Article

Dawn song in superb fairy-wrens: a bird that seeks extrapair copulations during the dawn chorus

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Abstract

Functional explanations of the dawn chorus in birds remain elusive. One hypothesis suggests that this acoustic display may play a role in female choice of extrapair males. Most young in cooperatively breeding superb fairy-wrens, Malurus cyaneus, are sired by extra-group males. Females initiate extra-group copulations exclusively through predawn forays to males singing in the dawn chorus. We measured variation between males in dawn singing at three levels of song production: song components, structured into songs, which make up recitals. We related this variation to independent measures of male quality and social status. Males sing two distinct categories of songs during the dawn chorus: a complex and variable chatter song and a more repeatable trill song. Dominant males with male subordinate helpers produced chatter songs at a greater rate than either dominant males without helpers or subordinates, suggesting a role in the competition between male group members. However, the trill song is implicated in female choice because older males sing songs with a longer trill component and have greater extrapair success, and trade-offs between phrases within the trill component imply constraints on the length of the trill component in entirety that could enforce honesty. The dawn chorus of the superb fairy-wren may thus have a duel role, involving enforcement of dominance among male group members (male–male competition), and signalling attractiveness to mates (female choice).

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... Other males can initiate the return to breeding plumage at any time of the year, including before the post-breeding moult is complete, and at the opposite extreme, after females have started to breed. The probability that males will moult well before the breeding season in Superb Fairy-wrens increases up to 9 years of age but among older birds is also facilitated by high rainfall in the months preceding the moult (Dunn and Cockburn 1999;Cockburn et al. 2008a;van de Pol and Cockburn 2011;van de Pol et al. 2012) Finally, although both males and females in all species have songs that appear to function primarily in territorial defence, males in at least some species have an additional song (Type II or trill song), that is sung during the day in response to the calls or wing-beats of predators and other loud noises (Langmore and Mulder 1992;Dalziell and Cockburn 2008;Greig and Pruett-Jones 2009;Greig et al. 2010). This song is also sung unprompted in the dawn chorus by incorporation into song sequences that include territorial songs (Dalziell and Cockburn 2008). ...
... The probability that males will moult well before the breeding season in Superb Fairy-wrens increases up to 9 years of age but among older birds is also facilitated by high rainfall in the months preceding the moult (Dunn and Cockburn 1999;Cockburn et al. 2008a;van de Pol and Cockburn 2011;van de Pol et al. 2012) Finally, although both males and females in all species have songs that appear to function primarily in territorial defence, males in at least some species have an additional song (Type II or trill song), that is sung during the day in response to the calls or wing-beats of predators and other loud noises (Langmore and Mulder 1992;Dalziell and Cockburn 2008;Greig and Pruett-Jones 2009;Greig et al. 2010). This song is also sung unprompted in the dawn chorus by incorporation into song sequences that include territorial songs (Dalziell and Cockburn 2008). The capacity of males to sing these songs also improves with age (Dalziell and Cockburn 2008). ...
... This song is also sung unprompted in the dawn chorus by incorporation into song sequences that include territorial songs (Dalziell and Cockburn 2008). The capacity of males to sing these songs also improves with age (Dalziell and Cockburn 2008). ...
Article
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Fairy-wrens (genus Malurus) maintain territories year round, and breed cooperatively, with all members of the social group provisioning young. Despite living with several adult males, the breeding female typically cuckolds all of them, seeking fertilisations from extra-group males that provide no care to her offspring, instead caring for the young reared on their own territory. We trace the evolutionary origins and persistence of this extraordinary combination of traits. We argue that the high rate of infidelity in some fairy-wrens facilitates social pairing among nuclear family relatives, rather than being an evolutionary response to avoid inbreeding. It seems likely that females mate with extra-group males to improve the genetic quality of their offspring. The ability of males to maintain breeding plumage for long periods is the primary criterion for female choice; only older males can do so. Several features of the mating system undermine the accuracy of female choice, and low-quality males exploit this uncertainty. Extra-group matings by low-quality males can help stabilise the mating system but may leave it vulnerable to collapse under certain circumstances. Nonetheless, sexual selection in most species is very strong, confirming the utility of fairy-wrens as model organisms for the study of mate choice and intersexual selection.
... Different experimental stimuli were created by manipulating the length of trills in male trill songs. Trill length is linked to male quality in superb fairy-wrens, with older males singing longer trills (Dalziell and Cockburn 2008), but conspecific responses to variation in trill length have not previously been assessed. Because studies on other species show that longer songs generally elicit more aggressive responses (see Table 2 of Nelson and Poesel 2012), and that trills can be an aggressive signal (Illes et al. 2006;Schmidt et al. 2008;Sprau et al. 2010), we predicted that long trill songs would be perceived as more threatening than short trill songs. ...
... To create playback stimuli, we experimentally manipulated male trill songs to produce songs with short and long trill phrases (Figure 1 and Supplementary Material). All trill songs were recorded in January 2013 during the dawn chorus (5:00 to 5:45 AM), when male superb fairy-wrens sing trill songs frequently and unprompted (Dalziell and Cockburn 2008). Songs were recorded with a Sennheiser ME67/K6 shotgun microphone with a Rycote Softie windshield and a PMD-660 Marantz digital recorder. ...
... df = 27, P < 0.001). We recorded trill components up to 3.27 s in length, and a previous study in a different population of superb fairy-wrens reported lengths of trill components up to 2.2 s and mean ± standard deviation (SD) = 1.09 ± 0.34 s (Dalziell and Cockburn 2008). Thus our experimental manipulation resulted in trill lengths within the natural range, with an average difference in trill component length of 0.68 s, representing approximately 2 SDs. ...
Article
In many animal taxa, behavior varies both among individuals (animal “personalities”) and within individuals (“plasticity”). Personality and plasticity may co-vary if individuals differ in responsiveness to changes in their environment (“I × E” interaction). The nature and fitness implications of individual differences in behavioral plasticity in the wild are poorly understood. In territorial animals, fitness depends fundamentally on resource-defense behavior—their response to various threats from conspecific competitors. Such systems thus offer an ideal opportunity to investigate individual differences in behavioral plasticity. We used male superb fairy-wrens (Malurus cyaneus) to test for individual differences in the intensity and plasticity of territorial defense behavior. Using captive assays, we identified behavioral types on the basis of fast versus slow exploration of a novel environment (the “proactive–reactive” axis of behavior). Then we simulated territorial intrusions in the wild, using playback of experimentally manipulated songs that differed in trill length in a pair-wise design. Although previous work suggests that proactive individuals are more aggressive and less responsive than reactive individuals, we found no support for these differences in the context of territorial defense in the wild. Fast explorers (proactive) and slow explorers (reactive) responded equally aggressively to a simulated territorial intrusion overall. Furthermore, although fast explorers responded equally strongly to the two different playback stimuli, there was little evidence that slow explorers differentiated between the two stimuli, and this “I × E” interaction was not statistically significant. Further work is needed to determine the prevalence in the wild of personality-related differences in behavioral plasticity.
... Elements were defined as a single continuous trace on a spectrogram that did not overlap with other traces (Dalziell & Cockburn, 2008;Kroodsma, 2005;Marler & Slabbekoorn, 2004). Element categories were identified by visual inspection according to their overall appearance on the basis of structural similarities and frequency and temporal modulations, following previously described methods for fairy-wren songs (see Colombelli-N egrel, Robertson, & Kleindorfer, 2011;Dalziell & Cockburn, 2008;Greig & Pruett-Jones, 2008;Kleindorfer et al., 2013;Langmore & Mulder, 1992). ...
... Elements were defined as a single continuous trace on a spectrogram that did not overlap with other traces (Dalziell & Cockburn, 2008;Kroodsma, 2005;Marler & Slabbekoorn, 2004). Element categories were identified by visual inspection according to their overall appearance on the basis of structural similarities and frequency and temporal modulations, following previously described methods for fairy-wren songs (see Colombelli-N egrel, Robertson, & Kleindorfer, 2011;Dalziell & Cockburn, 2008;Greig & Pruett-Jones, 2008;Kleindorfer et al., 2013;Langmore & Mulder, 1992). This manual method was chosen because visual categorization of song types or elements is a task for which humans are believed to perform better than automated methods (Keen, Ross, Griffiths, Lanzone, & Farnsworth, 2014;Von Ahn, 2009). ...
... Therefore, in these cases, the previously used category names for these elements were retained. Syllables were defined as the same repetitions of two or more distinctive elements (Dalziell & Cockburn, 2008; see Fig. 1). ...
Article
Contrary to the traditional view that territory defence is a male behaviour, there is now evidence that female birds actively engage in territory defence, either alone or with their mate. In males, song sharing between neighbours has been shown to facilitate territory defence, but little is known about the importance of song sharing for such behaviour in females. Here, I examined sex roles and song element sharing in two related species: the splendid fairy-wren, Malurus splendens, and the variegated fairy-wren, Malurus lamberti. I first described song structure and song element sharing between partners and neighbours in both male and female songs. I then simulated conspecific intrusions by broadcasting a female or a male song within a pair's territory. Both splendid and variegated fairy-wren females sang songs as complex as their male counterparts and responded to playback of simulated conspecific intrusions. Song element sharing with neighbours was common in both species, but only splendid fairy-wren females shared more elements with their mate than with other recorded males on average. Females in each species engaged in different strategies when responding to territory intruders: female splendid fairy-wrens competed with female intruders, while variegated fairy-wren females coordinated their defence with their mates and exhibited cooperative defence behaviours toward male intruders. I discuss the ideas that variation in levels of extrapair paternity and/or female competition may drive the evolution of different female strategies when responding to territory intruders.
... Erne and Amrhein 2013) and Rusty-crowned Ground-Sparrows (Melozone kieneri; Sandoval and Mennill 2014). It has been suggested that the intensification of vocal characteristics at dawn may be associated with greater mating activity (Harper 1988;Dabelsteen et al. 1998;Dalziell and Cockburn 2008) and intensified mate guarding (Otter et al. 1997) during dawn. Higher song output, for example, functions to prevent the singing male from being cuckolded (Møller 1991). ...
... The inset shows a unit circle (radius = 1) with vector length describing the Spearman rank correlation of the song variables. copulations exclusively during the dawn chorus (Dalziell and Cockburn 2008). Furthermore, the dawn chorus in great tits (Parus major) is directly related to female fertility (Mace 1987). ...
... Furthermore, the dawn chorus in great tits (Parus major) is directly related to female fertility (Mace 1987). During the dawn chorus, males increase both their song rate and song duration in the lead up to egg laying, suggesting that there are differential functions of song at specific times of day (Dalziell and Cockburn 2008). This suggests that the dawn chorus could function as a mate-guarding tactic (Otter et al. 1997), although other evidence suggests that dawn song functions for males to attract their own mates, replacement females for widowed males, and extra-pair mates (Slagsvold et al. 1994). ...
Article
Full-text available
Dawn is a critical period for vocal displays in songbirds. At dawn, songbirds intensify their vocalisations, for example increasing their singing rates in response to increased intruder pressure at this time, and for mate guarding. However, little is known about diurnal variations in song complexity, a sexually selected vocal trait associated with mate choice and territorial defence. We compared song complexity in 17 territorial male tui (Prosthemadera novaeseelandiae) between dawn, solar noon and dusk. In addition, we investigated whether song complexity correlated directly with rival intrusion rate. Our results indicated that song complexity and intrusion rate were significantly higher at dawn than dusk. Analyses also suggested that higher entropy (spectral complexity) and syllable rate, in addition to shorter song duration, were associated with reduced intrusion rate into the singer’s territory. Males with higher song complexity may be perceived as stronger competitors and therefore would attract lower rival intrusion. Our study presents evidence of both diurnal changes in tui song complexity and associations between song complexity and intrusion rate. These findings support the theory that dawn is important for songbird vocal communication in terms of territory assertion.
... Despite this predator context, in superb, splendid and purple-crowned fairywrens the trills do not seem to have an alarm, mobbing or pursuitdeterrent function, but instead appear to be displays directed at conspecifics at a time when receivers are particularly attentive (i.e. alerted by conspicuous predator calls; Dalziell & Cockburn, 2008;Greig & Pruett-Jones, 2009Hall et al., 2013;Langmore & Mulder, 1992). In support of this interpretation, silent predator mounts at the nest do not elicit Type II songs (Greig & Pruett-Jones, 2009), conspecifics respond to Type II songs as if they were standard display songs rather than alarm calls (Greig & Pruett-Jones, 2009Langmore & Mulder, 1992), and aspects of Type II song structure have been show to correlate with measures of male quality (trill duration and male age in M. cyaneus: Dalziell & Cockburn, 2008; trill low frequency and body size in M. coronatus: Hall et al., 2013). ...
... alerted by conspicuous predator calls; Dalziell & Cockburn, 2008;Greig & Pruett-Jones, 2009Hall et al., 2013;Langmore & Mulder, 1992). In support of this interpretation, silent predator mounts at the nest do not elicit Type II songs (Greig & Pruett-Jones, 2009), conspecifics respond to Type II songs as if they were standard display songs rather than alarm calls (Greig & Pruett-Jones, 2009Langmore & Mulder, 1992), and aspects of Type II song structure have been show to correlate with measures of male quality (trill duration and male age in M. cyaneus: Dalziell & Cockburn, 2008; trill low frequency and body size in M. coronatus: Hall et al., 2013). Additionally, trills are sometimes given unprompted by predators during dawn chorus displays, and males often incorporate them into songs (Dalziell & Cockburn, 2008;Greig & Pruett-Jones, 2008;Hall et al., 2013). ...
... In support of this interpretation, silent predator mounts at the nest do not elicit Type II songs (Greig & Pruett-Jones, 2009), conspecifics respond to Type II songs as if they were standard display songs rather than alarm calls (Greig & Pruett-Jones, 2009Langmore & Mulder, 1992), and aspects of Type II song structure have been show to correlate with measures of male quality (trill duration and male age in M. cyaneus: Dalziell & Cockburn, 2008; trill low frequency and body size in M. coronatus: Hall et al., 2013). Additionally, trills are sometimes given unprompted by predators during dawn chorus displays, and males often incorporate them into songs (Dalziell & Cockburn, 2008;Greig & Pruett-Jones, 2008;Hall et al., 2013). Assessing the frequency of occurrence, context and structure of Type II songs across the five additional Australian Malurus offers an opportunity to investigate the evolutionary origins of these predator-elicited displays as well as the possible consequences of context shifts in generating novel signal phenotypes. ...
