Ectoparasitism in marsh tits: Costs and functional explanations

Abstract

Among hole-nesting birds, the blood-sucking hen flea is a common parasite affecting both nestlings and parents. By adding fleas to marsh tit (Parus palustris) nests, I aimed to investigate the effect of fleas on nestling growth rate and parental effort as well as evaluating a potential mechanism by which fleas affect nestlings (i.e., resting metabolic rate; RMR). Nestlings from flea-infested broods were lighter than nestlings from control broods. This reduced growth rate was evident as soon as 3 days after adding extra fleas to the nest, but the reduction did not increase after this initial drop in mass. Parents did not alter their feeding frequency in response to the manipulation; thus the small size of nestlings in manipulated nests seems to be directly caused by the fleas. Mass-specific RMR was significantly higher in nestlings from flea-infested nests compared to nestlings from control nests. I used the results to evaluate the suggested mechanisms for parasite-related decrease in host growth rate. The increase in RMR and the very rapid reduction in nestling growth rate after experimental addition of fleas can be explained by an immune reaction, mainly by the innate immune system, to substances in the saliva of the fleas.