Singing strategies among male Black-browed Reed Warblers Acrocephalus bistrigiceps during the post-fertile period of their mates

Bird song is critical to mate attraction. Because singing involves fitness costs, males that sing vigorous and complex songs are thought to be of high quality. Males of the Black-browed Reed Warbler Acrocephalus bistrigiceps sang actively when they were solitary, but stopped singing as soon as they had attracted a female. Males exhibited two distinct patterns of singing behaviour after the fertile period of their mates: some resumed singing, whereas others did not. Males that resumed singing acquired secondary females more frequently than those that did not sing, suggesting that resuming males seek polygynous mating. The occurrence of extra-pair fertilization was rare (6.4%) in the study population, and extra-pair young were sired by both resuming and non-resuming males. There is no strong evidence that non-resuming males compensate for their disadvantage in social mate acquisition by extra-pair paternity. Resuming males arrived at the breeding ground earlier, suggesting that they were high-quality males.     

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.     

Do female great tits (Parus major) assess males by eavesdropping? A field study using interactive song playback

Male singing behaviour correlates with extra-pair success in several passerine birds. Singing interactions during territorial contests provide relative information on the males involved. Such information may be important in female extra-pair behaviour and eavesdropping on singing interactions among males may allow females to make such relative assessments. We used interactive playback to instigate singing contests with male great tits during the peak fertile period of their mate in an attempt to alter females'' assessment of mates'' quality relative to neighbours (potential extra-pair partners). We escalated a contest to one male (by overlapping his songs) and then subsequently de-escalated a contest (by alternating) to a neighbour. Intrusions onto neighbouring territories by females mated to either treatment male were then monitored. Females mated to escalation treatment males were more likely to intrude following playbacks than females mated to de-escalation treatment males. Although the absolute song output of males did not differ between treatments, males produced more song relative to playback in de-escalation treatments and relative song output was positively correlated with female intrusions. Therefore, female great tits eavesdrop on singing interactions and change their visitation rates to neighbouring territories according to their mate''s singing performance relative to neighbours.     

Polygyny in Willow Warblers <Emphasis Type="Italic">Phylloscopus trochilus</Emphasis> (Sylviidae,Passeriformes) in Middle European Russia: Differences in songs of polygynous and monogynous males

The study was performed in May to July of 1995 in Middle Russia (Skadovskii Zvenigorod Biostation, MSU, Moscow oblast: 55°44′ N, 36°51′ E). Monoterritorial polygyny was observed in one of seven studied Willow Warbler males Phylloscopus trochilus. The distance between the nests of the first and second females was 90 m. In the nest of the first female, five nestlings hatched on June 10 and the flight of the fledglings occurred on June 23. In the nest of the second female, a 5-to 6-day-old nestling of the cuckoo Cuculus canorus was found on June 18. The male actively participated in feeding the young in the first nest and did not participate in the feeding of the young in the second nest. The songs of the bigamous male differ significantly from the songs of monogamous males in the middle and final parts of the breeding cycle. The song of the bigamous male in the idle and end of the breeding season is similar to that in the beginning of the breeding season. Unmated males in the middle of the breeding season also retain a more permanent structure of their songs in comparison with breeding males. This case of polygyny seems to be related to special characteristics of the males such as their singing activity and the structure of their songs.     

Interspecific song imitation by a Prairie Warbler

Song development in oscine songbirds relies on imitation of adult singers and thus leaves developing birds vulnerable to potentially costly errors caused by imitation of inappropriate models, such as the songs of other species. In May and June 2012, we recorded the songs of a bird that made such an error: a male Prairie Warbler (Setophaga discolor) in western Massachusetts that sang songs seemingly acquired by imitating the songs of a Field Sparrow (Spizella pusilla). Another song type in the bird's repertoire was a near‐normal Group A Prairie Warbler song, but the bird used this song in contexts normally reserved for Group B songs. Despite its abnormal singing behavior, the aberrant bird successfully defended a territory and attracted a mate that laid two clutches of eggs. Results of playbacks of the focal bird's heterospecific song suggested that neighboring conspecific males learned to associate the Field Sparrow‐like song with the focal male, and responded to the song as if it were a Prairie Warbler song. Our evidence suggests that the focal bird's aberrant singing evoked normal responses from potential mates and rivals. If such responses are widespread among songbirds, the general failure of heterospecific songs, once acquired, to spread through populations by cultural transmission is probably not attributable to a lack of recognition by conspecifics of the songs of heterospecific singers.     

