Wiki => Brood Parasite

The host may be the one that ultimately ends up raising offspring after they return from foraging. Once parasitism has occurred, the next most optimal defense is to eject the parasitic egg. According to parental investment theory, the host can possibly adopt some defense to protect their own eggs if they distinguish which eggs are not theirs. Recognition of parasitic eggs is based on identifying pattern differences or changes in the number of eggs.[18] This can be done by grasp ejection if the host has a large enough beak, or otherwise by puncture ejection. Ejection behavior has some costs however, especially when host species have to deal with mimetic eggs. In that case, hosts will inevitably mistake one of their own eggs for a parasite egg on occasion and eject it. In any case, hosts will sometimes damage their own eggs while trying to eject a parasite egg.