Article
Revealing the evolutionary origin of novel traits is a long-standing challenge in evolutionary biology. The dynamics of antipredator signalling and conspecific advertisement provide one framework in which to investigate this phenomenon, because shifts in signal context may lead to new signal functions, novel evolutionary pressures and ultimately novel phenotypes. Several species of fairy-wrens (Maluridae: Malurus) give song-like trills (‘Type II song’) in response to vocalizations of avian predators. Despite this predator context, in some species the trills appear to function as conspecific-directed displays. We investigated two hypotheses for the evolutionary origin of predator-elicited Type II songs: (1) they originated as antipredator signals, then shifted to a display context and subsequently became more elaborate because selection pressures changed; or alternatively (2) they originated as conspecific-directed songs, then shifted to a predator context to exploit an effective communication window. Using predator playbacks and samples of natural dawn chorus recordings, we found that many Malurus species gave trills in response to predators, but only a subset gave unprompted trills during dawn chorus displays, and ancestral state reconstructions suggested that the predator-elicited context evolved first. Additionally, species that used trills more often (in both predator and unsolicited contexts) tended to have longer trills with a faster note rate, suggesting that trills have evolved a higher performance as they became a more important part of the display repertoire. Our results support the hypothesis that trill displays originated through the elaboration of predator context calls and provide an example of a shift in signal context leading to novel signal phenotypes.
... Furthermore, song output (number of songs produced) is greater at dawn than at dusk in winter wrens (Troglodytes troglodytes, Erne & Amrhein 2008) and rusty-crowned ground-sparrows (Melozone kieneri, Sandoval & Mennill 2014). It has been suggested that the intensification of vocal characteristics at dawn may be associated with greater mating activity (Harper 1988;Dabelsteen et al. 1998;Dalziell and Cockburn 2008) and intensified mate guarding (Otter et al. 1997) during dawn. Higher song output for example functions to prevent the singing male from being cuckolded (Møller 1991). ...
... Diurnal variation in reproductive behaviour such as both within-and extra-pair copulations (Harper 1988;Dabelsteen et al. 1998) There is evidence that the male dawn chorus has a dual function of both enforcement of dominance among male group members in addition to signalling attractiveness to females. Male superb fairy-wrens (Malurus cyaneus) for example will seek extrapair copulations exclusively during the dawn chorus (Dalziell & Cockburn 2008). ...
... Furthermore, the dawn chorus in great tits (Parus major) is directly related to female fertility (Mace 1987). During the dawn chorus, males increase both their song rate and song duration in the lead up to egg laying, suggesting there are differential functions of song at specific times of day (Dalziell & Cockburn 2008). This suggests the dawn chorus could function as a mate-guarding tactic (Otter et al. 1997), ...
Thesis
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In songbirds, song is important for mate attraction and territory defence. Females of some species preferentially select males that have more complex songs, an honest signal for male fitness. Examining variation in song complexity provides important insights into the evolution of sexually-selected vocal characteristics. In this thesis, hypotheses examining song complexity variation and a series of biological and environmental factors were tested. A socially monogamous songbird with highly complex songs and high extra-pair paternity (tui, Prosthemadera novaeseelandiae) was selected as the main study model. Firstly, the hypothesis that song complexity in songbird broadcast songs would be higher than in interactive songs was tested. In addition, it was predicted that there would be a positive association between song complexity and extra-pair paternity frequency. This was conducted across 78 songbird species, the most comprehensive analysis in this study area to date. Concordant with the predictions, tui broadcast songs were found to have higher complexity than interactive songs. Furthermore, after controlling for phylogenetic relatedness, a significant positive association between extra-pair paternity frequency and within-song complexity was found across multiple species. Secondly, I tested the hypothesis that tui song complexity would be higher at dawn than at solar noon and dusk. It has previously been established that dawn is a critical period for intensified songbird vocal displays, such as increased song rate. However, little research has been conducted on diurnal variations in song complexity, which was predicted to be higher at dawn. As predicted, both tui song complexity and intrusion rates were significantly greater at dawn than at dusk. In addition, two song complexity variables were inversely correlated with intrusion rate. Thirdly, the hypothesis that male tui would respond more aggressively to more complex songs was tested, to assess whether song complexity plays a role in male-male interactions. Male responses to rival male songs of different degrees of complexity were subsequently examined using playback experiments. Male tui songs with higher complexity evoked stronger and more aggressive intrasexual responses than simple song as predicted. Fourthly, I tested the hypothesis that habitat complexity would correlate positively with tui song complexity. The association between habitat structure and tui song complexity was investigated by comparing male song complexity in two types of habitat: forest remnants with high complexity, and open habitats with lower complexity. As predicted, habitat complexity correlated positively with tui song complexity. Overall, the findings in this thesis provide evidence that several biological and environmental factors are associated with the evolution of song complexity; a socially-selected vocal trait. This study suggests that complex songs in vocally complex songbirds may have evolved under extra-pair paternity, territorial and environmental pressures. It therefore has implications for furthering our understanding of song complexity evolution in songbirds.
... Compared with mainland birds, island birds of both sexes: (1) occupied a wider niche breadth; (2) were significantly larger in body size and (3) had narrower bills (there was no difference in bill-length) (Schlotfeldt and Kleindorfer 2006;Dudaniec et al. 2011; see also Myers et al. 2010). The Superb Fairy-wren is a non-duetting species in which both males and females sing a solo chatter song throughout the year to defend their permanent territories (Cooney and Cockburn 1995;Rowley and Russell 1997;Dalziell and Cockburn 2008). They are, therefore, a model system for testing the response of resident males and females to the singing behaviour of male and female intruders. ...
... The species is known for its complex vocalisations, with eight types described: Type I song (chatter song), Type II song (trill song), Type III song (alarm song), alarm call, incubation call, brooding purr, feeding-young call and contact call (reviewed in Colombelli-Négrel 2008;Colombelli-Négrel et al. 2011, 2012. Here we focus on the Type I or chatter song because it is the most common vocalisation sung by both males and females, it is used by both sexes for territorial defence, and is used by males for attracting extra-pair copulations (Langmore and Mulder 1992;Cooney and Cockburn 1995;Dalziell and Cockburn 2008;Cockburn et al. 2009). Evidence for a territorial defence function of chatter song is: (1) rates of chatter song increase at the onset of the breeding season after several months of communal foraging; ...
... (2) birds in newly established territories have higher rate of chatter song and (3) females are more likely to produce chatter song in response to intruding neighbours and strangers than to their mates (Cooney and Cockburn 1995). Evidence for a mateattraction function of chatter song includes: (1) males sing chatter song in a dawn chorus; (2) males in the dawn chorus are visited by females seeking extra-pair copulations and (3) males that produce more chatter song have more extra-pair copulations (Dalziell and Cockburn 2008). The role of female preference for male chatter song and reproductive success has not yet been studied, although we predict assortative pairing for this trait given that both males and females produce the chatter song. ...
Article
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The widely accepted functions of complex bird song – to defend a territory or attract a mate, or both – have generally been tested in northern hemisphere species in which males produce the song and females choose the singer. In our study species, the Superb Fairy-wren (Malurus cyaneus), both males and females sing a solo song throughout the year. We compare the chatter song in males and females of two genetically distinct subspecies, and test if resident birds respond to the sex and subspecies of the intruder song. Compared with island birds (M. c. ashbyi), mainland Superb Fairy-wrens (M. c. leggei) produced songs with lower frequency and fewer elements. Compared with females, males produced longer songs with more elements. Resident birds showed acoustical discrimination for the sex and subspecies of the intruder bird. The response of resident pairs was positively correlated, but each sex showed a solo response. Resident males were the first to respond to male intruders, and resident females were the first to respond to female intruders. Fairy-wrens had the strongest response towards (1) intruders of the same subspecies and (2) male intruders. The finding of signal divergence and acoustical discrimination in males and females makes this a model system to test the mechanism of reproductive isolation when both sexes sing.
... Adult males sing longer, more complex songs than females in some populations (Kleindorfer et al., 2013). Males also have a larger song repertoire than females: males sing chatter song and trill song (Type II song) to attract extrapair copulations (Langmore and Mulder, 1992;Cooney and Cockburn, 1995;Dalziell and Cockburn, 2008;Cockburn et al., 2009;Colombelli-Négrel et al., 2011). There is evidence that male trill song is learned: introductory elements of trill song were more similar between males and their social fathers than males and their genetic fathers; males that dispersed from the natal territory acquired the local trill song dialect (Blackmore, 2002). ...
... We define an element in the song as a single, continuous trace on a spectrogram. We created an element library (Figure 1) based on the existing element classifications developed by Langmore and Mulder (1992), Blackmore (2002), Dalziell and Cockburn (2008), Colombelli-Négrel et al. (2011) and Kleindorfer et al. (2013), and comparing these classifications of elements to songs of our monitored populations. We identified 10 element types that have previously been classified in different populations (A, F, O, P, Q, R, T, U, V, W,) and 6 new elements found in our populations (FL, G, K, L, Z, ZN). ...
... A wealth of research has shown that song complexity is an honest signal of male quality (Buchanan et al., 2004;Spencer et al., 2005;Schmidt et al., 2013), important for female mate choice (Catchpole, 1980;reviewed in Byers and Kroodsma, 2009). In superb fairy-wrens, different male song types predicted extra-pair fertilisations (Dalziell and Cockburn, 2008), and sexes had different element complexity (Kleindorfer et al., 2013). A theoretical framework for functions of female song complexity mostly focuses on resource defense Illes, 2015). ...
Article
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Birdsong is regarded as a classic example of a sexually-selected trait and has been primarily studied in systems with male song. Complex solo female song is emerging from the shadows of overlooked phenomena. In males, rearing conditions affect male song complexity, and males with complex songs are often more successful at mate attraction and territorial defense. Little is known about the ontogeny or function of complex female song. Here we examine song elements in fledgling superb fairy-wrens (Malurus cyaneus) in relation to the song elements of adult tutors. Male and female superb fairy-wrens produce solo song year-round to defend a territory. We ask if sons and daughters acquire song elements from sex-specific vocal tutors. We found that sons and daughters produced the song elements of their mothers and social fathers, and that sons and daughters had comparable song element repertoires at age 7-10 weeks. We conclude that sons and daughters increase their song element repertoire when vocally imitating elements from several vocal tutors, and that both sexes acquire elements from male and female vocal tutors in this system.
... In temperate zones, this is most noticeable in spring, when males defend breeding territories and attract mates. Dawn song has been shown to be particularly important in female attraction, extra-pair matings, and territory defence (Kacelnik & Krebs, 1983;Slagsvold et al., 1994;Poesel et al., 2001;Kunc et al., 2005;Dalziell & Cockburn, 2008;Murphy et al., 2008;Suter et al., 2009). There are several factors which may have selected for this peak in dawn song, including female behaviour, sound transmission characteristics, territory invasions, and low foraging success at dawn (reviewed in: (Kacelnik & Krebs, 1983;Kunc et al., 2005)). ...
... The finding that singing was most pronounced at dawn and peaked during egg laying, the fertile period of the female, and declined thereafter supports a previous study in great tits (Amrhein et al., 2008) and studies in other songbirds (Ballentine et al., 2003;Dalziell & Cockburn, 2008;Bruni & Foote, 2014) providing further correlative evidence that dawn song in great tits, as in other species (Gil et al., 1999), functions also beyond the fertile period. Even though increased singing at dawn during mate fertility had been suggested to be a handicap signal as only high quality males would benefit from high singing activity (Møller, 1991), this idea is not generally supported due to evidence from several species showing that singing activity often is higher during other reproductive stages (Gil et al., 1999). ...
Thesis
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To tweet or not to tweet: The role of personality in the social networks of great tits By: Lysanne Snijders Project video: https://www.youtube.com/watch?v=zy0HysxhQz0 When mentioning social networks it is easy to think of online networks for people, such as Facebook and Twitter. But many animals also have social networks. In proximity networks they encounter each other physically and in communication networks they connect to each other by using signals. Their position in such social networks is important. It can influence the likelihood of finding new food, acquiring novel foraging techniques, rising in social status and acquiring a mate. However, having many contacts can also be risky as it increases the likelihood of encountering infectious diseases, social stress or ending up in a fight. As social network position can be so significant, it is essential that we know what determines it. A likely key factor is personality. Individuals consistently differ in how risk-prone (pro-active) and risk-averse (re-active) they tend to behave. As making face-to-face contact is not without risk, bolder individuals might have more social contacts. An ideal model to study this hypothesis is the great tit. A common garden bird. There are well established methods to quantify personality differences in great tits and with the newest tracking technologies we can now also monitor their face-tot-face contacts. What makes the great tit even more interesting is that they like to breed in nest boxes and so we can also study potential fitness effects of specific network positions. Additionally, great tits are songbirds, which makes them also ideal to answer a second question: Do individuals that are shy to approach others, use communication instead? Since communication is often a less risky connection strategy than face-to-face contact. In this PhD thesis I reveal how and when personality explains why some birds are better connected than others. In wild territorial populations pro-active males were better connected to other males and were most likely to approach a rival. In contrast, when removing the risk of fights during male-to-male spatial associations, via a video-playback experiment in captivity, the re-active males appeared to be most social. When confronted with the life-size video image of a novel conspecific, they spent the most time associating with it. When lowering the risks associated with spatial associations the social preferences of re-active individuals might thus increase. No relationship was found between social network position in the wild and reproductive success, an important fitness component. Wild male great tits that were less likely to approach a rival, sang more actively at dawn. Dawn song is the peak time for male great tit singing activity and operates as a large communication network. Since a prime function of singing at dawn is territory advertisement, these birds might thus try to prevent rival territory intrusions by singing more fiercely at dawn. No direct links were found between personality and an individual’s place in the communication network, however pro-active birds vocalized most actively during territory intrusions and increased their singing activity significantly during the fertile period of their mate. Communication networks and proximity networks can influence each other via song, by attracting or repulsing conspecifics to come close. For example, the vocal response of an intruded male to its rival significantly influenced whether female neighbours would come close to the intrusion site and if male neighbours would stay away. What determines the place in a social network? By knowing this we learn more about how groups function and how different social strategies in the same population can co-exist.
... Radio-tracking has shown that females initiate extra-group mating in the half-hour before dawn, usually on the second and third day prior to the start of egg-laying . Th ey do this by making one or two forays on consecutive mornings three days prior to egg-laying from the (Dalziell and Cockburn 2008 ;Cockburn et al. 2009 ). Females engaging in extra-group matings show a common preference for males that have been displaying to them for months prior to the breeding season, with the onset of display by males directly associated with the time of year at which he attains full nuptial plumage. ...
... Finally, males display with song. While both sexes use a chatter song for territory defense, males have an additional "trill song" that is incorporated unprompted in the dawn chorus when females are making forays to visit extra-group mating partners (Dalziell and Cockburn 2008 ). ...
