Enhanced testosterone levels affect singing motivation but not song structure and amplitude in Bengalese finches.

Song is a fundamental component of territory defense and mate attraction in birds, and androgens (like testosterone) are known to play a key role in controlling it. However, little is known about how differences in testosterone levels between males translate into inter-individual song variation. Indeed, testosterone could affect both the motivation to sing and the structure of song itself. Here, we tested whether experimentally elevated testosterone levels in adult Bengalese finches (Lonchura striata var. domestica), an oscine bird species, have an activational effect on 1) song performance, and 2) song structure. Our results show that testosterone-treated males, in contrast to sham-control males, sang more when confronted with a female. Other performance-related traits, however, such as latency to sing and song amplitude, were not affected. Testosterone-treated males also showed no differences in our two measures of song structure: fundamental element frequency and mean song frequency. Because song structure is known to be organizationally affected by testosterone, our results, synthesized together with findings from the current literature, suggest that in oscine birds, song contains multiple messages about the signaler's hormonal status. First, song performance may reflect current hormonal condition, and second, song structure may reflect the past hormonal state.