Meeting Abstract
Bird song has historically been considered a male endeavor. Compared to tropical species where duetting is common, female song in temperate-zone species has been considered rare. In the last decade, however, the number of species with previously undocumented female song has expanded rapidly. In house wrens (Troglodytes aedon), females in several North temperate populations sing. Female house wren song structure is highly variable, ranging from a single syllable to songs nearly indistinguishable from male songs. The acquisition and production of bird song is controlled by a series of discrete brain regions that collectively form the song control circuit. We asked whether sexual dimorphism in the song circuit reflects the sexual dimorphism in singing behavior. We caught 18 male and 18 female house wrens from a wild population in Michigan and quantified the volume, cell number, cell density, and average cell (soma) size in three regions of the song control circuit (HVC, RA, Area X). Unlike some species that lack female song entirely, we found regions comparable to the male HVC, RA, and Area X for 94% of the females in the study. For all three regions, the volumes were larger, more cells were present, and the average soma sizes were greater in males than females. For HVC and RA, males also had lower cell densities. In contrast, the nucleus Rotundus (Rt), a visual processing center, showed no sexual dimorphism. This is the first study to examine the song control circuit in either sex in the house wren. Follow-up work will explore whether intrasexual variation in the morphology of song control regions reflects intrasexual variation in song structure.
