Song characterization in the spectacled warbler (Sylvia conspicillata): a circum-Mediterranean species with a complex song structure

The spectacled warbler (Sylvia conspicillata) is a small passerine with a patchy distribution throughout the circum-Mediterranean region, including the North Atlantic archipelagos of Madeira, Canary Islands and Cape Verde. Here we characterize the species song structure on the island of Fuerteventura, quantifying repertoire size, inter- and intra-individual spectrographic variation, to determine whether acoustic variation occurred within an island population. Male song display was organized in song bouts of a variable number of song phrases, which in turn were made up of 4–69 syllables. We classified syllable types to derive a measure of repertoire size (number of different syllables) per song bout, and then used rarefaction methods to calculate the estimated repertoire size for our population of males. Three categories of song bout length were considered in analyses: short song bouts of 10 phrases, average bouts of 19 phrases and long bouts of ≥ 29 phrases. The observed and estimated repertoire size per male (between 43 and 126 syllables per male) increased with song bout duration, although the relationship was not significant for the estimated values. To test whether songs could be individually specific, we measured 11 spectrotemporal parameters of the song. A discriminant analysis using these variables performed poorly in classifying songs to the individuals that uttered them, but we found less variation in the individual than in the population for three out of the 11 variables. These individually specific variables, involving the first or the most common syllable of the song, the trill, were the duration of the first syllable of the phrase, the duration and the dominant frequency of the trill syllable. Our study emphasizes the complexity of spectacled warbler songs, in which males continuously add novel syllables over the entire song bout. This complexity appears to be determined by individual innovation capabilities rather than by the behaviour of copying neighbour repertoires, since songs of close birds were not more similar than songs from far-away territories.     

Mechanisms of song differentiation in introduced populations of Chaffinches Fringilla coelebs in New Zealand

Chaffinches Fringilla coelebs were introduced to New Zealand from Great Britain over 100 years ago, and since then their songs have diverged from British ones in both syllable structure and basic organization of syllable sequences. The New Zealand populations seem to be unique in that their songs have undergone differentiation of trill segments by progressive elaboration of syllable morphology and hp ascending and descending changes of pitch. Published sonagrams of British song types have significantly more trill phrases and significantly fewer syllables in the end phrase than do Yew Zealand ones. Many New Zealand song types have much elaborated end phrases and concomitantly simpler trill segments, with songs quite commonly having only one trill phrase. This reversal of complexity between the trill and end phrase in New Zealand seems to have been derived by progressive reduction of the ultimate trill phrase to one syllable, and by recombination of end phrase syllables from different song types into one compound end phrase. The significance of the increased complexity in the end phrases of many song types may relate to the sound transmission properties of dense pine forests in New Zealand, in which Chaffinches are ubiquitous. Elaborate end phrases degrade much less from reverberation in pine forests because individual syllables have more dispersed temporal patterning.
Recombination of syllables to form new song types is a major mechanism of song differentiation in New Zealand. Although whole song copying is the predominant mode of replication, very few song types in a locality sample are composed of a unique set of syllables. Rather, song types in an area are interconnected by different combinations of shared syllables, suggesting that the incorporation of some local syllables in a bird's repertoire is sufficient to signal its status as a member of a neighbourhood and also allows the evolution of broadcast complexity.     

Cultural Evolution of Puget Sound White-Crowned Sparrow Song Dialects

The songs of male Puget Sound white‐crowned sparrows currently form about 12 dialects along the Pacific Northwest coast. In his survey of 1970, Baptista (Condor 1977; 79: 356–370) defined six of the dialects based on the song's terminal trill because most males at each locality shared the simple syllables (SSs) in this trill. The complex syllables (CSs) in the song's introduction varied among males at a locality, and were often shared among localities. From 1997 to 2004 we revisited nine of the sites Baptista studied to determine whether the SSs and CSs had changed over the 30‐yr interval. Using Baptista's catalogs of SS and CS types as bases for comparison, we found that the relative proportions of CS types changed significantly more over time than did the proportions of SS types. These results suggest that SSs and CSs evolve independently. Observations were also made on the developmental mechanisms that either produce diversity or maintain uniformity in song phrases. In a survey of 670 field‐recorded songs, unique improvizations occurred significantly more often in CSs than in SSs. In a laboratory experiment using hand‐reared males and multiple song tutors, males were significantly more accurate in imitating SSs than CSs. In choosing their final song to keep from their overproduced repertoire, yearling males tended to retain the song type that matched the SSs in the song played back to them. We conclude by discussing how differences in the functions served by these two song phrases may have led to their different rates of cultural evolution.     

