CLUTCH SIZE MANIPULATION IN THE PIED FLYCATCHER - EFFECTS ON NESTLINGGROWTH, PARENTAL CARE AND MOLT

To study parental responses during the incubation and nestling periods , nestling growth and adult moult, two eggs were either removed from o r added to Pied Flycatcher Ficedula hypoleuca clutches shortly after c lutch completion. Incubation period and hatching success did not diffe r 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 experi mental change in clutch size, and this effect arose entirely in the fi rst four days after hatching. The results suggest that the embryo deve lopment during the incubation period and nestling growth during the fi rst days after hatching are important for the subsequent nestling grow th and should be taken into account when analysing the results of broo d size manipulations. Fledging and breeding success, fledgling mass an d 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 calend ar 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.