Songbirds learn their song by trial-and-error experimentation, singing highly variable songs as juveniles. We show that this vocal variability is induced by the output of a basal ganglia like circuit (LMAN) that projects to the motor cortex analogue brain region RA. To find the neural correlate of song variability, we record the firing patterns of premotor neurons in RA during singing in juvenile zebra finches with and without LMAN active. In juvenile birds with intact LMAN, RA activity was significantly more variable and much less sparse and bursty than in adult birds. Inactivating LMAN made the song-aligned firing patterns of RA neurons adult-like in their stereotypy, without dramatically affecting the juvenile spike statistic or the overall firing patterns. We show that motor variability required for vocal learning in the songbird can be produced by a simple summation of inputs at the level of RA neurons: HVC - an upstream motor nucleus, provides a stereotyped sequence, while LMAN, acts as the source of variability. Given this model, we show that the decrease in motor variability that accompanies learning can be explained by a gradual increase of in the strength of HVC to RA synapses.