Song duration mediates responses of territory owner in a songbird species with a small song repertoire

Song is a sexually selected trait that is involved in mate attraction and territory defence in birds. Songs may convey information about different male quality components. They are flexible in terms of frequency, amplitude, and duration. Although changes in song duration are common, the function of this behaviour has been studied less strongly. It is known that song duration changes within a singing bout and may provide information about aggressive motivation. We tested whether the elongation and shortening of songs affects the responses of territorial ortolan bunting males to neighbour song playback. If changing song duration signals level of aggressiveness, then songs differing solely in duration may elicit behavioural responses of different strength. We performed two tests with different males assigned to two experimental groups and measured approaching and vocal response. In Experiment 1, we tested 18 males, which responded to the playbacks of elongated and normal (control) neighbour songs. In Experiment 2, we tested 17 males, which responded to the playbacks of shortened and normal (control) neighbour songs. Males responded significantly stronger to longer songs in both experiments as measured by the approach variable. Vocal response was not affected by treatment, but it was affected by the order of playback presentation. Our results indicate that song duration might be used for signalling current aggressive motivation during close interactions with rivals.     

Birds reveal their personality when singing

Background

Individual differences in social behaviour may have consequences for mate choice and sexual signalling, because partners should develop preferences for personalities that maximize reproductive output. Here we propose that behavioural traits involved in sexual advertisement may serve as good indicators of personality, which is fundamental for sexual selection to operate on temperament. Bird song has a prominent and well-established role in sexual selection, and it displays considerable variation among individuals with a potentially strong personality component. Therefore, we predicted that features of song would correlate with estimates of personality.

Methodology/Principal Findings

In a field study of free-living male collared flycatchers, Ficedula albicollis, we characterised personality based on the exploration of an altered breeding environment, and based on the risk taken when a potential predator was approaching during a simulated territorial interaction. We found that explorative and risk-taker individuals consistently sang at lower song posts than shy individuals in the presence of a human observer. Moreover, males from lower posts established pair-bonds relatively faster than males from higher posts.

Conclusions/Significance

Our results may demonstrate that risk taking during singing correlates with risk taking during aggression and with exploration, thus personality may be manifested in different contexts involving sexual advertisement. These findings are in accordance with the hypothesis that the male''s balance between investment in reproduction and risk taking is reflected in sexual displays, and it may be important information for choosy females that seek partners with personality traits enhancing breeding success.     

Behavioural mechanisms of sexual isolation involving multiple modalities and their inheritance

Speciation research dissects the genetics and evolution of reproductive barriers between parental species. Hybrids are the “gatekeepers” of gene flow, so it is also important to understand the behavioural mechanisms and genetics of any potential isolation from their parental species. We tested the role of multiple behavioural barriers in reproductive isolation among closely related field crickets and their hybrids (Teleogryllus oceanicus and Teleogryllus commodus). These species hybridize in the laboratory, but the behaviour of hybrids is unusual and there is little evidence for gene flow in the wild. We found that heterospecific pairs exhibited reduced rates of courtship behaviour due to discrimination by both sexes, and that this behavioural isolation was symmetrical. However, hybrids were not sexually selected against and exhibited high rates of courtship behaviour even though hybrid females are sterile. Using reciprocal hybrid crosses, we characterized patterns of interspecific divergence and inheritance in key sexual traits that might underlie the mating patterns we found: calling song, courtship song and cuticular hydrocarbons (CHCs). Song traits exhibited both sex linkage and transgressive segregation, whereas CHCs exhibited only the latter. Calculations of the strength of isolation exerted by these sexual traits suggest that close‐range signals are as important as long‐distance signals in contributing to interspecific sexual isolation. The surprisingly weak mating barriers observed between hybrids and parental species highlight the need to examine reproductive isolating mechanisms and their genetic bases across different potential stages of introgressive hybridization.     

