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No Correlation Between Three Selected Trade-Offs in Birdsong Performance and Male Quality for a Species With Song Repertoires
Abstract
Demanding performance of vocal signals, such as birdsong, may be evaluated by trade‐offs among acoustic traits. If individuals differ in their ability to sustain physiologically demanding singing, then aspects of song performance resulting from such trade‐offs could signal individual quality. Song performance can also differ among song types, and it is not known whether this influences the assessment of individual quality. We asked whether three trade‐off‐based measures of song performance indicate male age or aspects of condition (body condition, hematocrit and ectoparasite load) in the dark‐eyed junco (Junco hyemalis), a species with small repertoires. Across a sample of over 100 males, no measure of song performance was related to male age or condition, nor did song performance improve with age for those males recorded in consecutive years. In all cases, the variation in song performance explained by these predictors was small ( Document Type: Research Article DOI: http://dx.doi.org/10.1111/j.1439-0310.2012.02047.x Publication date: June 1, 2012 (document).ready(function() { var shortdescription = (".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } (".shortdescription a").click(function() { (".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher In this Subject: Animal Culture , Zoology , Psychology By this author: Cardoso, Gonçalo C. ; Atwell, Jonathan W. ; Hu, Yang ; Ketterson, Ellen D. ; Price, Trevor D. GA_googleFillSlot("Horizontal_banner_bottom");
... In all of these parameters, the production of syllables or syllable sequences with gradually or steadily shifting frequencies should entail less vigorous motor activity than the production of syllables or syllable sequences with rapid or numerous frequency shifts or reversals. A second main limitation of the vocal deviation index is that it can be applied only to trilled sequences (Cardoso, 2014;Geberzahn & Aubin, 2014). While many species trill, others do not, and at present we have no clear guideline for quantifying nontrilled song performances, or for comparing performances of songs with trilled versus nontrilled syntax. ...
... Frequency excursion thus provides a cumulative assessment of frequency modulations that occur across the course of an entire song or song segment. As in Geberzahn and Aubin (2014), frequency excursion accounts for the mechanical performance assumed to occur during silent intervals between notes, following the assumption that reconfigurations of the vocal apparatus are more extensive when note transitions involve larger frequency jumps (see also Cardoso, 2014;Podos et al., 2004b;Westneat et al., 1993). Higher-frequency excursion values should correspond to more active, rapid or extensive vocal activity (i.e. more pronounced reconfigurations of the vocal apparatus per unit time), and thus indicate greater required vocal performance. ...
... they will preferentially crystallize lower-performance songs, which would increase the prevalence of low-performance songs in a population and, correspondingly, the likelihood that they would be shared. Of particular interest in future work will be attention to the interplay of song performance and song use in species like swamp sparrows that have song repertoires (as in Cardoso, Atwell, Hu, Ketterson, & Price, 2012;DuBois et al., 2011). In a final sample application, we asked whether frequency excursion values were greater for trilled than nontrilled components of song sparrow songs. ...
Our understanding of the evolution and function of animal displays has been advanced through studies of vocal performance. A widely used metric of vocal performance, vocal deviation, is limited by being applicable only to vocal trills, and also overlooks certain fine-scale aspects of song structure that might reflect vocal performance. In light of these limitations we here introduce a new index of vocal performance, ‘frequency excursion’. Frequency excursion calculates, for any given song or song segment, the sum of frequency modulations both within and between notes on a per-time basis. We calculated and compared the two performance metrics in three species: chipping sparrows, Spizella passerina, swamp sparrows, Melospiza georgiana, and song sparrows, Melospiza melodia. The two metrics correlated as expected, yet frequency excursion accounted for subtle variations in performance overlooked by vocal deviation. In swamp sparrows, frequency excursion values varied significantly by song type but not by individual. Moreover, song type performance in swamp sparrows, according to both metrics, varied negatively with the extent to which song types were shared among neighbours. In song sparrows, frequency excursion values of trilled song segments exceeded those of nontrilled song segments, although not to a statistically significant degree. We suggest that application of frequency excursion in birds and other taxa will provide new insights into diverse open questions concerning vocal performance, function and evolution.
... We focus our comparisons on metrics of song performance based on trade-offs among acoustic traits related to ventilation, repetition rate, sound amplitude or frequency modulation, for example, that suggest motor or physiological limitations (reviewed in [16,17]; in juncos [18,19]). In the junco, such metrics of performance do not appear to reveal male quality [20], but are instead a property of the different song types, and higher-performance song types are preferentially used during more motivated singing [19]. Similar aspects of song performance are related to aggressive singing in many other songbirds [21][22][23][24][25][26][27][28][29][30]. ...
... University of California at San Diego, UCSD, and 50 males in Mount Laguna, ML), made during the breeding seasons of 2006 and 2007 [18,31]. These recordings comprise over 250 different song types sung in these populations, but were not designed to sample complete song repertoires of individual birds [19,20]. From the recorded songs, we computed four metrics of song performance: (1) proportion of sound and (2) residual intervals, which are metrics related to ventilation; (3) vocal deviation, which is related to motor performance; and (4) predicted amplitude, which reflects trade-offs between syllable complexity and relative sound amplitude [19]. ...
Social learning enables the adjustment of behaviour to complex social and ecological tasks, and underlies cultural traditions. Understanding when animals use social learning versus other forms of behavioural development can help explain the dynamics of animal culture. The dark-eyed junco (Junco hyemalis) is a songbird with weak cultural song traditions because, in addition to learning songs socially, male juncos also invent or improvise novel songs. We compared songs shared by multiple males (i.e. socially learned) with songs recorded from only one male in the population (many of which should be novel) to gain insight into the advantages of social learning versus invention or improvisation. Song types shared by multiple males were on average of lower performance, on aspects of vocal performance that have been implicated in agonistic communication in several species. This was not explained by cultural selection among socially learned songs (e.g. selective learning) because, for shared song types, song performance did not predict how many males shared them. We discuss why social learning does not maximize song performance in juncos, and suggest that some songbirds may add novel songs to culturally inherited repertoires as a means to acquire higher-quality signals.
... Each crystallized song in the final repertoire varies relatively little across renditions in syllable morphology and/or in the number of elements, yet males may differ in how far they can push physiological limitations during sound production (Lambrechts 1996;Suthers & Goller 1997). This ability to perform songs close to a limit may improve with time, from 1 yr to the next (Ballentine 2009; but see Cardoso et al. 2012) and older males may be able to perform songs better than younger birds De Kort et al. 2009). Age-related changes in song consistency may reflect vocal practice and provide a cue to male quality (Sakata & Vehrencamp 2012). ...
... Researchers have used spectrogram crosscorrelation coefficients or measured acoustic characters to quantify performance (Cramer 2013). For example, Cardoso et al. (2012) used three different measures to estimate performance in the songs of dark-eyed juncos (Table S1). We here examined performance of the note complex because the note complex is shared between territory neighbours and appears to be important in individual recognition and social mate choice (Nelson & Poesel 2007;Poesel et al. 2012). ...
Song of passerine birds is one of the few animal signals that is learned and that improves with practice. Vocal practice is crucial early in life to perfect a song imitation, but it also occurs throughout life and may continue to improve aspects of song performance. Differences in song performance among males that share song types, that is sing structurally similar songs may be particularly salient to receivers. We here test the hypothesis that aspects of song performance improve in a songbird species that deletes song types from its repertoire early in the first breeding season to share their final single song type with territorial neighbours. Over 3 yrs, we recorded songs in a population of Puget Sound white-crowned sparrows Zonotrichia leucophrys pugetensis and measured percentage peak performance and consistency thereof in all of the song types in each male's repertoire. We found that within the first year on territory, percentage peak performance was higher in shared than unshared songs but did not change from first to second recording. Contrary to the hypothesis that song performance improves with age, song performance declined from the first to the second year. Our results support the hypothesis that high-performance singers share songs. We did not find support for song performance improving within or between years, like it does in some other songbird species.
... This might strongly limit the trill rate as such reconfiguration needs some time. Contrarily, in songbird species singing trills mainly consisting of an alternating sequence of down-and up-sweeping syllables, a syllable might begin at the same frequency as the preceding one ended (for example, house wrens, Troglodytes aedon [19,20]; dark-eyed junco, Junco hyemalis [21]; compare with figure one A in [4]). Thus, males may be able to shorten gaps between such syllables more easily as the vocal tract does not need to be largely reconfigured. ...
... These authors suggested that the production of syllables in which the end of one syllable is produced at a different frequency than the start of the subsequent syllable might be more likely to be subject to performance constraints than syllables in which the inter-syllable frequency shift is small. Indeed, studies on species with trilled song components containing mainly either up-or down-sweeps have found a relationship between vocal performance and the aggressive motivation or quality of males (for example, swamp sparrows [25], banded wren, Thryophilus pleurostictus [26]) whereas most studies on species with trill components also made up by chevron-shaped syllables or consisting of an alternating sequence of down-and upsweeping syllables so far failed to find such relationships (for example, house wren [19,20], dark-eyed junco [21], but see [27]). We here provide clear empirical evidence supporting the hypothesis that performance constraints vary with the structure of syllable sequences of birdsong. ...
Background: Vocal performance refers to the ability to produce vocal signals close to physical limits. Such motor skills can be used by conspecifics to assess a signaler's competitive potential. For example it is difficult for birds to produce repeated syllables both rapidly and with a broad frequency bandwidth. Deviation from an upper-bound regression of frequency bandwidth on trill rate has been widely used to assess vocal performance. This approach is, however, only applicable to simple trilled songs, and even then may be affected by differences in syllable complexity.
... This might strongly limit the trill rate as such reconfiguration needs some time. Contrarily, in songbird species singing trills mainly consisting of an alternating sequence of down-and up-sweeping syllables, a syllable might begin at the same frequency as the preceding one ended (for example, house wrens, Troglodytes aedon [19,20]; dark-eyed junco, Junco hyemalis [21]; compare with figure one A in [4]). Thus, males may be able to shorten gaps between such syllables more easily as the vocal tract does not need to be largely reconfigured. ...
... These authors suggested that the production of syllables in which the end of one syllable is produced at a different frequency than the start of the subsequent syllable might be more likely to be subject to performance constraints than syllables in which the inter-syllable frequency shift is small. Indeed, studies on species with trilled song components containing mainly either up-or down-sweeps have found a relationship between vocal performance and the aggressive motivation or quality of males (for example, swamp sparrows [25], banded wren, Thryophilus pleurostictus [26]) whereas most studies on species with trill components also made up by chevron-shaped syllables or consisting of an alternating sequence of down-and upsweeping syllables so far failed to find such relationships (for example, house wren [19,20], dark-eyed junco [21], but see [27]). We here provide clear empirical evidence supporting the hypothesis that performance constraints vary with the structure of syllable sequences of birdsong. ...
Background
Vocal performance refers to the ability to produce vocal signals close to physical limits. Such motor skills can be used by conspecifics to assess a signaler’s competitive potential. For example it is difficult for birds to produce repeated syllables both rapidly and with a broad frequency bandwidth. Deviation from an upper-bound regression of frequency bandwidth on trill rate has been widely used to assess vocal performance. This approach is, however, only applicable to simple trilled songs, and even then may be affected by differences in syllable complexity.
