Song Potency Research Articles

Female signal jamming in a socially monogamous brood parasite

Acoustic signalling is vital to courtship in many animals, yet the role of female vocalizations is understudied. Here, we combine observational and experimental methods to assess the courtship function of the female chatter call in brown-headed cowbirds, Molothrus ater. While the chatter call is likely multifunctional, it is frequently used in social interactions and overlapping duets with males during the breeding season. Based on a combination of focal- and scan-sampling data from large naturalistic aviaries, we did not find support for the hypothesis that the chatter call elicits male attention or encourages continued courtship. However, we did find evidence that the chatter call plays a role in pair bond formation, as females preferentially chattered in response to songs from pair-bond males in the 2 weeks leading up to the median date of first copulation. Females were less selective in male-directed chatter use after copulations began. We also found support for the hypothesis that chatter is used to signal-jam male songs. Frame-by-frame video analysis revealed that the majority of female chatter calls were tightly time-locked to song, occurring less than 500 ms after male vocal onset. To test the effect of signal jamming on male song potency, we designed a laboratory experiment in which male song playbacks were jammed by various recorded stimuli. Natural chatter calls more effectively reduced female copulatory responses to song than high-pass filtered chatter calls, suggesting that the low frequencies in natural chatter (2-4 kHz) are important for interfering with male song and reducing its potency. Our results suggest that sexual conflict is operating in cowbird courtship, with signal jamming serving as a mechanism by which females guard, resist or select their mates. We also discuss ways in which cowbird vocal interactions may function cooperatively to coordinate reproduction or transition females into breeding condition.

Non‐Vocal Shaping of Avian Song Development: Parallels to Human Speech Development

AbstractVocal development in young male cowbirds (Molothrus ater) is sensitive to acoustical stimulation from males, but also to social feedback from female cowbirds, even though females do not sing. Juvenile males show different vocal trajectories if housed with local or distant population females. The major goal of the present study was to identify differences in the form and timing of non‐vocal cues from females during the period in early spring when juvenile males begin to sing stereotyped song and to finalize their repertoires. We housed juvenile males with either local or distant population females and no adult males. We found significant differences between the two groups of females in the use of wing stroking and in male reactions to wing strokes and gapes. There were also differences between the groups in male song performance. To understand further the potential consequences of these differences, we correlated measures of male and female responsiveness to results reported in Smith et al. (2000) on vocal ontogeny and song potency. We found that wing stroking by females was associated with a faster rate of song development and tended to relate to differences in song potency. The non‐vocal shaping seen here may represent a general mechanism for the development of vocal communication, as similar processes influence phonological development in human infants.

A role of her own: female cowbirds, Molothrus ater, influence the development and outcome of song learning

Previous work has shown that captive female cowbirds, Molothrus ater, can influence the outcome of male song development by affecting retention or deletion of song elements and by stimulating improvization. Here we looked for evidence of female influence during the process of learning, as males progress from subsong to plastic song to stereotyped song. In a longitudinal study, we measured the rate and timing of vocal development in captive, juvenile male brown-headed cowbirds,M.a.artemisiae . Half the young males were housed with female cowbirds from their own population (South Dakota: SD) and half with female cowbirds from a M.a.ater population (Indiana: IN). Both populations of females prefer local songs and differ in the time of breeding, with SD females breeding 2 weeks later than IN females. The results showed significant effects of female presence on the age at which males advanced through stages of vocal development: the SD males with SD females, as opposed to SD males with IN females, developed stereotyped song earlier, reduced motor practise earlier, and produced more effective playback songs. Longitudinal observations of social interactions showed that the two groups of females reliably differed in social responses to males. Degree of social proximity of females to males in the winter predicted song maturity, rate of rehearsal and song potency. Thus, females can stimulate the progression of song learning, as well as prune song content.

