Blackbird Song Research Articles

A highly anomalous Red-winged Blackbird (<i>Agelaius phoeniceus</i>) song

Red-winged Blackbird (Agelaius phoeniceus) is a highly vocal species with a repertoire of similar, yet acoustically distinct songs. These songs may be altered drastically if, as a nestling, the male goes deaf or becomes acoustically isolated. In deaf Red-winged Blackbirds, these dramatic song alterations may present as songs bearing slight resemblance to the introductory phrase of their normal song. Here, we present a Red-winged Blackbird song observed in Ottawa, Ontario, Canada, that is far outside any normal variation in Red-winged Blackbird songs. Given the individual’s age and the consistency of the anomalous song, it is possible that this is a deaf bird.

Heterospecific eavesdropping of jays (Garrulus glandarius) on blackbird (Turdus merula) mobbing calls

Heterospecifics eavesdrop on mobbing calls and respond with appropriate behavior, but the functional aspects are less studied. Here, I studied whether jays (Garrulus glandarius) eavesdrop on blackbird (Turdus merula) mobbing calls in comparison to blackbird song. Furthermore, it was studied whether jays provided with extra information about predators differ in their response. Three different experimental designs were carried out: (1) control playback of blackbird song to control for the species’ presence, (2) experimental playback of different mobbing events of blackbirds towards different predators, (3) experimental playback similar to (2) but combined with different predator models. In the combined experiments, mobbing calls were tied to the respective visual stimuli. Comparing the experiments with and without predator presentation, a similar number of jays occurred during the playback-only experiment (n = 7) and the playback combined with model presentation (n = 6). However, during the playback-only experiment, jays approached the speaker closer and stayed for longer time in the nearer surrounding. These results show that jays need extra information to make an informed decision.

European Blackbirds Exposed to Aircraft Noise Advance Their Chorus, Modify Their Song and Spend More Time Singing

Noise pollution has a strong impact on wildlife by disrupting vocal communication or inducing physiological stress. Songbirds are particularly reliant on vocal communication as they use song during territorial and sexual interactions. Birds living in noisy environments have been shown to change the acoustic and temporal parameters of their song presumably to maximize signal transmissibility. Also, research shows that birds advance their dawn chorus in urban environments to avoid the noisiest hours, but little is known on the consequences of these changes in the time they spent singing at dawn. Here we present a comprehensive view of the European blackbird singing behaviour living next to a large airport in Madrid, using as a control a population living in a similar but silent forest. Blackbird song is composed of two parts: a series of loud low-frequency whistles (motif) and a final flourish (twitter). We found that airport blackbirds were more likely to sing songs without the twitter part. Also, when songs included a twitter part, airport blackbirds used a smaller proportion of song for the twitter than control blackbirds. Interestingly, our results show no differences in song frequency between airport and control populations. The most relevant finding of this study shows that airport blackbirds not only sang earlier but also increased the time they spent singing when chorus and aircraft traffic coincide on time. This effect disappeared as the season progressed and the chorus and the aircraft traffic day-time schedule were separated on time. We propose that the typical urban upshift in frequency might not be useful under the conditions of noise and landscape structure found near airports. We suggest that the modifications in singing behaviour induced by aircraft noise may be adaptive and that they are specific to airport acoustic habitat. Moreover, we found that adjustment of singing activity in relation to noise is plastic and possibly optimized to cope with aircraft traffic activity. In a soundscape characterised by intermittent and strong noise bursts, singing for longer could be more advantageous than modifying frequency parameters, although it is likely more costly.

Fields of dreams Four Fields Tim Dee Jonathan Cape, 2013. 288 pp.

Fields of dreams <b>Four Fields</b> <i>Tim Dee</i> Jonathan Cape, 2013. 288 pp.

Blackbird's Song: Andrew J. Blackbird and the Odawa People

Blackbird's Song: Andrew J. Blackbird and the Odawa People

Blackbird's Song: Andrew J. Blackbird and the Odawa People by Theodore J. Karamanski (review)

Blackbird's Song: Andrew J. Blackbird and the Odawa People by Theodore J. Karamanski (review)

Blackbird's song: Andrew J. Blackbird and the Odawa people

Blackbird's song: Andrew J. Blackbird and the Odawa people

Anthropogenic noise affects song structure in red-winged blackbirds (Agelaius phoeniceus)