Results
Using skylarks (Alauda arvensis) as a birdsong model with a very complex song structure, we detected another performance trade-off: minimum gap duration between syllables was longer when the frequency ratio between the end of one syllable and the start of the next syllable (inter-syllable frequency shift) was large. This allowed us to apply a novel measure of vocal performance - vocal gap deviation: the deviation from a lower-bound regression of gap duration on inter-syllable frequency shift. We show that skylarks increase vocal performance in an aggressive context suggesting that this trait might serve as a signal for competitive potential.
Conclusions
We suggest using vocal gap deviation in future studies to assess vocal performance in songbird species with complex structure.
Electronic supplementary material
The online version of this article (doi:10.1186/s12915-014-0058-4) contains supplementary material, which is available to authorized users.
... This might strongly limit the trill rate as such reconfiguration needs some time. Contrarily, in songbird species singing trills mainly consisting of an alternating sequence of down-and up-sweeping syllables, a syllable might begin at the same frequency as the preceding one ended (for example, house wrens, Troglodytes aedon [19,20]; dark-eyed junco, Junco hyemalis [21]; compare with figure one A in [4]). Thus, males may be able to shorten gaps between such syllables more easily as the vocal tract does not need to be largely reconfigured. ...
... These authors suggested that the production of syllables in which the end of one syllable is produced at a different frequency than the start of the subsequent syllable might be more likely to be subject to performance constraints than syllables in which the inter-syllable frequency shift is small. Indeed, studies on species with trilled song components containing mainly either up-or down-sweeps have found a relationship between vocal performance and the aggressive motivation or quality of males (for example, swamp sparrows [25], banded wren, Thryophilus pleurostictus [26]) whereas most studies on species with trill components also made up by chevron-shaped syllables or consisting of an alternating sequence of down-and upsweeping syllables so far failed to find such relationships (for example, house wren [19,20], dark-eyed junco [21], but see [27]). We here provide clear empirical evidence supporting the hypothesis that performance constraints vary with the structure of syllable sequences of birdsong. ...
Background
Vocal performance refers to the ability to produce vocal signals close to physical limits. Such motor skills can be used by conspecifics to assess a signaller¿s competitive potential. For example it is difficult for birds to produce repeated syllables both rapidly and with a broad frequency bandwidth. Deviation from an upper-bound regression of frequency bandwidth on trill rate has been widely used to assess vocal performance. This approach is, however, only applicable to simple trilled songs, and even then may be affected by differences in syllable complexity.ResultsUsing skylarks (Alauda arvensis) as a birdsong model with a very complex song structure, we detected another performance trade-off: minimum gap duration between syllables was longer when the frequency ratio between the end of one syllable and the start of the next syllable (inter-syllable frequency shift) was large. This allowed us to apply a novel measure of vocal performance ¿ vocal gap deviation: the deviation from a lower-bound regression of gap duration on inter-syllable frequency shift. We show that skylarks increase vocal performance in an aggressive context suggesting that this trait might serve as a signal for competitive potential.Conclusions
We suggest using vocal gap deviation in future studies to assess vocal performance in songbird species with complex structure.
... However, even when selection pressures favor escalated trill performance, an individual bird might still be able to maintain complex acoustic signals without sacrificing trill performance by having a larger repertoire of high-performance trilled songs. In dark-eyed juncos (Junco hyemalis), a species with song repertoires, trill performance was not related to male physical condition, but rather to the number of songs per male sampled by the researchers (Cardoso et al., 2012), suggesting that trill performance and song repertoire go together. These mixed results in previous studies led us to explore tradeoffs between trilled structures and song complexity in species with only one song type and also to test whether multiple traits reflect male physical condition. ...
... how trill performance and other aspects of song performance and complexity are balanced within individuals songs. Although recent interspecific and among-population studies have shown a compromise between trill performance and song complexity (Ballentine, 2006;Cardoso et al., 2012), we found no tradeoffs between trill performance and note repertoire size or linearity, two measures of complexity. Nor did we find associations between trill performance and other performance-related song traits, such as song duration or the proportion of trilled parts. ...
Bird songs have evolved under sexual selection pressure. Songs include multiple features that are subject to female preference, but recent comparative research has indicated evolutionary tradeoffs between song performance and complexity in some species. Trill, a repetition of the same sound, is a performance-related song trait; higher trill performance can be achieved at the cost of song complexity at the among-species or population level. The aim of this study was to examine whether such tradeoffs also account for within-species variation in Java sparrow songs, which include both multiple trill types and non-trill parts. We found a great individual variation in trill proportion, trill performance, and song complexity. A positive association between trill performance and body size suggested that trills can serve as an indicator of male quality. However, contrary to the tradeoffs predicted by previous studies based on other passerine species, trill performance and song complexity, i.e. note repertoire, were positively correlated: males in better condition can sing songs with larger note repertoires and higher trill performance, which may explain how trills and non-trill notes are both maintained and have co-evolved by sexual selection in Java sparrow songs.
... In several species, females prefer males with lower deviation, more challenging trills151617181920, and may even alter investment in eggs depending on the vocal deviation of males' songs ([21] and references therein). Vocal deviation correlates with male quality (e.g., age and mass, [22,23] but see [24]) and affects how males respond to playback in several species2526272829 but see [30]). Consistency is a measure of how precisely a sound is reproduced each time the bird repeats it, and it can be measured at the level of either whole songs or individual, repeated syllables. ...
... While most measures of male quality did not correlate with trill quality (also see [24]), older males did sing with higher trill consistency (Table 2), a result that is highly consistent with the current literature. In several other species (reviewed by [33,76]), as in house wrens, older males sing more consistently than males in their first breeding season. ...
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.
... Indeed, in the swamp sparrow Melospiza georgiana, larger and older (i.e., presumably higher-quality) males sing, on average, with a higher performance (Ballentine, 2009). However, in the dark-eyed junco Junco hyemalis, song performance was not associated with the quality and/or age of the male (Cardoso et al., 2012). Recently, the postulate that there is a correlation between song performance and male quality has been seriously criticized (Kroodsma, 2017): differences in song performance between males can be well explained by random factors of the learning process (e.g., the way that a suitable male teacher sings) without involving ideas about individuals having different qualities. ...
Birdsong is one of the most complex signals in the animal world, as it can consist of many different sounds grouped according to certain rules. Singing acts as a distant signal, indicating, e.g., the species and sex of the singer. However, territorial songbirds also use singing as an interactive social signal during territorial disputes, as well while interacting with females. In these contexts, males vary the type and timing of their songs to convey graded information about their motivational state, and those variations can play a role in communication. In this review, we considered how male songbirds vary their singing in the territorial context. To study such variations, researchers usually simulated territorial intrusion by playing back conspecific singing in territories, including singing modified in a manner necessary for the researcher. For comparison, I considered briefly how singing varies in intersexual context. I focus on the role of singing complexity in communication. Therefore, not all known context-dependent changes in singing are considered, but only those related to "complexity": the diversity of song/sound types and the transitional patterns of different song/sound types in the course of singing. My review has shown that males change their singing when they detect environmental changes such as the appearance of a female or a competitor as follows: (1) the song rate increases, (2) the syllable rate increases, (3) the song-type switching rate increases, (4) the song-type diversity increases (i.e., the observed repertoire size), and (5) longer and more complex songs are predominantly used. In some species, the song bout organization may also change, but the data are still scarce. Typically, one or more, but not all, of the aforementioned acoustic behaviors have been found in a given songbird species. All these behaviors (tactics) come down to a single strategy, namely, maximizing the acoustic diversity over a short period of time (e.g., several minutes), that is, increasing the number of different song and/or note types. The proximate causes of how the increased acoustic diversity work in the territorial competition context might lie in a sensory or perceptual bias of the receiver. Namely, habituation should occur to repeated presentation of the same song type faster than to presentation of different song types. Therefore, by vocalizing more diversely, males more effectively influence the signal recipient's behavior.
... предположительно более качественные) самцы поют в среднем с большей производительностью . Однако у серого юнко Junco hyemalis песенная производительность не была связана с качеством и/или возрастом самца (Cardoso et al., 2012). Не так давно постулат о связи песенной производительности с качеством самца был подвергнут серьёзной критике . ...
Пение птиц – один из самых сложных сигналов в мире животных, так как оно может состоят из многих разных звуков, группирующихся по определённым правилам. Пение выступает в качестве дальне-дистантного маркёра, обозначая, например, видовую и половую принадлежность певца. Но также оно используется во время непосредственных взаимодействий, например при территориальных конфликтах. В таких ситуациях пение может меняться, становясь отличным от обычного спонтанного пения. Эти модификации могут отражать сиюминутное мотивационное состояние исполнителя и играть роль в коммуникации. В обзоре они рассмотрены на примере территориальных взаимодействий самцов. Эти данные получены в основном в экспериментах с трансляцией самцам видоспецифичного пения, в том числе измененного нужным для экспериментатора образом. Так имитируется вторжение постороннего самца на территорию резидента. Для сравнения были использованы данные об изменениях в пении самцов, отмеченных при взаимодействиях с самками. В фокусе внимания автора статьи – роль сложности пения в коммуникации. Поэтому рассмотрены не все известные ситуативные изменения в пении, а только имеющие отношение к «сложности»: это разнообразие используемых типов песен и/или звуков и правила их комбинирования при пении. Обзор показал, что при изменении внешней обстановки (при появлении самки или конкурента) у певчих птиц происходят следующие изменения в пении (у конкретного вида обычно одно или несколько, но не все сразу): 1) повышается частота пения, 2) возрастает частота эмиссии звуков, 3) повышается частота смены напева, 4) увеличивается разнообразие пения (наблюдаемый размер репертуара), 5) преимущественно используются более продолжительные и разнообразные песни. У некоторых видов, возможно, меняется и организация пения, но данных недостаточно. Все названные пять тактик изменений в пении сводятся к единой стратегии: это максимизация разнообразия акустической продукции на коротких промежутках времени (несколько минут), т.е. увеличение числа разных типов песен и/или звуков. Смысл (проксимальный механизм) максимизации разнообразия может состоять в увеличении времени привыкания к стимулу. К сложному пению, состоящему из многих типов песен и/или звуков, привыкание будет происходить дольше – по сравнению с пением простым и однообразным. Значит, вокализируя разнообразнее, самцы эффективнее воздействуют на получателей сигнала – своих конкурентов либо брачных партнёров.
... By contrast, White-crowned sparrow (Zonotrichia leucophrys) males approached high-performance songs (having both fast trill and wide frequency bandwidth) more closely than they did lower-performance songs (Phillips & Derryberry 2017). In Dark-eyed junco (Junco hyemalis), song performance was not related to male condition or age (Cardoso et al. 2012), thus not aligning with the earlier finding in Swamp sparrows (see above). ...
Performance of vocal signals, such as birdsong, may be a subject to trade-offs among acoustic traits that limit the signal outcomes. Trilled songs in which syllables are repeated in rapid succession present males with a performance challenge resulting in a trade-off between trill rate (rate of repetition) and frequency bandwidth (range of frequency). Individuals of a species might differ in ability to produce high-performance songs that are close to a performance limit. It was suggested that high-performance songs might honestly reveal a high-quality singer, and both males and females might use those songs to detect high-quality singers. To test further this performance hypothesis, I asked whether the usage of song types depended on their performance in the Pale-legged leaf-warbler (Phylloscopus tenellipes), a species with individual repertoires of up to 11 trilled song types. I analyzed 125 song types (n = 25 males) taken from both spontaneous singing and singing elicited by conspecific playback. Songs showed the same performance trade-off between trill rate and frequency bandwidth as found in other passerines. Individuals did not differ relative to one another in their average vocal performance. Males did not preferentially use either high-or low-performance song types in response to playback-simulated territorial intrusion. They also did not modulate the performance of the same song type to signal aggression. Besides, song performance did not differ between predominant song types and all other song types. Since the predominant song type of a given male usually the only one that used in spontaneous singing, a receiver presumably cannot obtain information about the male's performance ability from his spontaneous singing. Overall, my results did not confirm the role of vocal performance in male-male interaction.