Are good ornaments bad armaments? Male chaffinch perception of songs with varying flourish length

Birdsong functions as both a territorial and a mate-attracting signal, and is therefore subject to inter- and intrasexual selection through male-male competition and female mate choice. Consequently, differences in song perception between males and females could potentially lead to conflicting selection pressures on song structure. Chaffinch,Fringilla coelebs , songs have two distinctive parts: a series of rapidly repeated notes (the trill) followed by a sequence of more complex and often nonrepeated elements (the flourish). Males often spontaneously sing incomplete songs consisting mainly of the trill part, but their communicative function is unclear. We tested the reaction of males to songs with and without the terminal flourish in a dual speaker playback design by measuring their approach to the speakers. Like female chaffinches tested with the same stimuli in a previous study, males responded more to songs with both trill and flourish than to those consisting of a trill only. However, although females had preferred songs with a relatively longer flourish, males showed the strongest reaction (closest approach to the speaker) to songs with longer trills and shorter flourishes. The results suggest that males and females may perceive aspects of chaffinch song structure differently, in which case it could be under conflicting pressure of intra- and intersexual selection. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Song Learning in the Anna Hummingbird (Calypte anna)

Songs of wild male Anna hummingbirds (Calypte anna) consist of syllables grouped into phrases. Nearest neighbors tend to share similar syllable types, rhythms and syntax. Songs from different localities contain different syllable types, syntax and repetition indices. A male raised by hand in isolation produced a song consisting of highly variable syllable types of a wide frequency range. The song was simple in structure, and syllables were not grouped into phrases. Three males raised by hand as a group sang songs containing two stereotyped syllable types sung in alternating sequence and without phrase structure. These three males shared syllable types and syntax. The data from our study indicate that despite its relatively simple syrinx the Anna hummingbird learns syllable types, frequency, rhythm and syntax (as do oscines with their more complex syringes) during the song development process.     

Inferring performance in the songs of dark-eyed juncos (Junco hyemalis)

Within bird species, songs differ in their attractiveness tofemales or effectiveness in male–male interactions. Somesongs are more difficult to sing than others, and receiversmay use a singer's performance of difficult songs as a meansfor evaluating the quality of the singer. The concept of songperformance aims at quantifying how physiologically demandingare different songs. Using variation between song types of dark-eyedjuncos, Junco hyemalis, we show that some song traits tradeoff with costly aspects of song output—short intervalsbetween syllables or loud sound amplitude—suggesting thatthose traits are difficult to sing. First, after controllingfor other traits, long syllables require longer intervals forrecovery. This supports the idea that a measure of "respiratoryperformance" could be based on the relative lengths of syllablesand intervals. Second, some syllable traits trade off stronglywith sound amplitude, suggesting that these traits may be difficultto sing at high amplitudes. The ratio of frequency bandwidthand trill rate has been used to infer performance in other birdspecies, but we found no evidence that frequency bandwidth tradesoff with any aspect of song output in the junco. The negativeassociation of bandwidth with trill rate may instead be a passiveconsequence of syllable length, with longer syllables randomlyaccumulating frequency modulation. We conclude that bird receiversmay best evaluate how well a song is performed if they integratemultiple cues and discuss how researchers may similarly devisemeasures of song performance.     

Frequency shift in homologue syllables of the Ortolan Bunting Emberiza hortulana

Results of this study indicate that in the Ortolan Bunting Emberiza hortulana, syllables of the same shape on sonograms (i.e. homologue syllables) often significantly differ between males in frequency parameters. Typically, homologue syllables of different males in the studied population had a similar bandwidth but shifted minimal and maximal frequencies. We found no strong evidence supporting that the frequency of homologue syllables is affected by the body size variation of males. Besides, frequency parameters of different song types within a male's repertoire did not correlate with each other. Moreover, we found that some males within the population sing two versions of apparently 'the same' song type, which differ in frequency parameters of syllables. Such different frequency versions were sung with eventual variety, which suggests that they are treated as different song types by birds. All these results support the idea that the fine acoustic structure of syllables (and song) is under a strong influence of the acoustic template (i.e. depend mainly on from whom the song was copied). We also found that the frequency of initial syllables within the song strophe is much more variable between males than in case of final syllables. Regardless of the great between-individual variation in initial syllable frequency, the syllables forming the final part of the song are kept within a very restricted bandwidth. These results support our earlier finding that strict syntactic rules of song formation exist in this species. These rules condition the acoustic variation of the initial and final part of the song. At least potentially, such a system enables species recognition and individual variation irrespective of repertoire level. Results of this study indicate that more attention should be paid to the problem of minimal units of song repertoire and to identity of such units within the bird population.     