A Test of the Effect of Male Song on Female Nesting Behaviour in the Serin (Serinus serinus): a Field Playback Experiment

It is well established, through laboratory experiments, that male song in birds can stimulate female reproductive activity, affecting their behaviour and physiology, such as follicular growth, nest building and egg‐laying. However no clear demonstration has yet been provided that this effect works under natural conditions. Previous work in natural populations of serins showed that female nest‐building behaviour correlated with male singing time. Furthermore male serin song peaked exactly in the day that rapid follicular growth was estimated to start in females, suggesting that in this species song may also serve to stimulate the female's reproductive development. Direct causal evidence, however, was lacking. We conducted field playback experiments to investigate how song can influence female nesting activity during nest building. Our results show that females who listened daily to playbacks of serin songs, during the nest‐building stage, spent more time nest building than females that were not exposed to additional songs. Moreover, the singing behaviour of the mated males was not affected by the playbacks, suggesting that the song playback treatment had a direct positive effect on female nesting behaviour.     

Wing shape variation of Finnish and Central European Willow Warblers Phylloscopus trochilus and Chiffchaffs P. collybita

Wing shape variation of European Willow Warblers Phylloscopus trochilus and Chiffchaffs P. collybita was studied using indices calculated from wing formulae. Our data were from free-living local populations of P. t. acredula and P. c. abietinus from southern Finland, and P. t. trochilus and P. c. collybita from southwestern Germany.
There were no significant shape differences between the subspecies of the Willow Warbler in which sexual dimorphism was pronounced. The subspecies of the Chiffchaff were significantly different while the sexes were not. There were also significant differences between adult and immature individuals in the autumn. The intrapopulation variation must be considered in attempts to recognize different subspecies or populations in data on birds caught during migration.
In the Willow Warbler at least, the difference between age-groups was larger in males than in females. If the change in wing formula due to the complete pre-nuptial moult is similar in both sexes, juvenile males intermediate between adult females and adult males suffer disproportionately high mortality. It was earlier suggested that sexual selection increases body size in Willow Warbler males, but the present results imply additional selection pressures for increasing sexual dimorphism.     

The presence of non-territorial males in Willow Warbler Phylloscopus trochilus populations–a removal study

A total of six (unmarked) and 24 (individually colour-ringed) male Willow Warblers Phylloscopus trochilus were removed from their territories in two study areas: subalpine birch and lowland mixed forest, respectively. The removals were made during three separate periods throughout the breeding season: (1) pair-formation and egg-laying; (2) early incubation; and (3) middle and second half of the incubation period. During Period 1 all of the males removed ( n = 10) were quickly replaced by new males, while during Period 2 eight of the 11 males removed were replaced. The new males defended basically the same territorial borders as the males they replaced. During Period 3 only one of the nine males removed was replaced. Since the replacements occurred within a few hours of the removals, it is suggested that the new settlers were non-territorial males that were already present in the respective areas before the experimental removals were made. The mean wing-lengths of the two groups of males indicated that the initial occupants of the territories were 2 years old or older in both study areas, whereas the new settlers in the subalpine birch forest (mean Willow Warbler density: 55 territories/km²) were 1-year-old birds, and two years old, or older, in the mixed forest area (mean Willow Warbler density: 133 territories/km²).     