... Evidence from a range of taxa indicates that songs can convey honest information on singer's motivation and quality which may be used both by females in mating decisions, and by other males in competitive interactions [4,5]. However, there are also species in which song traits do not correlate with male quality [62] and further research is needed to directly test this hypothesis in fin whales. The effect of year on singing activity was greatly influenced by 2012, which showed significantly lower call rates when compared to 2008, 2010 and 2011. ...
Animals use varied acoustic signals that play critical roles in their lives. Understanding the function of these signals may inform about key life history processes relevant for conservation. In the case of fin whales (Balaenoptera physalus), that produce different call types associated with different behaviours, several hypotheses have emerged regarding call function, but the topic still remains in its infancy. Here, we investigate the potential function of two fin whale vocalizations, the song-forming 20-Hz call and the 40-Hz call, by examining their production in relation to season, year and prey biomass. Our results showed that the production of 20-Hz calls was
strongly influenced by season, with a clear peak during the breeding
months, and secondarily by year, likely due to changes in whale abundance. These results support the reproductive function of the 20-Hz song used as an acoustic display. Conversely, season and year had no effect on variation in 40-Hz calling rates, but prey biomass did. This is the first study linking 40-Hz call activity to prey biomass, supporting the previously suggested food-associated function of this call. Understanding the functions of animal signals can help identifying functional habitats and predict the negative effects of human activities with important implications for conservation.
... Their long songs and large among-and within-species differences in song duration could buffer against losses of syllable diversity when singing longer trills. Furthermore, using diverse repertoires can make it difficult for receivers to compare song motor performance among individuals (Logue and Forstmeier 2008;Cardoso et al. , 2012bPodos et al. 2016;Liu et al. 2018). As a consequence, other aspects of singing, such as syllable diversity, may be equally or more important for communication in this group and perhaps less likely to be compromised evolutionarily. ...
The diversity and the motor performance of birdsongs can both be sexually selected. In wood warblers, most species with high motor performance sing a greater proportion of trills, presumably to advertise performance, and thus have lower syllable diversity. We tested if this trade‐off between motor performance and syllable diversity extends to canaries, goldfinches and allies, a clade with much longer and more varied songs. We assembled a molecular phylogeny and inferred song motor performance based on the speed of frequency modulation either in trills or in within‐song intervals. The two metrics of performance were positively, but only mildly, related across species. While performance evaluated in intervals had high phylogenetic signal, performance evaluated in trills changed independently of phylogeny and was constrained by body size. Species in densely vegetated habitats sang fewer trills, but did not differ in motor performance. Contrary to wood warblers, song motor performance did not predict the proportion of trilled syllables nor within‐song syllable diversity, perhaps because large differences in the song duration of canaries, goldfinches and allies prevent trills from severely compromising syllable diversity. Opposed results in wood warblers and in these finches indicate the existence of clade‐specific trade‐offs in the evolution of birdsong.
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... This preference requires that females be able to assess male age, a capability that is generally thought to be based on discrimination of age-correlated plumage or song traits (de Kort et al. 2009). The song of male juncos does not differ between age groups (Corbitt and Deviche 2005;Cardoso et al. 2012), making it more probable that female juncos identify older males based on age-related plumage traits such as quantity of tail white. Our finding that afterhatch-year juncos have more white on the fourth rectrix than hatch-year juncos is consistent with this possibility. ...
Differences in environmental conditions are expected to generate distinct selective pressures favoring different phenotypes. For example, environmental conditions that affect the timing of breeding may influence opportunities for extra-pair copulations and thus the strength of sexual selection on males. To explore these relationships quantitatively, we compared breeding synchrony, rates of extra-pair paternity, and expression of a sexually selected plumage trait (the amount of white on the tail feathers) in populations of dark-eyed junco (Junco hyemalis) breeding at elevations from 1960 to 2660 m in California. Microsatellite parentage analysis revealed that extra-pair paternity rates varied by elevation, with intermediate elevations having the highest rate. Differences in breeding synchrony could not explain this variation. Extra-pair males had more tail white than the social males they cuckolded, consistent with tail white being a sexually selected trait. Although the observed differences in rates of extra-pair paternity suggested that sexually selected traits should also vary with elevation, there were no differences among elevations in the amount of white on male tails or in the correlation between tail white and proxies for male condition. Multiple factors may have contributed to this result, including persistent gene flow among elevations, which may counter the effects of local differences in selective pressures. These findings demonstrate the complexity of interactions among environmental conditions, selective pressures, and variation in phenotypic traits, and underscore the importance of assessing the impacts of sexual selection in the larger context of population genetic structure.
Significance statement
Environmental differences, such as those occurring along elevation gradients, can lead to differences in sexual selection. We found that juncos at mid elevations had higher rates of extra-pair paternity than juncos at high and low elevations. Our results also provide evidence that male tail plumage is sexually selected, as females preferred to copulate with males with more white on their tail plumage than the females’ social mates. This suggests that male tail white should differ among elevations, as the reproductive rewards of having an attractive tail would be greater at mid elevations. However, we found no differences in male tail white among elevations. This may be due to the birds breeding freely across elevations, as evidenced by a lack of genetic structure, i.e., gene flow swamping out any differences that might otherwise form.
... Thus, in some environments, we might predict that either trill rate or frequency bandwidth may become the more salient trait or even a different performance trait (e.g. song complexity or consistency) may be more likely to indicate sender quality (Cardoso, Atwell, Hu, Ketterson, & Price, 2012;Cardoso, Atwell, Ketterson, & Price, 2007;Sakata & Vehrencamp, 2012). The idea that different types of performance may be favoured depending on the type of environment remains to be tested and provides an interesting path for future vocal performance research. ...
Sexual signals that are physically limited can be reliable indicators of quality or motivation in male–male competition. One such example of a motor constraint in birds is the production of repeated notes, which are limited in the frequency bandwidth and trill rate at which notes can be produced, such that it is difficult to produce wide-bandwidth notes at fast rates. How well birds maximize frequency bandwidth and trill rate is one measure of vocal performance, commonly referred to as ‘vocal deviation’. In theory, fast songs with narrow bandwidths and slow songs with wide bandwidths should have similar values of vocal deviation. In many species, males respond to variation in vocal deviation, supporting the notion that it is a sexually selected signal. However, most studies test only one of these components, either trill rate or bandwidth, rather than both individually, when testing receiver response to vocal deviation. Therefore, a question remains as to whether songs with equivalent values of vocal deviation (e.g. fast songs with narrow bandwidths and slow songs with wide bandwidths) elicit similar levels of response from receivers. We tested whether receivers respond specifically to the trade-off between trill rate and bandwidth (i.e. vocal deviation) or only to variation in one of the component parts. Using territorial playback experiments with wild male white-crowned sparrows, Zonotrichia leucophrys, we found that males approached high-performance songs (fast trill, wide bandwidth) more closely than they did lower-performance songs (fast trill, narrow bandwidth; slow trill, wide bandwidth) and they did so regardless of whether performance varied because of differences in trill rate or bandwidth. Furthermore, we found that males gave similar responses to songs of similar vocal deviation. Our results empirically support the hypothesis that receivers respond specifically to the physical limitation on the production of repeated notes.
... Comparisons among song types may thus require integrating the effects of many acoustic traits, or using several different metrics. For example, comparisons among dark-eyed juncos, Junco hyemalis, singing different song types used several metrics of performance, including some that integrate effects of many acoustic traits Cardoso, Atwell, Hu, Ketterson, & Price, 2012), and comparisons among swamp sparrows singing different song types used a metric that assesses frequency modulation quite exhaustively throughout the entire length of songs ('frequency excursion'; Podos et al., 2016). Otherwise, it would not have been convincing to show absence of individual differences in performance. ...
It is appealing to integrate different acoustic traits to infer differences in performance demands among birdsongs, and to use this as a tool for investigating which roles song performance plays in communication. But inferring performance from acoustic measurements introduces a degree of interpretation that can cause disagreement. Here I give an overview of approaches to assess song performance, associated methodological issues, and ways of addressing them. I note advantages and limitations of performance metrics derived from physiological principles or from acoustic trade-offs, discuss issues with the scaling of performance metrics, and with choosing and adapting metrics to different study species and research goals. Throughout I emphasize that these metrics provide tentative assessments of performance, and that empirical results should be interpreted by comparison to alternative hypotheses.
... Advertising the performance of fast and wide frequency modulations might therefore contribute to explain the evolution of simple trilled songs in dark-eyed juncos. While there is no evidence that this aspect of trill performance indicates male quality in juncos (Cardoso et al. 2012a), it nonetheless appears meaningful for communication, since higher performance song types are used during more motivated singing ). Similarly, by making it easier to assess by receivers, these simple trilled songs could be a means to advertise song consistency (Sakata and Vehrencamp 2012) or resistance to occasional mistakes (Cardoso 2013), both of which convey information on individual quality in dark-eyed juncos (Ferreira et al., submitted). ...
Male dark-eyed juncos sing simple, trilled LRS, with much lower syllable diversity than in other junco species. Development of LRS is peculiar in that some song types are socially learned and shared with other males in the population while others are improvised or invented during development. The input of these novel songs explains the low levels of song sharing among males and buffers against geographic differentiation by cultural mechanisms. In fact, while dark-eyed junco LRS can diverge rapidly, for example under changing acoustical conditions of habitats, LRS differs minimally across the large geographic distribution of subspecies in North America, indicating little potential for mediating reproductive isolation. Simpler LRS than in related species and the use of improvised or invented songs, with the consequent low song sharing among males, are functionally unexpected for a species with the ecological characteristics of dark- eyed juncos. Yet these song traits seem responsible for the low song divergence across subspecies. Explaining those traits functionally is a challenge for future research.
In contrast, SRS of dark-eyed juncos is a quiet, complex vocalization that differs substantially from LRS and is particularly important during courtship. Owing to the fact that SRS is directed to a close receiver, it is likely less affected by selection for efficient sound transmission than LRS, which may facilitate divergence between populations, for example in response to differences in female preferences. Similarly to LRS, the likelihood that SRS will diverge rapidly and serve as a reliable indicator of population origin will depend heavily on how much of SRS is socially learned, an important topic for future study. It is unlikely that SRS is the sole determinant of mating success in juncos, and thus the relative importance of junco courtship signals in each modality (acoustic, visual, olfactory) must be considered to fully understand the potential for premating isolation through divergent courtship signals.
