Song Rate Research Articles

Song overlapping, noise, and territorial aggression in great tits

Abstract Communication often happens in noisy environments where interference from the ambient noise and other signalers may reduce the effectiveness of signals which may lead to more conflict between interacting individuals. Signalers may also evolve behaviors to interfere with signals of opponents, for example, by temporally overlapping them with their own, such as the song overlapping behavior that is seen in some songbirds during aggressive interactions. Song overlapping has been proposed to be a signal of aggressive intent, but few studies directly examined the association between song overlapping and aggressive behaviors of the sender. In the present paper, we examined whether song overlapping and ambient noise are associated positively with aggressive behaviors. We carried out simulated territorial intrusions in a population of great tits (Parus major) living in an urban–rural gradient to assess signaling and aggressive behaviors. Song overlapping was associated negatively with aggressive behaviors males displayed against a simulated intruder. This result is inconsistent with the hypothesis that song overlapping is an aggressive signal in this species. Ambient noise levels were associated positively with aggressive behaviors but did not correlate with song rate, song duration, or song overlapping. Great tits in noisy urban habitats may display higher levels of aggressive behaviors due to either interference of noise in aggressive communication or another indirect effect of noise.

Heterospecific song quality as social information for settlement decisions: an experimental approach in a wild bird

Assessing local habitat quality via social cues provided by conspecific or heterospecific individuals sharing the same needs is a widespread strategy of social information use for breeding habitat selection. However, gathering information about putative competitors may involve agonistic costs. The use of social cues reflecting local habitat quality acquired from a distance, such as acoustic cues, could therefore be favoured. Bird songs are conspicuous signals commonly assumed to reliably reflect producer quality, and thereby local site quality. Birds of various species have been shown to be attracted to breeding sites by conspecific and heterospecific songs, and to use conspecific song features as information on producer (and by extension habitat) quality. Whether they can do the same with heterospecific song features, and whether this depends on the individual's own phenotype and especially its competitive ability, remains unknown. We used a playback experiment in a wild population of collared flycatchers, Ficedula albicollis, a species known to eavesdrop on the presence and performance of dominant great tits, Parus major. We tested whether flycatchers, whose aggressiveness was experimentally assessed, preferred to settle near playback of a high-quality great tit song (i.e. song with large repertoire size, long strophes, high song rate), a low-quality great tit song or a chaffinch song (control). Among old females, aggressive ones preferred to settle near playback of high-quality tit song and avoided playback of low-quality tit song, while less aggressive females preferred to settle near playback of low-quality tit song. Male personality or age did not influence settlement decisions. This shows that collared flycatcher females use great tit song quality features as information for settlement decisions, although this depended on their own competitive ability and/or previous experience with great tit songs. Our study therefore further illustrates the complex condition-dependent use of heterospecific social information for breeding habitat selection.

Can singing rate be used to predict male breeding status of forest songbirds? A comparison of three calibration models

AbstractFor male songbirds, song rate varies throughout the breeding season and is correlated with breeding cycle stages. Although these patterns have been well documented, this relationship has not been used to predict a bird's breeding status from acoustic monitoring. This challenge of using a response (i.e., behavior) to indirectly measure an underlying biological state is common in ecology, but correctly addressing the associated statistical challenge of calibration is rare. The objective of this study was to determine whether variation in song rate can be used to predict the breeding status of the Olive‐sided Flycatcher (Contopus cooperi). In 2016, song rates from 28 male Olive‐sided Flycatchers were collected from human observers (n = 545 five‐minute counts) and breeding status (i.e., single, paired, and feeding young) was monitored throughout the breeding season. The predictive ability of three modeling approaches—regression, hierarchical, and a classification tree—was evaluated using sensitivity and specificity to determine the best modeling approach. The hierarchical model was the best at predicting all three breeding status classes, with a mean sensitivity of 69%, compared with 54% and 50% from the regression and machine learning models, respectively. Our results suggest that song rate can be used as an indirect measurement of breeding status in the Olive‐sided Flycatcher when using a hierarchical modeling approach to calibrate the breeding status–song rate relationship. This novel modeling approach provides a cost‐effective tool to collect much needed demographic information over large spatial extents and inform species status assessments, recovery strategies, and management plans for species of conservation concern.

