Muscle fibers alone can’t explain sex differences in bird song

Male birds tend to be better singers than females — but does the basis for this difference lie in the brain or in the syrinx, their equivalent of our larynx? The researchers behind a new study analyzed the muscle fibers in the syrinxes of male and female birds from a range of species and found, to their surprise, that the amount of ‘superfast’ muscle didn’t explain differences in vocal ability between the sexes.