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IntroductionFairy-wrens have always played a pivotal role in the study of cooperative breeding. So far as we are aware, the first recognition that more than two birds could combine to rear a single brood of young comes from John Gould’s (1841) depiction of the superb fairy-wren Malurus cyaneus in his treatise on the birds of Australia, many decades before Alexander Skutch’s explorations of the biology of Neotropical birds (Boland and Cockburn 2002). Indeed, experiments on cooperative breeding were reported for the superb fairy-wren M. cyaneus as early as 1910, and in the 1950s this was also the first cooperatively-breeding species to be studied using color-rings to distinguish between individuals (Rowley 1957; Bradley and Bradley 1958). Since then there have been three intensive demographic studies of Malurus species lasting more than fifteen years (Russell and Rowley 1993, 2000; Cockburn et al. 2008b). Comparative studies between populations also have access to additional data from 13 populations of 7 congeneric species (van de Pol et al. 2013). It is certain that early detection and sustained interest in cooperative breeding in fairy-wrens reflects the comparative ease with which they can be studied. At least some species are abundant, adapt to the presence of humans, and build nests conveniently close to the ground. In addition, in contrast to many cooperatively breeding species, the sexes are easily distinguished, as adult males are among the most brilliantly-colored of birds, while females and juveniles in most species are much drabber. Species can therefore be instantly identified as cooperative breeders if two males are seen carrying food to the nest (Buchanan and Cockburn 2013). While early work on fairy-wrens repeatedly informed theory concerning cooperative breeding (Margraf and Cockburn 2013), the current explosion of interest in this group stems from the surprising discovery that most young in most species are not sired by the males that provision and defend them (Brooker et al. 1990; Mulder et al. 1994; Cockburn et al. 2013). Instead, parentage is dominated by extra-group fertilizations initiated by the female. Such rampant infidelity undermines the expectation that helping behavior by subordinate males will be directed toward full-siblings, immediately reducing the potential for indirect fitness benefits at nests with helpers.
... In temperate zones, this is most noticeable in spring, when males defend breeding territories and attract mates. Dawn song has been shown to be particularly important in female attraction, extrapair matings, and territory defense (Kacelnik and Krebs 1983;Slagsvold et al. 1994;Poesel et al. 2001;Kunc et al. 2005;Dalziell and Cockburn 2008;Murphy et al. 2008;Suter et al. 2009). There are several factors that may have selected for this peak in dawn song, including female behavior, sound transmission characteristics, territory invasions, and low foraging success at dawn (reviewed in Kacelnik and Krebs 1983;Kunc et al. 2005). ...
... The finding that singing was most pronounced at dawn and peaked during egg laying, the fertile period of the female, and declined thereafter supports a previous study in great tits ) and studies in other songbirds (Ballentine et al. 2003;Dalziell and Cockburn 2008;Bruni and Foote 2014) providing further correlative evidence that dawn song in great tits, as in other species (Gil et al. 1999), functions also beyond the fertile period. Even though increased singing at dawn during mate fertility had been suggested to be a handicap signal as only high-quality males would benefit from high singing activity (Møller 1991), this idea is not generally supported due to evidence from several species showing that singing activity often is higher during other reproductive stages (Gil et al. 1999). ...
Article
Expression of sexually selected signals in many species varies over time of day and season. A key model system to study this variation in signal expression is birdsong. Yet, despite good ecological understanding of why song varies across time of day and season, much of the individual variation remains unexplained. Although some of the interindividual variation in singing depends on the quality or motivation of an individual, it can also vary with other characteristics. Because singing has been shown to vary with personality traits in specific contexts, personality is thus an important candidate to explain part of the variation in seasonal and daily singing. Using a personality-typed field population of great tits (Parus major), we here show that singing activity peaked at dawn during the fertile period of the females and that the association between male personality and singing activity depended on the reproductive stage of his mate; faster explorers significantly increased in singing activity during main periods of fertility and maternal investment (egg laying and incubation). Moreover, males with higher singing activity tended to raise more fledglings. Increased singing by faster explorers during key periods of female reproductive investment suggests that faster explorers are more responsive to changes in female reproductive stage, contrasting the general view that faster explorers are less responsive to environmental and social changes. Most importantly, these findings highlight that multiple factors including personality need to be integrated when assessing causes of variation of highly variable sexually selected signal traits.
... Fairy-wrens are also a good study system for this investigation because both males and females regularly sing Mahr et al., 2016;Rowley & Russell, 1997). Male and female songs have been well-studied in certain species, providing evidence that male and female songs play a role in territory defense and samesex competition Colombelli-Négrel, 2016;Cooney & Cockburn, 1995;Dalziell & Cockburn, 2008;Dowling & Webster, 2013;Hall & Peters, 2008;Kleindorfer et al., 2013), and female song is related to annual reproductive success and habitat quality Cain & Langmore, 2016). Male fairywrens of many species give two song types: type I and type II songs (Langmore & Mulder, 1992); whereas females largely only give type I songs (Langmore & Mulder, 1992;Rowley & Russell, 1997; but see Greig & Pruett-Jones, 2008). ...
... Male fairywrens of many species give two song types: type I and type II songs (Langmore & Mulder, 1992); whereas females largely only give type I songs (Langmore & Mulder, 1992;Rowley & Russell, 1997; but see Greig & Pruett-Jones, 2008). Type I songs are frequently produced throughout the day by both sexes and by males at dawn and appear to be used in territory defense, whereas male type II songs are delivered either in the dawn chorus or during the day immediately following a loud sound, such as the call of a predatory bird (Dalziell & Cockburn, 2008;Greig & Pruett-Jones, 2010;Greig & Webster, 2014;Langmore & Mulder, 1992). Comparative studies across fairywrens suggest that male type I song structure is shaped by sexual selection, as well as other selective pressures (Greig et al., 2013). ...
Article
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Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male–female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male–female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.
... ERUB -červenka obecná Erithacus rubecula (n = 429), POCH -rehek domácí Phoenicurus ochruros (n = 463), SVUL -špaček obecný Sturnus vulgaris (n = 642). Fig. 4. Seasonal patterns of singing activity in three passerine species singing in the fall (Třeboň and České Budějovice regions, S Bohemia, Czech Republic, 1993, 2008 obr. 5. Příklad rozdílného průběhu cirkanuální zpěvní aktivity více druhů jednoho rodu (rod Acrocephalus, Parížske močiare, 1988Parížske močiare, -2005. Hodnoty jsou uvedeny sumárně pro jednotlivé dekády měsíců. ...
... Průběh a intenzitu hlasové aktivity ovlivňují také ekologické faktory prostředí, vnitřní vyladění ptáků, ale např. i početnost daného druhu v lokalitězpěvní aktivita samců se zvyšuje ve vztahu k přítomnosti ostatních samců nebo samic (Westcott 1992, Staicer et al. 1996 a může také souviset s postavením samce (Dalziell & Cockburn 2008). Známá je i reakce samců na přehrávání hlasů (playback) téhož i jiných druhů; také nespárovaní samci obvykle zpívají intenzivněji než spárovaní (Melemis & Falls 1982, Galeotti & Pavan 1993. ...
Article
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Although there are many studies focused on various aspects of bird vocalizations, most species are data deficient concerning detailed information on their diel, seasonal and annual patterns of vocal activity. In many species, we still do not know when they show distinct peaks of vocal activity and, on the other hand, when birds cease singing within the day and season, and how representative researcher's data on the number of singing and/or calling individuals are in the context of singing period or breeding population. In this study we try to address these crucial questions and demonstrate some examples of vocal activity patterns in different bird species. We refer to the fact that the vocal activity of birds is highly variable, and, on the other hand, we draw attention to the fact that individual species tend to exhibit characteristic patterns of vocal activity that are important to know when planning fieldwork. In studies targeted on estimating the maximum number of singing individuals during a short time period and using a limited number of samples, it is difficult to recommend an appropriate time of sampling. In general, samples should be taken at least several times over a wider time frame (such as breeding season), however, the best time to sample depends on the studied species and locality. Avoid limiting your censuses to early morning hours only and concentrate your effort on extended time period from the twilight and sunrise through the later morning hours so that the sampling is more robust. On the other hand, some species are best sampled in the evening or at night. Assessing the data obtained without detailed knowledge of patterns of vocal activity of birds may be biased in an unknown extent.
... singing style or song repertoire), to the extent that song directed to males may differ from that directed to females (Collins et al. 2009). However, since the two main functions of song may entail honest signalling (Berglund et al. 1996), differences in repertoire size or song rate between dawn and other times of the day may not tell us much about the likely target of the dawn chorus (Dalziell and Cockburn 2008). Instead, more subtle characteristics, such as singing patterns (song matching, overlapping, singing site within the territory, etc.), may be more informative. ...
... Although territory turnover may be generally too low to explain the strength and ubiquity of the dawn chorus, some data do suggest that invasion rates in the early morning are higher than later in the day (Amrhein et al. 2004a;Kacelnik and Krebs 1983). Floaters in some species actively seek territories at this time (Amrhein et al. 2004a;Dalziell and Cockburn 2008), perhaps because all males are singing and it is easier to detect vacant areas than later on in the day (Amrhein et al. 2004a). In this sense, the hypothesis could generalise to the fact that dawn is a time of high risk for territory owners. ...
Chapter
The bird dawn chorus has fascinated humans since ancient times, but still today numerous questions remain unclear. This chapter will explore this puzzling phenomenon, a communal display that likely involves the highest level of sound complexity found among animal signals. Covering from the first descriptive studies to recent multidisciplinary approaches, we review the physiological, behavioural and environmental factors affecting dawn chorus. In addition, we provide a critical assessment of the supporting evidence for the functional hypotheses proposed so far to disentangle its proximal and ultimate causes. We find that, despite the latest empirical and theoretical studies, there is still a good degree of confusion, and that four out of the nine hypotheses proposed so far in the literature have not been empirically tested. We show that most of these hypotheses are not incompatible with each other, and that their explanatory value changes depending on the species and the season. We argue that, at any rate, a single explanation may not be a reasonable expectation. The best-supported hypotheses for early singing provide three complementary lines of explanation: (1) singing at dawn has a relatively low energetic cost, most likely because it does not interfere with feeding; (2) is optimal to manipulate female mating or settle territory boundaries; and (3) may promote a handicap mechanism that prevents dishonest signalling. Thus, it follows that a combination of hypotheses based on both an optimality standpoint and costliness assumptions is needed to understand the phenomenon. We provide a series of specific suggestions for further research to refine our knowledge of this intriguing aspect of animal behaviour.
... suggesting that the performance level of an individual's song could be an honest badge of his condition during development. In addition, lab and field experiments are beginning to reveal that trill rate performance is a salient signal for potential mates and competitors (Ballentine et al. 2004;Illes et al. 2006;Cramer & Price 2007;Dalziell & Cockburn 2008;Schmidt et al. 2008;de Kort et al. 2009;Dubois et. al 2009). ...
... Yet most studies, excluding that of Sheldon & Ellegren (1999) which shows no association, reveal a positive association between age and expression of the sexually selected trait (Sundberg & Dixon 1996;Dunn & Cockburn 1999;Thusius et al. 2001;Budden & Dickinson 2009) or do not report if there is an association between age and the signal (Safran et al. 2005;Kleven et al. 2006;Balenger et al. 2009). Similarly, for extra pair paternity and bird song, Forstmeier et al. (2002) report no association between age and the trait, but most studies report a positive association (Hasselquist et al. 1996;Kempenaers et al. 1997;Gil et al. 2007;Dalziell & Cockburn 2008;Suter et al. 2009) or do not report if there is an association (Byers et al. 2007;Dolan et al. 2007;Chiver et al. 2008 (Andersson 1994). Under this scenario males are able to win contests by successfully advertising their high quality, and withdraw from contests where another individual advertises superiority. ...
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Elaborate sexual signals are thought to evolve because they honestly signal heritable condition to potential mates or competitors, but it has proven difficult to predict which aspects of sexual signals should be the best indicators of condition, and thus the targets of selection. For bird song, the tradeoff between frequency bandwidth and trill rate provides a theoretical framework within which songs of rapid trill rate, large frequency bandwidth or both should be good indicators of condition, because these songs are likely more challenging to learn and/or sing. Previous work showed that Black-throated Blue Warblers (Dendroica caerulescens) in a northern population differed from those in a southern population, with northern songs varying primarily along a trill rate axis, and those in the south varying primarily along a frequency bandwidth axis. This observation led to an a priori prediction that sexual selection should be acting on trill rate, but not frequency bandwidth, in the northern population. In a study of extra-pair paternity, extra-pair sires had faster trill rates (but not larger frequency 1 bandwidths) than the males they cuckolded, and trill rate was the best (and only significant) predictor of the total genetic offspring that a male sired in a given year. In a playback experiment, males responded more strongly to playbacks of songs with artificially increased trill rates compared to songs with reduced trill rates. In addition, trill rate did not change as individuals aged, indicating that this acoustic variable may be a badge of intrinsic quality. These results add to a growing body of evidence that emphasizes the importance of performance constraints in sexual selection, and provide a rare vertebrate example of sexual selection acting on a signal that does not change with age.
... More complex components may be difficult to imitate accurately, leading to greater variation (Nelson, 2017). Different components may be important for inter-versus intraspecific communication (Dalziell & Cockburn, 2008;Leitão & Riebel, 2003) or may encode different kinds of information (Nelson & Poesel, 2007;Richards, 1981). ...
... Examining the spectrograms and the results of the PCA on all elements ( Figure 3) revealed a three-part structure in the whistle song that was present across the entire range: the introduction, the body, and the final element. A consistent overall structure, with variation in the exact elements or syllables, has been reported in other species (Barišić et al., 2018;Dalziell & Cockburn, 2008;Lee et al., 2019;Nelson & Poesel, 2007;Williams et al., 2013). This consistency of the whistle song structure, and the temporally discrete manner in which songs were produced, implies that the whistle songs are perceived as a whole unit, and makes the differing patterns of variation within the song even more interesting. ...
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Geographic variation in bird song has received much attention in evolutionary studies, yet few consider components within songs that may be subject to different constraints and follow different evolutionary trajectories. Here, we quantify patterns of geographic variation in the socially transmitted “whistle” song of Albert's lyrebirds (Menura alberti), an oscine passerine renowned for its remarkable vocal abilities. Albert's lyrebirds are confined to narrow stretches of suitable habitat in Australia, allowing us to map likely paths of cultural transmission using a species distribution model and least cost paths. We use quantitative methods to divide the songs into three components present in all study populations: the introductory elements, the song body, and the final element. We compare geographic separation between populations with variation in these components as well as the full song. All populations were distinguishable by song, and songs varied according to the geographic distance between populations. However, within songs, only the introductory elements and song body could be used to distinguish among populations. The song body and final element changed with distance, but the introductory elements varied independently of geographic separation. These differing geographic patterns of within‐song variation are unexpected, given that the whistle song components are always produced in the same sequence and may be perceived as a temporally discrete unit. Knowledge of such spatial patterns of within‐song variation enables further work to determine possible selective pressures and constraints acting on each song component and provides spatially explicit targets for preserving cultural diversity. As such, our study highlights the importance for science and conservation of investigating spatial patterns within seemingly discrete behavioral traits at multiple levels of organization.
