Generating sexually differentiated songs.

The past year has witnessed increased confusion as to the role of gonadal hormones in the development of neuroeffectors for sexually differentiated vocalizations in several species. Are sex differences in levels of circulating gonadal hormones robust enough to account for the full spectrum of male/female differences? Understanding how vocal behaviors are generated has improved, permitting greater insights into how differences in cell number and type contribute to male- and female-specific songs in frogs and birds.