Low male return rate due to clutch enlargements in the pied flycatcher (Ficedula hypoleuca)

Abstract

:Increased investment in reproduction during current breeding event may entail future fitness costs. Even though a wide array of both theoretical and empirical work has been devoted to solve the problem of optimal reproductive rate, evidence for costs of reproduction has been equivocal. In the present study we examined the survival of pied flycatcher parents after a clutch size manipulation where we altered clutch size with one or two eggs. We monitored return rates and dispersal of parents during subsequent years after manipulation. An artificial increase in reproductive effort caused lowered return rates of males. Results on breeding dispersal did not support the explanation that observed low return rate was due to differences in dispersal. Thus, it seemed that low return rate of males with increased reproductive effort was due to lower local survival. No survival cost on females was evident, but return rate of females was too low for a proper test. An analysis on reproductive success revealed that within treatment groups the returning males tended to be more successful in their previous reproductive event than non-returning ones. These results together imply that phenotypic quality of individuals varies considerably causing fitness differences between individuals.