... Status signals are not limited to coloration, and in some animals vocal signals can function to advertise status. This can be observed as particular vocalizations made by dominant individuals (Dalziell and Cockburn 2008) or as dominant-specific acoustic characteristics in dominant individuals' vocalizations (Hoeschele et al. 2010;Hahn et al. 2013). Dominant individuals may also advertise their status by making vocalizations more frequently than subordinates, such as in the domestic chicken (Gallus gallus), where calling rate is correlated with dominance status (Leonard and Horn 1995), or in the Black-capped Chickadee (Poecile atricapillus), where dominant individuals produce songs at a higher rate than subordinates (Ficken et al. 1987;Otter et al. 1997). ...
Article
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Individual animals of social species that form dominance hierarchies use status signals to advertise their dominance status to conspecifics. Bird species often have a visual status signal known as a “badge of status.” However, the hierarchies of some social species are fluid, and dominance status may change depending on the composition of the group. In such situations, vocal signals are more suitable as a status signal because they are readily modifiable by the signaler. In this study, we investigated the relationship between social dominance rank and calling rate in the Large-billed Crow (Corvus macrorhynchos) by observing a captive flock of Large-billed Crows and determining the dominance rank of each individual. The number of vocalizations each individual produced during the study period were also recorded. Our results revealed that there was a clear linear dominance hierarchy within the flock and that more dominant crows produced sequential-note calls more frequently than their subordinate counterparts. Contact call rate, however, was not affected by dominance status. These results suggest that sequential-note calls function as status signals in groups of Large-billed Crows.
... All group members, including auxiliary helper males, sing and all join their songs to form overlapping, polyphonic duets and choruses that appear to function in intergroup territorial interactions (Dowling & Webster, 2013). Red-backed fairy-wren songs are similar to the chatter song of the superb fairy-wren, Malurus cyaneus (Dalziell & Cockburn, 2008) and the type I song of the splendid fairy-wren, Malurus splendens (Greig & Pruett-Jones, 2008). Unlike these species, the red-backed fairy-wren sings only one song type, but varies the number, type and order of notes within songs (Dowling & Webster, n.d.-b). ...
Article
Variation in song structure and song production of birds are thought to relate to variation of both androgen levels and neural nuclei in the song system, as typically these nuclei are larger in males than in females, vary in size among males and are sensitive to steroid hormones. We investigated the relationships among song and note structure, singing rate, androgen levels and the sizes of two song nuclei, the higher vocal centre (HVC) and the robust nucleus of the arcopallium (RA) in male and female red-backed fairy-wrens, Malurus melanocephalus. Males of this duetting species express three discrete reproductive phenotypes that differ in plumage colour and behaviour. Although HVC and RA structure differed between the sexes, there were no sex differences in note structure and complexity of songs, although females differed from some male types in song rate and frequency characteristics. Both auxiliary males and females had significantly lower androgen levels than the two breeding male phenotypes. Male reproductive phenotypes had similar song characteristics and HVC and RA structure, but differed in androgen levels. Sexes and male phenotypes varied in song rate, but these differences did not correspond to differences in androgen levels. Thus, sex differences in song nuclei anatomy and androgen levels were not associated with differences in song structure and singing rate; and, the differences in androgen levels among male phenotypes were not reflected in differences in singing rate, song structure or the song nuclei. We conclude that, similar to other recent findings, the sexes of the red-backed fairy-wren can produce similar song and express similar singing behaviour despite differences in song system structure and circulating androgen levels; singing and song system anatomy appear not to be part of the suite of traits associated with differences in androgen levels in male red-backed fairy-wrens.
... A well studied acoustic communication system is bird song, which is mostly used by territorial males, to repel competitors and to attract potential mates . In some bird species, resource holding males signal their quality to females mainly at dawn (Otter et al. 1997;Double and Cockburn 2000;Dalziell and Cockburn 2008;Murphy et al. 2008). In other species, dawn singing seems to be relatively unimportant in mate attraction, but males may address potential mates during other times of the day Staicer et al. 1996). ...
... Additionally, songs in Maluridae range from fairly simple note repetitions to extremely complex assortments of rapidly repeated notes (Rowley and Russell 1997). Songs are used during territorial disputes and during dawn-chorus displays (Rowley and Russell 1997; Dalziell and Cockburn 2008; Greig and Pruett-Jones 2008, 2010 Hall and Peters 2008; Dowling and Webster 2013), and song playbacks are reported to elicit territorial responses in most studied species (Rowley and Russell 1997). Thus, song is likely important in mate attraction and territory defence in Maluridae, and other social functions of song such as mate guarding or within-group communication may be important as well (Payne et al. 1988Payne et al. , 1991; Hall and Peters 2008; Dowling and Webster 2013). ...
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Many factors may influence the evolution of acoustic signals, including sexual selection, morphological constraints and environmental variation. These factors can play simultaneous and interacting roles in determining signal phenotypes. Here, we assess the evolution of song features in the Maluridae, a passerine family with significant variation among taxa in levels of sperm competition, morphological features and breeding habitats ranging from arid grasslands in Australia to tropical rainforests in New Guinea. We used phylogenetic comparative methods and a robust molecular phylogeny to compare song characteristics with a variety of other measures, including testes mass, body-size and latitude. Several aspects of the temporal and frequency structure of song were associated with relative testes mass, suggesting that sexual selection may influence some song characteristics in this family. The lowest frequencies of song were strongly predicted by body-size, indicating that morphological constraints have also likely influenced acoustic phenotypes. Song versatility, reflecting the diversity of note types in a song, was positively correlated with latitude, suggesting that complexity may increase in association with more temperate or variable environments. Variation in song structure across the family appears to reflect a complex interaction between natural and sexual selection.
... The Superb Fairy-wren is an ideal model species to answer our questions because both males and females sing solo chatter songs year-round for territorial defense (Cooney and Cockburn, 1995;, and the structure and complexity of female chatter song is similar to male chatter song (Kleindorfer et al., 2013). Mate attraction may be a secondary function of male chatter song (Dalziell and Cockburn, 2008), but to our knowledge there is no study investigating whether this function applies to female song. In contrast to song, Superb Fairy-wrens have a strong sexual plumage dichromatism. ...
Article
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Showy ornaments are considered as outcomes of sexual selection processes. They provide a “badge of status” to impress conspecific rivals or potential mating partners. Single ornaments may signal attractiveness or individual quality, yet many species display multiple ornaments. There are several hypotheses that explain the existence of multiple ornaments, suggesting that different ornaments serve as different information sources. They may provide either additive or redundant information on the same quality traits, or are simply evolutionary leftovers with no further relevant information. Although females of many species display elaborated traits, most studies regarding multiple ornaments focus on males. However, given that in many species females also display multiple ornaments, the question about their functional significance arises. To understand the existence of female multiple ornaments we investigated ornamental features of female Superb Fairy-wrens (Malurus cyaneus), focusing on song and variation in plumage characteristics. Female Superb Fairy-wrens produce complex solo songs, for territorial defense, and have bright blue tail feathers. We examined the relationships between song and plumage coloration characteristics in relation to female quality parameters to investigate whether, and to what extent existing hypotheses on multiple ornaments in males may also apply to females. Based on song recordings and spectrometric measurements of UV-coloration of tail feathers, we derived a series of different song and plumage parameters. Our results indicate interrelationships between the song length (total number of elements in female song) and female body size, but not UV-coloration. Interestingly, song complexity (number of different elements in female song) did not correlate with morphological parameters, UV-Chroma and song length respectively. This suggests that i) song and plumage characteristics evolved independently and ii) even within one trait, namely song, multiple signalling should be considered. To our knowledge, this is the first study investigating multiple traits in female songbirds, raising the idea that multiple signalling of sexually selected traits is not restricted to males only.
... Mulder et al. 1994). It is difficult to determine the potential risks for females pursuing EPP in this situation without more precise information on territory quality, patterns of adult movement, adult displays or risk of adult predation (Dalziell and Cockburn 2008). ...
Article
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The Superb Fairy-wren (Malurus cyaneus) is a model system in which to study cooperative breeding and extra-pair paternity. Previous studies in this species have shown that 61-76% of nestlings were extra-pair young and 92-95% of nests contained at least one extra-pair young. Furthermore, the probability of extra-pair paternity was higher when auxiliary males were present. We studied group size and extra-pair paternity in South Australia where, unlike other study sites, auxiliary males were relatively uncommon: 16% of nests had one auxiliary male compared to 37-80% with at least one auxiliary per nest in other studies. We predicted a lower incidence of extra-pair paternity, given the shortage of auxiliary males. Our results did not support this prediction: we found extra-pair paternity among 67% of nestlings and 83% of nests.
... In some cases, the signaller may employ entirely different signals for different receivers, or in different contexts (Andersson et al., 2002;Balakrishnan & Pollack, 1996;Baptista, 1978;Byers & Kroodsma, 2009;Centeno et al., 2021;Karubian et al., 2009;Leo, 1959;Rosenthal et al., 2018;Vanderbilt et al., 2015;Zambre & Thaker, 2017). Alternatively, signallers with limited repertoires may modify the sequence in which notes are emitted, such that similar signals may convey different messages to different receivers (Berglund et al., 1996;Dalziell & Cockburn, 2008;Mosk at & Hauber, 2019;Myberg Jr, 1997;Vasconcelos et al., 2010). Studies have modelled vocal sequences as first-order Markov chains, or used Shannon entropy to characterize sequence variability (Kershenbaum et al., 2016). ...
Article
Acoustic signals in animals serve to convey context-dependent information to receivers. Birds and mammals combine diverse sounds into complex sequences to communicate, but the role of temporal sequencing of signals remains understudied in other taxa. Anuran vocalizations are a prominent feature of their life history, and function in defence of territories and to attract mates. However, there are few data on whether anurans pattern their calls into sequences, and whether temporal sequences convey information about context. Here, we investigated the context-dependent vocal repertoire and the use of vocal sequences by two anuran species belonging to different lineages, comparing frogs vocalizing alone and in the presence of a territorial rival. Using a robust analytical framework, we present evidence that both species modify their vocal sequence structure according to context. Specifically, one species (with a smaller repertoire, from a more basal lineage) appends notes to generate more complex sequences, whereas the other (more recently diverged and with a larger repertoire) shifts to different note types, resulting in different sequences for different contexts. Thus, despite differences in repertoire size, both frog species are capable of adjusting the temporal sequence of vocalizations to communicate in different contexts. Vocal sequences and context-dependent ‘syntax’ may be more common in anurans than previously thought, and our methodology presents a paradigm to study the evolution and function of these complex vocal patterns.
... An analogous vocalisation (labelled Type II song or trill song) given primarily in response to Australian Ravens (Corvus coronoides) and Pied Currawongs (Strepera graculina) has been described in Superb Fairy-wrens (Langmore and Mulder 1992). In both these species of Malurus it is thought that Type II songs are sexual or territorial displays directed towards conspecifics (Langmore and Mulder 1992;Dalziell and Cockburn 2008;Greig and Pruett-Jones 2009). One explanation for why males sing after predator calls may be because conspecific receivers are alerted by predator vocalisations and are thus more likely to detect and respond to subsequent Type II songs (Langmore and Mulder 1992;Greig and Pruett-Jones 2009). ...
Article
We document a previously undescribed vocalisation in the Variegated Fairy-wren (Malurus lamberti), the Type II song, which is given in response to the calls of a specific avian predator. We used playbacks of five species of both predators and non-predators to determine which species most commonly elicit Type II songs. Calls of Grey Butcherbirds (Cracticus torquatus) were the only stimuli to elicit Type II songs. Two other species in the genus Malurus, the Splendid Fairy-wren (M. splendens) and the Superb Fairy-wren (M. cyaneus), are also known to sing Type II songs in response to the calls of specific avian predators. In all these species, Type II songs may function as displays to conspecifics. This study highlights the possibility that predator-elicited display behaviour may be more widespread in the genus Malurus than was previously recognised.
... Indeed, some studies found female movements into the territory of other males (so called extra-territorial forays) to be correlated with aspects of male song (Chiver et al. 2008), indicating that females specifically visited males producing higher quality song. Although many studies also support female choice of an extra-pair mate based on song traits (Hasselquist et al. 1996;Byers 2007;Dalziell and Cockburn 2008), others failed to find such a correlation and a recent meta-analysis found no effect of song on extra-pair paternity occurrence (Garamszegi 2004). It is thus possible that females use song for an initial assessment from a distance to decide on whom to approach and then use additional male traits such as plumage coloration for a final assessment (Otter and Ratcliffe 2005). ...
Chapter
The behavioural decisions animals take directly influence their fitness and thus have a fundamental impact on evolutionary processes. In many animals, acoustic signals play an important role in social decisions with mate choice being among the most apparent ones. Male bird song has played a key role along this line, yet the understanding of how female birds use song to prospect, assess and choose mates in their natural environment is surprisingly limited. A main reason for this limited understanding is that it is very difficult to follow a female during her prospecting and decision process and quantify her experience with different males before she makes a final decision. Here we integrate insights from communication networks, male song traits and female prospecting behaviour to stimulate a more integrative approach on the role of signalling in behavioural and reproductive decisions.
... If information regarding a male's dominance rank means something different for a listening female compared to a listening male, how the sexes respond to the signal should also vary. In addition, the type of signal produced by an individual may also vary depending on what audience is present (Dalziell & Cockburn, 2008). ...
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Many species form social groups with dominance hierarchies. Often, individuals possess a status signal that indicates dominance rank. Songbirds produce songs that are used to attract mates or repel rivals, and acoustic features within songs can also indicate an individual's quality, including dominance rank. Acoustic status signals have been reported in the songs of male black-capped chickadees, Poecile atricapillus, a nonmigratory North American songbird. Here we used two operant conditioning tasks to examine acoustic preference for and discrimination of conspecific songs produced by males varying in dominance rank. We used a choice preference task to examine birds' preferences for listening to dominant or subordinate songs and conducted an instrumental learning task to determine whether chickadees considered dominant and subordinate songs as belonging to separate signal categories based on acoustic features. Overall, our results provide little evidence that birds used open-ended categorization when discriminating, but there is evidence that songs from different geographical regions may contain acoustic similarity based on dominance rank. Consistent with previous song discrimination studies with black-capped chickadees, we found sex differences in discrimination abilities, with females learning the discrimination faster than males. We also found evidence that performance accuracy during the instrumental learning task correlates with acoustic song preference. Overall, these results suggest that when biologically relevant signals (e.g. male songs) are used as stimuli during a perceptual task, the birds' responses may be differentially affected based on individual differences among the subjects performing the task (including sex and underlying preference) and the salience associated with the stimuli (e.g. dominance rank of the singer).
