Strophe Length in Spontaneous Songs Predicts Male Response to Playback in the Hoopoe Upupa epops

Hoopoe (Upupa epops, Coraciformes) males produce a very simple song during the breeding season in order to attract females and repel intruders. Strophes vary in length (i.e. number of elements) both within and between males, and previous studies have shown that this song cue is positively correlated with male condition and breeding success. In the present study we tested whether strophe length of males influences male behaviour during intra‐sexual contests, in a colour‐ringed population in southeast Spain. Paired males were presented with a recorded song with long strophes during the pre‐laying period, while they were near their mates, in order to provoke male mate‐defence behaviour. Most males responded to the playback, but the strategy of defence adopted depended on their own strophe length in spontaneous songs recorded before the experiments. While singing responses were common to most of the males, only those using long strophes adopted the most risky strategy of approaching the loudspeaker. However, the males that approached produced abnormal songs during playback, that were shorter and with fewer strophes than those of males that did not approach, and used shorter strophes in comparison with spontaneous songs before the experiment. These differences in quality of the song produced in response to the playback suggest that long‐strophe males were basing their response mainly on attacking rather than singing, while short‐strophe males tried to resolve the contest at a distance by means of their song. These results show that strophe length reflects some component of the competitive ability of males (either physical strength or aggressiveness) in the hoopoe, which together with previous results regarding its role for female choice, show that it is a sexual signal with dual function.     

Song strophe-length and reproductive success in a non-passerine bird, the Hoopoe Upupa epops

Hoopoe Upupa epops males produce a very simple song, with a repertoire size of one, in which the main difference between different strophes of a male and between the songs of different males is the number of elements they include (strophe-length). In several passerine species it has been shown that strophe-length is a sexually selected trait that reflects male quality and correlates with reproductive success. Here we analyse whether in a non-passerine, the Hoopoe, strophe-length of males is correlated with several variables of their reproductive success. Females paired with males singing long strophes laid their first clutch earlier, produced larger first clutches and laid second clutches after a successful first one more frequently than those paired with males singing short strophes. Moreover, males with long strophes produced more fledglings in their first clutches and in the whole season, partly because they brought more food for the brood than males with short strophes. The relationships found are not mediated by age effects. Previously we have shown that Hoopoe females in the early spring are attracted preferentially to songs with long strophes. Here we show that males singing long strophes also obtain postpairing benefits in terms of reproductive success, and that females paired with these males obtain direct benefits because these males provide greater feeding effort in the second half of the nestling period. These findings support the hypothesis that in the Hoopoe, strophe-length is a sexually selected cue under direct selection.     

Song structure in the Hoopoe (Upupa epops) — Strophe length reflects male condition

Summary The structure of Hoopoe (Upupa epops) song is analysed in a colour ringed population in southern Spain. The song of males in this species is very simple, with a repertoire size of one. The strophes of a male only differ in the number of elements that they include (strophe length), and strophe length is the main song feature differing between males. During the prelaying period each individual used mainly strophes of only two lengths, between 2 and 6 elements per strophe, and mean strophe length of males during this period was highly repeatable. However, some males changed the range of strophe types produced and decreased their mean strophe length after unsuccessful breeding or spending long periods of time singing (unpaired males). These changes show that strophe length is phenotypically plastic, and suggest that singing long strophes is energetically more costly than singing short ones. The significant relationship between strophe length and body condition, and the fact that long strophes were associated with longer previous pauses than short strophes, also suggest that increasing strophe length is costly. All these findings are in accordance with the hypothesis that strophe length reflects male condition in the Hoopoe, although it is not clear what the actual cost of singing long strophes is.

