Song control regions in passerine birds are sexually dimorphic in the adult brain of species like the zebra finches in which males sing whereas females do not. In the majority of tropical bird species, however, females sing as well. The issue of female song production began to attract more attention recently, but the neural mechanisms involved in the female song production are still poorly understood. Here we study for the first time the ontogeny of the song control system in a species, in which both male and female sing regularly. In blue-capped cordon blues (Uraeginthus cyanocephalus), a close relative of the zebra finch, females sing but have shorter songs with fewer syllables compared to the males. Volumetric changes of forebrain song control regions (the HVC, the RA and the LMAN) of the blue capped cordon bleu have been quantified in both sexes at 20, 30, 50 and ≥100 days posthatching, by using the Nissl- taining method and in situs hybridization. In both sexes, no significant differences in the volumetric development of HVC (proper name) were detected. The Nissl-efined volume of the HVC in males was always superior to the females values, including the adulthood, when the volume values became significant bigger in males than in females. In contrast, the volume of the robust nucleus of the
archistriatum (RA) increased with age reaching the highest values in adulthood. The Nissl-defined RA volume incresed by 2,21 times in males (from 0,104 mm3 at 20 days to 0,236 mm3 in adulthood). In females, no significant differences in the volumetric development of RA were detected.
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