LOW MALE RETURN RATE DUE TO CLUTCH ENLARGEMENTS IN THE PIED FLYCATCHER (FICEDULA-HYPOLEUCA)

Increased investment in reproduction during current breeding event may entail future fitness costs. Even though a wide array of both theoret ical and empirical work; has been devoted to solve the problem of opti mal reproductive rate, evidence for costs of reproduction has been equ ivocal. In the present study we examined the survival of pied flycatch er parents after a clutch size manipulation where we altered clutch si ze with one or two eggs. We monitored return rates and dispersal of pa rents during subsequent years after manipulation An artificial increas e in reproductive effort caused lowered return rates of males. Results on breeding dispersal did not support the explanation that observed l ow return rate was due to differences in dispersal. Thus, it seemed th at 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 tao low for a proper test. An analysis on reproductive success revealed that within treatment groups the returni ng males tended to be more successful in their previous reproductive e vent than non-returning ones. These results together imply that phenot ypic quality of individuals varies considerably causing fitness differ ences between individuals.