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Struktur des Gesangs des Wiedehopfs (Upupa epops) — Strophenlänge reflektiert Männchen-Qualität

Zusammenfassung Die Struktur des Gesangs des Wiedehopfs wurde in einer farbberingten südspanischen Population untersucht. Der Gesang des Männchens ist sehr einfach und umfaßt nur ein Repertoire. Die Strophen eines Männchens differieren nur in der Anzahl Elemente (Strophenlänge), und die Männchen unterscheiden sich vor allem in der Strophenlänge voneinander. In der Vorbrutphase verwendeten die Männchen meist nur zwei verschieden lange Strophen, bestehend aus 2 und 6 Elementen je Strophe, und die durchschnittliche Strophenlänge war in dieser Phase sehr konstant. Nach Brutverlust oder bei kontinuierlich singenden, ledigen Männchen kam es zu einer Verkürzung der mittleren Strophenlänge. Die Strophenlänge ist phänotypisch plastisch, und lange Strophen zu singen scheint energetisch aufwendiger als kurze Strophen. Der enge Zusammenhang zwischen Strophenlänge und männlicher Konstitution einerseits und die Beobachtung, daß lange Strophen mit langen Pausen korrelieren andererseits, zeigen ebenfalls, daß längere Strophen energetisch aufwendiger sind. Die wirklichen Kosten dafür sind jedoch noch nicht bekannt.

     

Extrapair paternity in the Hoopoe Upupa epops: an exploration of the influence of interactions between breeding pairs, non-pair males and strophe length

Previous studies of the Hoopoe Upupa epops have shown that the strophe length of male songs influences female mate choice, and is correlated with female reproductive rates and male production of fledglings in the male’s own brood. However, frequent interactions between breeding pairs and non‐pair males suggests that extrapair copulations could occur and could affect the real number of fledglings sired by males, and therefore the relationship between strophe length and breeding success. Here we analyse the incidence of interactions between breeding pairs and non‐pair males, and of extrapair paternity, the interrelation of these parameters, the influence of male strophe length on them, and whether extrapair fertilizations affect the correlation between strophe length and breeding success of males, in a colour‐ringed population of Hoopoes in south‐eastern Spain. Multilocus DNA‐fingerprinting revealed that 10% of the broods contained offspring sired by extrapair males, representing 7.7% of the chicks. However, the interactions between pairs and non‐pair males were more frequent, with more than 25% of broods being visited by non‐pair males, and about 10% being helped (fed or defended) by males other than the nest owner. Most of these relationships were apparently attempts by visitor males to obtain copulations with paired females, or to obtain access to such females or nests in future breeding attempts. However, there was no significant link between the detection of interactions with alien males in a nest and the occurrence of extrapair paternity in it, indeed extrapair paternity was found in only 30% of the nests with interactions, and therefore the detection of visits or helping by non‐pair males cannot be considered evidence of extrapair paternity in visited or helped broods. Males that sang with long strophes never suffered losses of paternity within their broods, while 25% of males that sang with short strophes did. However, these differences were not significant. Nevertheless, strophe length of males was significantly positively correlated with per brood and seasonal production of fledglings after accounting for losses of paternity within their own broods.     

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     

INDIVIDUAL AND SPECIES-SPECIFIC SONG PATTERNS OF ROCK AND MEADOW PIPITS: PHYSICAL CHARACTERISTICS AND EXPERIMENTS

ABSTRACT

The songs of Anthus spinoletta littoralis and A. pratensis, in sympatric populations in SW Sweden were recorded, analysed in sound spectrographs and tested in the field. The purpose was to investigate: a) if the strophes are species specifically and individually distinct and, if so, whether pipits are able to make such distinctions; b) if the species-specific and individual-specific patterns are concentrated in different sections of the song and, if so, whether the species-specific section transmits individual-specific information and the individual-specific section transmits species-specific information as well.