Song structure and singing activity of two separate humpback whales populations wintering off the coast of Caño Island in Costa Rica.

Central American (CA) and Breeding Stock-G (BSG) humpback whales are known to winter off Caño Island, Costa Rica at different times of the year. To study their singing behavior, autonomous underwater recorders were used to record the whales. Song detection for BSG whales was higher than CA whales, and song structure was distinct for each population. No strong evidence for cross-equatorial connectivity was found. This study provides the first humpback whale song reference for both populations in Costa Rica, which can help advance understanding of CA and BSG whale song rate of change and connectivity with other wintering areas.

In vivo online monitoring of testosterone-induced neuroplasticity in a female songbird

Adult neuroplasticity in the song control system of seasonal songbirds is largely driven by photoperiod-induced increases in testosterone. Prior studies of the relationships between testosterone, song performance and neuroplasticity used invasive techniques, which prevent analyzing the dynamic changes over time and often focus on pre-defined regions-of-interest instead of examining the entire brain. Here, we combined (i) in vivo diffusion tensor imaging (DTI) to assess structural neuroplasticity with (ii) repeated monitoring of song and (iii) measures of plasma testosterone concentrations in thirteen female photosensitive starlings (Sturnus vulgaris) who received a testosterone implant for 3 weeks. We observed fast (days) and slower (weeks) effects of testosterone on song behavior and structural neuroplasticity and determined how these effects correlate on a within-subject level, which suggested separate contributions of the song motor and anterior forebrain pathways in the development of song performance. Specifically, the increase in testosterone correlated with a rapid increase of song rate and RA volume, and with changes in Area X microstructure. After implant removal, these variables rapidly reverted to baseline levels. In contrast, the more gradual improvement of song quality was positively correlated with the fractional anisotropy values (DTI metric sensitive to white matter changes) of the HVC-RA tract and of the lamina mesopallialis, which contains fibers connecting the song control nuclei. Thus, we confirmed many of the previously reported testosterone-induced effects, like the increase in song control nuclei volume, but identified for the first time a more global picture of the spatio-temporal changes in brain plasticity.

Great tits responding to territorial intrusions sing less but alarm more on colder days

AbstractBird song transmits information required to defend territories and attract mates. These functions contribute to fitness by affecting survival and reproductive success. Singing is also costly due to physiological costs. We used observational data to evaluate support for the hypothesis that lower temperatures result in decreased singing behaviour in wild great tits due to increased energy consumption during cold conditions required for thermoregulation. More than 6,500 simulated territorial intrusions were performed over an 8‐year period in twelve nest box populations of great tits Parus major south of Munich, Germany. We measured song rate as well as the number of alarm calls and the aggressive response of territorial males to a simulated territorial intrusion. We found a decrease in song rate with decreasing current temperature, but also a concurrent increase in the number of alarm calls. Night temperature did not affect these acoustic traits. We conclude that warmer conditions allow birds to choose more energetically expensive (yet functionally superior) activities during territorial intrusions, thereby facilitating avoidance of physical aggressiveness during territorial intrusions.

Song characters as reliable indicators of male reproductive quality in the Savannah Sparrow (Passerculus sandwichensis)

Bird song may provide female birds with signals of male quality. To investigate this potential for sexual selection via female choice, we assessed the relationships between male song variation and male mating and reproductive success of the Savannah Sparrow (Passerculus sandwichensis (J.F. Gmelin, 1789)) over 3 years (2001–2003) in a population of Savannah Sparrows near London, Ontario, Canada. We measured song rate, as well as temporal and frequency attributes of song structure, as possible predictors of male quality, and then related these measures to attributes of male reproductive performance (mating and breeding success and territory size of males). We found significant correlations between male reproductive performance and several song features, such that the combined effects of two trill sections could potentially play an important role: males possessing such songs arrived and paired earlier and had higher fledging success. The results suggested that the trill segments of the song may signal important aspects of male quality. Possible reasons for significant roles of such songs in open-habitat birds are discussed.