... Another unexplored possibility in vermilion flycatchers is that an increased song rate and song duration is a signal directed toward neighboring females. Increasing song rate or song length may be done to stimulate females for reproduction (Wasserman and Cigliano 1991), to protect paternity from neighboring males or to attract extra-pair females to increase breeding success (Dalziell and Cockburn 2008;Houtman 1992;Mennill et al. 2006;Ríos-Chelén et al. 2005;Ríos-Chelén et al. 2008; but see Garamszegi and Møller 2004). ...
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Most studies on the effects of urbanization on animal communication have focused on the influence of acoustic pollution on vocal production. Comparatively few studies have addressed the potential impact of light pollution on animal acoustic signals, with no studies having looked at the structure of vocalizations. We know, however, that light is related to melatonin production, influencing activity patterns of organisms, which opens the possibility that artificial light at night may affect also the structure of animal vocalizations. Here we studied whether there are associations between urban noise and nocturnal light with the structure of songs produced by vermilion flycatchers. We also considered the effects of moonlight by recording a subsample of males during full moon, new moon, and full moon again. Contrary to previous findings, males did not sing longer songs with noise; they produced longer songs and at a higher rate in brighter territories. Males also increased song rate and sang songs with more elements during full moon nights when compared to new moon nights (vocal flexibility). This study highlights the importance of considering several pollutants along with moon phase to better understand how they influence animal signals, links light at night with birdsong structure, and provides additional evidence of a circa-lunar rhythm of song output. We discuss our results in the context of proximate and ultimate causes and provide a possible explanation of the seemingly contradictory result with previous research.
... In some cases, measuring a broad acoustic unit is designated by the research question. For example, for research questions about total duration or frequency modulation over an entire multisyllabic bird song, the entire song is the appropriate acoustic unit to measure (Podos, 1997;Dalziell & Cockburn, 2008). In other instances, researchers may want to measure multiple hierarchical levels of acoustic structure. ...
Article
Animals produce a wide array of sounds with highly variable acoustic structures. It is possible to understand the causes and consequences of this variation across taxa with phylogenetic comparative analyses. Acoustic and evolutionary analyses are rapidly increasing in sophistication such that choosing appropriate acoustic and evolutionary approaches is increasingly difficult. However, the correct choice of analysis can have profound effects on output and evolutionary inferences. Here, we identify and address some of the challenges for this growing field by providing a roadmap for quantifying and comparing sound in a phylogenetic context for researchers with a broad range of scientific backgrounds. Sound, as a continuous, multidimensional trait can be particularly challenging to measure because it can be hard to identify variables that can be compared across taxa and it is also no small feat to process and analyse the resulting high-dimensional acoustic data using approaches that are appropriate for subsequent evolutionary analysis. Additionally, terminological inconsistencies and the role of learning in the development of acoustic traits need to be considered. Phylogenetic comparative analyses also have their own sets of caveats to consider. We provide a set of recommendations for delimiting acoustic signals into discrete, comparable acoustic units. We also present a three-stage workflow for extracting relevant acoustic data, including options for multivariate analyses and dimensionality reduction that is compatible with phylogenetic comparative analysis. We then summarize available phylogenetic comparative approaches and how they have been used in comparative bioacoustics, and address the limitations of comparative analyses with behavioural data. Lastly, we recommend how to apply these methods to acoustic data across a range of study systems. In this way, we provide an integrated framework to aid in quantitative analysis of cross-taxa variation in animal sounds for comparative phylogenetic analysis. In addition, we advocate the standardization of acoustic terminology across disciplines and taxa, adoption of automated methods for acoustic feature extraction, and establishment of strong data archival practices for acoustic recordings and data analyses. Combining such practices with our proposed workflow will greatly advance the reproducibility, biological interpretation, and longevity of comparative bioacoustic studies.
... Staicer (1996) concluded that the best-supported functions of dawn chorus participation were to (1) stimulate male hormone production in preparation for social interactions, and (2) mediate social relationships among males. More recently, evidence from a variety of species has accumulated in support of the second hypothesis (Burt and Vehrencamp 2005, Sexton et al. 2007, Dalziell and Cockburn 2008, Foote et al. 2010, Xia et al. 2014. Our results are also consistent with this function of exaggerated dawn singing. ...
Article
en Among songbirds with large song‐type repertoires, there may be functional variation in how individuals organize and display song‐type diversity over time. Past studies focusing on conventional measures of song production have been extremely productive. However, network analysis offers a novel set of tools to quantify additional, previously unstudied elements of song organization and display. We studied protracted bouts of singing by 10 male House Wrens (Troglodytes aedon) to (1) test functional hypotheses of variation in song diversity in this species, and (2) evaluate the utility of network metrics in such research. Our analysis included a variety of conventional measures of song production and several standard metrics from network theory to quantify how variably the many song types in a male’s repertoire could be connected to one another and the limitations or diversity of their song sequences. Analysis of conventional variables showed that males produced more and longer songs, at shorter intervals, containing more syllables and more different syllable types, and also more different song types, prior to than after pairing and early in the morning regardless of breeding stage. These results are consistent with the hypothesis that song diversity functions in mate attraction and possibly in territory signaling. In contrast, analyses of network metrics revealed variety in song sequencing by males, but comparatively few and weak effects associated with either breeding stage or time of day. Overall, most song types connected to only a few others and a relatively small proportion of all possible song‐type transitions actually occurred. Hence, much of the variety in song sequencing that was possible with the large song repertoires of males was not realized. The latter outcomes, brought to light via network analyses, highlight an important paradox for future research on this and related species with large song repertoires. RESUMEN es Análisis de redes y convencionales de la organización y complejidad del canto en Troglodytes aedon parkmanii En aves cantoras con un alto número de repertorios, puede existir variación funcional en como los individuos organizan el canto y presentan diversidad en los tipos de canto a través del tiempo. En el pasado los estudios enfocados en medidas convencionales de la producción del canto han sido extremadamente productivos. Sin embargo, el análisis de redes provee una serie de herramientas novedosas para cuantificar elementos de la organización y presentación de los cantos adicionales que no se han estudiado en el pasado. Estudiamos cantos prolongados de 10 individuos machos de Torglodytes aedon con el fin de (1) comprobar hipótesis funcionales de la variación en la diversidad del canto en esta especie y (2) evaluar la utilidad de métricas de teoría de redes en este tipo de investigaciones. Nuestro análisis incluyo una diversidad de métricas convencionales de la producción del canto y varias métricas estándar de teoría de redes para cuantificar, que tan variable muchos tipos de cantos en los repertorios de los machos pueden ser conectados entre ellos y las limitaciones o la diversidad de las secuencias de sus cantos. El análisis de variables convencionales mostró que los machos producen más cantos y más largos, en intervalos de tiempo mas cortos, que contienen una mayor cantidad de sílabas y tipos de sílabas más diferentes y también tipos de canto más diferentes antes del apareamiento y temprano en la mañana independientemente del estado reproductivo. Estos resultados son consistentes con la hipótesis que la diversidad en el canto es utilizado en la atracción de pareja y posiblemente enviando señales de territorialidad. En contraste, los análisis utilizando métricas de teoría de redes revelaron variación en la secuencia de los cantos por parte de los machos, pero comparativamente pocos efectos y débiles asociados con la etapa reproductiva o la hora del día. En general, la mayoría de los tipos de cantos estuvieron conectados a pocos cantos y ocurrió una proporción relativamente pequeña de transiciones entre todos los tipos de cantos posibles. Por lo tanto, mucha de la variabilidad en la secuencia de los cantos posible, dado el amplio repertorio de los machos, no fue realizada. Estos resultados, obtenidos a través del análisis de redes, resaltan la paradoja importante para investigaciones futuras en esta y otras especies emparentadas con repertorios extensos.
... Each individual has a repertoire of different song types within this broad category. A "Type II" song ( Figure 1), comprising a long trill followed by the typical reel, is commonly produced by males in response to a loud sound (Langmore and Mulder 1992) and during the dawn chorus (Dalziell and Cockburn 2008). There have been no prior studies of how these song types are used in song overlap. ...
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Avian duets are formed when 2 birds coordinate their songs. Most research on the evolution and function of duetting has focused on species with highly coordinated duets, and less is known about the context and function of overlapping songs that are more loosely coordinated, in part due to the challenge of determining whether such vocalizations coincide by chance or through coordination between the partners. Here, we use field recordings and playback experiments to test whether breeding pairs of superb fairy-wrens, Malurus cyaneus, coordinate their territorial songs to form duets. We test 3 key characteristics of duetting; whether partners’ songs 1) overlap more than expected by chance; 2) have a stereotyped structure that occurs repeatedly and predictably in time, and 3) show evidence of a constant time lag between the contributions of the 2 participants, indicating that individuals are coordinating their songs. This is the first study to quantify the temporal precision of song between partners to investigate coordination in the Malurus genus, an important model taxon for song, sexual selection, and speciation. We found variation in the extent to which partners’ songs overlapped, with some individuals overlapping their partners’ songs more than expected by chance, no difference in structure of solo and overlapping songs, and no evidence of a consistent response interval. Thus song overlap in superb fairy-wrens meets only some criteria for duetting. We suggest that overlapping songs in this species may be due to individuals responding independently of the same stimulus and/or “call and answer” between pair members.
... Other cross-sectional and short-term longitudinal studies suggest that some changes may occur in birdsong throughout adulthood as well. For example, studies in European starlings (Sturnus vulgaris, Mountjoy and Lemon 1995), great reed warblers (Acrocephalus arundinaceus, Forstmeier et al. 2006), red-winged blackbirds (Agelaius phoeniceus, Yasukawa et al. 1980), barn swallows (Hirundo rusticai, Galeotti et al. 2001), superb fairy wrens (Malurus cyaneus, Dalziell and Cockburn 2008), and banded wrens (Thryophilus pleurostrictus, de Kort et al. 2009) suggest that changes in repertoire size, repertoire composition, or song length may continue to occur in 3-year-old males or beyond. In the absence of more complete life course data, however, it is impossible to know whether song characteristics vary continuously with age or whether behavioral senescence eventually reverses the direction of age-related change. ...
Article
Signalers may benefit in some contexts from advertising their ages, for example in courting potential mates. Receivers in turn may benefit from assessing a signaler's age, even in cases where their doing so is against the signaler's interests. Indicators of age contained in signals thus may have important fitness consequences for both signalers and receivers. In birds, males of many species have been shown to display delayed maturation of their songs, resulting in older males singing songs that are higher in quality in one or more characteristics. Conversely, it seems possible that songs might eventually deteriorate with age as an aspect behavioral senes-cence. Studies of birdsong long enough to test both possibilities are quite uncommon, with nearly all studies aspect of age-dependent changes in birdsong spanning 3 or fewer years of males' lives. Here, we present the longest longitudinal analysis of male birdsong to date, in which we analyze songs recorded for 4-11 years of the lives of captive male swamp sparrows. We find that males displayed delayed maturation of three song characteristics: song rate, song length, and consistency between songs. Delayed maturation was followed by behavioral senescence of three characteristics: song rate, stereotypy within songs, and consistency between songs. Because song quality declined in males beyond 2 years of age, this evidence is inconsistent with a signaling system in which females both prefer increasingly older males and are able to accurately determine male age through song assessment. Rather, our evidence suggests that swamp sparrows should be able to use song to distinguish intermediate-aged males from 1-year-old and very old males.
... Forays in other species have been identified by visually watching focal individuals leave their territories (Kleven et al. 2006;Dalziell and Cockburn 2008;Barron et al. 2015). However, we took a different approach and determined which utilization distribution (UD) best matched the territories of males. ...
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In many territorial species, occasional movements beyond territory boundaries (extraterritorial forays) have been documented in many species. While many explanations for the occurrence of extraterritorial forays have been proposed, a logical and proposed function of extraterritorial forays is to engage in extra-pair copulations with extra-pair mates outside of their territories. We used an automated radio-telemetry system (ARTS) to examine the patterns and correlates of foray behavior of male and female field sparrows (Spizella pusilla) and investigated if forays were associated with extra-pair paternity (EPP) and cuckoldry. We found that male and female field sparrows regularly engaged in extraterritorial forays. In males, age and time of foraying (day vs. night) were important factors explaining foray rates (foray/h); older (ASY) males forayed more than younger (SY) males and, while we detected many nocturnal forays, most forays occurred during the day. For females, fertility stage and age appeared to be important in explaining foray rates; older females forayed more during pre-fertile period than fertile and post-fertile periods. Unlike foray rates, the duration of forays (min) was not explained by any of the variables examined. Surprisingly, despite the large number of forays documented (>3500), greater foray rates or duration of forays were not associated with higher probability of EPY for males or females or with cuckoldry in males. Forays may play a role in prospecting and acquiring information about their social and ecological environment, which ultimately may help them to achieve greater reproductive success, but not necessarily in the form of EPP. Significance statement Despite many territorial species are known to conduct extraterritorial forays (movements beyond their territory), very little is known about this behavior. We used an automated radio-telemetry system (ARTS) to examine the patterns, correlates, and paternity consequences of extraterritorial foray behavior in male and female field sparrows (Spizella pusilla). We documented more than 3500 forays and found that both male and female field sparrows regularly engaged in extraterritorial forays; however, different factors explain their foray rates (age, time of foraying (day vs. night), and fertility stage) but not the duration of forays. Surprisingly, greater foray rates or duration of forays were not associated with higher probability of EPY in males or females or with cuckoldry in males. Rather than exclusively acquiring extra-pair matings, forays likely serve multiple purposes, such as prospecting and acquiring information about their social and ecological environment, which ultimately may help individuals achieve greater reproductive success.