Versatility and Stereotypy of Free-Tailed Bat Songs

In mammals, complex songs are uncommon and few studies have examined song composition or the order of elements in songs, particularly with respect to regional and individual variation. In this study we examine how syllables and phrases are ordered and combined, ie “syntax”, of the song of Tadarida brasiliensis, the Brazilian free-tailed bat. Specifically, we test whether phrase and song composition differ among individuals and between two regions, we determine variability across renditions within individuals, and test whether phrases are randomly ordered and combined. We report three major findings. First, song phrases were highly stereotyped across two regions, so much so that some songs from the two colonies were almost indistinguishable. All males produced songs with the same four types of syllables and the same three types of phrases. Second, we found that although song construction was similar across regions, the number of syllables within phrases, and the number and order of phrases in songs varied greatly within and among individuals. Last, we determined that phrase order, although diverse, deviated from random models. We found broad scale phrase-order rules and certain higher order combinations that were highly preferred. We conclude that free-tailed bat songs are composed of highly stereotyped phrases hierarchically organized by a common set of syntactical rules. However, within global species-specific patterns, songs male free-tailed bats dynamically vary syllable number, phrase order, and phrase repetitions across song renditions.     

Physically Challenging Song Traits,Male Quality,and Reproductive Success in House Wrens

Physically challenging signals are likely to honestly indicate signaler quality. In trilled bird song two physically challenging parameters are vocal deviation (the speed of sound frequency modulation) and trill consistency (how precisely syllables are repeated). As predicted, in several species, they correlate with male quality, are preferred by females, and/or function in male-male signaling. Species may experience different selective pressures on their songs, however; for instance, there may be opposing selection between song complexity and song performance difficulty, such that in species where song complexity is strongly selected, there may not be strong selection on performance-based traits. I tested whether vocal deviation and trill consistency are signals of male quality in house wrens (Troglodytes aedon), a species with complex song structure. Males’ singing ability did not correlate with male quality, except that older males sang with higher trill consistency, and males with more consistent trills responded more aggressively to playback (although a previous study found no effect of stimulus trill consistency on males’ responses to playback). Males singing more challenging songs did not gain in polygyny, extra-pair paternity, or annual reproductive success. Moreover, none of the standard male quality measures I investigated correlated with mating or reproductive success. I conclude that vocal deviation and trill consistency do not signal male quality in this species.     

Species Recognition by Song in the Veery (Catharus fuscescens: Aves)

Territorial male veeries (Catharus fuscescens) were presented with three series of reorganised songs to determine the functional properties of song structure. Songs consist of three parts: a low frequency initial phrase, a higher frequency middle phrase, and again a lower frequency end phrase. The latter two consist of vibrato syllables. Three series of experiments were performed, using various combinations of song syllables. In Series I, songs consisted of repetitions of a single syllable, one from each part of the song. Veeries responded to syllables from the middle and end phrases as to normal songs, both in localisation and in vocal responses. However, they showed little localisation and vocalisation responses to the introductory syllables. In Series II and III, veeries responded significantly more to songs in which syllables from the middle and end phrases were presented in proper sequence, rather than not. The minimum requirements for intraspecific recognition were determined in relation to the number and order of syllables in the song.     

Variation in Trill Characteristics in Tree Pipit Songs: Different Trills for Different Use?

Transmitting information about singer's quality is an important function of song in many bird species, and this information should be useful in territorial interactions. Fast trills, being physically demanding song structures, are particularly suitable candidates for signalling of quality or aggressive motivation. We have evaluated trill characteristics in songs within a population of the Tree Pipit, a common European songbird with no sexual dimorphism, in which song apparently plays a key role in territory defence as well as mate choice. Two types of relatively fast trills (each of them in multiple variants differing in complexity) were commonly observed in repertoires of Tree Pipit males. Trill rates significantly differed among individuals, suggesting that these song structures may carry information about male quality in this species. We tested by playback experiments whether both trill types are used in territorial encounters. Only one of the trill types was sung by males in response to playback, regardless on the trill type played to them. In an immediate response to playback, they increased the frequency of use of this trill, and also significantly increased the trill rate in comparison with spontaneous songs. This confirmed field observations, suggesting that this trill is important in male–male interactions. On the contrary, the use of the fastest, apparently more demanding, trill type actually decreased after the simulated territorial intrusion. We hypothesize that the latter one is more directed towards females, and that while performance of both trill types may reflect male quality, they are primarily used in different contexts.     

