Effects of experimental reduction in nest micro-parasite and macro-parasite loads on nestling hemoglobin level in blue tits Parus caeruleus

Theory suggests that macro- and micro-parasites may be important factors of selection for life-histories. They generate selection pressures by detrimental effects on host health. Nests of secondary cavity nesters provide a convenient habitat for an assemblage of parasites exploiting nestlings. In this study, natural blue tit Parus caeruleus nests (26) were replaced with clean artificial nests, twice during the nestling stage. This treatment caused an increase of 7-10.5 g/l in hemoglobin level of 12-day-old nestlings in comparison with control nestlings. Nestlings that developed in parasite-pathogen-free nests improved their health status. The experimental sterilization did not affect a morphometric index of condition. Potential effects on condition indices might be masked by trophic conditions.