Patterns of dawn singing by Buff-breasted Flycatchers

ABSTRACT.   Many passerine species exhibit a "dawn chorus"—a bout of intense singing activity before or at dawn, but our understanding of this phenomenon is poor. Tyrant flycatchers (Tyrannidae) exhibit pronounced daily bouts of dawn singing. I documented this behavior in several populations of Buff-breasted Flycatchers ( Empidonax fulvifrons ) in Arizona, tape recording >30,000 songs of 23 individuals during dawn singing. Individual males sang a dawn bout each morning, even during breeding phases when daytime song was almost completely absent. Dawn bouts began 5–10 min before local civil twilight and continued for 25–30 min. Each male possessed two song types delivered at high rates during dawn singing (four times the rate during sustained daytime singing). Song rate varied significantly over the course of dawn bouts, increasing to 55 songs / min at mid-bout, then declining to the end of the bout. Type 2 songs comprised about 30% of songs during dawn singing, and decreased significantly in proportion during the final 10 min of the bout. Songs of the two types were delivered in a nonrandom fashion. Males sang at locations near territory boundaries and pairs of neighbors engaged in counter-singing from the same locations each morning. A number of dawn singing bouts ended with attempted or successful copulations. These observations are consistent with the social dynamics hypothesis for the functional significance of dawn singing in this species.     

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

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

Conveying information with one song type: changes in dawn song performance correspond to different female breeding stages

Many bird species participate in dawn singing, a behaviour categorized by intensive singing at dawn; however, many of these species deliver only one song type at dawn. While there are many proximate and ultimate hypotheses for why birds sing at dawn, little is known about whether males are able to vary one simple song to convey different information. We used autonomous acoustic recorders to record dawn songs of field sparrows and quantified three parameters of singing performance: 1) bout length, 2) song rate, and 3) song complexity. We found that males sang the longest dawn bouts during their mate's fertile period, the highest song rates during the post-fertile period, and the most complex songs during the pre-fertile period. The change in dawn singing behaviour with their mate's breeding stage suggest the purpose of dawn song may be context dependent. Our results demonstrate that male field sparrows, while only having a single song type sung at dawn, may convey information for both intra- and intersexual purposes. While it is generally assumed that dawn song has a specific function, the variability in the duration, rate, and complexity of dawn song in field sparrows suggests that they are conveying different information and that dawn song likely has multiple functions.     

Responses of a sub-oscine bird during playback: effects of different song variants and breeding period

Vermilion flycatchers (Pyrocephalus rubinus) vary their song rate and song length across the breeding season. Males sing more and longer songs after nest construction than before. Here we explored the possibility that this variation is meaningful to territorial males. Using a playback approach, we tested several males with different variations in song output (i.e. variations in song length and song rate) in different periods of the breeding season (i.e. before and after the onset of nest construction). We found that males call more in response to playbacks of long and short songs before the onset of nest construction. However, after nest construction began they responded flying more when exposed to long songs than to short songs. These results show that vermilion flycatcher discriminates between different variants of song length, and suggest that males react to long songs as if they were more threatening signals than short songs, especially after the onset of nest construction. We did not find evidence of males discriminating between a high and a low song rate. We discuss some possible implications for song function in this sub-oscine species, and compare these findings with other results in oscine species.     

Sexual Selection and Information Content in Gibbon Song Bouts

Male and female gibbons (Hylobates) produce sexually dimorphic song bouts which appear to serve to guard mates and defend territories respectively. On the basis of differences in both the familiarity and the costs of conflict between sender and receiver, males but not females are hypothesized to use high-energy assessment signals to advertise resource-holding potential. This hypothesis is tested by examining the evidence for differential energy constraints in the production of male and female song bouts across 21 gibbon populations. The results indicate that song performance is reduced when the availability of high-energy foods is reduced and that this effect is greatest in males. Male song bout frequency also declines in populations where the energetic costs of thermoregulation are likely to be greater (i.e. in high-latitude populations). Females do not show this pattern. Females appear to perform the minimum number of songs per bout required for signal transmission and may perform bouts less often when more songs are required. In contrast, males sing for longer periods the more frequently bouts are performed. Overall, these results support the hypothesis that the song bouts of males but not females act as assessment signals. Observational and experimental studies which would provide a more powerful test of this hypothesis are briefly outlined.     

