Interactions between hemoparasite status and female age in the primary reproductive output of pied flycatchers

The relationship between hemoparasite infection (measured just after egg la ying) and primary reproductive output (laying date, clutch size and egg vol ume) was studied in female pied flycatchers, Ficedula hypoleuca, of differe nt ages (2 years old vs. 4 or more years old). The hemoparasite (Haemoprote us balmorali and Trypanosoma spp.) prevalence increased with advancing fema le age, H. balmorali-infected females initiated egg laying earlier and laid larger clutches. There was no evidence that infected females laid smaller eggs or had a lower body mass after egg laying than non-infected ones. Only for H. balmorali-infected females was there an increase in clutch size bet ween age groups. The present results suggest that primary reproductive outp ut of females will depend on their health-dependent residual reproductive v alue. Only old females may he able to control a chronic or latent infection by hemoparasites and thereby invest more heavily in reproduction than youn ger but experienced females. Alternatively, high hemoparasite prevalence ma y be the cause of increased female primary reproductive output in old femal es.