Dupont’s Lark males start to sing earlier but reduce song rate on full moon dawns

Moon phase affects the ecology and behaviour of animals and may thus affect both circadian and circannual rhythms. Its influence on nocturnal and dawn bird behaviour is known, but fewer studies have examined its effect on passerines’ singing activity, some of which have yielded contradictory findings. With the aim of elucidating whether moon phase affects dawn singing in passerines, we recorded dawn singing activity of the Dupont’s Lark Chersophilus duponti in three mediterranean shrub-steppes, through repeated sampling over three lunar cycles per breeding season in 2 years. Our results corroborate the idea that moon phase affects signalling behaviour of passerines. We found that, on average, dawn singing started 15 min earlier when the moon was full, due to variations in the light intensity, which seems to act as a trigger for singing activity in the Dupont’s Lark. Nonetheless, the dawn chorus finished at the same time regardless of moon phase, maybe due to a low contribution of moonlight as sunrise approaches. As a consequence, performance time increased during full moon nights. However, the total production of songs did not differ between moon phases, and therefore, song rate was lower during full moons. Reduced song rate on full moon nights could be a response of singing males to reduce their predation risk, since singing on bright nights can increase the ability of predators to locate them, but it could be also related to the energetic cost of longer choruses. The consequences of moon phase for mate attraction, reproductive success and behaviour in this and other bird species remain unknown, and thus our research can serve as a starting point from which to develop new studies.

Full life course analysis of birdsong reveals maturation and senescence of highly repeatable song characteristics

AbstractSignalers 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 senescence. 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.

Bioacoustic monitoring reveals shifts in breeding songbird populations and singing behaviour with selective logging in tropical forests

Abstract Selective logging is the primary cause of tropical forest degradation and is rapidly expanding worldwide. While the impacts of logging on species diversity and distributions are well understood, little is known about the effects of logging on animal behaviours central to individual fitness and population persistence. The song rate of breeding songbirds is a behavioural trait that is often positively associated with male density and used by conspecific females as an indicator of territory and male quality. Thus, contrasting logging‐induced adjustments in song rates of individual birds with population shifts may illuminate potential mechanisms underlying population distributions. We present a novel application of bioacoustic monitoring, integrating counts of individuals, songs and duets from single automated recording units (ARUs) with N‐mixture models, to estimate shifts in population parameters (occupancy, abundance) and singing behaviours (per‐capita song rates, per‐pair duet rates) of 32 Bornean songbird species with logging. We tested hypotheses on the relationships between adjustments in behavioural and population parameters with logging, and further tested the extent to which species traits predicted behavioural and population shifts. Adjustments to singing behaviour in 59 and 53% of species (57% of duetting species) were concordant with differences in occupancy and abundance respectively, such that species showing reduced populations with logging also produced fewer songs per‐capita, and vice versa. Species known to prefer undisturbed habitats and large‐bodied species showed the most negative effects of logging on singing behaviour and population distributions. Species known to exploit degraded habitats exhibited the opposite pattern. Subdued singing in logged forests by species of conservation concern suggests limited competition between territorial males in small populations and may also signal low‐quality territories. Synthesis and applications. We demonstrate that bioacoustic monitoring can be used to not only estimate important population parameters of occupancy and abundance across a diverse tropical songbird community, but also enables quantification of behaviours considered relevant to individual fitness, yet unobtainable with conventional methods (e.g. point counts). Bioacoustics provides a viable approach to reliable automated large‐scale monitoring of hyperdiverse tropical forest systems under logging operations and other land‐use pressures.