Visual and song nuclei correlate with courtship skills in brown-headed cowbirds

We assessed courtship success in 14 adult male brown-headed cowbirds,Molothrus ater. Volumes of song control nuclei and visual nuclei were measured in Nissl stained tissue. Variation in courtship success was found to be related to variation in two areas of the avian brain: the song control nucleus, area X, and the thalamic visual area, nucleus rotundus. Volume of area X was negatively correlated with song potency, as assessed by female playback, and with rate of vocalizing. Volume of nucleus rotundus was positively correlated with song potency, vocalizing to females and courtship persistence. These data are the first to implicate a visual nucleus in the use of song. The data also complement previous findings with cowbirds suggesting that song learning involves visual attention to females. Taken as a whole, these results suggest that use of song depends on integration of auditory, vocal and visual information. In that female songbirds in many species assess multimodal performance of song, these findings with cowbirds suggest that future studies of brain and behaviour include a broader view of possible behavioural and neural correlates.

Social malleability in cowbirds (Molothrus ater artemisiae): Species and mate recognition in the first 2 years of life.

In a longitudinal study, the authors housed wild-caught juvenile male cowbirds (Molothrus ater artemisiae) with female cowbirds or canaries (Serinus canaria) from August until May. The males were then exposed to 3 social contexts. Males housed with canaries directed more vocalizations to canaries than to female cowbirds. Males housed with female cowbirds vocalized most to other males. The data revealed plasticity at a rudimentary level of reproductive behavior, selective responding to members of one's own species. Song potency, as assayed by playback, did not predict vocal use. To test adult malleability, the authors studied the males for a 2nd year. Half were housed with conspecific females and experienced males and half with only females. The manipUlation eradicated any signs of the males' 1st-year experiences. The data suggest malleability in species and mate recognition in cowbirds. Considerable evidence indicates that male cowbirds' vo­ cal repertoires are socially malleable. The timing and extent of exposure to adult male models affects the content of two vocal signals, the song and the flight whistle (Dufty, 1985; King & West, 1990; King, West, & Eastzer, 1980; O'Loghlen & Rothstein, 1993). Moreover, in some parts of the species' range, female cowbirds, which do not sing, can shape the content of the males' vocal repertoires through visual responses (West & King, 1988). In this report, we pose a broader question about male cowbirds' vocal capac­ ities: How does a juvenile male's access to social stimula­ tion affect his ability to use vocal signals effectively during the breeding season? To this end, we housed young males either with conspecific females or with canaries during their 1st year and then measured patterns of vocal behavior in the context of mate assortment during the breeding season. We followed this experiment with a second one in which we looked for evidence of plasticity in vocal and courtship skills in the same males' 2nd year. Although abundant evidence exists on the role of learning in songbirds' acquisition of vocal signals, few such studies include assessments of how males actually use their vocal­ izations in species-typical circumstances. Studies of blue

Song repertoire development in male cowbirds (Molothrus ater): Its relation to female assessment of song potency.

Two studies were conducted to investigate the relation between the male cowbird's (Molothrus ater ater) development of a song repertoire and the female cowbird's assessment of song potency. Male development was assayed by vocal copying and female assessment by copulatory responsiveness to song playback. The results demonstrate that males do not copy most often the particular songs that females respond to most often. Whereas rank orderings of potency were highly correlated across two independent samples of playback females, male and female rank orderings were not significantly correlated. The data highlight the potential significance of social interactions between and across the sexes for repertoire development.

Song repertoire development in male cowbirds (Molothrus ater): Its relation to female assessment of song potency.

Song repertoire development in male cowbirds (Molothrus ater): Its relation to female assessment of song potency.

Social Guidance of Vocal Learning by Female Cowbirds: Validating its Functional Significance

AbstractJuvenile male M. a. ater cowbirds, who have never heard other male cowbirds sing, develop distinctively different repertoires when housed with M. a. ater females from their own area versus M. a. obscurus females from a distant population. Because female cowbirds do not sing, the differences in the males' songs do not arise through vocal imitation. Here we provide data demonstrating that the songs of female‐housed males are functionally, as well as acoustically, distinctive. The songs of 8 groups of males were tested where the groups differed by age of singer, acoustic experience, and identity of social companion. The playback results demonstrate that non‐singing female cowbirds not only stimulate the male to modify song content, but song potency. As such, they demonstrate the critical role female cowbirds may assume in the proximate and ultimate regulation of vocal development.