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As in many species of cooperative breeders, western bluebirds, Sialia mexicana, have adult male offspring that help at nests of close relatives. They are unusual in maintaining helping at a low level; only 11% of sons help and, when they do, they feed at nests of one or both parents, nestmate brothers, or rarely, grandfathers. On average, only 7% of pairs have helpers, although the range is 3-16% depending upon the year (Dickinson et al. 1996). Helping is facultative, with males able to switch from helping to breeding and back again within a season (Dickinson and Akre 1998). While their most common behavior is to breed in pairs, three characteristics render western bluebirds useful for understanding the evolution and maintenance of helping behavior as a facultative trait. First, the mode of helping is unusually fluid: in addition to the typical “stay-at-home” helpers, which delay dispersal, remain on their natal territory, and then help as yearlings, western bluebirds have “redirected helpers,” which help mid-season after their mate is killed or their nest fails (Figure 2.1). This makes the territorial system of western bluebirds more similar to that of colonial white-fronted bee-eaters (Merops bullockoides) in Kenya (Emlen and Wrege 1989) or Galápagos mockingbirds (Mimus parvulus; Curry and Grant 1990) than to the acorn woodpeckers (Melanerpes formicivorus) with which they often share cavity trees and space (Chapter 13). Western bluebirds also have a third type of helper, “simultaneous breeder-helpers,” which breed adjacent to their parents and feed at both their parents’ nest and their own nest within a single day. This cross-territorial helping was our first hint that western bluebirds favor kin even while living on different territories. A strength of the study system is that we have been able to follow birds as they adopt these different options to gain important insights into each option’s relative fitness benefits. Second, although western bluebirds are marginal cooperative breeders in spring, they exhibit high levels of kin-based sociality in winter, living in stable family groups on their territories (Kraaijeveld and Dickinson 2001). This has afforded us the opportunity to examine the drivers and fitness consequences of delayed and localized dispersal, which we hypothesize provide the permissive conditions for kin-based helping.
Article
Here we describe the vocal repertoire of a population of Splendid Fairy-wrens (Malurus splendens melanotus) in South Australia. During 2005 and 2006 we identified 14 different vocalisations. The primary vocalisation, Type I song, was given by both males and females throughout the breeding season and appeared to function in territorial defence. Type I song was structurally similar between the sexes, although males sang a more complex version of the song with greater note-versatility (number of note types divided by total number of notes). The rate of female singing did not differ between breeding stages, but the rate of male singing was higher in the early breeding stages than in the later breeding stages. The second major vocalisation, Type II call, was given almost exclusively by males. Type II calls were generally given in response to avian predators, but males also appended Type II calls to the primary song. Additionally, Type II calls featured prominently in the dawn chorus, and the structure of these calls varied significantly between males. We discuss hypotheses for the function of Type I songs and Type II calls and describe the structure of 12 other vocalisations, using contextual information to infer their function.
Article
Birds sing mostly to attract partners or to defend territories or resources. In relation to the first function, song can vary with age if older experienced males signal their quality through their vocal output. Regarding the second function, song can also vary with age if singing behavior helps mediate social interactions through repertoire sharing with neighbors. Here, we investigate whether song parameters change with age, and in which direction, in saffron finches Sicalis flaveola pelzelni, obligate secondary cavity nesters which produce elaborate melodious songs and show delayed plumage maturation. Cross‐sectional comparisons revealed that second year (SY) males sing shorter syllables, and shorter and less versatile songs than older after second year males (ASY), as expected if the latter are more experienced singers. Longitudinal comparisons, which better depict age‐related changes, showed that as birds age one year, song length and repertoire size do not change significantly, syllable duration shortens and, as expected for experienced singers, song versatility increases. Correlations between repertoire distance and nesting distance suggest that both SY and ASY males might be adjusting their repertoires to those of ASY neighbors; the former pattern conforms to the expectations if young birds try to emulate the songs of more experienced birds, while the latter is expected if song sharing helps de‐escalating antagonistic social interactions amongst males. This research, which provides the first description of song parameters in young second year saffron finches, expands our knowledge of song variation across age classes in songbirds. This article is protected by copyright. All rights reserved.
Article
en Previous studies have revealed diel patterns in the songs of Chipping Sparrows (Spizella passerina), with songs shorter in duration before dawn than after. However, the extent to which this phenomenon generalizes to the full geographic range of these sparrows is unclear, as is the question of whether citizen-science data can be used to detect diel patterns in song. We analyzed all available songs of Chipping Sparrows from the Macaulay Library and xeno-canto databases and compared the distributions of song features of recordings made at different times of day. We show that, across their entire geographic range in North and Central America, Chipping Sparrows sing shorter songs before sunrise (dawn song) than after sunrise (day song). Furthermore, we show that Chipping Sparrows shorten their songs by singing fewer syllables, not by singing faster: the number of syllables per song accounts for the observed difference in duration, not the syllable nor the intersyllable duration. Our results demonstrate that recordings from public repositories can be used to determine whether daily song patterns exist in species even in the absence of prior fieldwork, and we further propose that citizen-science recordings can be used to inform cross-species hypotheses and facilitate future studies to determine whether diel patterns in song are associated with differences in social behavior. RESUMEN es Detectando patrones diarios en los cantos del chimbito común (Spizella passerina) usando datos de ciencia ciudadana. Estudios previos han revelado patrones diarios en los cantos del chimbito común (Spizella passerina), con cantos de menor duración antes del amanecer que después. Sin embargo, la medida en que este fenómeno se generaliza al rango geográfico completo de estos gorriones no está claro, al igual que la cuestión de si los datos de la ciencia ciudadana se pueden usar para detectar patrones diarios en los cantos. Analizamos todas los cantos disponibles de Spizella passerina en la Biblioteca Macaulay y las bases de datos de xeno-canto y comparamos las distribuciones de las características de los cantos grabados en diferentes momentos del día. Mostramos que, en todo su rango geográfico en América del Norte y Central, Spizella passerina producen cantos más cortos antes del amanecer (el canto del amanecer) que después del amanecer (el canto del día). Además, mostramos que Spizella passerina acortan sus cantos por producir menos sílabas, no por cantar más rápido. El número de sílabas por canto explica la diferencia observada en la duración, no la duración sílaba o intersílaba. Nuestros resultados demuestran que las grabaciones en los repositorios públicos se puede utilizar para determinar si existen patrones diarios de cantos en las especies, incluso en ausencia de trabajos de campo, y proponemos además que las grabaciones de ciencia ciudadana se pueden utilizar para informar hipótesis entre especies y facilitar futuros estudios para determinar si los patrones diarios en los cantos están asociados con diferencias en el comportamiento social.
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Choice of mating partners may affect fitness. Both phenotypic and genetic traits have been shown to play roles in the mating processes of animals. We investigated the roles of phenotypic and genetic characteristics in the patterns of social mating in the Silver-throated Tit (Aegithalos glaucogularis), a sexually monochromatic species that exhibits sexual size dimorphism, rarely sings, does not occupy territories, and has a relative low level of extrapair paternity. To explore the role of phenotype traits, we tested for assortative mating based on the sizes of seven morphological traits. To explore the role of genetic traits, we tested for assortative mating with respect to genetic heterozygosity (the heterozygous mate hypothesis) and whether birds mated with genetically dissimilar individuals (the compatible mate hypothesis). We found significant correlations between paired individuals for bill length and body length, indicating possible assortative mating based on these two traits. In contrast, genetic heterozygosity was not correlated between paired individuals, and the mean relatedness of the mates was not significantly different from that of randomly mated individuals, which do not support the idea that Silver-throated Tits assortatively mate with heterozygous individuals or choose genetically dissimilar mates. Also, individual heterozygosity was not reflected in the measured morphological traits, as no correlation was detected. Neither the individual heterozygosity nor the relatedness between mates was correlated with reproductive performance measures, including clutch size, brood size, and number of fledglings. However, we found that clutch size increased with female body length, which could explain the benefit to males of mating with larger females. Taken together, while our current data failed to provide evidence for an effect of genetic characteristics on the social mating pattern of Silver-throated Tits, the results suggest that phenotypic traits are likely associated with their mating pattern.
Article
Cooperative breeding among birds was first discovered in the genus Malurus (Maluridae), the fairy-wrens. Cooperative care arises because male, and sometimes female, offspring remain in their natal territory and help the adults rear offspring. Early uses of data from Superb Fairy-wrens (Malurus cyaneus) to illustrate how kin altruism can explain helping behaviour were based on flawed assumptions. Most importantly, high rates of extra-group mating mean that the helpers often assist adults to which they are unrelated. However, measuring the costs and benefits of altruism has also proved difficult. Helping behaviour and its outcomes among species of Malurus are surprisingly diverse, despite similar founding conditions for cooperative breeding. First, species differ in whether help provides fitness benefits, in the recipients of those benefits, and whether benefits are immediate or deferred. Second, species vary greatly in whether females are philopatric and the extent to which female auxiliaries (supernumeraries), when present, provide care. Finally, male auxiliaries are much less sensitive to the needs of the brood than females. In this review we show that these three aspects of helping behaviour lack compelling explanations. We develop hypotheses to explain each phenomenon. Distinguishing among these hypotheses will greatly enhance our understanding of the remarkable social system of Malurus, and inform the study of cooperative breeding and sexual conflict in general.
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Introduction African mole-rats (Family: Bathyergidae) have become well established as a model taxon with which to investigate the evolutionary origins and maintenance of cooperative breeding. They occupy an unusual position among vertebrates in having members whose breeding systems range from solitary to eusocial, defined by Michener (1969) and later generalized by Wilson (1971) as having overlapping generations, cooperative brood care, and reproductive division of labor. Following the first report of “eusociality” in naked mole-rats, Heterocephalus glaber, more than 30 years ago (Jarvis 1981), similar eusocial behavior was observed in Damaraland mole-rats, Fukomys damarensis, paving the way for phylogenetically controlled comparative studies (Bennett and Jarvis 1988; Jarvis and Bennett 1993). The use of genetic techniques to reconstruct molecular phylogenies and reassess evolutionary relationships and biodiversity within the family has indicated that the Bathyergidae are an extensive adaptive radiation of subterranean rodents. Current estimates suggest that there are more than 30 species comprising six genera that range from strictly solitary to eusocial species, including the eusocial genus, Heterocephalus (with the monotypic naked mole-rat), solitary dwelling Heliophobius, Bathyergus, and Georychus, social Cryptomys, and social/eusocial Fukomys (Figure 19.1). Of particular significance to comparative studies is the fact that there have been convergent gains and losses of sociality within the family, which makes the Bathyergidae an excellent group with which to investigate the evolution of sociality and cooperative behavior. Given the phylogenetic reconstruction in Figure 19.1a, it is apparent that irrespective of the status of the common ancestor of the family at Node A of the phylogeny, there have been phylogenetically independent gains and/or losses of social/solitary behavior and cooperative breeding at some or all of Nodes B, C, and D. In particular, naked and Damaraland mole-rats are highly divergent within the family, and it is likely that further social elaboration has occurred along their respective lineages, although on different timescales. Heterocephalus is the basal lineage within the family and constitutes an ancient divergence, with the molecular phylogeny forming relatively deep branches among populations across its range. Molecular clock estimates of divergence times suggest that Heterocephalus separated from the common ancestor of the Bathyergidae more than 30 million years ago (MYA), and fossils resembling naked mole-rats have been dated to approximately 18 MYA or earlier (Bishop 1962).
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Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fish, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Introduction Avian cooperative breeders occupy climatically and ecologically diverse habitats. Such diversity will inevitably result in contrasting challenges, and might partly explain their variable social systems. If so, our current appreciation of the key selective forces shaping the form and function of avian cooperative breeding systems is likely to be biased because study sites are distributed nonrandomly across the globe (Introduction, Figure 1). To derive a more complete understanding, it is imperative that studies encompass the full range of climatic and ecological settings (Cockburn 2003; Cockburn and Russell 2011). My primary motivation for establishing a long- term study of the 50 g sexually-monomorphic chestnut-crowned babbler (Pomatostomus ruficeps) of outback Australia was twofold. First, it offered an investigation of a cooperative breeding system in a novel arid zone environment. Second, nothing was known about the social or cooperative system of this species, other than a published remark by an enlightened dog-walker who declared from observing three birds simultaneously bringing food to a nest that, like other Australian babblers, it must be a cooperative breeder (Smith 1992). There are obvious drawbacks to establishing a long-term study on a species that has never been studied before, especially as it turns out, one with such a complicated social system. Nonetheless, I was excited by the prospect, and even a baffled smile from Andrew Cockburn could not deter me. Phylogeny The chestnut-crowned babbler is not a true babbler, but one of five extant members of the ancient Australo-Papuan babblers (Pomatostomidae). Recent phylogenetic evidence (Jetz et al. 2012) suggests that this babbler clade branched from the main avian tree ~ 51 million years ago (Ma) along with the family-living but noncooperative Orthonychidae (Australo-Papuan logrunners). Babblers and logrunners diverged 3 million years later, and chestnut-crowned babblers emerged ~ 11 Ma. All five extant Pomatostomid babbler species show cooperative breeding, suggesting this breeding system to be ancestral in the clade. The antiquity of Pomatostomid babblers renders any consideration of the original pressures selecting for cooperative breeding beyond the scope of this chapter, especially since it probably emerged when Australia was covered in forest.
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Cambridge Core - Animal Behaviour - Cooperative Breeding in Vertebrates - edited by Walter D. Koenig
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Introduction Although until late 1990s Carrion crows Corvus (corone) corone were thought to breed in socially monogamous pairs (Cramp and Perrins 1994) with examples of cooperative breeding being rare, we discovered a truly cooperatively breeding population of carrion crows in northern Spain in 1995. In this population, approximately 75% of territories are held year-round by groups of up to nine individuals that share in chick provisioning as well as other parental duties (Baglione et al. 2002b). Discovery of such striking geographical variation of the social organization was the starting point of our long-term research project. As our study progressed, we uncovered the complexity of the crow society, which proved to be suitable for testing the adaptive value of helping at the nest and the role of kin selection in the evolution and maintenance of cooperative breeding. Crows are challenging birds for ornithologists: a long history of human persecution has made them wary and intolerant of humans such that catching and banding them requires many hours in the field. Behavioral observations must be done almost exclusively by automatic video recording. Uncovering their fascinating social life has, however, repaid all the effort that our team has put into this research. Today carrion crows provide a model system for investigating the ecological correlates of cooperative breeding, including insights gathered from comparing populations instead of species, which overcomes the confounding effects of phylogeny and differences in life history, and had allowed for novel field experiments that shed light on the role of the environment in family formation and cooperation. Phylogeny, phylogeography, and natural history There is considerable debate regarding the taxonomy of the carrion crow, Corvus (corone) corone, and the hooded crow, Corvus (corone) cornix, which differ in coloration but exhibit near absence of genetic differentiation (Haas et al. 2009; Poelstra et al. 2013, 2014). In this chapter we regard carrion/hooded crows as “phenotypes” because hybridization occurs and produces viable descendants. Although our study focuses mostly on carrion crows, we will also use data on hooded crow populations for some comparisons. Regardless of the phenotype, early studies of several European populations always reported the crows as breeding in socially monogamous pairs whose offspring leave home as soon as they are independent at approximately two months of age (Cramp and Perrins 1994).
