Brood Parasitism in the Moorhen: Brief Encounters between Parasites and Hosts and the Significance of an Evening Laying Hour

Abstract

Female Moorhens Gallinula chloropus laid their eggs in the evening, with more than 80% being laid between 1900 and 2200 hours BST. Parasitic eggs were laid within the same range of times as eggs laid by females in their own nests. Observation from videotape of laying events by eight different brood parasites revealed that parasitic laying is a stereotyped behaviour, consistent between females and characterized by speed and stealth. Parasitic females travelled directly to the host nest. By contrast with females laying at their own nests, brood parasites did not stop and wait for the host males to get off the nest before getting on, and they did not remain on the nest longer than was necessary to lay an egg. As predicted, hosts were aggressive toward brood parasites. Yet, brood parasites tolerated the hosts' aggression, and laid successfully in host nests in spite of the hosts' attacks. Although parasitic females and their mates both stood to benefit from brood parasitism, the act of laying parasitically was initiated entirely by (and entailed a potential risk for) the female alone. I discuss the implications of an evening laying hour for the evolution of intraspecific brood parasitism.