Dawn song of male blue tits as a predictor of competitiveness in midmorning singing interactions

During the dawn chorus, territorial male songbirds vocalise intensively within signalling range of several conspecific males and can therefore be considered members of a busy communication network. The more or less continuous singing over a long period of time under standardised stimulus conditions makes the dawn song a potentially important information source both for simple receivers and for eavesdroppers. Male blue tits (Parus caeruleus) vary in features of their dawn song, e.g. older males sing longer strophes, and females choose males that sing longer strophes as extra-pair partners. However, so far, dawn song in the blue tit has been investigated separately from other singing behaviour of the same males. In this study, we investigate aspects of blue tit male quality, reflected in dawn song characteristics, and their predictive value for how males behave during singing interactions later in the morning. We acted as simple receivers by recording the singing activity of one male at a time at dawn and compared features of its dawn song, such as onset before sunrise, repertoire size, mean bout length, strophe length and percentage performance time to responses of the same male to a territory intrusion simulated by playback of synthesised songs later during the same morning. We assume that an aggressive response towards an intruder will involve a fast approach to the loudspeaker broadcasting strophes of blue tit song, searching for the intruder (flying around), and a high amount of counter singing and overlapping of the intruders songs. Aspects of vigour of response to the simulated intrusion could be predicted from all five investigated dawn song parameters as well as male age. This is, to our knowledge, the first indication that a simple receiver could extract reliable information from a males dawn singing behaviour about its competitiveness later in the day.Communicated by P.K. McGregor     

The song structure and seasonal patterns of vocal behavior of male and female bellbirds (Anthornis melanura)

The bellbird (Anthornis melanura) is a honeyeater endemic to New Zealand, which uses song to defend breeding territories and/or food resources year round. Both sexes sing and the song structure and singing behavior have not yet been quantified. The number of song types, spectral structure, repertoire size, and singing behavior of male and female bellbirds was investigated for a large island population. Song types differed between the sexes with males singing a number of structurally distinct song types and females producing song types that overlapped in structure. Singing behavior also differed between the sexes; males often sung long series of songs while females sung each song at relatively long and variable intervals. Singing by both sexes occurred year round but the frequency of male and female singing bouts showed contrasting seasonal patterns. The frequency of female singing bouts increased as the breeding season progressed, whereas male singing bouts decreased. In contrast to almost all studied passerines, female bellbirds exhibited significant singing behavior and sung songs of complex structure and variety that parallel male song. These results provide a quantitative foundation for further research of song in bellbirds and in particular the function of female vocal behavior.     

Matched Counter-singing Signals Escalation of Aggression in Black-capped Chickadees (Parus atricapillus)

Black-capped chickadees (Parus atricapillus) have the ability to shift their songs up and down over a wide range of absolute frequencies. Males can shift their songs over 465 ± 52.9 (SE) Hz. During the dawn chorus, males shift their songs by 80 Hz or more every 41 ± 8.8 (SE) songs, but it appears that males can sing at any frequency within their range. Frequency shifting may allow males to match counter-sing with rival males; that is, to switch song output to match that of a rival. During simultaneously recorded dawn choruses, however, there was no correlation over time in the frequency of neighbouring males' songs, nor was there a correlation over time in the size of shifts between their songs. Moreover, males did not match the frequencies of songs presented on a played-back tape at the edge of their territories during the dawn chorus. Matching was observed during some bouts of counter-singing between males. In these cases, matched counter-singing was highly associated with escalation of the conflict. We suggest that frequency matching in this species may be a graded signal that allows the singer to direct aggression towards a particular rival.     

The anti-exhaustion hypothesis: a new hypothesis to explain song performance and song switching in the great tit

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.     

