Morphological changes in the thymus of young and adult red-billed queleas Quelea quelea (aves)

In a wild population of red-billed queleas Quelea quelea L. (Ploceidae: weaver-birds) sampled throughout the year in East Africa, the thymus was found to enlarge in young birds shortly after hatching, remain enlarged during the juvenile stage, and regress towards the end of the postjuvenile moult. In adults, recrudescence occurred in many individuals during the prenuptial and postnuptial moults, and also in most if not all individuals, of both sexes, for a brief period during a breeding session. Thymus enlargement in both young and adults has been found to be accompanied by marked erythropoietic activity within the gland, and it is suggested that this activity is related to an increased demand for erythrocytes which may occur during moult and breeding.