... Females prefer lowdeviation songs in laboratory female choice assays (Vallet et al. 1998;Drǎgǎnoui et al. 2002;Ballentine et al. 2004;Caro et al. 2010), males that sing lower deviation songs pair earlier in the field (Christensen et al. 2006), and extrapair sires sing lower deviation songs than the within-pair males they cuckold (Cramer et al. 2011). Moreover, males' vocal deviation capabilities correlate with phenotypic measures of quality in some passerine species (Ballentine 2009;Sockman 2009; though not others, Cardoso et al. 2012). Males either use lower deviation trill types or decrease the vocal deviation of a given trill type in social contexts where signaling at a high level may be more important (Beebee 2004;Trillo and Vehrencamp 2005;Kunc et al. 2006;Cardoso et al. 2009;DuBois et al. 2009). ...
Signals that require a high degree of skill to produce are expected to honestly indicate signaler quality. In trilled birdsong, 2 parameters that likely reflect performance difficulty are vocal deviation (how rapidly sound frequency is modulated) and trill consistency (how precisely syllables are repeated). These parameters function as intra-and intersexual signals in most bird species tested to date, but they may not adequately capture song performance difficulty in all species. I used 2 playback protocols to test whether males respond differently to songs that differ in vocal deviation and trill consistency in house wrens (Troglodytes aedon). Despite large sample sizes, male responses did not depend on playback treatment. Males sang each trill type at a range of pitches, and the vocal deviation of the trill depended strongly on the pitch at which it was sung, consistent with models of song production mechanics. I propose that the addition of the pitch covariate may complicate the evaluation of vocal deviation, limiting the usefulness of this potential signal for this species. Moreover, producing each trill type at a range of pitches may itself serve some communication function, which could override the potential signal value of trill consistency. Although vocal deviation and trill consistency are male quality indicators in some species, these results suggest that species-specific differences in what constitutes a "challenging" song may prevent these measures from being universally applicable.
... However, if syllable duration and gap duration both vary independently, then sound density may quantify a different facet of signal intensity than syllable rate. Measures related to sound density have been shown to be intersexually selected (e.g., in zebra finches, Taeniopygia guttata; Holveck and Riebel 2007) and tended to covary with body condition of male dark-eyed juncos (Junco hyemalis; Cardoso et al. 2012). Furthermore, a similar song measure termed "duty cycle" has been suggested to convey information about the motivational state of a signaler in an alarm context (black-capped chickadees, Poecile atricapillus; Wilson and Mennill 2011). ...
In songbirds of the temperate zone, often only males sing and their songs serve to attract females and to deter territorial rivals. In many species, males vary certain aspects of their singing behavior when engaged in territorial interactions. Such variation may be an honest signal of the traits of the signaler, such as fighting strength, condition, or aggressive motivation, and may be used by receivers in decisions on whether to retreat or to escalate a fight. This has been studied intensively in species that sing discontinuously, in which songs are alternating with silent pauses. We studied contextual variation in the song of skylarks (Alauda arvensis), a songbird with a large vocal repertoire and a continuous and versatile singing style. We exposed subjects to simulated territorial intrusions by broadcasting conspecific song and recorded their vocal responses. We found that males sing differently if they are singing spontaneously with no other conspecific around than if they are territorially challenged. In this last case, males produced lower-frequency syllables. Furthermore, they increased the sound density of their song: they increased the proportion of sound within song. They seem to do so by singing different elements of their repertoire when singing reactively. Furthermore, they increased the consistency of mean peak frequency: they repeated syllable types with less variability when singing reactively. Such contextual variation suggests that skylarks might use low frequencies, sound density, and song consistency to indicate their competitive potential, and thus, those song features might be important for mutual assessment of competitive abilities.
... These results support the original conclusions that there are strong differences in performance between song types, which might have communication functions (e.g. signals of graded intensity), but that large variation and weak repeatability within males make it unlikely that this aspect of song performance signals individual quality in juncos (see Cardoso et al. 2009 Cardoso et al. , 2012 for tests of these hypotheses). Therefore, in this within-species example in which individuals used approximately the same range of absolute frequencies, measurements based on logarithmic or linear frequency scales were highly correlated, and changing to frequency logarithms yielded nearly identical results. ...
Most research on animal vocal communication analyses frequency measurements on a linear scale, but the mechanisms of pitch perception and of certain aspects of vocal production are better described on a logarithmic scale, that is, as frequency ratios. Thus, for the majority of questions in vocal communication it is advisable to use log-transformed frequency, and the objective of this article is to encourage researchers to adopt this procedure. To illustrate this transition in methodology, I present two reanalyses of work on vocal communication, at the within- and among-species levels. Changing from linear to logarithmic scales yielded qualitatively identical conclusions, even in the among-species example where larger differences in absolute frequency can weaken the correlation between measurements at these two scales. These results suggest that conclusions of past work should generally be robust, at least when the absolute frequencies being compared do not diverge excessively. Results became stronger in the amongspecies example, suggesting that, as expected, frequency logarithms improve the ability to demonstrate biological phenomena. I hope that this discussion will motivate researchers to analyse frequency on a logarithmic scale for most research goals on vocal communication.
... ends are consistent with earlier findings of a terminal investment effect on song rates during playback, in which males that subsequently died sang songs at higher rates than males that survived (Hall et al. 2009). Our condition index does not seem to reflect the probability of mortality in this long-lived tropical bird (75 % annual survival rate). Cardoso et al. (2012) likewise found no associations between components of trill performance and condition in dark-eyed juncos (Junco hymenalis). A direct effect of health and condition on song performance parameters has only been described in a few species (Pasch et al. 2011;), but senescence is associated with decreased song performance in two avian specie ...
Acoustic displays with difficult-to-execute sounds are often subject to strong sexual selection, because performance levels are related to the sender's condition or genetic quality. Performance may also vary with age, breeding stage, and motivation related to social context. We focused on within-male variation in four components of trill performance in banded wren (Thryophilus pleurostictus) songs: note consistency, frequency bandwidth, note rate and vocal deviation. The latter is a composite measure reflecting deviation from the performance limit on simultaneously maximizing both frequency bandwidth and note rate. We compared the changes in these song parameters at three time scales: over the course of years, across the breeding season, and at different times of the day with contrasting agonistic contexts. Vocal deviation decreased and note consistency increased over years, suggesting that experience may improve individual proficiency at singing trills. Consistency also increased across the season, confirming that practice is important for this parameter. Although there was no significant seasonal change in vocal deviation, one of its components, note rate, increased during the season. Neither vocal deviation nor consistency varied with agonistic context. However, note rate increased during playback experiments simulating territorial intrusions compared to dawn chorus singing. The magnitude of a male's increase in note rate was positively correlated with his aggressive behavior during the playback experiment. Thus consistency, bandwidth, and vocal deviation indicate age, whereas trill rate flexibly indicates the singer's aggressive motivation. We also found evidence of a within-male trade-off between vocal deviation and consistency.
The song of male birds is implicated in mate attraction and territory defence and assumed to evolve through sexual selection. Song production is hypothesized to represent a biomechanical challenge under physical, respiratory and neural limitation, leading to trade-offs. Although both sexes sing in numerous species, vocal performance has been little studied in females. European robins, Erithacus rubecula, of both sexes sing in autumn and winter to defend exclusive individual territories. We recorded robins singing spontaneously, that is, when not engaged in overt territorial interactions. We identified a trade-off between two acoustic parameters: (1) the frequency ratio between successive song elements and (2) the duration of gaps between these elements. This trade-off might represent a vocal production limit. To compare vocal performance between the sexes we used two measures: vocal gap deviation (the difference between how the bird sings and the theoretical performance maximum according to the putative vocal production limit we had identified) and sound density (the proportion of the song over which sound is present). Males and females did not differ in these two measures of vocal performance suggesting that the territory defence function of the song is used in social competition with members of either sex. In both sexes, vocal performance was not correlated with morphometric measures and repeatability coefficients were very small. Thus, vocal performance probably does not convey information about the signaller's body size or body condition, at least in spontaneous song of robins. These results inform the debate on selection forces driving female song.
Motor performance describes the vigour or skill required to perform a particular display. It is a behaviourally salient variable in birdsong and other animal displays, but little is known about within-individual variation in performance over short timescales. The metric ‘frequency excursion’ (FEX) quantifies birdsong performance as cumulative frequency modulation per unit time. We measured FEX in a large sample of recordings from free-living male Adelaide's warblers, Setophaga adelaidae. Our objectives were to quantify natural variation in performance and test the hypotheses that performance (1) improves as a function of recent practise, (2) decreases over consecutive repetitions of a single song type, (3) improves with rest between songs, (4) varies by singing mode and (5) changes during vocal interactions with neighbours. We found significant variation in performance among individuals and song types. Consecutive repetition of a song type, rest between songs, singing mode and vocal interaction did not strongly affect performance. Performance consistently increased with song order, however, indicating that males warm up during morning singing. This is the first demonstration of such an effect in a sexual display. The warm-up effect may explain the prevalence of intense dawn singing in birds (dawn chorus), if rivals engage in an arms race to warm up.
Birdsong biologists interested in sexual selection and honest signalling have repeatedly reported confirmation, over more than a decade, of the biological significance of a scatterplot between trill rate and frequency bandwidth. This ‘performance hypothesis’ proposes that the closer a song plots to an upper bound on the graph, the more difficult the song is to sing, and the more difficult the song the higher quality the singer, so that song quality honestly reveals male quality. In reviewing the confirming literature, however, I can find no support for this performance hypothesis. I will argue here that the scatter in the graph for songbirds is better explained by social factors and song learning. When songbirds learn their songs from each other, multiple males in a neighbourhood will sing the same song type. The need to conform to the local dialect of song types guides a male to learn a typical example of each song type for that population, not to take a memorized song and diminish or exaggerate it in trill rate or frequency bandwidth to honestly demonstrate his relative prowess. When data in this scatterplot are coded both by song type and by male, it is the song type and the need to conform that explains the variability, not the quality of different males. There is no consistent, reliable information in the song performance measures that can be used to evaluate a singing male.
Song birds that have been artificially introduced to isolated areas are fruitful material for investigating changeability of songs within a limited period of time. I studied songs of Japanese Bush-warblers, Cettia diphone, which were introduced from Japan to the island of O‘ahu (Hawaiian Islands) ca. 80 yr ago. These warblers on O‘ahu sang acoustically simpler songs at lower frequencies than the warblers on Honshu, the main island of Japan. Previous studies found similar tendencies on small peripheral Japanese islands. Morphological characteristics indicated that the warblers on the Hawaiian Islands did not originate from insular subspecies in Japan. Therefore, the acoustic structure of their songs may have changed during their 80 yr on O‘ahu. Possible factors driving this rapid change are relaxed sexual selection and/or the sound transmission properties of the island habitat.
Abstract Studies of trilled vocalizations provide a premiere illustration of how performance constraints shape the evolution of mating displays. In trill production, vocal tract mechanics impose a trade-off between syllable repetition rate and frequency bandwidth, with the trade-off most pronounced at higher values of both parameters. Available evidence suggests that trills that simultaneously maximize both traits are more threatening to males or more attractive to females, consistent with a history of sexual selection favoring high-performance trills. Here, we identify a sampling limitation that confounds the detection and description of performance trade-offs. We reassess 70 data sets (from 26 published studies) and show that sampling limitations afflict 63 of these to some degree. Traditional upper-bound regression, which does not control for sampling limitations, detects performance trade-offs in 33 data sets; yet when sampling limitations are controlled, performance trade-offs are detected in only 15. Sampling limitations therefore confound more than half of all performance trade-offs reported using the traditional method. An alternative method that circumvents this sampling limitation, which we explore here, is quantile regression. Our goal is not to question the presence of mechanical trade-offs on trill production but rather to reconsider how these trade-offs can be detected and characterized from acoustic data.