Anthropogenic noise can mask animal signals that are crucial for communicating information about food, predators and mating opportunities. In response to noise masking, signallers can potentially improve acoustic signal transmission by adjusting the timing, frequency or amplitude of their signals. These changes can be a short-term modification in response to transient noise or a long-term modification in response to chronic noise. An animal's ability to adapt to anthropogenic noise can be crucial to its success. In this study, we evaluated the effects of anthropogenic noise on the structure of red-winged blackbird song. First, we manipulated the presence of anthropogenic noise by experimentally broadcasting either silence or low-frequency white noise to subjects inhabiting quiet marshes located away from roadsides. Subjects exhibited increased signal tonality when temporarily exposed to low-frequency white noise, suggesting that red-winged blackbirds can alter their signals rapidly in response to sudden noise. Second, we compared songs produced in quiet marshes located away from roadsides with songs produced during quiet periods at roadside marshes that are normally noisy. This allowed us to test whether birds that are exposed to chronic anthropogenic noise exhibit altered song structure during temporarily quiet periods. Subjects residing in roadside marshes that are normally polluted with anthropogenic noise sang songs with increased tonality during quiet periods. Overall, our results show that anthropogenic noise influences the structure of birdsong. These effects should be considered in conservation and wildlife management.

Does song repertoire size in Common Blackbirds play a role in an intra-sexual context?

Bird song is thought to have a function in both inter- and intra-sexual contexts with song complexity serving as an honest signal of male quality. Theory predicts that males use repertoire sizes to estimate rivals’ fighting ability. Here we tested whether element repertoire size plays a role in an intra-sexual context in the Common Blackbird Turdus merula, a songbird with a large repertoire. In a territory intrusion playback experiment, we broadcast Common Blackbird song with different element repertoire sizes to territorial males. The test birds did not respond differently to the different repertoire sizes. This was also the case when we considered the test birds’ own repertoire sizes in the analysis. Thus, we found no evidence for the hypothesis that males use repertoire size for estimating rivals’ fighting force. However, this does not exclude the possibility that repertoire size plays a role in different intra-sexual contexts in Common Blackbirds. In the discussion, we address alternative scenarios.

Habitat-related birdsong divergence: a multi-level study on the influence of territory density and ambient noise in European blackbirds

Song plays an important role in avian communication and acoustic variation is important at both the individual and population level. Habitat-related variation between populations in particular can reflect adaptations to the environment accumulated over generations, but this may not always be the case. In this study, we test whether variation between individuals matches local conditions with respect to noise level and territory density to examine whether short-term flexibility could contribute to song divergence at the population level. We conducted a case study on an urban and forest population of the European blackbird and show divergence at the population level (i.e. across habitats) in blackbird song, anthropogenic noise level and territory density. Unlike in several other species, we found a lack of any correlation at the individual level (i.e. across individuals) between song features and ambient noise. This suggests species-specific causal explanations for noise-dependent song differentiation which are likely associated with variation in song-copying behaviour or feedback constraints related to variable singing styles. On the other hand, we found that at the level of individual territories, temporal features, but not spectral ones, are correlated to territory density and seasonality. This suggests that short-term individual variation can indeed contribute to habitat-dependent divergence at the population level. As this may undermine the potential role for song as a population marker, we conclude that more investigations on individual song flexibility are required for a better understanding of the impact of population-level song divergence on hybridisation and speciation.

Acoustic directionality of red-winged blackbird ( Agelaius phoeniceus) song relates to amplitude and singing behaviours

Sound waves typically radiate from a vocalizing animal with unequal amplitude in different directions; this may profoundly affect communication, favouring adaptations that use or compensate for this directionality. Previous studies suggest that variation in directionality among vocalization types is related to function, with vocalizations such as alerts being relatively omnidirectional, thus maximizing the number of surrounding receivers, and vocalizations such as courtship calls being relatively directional, thus reducing eavesdropping by beaming sounds at the targeted receiver. Here we examine variation within a vocalization type, bird songs, to test hypotheses about how variation in song directionality relates to singing behaviour and the social context of singing. We measured the directionality and amplitude of red-winged blackbird songs in the field using calibrated microphones encircling the bird. We found variation in directionality among song types, possibly allowing males to select songs from their repertoires with directionality to suit the social context. We found support for the hypothesis that the amplitude and directionality of songs are related, with more-directional songs delivered at higher amplitudes. In addition, we found support for the hypothesis that directionality is negatively related to the degree of male rotation on the perch between vocalizations, suggesting that males may combine omnidirectional songs and rotation to broadcast their songs, and may face the receiver and produce directional songs during direct interactions. We also observed variation in directionality among note types within songs. These results suggest that directionality plays an important role in shaping song structure and singing behaviour in red-winged blackbirds.

