Increased exposure to yolk testosterone has feminizing effects in chickens, Gallus gallus domesticus

► We studied effects of increased prenatal testosterone (T) exposure in the chicken. ► T increased competitiveness in males up to the level of the female chicks. ► No effect of T on social rank, body mass or circulating plasma testosterone. ► Comb colour but not comb size tended to be feminized by testosterone. ► Maternal androgens interact with the process of sexual differentiation.