Nest Sharing Between an American Robin and a Northern Cardinal

Abstract

Mixed-clutch nest sharing was observed between an American Robin (Turdus migratorius) and a Northern Cardinal (Cardinalis cardinalis) in Saylor Township, Polk County, Iowa in May 2007. The nest contained three American Robin eggs and two Northern Cardinal eggs, but only American Robin young were fledged successfully. This was not a case of brood parasitism, as both females were observed alternating incubation of the nest. Competition for desirable nest sites might be a possible cause for this type of interspecific behavior.