Studies in zebra finches failed to demonstrate the involvement of the NIf, a higher-order song nucleus afferent to the HVc, in the production of learned song. The song of the Bengalese finch, a related species, has a higher level of temporal organization; multiple song phrases are organized into a song. We hypothesized that the Nlf might control this complexity. To test this, we bilaterally lesioned the Nlf in adult male Bengalese finches. The songs of birds with multi-phrase organization changed into simpler, mono-phrase songs. This is the first demonstration of the Nlf's involvement in the production of birdsong. Zebra finch songs are syntactically simple and deterministic, and this might have caused the difficulty in demonstrating the function of the Nlf in zebra finches.