Pied Flycatchers Ficedula hypoleuca prefer ectoparasite-free nest sites when old nest material is present

Abstract

Nest-dwelling ectoparasitic arthropods may have detrimental effects on avian breeding success and fitness. Birds should therefore be selected to avoid nest sites where the risk of being infested by ectoparasites is high. However, studies testing this hypothesis have produced mixed results. We performed an experiment in south Norway to test whether Pied Flycatchers Ficedula hypoleuca select nest site according to the presence of ectoparasites. We used artificial nest boxes in this experiment which had all been successfully used by conspecifics in the previous breeding season and still contained the old nest material. Five different groups of ectoparasites were recorded in flycatcher nests in the study area, of which the haematophagous hen flea Ceratophyllus gallinae and mites (Dermanyssus sp.) occurred in all examined nests. We offered each flycatcher pair (n = 13) a choice between 1) a box where ectoparasites had been removed by insecticide fumigation and 2) a box in which the old nest had not been fumigated. Flycatchers were highly selective in their choice of nest site, all but one settling in the fumigated, parasite-free nest box. This finding differs from a similar Swedish study (Olsson & Allander 1995) which did not find any evidence that Pied Flycatchers avoided nest boxes with ectoparasites. A likely explanation for this discrepancy is between-population differences in parasite abundance, as the mean number of hen fleas per infested nest was about five times higher in Norway than in Sweden.