The Effect of Hemosporidian Infections on White-Crowned Sparrow Singing Behavior

Relatively little is known about the effects of specific parasites on sexually selected behavioral traits. We subjected free‐living mountain white‐crowned sparrows (Zonotrichia leucophrys oriantha) to a playback experiment to identify the effect of hemosporidian parasites on potentially sexually selected song characteristics. We recorded song after a playback of a novel white‐crowned sparrow song, meant to simulate a territorial intrusion. Infections with Leucocytozoon or Plasmodium influenced singing behavior, while infection with Haemoproteus had no detectable effect. Specifically, song consistency, as measured using a spectrogram correlation, was influenced by both Plasmodium and Leucocytozoon infection. Additionally, birds infected with Plasmodium sang fewer songs following experimental playback. Thus, relatively widespread parasites, like Plasmodium, may have a strong effect on potentially sexually selected song characteristics.     

Birdsong performance and the evolution of simple (rather than elaborate) sexual signals

Sexual signals are often elaborate as a result of sexual selection for signals of individual quality. Contrary to expectation, however, the elaboration of signals such as birdsong is not related to the strength of sexual selection across species. With a comparative study across wood warblers (family Parulidae), we show a compromise between advertising the performance of trills (syllable repetitions) and song complexity, which can result in the evolution of simple, rather than elaborate, song. Species with higher trill performance evolved simple songs with more extensive trilled syntax. This advertises trill performance but reduces syllable diversity in songs. These two traits are commonly sexually selected in songbirds, but indexes of sexual selection were not related to either in wood warblers. This is consistent with sexual selection targeting different traits in different species, sometimes resulting in simple signals. We conclude that the evolution of sexual signals can be unpredictable when their physiology affords multiple or, as here, opposing ways of advertising individual quality.     

Behavioural response of a migratory songbird to geographic variation in song and morphology

Introduction

Sexually selected traits contribute substantially to evolutionary diversification, for example by promoting assortative mating. The contributing traits and their relevance for reproductive isolation differ between species. In birds, sexually selected acoustic and visual signals often undergo geographic divergence. Clines in these phenotypes may be used by both sexes in the context of sexual selection and territoriality. The ways conspecifics respond to geographic variation in phenotypes can give insights to possible behavioural barriers, but these may depend on migratory behaviour. We studied a migratory songbird, the Stonechat, and tested its responsiveness to geographic variation in male song and morphology. The traits are acquired differently, with possible implications for population divergence. Song can evolve quickly through cultural transmission, and thus may contribute more to the establishment of geographic variation than inherited morphological traits. We first quantified the diversity of song traits from different populations. We then tested the responses of free-living Stonechats of both sexes to male phenotype with playbacks and decoys, representing local and foreign stimuli derived from a range of distances from the local population.

Results

Both sexes discriminated consistently between stimuli from different populations, responding more strongly to acoustic and morphological traits of local than foreign stimuli. Time to approach increased, and time spent close to the stimuli and number of tail flips decreased consistently with geographic distance of the stimulus from the local population. Discriminatory response behaviour was more consistent for acoustic than for morphological traits. Song traits of the local population differed significantly from those of other populations.

Conclusions

Evaluating an individual’s perception of geographic variation in sexually selected traits is a crucial first step for understanding reproductive isolation mechanisms. We have demonstrated that in both sexes of Stonechats the responsiveness to acoustic and visual signals decreased with increasing geographic distance of stimulus origin. These findings confirm consistent, fine discrimination for both learned song and inherited morphological traits in these migratory birds. Maintenance or further divergence in phenotypic traits could lead to assortative mating, reproductive isolation, and potentially speciation.

