Utilization of a new host in the host-specialist brood parasite Molothrus rufoaxillaris: host switch or host acquisition?

MAHLER, B.; SARQUIS ADAMSON, Y.; DI GIACOMO, A. G.; CONFALONIERI, V. A.; REBOREDA, J. C.

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY

Springer Verlag

Lugar: Heidelberg; Año: 2009 vol. 63 p. 1603 - 1608

0340-5443

The screaming cowbird Molothrus rufoaxillaris has been long known as a host-specialist brood parasite. However, in the past years, the utilization of two new hosts has been documented. We examined the variation in mitochondrial control region sequences from screaming cowbird chicks found in nests of two hosts, the bay-winged cowbird (Agelaioides badius), which is its regular host, and the chopi blackbird (Gnorimopsar chopi), which is a new host, in Formosa Province, Argentina. If a group of females switched to this new host, we expected to find an association between host use and haplotype frequency distribution, indicating the presence of host-specific female lineages, whereas we expected no such association if the cowbird population incorporated this new host and females use both hosts simultaneously. Haplotype frequency distributions differed between cowbird chicks from nests of both hosts. This indicates that nest choice by females of this brood parasite is not random and that they preferentially parasitize the nests of the same host species.