Interactions of the Parasitic Screaming and Shiny Cowbirds (Molothrus rufoaxillaris and M. bonariensis) with a Shared Host, the Bay-Winged Cowbird (M. badius)

Abstract

Abstract This chapter deals with the triangular interactions of three avian species currently classified in the genus Molothrus, a system consisting of two brood parasites sharing a host. The host species is the bay-winged cowbird (Molothrus badius), quite different from the other cowbirds because it is nonparasitic, has extensive parental care, and lives in permanent groups that show cooperative breeding (Fraga 1972, 1991, 1992). The screaming cowbird (Molothrus rufoaxillaris) is one of the most specialized avian brood parasites and has M. badius as its only host over most of its range. Lastly, the shiny cowbird (M. bonariensis) is a generalist avian parasite with hundreds of hosts (Friedmann and Kiff 1985) that regularly parasitizes M. badius. A recent phylogeny based on mitochondrial DNA (Lanyon 1992) suggests that M. badius is not closely related to the parasitic cowbirds.