocean basins. In contrast, humpback and bowhead whales produce equally powerful, but more complex broadband vocalizations composed of higher frequencies that suffer from higher attenuation. Here we evaluate the active space of high frequency song notes of bowhead whales (Balaena mysticetus) in Western Greenland using measurements of song source levels and ambient noise. Four independent, GPS-synchronized hydrophones were deployed through holes in the ice to localize vocalizing bowhead whales, estimate source levels and measure ambient noise. The song had a mean apparent source level of 185±2 dB rms re 1 µPa @ 1 m and a high mean centroid frequency of 444±48 Hz. Using measured ambient noise levels in the area and Arctic sound spreading models, the estimated active space of these song notes is between 40 and 130 km, an order of magnitude smaller than the estimated active space of low frequency blue and fin whale songs produced at similar source levels and for similar noise conditions. We propose that bowhead whales spatially compensate for their smaller communication range through mating aggregations that co-evolved with broadband song to form a complex and dynamic acoustically mediated sexual display.