Egg Rejection: Getting Rid of a Parasite in the Nest

Abstract

Some species of birds, called brood parasites, lay their eggs in the nests of other species (called the hosts). Male and female hosts take care of the parasitic offspring. In most cases, the hosts raise only the parasitic chicks, which reduces the breeding success of the host birds. However, hosts can defend themselves from brood parasitism by developing the ability to recognize and reject parasitic eggs from their nests. In this article, we explore how host age influences the ability to reject foreign eggs. We show that female magpies improve their ability to reject foreign eggs added to their nests as they age, and we discuss what this might mean for both the magpies and cuckoos. Our results might ultimately help us to better understand how animals and humans defend themselves against the disease-causing parasites that infect them.