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; b oth these acoustic features play a critical role in mate choice. A mor phometrical analysis of the midbrain nucleus intercollicularis showed a cell size increase in T-treated birds regardless of their sex. Histo logical study of the syrinx did not reveal any sexually dimorphic stru cture in experimental and control birds; the major T-induced change wa s a thickening of the external membranes, reported to be the main soun d source in Galliforms. In conclusion, T appears able to modify not on ly some acoustic parameters, but also certain anatomical structures at the peripheral and central levels of the vocal system in a nonoscine species.