Song system neuroanatomy, and immediate early gene expression in a finch species with extensive male and female song.

Birdsong is a relatively well-studied behavior, both due to its importance as a model for vocal production learning and as an intriguing complex social behavior. Until the last few decades, work on birdsong focused almost exclusively on males. However, it is now widely accepted that female song not only exists, but is fairly common throughout the oscine passerines. Despite this, and the large number of researchers who have begun exploring female song in the field, researchers in the lab have been slow to adopt model species with female song. Studying female song in the lab is critical for our understanding of sex-specific factors in the physiology controlling this fascinating behavior. Additionally, as a model for vocal production learning in humans, understanding the mechanistic and neuroendocrine control of female song is clearly important. In this study, we examined the red-cheeked cordon bleu (RCCB), an Estrildid finch species with extensive female song. Specifically, we found that there were no significant sex differences in circulating levels of testosterone and progesterone, nor in song production rate. There were no significant differences in cell densities in the three nuclei of the song control system we examined. Additionally, the volume of the robust nucleus of the arcopallium was not significantly different and we report the smallest sex difference in HVC yet published in a songbird. Finally, we demonstrated similar levels of motor driven immediate early gene expression in both males and females after song production.

Neuroendocrine and behavioral response to testosterone-induced female song in canaries (Serinus canaria).

Male song in songbirds is a critical and elaborate signal for mate attraction. In many species female listeners respond to male song both behaviorally and physiologically (e.g. copulation solicitation displays and production of the immediate early gene ZENK in auditory regions). It is becoming increasingly well known that females in many species also sing. However, in common lab species, such as canaries (Serinus canaria), female song is limited and has been primarily studied in the context of administering of exogenous testosterone (T) to increase song rate and length. In this study we addressed to what extent female canary songs are masculinized by the administration of exogenous T based on the behavioral and physiological responses of avian receivers. Specifically, are T induced female songs sufficient to elicit courtship behaviors and auditory ZENK expression in female listeners? We found that female songs after 3 weeks of exogenous T were significantly longer and more complex than female songs after 12 weeks of exogenous T. Additionally, we found that playback of 3-week T song significantly increased sexual response behaviors and the expression of ZENK in the auditory brain regions of female listeners. Finally, we conclude that extended periods of T do not necessarily maintain the masculinization of female song.