Clutch Size Manipulation in the Pied Flycatcher: Effects on Nestling Growth, Parental Care and Moult

Abstract

To study parental responses during the incubation and nestling periods, nestling growth and adult moult, two eggs were either removed from or added to Pied Flycatcher Ficedula hypoleuca clutches shortly after clutch completion. Incubation period and hatching success did not differ between experimental groups. In the enlarged group the rate of male incubation feeding of the female was higher than in the other groups. Fledgling mass and tarsus length were negatively related to the experimental change in clutch size, and this effect arose entirely in the first four days after hatching. The results suggest that the embryo development during the incubation period and nestling growth during the first days after hatching are important for the subsequent nestling growth and should be taken into account when analysing the results of brood size manipulations. Fledging and breeding success, fledgling mass and tarsus length differed between experimental groups with lower values in the enlarged group. There was an effect of experimental treatment on female and male feeding rates, with higher number of feeding visits in the enlarged group. The onset of adult moult was related to calendar date and there was no effect of the experiment on the proportion of birds moulting at any given time. At least in this population, moult may not be a mechanism mediating costs of reproduction.