1. Introduction
2. Song and song learning
2.1 Behavior
2.2 Structures controlling song learning and production in songbirds
2.3 Relationships between structure and function: sex differences in the song circuit
2.4 Mechanisms regulating sexual differentiation of the song system
2.4.1 Steroid hormones
2.4.2 Sex chromosome genes
2.5 Relationships between structure and function: adult plasticity in the song circuit
2.6 Structures controlling song learning and production in other orders of birds
3. Other social/reproductive behaviors
4. Conclusions and ideas for future directions
References
Author biography.