The passerine bird song system as a model in neuroendocrine research

In the neural system controlling song in passerine birds, gonadal steroid hormones have potent effects on neural growth and differentiation. During ontogeny, sex differences in the secretion of steroid hormones lead to dramatic sex differences in neuron number and structure. In adulthood, sex steroid hormones also cause a significant reorganization of neural circuits. These studies of hormone action have been influential in the development of the field of neuroendocrinology.