Rufous‐capped Warblers Basileuterus rufifrons show seasonal,temporal and annual variation in song use

In the majority of songbird species, males have repertoires of multiple song types used for mate attraction and territory defence. The wood‐warblers (family Parulidae) are a diverse family of songbirds in which males of many migratory species use different song types or patterns of song delivery (known as ‘singing modes’) depending on context. The vocal behaviour of most tropical resident warblers remains undescribed, although these species differ ecologically and behaviourally from migratory species, and may therefore differ in their vocal behaviour. We test whether male Rufous‐capped Warblers Basileuterus rufifrons use distinct singing modes by examining song structure and context‐dependent variation in their songs. We recorded multiple song bouts from 50 male Warblers in a Costa Rican population over 3 years to describe seasonal, diel and annual variation in song structure and vocal behaviour. We found that Rufous‐capped Warbler songs are complex, with many syllable types shared both within and between males’ repertoires. Males varied their song output depending on context: they sang long songs at a high rate at dawn and during the breeding season, and shortened songs in the presence of a vocalizing female mate. Unlike many migratory species, Rufous‐capped Warblers do not appear to have different singing modes; they did not change the song variants used or the pattern of song delivery according to time of day, season or female vocal activity. Our research provides the first detailed vocal analysis of any Basileuterus warbler species, and enhances our understanding of the evolution of repertoire specialization in tropical resident songbirds.     

Song type switching in the chaffinch, Fringilla coelebs : timing or counting?

The song of many bird species is relatively constant in form, yet each bird has more than one song type, making it an excellent model for studies of the mechanisms underlying switching between behaviour patterns. The chaffinch is a good example. Males sing with eventual variety, repeating each song type in the repertoire a few times before switching to another type. The mechanism triggering these switches is not known. We investigated long continuous recordings of spontaneous singing by six wild males to test two hypotheses: (1) that a maximum number of repetitions limits bout length; or (2) that a switch occurs after a song type bout reaches a maximum duration ('time window'). Strong evidence was found for a temporal limitation: song type bouts with many repetitions were delivered only at a fast rate, whereas bouts consisting of few songs were delivered either fast or slow. Copyright 1999 The Association for the Study of Animal Behaviour.     

Calling in wild silvery gibbons (Hylobates moloch) in Java (Indonesia): behavior, phylogeny, and conservation

Hardly any behavioral data are available for the silvery gibbon (Hylobates moloch), an endangered primate that is endemic to the island of Java, Indonesia. We studied the singing behavior of the easternmost population of this species in the Dieng mountains, central Java, in 1998-1999. We aimed to document the timing of singing, quantify the amount of singing by the respective sexes, and explore the role of bioacoustics in density estimation. A total of 122 song bouts in at least 12 groups were monitored. No duet songs were heard. Most of the song bouts (91.5%) were female solo song bouts or female scream bouts. In contrast to an earlier study on the westernmost population of silvery gibbons, during which few if any male songs were heard, at least 8.5% of the song bouts in our study were male solo song bouts. They were significantly longer in duration than the female songs. All male song bouts uttered before dawn (0520 hr) were produced in a chorus fashion, with at least three individuals participating. Choruses occurred about once every 8.5 days, and lasted longer and occurred earlier than female solo song bouts. Most male songs (60%) started between 0355-0440 hr, when it was still dark. All female songs, in contrast, started after 0500 hr, and female singing activity peaked around 0600. Regular male singing, male chorusing, and regular predawn singing have not previously been reported for silvery gibbons. Similarly separated periods of male and female solo songs and the absence of duetting have been observed in Kloss's gibbons (H. klossii) on the Mentawai Islands, and may represent synapomorphies shared by both species. The pronounced individual-specific song characteristics of silvery gibbons allow accurate mapping of groups. The density of gibbons at our study site was established to be 1.9-3.7 groups/km2, corresponding to 6.7-13.1 individuals/km2. We reassess the suitability of gibbon songs as a means of estimating the density and size of gibbon populations, and discuss the proximate causes for the absence of duetting in silvery gibbons.     

