Season-related changes in circulating androgen, brain aromatase, and perch-calling in male ring doves.

The perch-call of ring doves (Streptopelia risoria) is related to territorial defence and mate attraction. Perch-calls are sexually dimorphic and individually different in structure. The expression of perch-call is androgen-dependent and is controlled by the action of testosterone on the preoptic-hypothalamic areas. However, it is not known whether the acoustic features of the call vary with the reproductive condition. We studied plasma androgen levels, brain steroid metabolism, and perch-calling of male ring doves kept in winter-like (low temperature, short days) or spring-like (mild temperature, long day) conditions. Circulating levels of androgen were higher in males kept on spring-like condition. Spring males spent more time in perch-calling than winter males. However, a detailed analysis of the call structure revealed no difference for any time or frequency parameter between groups. This work shows that in ring doves season-dependent variations in the circulating levels of androgen are correlated with differences in the amount of time males spend in perch-calling. In addition, the study suggests that in adult males the acoustic structure of the perch-calls is not influenced by season-related changes in androgen levels.

Aromatase inhibition affects testosterone-induced masculinization of song and the neural song system in female canaries.

Songbirds have a specialized steroid-sensitive network of brain nuclei, the song system, for controlling song. Most nuclei of the song system express androgen receptors, and the sensory-motor integration nucleus High Vocal Center (HVC) alone also expresses estrogen receptors. Apart from expressing estrogen receptors in the vocal control system, songbirds are unique among birds because they have high concentrations of the estrogen-synthesizing enzyme aromatase in the neostriatum surrounding HVC. However, the role of estrogen in controlling the development of the song structure has been scarcely investigated. In this work, we show that blocking the production of estrogen during testosterone-induced song motor development in adult female canaries alters the song pattern compared to control females treated with testosterone only. These effects were correlated with inhibition of the expression of estrogen-sensitive genes, such as brain-derived nerve growth factor, in HVC. The expression of the ATP-synthase gene, an indicator of cell activity, in HVC, and the size of HVC, were not affected by the treatment. Our results provide the first example of estrogen-sensitive mechanisms controlling the structural features of adult birdsong.