Host–parasite interactions in natural holes: marsh tits (Parus palustris) and blow flies (Protocalliphora falcozi)

Infestation of marsh tit (Parus palustris, Paridae, Passeriformes) broods by bloodsucking larvae of Protocalliphora falcozi Séguy 1928 (Calliphoridae, Diptera) was studied over an 8-year period in a population breeding in natural holes, in the primeval forest (Białowieża National Park, eastern Poland). Overall 54% of 222 marsh tit nests were parasitized. Prevalence (27–88%) significantly changed across years. This variation did not depend on the timing of the marsh tit breeding season, or winter/spring temperatures. Frequency of infestation did not depend on forest type or hole attributes. Infestation intensity was rather low (median 8, max. 75 flies/nest, 85% of nests with