Long-term influence of simulated territorial intrusions on dawn and dusk singing in the Winter Wren: spring versus autumn

Males of many songbird species have peaks of singing activity at dawn and dusk. Singing during those twilight periods can function in territory proclamation, and males are suggested to adjust song output to the level of intruder pressure. We used song playback during the breeding season to simulate intrusions into territories of male Winter Wrens (Troglodytes troglodytes) shortly after dawn. We then compared male singing behaviour during the dawn and dusk chorus before and 1 day after the simulated intrusion. One day after the playback, male Wrens increased their song output before sunrise, which confirms our results from a previous study on dawn singing in autumn territories. At dusk, on the evening following the playback, males slightly increased song output after sunset, but singing activity at dusk was generally very low. We found no significant changes of song output after sunrise, before sunset, and between 2 days of control without playback. These results are consistent with the hypothesis that dawn and dusk singing is important for territory defence in spring. Unlike in autumn, however, increased singing in spring at dawn and dusk could also serve to defend other resources such as fertile mates or to strengthen the pair bond after a territorial challenge. In comparison with the results on autumnal singing, male Wrens started singing earlier at dawn during the breeding season, and they generally sang more songs at dawn and immediately after playback. The increase in absolute numbers of songs sung in the morning after playback seemed greater in spring than in autumn; however, the proportional increase relative to overall song output was similar in both seasons.     

Female European starling preference and choice for variation in conspecific male song

Data from several field studies support the hypothesis that female European starlings, Sturnus vulgaris, attend to variation among the songs of conspecific males when making mate-choice decisions. However, for a variety of methodological reasons, direct evidence for female preferences based on song in starlings has been lacking. This study presents a novel technique for assaying directly female preference and choice in European starlings by using the presentation of conspecific male song as an operant reinforcer in a controlled environment. Using an apparatus in which the playback of songs from different nestboxes is under the operant control of the subject, we demonstrate how the reinforcing properties of conspecific song can be used to measure female preference and choice. The results of the study suggest three conclusions. First, female starlings prefer naturally ordered conspecific male songs over reversed songs. Second, female starlings display robust preferences for longer compared with shorter male song bouts. Behaviour in the operant apparatus varied directly with male song bout length. Third, preferences based on song bout length are sex specific. Male starlings failed to respond differentially to the same stimuli for which females showed strong preferences. These results suggest that male-male variation in song bout length is important for mate choice among starlings. In addition, we detail the use of a novel behavioural assay for measuring female preferences that can be applied to similar behaviours in other species of songbirds. Copyright 2000 The Association for the Study of Animal Behaviour.     

Male House Finches with Elaborate Songs have Higher Reproductive Performance

The elaborate songs of male animals are thought to function in either territory defense (male–male communication) or mate attraction (male–female communication). In non‐territorial animals, male vocalizations are expected to function primarily in mate attraction, yet the reproductive consequences of male vocalizations in non‐territorial animals are poorly described. Here we explore the relationship between male song and male reproductive performance in a free‐living population of house finches, Carpodacus mexicanus, a non‐migratory, non‐territorial songbird. Based on recordings of 20 males, we analyzed three song features (song length, number of unique syllables per song, and song rate) and compared male song with two measures of within‐pair reproductive performance (nest initiation date and clutch size) and one measure of extra‐pair reproductive performance (whether males sired extra‐pair young). We demonstrate a positive association between male song and within‐pair reproductive performance; males that sang long songs initiated their first clutch significantly earlier and males that sang songs at a faster rate had larger clutches. Despite the fact that only one of our recorded males sired extra‐pair young in the nest of another male, this male's songs were the most elaborate for two of three song features measured, anecdotally suggesting that male song may play a role in both within‐pair and extra‐pair partner choice. These results suggest that male song is a sexually selected trait in non‐territorial house finches.     

