An Overview of Brood Parasitism

Abstract Laying eggs in the nest of another individual, and allowing or tricking the nest owner to rear such “parasitic” young rather than, or in addition to, its own, is one of the rarest forms of reproduction known. Except for the social insects, in which intraspecific brood parasitism is sometimes well developed (Wilson, 1971), such social parasitism is almost unknown in animal groups other than birds. Brood parasitism occurring within members of the same species (intraspecific or conspecific brood parasitism) has been reported for fewer than 100 species of birds (Yorn Tov, 1980), and possibly occurs among other vertebrates only in a few fish. Likewise, fewer than 100 species of birds are known to be obligatory brood parasites (Payne, 1977b). Sporadically interspecific egg dumping, or “facultative” brood parasitism, occurs among even fewer species, based on the available evidence. The rarity of brood parasitism as a reproductive strategy is rather surprising, considering that exploiting the energy of another species through true external or internal parasitism is extremely common among animals. Indeed, some phyla of animals are predominantly or even exclusively parasitic and, at least in terms of actual numbers of individuals, there are probably far more parasitic than free-living animals alive in the world.