The basic structure of the syllables in the terminating section of the strophe was found to be intraspecifically stereotyped, but varied between the two species. Replay experiments showed that territorial males could discriminate between con- and heterospecific strophes and this ability persisted when the terminating section of the strophe was replayed alone. The terminating part of the strophe did not seem to transmit individual-specific information to conspecific males. On the other hand, the basic structure of the syllables in the first section of the strophe was intraindividually stereotyped but varied between most conspecific males. Playback experiments showed that a territorial male could discriminate his neighbours' song patterns and this ability remained intact when the introductory phrase of the strophe was replayed alone. Both song pattern and position were necessary properties of the identifying signal in these pipits. But the introductory phrase of a total stranger did not seem to transmit unambiguous species-specific information to conspecific males.     

The effects of calling song spacing and intensity on the attraction of flying crickets (orthoptera: Goryllidae: Nemobiinae)

Previous studies have shown that sexually signaling males across different taxa show stereotyped spacing behavior that may be related to aspects of their signals, such as intensity. However, few studies have shown that the separation between signaling males affects their relative attractiveness. Using two sound traps broadcasting the calling song of the cricketEunemobius carolinus, we show that the separation, relative intensity, and absolute intensity of the calling songs influence calling song attractiveness. For calling songs separated by 5 m, the proportion of individuals attracted to the higher intensity song increased as the relative intensity difference of the two songs increased from 3 to 6 dB. For calling songs that differed by 6 dB, relative attraction to the less intense song decreased with decreasing song separation. These two results are consistent with the predictions of a model (Forrest and Raspet, 1994) that suggests that dense spacing is more costly for less powerful singers and that this cost increases with increasing differences in relative intensity. When the relative intensity of the songs was held constant (6 dB), we found that discrimination between songs decreases as the song absolute intensity increases. In particular, a greater proportion of individuals was attracted to the high-intensity song when the songs were broadcast at 103 and 97 dB than when the songs were broadcast at 109 and 103 dB. Unlike mammals and birds, the ability ofE. carolinus to discriminate between songs that differ in intensity may decrease as the absolute intensity increases. This may mean that females are less discriminating when they are closer to singing males.     

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.     

Mate choice in Pied Flycatchers Ficedula hypoleuca: can females use song to find high‐quality males and territories?

High-quality male Pied Flycatchers Ficedula hypoleuca (defined by brighter plumage, better condition and more experience) have previously been shown to have larger syllable repertoires and greater song versatility than males of inferior quality. Thus, by preferring more complex songs, females could choose a high-quality male. Females may also use song as a cue to find a high-quality territory since early arriving males may obtain the best territories and these males have more complex songs than late-arriving males. We found that males with more complex songs had a greater chance of becoming paired and stayed unpaired for a shorter period than males with less elaborate songs. When controlling for arrival order, however, only strophe versatility was still correlated with pairing order. Males defending popular territories had more complex and longer songs and were also in better body condition than males in less popular territories. A multiple logistic regression showed that song length was important in explaining whether a male defended a popular nestbox or not. Thus, male arrival time seems to be important in deciding the quality of a male's territory, which in turn explains female choice. However, song quality seems to add important information. Thus, females could find both high-quality males and high-quality territories by using song cues during mate choice.     

Male quality and territory quality in the great tit parus major

In this study there was no positive significant relationship between the quality of male great tits, as measured by average strophe length (a strophe is a short burst of song), and territory quality. (1) Males singing longer strophes did not defend territories in areas of higher recruitment, and (2) naturally settling males were better singers than replacement birds were. The second result was probably caused by a difference in age composition of the two groups, because naturally settling yearlings and replacement yearlings did not differ significantly in average strophe length. These observations on a non-migratory species are in contrast to those of several other studies on passerine birds, which were mostly concerned with migratory species. The relationship between male quality and territory quality is predicted to be closer in species that migrate than in non-migratory species.     

