Juvenile sparrows preferentially eavesdrop on adult song interactions

Recent research has demonstrated that bird song learning is influenced by social factors, but so far has been unable to isolate the particular social variables central to the learning process. Here we test the hypothesis that eavesdropping on singing interactions of adults is a key social event in song learning by birds. In a field experiment, we compared the response of juvenile male song sparrows (Melospiza melodia) to simulated adult counter-singing versus simulated solo singing. We used radio telemetry to follow the movements of each focal bird and assess his response to each playback trial. Juveniles approached the playback speakers when exposed to simulated interactive singing of two song sparrows, but not when exposed to simulated solo singing of a single song sparrow, which in fact they treated similar to heterospecific singing. Although the young birds approached simulated counter-singing, neither did they approach closely, nor did they vocalize themselves, suggesting that the primary function of approach was to permit eavesdropping on these singing interactions. These results indicate that during the prime song-learning phase, juvenile song sparrows are attracted to singing interactions between adults but not to singing by a single bird and suggest that singing interactions may be particularly powerful song-tutoring events.     

Territory establishment,song learning strategies and survival in song sparrows

In most songbirds, the processes of song learning and territory establishment overlap in the early life and a young bird usually winds up with songs matching those of his territorial neighbors in his first breeding season. In the present study, we examined the relationships among the timing of territory establishment, the pattern of song learning and territorial success in a sedentary population of song sparrows (Melospiza melodia). Males in this population tend to learn their songs from their neighbors and consequently they show high song sharing with neighbors and use these shared songs preferentially in interactions with them. Males also show significant variation in the timing of territory establishment, ranging from their natal summer to the next spring. Using a three-year dataset, we found that the timing of territory establishment did not systematically affect the composition of the song repertoire of the tutee: early establishers and late establishers learned equally as much from their primary tutors and had a similar number of tutors and similar repertoire sizes, nor did timing of territory establishment affect subsequent survival on territory. Therefore, the song-learning program of song sparrows seems versatile enough to lead to high song sharing even for birds that establish territories relatively late.     

Context-dependent effects of castration and testosterone treatment on song in male European starlings

Most seasonally breeding songbirds display dramatic seasonal fluctuations in plasma testosterone (T) levels and mate attraction behaviors, including song. However, males of some songbird species, such as the European starling (Sturnus vulgaris), continue to sing at high levels after the breeding season, when T levels are basal. In male starlings song during the breeding season functions mainly to attract mates, whereas song during the nonbreeding season appears unrelated to reproduction. This suggests that song produced in a context unrelated to female courtship, unlike song directed toward females, is not regulated by plasma T. In captive males housed in large outdoor aviaries we explored the relationship between plasma T and song produced during the breeding season within and outside a courtship context. This was achieved by determining the effects of castration and subsequent T treatment on song and mate attraction behaviors in both the presence and the absence of a female. Compared to intact males, castrated males did not show reduced song activity in the absence of a female for at least 6 months after the operation, strongly suggesting that the expression of noncourtship song is not regulated by plasma T. Likewise, we found that experimentally elevating T levels in castrated males did not affect noncourtship song rates. However, control castrated males receiving empty implants tended to show reduced noncourtship song rates after implantation. This may have been due to a suppressive effect caused by the presence of the T-implanted castrated males in the same aviary. In contrast, courtship singing was clearly controlled by plasma T: it was abolished by castration and restored by subsequent T replacement when males were housed both individually and in a group situation. High plasma levels of T also appeared necessary for the activation of three other behavioral traits critical for mate attraction, namely, nesthole occupancy, spending time (singing) in a nesthole, and carrying green nesting material into a nesthole.     

Nightingales in space: song and extra-territorial forays of radio tagged song birds

Summary Most temperate zone passerines defend territories during the breeding season. Commonly the size of these territories is estimated by plotting the singing locations of the males. However, an individual's activities need not be restricted to the area used for singing. So far, only little quantitative information has been available to determine how the singing territory relates to the activity range of male songbirds. Here, we present a study in which we used radio-tracking techniques to collect quantitative data on the spatial behaviour of 11 male territorial Nightingales (Luscinia megarhynchos). The results show that the singing territories made up only about 50% of the activity ranges. Nevertheless, males spent over 90% of the time within the singing territory. Singing territories almost never overlapped but activity ranges overlapped in all cases with the activity range of at least one neighbour. Males intruded into neighbouring territories throughout the season but the longest excursions were made before and during the female fertile period. The time spent for forays correlated significantly with song rate and territories of males with higher song rates in turn were less frequently the object of forays by other males. Song rate can be indicative of male quality, so that our findings strongly suggest that foray behaviour is related to male quality in nightingales.