     

Communication in the third dimension: song perch height of rivals affects singing response in nightingales

Many animals use long-range signals to compete over mates and resources. Optimal transmission can be achieved by choosing efficient signals, or by choosing adequate signalling perches and song posts. High signalling perches benefit sound transmission and reception, but may be more risky due to exposure to airborne predators. Perch height could thus reflect male quality, with individuals signalling at higher perches appearing as more threatening to rivals. Using playbacks on nightingales (Luscinia megarhynchos), we simulated rivals singing at the same height as residents, or singing three metres higher. Surprisingly, residents increased song output stronger, and, varying with future pairing success, overlapped more songs of the playback when rivals were singing at the same height than when they were singing higher. Other than expected, rivals singing at the same height may thus be experienced as more threatening than rivals singing at higher perches. Our study provides new evidence that territorial animals integrate information on signalling height and thus on vertical cues in their assessment of rivals.     

Sex and the Syndrome: Individual and Population Consistency in Behaviour in Rock Pool Prawn Palaemon elegans

Animal personality has been widely documented across a range of species. The concept of personality is composed of individual behavioural consistency across time and between situations, and also behavioural trait correlations known as behavioural syndromes. Whilst many studies have now investigated the stability of individual personality traits, few have analysed the stability over time of entire behavioural syndromes. Here we present data from a behavioural study of rock pool prawns. We show that prawns are temporally consistent in a range of behaviours, including activity, exploration and boldness, and also that a behavioural syndrome is evident in this population. We find correlations between many behavioural traits (activity, boldness, shoaling and exploration). In addition, behavioural syndrome structure was consistent over time. Finally, few studies have explicitly studied the role of sex differences in personality traits, behavioural consistency and syndrome structure. We report behavioural differences between male and female prawns but no differences in patterns of consistency. Our study adds to the growing literature on animal personality, and provides evidence showing that syndromes themselves can exhibit temporal consistency.     

Personality and urbanization: behavioural traits and <Emphasis Type="Italic">DRD4</Emphasis> SNP830 polymorphisms in great tits in Barcelona city

Most examples of adaptation to the urban environment relate to plasticity processes rather than to natural selection. Personality, however, defined as consistent individual differences in behaviour related to exploration, caution, and neophobia, is a good behavioural candidate character to study natural selection in relation to the urban habitat due to its heritable variation. The aim of this paper was to analyse variation in personality by comparing urban and forest great tits Parus major using standard tests of exploratory behaviour and boldness. We studied personality in 130 wild great tits captured in Barcelona city and nearby forests and found that urban birds were more explorative and bolder towards a novel object than forest birds. Genotype frequencies of the DRD4 SNP830 polymorphism, a gene region often associated with personality variation, varied significantly between forest and urban birds. Behavioural scores, however, were not correlated with this polymorphism in our population. Exploration scores correlated to boldness for forest birds but not for urban birds. Our findings suggest that the novel selection pressures of the urban environment favour the decoupling of behavioural traits that commonly form behavioural syndromes in the wild.     

Environmental and genetic effects shape the development of personality traits in the mangrove killifish Kryptolebias marmoratus

Consistent individual differences in behaviour are well documented, for example, individuals can be defined as consistently bold or consistently shy. To date our understanding of the mechanisms underpinning consistent individual differences in behaviour (also termed behavioural types (BTs)) remains limited. Theoretical work suggests life‐history tradeoffs drive BT variation, however, empirical support is scarce. Moreover, whilst life‐history is known to be phenotypically plastic in response to environmental conditions during ontogeny, the extent to which such plasticity drives plasticity in behavioural traits and personality remains poorly understood. Using a natural clonal vertebrate, Kryptolebias marmoratus, we control for genetic variation and investigate developmental plasticity in life‐history and three commonly studied behavioural traits (exploration, boldness, aggression) in response to three ecologically relevant environments; conspecific presence, low food and perceived risk. Simulated predation risk was the only treatment that generated repeatable behaviour i.e. personality during ontogeny. Treatments differed in their effects on mean life‐history and behavioural scores. Specifically, low food fish exhibited reduced growth rate and exploration but did not differ from control fish in their boldness or aggression scores. Conspecific presence resulted in a strong negative effect on mean aggression, boldness and exploration during ontogeny but had minimal effect on life‐history traits. Simulated predation risk resulted in increased reproductive output but had minimal effect upon average behavioural scores. Together these results suggest that life‐history plasticity/variation may be insufficient in driving variation in personality during development. Finally, using offspring derived from each rearing environment we investigate maternal effects and find strong maternal influence upon offspring size, but not behaviour. These results highlight and support the current understanding that risk perception is important in shaping personality, and that social experience during ontogeny is a major influence upon behavioural expression.     