A binomial N‐mixture model for estimating arrival and departure timing

AbstractThe timing of life cycle events has strong fitness consequences, suggesting that monitoring of arrival and departure timing may help understand spatial and population dynamics. Several existing models with inference to arrival and departure in unmarked populations are applicable to detection/non‐detection data which is a reduced information summary of the underlying population and phenological dynamics. These models also do not directly address the dependence of seasonal variation in availability (e.g. song rate) on arrival timing, often treating the seasonal distribution of availability as fixed across years despite allowing variation in arrival. Model development in an abundance framework has largely occurred in the context of stopover populations, rather than populations that exhibit some period of closure between arrival and departure phases.We developed an N‐mixture model that accommodates the dependence of seasonal availability on arrival timing, providing inference about abundance and both arrival and departure timing based on repeated count data. The model is applicable to populations in which there exists some period of closure between the arrival and departure phases. We developed two general formulations of the model, both of which include a model for the arrival process, but differ in the model for seasonal availability. The first formulation is applicable to cases in which seasonal availability is a function of cue production. The other is applicable to situations where seasonal availability is a function of departure of individuals or their transition to a state in which they remain unavailable for detection.We demonstrated through simulation that both versions provide unbiased and precise estimates of phenology and abundance and illustrated the cue production formulation using data collected in Denali National Park, Alaska for three passerine species.We expect that our inference framework will be broadly applicable in studies of unmarked populations where joint assessment of population, spatial and phenological dynamics is of interest.

Risk allocation: acute and chronic predator exposure have contrasting effects on Song Sparrow (Melospiza melodia) singing behaviour

Increasing the danger posed by predators may cause prey animals to alter their behaviour. For example, they may be more vigilant and so feed more slowly. Breeding male Song Sparrows (Melospiza melodia (A. Wilson, 1810)) spend much time in conspicuous, loud song, which is an important behaviour for territorial defense and for mate attraction. We measured their singing behaviour in relation to both chronic (active Cooper’s Hawk (Accipiter cooperii (Bonaparte, 1828)) nest nearby) and acute (playback of hawk calls) predator exposure. We found that proximity to a Cooper’s Hawk nest had little or no influence. In contrast, the response to acute exposure was strong and immediate: Song Sparrows reduced the song rate and the proportion of time spent singing, lowered perch height, and increased concealment. The decline in the amount of song during the few minutes following playback attributable to the acute exposure was 34.6%. We analyze these results in light of theories about how animals adjust risk taking in response to predation danger. Given that the numbers of their predators have risen steadily for the past few decades and affect the level of singing, we consider the implications for trend estimates of songbird populations based on surveys using auditory methods.

Effect of testosterone blockers on male aggression, song and parental care in an arctic passerine, the Lapland longspur (Calcarius lapponicus)

In many passerine birds, testosterone stimulates song and aggression but inhibits paternal care, but few studies have explored whether such effects can be reversed with testosterone blockers. We explored the effect of testosterone blockers on song, aggression and paternal care of Lapland longspurs (Calcarius lapponicus), an arctic passerine with a short breeding season. Twenty-one “blocker males” received implants containing an androgen receptor blocker and an aromatase inhibitor, compared to 27 control males with empty or no implants. Song, aggression and other behaviors were evaluated with simulated territorial intrusions (STI) during mate-guarding, and with focal observations (without STI) during mate-guarding and incubation. Nests were monitored and nestlings weighed as an indirect measure of paternal care. During STI, blocker males exhibited similar song rates, significantly lower aggression, and were significantly less likely to be found on territory than control males. Focal observations revealed no differences in spontaneous song, aggression, foraging, preening, or flight activity. Blocker males' nestlings had greater body mass on day 5 after hatching, but this difference disappeared by fledging, and both groups fledged similar numbers of young. Two blocker males exhibited unusual paternal care: incubation and brooding of young, or feeding of nestlings at another male's nest. In sum, testosterone blockers affected aggression but not song, contrasting with results from previously published testosterone implant studies. Effects on paternal care were concordant with testosterone implant studies. These patterns may be related to rapid behavioral changes characteristic of the short breeding season of the Arctic.