Degradation of acoustic signals during transmission presents a challenging selection pressure for animals dependent on vocal communication. Sound transmission properties differ among habitats and may drive the evolution of vocal signals in different directions. Urban habitat is expanding worldwide and an increasing number of species, including many birds, must now communicate around buildings and over concrete. Urban habitats are evolutionarily new, although to some extent they may acoustically resemble rocky habitat such as cliffs and canyons. Neither urban nor these natural habitats have been studied in any detail for the selection pressure they may exert on animal communication. Dark-eyed Juncos (Junco hyemalis) commonly inhabit montane pine forests across North America, but for about 25 years an isolated population has been successfully breeding in an urban environment in southern California. We investigated potentially divergent selection pressures on junco songs, using sound transmission experiments with artificial sound stimuli, in natural forest habitat and in this urban habitat. Transmission properties differed significantly, resulting in tails of reflected sound with gradually declining amplitude in the forest and in multiple discrete echoes in the urban environment. We expected environmental selection in urban habitat to favor shorter songs with higher frequencies and slower trill rates. Despite the presence of relatively short urban songs, there was no significant shortening overall. There were also no differences in trill rates, but we did find a significantly higher minimum frequency in the urban junco population compared to three of four forest populations. Although the pattern of song divergence was not consistent and it is difficult to draw firm conclusions from this single urban population, our transmission results suggest that echoes could be important in shaping urban birdsong.
Gull chicks beg for food from their parents. Peacocks spread their tails to attract potential mates. Meerkats alert family members of the approach of predators. But are these--and other animals--sometimes dishonest? That's what William Searcy and Stephen Nowicki ask inThe Evolution of Animal Communication. They take on the fascinating yet perplexing question of the dependability of animal signaling systems. The book probes such phenomena as the begging of nesting birds, alarm calls in squirrels and primates, carotenoid coloration in fish and birds, the calls of frogs and toads, and weapon displays in crustaceans. Do these signals convey accurate information about the signaler, its future behavior, or its environment? Or do they mislead receivers in a way that benefits the signaler? For example, is the begging chick really hungry as its cries indicate or is it lobbying to get more food than its brothers and sisters? Searcy and Nowicki take on these and other questions by developing clear definitions of key issues, by reviewing the most relevant empirical data and game theory models available, and by asking how well theory matches data. They find that animal communication is largely reliable--but that this basic reliability also allows the clever deceiver to flourish. Well researched and clearly written, their book provides new insight into animal communication, behavior, and evolution.
The validity of the haematocrit or packed cell volume as an indicator of condition in wild birds has recently been questioned. We reviewed over 300 published papers on haematocrit values for wild birds. These studies show that changes in haematocrit could be caused by a number of different natural factors that include age, sex, geographical elevation, energy expenditure, parasitism, nutrition and genetics. Haematocrit also increased with age from hatching, due to increased erythropoiesis, so that adult birds generally have greater haematocrit values than nestlings or juveniles. Haematocrit values were either independent of elevation or increased with elevation. A meta-analysis of 36 studies showed no difference in haematocrit between the sexes. Relationships between haematocrit value and both energy expenditure and parasitic infection vary between studies. In temperate climates, haematocrit tended to be higher in winter than in summer, which may be due to dehydration or increased oxygen demand caused by thermogenesis, moult or acquisition of reproductive status. Our review indicates that the use of haematocrit as a sole indicator of condition or health could lead to incorrect conclusions if natural factors that can affect haematocrit are not taken into consideration.
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.
Frequency of singing by birds may vary with reproductive stage in ways that reflect variation in the functions of song in
intersexual and intrasexual communication. In dark-eyed juncos (Junco hyemalis) high-amplitude song is produced only by males. To investigate the function of this song, we tested whether fertility of
females affected singing by their mates or by neighboring males. Using focal observations, song censuses, and radiotracking
data, we determined whether song production varied between and among periods when females were fertile and non-fertile. Our
findings show that males do not increase song production when their mates are fertile, nor do they increase song production
when neighboring females are fertile. These results suggest that male juncos do not signal their intent to defend territories
(or mates) more when females are fertile and that they do not use song to advertise to specific potential participants in
extra-pair fertilizations.
This article describes the organisation of song in the serin (Serinus serinus) and analyses its variation among individuals. Serins have a repertoire of about 50 complex syllables that are sung at a
very fast rate and in a very stereotyped order, forming discrete songs. Songs are high pitched for the serin’s body size.
Song organisation is circular, with a limited number of starting points. Songs can stop at any point in their cycling. Within
songs there are trilled sections and fast, non-repeated sections that account for the greatest part of songs. These two modes
of singing also differ in average inter-element intervals and probably in their respiratory kinematics. Bird repertoire size
was measured and the difficulties of measuring it in this species are discussed. Repertoires are individually specific and
have a variable amount of syllable sharing with other birds. We found evidence for geographical variation in the composition
of repertoires. Considering our current knowledge of song in carduelines, the stereotyped and circular nature of serin song
appear to be unique within this group of birds.
Theory predicts that sexually selected characters should be condition dependent if they are to be used as honest signals of male quality. One consequence of this dependence is that young and older males will differ in the expression of these characters. Many bird song characteristics, such as repertoire size or song length, are considered to have evolved through sexual selection. Consistent with this, several studies have shown that repertoire size increases with age. However, many of these studies used cross-sectional methods, comparing song characteristics in different age classes. This approach has the disadvantage that differential survival related to song can confound the data, emphasizing or hiding individual changes. To avoid this we combined a cross-sectional with a longitudinal analysis, where the same cohort is compared at different ages, to study how song characteristics change with age in the willow warbler. The longitudinal analysis showed that song repertoire size (the set of different song elements) and element rate (number of elements produced divided by song duration) increased between the first and second year. The cross-sectional analysis gave similar results, but there were no changes in element rate. From these results we can infer that the development of several song characteristics is costly in this species. The different results provided by the two methods for element rate suggest a negative correlation between element rate and the probability of survival. The discrepancy between the methods implies that cross-sectional methods can provide erroneous conclusions in the study of changes with age in bird song.
The function of bird song is closely linked to sexual selection. A fundamental question regarding the evolution of sexually selected male signals is how their honesty is maintained. The neural space required for storing a large song repertoire size has traditionally been identified as a key constraint. However, it is often forgotten that bird song is a multifaceted behaviour, and that the different characters that comprise it have specific costs. Recent research has revealed the existence of new constraints, such as social aggression or learning opportunities, which limit the expression of several song characteristics. We review the existing evidence for each of these constraints, revealing some major gaps in our knowledge of this fascinating biological system.Bird song is a multifaceted behaviour comprising of different characteristics that have specific costs. New constraints are highlighted that limit the expression of several of these characteristics
This chapter addresses the interplay of vocal performance, sensorimotor learning, and vocal evolution in songbirds. Vocal performance is increasingly recognized as an influential factor in song evolution, particularly with respect to vocal output, song consistency, and trill structure. We argue here that a comprehensive understanding of vocal performance requires attention to sensorimotor learning, a developmental phase during which birds attempt to reproduce song models memorized earlier in life. New research indicates that birds calibrate song structure during sensorimotor ontogeny in order to best match their own vocal performance capacities. Because of this relationship, performance-related features may provide reliable indicators of male quality as manifest during sensorimotor learning. We review evidence in support of the “developmental stress” hypothesis and propose that this hypothesis be expanded to also consider vocal features crystallized during sensorimotor learning. We suggest avenues for future research that document relationships between vocal performance, morphology, and song learning programs.
Many species of territorial songbirds exhibit a behavior known as song-type matching, in which a male sings the same song type that his neighbor is singing. Song-type matching is associated with increased aggression, but researchers have not come to a consensus on its adaptive function. Building on studies that identify singing performance as a variable relevant to sexual selection, we hypothesize that higher-performance singers benefit from matching their opponent's song type because matching improves eavesdroppers' ability to compare the two males' performances. We present a model of song-type choice that predicts that males that can outperform their rivals benefit by matching. In contrast, lower-performance males should avoid both matching and being matched. Our hypothesis is compatible with some existing hypotheses of song-matching function, but it is not compatible with the hypothesis that song matching is a conventional signal of aggression. We offer unique predictions that could be used to test our idea. We speculate that lower-performance individuals might have driven the evolution of repertoire complexity because they stand to benefit from novel, unmatchable songs. The phenomenon that dissimilar signals are less accurately compared than similar signals may favor the evolution of multiple ornaments and of plastic signal development (e.g., song learning) in general.
Birdsong is a sexually selected and culturally transmitted multidimensional signal. Sexually selected traits are generally assumed to indicate condition. In oscine songbirds, song is learned early in life. The developmental stress hypothesis proposed that poor early developmental condition can adversely affect song learning. The quality and accuracy of learned song features could thus indicate male quality to conspecifics. Surprisingly, studies testing this hypothesis to date mostly compared adult males' song repertoires without looking at song imitation. The few that did reported inconsistent effects and analyzed a limited number of song features. Here, we examined the effects of early condition (by brood size manipulation) on learned song in zebra finches, Taeniopygia guttata, in comparing both the number of specific elements copied from an adult song tutor and a great number of previously neglected syntax-, complexity-, and performance-related song features. The treatment did not significantly affect average number of imitated elements, the standard measure of quality of song imitation in this species. However, developmental condition had 2 significant main effects on adult song: birds from large broods (i.e., of poor early condition) in comparison to birds from small broods copied syntactical dependencies of song elements from the song motif of their tutor less accurately and had less consistent sound duration between song motifs. These findings support the developmental stress hypothesis. We discuss how this sheds light on the potential role of such long-term signals of male developmental condition in female mate choice and potential constraints underlying condition-dependent expression of song features. Copyright 2008, Oxford University Press.
Song performance encompasses the idea of how physiologically demanding different songs are to sing, and this is thought to reflect the singing ability of individual birds. In the dark-eyed junco (Junco hyemalis), each male has a repertoire of song types, some of which are shared with other males in the population. We used 4 measures of performance, based on trade-offs between song traits, to test if song performance is consistent among the song types making up the repertoire of individual males. We also tested if song types differ consistently in performance regardless of which males sing them. We found low but significant correlations of performance measures among the song types of individual males. This contrasts with highly consistent differences in performance among song types, regardless of which males sing them. We conclude that performance of single song types, as evaluated by trade-off--based measures of performance, gives little information about male singing ability. As song types differ in performance, we asked if males use the song types in their repertoires differently. We found that juncos use higher performance song types during bouts of more motivated singing, as evaluated by the length of songs, suggesting that song types may be preferentially used in different contexts depending on their performance. Copyright 2009, Oxford University Press.
The elaborateness of many bird songs is commonly presumed to have evolved under the influence of sexual selection by female mate choice. Thus, aspects of acoustic diversity, such as song repertoire size, are seen as likely targets of female choice. In many songbird species with song repertoires, however, the repertoires are small. In such species, female choice might be based on song features other than, or in addition to, song diversity. To investigate this conjecture, I assessed singing and paternity in a population of chestnut-sided warblers (Dendroica pensylvanica), a species in which song repertoires are of modest size. Twenty-two song traits were evaluated to determine which ones best predicted male extrapair reproductive success. The candidate traits encompassed measures of song diversity (e.g., song repertoire size), gross-scale song performance (e.g., singing rate), and fine-scale song performance (e.g., variability among songs in a bout). Regression analysis revealed that the best predictor of extrapair success was singing with little variability. In particular, the most successful males sang with consistent pitch and timing, as well as high pitch. The greater extrapair success of males with more consistent vocal performance may be due to female preference for such performance, which could be an indicator of male quality. Copyright 2007.