BIOACOUSTICS IN NEW ZEALAND AND JAPAN

Although it is highly recognisable, relatively little is known about the repertoire composition and singing behaviour of the Hermit Thrush (Catharus guttatus). To address this, we recorded spontaneously singing males in two eastern populations (Halifax, NS (n = 11) and Hancock County, ME (n = 7)) and analysed the recordings with respect to repertoire size, basic song type characteristics and song syntax. Males had song type repertoires of 7–12 song types, and no song type sharing between individuals was observed within or between populations. While frequency-related structural characteristics of the song types were the same between the populations, song type duration (especially that of the introductory note) differed significantly. The song types within each repertoire could be categorised into high and low song types based on introductory note frequency, and these song type categories also differed with respect to the amount and distribution of spectral energy. In both populations, males sang with immediate variety, never repeating the same song type consecutively, and preferentially used some song-type to song-type transitions more than others. In addition, we found correlational evidence of changes in singing behaviour (e.g., the relative use of low versus high song types) over the course of the breeding season. We discuss these findings in the context of other songbird research as well as their implications for future work examining how Hermit Thrush males utilise their songs in defending territories and attracting mates.     

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.     

Microhabitat use and feeding strategies of the Pied Flycatcher and the Willow Warbler in their West-African winter quarters compared with resident species

Salewski, V. 2000. Microhabitat use and feeding strategies of the Pied Flycatcher and the Willow Warbler in their West-African winter quarters compared with resident species. Ostrich 71 (1 & 2): 191–193.

Habitat choice, microhabitat and foraging behaviour of the palaearctic Pied Flycatcher and Willow Warbler are described in their West-African wintering areas and are compared with those of resident species. The migrants were more flexible in habitat choice and foraging techniques, but in general did not feed in more open habitat.     

Dawn singing of the Brownish‐flanked Bush Warbler influences dawn chorusing in a bird community

Despite numerous studies on the function of the avian dawn chorus, few studies have examined whether dawn singing may influence the singing of other species. Here, we built on our previous study which found male Brownish‐flanked Bush Warblers (Horornis fortipes) increase their dawn singing intensity after conspecific playback on the previous day. We reanalyzed those recordings to quantify the start of dawn singing in other nine sympatric songbird species. Ranking‐scaling analyses identified a distinctive sequential pattern of dawn singing among these bird species between the first and the second dawn chorus, and meta‐analysis showed a significant trend to singing earlier in the bird community accompanied by the increase in dawn singing intensity in Brownish‐flanked Bush Warbler. Species with songs most similar to that of the Brownish‐flanked Bush Warbler and species that were phylogenetically distantly related to the Brownish‐flanked Bush Warbler showed a greater shift in the onset of dawn singing. Our study is one of the few studies showing how bird song influences heterospecific singing, and this may influence the temporal organization of song activity in the community, and result in synchronization in singing activities among different species, such as singing in dawn and dusk chorus.     

Song matching in a long-lived,sedentary bird with a low song rate: The importance of song type,song duration and intrusion

Territorial songbirds often match the song features or singing patterns of rivals, commonly as an aggressive signal. Most studies of song matching have been on Northern Hemisphere species with short lifespans and high song rates, but vocal matching is predicted to be affected both by longevity and territorial stability. We studied song matching in males of the white-browed scrubwren, Sericornis frontalis, a long-lived, sedentary, territorial Australian songbird. We quantified natural song rate and diversity, and then conducted three playback experiments to test: (a) whether males match by song type; (b) how they respond physically and vocally to territorial intrusion; and (c) whether they match by song length, and use it as an agonistic signal. Males naturally had very low song rates, singing on average less than three times per hour, and moderate repertoires, with an estimated mean of 17.5 song types for individual males. Males did not engage in extended counter-singing bouts. The first experiment showed that males matched the song type of immediate neighbours almost 90% of the time, if that type was in their repertoire. The remaining experiments revealed that song-type matching was an aggressive signal; males responded more aggressively to, and were more likely to match, playback simulating a neighbour's territorial intrusion than song from their shared boundary. Males did not match songs by length, but they produced longer songs after simulated intrusion. Males also responded more aggressively to playback of longer songs that simulated intrusion, but less aggressively to longer songs from the territory boundary. Overall, we show that sedentary, long-lived songbirds with low song rates, can use song-type matching as an aggressive signal to communicate with neighbours and intruders. Song length had a different role in communication, possibly related to individual quality or territory ownership.     

