Endocrine correlates of brood size in adult pied flycatchers, Ficedula hypoleuca

Abstract

Plasma levels of corticosterone, testosterone, and dihydrotestosterone (DHT) are measured in adult Pied Flycatchers with broods of different sizes, including experimentally enlarged broods. Breeding success is also recorded as well as body weights of both the adults and the nestlings. For both parents plasma levels of corticosterone are significantly elevated with large broods. No differences in the plasma levels of testosterone and DHT can be observed between adult birds' feeding broods of different sizes. Experimentally enlarged broods and normal-sized broods produce the same number of fledglings. Body weights of nestlings in enlarged broods, however, are significantly lower than those of nestlings from normal-sized broods. Females feeding the nestlings alone have a significantly higher level of corticosterone in the blood than paired females and males raising the same number of nestlings. No differences in testosterone and DHT can be observed between these two categories.