No Correlation Between Three Selected Trade‐Offs in Birdsong Performance and Male Quality for a Species With Song Repertoires

Demanding performance of vocal signals, such as birdsong, may be evaluated by trade‐offs among acoustic traits. If individuals differ in their ability to sustain physiologically demanding singing, then aspects of song performance resulting from such trade‐offs could signal individual quality. Song performance can also differ among song types, and it is not known whether this influences the assessment of individual quality. We asked whether three trade‐off‐based measures of song performance indicate male age or aspects of condition (body condition, hematocrit and ectoparasite load) in the dark‐eyed junco (Junco hyemalis), a species with small repertoires. Across a sample of over 100 males, no measure of song performance was related to male age or condition, nor did song performance improve with age for those males recorded in consecutive years. In all cases, the variation in song performance explained by these predictors was small (<4%). Instead, the more song types we recorded from a male, the more likely we were to record high‐performance songs, and this sampling effect was stronger than putative correlations with male quality. These results complement a previous study on this population showing that most variation in performance is found among song types rather than among males. Collectively, the lack of association between trade‐off‐based aspects of song performance and male age or condition, plus variation among song types that interferes with rapid assessment of a male's best performance, indicate that these aspects of song performance do not allow a good assessment of male quality in juncos, and perhaps more generally in species with song repertoires.     

Long-term repeatability of behaviours in zebrafish (Danio rerio)

Animal personality is defined as individual variation in behaviour that is consistent over time and/or across contexts. Animal personality is now considered a fundamental aspect in the fields of animal behaviour and behavioural ecology, yet the majority of studies assess repeatability of behaviours over only relatively short time periods (e.g. a week) using just two measures. Understanding whether behavioural traits are repeatable over longer periods is important for the assessment of individual differences in behaviour. Using zebrafish (Danio rerio), we investigated the repeatability of activity and exploratory behaviours, including distance travelled, time spent in the bottom of the arena, stationary time and overall exploration of the novel arena over a 28-week period, using five intervals. All measures were repeatable over 28 weeks, but the repeatability estimates were much lower when comparing the initial week one and week two behaviours. There were clear sex differences in aspects of activity, with males more active than females. Importantly, our behavioural assays suggest that zebrafish require an initial “tank experience,” prior to the main phenotyping session, to ensure that behaviours being measured are repeatable—these effects are often not considered, but have implications for the many studies that measure behaviour at a single time point only.     

Determining Behavioural Syndromes in Voles – The Effects of Social Environment

Animal personality and behavioural syndromes have experienced rapid increase in interest in the last few years because of their possible role in the evolution of life histories. However, there is still a scarcity of studies concerning the mechanisms maintaining variation in behaviour as well as addressing their relationships to each other. In this paper, we tested the main assumptions of personality, focusing on the individual variability and repeatability of behaviour, and the identification of behavioural syndromes using the common vole (Microtus arvalis) as the species being studied. We also studied the effects of family group characters (group size, sex ratio and affinity to family) on the behaviour in this rodent. The animals were repeatedly tested in two behavioural experiments – novel environment (NE) test and radial‐arm maze (RAM) test, from which seven personality traits were extracted. The study revealed that inter‐individual variance in vole behaviour was consistent and repeatable. Individual‐specific responses to NE corresponded with the performance in the maze, which revealed behavioural syndromes and possible trade‐offs. Anxiety was determined by the size of the family group, whereas escape‐related behaviours and maze‐exploring tactic were more dependent on the affinity to the family. It seems that the development of personality traits we identified here is determined by the effects and structure of the family groups. Further studies are needed to confirm whether the observed variance in vole personalities is maintained by the fitness costs and benefits of the opposite tactics (here fast‐random vs. slow‐systematic exploration) in more natural circumstances.     

