Maternal clutch reduction in the pied flycatcher Ficedula hypoleuca: an undescribed clutch size adjustment mechanism

摘要

During eight years of study of a population of pied flycatchersudFicedula hypoleuca breeding in central Spain, we observedudthroughout incubation 22 cases of intact eggs being placed onudthe nest rim and clearly outside of the nest bowl and remainingudthere, with consequent embryo mortality. We assume that theudremoval of eggs had been performed by the incubating female.udThere is no evidence that pied flycatcher parents can detectudembryo mortality and eject unhatchable eggs. Maternal eggudejection constitutes a direct mechanism of clutch size adjustmentudduring incubation and before hatching of any young of the brood.udThis adjustment of clutch size happened when the mean andudminimum temperature of the day before ejection were especiallyudlow. Also, clutch-reducing females were significantly more proneudto show moult-breeding overlap than other females, suggesting audlower disposition to invest in reproduction. Clutch-reducingudfemales were also frequently older than four years and hadudindications of a lower immunocompetence than females notudejecting eggs. Our results support the hypothesis that adverseudconditions can elicit parental family size adjustment at every stageudof reproduction without the need to depend on mechanisms ofudsibling competition.