Identification of the Sex Responsible for Recognition and the Method of Ejection of Parasitic Eggs in Some Potential Common Cuckoo Hosts

Egg rejection is the most common defence used by hosts against avian brood parasites and experimental studies have provided some of the best documented demonstrations of the coevolutionary process. However, the sex responsible for egg ejection and whether eggs are grasped or punctured are two essential questions that remain unanswered for most host species. In this paper, by filming the behaviour of individuals of three different species confronted with a foreign egg experimentally introduced into their nests, we first determine the relationship between recognition (when the birds aggressively pecked the experimental egg) and ejection. Secondly, we demonstrate that in the species where only the female incubates, only the female recognizes and ejects the model egg, whereas in the two species where both sexes incubate, both sexes eject the foreign egg. Finally, the large host species ejected the model egg by grasping it with the bill, whereas the two small species ejected it by puncturing it first. Furthermore, our data suggest that puncture ejection is more costly than grasping ejection considered both in terms of energetic and ejection costs.