Social metrics of song learning

Five metrics of song learning are described for brown-headed cowbirds ( Molothrus ater). The intent of these metrics is to capture not only the behavior of the song learner but the social context in which song learning occurs. Playback procedures, observations of mating, and acoustic and functional assessment of song content are combined to yield measures of song potency, functional validity, social dynamics, vocal flexibility, and social reactivity. Taken as a whole, the results revealed by these metrics indicate that males learn to be effective singers by attending to the social consequences of their behavior.

Dissecting Cowbird Song Potency: Assessing a Song's Geographic Identity and Relative Appeal

Abstract and SummaryTo investigate the acoustic elements that constitute song potency in cowbirds, a playback experiment was carried out using the female cowbird's copulatory posture as a bioassay of song potency. Experimentally altered versions of the song of an Molothrus ater obscurus male were presented to M. a. ater and M. a. obscurus females. Song elements of special interest were those thought to communicate a male's geographic status and those indicating song quality. Several song elements were critical to the communication of inter‐ and intraspecific information. Moreover, the data demonstrate that the same semantic information (e. g., geographic identity or relative appeal) may be mediated through different song structures for the two subspecies. Finally, the data reveal a new song parameter relying upon the operation of the cowbird's two voices that contributes to song potency. This latter finding may represent the first functional test of the two voice phenomenon in passerines.ZusammenfassungDie Begattungsreaktionen gefangengehaltener Weibchen der beiden Kuhstar‐Unterarten Molothrus ater ater und M. a. obscurus auf die Tonband‐wiedergabe eines M. a. obscurus‐Gesangs wurden untersucht. Der Gesang wurde experimentell verändert, um die Rolle verschiedener akustischer Elemente zu isolieren. Der Gesang des Kuhstars enthält mindestens zwei Informationen; eine betrifft die geographische Herkunft, die andere die Qualität oder Anziehungskraft des Gesangs. Weibchen der beiden Unterarten reagierten charakteristisch verschieden auf Veränderungen des Gesangs und sprachen auf verschiedene Gesangstrukturen an. Die Ergebnisse weisen darauf hin, daß der Gesang des Kuhstars hierarchisch aufgebaut ist und daß die Weibchen Gesänge an mehreren Merkmalen der Gesangsstruktur unterscheiden.

An experimental investigation of the bioacoustics of cowbird song

Female cowbirds (Molothrus ater ater), maintained in isolation from males during the breeding season, respond to the playback of male song with copulatory postures. They respond to some songs more than to others. Cowbird song potency can thus be operationally defined by the proportion of copulatory postures a song elicits across multiple playbacks. The purpose of the present study was to explore whether song potency changes with distance in the field. No field recordings elicited high levels of responding by the females. When songs of known high potency are systematically degraded, the results indicate that female cowbirds are sensitive to small changes in signal to noise ratio and to atmospheric attenuation. The data suggest that cowbird song potency degrades very rapidly with transmission distance in the field.

Validating the female bioassay of cowbird song: Relating differences in song potency to mating success

Female cowbirds ( Molothrus ater), maintained in isolation from males during the breeding season, respond to the playback of male song with copulatory postures. They respond more often to some songs than others. Song potency can thus be operationally defined by the number of copulatory responses a song elicits. The purpose of the present study was to validate this measure of song potency by investigating its relationship to mating success. We observed two colonies of cowbirds during the breeding season and recorded details of their courtship. In addition, song potency of the males was tested by playback with a different group of captive females. The results indicate a relationship between maximum song potency and mating success: the males that obtained the most copulations had songs of higher maximum potency and were also observed to have been more dominant during the winter and early spring.

Enriching cowbird song by social deprivation.

cowbirds showed no preferences for the songs of males they had been housed with. Comparisons of the behav­ iors of isolate and group-maintained birds when introduced into an estab­ lished cowbird colony revealed that isolate males sang more and received more attacks. These results indicate the critical importance of the male cowbird's social environment for song potency. Comparisons of the song potency among the adults also showed the reversibility of early species-typical or species-atypical experience with regard to song performance.