Secondary cavity-nesting species must find natural cavities or artificial nest boxes to reproduce. Cavities are often limited, which results in intense interference competition among species that rely on them. Nest site shortages may exclude subordinate individuals from cavities and force them to adopt alternative reproductive tactics such as laying eggs in the nests of conspecifics or in the nests of other species. The Prothonotary Warbler (Protonotaria citrea) is a secondary cavity-nesting bird that opportunistically parasitizes conspecifics that has never been recorded parasitizing heterospecifics. Here, we report brood parasitism of a House Wren (Troglodytes aedon) nest by a Prothonotary Warbler and the subsequent fledging of a warbler from this nest. This is the first observation of interspecific brood parasitism for the Prothonotary Warbler and the first instance of interspecific brood parasitism by any New World warbler species.

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