Behavioral correlates of sexual differentiation in the zebra finch song system.

The capacity for song is masculinized in female zebra finches by exposure to 17 beta-estradiol at hatching, and requires continual exposure to androgen for its behavioral expression in the adult. The stereotypy of the song developed by estrogenized females can be as good as that of male song. The sexual dimorphism in behavioral capacity for song parallels morphological sex differences in the efferent motor pathway which participates in the production of song. Estradiol induces the cytoarchitectonic masculinization of the telencephalic nuclei within the motor system for song, and renders them able to respond morphologically when song is induced in estrogenized females by exposure to androgen as adults.