Individual differences affect honest signalling in a songbird

Research in the past decade has established the existence of consistent individual differences or ‘personality’ in animals and their important role in many aspects of animal behaviour. At the same time, research on honest signalling of aggression has revealed that while some of the putative aggression signals are reliable, they are only imperfectly so. This study asks whether a significant portion of the variance in the aggression-signal regression may be explained by individual differences in signalling strategies. Using the well-studied aggressive signalling system of song sparrows (Melospiza melodia), we carried out repeated assays to measure both aggressive behaviours and aggressive signalling of territorial males. Through these assays, we found that aggressive behaviours and aggressive signalling were both highly repeatable, and moreover that aggressive behaviours in 2009–2010 predicted whether the birds would attack a taxidermic mount over a year later. Most significantly, we found that residual variation in signalling behaviours, after controlling for aggressive behaviour, was individually consistent, suggesting there may be a second personality trait determining the level of aggressive signalling. We term this potential personality trait ‘communicativeness’ and discuss these results in the context of honest signalling theories and recent findings reporting prevalence of ‘under-signalling’.     

Can We Predict Personality in Fish? Searching for Consistency over Time and across Contexts

The interest in animal personality, broadly defined as consistency of individual behavioural traits over time and across contexts, has increased dramatically over the last years. Individual differences in behaviour are no longer recognised as noise around a mean but rather as adaptive variation and thus, essentially, raw material for evolution. Animal personality has been considered evolutionary conserved and has been shown to be present in all vertebrates including fish. Despite the importance of evolutionary and comparative aspects in this field, few studies have actually documented consistency across situations in fish. In addition, most studies are done with individually housed fish which may pose additional challenges when interpreting data from social species. Here, we investigate, for the first time in fish, whether individual differences in behavioural responses to a variety of challenges are consistent over time and across contexts using both individual and grouped-based tests. Twenty-four juveniles of Gilthead seabream Sparus aurata were subjected to three individual-based tests: feed intake recovery in a novel environment, novel object and restraining and to two group-based tests: risk-taking and hypoxia. Each test was repeated twice to assess consistency of behavioural responses over time. Risk taking and escape behaviours during restraining were shown to be significantly consistent over time. In addition, consistency across contexts was also observed: individuals that took longer to recover feed intake after transfer into a novel environment exhibited higher escape attempts during a restraining test and escaped faster from hypoxia conditions. These results highlight the possibility to predict behaviour in groups from individual personality traits.     

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

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

Multiple signaling functions of song in a polymorphic species with alternative reproductive strategies

Vocal traits can be sexually selected to reflect male quality, but may also evolve to serve additional signaling functions. We used a long‐term dataset to examine the signaling potential of song in dimorphic white‐throated sparrows (Zonotrichia albicollis). We investigated whether song conveys multifaceted information about the vocalizing individual, including fitness, species identity, individual identity, and morph. We also evaluated whether song traits correlate differently with fitness in the two morphs, as the more promiscuous strategy of white, relative to tan, morph males might impose stronger sexual selection. Males with high song rates achieved higher lifetime reproductive success, and this pattern was driven by white morph males. In addition, males that sang songs with many notes survived longer, but this pattern was less robust. Thus, song traits reflect differences in fitness and may more strongly affect fitness in the white morph. Song frequency was unrelated to fitness, body size, or morph, but was individual specific and could signal individual identity. Songs of the two morphs displayed similar frequency ratios and bandwidths. However, tan morph males sang songs with longer first notes, fewer notes, and higher variability. Thus, song could be used in morph discrimination. Variation in frequency ratios between notes was low and could function in conspecific recognition, but pitch change dynamics did differ between four different song types observed. Our results support a multiple messages model for white‐throated sparrow song, in which different song traits communicate discrete information about the vocalizing individual.     

