Undirected (Solitary) Birdsong in Female and Male Blue-Capped Cordon-Bleus (Uraeginthus cyanocephalus) and Its Endocrine Correlates

Abstract

BackgroundBirdsong is a popular model system in research areas such as vocal communication, neuroethology or neuroendocrinology of behaviour. As most research has been conducted on species with male-only song production, the hormone-dependency of male song is well established. However, female singing and its mechanisms are poorly understood.Methodology/Principal FindingsWe characterised the song and its endocrine correlates of blue-capped cordon-bleus (Uraeginthus cyanocephalus), a species in which both sexes sing. Like other estrildids, they produce directed song during courtship and undirected (or solitary) song in isolation, i.e. when the mate is not visible or absent. We compare solitary song of blue-capped cordon-bleus to published descriptions of the song of its relative, the zebra finch (Taeniopygia guttata). Solitary song of cordon-bleus shared some overall song features with that of zebra finches but differed in spectro-temporal song features, sequential stereotypy and sequential organisation. The song of cordon-bleus was dimorphic with respect to the larger size of syllable repertoires, the higher song duration and the lower variability of pitch goodness (measuring the pureness of harmonic sounds) in males. However, in both sexes the overall plasma testosterone concentrations were low (ca. 300 pg/ml) and did not correlate with the sexually dimorphic song motor pattern. Despite such low concentrations, the increase in the rate of solitary song coincided with an increase in the level of testosterone. Furthermore, the latency to start singing after the separation from the mate was related to hormone levels.Conclusions/SignificanceOur findings suggest that the occurrence of solitary song but not its motor pattern might be under the control of testosterone in female and male cordon-bleus.

Mismatch in sexual dimorphism of developing song and song control system in blue-capped cordon-bleus, a songbird species with singing females and males

“…To this end, we studied both the song system development and the song development in a songbird species, the blue-capped cordon-blue (Uraeginthus cyanocephalus) in which males and females sing frequently both during ontogeny and in adulthood Gahr, 2011, 2013). Previous studies showed that male and female cordon-bleus learn parts of their song from both adult male and female tutors (Geberzahn and Gahr, 2013), with the adult female song being slightly shorter and less diversified than the male song (Geberzahn and Gahr, 2011). Here we quantify the song development of female and male cordon-bleus from juvenile age until adulthood, focusing on song parameters that were indicated previously to differ between adult males and females.…”

“…In order to obtain song that can be traced back unequivocally to a given subject, each bird was transferred temporarily to a soundattenuating chamber where song recordings were made following procedures described in Geberzahn and Gahr (2011) using Sound Analysis Pro (SAP) software (Version 2.062) at a sampling rate of 44 kHz and 16-bit resolution (Tchernichovski et al, 2004; freely available at http://soundanalysispro.com). Thus, we recorded so-called undirected songs.…”

“…Then, the following parameters, previously found to be sexually dimorphic in adult blue-capped cordon-bleus (Geberzahn and Gahr, 2011) were measured: the song duration, the syllable repertoire and the coefficient of variation (CV = SD/mean) of pitch goodness. The latter is described as the harmonicity of the sound and its CV indicates the degree of stereotypy of the harmonicity of a syllable.…”

“…The latter is described as the harmonicity of the sound and its CV indicates the degree of stereotypy of the harmonicity of a syllable. Songs were defined as sequence of at least three different syllables with pauses shorter than 600 ms. For each song, syllables were automatically delineated using a constant threshold for amplitude (23 dB) and entropy (-2.1) in the features batch window of SAP as described previously (Geberzahn and Gahr, 2011). In a next step, we printed images of spectral derivatives using SAP.…”

“…From these parameter tables we extracted the pitch goodness (mean, SD and CV). We calculated the coefficient of variation (CV = SD/mean) of pitch goodness of the four most frequent syllables similar to previous works (Geberzahn and Gahr, 2011). For those syllables we selected the first 20 renditions that occurred in the analyzed songs.…”