The importance of low host densities for successful parasitism of diederik cuckoos on red bishop birds

Abstract

Parasitism by diederik cuckoos Chrysococcyx caprius on their main southern African host, the red bishop bird Euplectes orix, was studied. Virtually all the cases of parasitism occurred where there were low densities of red bishop nests. Data from the present study were combined with published observations to show that the incidence of parasitism is much higher in small breeding colonies of red bishops than in large colonies. Aggression of red bishops towards diederiks is described. I suggest that diederik cuckoos cannot approach red bishop nests undetected where large concentrations of red bishops are found. High levels of brood failure in small red bishop colonies caused by brood parasitism may constitute a selective force for colonial breeding in this host species.