MITES AND BLOWFLIES DECREASE GROWTH AND SURVIVAL IN NESTLING PIED FLYCATCHERS

The effects of blood sucking mites (Acari) and blowfly larvae (Diptera) ectoparasites on the growth and survival of nestling pied flycatchers (Ficedula hypoleuca) breeding in nest boxes were studied. Mites significantly decreased mean within-brood tarsus length, a measure of skeletal size, and mass. High mite loads also increased within-brood variance in mass, although the effects varied depending on the quality of the nesting site. Significant interactions between the effects of mites and nest box quality and breeding phenology were detected, the lightest nestlings fledging from late, low quality nests with high mite loads. No effect of mite loads on nestling mortality was apparent. In contrast, blowfly larvae abundance contributed more to nestling mortality in one year, although this seemed to pave the way for brood survival in nests with high infestations. High abundances of both ectoparasite species were comparatively beneficial for pied flycatcher broods, suggesting a role for competition between ectoparasites that may ultimately increase host brood survival.