STEROID ACCUMULATION IN SONG NUCLEI OF A SEXUALLY DIMORPHIC DUETTING BIRD, THE RUFOUS AND WHITE WREN

This study tested the hypothesis that the relative proportion of neuro ns that are hormone sensitive in avian song control nuclei is related to the basic motor ability to sing, whereas the absolute number of suc h neurons is related to the complexity of song behavior. Either [H-3]t estosterone (T) or estradiol (E(2)) was injected into male and female rufous and white wrens (Thryothorus rufalbus), a tropical species in w hich females sing duets with males but have smaller song repertoires t han males, Autoradiographic analysis indicated that there were no sea differences in the proportions of T or E(2) target cells in two song n uclei: the high vocal center (HVC) and the lateral portion of the magn ocellular nucleus of the anterior neostriatum (IMAN). The density of l abeled cells per unit volume of tissue did not differ between the sexe s in either song nucleus. Males have larger song nuclei, however, whic h is consistent with their more complex song behavior, and therefore h ave a greater total number of hormone-sensitive neurons in these regio ns than do females, Comparison of these results with measures of hormo ne accumulation in zebra finches, canaries, and bay wrens supports the hypothesis presented. (C) 1996 John Wiley & Sons, Inc.