Testosterone-induced changes of call structure, midbrain and syrinx anatomy in partridges.

Testosterone (T) treated Grey partridges (Perdix perdix) of both sexes uttered significantly longer and lower-pitched calls than controls; both these acoustic features play a critical role in mate choice. A morphometrical analysis of the midbrain nucleus intercollicularis showed a cell size increase in T-treated birds regardless of their sex. Histological study of the syrinx did not reveal any sexually dimorphic structure in experimental and control birds; the major T-induced change was a thickening of the external membranes, reported to be the main sound source in Galliforms. In conclusion, T appears able to modify not only some acoustic parameters, but also certain anatomical structures at the peripheral and central levels of the vocal system in a nonoscine species.