Within bird species, songs differ in their attractiveness to females or effectiveness in male--male interactions. Some songs are more difficult to sing than others, and receivers may use a singer's performance of difficult songs as a means for evaluating the quality of the singer. The concept of song performance aims at quantifying how physiologically demanding are different songs. Using variation between song types of dark-eyed juncos, Junco hyemalis, we show that some song traits trade off with costly aspects of song output--short intervals between syllables or loud sound amplitude--suggesting that those traits are difficult to sing. First, after controlling for other traits, long syllables require longer intervals for recovery. This supports the idea that a measure of "respiratory performance" could be based on the relative lengths of syllables and intervals. Second, some syllable traits trade off strongly with sound amplitude, suggesting that these traits may be difficult to sing at high amplitudes. The ratio of frequency bandwidth and trill rate has been used to infer performance in other bird species, but we found no evidence that frequency bandwidth trades off with any aspect of song output in the junco. The negative association of bandwidth with trill rate may instead be a passive consequence of syllable length, with longer syllables randomly accumulating frequency modulation. We conclude that bird receivers may best evaluate how well a song is performed if they integrate multiple cues and discuss how researchers may similarly devise measures of song performance. Copyright 2007, Oxford University Press.
Female songbirds are thought to assess males based on aspects of song, such as repertoire size or amount of singing, that could potentially provide information about male quality. A relatively unexplored aspect of song that also might serve as an assessment signal is a male's ability to perform physically challenging songs. Trilled songs, such as those produced by swamp sparrows (Melospiza georgiana), present males with a performance challenge because trills require rapid and precise coordination of vocal tract movements, resulting in a trade-off between trill rate and frequency bandwidth. This trade-off defines a constraint on song production observed as a triangular distribution in acoustic space of trill rate by frequency bandwidth, with an upper boundary that represents a performance limit. Given this background on song production constraints, we are able to identify a priori which songs are performed with a higher degree of proficiency and, thus, which songs should be more attractive to females. We determined the performance limit for a population of swamp sparrows and measured how well individual males performed songs relative to this limit ("vocal performance"). We then compared female solicitation responses to high-performance versus low-performance versions of the same song type produced by different males. Females displayed significantly more to high-performance songs than to low-performance songs, supporting the hypothesis that females use vocal performance to assess males. Copyright 2004.
SYNOPSIS. The developmental processes through which songbirds acquire their species—typical songs have been well—studied from a proximate perspective, but less attention has been given to the ultimate question of why birds learn to sing. We present a new hypothesis for the adaptive significance of song learning in songbirds, suggesting that this specialized form of vocal development provides an indicator mechanism by which females can accurately assess the quality of potential mates. This hypothesis expands on the established idea that song can provide an indicator of male quality, but it explicitly links the variation in song expression that females use to choose mates to the developmental processes through which song is acquired. How well a male sings—reflected in repertoire size or in other learned features of a male's singing behavior—provides an honest indicator of quality because the timing of song learning and, more importantly, the timing of the development of brain structures mediating learning corresponds to a period in development during which young songbirds are most likely to undergo nutritional stress. This correspondence means that song learning can provide a sensitive indicator of early developmental history in general, which in turn reflects various aspects of the phenotypic and genotypic quality of a potential mate.
Several recent studies have tested the hypothesis that song quality in adult birds may reflect early developmental conditions, specifically nutritional stress during the nestling period. Whilst all of these earlier studies found apparent links between early nutritional stress and song quality, their results disagree as to which aspects of song learning or production were affected. In this study, we attempted to reconcile these apparently inconsistent results. Our study also provides the first assessment of song amplitude in relation to early developmental stress and as a potential cue to male quality. We used an experimental manipulation in which the seeds on which the birds were reared were mixed with husks, making them more difficult for the parents to obtain. Compared with controls, such chicks were lighter at fledging; they were thereafter placed on a normal diet and had caught up by 100 days. We show that nutritional stress during the first 30 days of life reduced the birds' accuracy of song syntax learning, resulting in poorer copies of tutor songs. Our experimental manipulations did not lead to significant changes in song amplitude, song duration or repertoire size. Thus, individual differences observed in song performance features probably reflect differences in current condition or motivation rather than past condition.
Using the responses of territory owners to playback to infer the territorial function of acoustic signals is common practice. However, difficulties with interpreting the results of such experiments have obscured our understanding of territorial signalling. For instance, a stronger response to playback is often interpreted as more aggressive, but there is no consensus as to whether this should be in response to the least or most threatening simulated intruder. Rather than following a gradual increase or decrease, the relationship between signal intensity and response strength may instead describe a peaked curve. We manipulated banded wren (Thryophilus pleurostictus) songs to simulate low-, median-, and high-performance singers and used these songs as stimuli in playback experiments. Banded wrens were less likely to approach the high-performance stimulus compared with the low- and median-performance stimuli. However, the birds that did approach the high-performance stimulus sang more than those that approached the low-performance stimulus. In addition, birds were more likely to match the songs when exposed to the median- and high-performance stimuli compared with the low-performance stimuli, and song matching predicted approach behavior. These results are in accordance with theoretical models of aggressive encounters in which low-performance opponents are challenged without further assessment. Median- and high-performance opponents, however, may require further assessment, and the latter may be perceived as too intimidating for approach.
Older males tend to have a competitive advantage over younger males in sexual selection. Therefore, it is expected that signals used in sexual selection change with age. Although song repertoire size in songbirds is often mentioned as an age-related trait, many species, including the banded wren (Thryothorus pleurostictus), do not increase their repertoires after the first year. Here, we show that banded wrens reproduce the trill notes in their songs with less variability between them (i.e. more consistently) when they grow older. In a playback experiment, we also show that banded wrens discriminate between younger and older birds based on structural aspects of their song. In a second experiment, banded wrens also respond differentially to natural songs versus songs with artificially enhanced consistency. We argue that consistency in trill note reproduction may be achieved through practice. Sexual selection in the form of male-male competition may therefore operate on a phenotypic trait, the expression of which is enhanced by practice.
Females of many songbird species show a preference for mating with males that have larger song repertoires, but the advantages associated with this preference are uncertain. We tested the hypothesis that song complexity can serve as an indicator of male quality because the development of the brain regions underlying song learning and production occurs when young birds typically face nutritional and other stresses, so that song reflects how well a male fared during post-hatch development. A key prediction of this hypothesis is that variation in nestling condition should correspond to variation in the adult song repertoires of individuals. We used data from a long-term study of the great reed warbler (Acrocephalus arundinaceus) to test this prediction, correlating two measures of nestling development with subsequent repertoire size of males. We found that the length of the innermost primary feather, a standard measure of development, significantly predicted first-year repertoire size. The relationship between repertoire size and body mass was nearly significant, in spite of the large variance inherent in this measure. These data support the idea that song may provide females with information about a male's response to developmental stress, which in turn is expected to correlate with indirect or direct benefits she might receive.
Behavioral evolution can be influenced by constraints, for example, of phylogeny and performance. In this paper I describe a pattern in the evolution of birdsongs that may reflect a constraint on vocal performance. Trilled vocalizations from 34 species of songbirds (Passeriformes: Emberizidae) were analyzed. Two acoustic variables, trill rate and frequency bandwidth, were measured for different trill types. In most species, maximal values of frequency bandwidth were found to decrease with increasing trill rates. Further, trills with low trill rates exhibited wide variance in frequency bandwidth, and trills with high trill rates exhibited only narrow frequency bandwidths. The bounded nature of this pattern suggests that performance constraints have limited the evolutionary diversification of trills. In particular, I explore the role of constraints associated with vocal tract modulations during song production and evolution. Identification of this constraint may enhance our ability to explain particular patterns of trill evolution.
Lymphoid neoplasia is the most common form of hemolymphatic neoplasia in birds. Most research on avian lymphoid neoplasia has been done on the virus-induced neoplasias affecting poultry, including Marek's disease, avian leukosis, and reticuloendotheliosis. There is evidence of virus-induced lymphoid neoplasia in psittacine and passerine species, but little research has been done to confirm it. We diagnosed multicentric lymphoma on histopathologic examination of tissues from a European starling (Sturnus vulgaris) that had presented because of inability to fly, dyspnea, emaciation, and abdominal distension. Macroscopic and histologic findings were similar to those for lymphoid leukosis as described in chickens. Polymerase chain reaction amplification using chicken reticuloendotheliosis virus primers was negative. Amplification of a pol fragment from primers by polymerase chain reaction showed the presence of retrovirus sequences in the starling tumor.
Communication signals can be divided into two functional classes: long-range signals and short-range signals. The study of bird song has concentrated almost exclusively on long-range songs. Because bird song often is used as a model system for studying learning, mate choice, and territoriality, this lack of attention to short-range songs may have misrepresented our understanding of communication systems. Short-range songs are expected to differ acoustically and functionally from those broadcast over long distances. Male Dark-eyed Juncos (Junco hyemalis) produce two classes of song that appear to function as long-range and short-range signals, respectively. These two classes differ markedly in frequency and syntax as well as in repertoire size. In terms of use, rates of short-range song production were highest in conjunction with courtship displays, when males were within close proximity to fertile mates, and during interactions with other males. In contrast, production of long-range song was not associated with courtship displays, did not vary significantly with the reproductive state of females, and was produced when males were relatively far from conspecifics.
Recent studies of vocal mechanics in songbirds have identified a functional role for the beak in sound production. The vocal tract (trachea and beak) filters harmonic overtones from sounds produced by the syrinx, and birds can fine-tune vocal tract resonance properties through changes in beak gape. In this study, we examine patterns of beak gape during song production in seven species of Darwin's finches of the Galápagos Islands. Our principal goals were to characterize the relationship between beak gape and vocal frequency during song production and to explore the possible influence therein of diversity in beak morphology and body size. Birds were audio and video recorded (at 30 frames s–1) as they sang in the field, and 164 song sequences were analyzed. We found that song frequency regressed significantly and positively on beak gape for 38 of 56 individuals and for all seven species examined. This finding provides broad support for a resonance model of vocal tract function in Darwin's finches. Comparison among species revealed significant variation in regression y-intercept values. Body size correlated negatively with y-intercept values, although not at a statistically significant level. We failed to detect variation in regression slopes among finch species, although the regression slopes of Darwin's finch and two North American sparrow species were found to differ. Analysis within one species (Geospiza fortis) revealed significant inter-individual variation in regression parameters; these parameters did not correlate with song frequency features or plumage scores. Our results suggest that patterns of beak use during song production were conserved during the Darwin's finch adaptive radiation, despite the evolution of substantial variation in beak morphology and body size.
