Japanese quail chicks produce the distress calls at a high rate when socially isolated from other individuals. Under the same conditions, chicks which were given chronical subcutaneous implantation of testosterone (T) produced the chick crowing which has similar acoustical structural characteristics to both the chick distress call and the adult crow. Electrical stimulation of dorso-medial areas of chick mesencephalon through a chronically implanted electrode elicited calls in freely moving chicks. The acoustical structure of the elicited call resembled that of the distress call with the harmonic structures and constant frequency before T implantation. At 6 days after T implantation, the chicks produced the chick crowing similar to the adult crow with a trill structure by electrical stimulation. The area in brainstem of chicks that exhibit two different kinds of vocal behavior upon electrical stimulation lies in the medial intercollicular nucleus (ICo). This suggests that the medial ICo of chicks has two different function, production of the distress call and the chick crowing with T implantation. We concluded that continual exposure of the neural substrate in the medial ICo of chick to T induced the functional change from emitting the distress call to producing the chick crowing.