Acoustic courtship signals in the Caribbean fruit fly, Anastrepha suspensa (Loew)

Male Caribbean fruit flies, Anastrepha suspensa (Loew) produce two sounds in sexual contexts, calling songs and precopulatory songs. Calling song occurs during pheromone release from territories within leks and consists of repeated bursts of sound (pulse trains). Virgin female A. suspensa became more active in the presence of recorded calling songs. Activity during the broadcast of a heterospecific song did not differ from movement during periods of silence. A conspecific song typical of smaller males, i.e. conspicuous for its long periods between pulse trains, also failed to elicit more activity by virgin females than silence. Mated females were most active during silences. Unmated males had no obvious reaction to sound. Calling songs are apparently sexually important communications which females discriminate among and may use as cues for locating and/or choosing between mates. Precopulatory song is produced by mounted males just before and during the early stages of copulation. Males that did not produce such songs remained coupled for shorter periods, perhaps passing fewer sperm. Wingless (muted) males were more likely to complete aedeagal insertion if a recorded precopulatory song was broadcast. Calling song played at the same level (90 dB) had no significant effect on the acceptance of males, nor did precopulatory song at a lower SPL (52dB). Precopulatory song may be used to display male vigour to choosing females.     

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.     

Song complexity and song structure in the Moustached Warbler Acrocephalus melanopogon

We examined different song parameters leading to a complex song configuration, and song output (production), and their relation in male Moustached Warblers and discuss them with reference to female choice. With more than 120 different syllables per two minutes of song, male Moustached Warblers can be regarded as one of the most complex singers within the genus Acrocephalus . We found significant differences between males for almost all song parameters investigated (repertoire size, switching and repetition rate, song speed and strophe length) but not for time spent singing per 20 minutes. This individual variation probably is an important cue for female mate choice. Male Moustached Warblers achieve song complexity mainly via frequent syllable switching. Song complexity seems to be consistent throughout the song and our results suggest that females could assess the overall song complexity of a singer by examining even very short song bouts. Furthermore, a high proportion of motifs – clusters of syllables with the same sequence – occurs within the song of each male which would also facilitate assessment of song complexity by females. However, repertoire size and strophe length were positively related, thus it remains to be investigated which song feature, if any, females actually use.     

ANNUAL CHANGES OF LEARNED BEHAVIOUR—VARIATION OF SONG PATTERN IN FREE-LIVING CHAFFINCHES,FRINGILLA COELEBS,DURING THE BREEDING SEASON

ABSTRACT

Seasonal changes of parameters of full song were studied in a free-living population of chaffinches Fringilla coelebs during one entire reproductive period. Approximately 7000 strophes sung by 14 male chaffinches were recorded and analysed by sonography and a particular oscillographic method. While the general pattern of song strophes, i.e. characteristics of elements, number and arrangement of phrases, and final flourish, remained constant throughout the reproductive period, full song varied with respect to the repetition rate of strophes, number of strophe types used, intensity of singing, duration of strophes, and percentage of incomplete strophes sung. These changes are discussed as results of learning processes, social interactions in the population, and endogenous mechanisms activating memorized information.     

Effects of an Immune Challenge on Multiple Components of Song Display in Barn Swallows Hirundo rustica: Implications for Sexual Selection

Bird song is believed to honestly reveal male quality including the ability of singers to face parasitism. In a natural population of barn swallows Hirundo rustica, we experimentally imposed a cost on song production by an immune challenge. We therefore vaccinated a group of reproducing males with an antigen (Newcastle disease virus), and injected phosphate‐buffered saline to a control group. Immune challenge significantly reduced one song feature, rattle duration. This decrease was related to male quality, as measured by tail length, because males with short tails reduced the duration of their rattle significantly more than males with long tails. In addition, another song feature, strophe duration, decreased in the control group, while it remained constant in the challenged group. Duration of the rattle has previously been found to be positively related to testosterone level, and it may hence reflect male competitive ability. Thus, male barn swallows may not have the potential to produce long rattles when their immune system is challenged. By maintaining their strophe duration after an immune challenge, males may compensate for the decrease in rattle duration. Our results suggest that different song features may convey different types of information, and that barn swallow song, in particular their rattle, may reliably reveal information about activation of the immune system.     