Sound Spectrum Characteristics of Songs of Hainan Gibbon (Nomascus hainanus)

Gibbons are characterized by their species-specific calls, or songs. There are few studies of songs of Hainan gibbon (Nomascus hainanus). To study the sound spectrum characteristics and test for intergroup differences in Hainan gibbon song, we studied the singing behavior of Hainan gibbons in Bawangling National Nature Reserve, Hainan Province, China, intermittently from August 2002 to February 2013, collecting 184 recordings. Our results show that: 1) Hainan gibbon song bouts occur mainly 0–4 h after dawn. 2) The songs of adult males living in groups are composed mainly of one to three short notes and one to five long notes, while solitary adult male songs consist only of long frequency modulated notes and no short or single notes. 3) The song chorus is dominated by adult males, while females add a great call. Males do not have a great call, unlike those in other gibbon species. There are no female solos. 4) The sound spectrum frequency is similar in adult males living in two different groups, but the duration of the first long note differed significantly between the groups. The sonic frequencies of male and female songs are lower than those of other gibbons: no more than 2 kHz. Hainan gibbon sound structure is simple, although females participate in the chorus, reflecting their primitive status among gibbon species.     

No overlap in song repertoire size between yearling and older Starlings Sturnus vulgaris

We recorded the song of 25 male Starlings Sturnus vulgaris to investigate differences in song characteristics between yearling and older males. Older males had significantly larger repertoire sizes and sang significantly longer average song bouts than yearling males. Since older males had almost twice as large a repertoire size as yearling males and since there was no overlap in repertoire size between yearling and older males, our data indicate that the repertoire size of Starlings increases after the first year of life. The largest difference between yearling and older males occurred in the 'variable song types' which are the song types containing most of the heterospecific imitations sung in a song bout.     

The Dawn Song of the Blue Tit Parus caeruleus and its Role in Sexual Selection

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.     

Complementary neural systems for the experience‐dependent integration of mate‐choice cues in European starlings

Choice of a particular mate phenotype may arise out of experience with the very phenotypes under consideration. Female European starlings (Sturnus vulgaris) prefer males that sing predominantly long‐bout songs over males that sing predominantly short‐bout songs, and thus, song‐bout length is a phenotypic parameter instrumental in releasing the female's mate choice. The preferred long‐bout songs induce higher expression of the immediate early gene (IEG) ZENK in the female auditory telencephalon than short‐bout songs do, but this sensitivity to song length depends on the female's recent song experience. Here, we compared the experience‐dependent modulation of ZENK with that of another IEG, FOS, and report that ZENK and FOS expression in the caudomedial mesopallium and caudomedial nidopallium show different modulation properties that complement natural variation in song‐bout length. As reported previously, ZENK expression was greater in response to novel long‐bout than to novel short‐bout songs following a 1‐week experience with long‐bout but not short‐bout songs. In contrast, FOS expression was greater in response to novel long‐bout than to novel short‐bout songs following a 1‐week experience with short‐bout but not long‐bout songs. Thus, the ZENK and FOS signaling pathways are made sensitive to variation in song length by experiences with songs at opposite ends of the starling song‐variation continuum, suggesting the presence of complementary neural systems made sensitive in register with the natural axis of phenotypic variation fundamental to the female's mate choice. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2005     

Understanding the function of nocturnal song in ovenbirds: males do not countersing at night

Many diurnal bird species vocalize at night, however the function of nocturnal song is, generally, still poorly understood. Previous research has suggested that nocturnal song may serve a social function and is influenced by environmental factors. To test whether males attend to the nocturnal song of conspecifics, we experimentally exposed ovenbirds Seiurus aurocapilla to nocturnal flight songs, and recorded their response both during the night and during the following dawn chorus. We compared latency to song and vocal output before and after playback exposure to determine if males altered their vocalizations in response to exposure to flight songs from an unknown male. We found no evidence of counter singing or change in nocturnal song output, nor a change in vocal output during the dawn chorus following playback exposure. Our results suggest that, in ovenbirds, nocturnal song does not serve as an intraspecific social function. Nocturnal song, through rare, may be significant in the mating systems of some diurnal bird species, and requires additional study.