Multivariate statistical analysis of songs of the male Common Blackbird (Turdus merula): an example from western Victoria, Australia

Variation in the song of the male Common Blackbird was investigated within and between two locations in western Victoria. Each of 400 phrases (100 phrases per male) was characterised by 61 measurements relating to 13 aspects of each phrase. Principal component and stepwise discriminant analyses were undertaken on these measurements. Classification of blackbird song for location and individuality was based on timing within the phrase of the loudest elements. Evidence was found for within-phrase variability, with the greatest variation in the middle of the phrase. Within- and between-site comparison found that blackbird song exhibited both individual and site-specific characteristics consistent with earlier suggestions of phrase sharing within local populations. The study demonstrated that an objective statistical approach to song analysis was able to disciminate between individual birds from different locations.

Song-based species discrimination and behaviour assessment by female blackbirds, Turdus merula

Abstract. The ability of female blackbirds to integrate information about a singer's species and possible ensuing behaviour from different parameters of the introductory part (i.e. the motif part) of the blackbird's song was tested. Females were made receptive to song stimulation by oestradiol injections and tested with tapes with modified motif parts in an anechoic chamber using a broad spectrum of female reproductive behaviour as response measures. Females, like males, attended to the natural upper and/or lower limits of variation in seven parameters in the process of species discrimination: (1) the frequency level and (2) the duration of sound figures (i.e. sounds separated by pauses greater than 50 ms); variation across the motif part in the sound figures' (3) frequency level, (4) duration and (5) amplitude; (6) the ratio of the sound pressure of the fundamentals to that of the first and second overtones; and (7) the relative proportions of the three types of sound figures (i.e. (a) whistles; (b) trills, gurgles and squeaks; and (c) compounds of a and b). The results suggest that females, unlike males, disregard both the upper limit of variation in the frequency level in the process of species discrimination, and the degree of modulation of the sound figures' amplitude functions (i.e. envelopes) and, perhaps, the pauses between the sound figures in the process of assessing the ensuing behaviour of the singer. The validity of such sexual differences in song decoding and possible factors leading to their evolution are discussed. The present differences all concern parameters that degrade more when passing through dense vegetation to females than when passing through the more open communication channels to males. This is consistent with the 'song-degradation' hypothesis that one of the sexes may pay less attention than the other to certain song features if these features are degraded to a different extent on their way to the two sexes.

Habitat-induced degradation of sound signals: Quantifying the effects of communication sounds and bird location on blur ratio, excess attenuation, and signal-to-noise ratio in blackbird song

The habitat-induced degradation of the full song of the blackbird (Turdus merula) was quantified by measuring excess attenuation, reduction of the signal-to-noise ratio, and blur ratio, the latter measure representing the degree of blurring of amplitude and frequency patterns over time. All three measures were calculated from changes of the amplitude functions (i.e., envelopes) of the degraded songs using a new technique which allowed a compensation for the contribution of the background noise to the amplitude values. Representative songs were broadcast in a deciduous forest without leaves and rerecorded. Speakers and microphones were placed at typical blackbird emitter and receiver positions. Analyses showed that the three degradation measures were mutually correlated, and that they varied with log distance. Their variation suggests that the broadcast song could be detected across more than four, and discriminated across more than two territories. The song’s high-pitched twitter sounds were degraded more rapidly than its low-pitched motif sounds. Motif sounds with a constant frequency projected best. The effect of microphone height was pronounced, especially on motif sounds, whereas the effect of speaker height was negligible. Degradation was inversely proportional to microphone height. Changing the reception site from a low to a high position reduced the degradation by the same amount as by approaching the sound source across one-half or one-whole territory. This suggests that the main reason for a male to sing from a high perch is to improve the singer’s ability to hear responses to its songs, rather than to maximize the transmission distance. The difference in degradation between low and high microphone heights may explain why females, which tend to perch on low brush, disregard certain degradable components of the song.

