Some endocrine correlates of renesting after loss of clutch or brood in the white-crowned sparrow, Zonotrichia leucophrys gambelii

Abstract

Through the course of incubation of eggs and feeding of young there is a decline in the plasma levels of luteinizing hormone (LH), testosterone, and estrogens to almost basal values by the time of fledging the young. If eggs or young are lost before the pair has become photorefractory, there is a resurgence in the plasma levels of these hormones that culminates in the laying of the replacement clutch. The plasma levels of corticosterone remains elevated in renesting birds of both sexes until just prior to the onset of the postnuptial molt when it declines precipitously. The rapid postbreeding regression of the gonads and the onset of the postnuptial molt are delayed in renesting birds, but the duration of the molt is decreased so that it is completed at the same time as that of non-renesting birds. It appears that the loss of clutch or nestlings somehow suppresses or removes an inhibitory function that normally decreases secretion of LH and sex hormones at this time. Since day length is still sufficiently long, the levels of these hormones are presumably increased through photoperiodically induced secretion and renesting ensues. The mechanisms that delay the onset of molt and decrease its duration are not known.