Sex ratio and male sexual characters in a population of blue tits, Parus caeruleus

Sex allocation theory proposes that parents should bias thesex ratio of their offspring if the reproductive value of onesex is greater than that of the other. In the monogamous bluetit (Parus caeruleus), males have a greater variance in reproductivesuccess than females, and high-quality males have higher reproductivesuccess than high-quality females due to extrapair paternity.Consequently, females mating with attractive males are expectedto produce broods biased toward sons, as sons benefit more thandaughters from inheriting their father's characteristics. Songand plumage color in birds are secondary sexual characters indicatingmale quality and involved in female choice. We used these malesexual traits in blue tits to investigate adaptive sex ratiomanipulation by females. We did not find any relationship betweenmale color ornamentation and brood sex ratio, contrary to previousstudies. On the other hand, the length of the strophe bout (i.e.,the mean number of strophes per strophe bout) of fathers waspositively related with the proportion of sons in their broods.The length of the strophe bout is supposed to reflect male qualityin terms of neuromuscular performance. We further showed thatsons produced in experimentally enlarged broods had shorterstrophe bouts than sons raised in reduced broods. These resultsare consistent with the hypothesis that females adjust the sexratio of their broods in response to the phenotype of theirmate.     

The development of stimulus‐specific auditory responses requires song exposure in male but not female zebra finches

Juvenile male zebra finches develop their song by imitation. Females do not sing but are attracted to males' songs. With functional magnetic resonance imaging and event‐related potentials we tested how early auditory experience shapes responses in the auditory forebrain of the adult bird. Adult male birds kept in isolation over the sensitive period for song learning showed no consistency in auditory responses to conspecific songs, calls, and syllables. Thirty seconds of song playback each day over development, which is sufficient to induce song imitation, was also sufficient to shape stimulus‐specific responses. Strikingly, adult females kept in isolation over development showed responses similar to those of males that were exposed to songs. We suggest that early auditory experience with songs may be required to tune perception toward conspecific songs in males, whereas in females song selectivity develops even without prior exposure to song. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2010     

INCOMPLETE SONG STROPHES IN THE CHAFFINCH FRINGILLA COELEBS L.: GENERAL INFLUENCES ON A SPECIFIC BEHAVIOURAL OUTPUT

ABSTRACT

Incomplete song strophes in free-living territorial Chaffinch males can be induced by different experimental as well as natural stimulus situations including replay of species- specific song, approaching of human beings, and aggressive encounters with con-specific males. While the first post-stimulus song strophe is shortest the following ones gradually attain their full number of elements again. The strength of this reaction differs with regard to different stimuli.     

Female dark‐eyed juncos Junco hyemalis thurberi produce male‐like song in a territorial context during the early breeding season

Reports of female song, once considered a rarity, have recently increased across a variety of avian taxa. Females of many species can be induced to produce male‐like song with exogenous testosterone, but observations of female song in free‐living birds remain limited by incomplete sampling of females. Here, we report three independent observations of female dark‐eyed juncos Junco hyemalis producing male‐like song early in the breeding season (i.e. post‐territory establishment, pre‐nesting) in a recently established non‐migratory, urban population. To elicit song, we presented 17 free‐living junco pairs with a live, caged female conspecific. Three unique females responded to our trials by diving at the intruding female, chasing their (male) mate, fanning their tail feathers, and singing a trilled song similar in structure to male long‐range (broadcast) song. We compared male and female songs quantitatively and found that the two sexes were statistically similar in many spectral and temporal characteristics, but female songs had significantly lower minimum and peak frequencies than males. This result is particularly surprising, as males in this urban population are known to sing at a significantly higher minimum frequency than males in a nearby montane population. Both the seasonal and social context in which these songs were observed suggest a potential function for female song in mate guarding and polygyny prevention, but more data are needed to test this hypothesis. Whether female song is common in all dark‐eyed juncos during the early breeding season or if it is restricted to this particular urban and non‐migratory population remains an important question for future research.