Song rate and duetting in the Chirruping Wedgebill (Psophodes cristatus): frequency, form and functions

ABSTRACTMuch of our current understanding of song originates from studies of species living in seasonal environments, where breeding seasons are short and highly synchronised at the population level. By comparison, the form and function of song are less well understood in aseasonal environments, where breeding cycles are less predictable. We examined song rates of male and female Chirruping Wedgebills (Psophodes cristatus), a passerine endemic to the arid regions of inland, south-eastern Australia, across a 4 month period of breeding activity. Our results show that both males and females sing, and provide evidence of duetting. The song rate of male Wedgebills was highest in the early morning and during breeding and was substantially higher than the song rate of female Wedgebills. Over the course of the day, bouts of male singing were two orders of magnitude longer than females. By contrast, female song rate was independent of the time of day or reproductive phase. Females more often sang in tandem with their partners than expected by chance and duets occurred at a relatively low rate, independently of breeding phase. We discuss the possibility that male and female song and duets serve different functions.

Song Does Not Function as a Signal of Direct Aggression in Two Leaf-Warbler Species

In many songbirds, males vary aspects of their singing behaviour when engaged in territorial interactions. Song rate, song type switching rate, song matching, song overlapping, and the use of specific song or call types have all been proposed to be aggressive signals. It is not clear why such variability in aggressive signaling mechanisms exists among different species. We used a comparative approach to study how two Phylloscopus warbler species respond to playback-simulated territorial intrusion. We examined whether the spontaneous songs of Large-billed Phylloscopus magnirostris and Sulphur-breasted P. ricketii leaf-warblers differed from songs produced in response to playback. Song bouts were analysed by measuring 10–12 parameters, but we found no differences between spontaneous songs and playback responses in either species. All males clearly responded to playback by approaching the loudspeaker and flying around it. Large-billed Leaf-warblers produced ‘crackling’ sounds in response to playback more frequently than during spontaneous singing, whereas the usually highly vocal Sulphur-breasted Leaf-warblers possibly (and surprisingly) did not use vocalizations (either songs or calls) to signal direct aggression. A comparison with other Phylloscopus species revealed that even closely related species (i.e. from a single genus) might use different strategies when responding to simulated territorial intrusion. The aggressive signalling strategy is therefore a labile trait that can potentially be exposed to fast evolutionary change.

The data set of spring song rates for forest birds collected by IC recorders

The data set of spring song rates for forest birds collected by IC recorders

Singing of Claudia’s Leaf-warbler (Phylloscopus claudiae) in aggressive contexts: role of song rate, song type diversity and song type transitional pattern

In many songbirds, males vary certain aspects of their singing behavior when engaged in territorial interactions. Song rate, song type switching rate, song matching, song overlapping, and the usage of specific song types were proposed to be aggressive signals. It is well known that transitions between different song types in a song sequence are non-random in many species, but the signaling significance of non-random vocal streams is poorly understood. We asked whether singing plays a role in male–male interactions in Claudia’s Leaf-warbler. Along with more traditional metrics (i.e., song length, song rate, song type switching rate and song type diversity), we used (1) song sequence linearity (SLIN) and consistency (SCONS) indexes, and (2) applied an information theory approach by means of a first-order relative entropy (RE1) calculation to analyze the role of song type transitional patterns in male–male interactions. The study was conducted in April–June 2016 in Hupingshan National Nature Reserve, Hunan province, China. We simulated territorial intrusion by broadcasting Claudia’s Leaf-warbler songs in territories. Experiments involved 14 different males. A comparison of spontaneous singing with that elicited by playback showed that song rate and song type diversity increased, and that entropy decreased. By contrast, SLIN and SCONS, though significantly correlated with RE1, did not differ between spontaneous singing and singing in response to playback. The decrease of entropy means that the transitions between different song types in a song sequence were determined more by specific factors and predictable and thus more non-random. However, these results were weak, as the decrease of RE1 did not coincide with the expected increase of SLIN, SCONS and S. Our results are thus partly consistent with the idea that non-random vocal structures, along with other song parameters, could play a role in male–male competition.

