Egg recognition in Yellow-billed and Black-billed Magpies in the absence of interspecific parasitism: implications for parasite-host coevolution

Research concerning the retention of anti-parasitism host defences through evolution from a common ancestor is presented. The Yellow-billed Magpie, although not parasitized, ejects all foreign eggs, a trait shared by its' nearest relative, the Black-billed Magpie, which is parasitized.