Abstract Large animals, having large vocal organs, produce low sound frequencies more efficiently. Accordingly, the frequency of vocalizations is often negatively related to body size across species, and also among individuals of many species, including several non-oscine birds (non-songbirds). Little is known about whether song frequency reveals information about body size within oscine species, which are characterized by song learning and large repertoires. We asked whether song frequency is related to body size in two oscines that differ in repertoire size: the dark-eyed junco (Junco hyemalis) and the serin (Serinus serinus). We also asked whether the extent to which receivers sample repertoires might influence the reliability of their assessment of body size. We found that none of the frequency traits of song that we investigated was related to male body size, nor did more extensive sampling of repertoires lead to any relationship between frequency and body size. Possible reasons for these results are the small range of variation in size within species, or the elaborate vocal physiology of oscines that gives them great control over a wide frequency range. We discuss these results as they relate to female preferences for high-frequency song that have been previously reported for oscine species.
Songbirds often sing at higher frequency (pitch) in urban, noise-polluted areas, which reduces acoustic masking by low-frequency anthropogenic noise. Such frequency shifts, however, are less efficient at overcoming background noise than simply singing louder. Therefore, it was suggested that highfrequency singing might not be a functional adjustment to noise, but a physiological consequence of singing louder (also known as the Lombard effect). We tested for the first time the main tenet of this hypothesis, for birdsong whether increasing sound amplitude has a concomitant effect on song frequency, using a representative species with higher urban minimum frequency, the dark-eyed junco, Junco hyemalis. The frequency bandwidth of songs and syllables increased with amplitude, involving lower minimum frequency in louder songs and syllables. Therefore, louder singing does not explain the higher minimum frequency of urban dark-eyed juncos. Amplitude and peak frequency were weakly positively related across but not within songs, suggesting that increased frequency is not an obligatory outcome of singing louder. Instead, birds may adjust both amplitude and frequency in response to changing noise or motivation across songs. Our results suggest that adjustments in song frequency and amplitude are largely independent and, thus, can be complementary rather than alternative vocal adjustments to noise. We discuss oscine vocal physiology and details of the behaviour of urban birds, both of which we argue are consistent with the increased frequency of urban birdsong generally being a functional adjustment to noise, rather than a consequence of singing louder.
Selection should favour female preferences for reliable signals of male quality when such preferences result in benefits to females. Research on bird song suggests that, because song is costly to produce or sustain, females are obtaining accurate information about male quality through song preferences. Females have been shown to express mating preferences for three general categories of costly song features: song output, song complexity and geographical variation. A novel mechanism for the reliability of song is suggested by constraints on the ability to produce rapid, broadband trills (i.e. 'vocal perfor- mance'). In several species of birds, females show a preference for superior vocal performance, sup- porting a key prediction of the hypothesis that vocal performance, like other features of song, may be a reliable indicator of male quality. In this study, I further test this hypothesis by investigating whether female swamp sparrows' preference for vocal performance is favoured by selection because it reliably reflects male quality. I found that vocal performance in male swamp sparrows was correlated with age and size, measured as mass. By preferring males with superior vocal performance, female swamp sparrows may obtain direct and indirect benefits by mating with older larger males. These results support the hypothesis that vocal performance in swamps sparrows is a reliable indicator of male quality. 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
To find out whether a mating preference could have initially evolved for adaptive reasons, one must determine whether the preferred trait could have provided useful information about mate quality at the time when the preference first arose.
One way to do so is to determine whether the preference evolved before or after the preferred trait. If the preference evolved first, then it cannot initially have served an adaptive function in mate choice, rather it must have arisen by random drift, or as a pleiotropic consequence of selection acting on other aspects of individual perceptual abilities.
A number of studies have shown that females exhibit a mating preference (e.g. for movement) in non‐sexual contexts also, which suggests that it may have evolved for reasons unconnected to mate choice. In addition, phylogenetic analyses have revealed that in several cases, females of a certain taxon exhibit a preference for a male trait that is absent in a sister taxon and in outgroup taxa, and that this preference is shared by females of the sister taxon tacking the male trait. The principle of parsimony suggests that such a preference has been inherited from a common ancestor, while the preferred trait arose only once in the lineage exhibiting the trait, i.e. that the preference predates the attractive trait.
While the above evidence indicates that females may possess ‘hidden’ preferences for male traits that are not exhibited by members of their own species, and that in at least some cases males have later evolved display traits that exploit preexisting preferences of this kind, there have been too few historical studies of preference evolution to allow one to assess the frequency of such exploitation. Moreover historical studies cannot provide strong support for the adaptive origin hypothesis, because coevolution of trait and preference (as opposed to exploitation of a pre‐existing bias) is compatible with Fisherian models of preference evolution as well as with honest advertisement and the handicap principle. One can conclude only that while some mating preferences did not originally evolve for adaptive reasons, others may or may not have done so.
To find out whether a mating preference is currently maintained by natural selection because the preferred trait provides useful information about mate quality, one must investigate the phenotypic and genotypic correlates of display, and the fitness consequences of mate choice.
A review of the published data reveals some support for the ideas of adaptive choice and honest advertisement. In a number of species, preferred display traits are correlated with putative measures of quality, and in a small proportion of these, there is evidence that reproductive success and/or offspring performance are higher for individuals mated to attractive partners. Very few studies report a failure to find any such correlates of display or any such benefits.
While the above result suggests that honest advertisement does sometimes occur in extant populations (which does not necessarily imply that preferred traits originally evolved as reliable indicators of mate quality), the possibility of publication bias means that one cannot assess how widespread it is. More data is needed to remedy this problem, particularly regarding the fitness consequences of mate choice for females. Experimental rather than observational methods are the best means to gather such data. Studies that look for correlates of display, for instance, should rely on experimentally induced rather than natural variation in ‘quality’.
The most common correlates of male display are age and dominance. The latter observation suggests that there may often be interactions between the processes of intersexual and intrasexual selection.
There is considerably more evidence to support the idea of female choice for direct than for indirect benefits. At the same time, however, it is apparent that mating decisions are commonly influenced by more than one measure of quality, so that these two kinds of choice need not be independent. To assess this possibility will require more studies of the relationship between male attractiveness and offspring performance.
Mate choice is frequently based on more than one display trait, and each trait is frequently influenced by more than one aspect of quality. ‘One quality, one trait’ views of honest advertisement are simplistic, and must be abandoned.
Honesty in sexual displays is sometimes maintained by cost (as in strategic handicap models) and sometimes, with approximately equal frequency, by physical necessity (as in revealing handicap models). In some cases, both mechanisms are involved in a single signalling system. To further distinguish between these possibilities will require experimental investigation of display cost, based on manipulation of display traits.
Important biological concepts typically have many definitions. Body condition is no exception; it is a multi-level phenomenon that can be defined either conceptually or operationally. Although at this time there is no clear consensus on the definition for body condition, conceptually, the term in many cases describes the degree to which an organism’s physiological state influences its performance (i.e., production, activity, or response to environmental conditions). Operational definitions for condition typically are based on some aspect of body composition (e.g., levels of nutrient stores or indirect indicators of such levels). Despite these complexities, numerous published studies have documented the effect of a bird’s nutritional status on some aspect of Darwinian fitness. The primary goals of this chapter are to describe the available methods of assessing condition, evaluate their accuracy and utility, illustrate how these methods have been applied, and clarify how they satisfy operational and conceptual definitions of body condition. The result will be to provide a primer for researchers interested in obtaining condition estimates, as well as for those wishing to improve upon existing methods.
Behavioral evolution can be influenced by constraints, for example, of phylogeny and performance. In this paper I describe a pattern in the evolution of birdsongs that may reflect a constraint on vocal performance. Trilled vocalizations from 34 species of songbirds (Passeriformes: Emberizidae) were analyzed. Two acoustic variables, trill rate and frequency bandwidth, were measured for different trill types. In most species, maximal values of frequency bandwidth were found to decrease with increasing trill rates. Further, trills with low trill rates exhibited wide variance in frequency bandwidth, and trills with high trill rates exhibited only narrow frequency bandwidths. The bounded nature of this pattern suggests that performance constraints have limited the evolutionary diversification of trills. In particular, I explore the role of constraints associated with vocal tract modulations during song production and evolution. Identification of this constraint may enhance our ability to explain particular patterns of trill evolution.
Peaks in song output at twilight, particularly dawn, are typical of many birds. Recent attention has focused on the honesty of male advertisement, and on whether dawn is a particularly good time for females to assess male quality. In the present model a male divides his times between singing and feeding. If he sings more he is more likely to starve. A natural outcome is that song acts as a strategic handicap and as an honest signal of male quality. By using stochastic dynamic programming, diurnal variation in female assessment is shown to have a profound influence on male daily routines, but dawn is rarely the best time for assessment of quality. Females do not much enhance their probability of pairing with a high-quality male by varying responsiveness to song with time of day; constraints on female time budgets probably have more influence on the timing of male song than does optimization of quality discrimination. But females do greatly enhance their discriminatory efficiency by remembering past song output (song is then more concentrated at certain times, particularly morning, and males may even remain silent on alternate days). In general, the harder the task demanded of a male, the more efficient is the female rule in discriminating male quality.
▪ Abstract Bird song provides an unusually impressive illustration of vertebrate behavioral diversification. Research on bird song evolution traditionally focuses on factors that enhance song diversity, such as cultural transmission and sexual selection. Recent advances in the study of proximate mechanisms of vocal behavior, however, provide opportunities for studying mechanistic constraints on song evolution. The main goal of this review is to examine, from both conceptual and empirical perspectives, how proximate mechanisms might temper patterns of song evolution. We provide an overview of the two “substrates” of song evolution, memes and vocal mechanisms. We argue that properties of vocal mechanisms (control, production, and ontogeny) constrain vocal potential and may thus limit pathways of meme evolution. We then consider how vocal mechanisms may constrain song evolution under five scenarios of drift and selection and examine four specific song traits for which mechanistic constraints appear to counte...
ABSTRACT Degradation of acoustic signals during transmission presents a challenging selection pressure for animals dependent on vocal communication. Sound transmission properties differ among habitats and may drive the evolution of vocal signals in different directions. Urban habitat is expanding worldwide and an increasing number of species, including many birds, must now communicate around buildings and over concrete. Urban habitats are evolutionarily new, although to some extent they may acoustically resemble rocky habitat such as cliffs and canyons. Neither urban nor these natural habitats have been studied in any detail for the selection pressure they may exert on animal communication. Dark-eyed Juncos (Junco hyemalis) commonly inhabit montane pine forests across North America, but for about 25 years an isolated population has been successfully breeding in an urban environment in southern California. We investigated potentially divergent selection pressures on junco songs, using sound transmission experiments with artificial sound stimuli, in natural forest habitat and in this urban habitat. Transmission properties differed significantly, resulting in tails of reflected sound with gradually declining amplitude in the forest and in multiple discrete echoes in the urban environment. We expected environmental selection in urban habitat to favor shorter songs with higher frequencies and slower trill rates. Despite the presence of relatively short urban songs, there was no significant shortening overall. There were also no differences in trill rates, but we did find a significantly higher minimum frequency in the urban junco population compared to three of four forest populations. Although the pattern of song divergence was not consistent and it is difficult to draw firm conclusions from this single urban population, our transmission results suggest that echoes could be important in shaping urban birdsong.