Song Features Essential for Species Discrimination and Behaviour Assessment By Male Blackbirds (Turdus Merula)

The present study tested the signal value of different parameters of the blackbird song by comparing territory owner's responses to unmodified motif parts. Parameters were modified with reference to their natural limits of variation which were known a priori for some of the parameters. Those for the frequency of occurrence of the three types of motif sound figures (unmodulated and/or complex toned FM-figures, and compound MIX-figures composed of pieces of both the CF- and the FM-type) and their modulations, and the relative sound pressure (SP) of their harmonics, were determined in this study. The following results were obtained: The frequency of occurrence of the sound figure types is essential for species discrimination in the sense that motif parts must contain CF-pieces with a relatively constant frequency (either as CF-figures or as parts of MIX-figures), and it communicates additional information: a high proportion of FM-figures giving a gurgling sound character communicates a high arousal and vice versa. The ratio of SP of the fundamental to that of the 1 st and the 2nd overtone is also essential for species discrimination. The ratio must be greater than about 1:0.2:0.2 making the motif parts relatively pure toned. Above this value the SP ratio may communicate additional information: a relatively low ratio giving a hoarse sound character seems to represent a high arousal and vice versa. Also, a high sound pressure level of the motif parts communicates a high arousal and vice versa. Neither the order of sound figures, nor the specific variation across the motif part of the sound figures' frequency level, duration and amplitude is essential for species discrimination. So is, however, a certain variation per se of each of the three features across the motif part. The results fit in with the 'room for variation hypothesis' on the principles of coding information into bird song. Thus the species-essential parameters seem to be 'tuned' to their natural limits of variation in the sense that species discrimination ceases when they are changed beyond these limits; within these limits some of them convey additional behavioural information; and they include all sorts of parameters, e.g. basic as well as higher order syntactical and sound type parameters, and invariant as well as variable ones.

An Analysis of the Full Song of the Blackbird Turdus merula with Respect to Message Coding and Adaptations for Acoustic Communication

The full song of the Blackbird was analysed quantitatively by means of sonagraph, level recorder and computer. Species-specific limits of variation are given for a number of song parameters. Some of these parameters vary between individuals, others vary within individuals in two situations, viz. dawn song with heavy stimulation from rivals and evening song with weak stimulation from rivals. The parameters and the differences between the variations of the parameters all seem to be within the range of auditory perception of oscines. It is therefore hypothesized that parameters varying within species-specific limits have a potential for conveying a message about the species, and that parameters varying within these limits with the individual or the situation have an additional potential for conveying individual or behavioural messages, respectively. Blackbird song was also studied with respect to adaptations for acoustic communication. Selection has favoured the evolution of a functionally divalent signal, the motif parts being adapted for long-range communication and the twitter parts for short-range communication.

The contribution of temporal song cues to species recognition in the red-winged blackbird

The trill portion of red-winged blackbird ( Agelaius phoeniceus) song is necessary and sufficient for species recognition. The present study demonstrates that trills of red-winged blackbird songs near Ithaca, New York contain 40–107 pulses/s. Playbacks of unpulsed sound matched in spectral structure to eastern red-winged blackbird trills, and of California blackbird trills with average pulse repetition rates of 32.5, 120 or 200 pulses/s, elicit little or no response from Ithaca red-winged blackbirds. These birds respond strongly, however, to presentation of a California red-winged blackbird trill with 50 pulses/s. Ithaca red-winged blackbirds thus discriminate against spectrally-appropriate signals with temporal structures not normally heard in the songs of this population. The upper and lower temporal limits to species recognition are sharply defined. Fine temporal intra-pulse structure was analysed in red-winged blackbird trills of varying pulse repetition rate, and in the trill portion of a northern mockingbird ( Mimus polyglottos) imitation of red-winged blackbird song, which evoked a northern response when played to blackbirds. Pulse duration remains relatively fixed even though pulse period changes widely in true red-winged blackbird trills. Red-winged blackbird trill pulses are much shorter in duration than mockingbird pulses. For a given trill rate, however, both signals share a common frequency emphasis. The equivalence of these two signals in playbacks with red-winged blackbirds suggests that pulse repetition rate and frequency composition are important in species recognition.

The active space of red-winged blackbird song

Active space, that distance from the source over which signal amplitude remains above the detection threshold of potential receivers, was determined for Red-winged Blackbird (Agelaius phoeniceus) song in an upland pasture near Ithaca, New York. Song amplitude, the rate of signal attenuation, the amplitude of ambient noise, and the sensitivity of redwings to song masked by noise determine active space and were measured in the field: 1. Maximum root-mean-square song amplitude at 1 m from a singing bird ranged from 88.5–93.5 dB SPL (\(\bar X\)± SE = 90.8±0.21 dB SPL). 2. Close to the source, song attenuates at a rate which closely matches that predicted by spherical spreading (6 dB/doubling of distance) alone. At distances beyond about 30 m, however, excess attenuation becomes important (Fig. 4). The rate of attenuation varies with relative wind direction (Table 1). 3. Ambient noise level is relatively low in early morning, rises in late morning and afternoon as air turbulence increases, and then drops again in the evening as turbulence decreases (Table 2 and Appendix). Measured on a 4 kHz octave filter scale (center frequency = 4 kHz, octave pass-band = 2.83– 5.66 kHz), noise during one day ranges from 15 dB SPL (at 06∶00 h) to 36 dB SPL (at 11∶00 h), more than a 10-fold variation in ambient sound pressure. 4. A 3 dB signal to noise ratio is sufficient for detection of song masked by noise in the field (Figs. 5 and 6). Also, redwings are able to detect differences in this ratio as small as 3 dB. 5. In the absence of wind, the maximum active space of redwing song is about 189 m for a signal SPL of 93.5 dB at 1 m. This distance varies with changes in ambient noise level during the day, and with relative wind direction.

