Post-hatching inhibition of aromatase activity does not alter sexual differentiation of the zebra finch song system.

Hatchling zebra finches were treated with fadrozole, an aromatase (estrogen synthesis) inhibitor, to test whether estrogen is required for normal masculine development of the song system. Injections on posthatching days 1-30 had no effect on the volumes of the robust nucleus of the archistriatum (RA) and area X or on neuron soma size in RA and high vocal center (HVC) measured on day 31. These results argue against the importance of estrogen in masculinization of the song system in males after hatching.