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Das Raum- und Gesangsverhalten von männlichen Nachtigallen in der Brutsaison: radiotelemetrische Untersuchungen

Zusammenfassung Männliche Singvögel markieren mit ihrem Gesang ein Revier. Empirische Studien zeigen allerdings, dass Männchen und Weibchen das Revier verlassen und in Reviere von Nachbarn eindringen. Solche Ausflüge sind vor allem in dichteren Habitaten schwierig zu beobachten, so dass für die meisten Vogelarten kaum Datenmaterial für die Raumnutzung außerhalb der Gesangsreviere vorliegt. In dieser Studie haben wir über den Verlauf der Brutsaison 11 männliche territoriale Nachtigallen telemetriert. Die Ergebnisse zeigen, dass die Aktionstradien im Mittel doppelt so groß waren, wie die Gesangsreviere und dass die Männchen ca. 8% der Zeit außerhalb der Gesangsreviere verbracht haben. Dabei überlappten die Aktionsräume benachbarter Männchen deutlich. Die Männchen drangen vor allem vor und während der fertilen Phasen der Weibchen in Nachbarreviere vor. Darüber hinaus drangen Männchen mit höherer Gesangsaktivität signifikant länger in Nachbarreviere ein, als Männchen mit geringerer Gesangsaktivität. Reviere von Männchen mit höherer Gesangsaktivität wurden dabei auch signifikant seltener von anderen Männchen besucht. Da die Gesangsaktivität mit der Qualität eines Männchens zusammenhängen kann, weisen die Ergebnisse darauf hin, dass qualitativ bessere Männchen mehr in Nachbarreviere eindringen als qualitativ schlechtere Männchen und die Reviere der qualitativ besseren Männchen auch weniger häufig von Rivalen besucht werden. Dass solche Ausflüge von Männchen für Versuche zu außerpaarlichen Kopulationen genutzt werden, ist anzunehmen, muss aber noch geklärt werden. Die räumlichen Beziehungen territorialer Männchen reflektieren darüber hinaus vermutlich Aspekte der sozialen Beziehungen.

     

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.     

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.     

Relationship between song characters and morphology in New World pigeons

We studied the pattern of variation in song characters among 16 New World pigeon species belonging to different taxonomic groups defined by morphological characters. Structural, temporal and frequency characters of the song were analysed. Principal components analyses showed that species belonging to the same taxonomic group were also grouped together by their song characters. In addition, individuals were correctly assigned into taxonomic groups by discriminant function analyses in more than 87.8% of cases. These analyses also showed that more than 87.5% of the individuals could be correctly classified by species when all song characters were included. Correct classification of individuals by species and taxonomic groups dropped when character types were analysed separately, thus showing that structural, as well as temporal and frequency characters are fundamental to define species- and group-specific identities of New World pigeon's songs. Correspondence between patterns of vocal and morphological variation found in this study can be a consequence of evolutionary changes in morphology affecting song production, as for example body size changes that constrain the syrinx to produce certain acoustic frequencies.     

Open-ended song learning in a hummingbird

Vocal learning in birds is typically restricted to a sensitive period early in life, with the few exceptions reported in songbirds and parrots. Here, we present evidence of open-ended vocal learning in a hummingbird, the third avian group with vocal learning. We studied vocalizations at four leks of the long-billed hermit Phaethornis longirostris during a four-year period. Individuals produce a single song repertoire, although several song-types can coexist at a single lek. We found that nine of 49 birds recorded on multiple days (18%) changed their song-type between consecutive recordings. Three of these birds replaced song-types twice. Moreover, the earliest estimated age when song replacement occurred ranged from 186 to 547 days (mean = 307 days) and all nine birds who replaced song-types produced a crystallized song before replacement. The findings indicate that song-type replacement is distinct from an initial early learning sensitive period. As half of lekking males do not survive past the first year of life in this species, song learning may well extend throughout the lifespan. This behaviour would be convergent to vocal learning programmes found in parrots and songbirds.