Conspecific challenges provoke female canyon wrens to sing but not to duet

Song by female birds is rare in some species, particularly at north-temperate latitudes. Nevertheless, female song can carry important signal content and may be used in functional ways, both when sung solo and when combined into partner duets. Evidence supports the idea that duets reflect elevated threat levels because they indicate partner cooperation, but this comes from species with frequent female song and duetting. Here we asked the following questions about infrequently given female song in canyon wrens (Catherpes mexicanus) in Western North America. Do female birds use song in a context that implies functional significance? Do canyon wren mates combine their songs to form duets? Are duets a more threatening signal than non-overlapping dual-sex solo songs? To address these questions, we challenged canyon wrens with paired simulated intruders singing alternating solo songs or duets formed by overlapping male and female songs with consistent timing. Results indicated that female canyon wrens approached and sang in response to conspecific song playback as quickly as males did and increased their song rates significantly. Partners did not overlap their songs to create duets more often than expected by chance, and neither sex responded more strongly to duets than to solo songs. Outcomes match the prediction that duets only carry different signal content from solo song in species that frequently duet, and suggest that canyon wren female song is highly functional despite being rarely used outside of contest situations. Animal signals mediate social interactions in myriad ways. The majority of studies of avian song have focused on conspicuous, frequently given, signals but infrequently given signals may also have important fitness consequences. We examined how the usage of a rare signal, canyon wren female song, changed during contest situations and in response to a coordinated duet versus non-coordinated solo songs. Rates of female song increased significantly during contest situations, but duets did not provoke stronger responses than solos. Although duets are threatening to species that duet (including many wren species), they do not appear to be universally salient. Canyon wren female song, in contrast, carries strong signal content despite being used infrequently outside of contest situations. Results highlight the potential functionality of rare signals, as well as the variability in signaling strategies across avian species.

The effect of early life conditions on song traits in male dippers (Cinclus cinclus).

Song complexity and singing frequency in male birds are shaped by female choice; they signal male quality because song is costly to develop and produce. The timing of song learning and the development of the brain structures involved occur during a period when chicks are exposed to a number of potential stressors. The quality and quantity of song produced by adults may therefore reflect the level of stress experienced during early life, a theory known as the ‘developmental stress hypothesis’. We tested this hypothesis using song recordings and life-history data from an individually marked, long-term study population of wild dippers (Cinclus cinclus). The extent to which early life conditions predict adult song traits was investigated using natal brood size as a measure of sibling competition; the rate of provisioning by parents as a proxy for nutritional stress; and residuals of the linear regression between body mass and tarsus length as a measure of nestling condition. The syllable diversity in the songs of adult males was positively correlated with their body condition as nestlings, but there was no significant correlation with either provisioning rate or brood size. Provisioning rate did, however, predict song rate; males in relatively poor condition as nestlings or those raised in smaller broods which were fed more frequently by their parents sang at a higher rate in adulthood. These results support the developmental stress hypothesis and provide some of the first evidence from a wild bird of how the conditions experienced during early life impact adult song. Song traits may therefore provide females with information regarding both the current condition and developmental history of males.

Sing and do not stray: male rufous-and-white wrens use duets and physical behaviours to guard their mates

In diverse animal taxa, breeding partners coordinate their vocalizations to produce vocal duets. One seldom-studied hypothesis for duets is the paternity guarding hypothesis, which states that male animals create duets to advertise their partner's mated status and minimize extrapair mating attempts between their partner and other males. We experimentally tested the paternity guarding hypothesis in rufous-and-white wrens, Thryophilus rufalbus, a neotropical duetting songbird. We designed a two-part playback experiment: males first experienced a simulated territorial intrusion by a rival male, and were then given opportunities to answer their female breeding partner's songs to create duets. We repeated this experiment during the female's fertile and nonfertile breeding stages. In support of predictions of the paternity guarding hypothesis, male wrens created more duets with their partner's songs during the fertile period compared to the nonfertile period. Additionally, male wrens appeared to physically guard their mates with greater intensity during the fertile period but did not increase their overall song rates, demonstrating that increased duetting rates during the fertile period were a result of a change in male duetting behaviour, rather than a change in song rate. Our study is among the first to experimentally test the paternity guarding hypothesis for duet function, and suggests that male rufous-and-white wrens use both vocal and physical behaviours to guard their paternity.