In many species of birds the propensity to learn songs from conspecifics is greatest during one or more distinct periods in life. These 'sensitive' learning periods, together with our detailed knowledge of the neural circuitry controlling avian song, have facilitated the discovery of radical neuroanatomical changes that accompany vocal development. One of the most remarkable of these changes is the production and incorporation of new, song-related neurons. The neurogenesis of specific cell types during song development helps create and recreate motor pathways for song production and provides synaptic plasticity that may both encourage and temporally constrain learning.