Innate differences in singing behaviour of sparrows reared in isolation from adult conspecific song

Innate differences in the singing behaviour of male swamp (Melospiza georgiana) and song (M. melodia) sparrows were identified by rearing males from the egg in the laboratory under identical conditions, in complete isolation from adult conspecific song. Isolation-reared males of both species displayed several abnormal song features, including reduced numbers of notes per song, longer durations of notes and inter-note intervals, and fewer notes per syllable. Despite these and other abnormalities, many species differences emerged that matched differences in the natural singing behaviour of the two species. These included differences in song repertoire size, song duration and degrees of segmentation, numbers of notes per song, durations of notes and inter-note intervals, and several measures reflecting the organization of songs into note complexes, syllables and trills. Although learning can influence all levels of organization of the motor patterns of song in swamp and song sparrows, its contribution to the achievement of normal song behaviour appears to be most crucial at the level of the fine structure of the notes and syllables from which the songs are constructed.     

THE SINGER AND THE SONG: ON THE RECEIVING END OF BIRD SONG

Variation in singing behaviour between males can involve fixed differences such as the song type composition of repertoires, as well as more flexible effects such as matched counter-singing (Krebs & Kroodsma, 1980; Section III. 4), differences in bout length (the number of songs in a period of song) and changes in strophe length. Short-term strophe length changes seem to be related to the willingness and ability of males to respond strongly to playback. Whether this is because strophe length indicates motivation or the degree of exhaustion of the neuromuscular song-production system, or both, is currently unclear.     

Dawn chorus and female behaviour in the Willow Tit Parus montanus

We studied the effect of female behaviour on the dawn chorus of Willow Tits Parus montanus. Ten females were temporarily kept in their nest holes in order to delay their dawn emergence. Simultaneously, their mates' singing behaviour was measured. We compared the control dawn behaviour (during which the females emerged when they wanted) with that during the experimental delay. The dawn song by the males lasted longer when the females' emergences were delayed. Our results show that the duration of the dawn chorus is directly related to the female's behaviour. We suggest that at least one function of the dawn song is intrapair signalling, which is often linked to sperm competition.     

Variation of song and plumage in the western (Phylloscopus trochiloides viridanus) and eastern (Phylloscopus trochiloides plumbeitarsus) forms of the greenish warbler in a sympatry zone: Is the hypothesis of ring speciation true?

The Greenish Warbler is a classical example of ring speciation in birds. Typical ring species are supposed to form a chain of intergrading populations encircling a geographic barrier, and the terminal forms in the secondary contact coexist without interbreeding. The Western (Phylloscous trochiloides viridanus) and Eastern (Phylloscous trochiloides plumbeitarsus) forms are considered to be a terminal taxa that come into secondary contact. The morphology and song characteristics of these forms in the zone of sympatry in southern Siberia were studied. The vocalization of 133 males from 13 localities was studied. In the zone of sympatry, the population of the Greenish Warbler is polymorphic. Only 30 of 66 birds were typical plumbeitarsus. The phenotypes of the other birds appeared to be intermediate between two taxa. No break of vocal characteristics in the sympatry zone was found. Thirty-one males had a typical ??east?? song. Vocalization of the other 12 males corresponded to a greater extent to the ??west?? singing. Both phonetic and syntactic features of the Greenish Warbler??s songs in the zone of sympatry show the presence of gradual and smooth transition in vocalization between two forms. Playbacks of viridanus never elicited a response within the allopatric plumbeitarsus populations, whereas playbacks of viridanus brought on strong or medium responses of some plumbeitarsus in the zone of sympatry. In the zone of sympatry, the convergence of viridanus and plumbeitarsus according to morphological and acoustic characteristics takes place. The data obtained do not confirm the concept of ring speciation in the Greenish Warbler.     