Chapter
Introduction Cooperatively breeding birds are species where “more than two individuals rear the chicks at one nest” (Emlen and Vehrencamp 1985), and were first described over a century ago by Australian naturalists (Ashby 1912; Boland and Cockburn 2002). Studies show that the social structure and mating patterns of such species vary widely, and may depend on numerous factors, such as phylogeny, number of individuals of each sex, levels of relatedness among individuals, habitat and climatic characteristics, among other possibilities. A relatively rare form of cooperative breeding is plural breeding with communal nesting (or joint-nesting), characterized by the occurrence of two or more breeding individuals of the same sex that care for the young. In such species, sharing of reproductive opportunities among individuals may occur among both males and females, and the degree of sharing generates reproductive skew that may vary from 0 (egalitarianism) to 1 (monopolization of reproduction by one individual) (Magrath et al. 2004). Here I describe the biology of the guira cuckoo (Guira guira), a species that combines some of the customary cooperative breeding traits with the added complexities of plural breeding in communal nests. The questions I have subjected to in-depth investigation over the course of this study include: (1) what are the possible selective pressures favoring the evolution of communal nesting? (2) can kin selection explain cooperation? (3) what are the costs and benefits of group living? (4) how does the group resolve conflicts? (5) is breeding relatively egalitarian or do some group members monopolize reproduction? and (6) can transactional models of reproductive cooperation and conflict improve our understanding of this system? The guira cuckoo Guira cuckoos (see cover photo) belong to the subfamily Crotophaginae, one of six subfamilies in the family Cuculidae. This clade is characterized by social nesting habits instead of the parasitic behaviors for which many of the other cuckoos are known. The Crotophaginae include four species that share the unique form of cooperative breeding described above: plural breeding with a joint-nesting system (Davis 1940, 1941, 1942). In these species, social groups consist of several females that lay their eggs in a single nest, resulting in a shared clutch of offspring. Worldwide, only a handful of species exhibit such characteristics, which inevitably raises questions about the convergence of taxonomic, evolutionary, and ecological factors that promote this breeding system.
Article
Geographic variation in song is widespread among birds, particularly in species that learn vocalizations. The relationship between geographic distance and song variation is likely related to the degree of isolation between populations. To assess this effect of geographic isolation on song divergence, we examined patterns of geographic song variation in four species of Australian fairy-wrens (Malurus), two with suspected histories of geographic isolation and two without. Song variation in all four species was consistent with patterns of isolation by distance, and allopatric subspecies in two species were more divergent in song than predicted by distance alone. Each species' pattern was unique, and some interspecific variation could not be explained by geographic distance. These results indicate that patterns of geographic variation can be influenced by more than geographic distance and historical isolation alone. We suggest that morphological constraints, environmental influences, and sexual selection may all contribute to the variation observed for each species.
Chapter
The evolution of cooperation has been a focus of interest for evolutionary biologists for over a hundred years (Darwin 1859; Kropotkin 1908; Williams 1966). While all forms of cooperation challenge the centrality of competition in the process of evolution, cooperative and eusocial breeding systems, where offspring produced by a small number of breeding individuals are reared by nonbreeding helpers or workers, raise some of the most fundamental questions about the level at which selection operates the measurement of....
Chapter
IntroductionLong-term study of Florida scrub-jays (Aphelocoma coerulescens) at Archbold Biological Station began in 1969 when Glen E. Woolfenden noticed extra jays at a nest, and color-banded birds in seven territories. Aware of growing interest in helpers-at-the-nest and the evolution of cooperation, Glen correctly guessed that he had found an informative species for examining the population biology of a group-living bird. By 1972, when John Fitzpatrick first joined him as a college intern, Woolfenden’s study tract had expanded to 18 territories and we witnessed our first example of “territorial budding” (Woolfenden and Fitzpatrick 1978). In 1991, Reed Bowman joined the team and expanded the study to include two nearby populations, one in suburban and the other in fragmented habitat; by 2003 we were studying Florida scrub-jays in over 150 territories. Here, we focus on data from the ongoing study in the original “demography tract” at Archbold (currently 75 to 85 territories), drawing also on insights gained from the other populations. The Florida scrub-jay presents an exceptional model for studying a comparatively simple cooperative breeding system. The species lives in naturally low-stature scrub on two-dimensional terrain, facilitating detailed observation and monitoring of both behavior and nesting. Every jay born into our population is color-banded and genetically sampled on a standardized post-hatch day (day 11), and immigrants are captured and banded readily. The Florida scrub-jay easily habituates to humans, and even learns to approach us if occasionally rewarded with peanut bits. Consequently, we have been able to census the study population exhaustively every month since April 1971, yielding an extraordinarily detailed record of survivorship, reproduction, and dispersal. Territories are vigorously defended year-round along narrow and clear-cut boundaries, permitting us to map precisely the tightly packed spatial configuration of the population each year. Because the Florida scrub-jay is nonmigratory, highly philopatric, and socially and genetically monogamous, we have accumulated a 14-generation pedigree of known-age, known-parentage individuals whose lifespans and breeding outputs we measured precisely. Moreover, the Florida scrub-jay is a singular-nesting species in which pre-breeding offspring typically remain in the natal territory for a minimum of one year, living as a cooperative family group with their parents or stepparents. These features make the Florida scrub-jay “blessedly simple” as a model species exhibiting an early stage along what we presume to be an evolutionary track toward more complex cooperative-breeding social systems (Fitzpatrick and Woolfenden 1986).
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Many songbirds are discontinuous singers with a relatively small repertoire of song types. They repeat each song type a variable number of times in a song bout with pauses between each strophe, before they switch to another song type. It was first described in great tits Parus major that song output declines over time when a male sings a particular song type. This phenomenon is referred to as drift and it is mainly caused by an increase in the pauses between strophes. Drift can be explained either by neuro-muscular exhaustion or by a decline in motivation to sing. We studied the occurrence of drift during a period of high song output (the dawn chorus) in the blue tit P. caeruleus. Drift occurred in 31% of 104 recorded song bouts. Most males significantly increased their song output again after switching to another song type. Some evidence suggests that drift in great and blue tits might be used by females as a cue reflecting male or territory quality. The anti-exhaustion hypothesis predicts that males that have a larger repertoire size should show less drift, because they can switch more frequently to other song types and thus avoid neuro-muscular exhaustion. Our data on 20 blue tit males provide at best weak evidence for this hypothesis. However, the prediction can also be tested at the interspecific level, although data on more species are needed. Great tits have the smallest repertoires and the highest levels of drift, while coal tits P. ater have the largest repertoires and drift is very rare.
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We studied the behavior of the Dusky Bush-Tanager (Chlorospingus semifuscus; Thraupinae) in southwestern Colombia, where it seems to exhibit singing assemblages resembling leks. A lek mating system would be paradoxical in a genus noted for its active participation in mixed-species flocks, largely insectivorous diet, and stable pair bond. We used the bird's behavior and the relations between fruit availability, its diet, and its participation in mixed flocks to try to explain the social system. We found males singing in dense linear assemblages, regularly spaced along ridgetops, during early morning and late afternoon hours during much of the year, with a peak from May through August. Singing males occupied small circular territories, which usually were reoccupied the next year by the same males. The critical resource is likely the males themselves, although fruit availability may permit them to remain on territories for long periods; nesting areas are apparently far from the ridgetops. Participation in flocks occured year-round but was somewhat reduced during the singing season and in the singing hours. The evidence of pair bonds in this species, in which males participate at least in nest-site selection and feeding of young, excludes the possibility of a lek mating system in the strict sense. Nevertheless, the system of singing linear assemblies appears to have been superimposed upon the typical social system of the genus. This social system is unique in the entire nine-primaried oscine assemblage.
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In cooperatively breeding superb fairy-wrens (Malurus cyaneus), all males contribute to the feeding and defence of young. Despite the expectation that such paternal care should be directed only to relatives, DNA fingerprinting revealed that most offspring (76%, 138 out of 181) were sired by extra-group males that contributed no care, and that almost all broods (95%, 38 out of 40) contained young sired by extra-group fathers. This is the highest known incidence of cuckoldry. This remarkable mating system is produced by female control of fertilization and consistent preference for certain extra-group male genotypes. This choice leads to the production of sons that also gain extra-group fertilizations. One constraint on the extra-pair mate choice of females is the level of parental assistance received from males. Males living in pairs contribute relatively more parental care and are more likely to gain paternity in one of their broods (85%, 11 out of 13) than dominant males in multi-male cooperative groups (30%, 8 out of 27). In groups helpers compensate for the lower parental assistance of dominant males, so the total feeding rate is similar between pairs and groups. This suggests that females allow males in pairs more paternity to ensure their assistance with parental care. Helpers provide an alternative source of paternal investment, and allow females to express unrestricted mate choice. Mating options for females in other species with female control of fertilization may also reflect a trade-off between acquiring the genes of high-quality males for their offspring and parental care of those offspring.
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Many male temperate zone passerines show a marked peak of singing activity before sunrise. The two main functions of this so-called dawn chorus are mate attraction and territory defence. We examined how seasonal patterns of different dawn song characteristics were related to mating status and to the breeding cycle of females in the common nightingale, Luscinia megarhynchos. We investigated two measures of song output: song rate and percentage performance time. We also calculated the proportion of ‘whistle songs’, a song category that is thought to be important in female choice.We predicted that if the main function of dawn singing in nightingales is to attract a social mate, then mated males should change their dawn singing behaviour after pair formation. In contrast, if dawn singing is mainly used in territory defence, we expected no difference in song traits between mated and unmated males throughout the season. We found that song rate and the proportion of whistle songs were low at the beginning of the season and did not predict future mating status. After arrival of females, all measures of dawn song performance remained largely constant throughout the breeding season, and we did not find significant differences in the seasonal variation between mated and unmated males. These findings are consistent with the hypothesis that song at dawn is important to defend a territory throughout the breeding season.
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Territory defence can be seen as a dynamic long-term process that involves some learning. For example, a resident may adjust its territory proclamation behaviour depending on its prior experience with territorial intruders. We investigated whether short territorial challenges could have long-lasting effects on the singing behaviour of male birds. We used song playbacks to simulate intrusions into autumn territories of male winter wrens, Troglodytes troglodytes, shortly after dawn and compared male singing behaviour immediately before and 1 day after the simulated intrusion. As in many other bird species, unchallenged male wrens tended to sing more songs before than after sunrise. One day after a simulated intrusion, however, this pattern was much more pronounced. Males significantly increased their song output before sunrise, but maintained or even reduced song output after sunrise. This result suggests that dawn singing before sunrise is particularly important for territory defence. On the day after the intrusion, the start of dawn singing varied less between males, although the average starting time remained the same. Our findings suggest that a territorial challenge can influence singing behaviour almost 24 h after the intrusion. The amount and timing of birdsong, as a preventive territorial proclamation, can thus be adjusted to past territorial challenges.
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Previous explanations for the dawn chorus in birds include favourable acoustic conditions1, low foraging profitability reducing the net cost of singing2–4, high risk of territorial intrusion3 and unpredictability in overnight energy requirements leading to spare reserves at dawn4. All these hypotheses assume that males sing either to attract mates or to defend a territory and/or that singing and foraging compete for time5. In the case of the dawn chorus in the great tit Parus major none of these assumptions apply. A peak of song at dawn only appears in late spring when territorial boundaries are established and birds are paired6,7. Conflict between singing and foraging cannot explain why males with more non-foraging time in longer days at northern latitudes roost earlier than birds at southern latitudes and still sing before dawn8. Female emergence from her nest hole terminates the dawn chorus in the great tit9. I show here that changes in the duration of male dawn song are closely related to changes in female fertility.
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This paper describes the results of a detailed analysis of 52 song bouts, recorded from 22 great tits, Parus major, during the dawn chorus. A song bout consists of a number of song bursts (called strophes) separated by periods of silence. High quality males, as measured by average strophe length, sang their bouts with a higher percentage performance time (i.e. the percentage of time spent singing in a bout), but the average number of strophes per bout was not related to male quality. In 31 of 52 bouts there was a systematic decrease in the percentage performance time throughout the bout. This was mainly caused by a prolongation of the pauses between the strophes, and sometimes by a shortening of the strophes. Both high and low quality males sang bouts with and without this decrease in the percentage performance time. Bouts that started with longer strophes and/or shorter inter-strophe pauses showed on average a more rapid decrease in the percentage performance time, and contained fewer strophes, than bouts that started with shorter strophes and/or longer inter-strophe pauses. After switching to another song type the males again used longer strophes and/or shorter inter-strophe pauses. An ‘anti-exhaustion’ hypothesis is proposed and discussed. This hypothesis gives a mainly causal explanation for the existence of song switching and song repertoires in passerine birds.
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Sexual selection arises when variance in male reproductive success is non-randomly related to phenotypic characters of males. Song can be considered as such a phenotypic character and several studies have shown that song complexity and/or song output are important in competition among males or in partner choice. In the blue tit Parus caeruleus a peak in male singing activity occurs at dawn during the female fertile period, i.e. after pair formation. The function of this dawn chorus is not well understood. In this study 20 male blue tits were recorded at dawn and song complexity and output were expressed as versatility, mean strophe length, mean percentage performance time and bouts with or without drift, i.e. with or without a systematic decline in percentage performance time. Females mated to males with a higher mean percentage performance time (output) and a higher versatility (complexity) started to lay eggs earlier, but the latter was not significant. Females mated to males that showed no drift in their song bouts laid significantly larger clutches. Our results thus suggest that in the blue tit, song output at dawn, rather than song complexity, might be a trait under sexual selection.
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Superb fairy-wrens are cooperatively breeding birds that combine stable, socially monogamous pair bonds and high levels of paternal care, with extreme levels of extra-pair mating and high levels of sexual competition. Our aim was to determine which testosterone correlates would prevail in such a life history that combines features that are conventionally associated with divergent hormone profiles. Unlike the situation in other species with monogamous pair bonds and high levels of paternal care, testosterone was elevated for a very long period of several months. During breeding there was a broad peak in testosterone followed by a gradual decline: this resembles the profile found in polygynous and promiscuous species. We found that three factors correlated with testosterone: development of the sexually selected nuptial plumage, social status and extra-group mating opportunities. Testosterone started increasing months prior to breeding, when the males that are later preferred as extra-group sires develop their nuptial plumage. Although these males did not have higher testosterone levels during breeding, they sustained high testosterone for much longer, and this might lend reliability to this sexual signal. Dominant males in groups had higher testosterone than pair-dwelling males and subordinate helpers. This was not due to differences in age, reproductive capability or mating opportunities, but was presumably associated with the assertion of dominance. In contrast to findings in other species, male testosterone level was not correlated with whether the resident female was fertile or had dependent nestlings. However, testosterone was strongly correlated with the total number of fertile females in the population, and hence with the opportunities for extra-group mating.
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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.
