Nest-dwelling ectoparasites of two sympatric hole-nesting passerines in relation to nest composition: An experimental study

There are often marked differences in the incidence of nest-dwelling ectoparasite species on different coexisting and similar avian host species. This has been shown especially for fleas (Siphonaptera), larvae of flies (Diptera), and mites (Acarina) in nests of tits and flycatchers breeding in nest-boxes in close proximity to each other. One of the possible reasons for these differences is the marked differences in nest composition between avian species. We show here differences in ectoparasite presence and nest composition for blue tits (Cyanistes caeruleus) and pied flycatchers (Ficedula hypoleuca) coexisting in oak forests in central Spain. There also may be intraspecific differences in local preferences for nest-building materials according to availability of plant materials, which could be due to arthropod repellent properties of different potential nest components. We show here a local difference in nest composition between 2 pied flycatcher populations in relation to availability of a preferred material associated with higher ectoparasite presence in the locality without the preferred nest material. We test the hypotheses that differential incidence of ectoparasites at the interspecific and intraspecific levels may depend on nest composition. We conducted a nest exchange experiment in one study locality in 2007 placing in nest-boxes occupied by flycatchers 1) nests constructed by blue tits in 2006 in another locality and removed before use and stored frozen, 2) nests constructed by flycatchers in 2006 in another locality with different nest composition and removed before use and stored frozen, and 3) nests constructed by other flycatcher pairs in the same study locality in 2007. Another group of flycatcher nests was kept as pure control, while a few blue tit nests constructed in 2007 and taken over by flycatchers were used for comparison with nests of treatment 1. No effect on presence of mites and blowflies of either nest-constructing species or locality of construction was observed for pied flycatcher nests, and for fleas only an effect of locality but not of nest constructing species was detected. On the other hand, presence of mites and blowflies differed between nests constructed by blue tits and occupied by either blue tits or pied flycatchers. Nest composition does not explain the differential incidence of nest-dwelling ectoparasites on coexisting avian host species.