Host Responses to Ectoparasites: Food Compensation by Parent Blue Tits

Parental food compensation has been proposed to account for the absence or small negative effects of parasites on offspring in various bird-parasite systems. An increase in the quantity of energy and nutrients provided by the adults would therefore compensate for the offspring's loss of blood to blood-sucking ectoparasites. We studied parental food compensation in a blue tit Parus caeruleus population with experimentally controlled infestations by the bird flea Ceratophyllus gallinae. Parental feeding effort, offspring quality, and parasite reproduction were measured in randomly assigned parasite-free and infested broods. Although the ectoparasites reproduced at a high rate in infested nests, the nestlings did not suffer higher mortality or reduced body size and body condition than nestlings in parasite-free nests. Fleas had a small negative effect on feather development of nestlings. Parent blue tits of infested nests increased rate of food provisioning by 29%. The results support the parental food compensation hypothesis. No short-term costs (i.e. lowered body condition) of parasites on the parents could be detected. Although the long-term costs of parasites on parents were not measured in this study, the results lend support to previous suggestions that the absence of an effect of ectoparasites on the offspring may be due to the fact that parents bear the cost of parasitism.