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Unlike most passerines, female superb fairy-wrens are prolific solo singers. Four hypotheses for the function of female song were evaluated: (1) to defend territories; (2) to maintain contact with mates; (3) to assess the amount of time mates are spending on the territory; and (4) to solicit displays from extra-group males. Female song rates increased as fairy-wrens reasserted territorial boundaries after a period of communal winter flocking. Song rates were not affected by the age of the female, the time she had been paired to her current mate, the time her mate had been the dominant male on the territory, or the composition of her group. However, females that had recently established territories, or had undergone significant changes in territorial borders, sang at higher rates than females that had been established in their territories for many years. Playback experiments revealed that: (1) females were more likely to sing in response to songs of male or female neighbours than to songs of their mates or their own song; (2) females responded more intensely to songs of female strangers than to songs of female neighbours; (3) extra-group males did not respond with extra-group courtship displays when a female's song was played back from her territory, although some territorial responses were elicited. The stronger response to neighbours indicates that mate location and mate assessment are not major functions of female song. The display solicitation hypothesis can be rejected because extra-group males did not respond to playbacks of females, and there was no correlation between female song rate and the incidence of male display. In contrast, the results suggest that the major function of female song is territorial defence, and that receivers use variation in the song to discriminate between different classes of individuals (self, mate, neighbour, stranger).
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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
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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.
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Despite great interest in the use of extra-pair mating as a tool for examining female choice and intersexual selection, the underlying assumption of female control has proved difficult to verify empirically. We combined microsatellite genotyping and radiotelemetry of fertile females in order to investigate mate choice in superb fairy-wrens Malurus cyaneus, the bird with the highest known rate of extra-pair fertilization. All five females radio tracked during the peak of fertility, two to four days before the first egg is laid, undertook pre-dawn forays. All extra-pair young produced by the female were sired by a male visited during their forays, indicating that females control extra-pair fertilizations. In a larger sample of paternity data, some broods were sired by two extra-group males. In virtually all the cases the territory of the two sires were on an identical linear trajectory from the female's territory. This again suggests that extra-group paternity in superb fairy-wrens is directly linked to female extra-territorial forays. In other species mixed paternity has been taken to indicate that females attempt to insure against infertile pairings or try to maximize the genetic diversity of their brood. However, in fairy-wrens the likelihood of multiple extra-group paternity increased greatly as females traversed more territories in order to mate, perhaps suggesting that females which foray further are more likely to have difficulties locating the preferred male.
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The immunocompetence handicap hypothesis proposes that the immunosuppressive effect of testosterone enforces honesty of sexual signalling via a physiological trade-off between signal intensity and immunocompetence. However, evidence that testosterone is immunosuppressive is scant, particularly in birds. I studied the correlation between immunocompetence and testosterone in superb fairy-wrens (Malurus cyaneus), a species with intense intersexual selection. Males are seasonally dichromatic and testosterone increases during the moult from dull brown eclipse plumage into bright nuptial plumage. I determined the primary antibody response to immunization with sheep red blood cells (SRBCs) in (i) control and testosterone-implanted males in captivity, and (ii) a cross-section of free-living males with basal and elevated testosterone (in eclipse plumage, moulting and in nuptial plumage). Experimental treatment with testosterone decreased the likelihood of an antibody response to SRBCs in captive birds. In contrast, free-living males which had acquired the nuptial plumage and had naturally elevated testosterone were more likely to respond to SRBCs than males in eclipse plumage with basal testosterone levels. The association between higher immunocompetence and higher immunosuppressive testosterone could arise if both are positively correlated with male phenotypic quality In addition, the association could result if males compensate for potential immunosuppression by enhancing their humoral immune responses, particularly since high testosterone is linked to other demanding activities such as moulting and courtship displays.
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Although elaborate bird song provides one of the prime examples of a trait that evolved under sexual selection, it is still unclear whether females judge the quality of males by attributes of their song and whether these song features honestly signal a male's genetic quality. We measured the ability of male dusky warblers Phylloscopus fuscatus to maintain a high sound amplitude during singing, which probably reflects an individual's physiological limitations. This new measure of singing performance was correlated with male longevity and with extra-pair paternity, indicating that females who copulated with better singers obtained 'good genes' for their offspring. Our findings are consistent with the idea that females assess male quality by subtle differences in their performance during the production of notes, rather than by the quantity or versatility of song. In addition, observations on territorial conflicts indicate that attractive males invest less in competition over territories because they can reproduce via extra-pair paternity.
Article
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.
Article
Bird song may play an important role for communication among territorial neighbours, but the effect of neighbours on song use is still not well known. My previous field observations suggested that male chipping sparrows, Spizella passerina, use the dawn chorus for interactions among neighbouring males, and use day song for female attraction. To determine how these social factors may influence dawn and daytime singing behaviour, I conducted a series of experiments in which I removed the male neighbours or the female mate of territorial males during 1998-2000. Following removal of all neighbouring males, the solitary male either stopped or reduced his dawn chorus (N = 9), but did not change his daytime singing behaviour. After one of the neighbouring males was returned to his territory the focal male resumed and increased his dawn bout, accompanied with close-range countersinging. Following the removal of a territorial male's mate, the widowed male did not change the dawn chorus, but significantly increased his day song. This study thus revealed that, in chipping sparrows, the presence or absence of neighbouring males has a significant effect on the dawn chorus singing behaviour of territorial males. The presence or absence of a male's mate, in contrast, has a strong influence on a male's daytime singing behaviour. This study also supports the hypothesis that the dawn chorus And daytime song have different functions.
Article
We studied the dawn chorus in the Willow Tit Parus montanus, a monogamous and territorial passerine. We expected that if the song is part of sperm competition, a male should invest most in singing during the period when his female is fertile. A total of 57 pairs of Willow Tits was observed during the spring of 1992. To express singing effort, two variables characterising the dawn chorus were measured for each morning: proportion of time devoted to singing and the onset of singing. Time singing peaked about ten days before commencement of laying, and decreased afterwards. The earliest singers were observed during the laying-period. Time singing differed between male age classes; old males sang more than yearlings. Our results indicate that the dawn chorus in Willow Tits functions as inter- and/or intrasexual communication used in sperm competition. Since adult (high quality) males tended to invest more in singing than yearlings, it is also possible that the dawn chorus is honest advertisement of male quality.
Article
In a number of passerine bird species, mated males sing at dawn and this song activity peaks in the fertile period of the mate. We present the hypothesis that an important function of such dawn singing is to maintain the territory. We suggest that mate guarding and territorial defence are demanding and often mutually exclusive activities. Losing paternity is so costly that males give priority to mate guarding. Males therefore use the early morning period, before their mate emerges from the roost, to claim territory ownership. We report some preliminary tests of this hypothesis from a study of great tits (Parus major). Simulating male intrusion by a playback experiment showed that the resident male was more often absent from central parts of the territory, following the mate, during the periods of nest building and egg laying than during incubation. This supports the assumption of conflicting demands between mate following and territorial defence. From the hypothesis we expected males to spend effort in defending their territory as soon as they were free to do so. Consistent with this prediction, we found that male song activity was high before the mate left the nest at dawn, when she temporarily visited the nest during the day, and when she entered the nest to roost at night. A female removal experiment showed that unmated males, having no mate to guard, sang as much at dawn as mated males. Only one of the eight widowed males succeeded to replace their mate. We discuss some alternative functions of dawn singing in the great tit, such as attraction of own mate, a replacement mate, and extra-pair mates. We conclude that the hypotheses are not mutually exclusive, and song may serve multiple purposes.
Article
This study describes a mathematical model designed to explore the relationships between sound transmission and microclimatic conditions present at different times of the day in different habitats. The model includes all attenuation mechanisms and is used to illuminate possible reasons for the dawn chorus obseved in birds and primates under a diverse array of environmental conditions. Also explored are the possible effects of calling height and calling frequency on broadcast coverage. Solely from the point of view of atmospheric attenuation mechanisms, early morning microclimatic conditions are as optimal for sound propagation as will be present at any other time during the day or night. Depending on the environment, calls voiced at such times are up to 20 times more effective in area of broadcast coverage than the same amplitude signal broadcast at midday. Such an advantage goes far in explaining why many animal species have selected these times for territorial and/or mate attracting communicatory announc...
Article
Bird song may play an important role for communication among territorial neighbours, but the effect of neighbours on song use is still not well known. My previous field observations suggested that male chipping sparrows, Spizella passerina, use the dawn chorus for interactions among neighbouring males, and use day song for female attraction. To determine how these social factors may influence dawn and daytime singing behaviour, I conducted a series of experiments in which I removed the male neighbours or the female mate of territorial males during 1998–2000. Following removal of all neighbouring males, the solitary male either stopped or reduced his dawn chorus (N=9), but did not change his daytime singing behaviour. After one of the neighbouring males was returned to his territory, the focal male resumed and increased his dawn bout, accompanied with close-range countersinging. Following the removal of a territorial male's mate, the widowed male did not change the dawn chorus, but significantly increased his day song. This study thus revealed that, in chipping sparrows, the presence or absence of neighbouring males has a significant effect on the dawn chorus singing behaviour of territorial males. The presence or absence of a male's mate, in contrast, has a strong influence on a male's daytime singing behaviour. This study also supports the hypothesis that the dawn chorus and daytime song have different functions.
Article
Costly female choice for mate quality is a phenomenon that is difficult to account for in the theory of sexual selection. We present a model to determine whether a specific case of mate choice-preference for old mates-can be justified by viability selection in mutation-selection balance only, or whether biotic interactions or random variations in the environment are necessary to maintain the preference if the age of the male does not yield any direct benefit for the female. The results of the model, considering multiple polygenic viability-related traits, show that choosiness will be favoured with any positive mutation rate, but the advantage will be slightly reduced rather than enhanced in the case of a Red Queen type process. Hence, observations of old-age preference indicate a far more important role for viability indicators based on mutation-selection balance alone than previously assessed. Because using age as a choice criterion is also less accountable as a Fisherian mating advantage, the result implies confidence in viability indicators (`good genes' models) as an explanation for female preferences in general.
Article
In many species of monogamous birds females copulate with males other than their social mates, resulting in extrapair fertilizations. Little is known about how females choose extrapair mates and whether the traits used to choose them are reliable indicators of male quality. Here we identify a novel male trait associated with extra-group mating success in the superb fairy-wren (Malurus cyaneus), a cooperatively breeding bird with one of the highest known frequencies of extra-group mating. Female fairy-wrens chose extra-group mates that molted earlier into breeding plumage. Males molted up to five months before the breeding season began, and only males that molted at least one month prior to its onset gained any extra-group fertilizations. This conclusion held after controlling statistically for the effect of age and social status on molt date. Once males acquired breeding plumage, they began courtship display to females on other territories. Thus, some males were displaying to females for several months before the breeding season began. This extraordinarily long period of advertisement by males may be facilitated by the long-term ownership of territories. We suggest that early acquisition of breeding plumage or the subsequent display behavior can be reliable cues for mate choice because they are costly to acquire or maintain.
Article
The development and evolution of bird songs may be influenced by the mechanisms that underlie sound production, although the nature of this influence is not well understood. Here it is shown experimentally that vocal development in songbirds can be affected by physical limits on how birds are able to sing. Young swamp sparrows, Melospiza georgiana, were presented with conspecific song models modified such that rates of syllable repetition were increased above normal rates. Imitations of these songs were inaccurate in ways that indicated motor constraints on vocal performance and that did not indicate perceptual or memory-based constraints. Some song imitations were deficient in trill tempo and/or syllable composition, and others were produced with a species-atypical 'broken' syntax, in which pauses were interspersed within songs. These results illustrate how the development and evolution of trill structure can be limited by motor constraints on vocal production, and also identify a possible mechanism for the evolution of a novel form of song syntax. (C) 1996 The Association for the Study of Animal Behaviour.
Article
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.
Article
Fitness loss among males as a result of cuckoldry is often large, and a number of paternity guards have evolved in response to the presence of cuckoldry risks. Paternity guards such as mate guarding protect the paternity of males but also indirectly announce the fertility status of the guarded female. When such "involuntary" fertility cues have arisen, the negative effects of the cues can be ameliorated either by modifying the paternity guard or by direct announcement of female fertility. Male announcement is a reliabile indicator of male quality, if the degree of mate fertility announcement depends on male phenotypic quality and the quality of his resources, and if costs of announcement are relatively higher for low- than for high-quality males. Cuckolder males would then maximize their reproductive success by preferentially intruding during female fertility on sites with little announcement. Intensive announcement of female fertility will be a phenotype-limited evolutionarily stable strategy (ESS), since benefits continue to accrue to males relative to their investment in announcement. If male announcement rate is an honest measure of male quality, neighboring females are predicted to choose males with a high announcement rate as extrapair copulation partners. Similarly, the interest taken by a male's own females in neighboring males should be inversely related to that male's announcement rate. Sexual selection should therefore drive the announcement strategy. Information on song activity in male passerine bird species provides empirical support for the model.
Book
Bird song is one of the most remarkable and impressive sounds in the natural world, and has inspired not only students of natural history, but also great writers, poets and composers. Extensively updated from the first edition, the main thrust of this book is to suggest that the two main functions of song are attracting a mate and defending territory. It shows how this evolutionary pressure has led to the amazing variety and complexity we see in the songs of different species throughout the world. Writing primarily for students and researchers in animal behavior, the authors review over 1000 scientific papers and reveal how scientists are beginning to unravel and understand how and why birds communicate with the elaborate vocalizations we call song. Highly illustrated throughout and written in straightforward language, Bird Song also holds appeal for amateur ornithologists with some knowledge of biology.
Article
Studies of variation in bird song within a species have tended to concentrate on repertoire size and on song rate, while other aspects of song delivery have received little attention even though they are also likely to play an important part in the signalling process. We here examine the pattern of delivery of individual males' repertoires in the chaffinch (Fringilla coelebs) to identify variation in a range of temporal parameters of song delivery. Coefficients of variation differed between song units and across hierarchical levels. Basic units (syllables) were delivered with great temporal precision. The larger building blocks of a song (the different phrases and the flourish) showed the highest variability while variation for song duration itself was intermediate. Most variables showed consistent differences between males, but there were also consistent differences between song types within a male's repertoire, as well as between the same song types as sung by different males. This suggests an interaction between a male's phenotype and song production, but because of consistent differences between song types within repertoires, there is potential for selection to act on aspects of song delivery both of the individual and of the song type (i.e. the culturally transmitted unit).
Article
The dawn chorus of the great tit can be interpreted from a functional point of view in terms of the following factors. (i) Climatic and other physical conditions in the early morning are unfavourable for foraging and favourable for acoustic communication. (ii) Overnight accumulation of territories favours early morning invasion by potential settlers. (iii) The combination of (i) and (ii) favours early morning territorial defence, including song. A laboratory experiment designed to investigate the proximate causes of allocation of time by territorial great tits to foraging vs. territorial activities (including song) showed that birds are more responsive to intruders when food availability is low. We discuss the relevance of our results to the dawn chorus in other animals and in other geographical regions.