Female songbirds are known to sing simpler songs than their male counterparts. Due to this basis, it was widely believed that testosterone-induced vocalization or song learning. The logic was since testosterone was much less in female songbirds, therefore, the singing ability is also lessened. With Goldman and Nottebohm’s studies, they found out that in fact, the ability to sing is much more of a neural development than a hormonal activity. Nottebohm's studies showed that the left hemisphere of the bird's brain is largely in control of the learning ability to sing and vocalise. Aside from that, bird's also regenerate their neuron cells unlike previous belief that at a certain age, neural development stops.
