Testosterone induction of male-like vocalizations in female budgerigars (Melopsittacus undulatus)

Budgerigars possess a complex learned vocal repertoire that includes a long rambling song called warble. While both males and females can warble, there are marked sex differences in the amount of song produced. Males generally warble daily at a high rate, while females rarely sing. Both the quantity and the quality of male warble are influenced by circulating levels of testosterone. Males have higher circulating levels of testosterone than females. In this study we asked whether administering testosterone to adult female budgerigars would activate male-like vocal behavior. Four females were implanted with 8-mm Silastic implants filled with testosterone and recorded before and after implantation. Within 10-14 days, all four birds showed: (1) changes in cere color to the male-like condition (blue), (2) male-typical patterns of precopulatory behavior, and (3) an increase in their rate of warbling to male-like levels. Sound analysis revealed that the acoustic structure of the testosterone-induced female warble is similar to the male warble. These data indicate that sex differences in budgerigar vocal behavior are not based on early organizational effects of steroid hormones, but rather are probably the result of adult sex differences in circulating testosterone levels.