It is no doubt that sex determination mechanism in birds is also chromosomal. The genetic sex is determined at the time of fertilization but the gonads are indistinguishable between male and female for the first week of developmental stage in the case of chickens. After this indifferent stage, the male gonad begins to display testicular characteristics and the female gonad starts to display ovarian characteristics. In analogy to mammalian sex determination mechanisms, avian female specific W chromosome might be expected to possess a gene encoding a protein for ovarian formation. However, presence of such a gene has not been identified.
Gonadal development is labile to hormonal influences in birds while it is at the indifferent stage.
On the other hand, testosterone induces gonadal masculinization in the genetic male. In mammals AMH gene expression is located downstream in the cascade of masculinization and is likely regulated by SOX9 . In the chicken, adult male displays copulation behavior, whereas females display receptive behavior. In the adult quail, intact male shows copulation behavior but gonadectomy abolishes this behavior. In male quail early treatment with estradiol benzoate on day 9 of incubation inhibits adult copulation behavior whereas the treatment on day 14 was ineffective.