This study will examine the effects of early learning on the adult neuroendocrine system. Specifically, it will examine the physiological and behavioral response of female white-crowned sparrows (Zonotrichia leucophrys oriantha) to male songs with which they have, or have not, had prior experience. White-crowned sparrows learn their songs during a sensitive phase early in life, but respond to these songs in adulthood. Juvenile females sparrows will be captured from their natal area and housed in captivity. Then they will be stimulated by long days and played back male courtship songs from either their natal area or another area. Songs from another species and no song will be used as control treatments. Behavioral responses to be examined will be nest-building and solicitation displays. Physiological responses to be examined will include ovarian development and circulating hormone levels. Photoperiodic species of birds exhibit remarkable plasticity in the size and number of neurons immunoreactive for gonadotropin releasing hormone (GnRH), and changes in this system will also be measured. Hormone levels will be determined by radioimmunoassay. Immunoreactive GnRH neurons will be measured by immunocytochemistry. These experiments will test two hypotheses: i) that young female white-crowned sparrows imprint on the song of their natal area, and that in adulthood this learned song facilities both reproductive behavior and neuroendocrine responses to photo-period; ii) that this physiological response to song is mediated directly by the hypothalamo-pituitary-gonad axis.