Socially cued anticipatory adjustment of female signalling effort in a moth

Juvenile population density has profound effects on subsequent adult development, morphology and reproductive investment. Yet, little is known about how the juvenile social environment affects adult investment into chemical sexual signalling. Male gumleaf skeletonizer moths, Uraba lugens, facultatively increase investment into antennae (pheromone receiving structures) when reared at low juvenile population densities, but whether there is comparable adjustment by females into pheromone investment is not known. We investigate how juvenile population density influences the ‘calling'' (pheromone-releasing) behaviour of females and the attractiveness of their pheromones. Female U. lugens adjust their calling behaviour in response to socio-sexual cues: adult females reared in high juvenile population densities called earlier and for longer than those from low juvenile densities. Juvenile density also affected female pheromonal attractiveness: Y-maze olfactometer assays revealed that males prefer pheromones produced by females reared at high juvenile densities. This strategic investment in calling behaviour by females, based on juvenile cues that anticipate the future socio-sexual environment, likely reflects a response to avoid mating failure through competition with neighbouring signallers.     

The effect of neighbours and females on dawn and daytime singing behaviours by male chipping sparrows

Bird song may play an important role for communication among territorial neighbours, but the effect of neighbours on song use is still not well known. My previous field observations suggested that male chipping sparrows, Spizella passerina, use the dawn chorus for interactions among neighbouring males, and use day song for female attraction. To determine how these social factors may influence dawn and daytime singing behaviour, I conducted a series of experiments in which I removed the male neighbours or the female mate of territorial males during 1998-2000. Following removal of all neighbouring males, the solitary male either stopped or reduced his dawn chorus (N=9), but did not change his daytime singing behaviour. After one of the neighbouring males was returned to his territory, the focal male resumed and increased his dawn bout, accompanied with close-range countersinging. Following the removal of a territorial male's mate, the widowed male did not change the dawn chorus, but significantly increased his day song. This study thus revealed that, in chipping sparrows, the presence or absence of neighbouring males has a significant effect on the dawn chorus singing behaviour of territorial males. The presence or absence of a male's mate, in contrast, has a strong influence on a male's daytime singing behaviour. This study also supports the hypothesis that the dawn chorus and daytime song have different functions.     

Sedentary life style of Neotropical sedge wrens promotes song imitation

To what extent has the style of song development among songbirds coevolved with other life history strategies? Among Cistothorus wrens in North America, it seems that sedentary or site-faithful habits of marsh wrens, C. palustris, favour song imitation, but seminomadic habits of sedge wrens, C. platensis, favour song improvisation, whereby each male generates a large but unique song repertoire. In this study, we tested whether more sedentary populations of sedge wrens in the Neotropics would imitate songs. At our primary study site near Cartago, Costa Rica, breeding birds were colour-banded during 1995 and 1996, and follow-up surveys revealed that the birds remained at this site the year round. Extensive tape recording and analysis of songs showed that males had large song repertoires (200-300+ songs), and that many songs were shared among neighbouring males. In addition, males only 27 km distant, at La Pastora, used different songs. Furthermore, matched countersinging, in which two males answer each other with identical song types, was recorded near Brasilia, in Brazil. The sharing of songs among permanent neighbours, microgeographical variation in song, and matched countersinging can be achieved only through song imitation, thus revealing a striking difference in the style of song development among different populations of the sedge wren. In the Neotropics, having predictable neighbours throughout life appears to have favoured song imitation, so that individuals can interact using a common, learned code typical of the local population; among more mobile populations in North America, however, individuals improvise large repertoires of species-typical songs, thereby enabling singing males to communicate with any individual, no matter what the population of origin. Strategies of song development must correlate with life history features, and further surveys are needed to make sense of the great diversity of singing behaviours among songbirds. Copyright 1999 The Association for the Study of Animal Behaviour.