Effects of personality on territory defence in communication networks: a playback experiment with radio-tagged great tits

Individuals often differ consistently in behaviour across time and contexts, and such consistent behavioural differences are commonly described as personality. Personality can play a central role in social behaviour both in dyadic interactions and in social networks. We investigated whether explorative behaviour, as proxy of personality of territorial male great tits (Parus major), predicts their own and their neighbours'' territorial responses towards simulated intruders. Several weeks prior to playback, subjects were taken from the wild to test their exploratory behaviour in a standard context in the laboratory. Exploratory behaviour provides a proxy of personality along a slow–fast explorer continuum. Upon release, males were radio-tracked and subsequently exposed to interactive playback simulating a more or a less aggressive territorial intruder (by either overlapping or alternating broadcast songs with the subjects'' songs). At the same time, we radio-tracked a neighbour of the playback subject. Male vocal responses during playback and spatial movements after playback varied according to male explorative behaviour and playback treatment. Males with lower exploration scores approached the loudspeaker less, and sang more songs, shorter songs and songs with slower element rates than did males with higher exploration scores. Moreover, neighbour responses were related to the explorative behaviour of the subject receiving the playback but not to their own explorative behaviour. Our overall findings reveal for the first time how personality traits affect resource defence within a communication network providing new insights on the cause of variation in resource defence behaviour.     

Match–Mismatch Experiments Using Photoperiod Expose Developmental Plasticity of Personality Traits

Behavioural differences between individuals are often found to be consistent across contexts and/or over time, although recent studies suggest that ontogenetic processes and learning might influence personality. During ontogeny, environmental influences may play an important role in shaping an individual's personality as well as its physiology. Seasonal changes are ubiquitous and known to influence development. To study developmental plasticity, of behaviour and physiology in the wild cavy (Cavia aperea), we manipulated the photoperiod in a fully crossed match–mismatch design by simulating spring and autumn photoperiod until weaning and subsequently moving half of the animals into the mismatching photoperiod. We found developmental plasticity in behavioural and physiological traits before and after sexual maturation for growth, resting metabolic rate and fearlessness. For fearlessness, changes in response to the opposite photoperiod were more pronounced in males than in females. Exploration and boldness were only influenced by early, but not by late photoperiod. No sex differences were found for these two traits. Even though our treatment changed average trait expression, some behavioural traits proved consistent over time, but physiological traits were not. Fearlessness was consistent only in animals that did not change photoperiod during development, whereas exploration and boldness were consistent over time regardless of photoperiodic treatment. Our study shows that in response to a change in photoperiod personality traits differ substantially in developmental plasticity.     

Song Perch Height in Rufous‐and‐White Wrens: Does Behaviour Enhance Effective Communication in a Tropical Forest?

Animal signals are distorted as they transmit through the environment, but many species have evolved strategies to minimize distortion of vocal signals. Song structure can change over evolutionary time, or signallers can modify their behaviour, to reduce attenuation and degradation in a specific habitat. We investigated signalling behaviour in rufous-and-white wrens, Thyothorus rufalbus , a Neotropical songbird in which both sexes sing, with a specific focus on perch height. Based on previous findings, including a detailed sound transmission study, we predicted that rufous-and-white wrens would choose elevated song perches in order to maximize the distance their songs travel, and that males and females would show different perch height choices. We observed 30 birds in 18 territories in a tropical forest in Costa Rica to determine the perch heights of birds when singing, producing non-song vocalizations, collecting nesting material, foraging, and engaging in other behaviours. We found that both activity and sex influenced perch height. Birds sang from a variety of heights, but the highest perches were used as song posts by males. Males minimized singing from within 1 m of the ground, and they generally perched higher than females, which may reflect sex differences in communication strategies. Both sexes foraged on or near the ground. The finding that rufous-and-white wrens vary their perch height with specific activities suggests that they modify their singing behaviour to enhance long-distance communication.