The effect of parasite density on host colonisation success by a mobile avian ectoparasite

Abstract

1. Full understanding of the dynamics of host–parasite interactions requires elucidation of the principles governing host colonisation. With respect to mobile parasites, little is known about their dispersal behaviour and the factors affecting host colonisation success.2. Here, the effect of parasite density manipulations on the colonisation success of the carnid fly Carnus hemapterus, an avian ectoparasite, was experimentally explored.3. Most host nests were colonised within the same breeding season, but the abundance of flies colonising the nests varied broadly both within and between years.4. Experimental increase in the density of carnid flies in the vicinity of host nests did not result in higher parasite abundance in these nests. Host colonisation success in terms of parasite abundance was not related to indices of parasite density around host nests.5. Parasite abundance in colonised host nests was positively related to host density and brood mass and negatively related to date. Host nests in trees held fewer carnid flies than those on cliffs and farmhouses.6. The dispersal ability of C. hemapterus is apt for rapid colonisation of new host nests, but it is unable to explain the broad heterogeneity in parasite abundance between host nests.