During natural colonization events, songs are expected to change as a result of both selection and drift-like processes. We studied song variation within a small isolated population of dark-eyed juncos, Junco hyemalis, which became established in an unusual environment on the University of California at San Diego (UCSD) campus in the early 1980’s, and compared this variation with the native range. At UCSD, the average repertoire size is 4.2 song types/male, which is similar to that in the native range. There is a low level of song-type sharing across the population. Typically a male shares at least one song type with on average 40% of his neighbors, and song-type sharing decreases rapidly with distance. Thus song-type diversity is high, and in this respect appears similar to that in ancestral mountain populations. These results suggest a moderate to large number of males founded and/or subsequently immigrated into the UCSD population, but several selection mechanisms, if coupled with a high cultural mutation rate, may also favor high song-type diversity. When combined with results from a previous study, songs are significantly shorter at UCSD than in the mountain population we studied. It appears that founder effects have not influenced the evolution of songs in this population. More generally, if song-type diversity and other features of song result from various social and natural selection pressures, many of these pressures may have remained similar between the native and the recently established population.
Wing feather mite burdens on seven species of passerine birds (Carduelis carduelis– goldfinch; C. chloris– greenfinch; Serinus serinus– serin; Sylvia atricapilla– blackcap; Sylvia melanocephala– Sardinian warbler; Turdus merula– blackbird; Passer domesticus– house sparrow) from Portugal were assessed by the subjective semi-quantitative scoring system of Behnke et al. (1995) in order to evaluate more fully the accuracy and reliability of the technique. Our analysis indicated that in all species, scores allocated to flight feathers showed a significant positive relationship with mite counts as assessed through microscopical examination of the same feathers. However, there were differences between species of birds. Of the species examined, goldfinches and greenfinches showed the weakest relationships between assigned mite scores and actual mite numbers indicating that the technique was less accurate when applied to these species compared with the remaining five. No evidence was found that anything more was to be gained from scoring both wings, rather than just one. Feather mites (Proctophyllodes spp., Trouessartia incisa) were also detected on tail feathers, but the assessment of these feathers presented additional problems and it was concluded that in the interests of minimizing handling time of birds, tail scores had little more to offer. We conclude that scoring all the flight feathers (including all primary, secondary, and tertiary feathers) on one entire wing, but alternating between left and right wings of birds within a species, represents an acceptable compromise between sufficiently detailed examination and minimization of bird handling time in the field.
To understand fully the function of vocal learning, it is important to know when, during an individual’s lifetime, learning occurs. Songbirds are generally categorized into two groups with respect to their adult song learning ability. ‘Open-ended’ song learners are able to learn to produce new songs in adulthood, whereas ‘age-limited’ song learners can only acquire songs during their first year of life. Researchers have long assumed that certain oscine species are open-ended or age-limited song learners, but the evidence to date has been inadequate to test these assumptions for most species. We tested the hypothesis that song sparrows (Melospiza melodia) are age-limited song learners who do not alter their song repertoires in adulthood by examining the song repertoires of 24 color-banded males who were fully recorded in two, three or four different years. We compared sonagrams of the song types produced by males in different years and looked for any changes in repertoire composition (i.e. added or dropped song types). With few exceptions, males produced song repertoires that were identical in every year they were recorded. The exceptions (four males who did not produce one of their song types during one recording session) were all cases in which we believe that we missed recording a song type that a male did indeed have, not that the males dropped a song type. The finding that adult males do not alter the composition of their song repertoires provides strong evidence that song sparrows are age-limited song learners. Although it is possible that song sparrows make subtle within-song type changes across years, such changes would not necessarily constitute new song learning.
The results of a 4 year project investigating species of mites infesting wing primary feathers on 21 species of Passeriformes are reported. The majority of species were identified as belonging to the genus Proctophyllodes Robin, 1877 with one new host record. In addition Pteronyssoides obscurus Berlese 1884 was found on European swallows, also a new host record. A novel method to enable quantification of mite intensities without causing harm to the birds was devised and evaluated. This relied on visual inspection of wing primary feathers and assignment of subjective infestation scores to individual feathers, the sum of the individual scores comprising the primary feather total mite infestation score (PTMIS). Comparisons between species revealed that birds could be grouped into four categoris depending on their infestation intensity with mites. Swallows, sand martins and greenfinches showed the highest prevalence and most intense infestations (mean PTMIS 6.8). Blackbirds, blackcaps, serins, goldfinches, Cetti's warblers, great tits and house sparrows showed moderate levels of infestation with prevalence in the range 60–90.9% but a mean PTMIS lower than in the former group (1.6–5.8). The third group comprised Sardinian warblers, nightingales and short-toed tree creepers and was characterized by a prevalence of mites 40% and a mean PTMIS of 0.6–1.4. The final group, representing wrens, chiffchaffs, fan-tailed warblers and waxbills were without detectable mites, the only exception being wrens on which mites were identified in only three birds of the 32 sampled. These results are interpreted in the light of published information and possible explanations for the observations are discussed.
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.
Male mating signals are often multidimensional, potentially providing multiple messages to females. However, the relative importance of different signal dimensions and their context dependency are poorly understood. Even in a well-studied species such as the zebra finch, Taeniopygia guttata, an important avian model for the study of mate choice, there is little consensus on the relative weighting of visual versus acoustic signals in mate choice. We therefore tested the consistency and repeatability of female mating preferences across different test contexts, presenting male song only or full courtship displays. We concurrently conducted a detailed analysis of male song characteristics and morphological traits. Females' individual preferences were consistent across three commonly used binary test paradigms (operant and phonotaxis tests with songs and association tests with live males). Preference direction was thus independent of test contexts. Preference strength was repeatable only between the operant and live male tests, possibly because these two tests allowed active interaction with songs or males whereas exposure to songs in the phonotaxis test was passive. The song structure parameters that predicted female preferences best were context independent and also predicted male morphology. We conclude from the combined results that song structure (in addition to song rate or absolute output as previously suggested) does contain sufficient information on the singer for female mate choice. We suggest that the earlier focus on song rate rather than song content might partly account for the differences between studies in the importance attributed to acoustic versus visual signals.
The recent finding that in zebra finches, Taeniopygia guttata, some males produce certain high-pitch song syllables during inspiration, a trait requiring unusual motor coordination, raises questions as to a possible role for these unusual sounds in mate attraction. If inspiratory syllables are indicative of a generally higher level of motor control, potentially relating to male quality, this might be reflected in other song characteristics. In a quantitative song analysis we found that the presence of inspiratory syllables in a male's individual-specific song motif covaried with both motif length and syllable rate. Furthermore, the unusually high frequencies at peak amplitude reached by such syllables exceed those of any other zebra finch syllable type. Hence, songs containing inspiratory phonation clearly differ both in performance aspects (syllable rate and motif length) and in structure from those that are wholly expiratory. These findings are in line with the idea that inspiratory syllables are indicative of enhanced motor control and performance. To test whether these differences bear on female receivers' preferences, we offered female zebra finches the choice between unmanipulated song motifs containing and lacking inspiratory phonation, in operant two-choice preference tests. Song motifs containing inspiratory phonation were not systematically preferred, both when songs were randomly paired and when motif length was controlled for, implying that this unusual trait does not impact significantly upon song attractiveness in an intersexual context.
Our goal in this essay is to review the hypothesis that females choose mates by the evaluation of male motor performance. We define motor performance as vigour, the ability to perform energetically expensive acts repeatedly, or as skill, the ability to perform difficult motor tasks well. Motor performance reflects most aspects of whole-organism performance that relate to survival, and thus should indicate, more reliably than ornaments do, individual male genetic quality and/or developmental history. Male sexual displays in many animal taxa contain elements of vigour and/or skill, and accumulating evidence suggests that females choose mates in nature based upon their evaluations of male motor performance. We note that male ornaments in many species are accompanied by conspicuous motor display, and we propose that ornaments often arise secondarily as a way to enhance the apparent skill or vigour of male motor performance. More and better methods to measure male vigour and skill are needed, as well as additional studies on the abilities of females to make discriminations of this type.
Many animals repeat standardized displays multiple times while attracting a mate or deterring a rival. In such contexts the ability to perform each display or signal type in a consistent fashion may be under direct selection. Studies on sexual selection on song learning in birds have focused on differences in repertoire size with less attention paid to the potential importance of being able to perform each song/syllable type with high consistency. We investigated whether syllable type consistency is related to age, social dominance and reproductive success in tropical mockingbirds, Mimus gilvus. The variation between renditions of each syllable type decreased as the birds grew older (i.e. they became more consistent). In addition, more consistent males tended to have higher dominance status and reproductive success. These findings stress the importance of consistency in the performance of sexual displays and suggest that this parameter may be very relevant even in species that are selected for high vocal diversity (i.e. large repertoires). We hypothesize that, in addition to signalling dominance status and age, syllable type consistency may also indicate the integrity of brain function in birds analogous to the tests used for neuropsychological assessment in humans.
Evolutionary approaches to culture remain contentious. A source of contention is that cultural mutation may be substantial and, if it drives cultural change, then current evolutionary models are not adequate. But we lack studies quantifying the contribution of mutations to directional cultural change. We estimated the contribution of one type of cultural mutations--modification of memes--to directional cultural change using an amenable study system: learned birdsongs in a species that recently entered an urban habitat. Many songbirds have higher minimum song frequency in cities, to alleviate masking by low-frequency noise. We estimated that the input of meme modifications in an urban songbird population explains about half the extent of the population divergence in song frequency. This contribution of cultural mutations is large, but insufficient to explain the entire population divergence. The remaining divergence is due to selection of memes or creation of new memes. We conclude that the input of cultural mutations can be quantitatively important, unlike in genetic evolution, and that it operates together with other mechanisms of cultural evolution. For this and other traits, in which the input of cultural mutations might be important, quantitative studies of cultural mutation are necessary to calibrate realistic models of cultural evolution.
Based on the assumptions that birdsong indicates male quality and that quality is related to age, one might expect older birds to signal their age. That is, in addition to actual body condition, at least some song features should vary with age, presumably towards more complexity. We investi- gated this issue by comparing repertoire sizes of free-ranging common nightingale males in their first breeding season with those of older males. Nightingales are a good model species as they are open-ended learners, where song acquisition is not confined to an early sensitive period of learning. Moreover, nightingales develop an extraordinarily large song-type repertoire (approx. 180 different song types per male), and differences in repertoire size among males are pronounced. We ana- lysed repertoire characteristics of the nocturnal song of nine nightingales in their first breeding season and compared them with the songs of nine older males. The repertoire size of older males was on average 53% lar- ger than that of yearlings. When analysing two song categories of night- ingales, whistle and non-whistle songs separately, we found similar results. Our findings show marked differences in repertoire size between age categories, suggesting that this song feature may reflect a male's age. We discuss those mechanisms that may constrain the development of larger repertoires in first-year males. Whether repertoire sizes are cru- cial for female mate choice or in vocal interactions among conspecific males remains open to further investigations. Ethology
An ESS model of Zahavi's handicap principle is constructed. This allows a formal exposition of how the handicap principle works, and shows that its essential elements are strategic. The handicap model is about signalling, and it is proved under fairly general conditions that if the handicap principle's conditions are met, then an evolutionarily stable signalling equilibrium exists in a biological signalling system, and that any signalling equilibrium satisfies the conditions of the handicap principle. Zahavi's major claims for the handicap principle are thus vindicated. The place of cheating is discussed in view of the honesty that follows from the handicap principle. Parallel signalling models in economics are discussed. Interpretations of the handicap principle are compared. The models are not fully explicit about how females use information about male quality, and, less seriously, have no genetics. A companion paper remedies both defects in a model of the handicap principle at work in sexual selection.