Sex differences in circulating androgens that occur shortly after birth are thought to be responsible for sex differences in programmed cell death. Early androgen treatment of females is associated with permanent rescue of these motor neurons. A more complex model for studying sex differences in brain and behavior is the control of birdsong, a learned behavior used to attract mates during the breeding season. Although progress toward understanding the development of sex differences in this system has been much slower than for the SNB, a complex, interconnected system of brain regions such as that for vocal control in birds might ultimately provide a better model for understanding sex differences in complex behaviors across vertebrates, including humans. Song has intrigued scientists and lay persons alike for centuries, in part because it is often pleasing to the human ear.
Young birds learn to sing from their adult companions.
This has been demonstrated in three ways. First, birds raised in isolation from members of their own species fail to develop normal song. Second, abnormal song occurs after deafening early in their lives. Third, birds raised in isolation but who are exposed to recordings of song will incorporate many of the song elements into their own vocal repertoire. The fidelity engendered by the vocal memory system in birds can be quite remarkable.