Testosterone stimulates the expression of male-typical socio-sexual and song behaviors in female budgerigars (Melopsittacus undulatus): An experimental study

The hormonal control of sex differences in behavior has been extensively studied, particularly in mammals and birds. Studies have shown that the activational potential of the androgenic sex steroid testosterone (T) on male-typical behaviors in females seems to be species- as well as behavior-specific in birds. It is therefore important to study the activational effects of T in a great variety of bird species and on a wide range of behaviors, preferably in social conditions that favor their expression. Here, we investigated the activational effects of T on vocal, socio-sexual (i.e. affiliative and non-vocal courtship behaviors), aggressive and approach behavior in females of the budgerigar, Melopsittacus undulatus, a highly social monogamous parrot species. We experimentally supplemented T-females with male-like plasma T levels compared to controls. First, we observed females when they were individually housed. We found that T-females performed male-like levels of warbling song, sang significantly longer, but not more song bouts and produced more socio-sexual behaviors than controls. Then, we consecutively confronted females with a female, a dummy, and a male conspecific. T-females showed a significantly shorter latency to interact in all three social contexts. In both intrasexual and intersexual contexts, T-females performed significantly higher levels of approach and socio-sexual behavior, including “mounting (attempts)”, a strictly male behavior, which was not observed in control females. Aggression in a non-reproductive context did not appear to be sensitive to T supplementation. Our data indicate that in the budgerigar even marked sex differences in socio-sexual behavior may depend on the activational effects of T, while this is generally not the case in other species.

► We studied vocal and social behavior in testosterone-implanted female budgerigars.
► Females with elevated testosterone sing more and sing longer but not more bouts.
► Intra- and intersexual non-reproductive aggression is not affected by testosterone.
► Testosterone-females produce more socio-sexual behavior and strictly male behaviors.
► Testosterone activates the production of vocal and socio-sexual behaviors in females.