Song Perception in the Song Sparrow: Importance of Different Parts of the Song in Song Type Classification

Song sparrow (Melospiza melodia) males have repertoires of 6 to 12 song types, each song consisting of four or five contrasting phrases. Song types vary both within individuals (a singer varies successive renditions of a type within a singing bout) and between individuals (neighbors sing slightly different versions of a type), and in both cases this variation is concentrated in the later parts of the song. We speculated that type variation in the later parts of the song might be correlated with a perceptual tendency to classify song types primarily on the basis of the earlier parts of the song. We tested this hypothesis using a laboratory conditioning technique, supplemented by a field playback experiment. In the lab, song sparrows and white crowned sparrows were trained to discriminate between two distinct song types. In test sessions, they were presented with hybrid songs synthesized from varying proportions of the two training song types. For most birds and most song pairs, song classification was influenced by all parts of the song, with the beginning elements being most important. The field playback experiment used song type matching as the response measure. Each subject was presented a hybrid stimulus song consisting of the first half of one of his song types and the second half of another of his song types. Subjects replied with both ‘front matches’ and ‘back matches’ (60% were front matches).     

Red-winged blackbirds Ageliaus phoeniceus respond differently to song types with different performance levels

Physical constraints on animal signals can have important consequences for communication. For bird songs that include a trill, performance is physically constrained by a trade-off between the rate at which notes are repeated in the trill and the sound frequency range covered, such that a trill cannot exceed a certain frequency range for a given note repetition rate. Producing trills that are closer to this performance limit is presumably more challenging for birds than producing trills that are farther from it. Male red-winged blackbirds Ageliaus phoeniceus have repertoires of two to eight song types containing trills that span a range of performance levels. We determined the approximate trill performance maximum for a population of red-winged blackbirds, then conducted playback experiments to measure the responses of territorial males to song types with either high or low performance levels relative to this limit. Males responded significantly more strongly to songs containing low performance trills. Our results show that male red-winged blackbirds can discriminate between different song performance levels, suggesting that vocal proficiency plays a role in male-male interactions.     

Macrogeographic Variation in Song – a Test of Competition and Habitat Effects in Blue Tits

Investigations into the environmental causes of phenotypic variation may reveal information regarding the selective pressures leading to the evolution of these phenotypes. Blue tit ( Parus caeruleus ) song varies geographically in the proportion of song types that contain a trill (i.e. a series of identical notes repeated in sequence at a very rapid rate produced at the end of a song). In order to determine the environmental factors influencing geographic variation in the proportion of blue tit songs with a trill, we conducted a comparative study. At macrogeographic and regional scales we examined the effect of three factors that could influence geographic variation in blue tit song: dominant vegetation type, intraspecific competition and interspecific competition with great tits ( Parus major ). Interspecific competition may result in song convergence or song divergence (hereafter called character shift). The results we obtained are consistent with predictions of the character shift hypothesis: the proportion of songs presenting a different syntax to great tit songs (songs with a trill) increases significantly with relative great tit density. Results do not support predictions of hypotheses concerning song convergence or intraspecific competition. The results are consistent with some of the predictions of the acoustic adaptation hypothesis.     

Directional female preference for an exaggerated male trait in canary (Serinus canaria) song

Motor constraints on vocal production impose a trade-off between trill rate and frequency bandwidth within birdsong. We tested whether domesticated canary (Serinus canaria) females, reared either in acoustic isolation or in aviary conditions, had a preference for broad bandwidth songs with artificially increased syllable rates. The copulation solicitation display (CSD) was used as an index of female preference. As predicted, both naive and experienced females were especially responsive to syllables with a broad bandwidth emitted at an artificially increased rate. Female preference for supernormal stimuli provide support for the honest-signalling hypothesis and our results are consistent with recent findings indicating that production of song phrases maximizing both bandwidth and syllable rate may be a reliable indicator of male physical or behavioural qualities. We suggest that female preference for vocal emissions, which simultaneously maximize these two parameters, could be a widespread pattern within songbirds.     

