Neural correlates of female song in tropical duetting birds.

Duetting involves production of song by female and male birds in close temporal coordination. We studied the neural network controlling song in 3 tropical duetting species. The volumes of song control regions (SCRs) in the brain, neuronal density in nucleus robustus of the archistriatum (RA) which is one of these SCRs, total number of neurons in RA, and somal size of neurons in RA were measured and compared to values published for zebra finches and canaries in which only males sing. The extent of sexual dimorphism in SCR volumes, RA neuronal density, and total neuronal number in RA varied in a graded fashion across species and was correlated with extent of sexual dimorphism in song repertoire size in any one species. Somal size of RA neurons was identical in males and females of each duetting species, regardless of relative repertoire size. Of all SCRs, the caudal nucleus of the ventral hyperstriatum appeared to have the greatest relative size in the song system of duetting birds compared to non-duetting species.