Visualizing Interaction and Sequential Data in Animal Behaviour: Theory and Application of Cluster-Analysis Methods

Abstract The results of behavioural studies can be difficult to assimilate, often because such enormous quantities of data are involved, both as the studies are carried out and often in their final published form. This paper is concerned with data occurring in two-way tables which summarise, for example, the time each individual in a social group spends with every other individual, or the frequency with which every phrase in a bird's song follows every other one. We present some methods of cluster-analysis which help us to produce visual representations of such data. We describe how to build a single-link dendrogram (which is a way of representing a single-link cluster-analysis or SLCA) in Section 3 and a Maximum spanning-tree (MST) in Section 4. We also describe the properties of non-metric Multidimensional scaling (MDS) in Section 5, and B(2) cluster-analysis in section 6. Because methods of cluster-analysis often make fewer assumptions, we use them rather than factor analysis, principal-component analysis or canonical variate analysis. Section 8 compares the results of factor analyses with those of our cluster-analyses. The methods we describe are illustrated with reference to the times eleven free-living chimpanzees were seen together, analysed by SLCA in Section 3, MST in Section 4 and MDS in Section 5. Section 6 shows how B(2) analyses are used for the chimpanzee data, and Section 7 shows their application to data about sequences of phrases in a blackbird's song. In order to begin the cluster-analyses we present, our tables of raw data must be recast as tables of similarities. Section 2 introduces the art of constructing similarities, and Appendix I (1) shows how different kinds of similarity can be constructed from the same raw data. With reference to Appendix I (2b) and also to the data from BAERENDS et al. (1970) study of the incubation behaviour of herring gulls (Section 8), we emphasise that the act of constructing a particular kind of similarity commits one to a particular way of interpreting the data. Moreover, a method of constructing similarities can conceal differences of precision, Appendix I (3). Appendix I (2), examines the problems posed for cluster-analyses by asymmetric tables such as occur when elements precede other elements more often than vice versa, or when an individual in a social group grooms another for longer than vice versa. In Section 8, we illustrate how methods of cluster-analysis help us to interpret association data for 11 chimpanzees, and we examine the consistency of the chimpanzees' patterns of association through two consecutive 4-month periods. We then examine the association data of the whole community to which the 11 belong, and we use three consecutive analyses to show how the males in the community began to split into two sub-groups. We also compare he association data for three captive groups of rhesus monkeys; and we follow one group, comparing 12 consecutive monthly analyses to discover periods of change in that group's social organisation. We apply cluster-analyses to preceding-following tables from WIEPKEMA (1961) and BAERENDS et al. (1970), and we compare our interpretations of the original data with theirs. Finally, we show how cluster-analysis helps us to understand the songs of a blackbird, originally described by HALL-CRAGGS (1962). While we have emphasised the need to produce visual representations of our data, the need to evaluate them statistically remains, and Section 8-4 and Appendix II discuss the statistical methods for comparing dendrograms.

An Experimental Analysis of the Function of Red-Winged Blackbird Song

AbstractThe social role of the male red-winged blackbirds' Ageliaus phoenicetts, advertising song was examined. Territorial male red-wings were captured on their territories and subjected to bilateral sectioning of the hypoglossal nerves where they descend along the trachea. This surgery resulted in males which delivered species atypical songs at the times when they attempted to sing the normal advertising song. A group of control males were captured and treated in the same way as the surgically treated males except the hypoglossal nerves were not sectioned. The following results were obtained: 1) Vocalization altered males were successful in maintaining territories for the remainder of the breeding season. 2) Vocalization altered males were able to mate with females and raise young successfully. 3) Five vocalization altered males returned to the same marsh the following breeding season, one year after the operation and successfully established and maintained territories. It was concluded that the ability to deliver species typical song was not necessary for the establishment and maintenance of a breeding territory under the environmental conditions encountered during these experiments.