Responses to Variation in Song Length by Male White‐Crowned Sparrows

Bird song has the potential to convey a variety of information about the singer, including the singer’s current motivational state. A recent review by Searcy & Beecher (2009) (Anim. Behav. 78, 2009; 1281) emphasized how little is currently known about whether song functions as an aggressive signal in territorial interactions. A recent observational study of song length variation in the Puget Sound white‐crowned sparrow reported that males shorten the terminal trill in their single song type while singing close by another male, and shorten the trill even further immediately before chasing the opponent. Here, we report the results of two song playback experiments designed to test whether males distinguish the differences in song length that occur in agonistic and non‐agonistic contexts. We found that males gave stronger responses, as measured by close approach distances, to either a series of songs increasing in duration (compared to a series decreasing in duration), or to long loud songs (compared to short soft songs). In both experiments, males gave weaker responses to the stimuli hypothesized to be more aggressive. Males shortened their songs in response to both simulated intrusions. Combined with the observational data on song variation in different contexts, these experiments support the conclusion that song length variation contains information about aggressive motivation in the white‐crowned sparrow.     

Acoustic structure of long calls in free-ranging groups of golden lion tarnarins,Leontopithecus rosalia

Like many other callitrichids, golden lion tamarins, Leontopithecus rosalia, emit Long Calls. Recordings of four free-ranging groups were made to explore different types of Long Calls. Three Long Call types were identified acoustically, and analyzed sonographically. The calls usually started with an Introductory Syllable (a chirp, a trill, or a whine) which was followed by either one, two, or three different phrases in a fixed sequential order. Each of the three phrases was unique and contained a typical number of syllables of characteristic shape, frequencies, and durations. Possible functions of these calls are discussed. © 1994 Wiley-Liss, Inc.     

Airflow and pressure during canary song: direct evidence for mini-breaths

Summary Male canaries (Serinus canaria) produce songs of long duration compared to the normal respiratory cycle. Each phrase in a song contains repetitions of a particular song syllable, with repetition rates for different syllables ranging from 3 to 35 notes/s. We measured tracheal airflow and air sac pressure in order to investigate respiratory dynamics during song.Song syllables (11–280 ms) are always accompanied by expiratory tracheal airflow. The silent intervals (15–90 ms) between successive syllables are accompanied by inspiration, except for a few phrases where airflow ceases instead of reversing. Thus, the mini-breath respiratory pattern is used most often by the five birds studied and pulsatile expiration is used only occasionally.Songs and phrases accompanied by minibreaths were of longer duration than those accompanied by pulsatile expiration, presumably because the animal's finite vital capacity is not a limiting factor when the volume of air expired for one note is replaced by inspiration prior to the next. Pulsatile expiration was used for only a few syllable types from one bird that were produced at higher repetition rates than syllables accompanied by mini-breaths. We suggest that male canaries switch to pulsatile expiration only when the syllable repetition rate is too high (greater than about 30 Hz) for them to achieve mini-breaths.Changes in syringeal configuration that may accompany song are discussed, based on the assumption that changes in the ratio of subsyringeal (air sac) pressure to tracheal flow rate reflect changes in syringeal resistance.     

Song types and their structural features are associated with specific contexts in the banded wren

We studied the use of song types and their acoustic features in different social contexts in the banded wren (Thryothorus pleurostictus), a resident tropical songbird in which males possess about 20 distinctive song types varying in duration, bandwidth, note composition, and trill structure. We recorded six focal males intensively for four days each while we observed context information such as during versus after dawn chorus, presence of the female, counter-versus solo-singing, location at the edge versus centre of the territory, and proximity to the nest. All males used at least some song types differentially during each of these pairs of alternative contexts. Males also preferentially used the song types they shared with a given neighbour when interacting with that bird. Songs delivered during dawn chorus were significantly longer, wider in bandwidth, often compound (double songs), and more likely to contain a rattle or buzz and an up-sweeping trill, compared to songs delivered after dawn chorus. Similar features were also more commonly observed when birds were engaged in intense male-male interactions and boundary disputes after dawn chorus, especially when countersinging at the edge of the territory. The presence of the female caused the male to deliver song types with narrower whole-song and trill bandwidth and fewer rattles and buzzes, and song-type diversity and fraction of compound songs were higher when the female was present. Thus, in addition to using type matching and variations in song-type switching and diversity to signal different levels of aggressive intention, male banded wrens also select song types based on their acoustic structure in different social contexts.