Two cases of a previously undocumented New World warbler hybrid (Setophaga magnolia × S. ruticilla) in eastern North America

Abstract

This study confirms 2 independent accounts of previously undocumented hybridization between Magnolia Warbler (Setophaga magnolia) and American Redstart (S. ruticilla) through morphological and genetic analyses. Hybrids were discovered in 2 locations in eastern North America: Ottawa County, Ohio, USA, and Laval, Québec, Canada. The hybrids, one male and one female, showed plumage intermediate to both parental species. White eye arcs, yellow wash on the belly, narrow white wing bars, and black lores reflect the Magnolia Warbler parentage, while dark yellow-orange coloration on the sides of the breast and under the wing, yellow on the base of most of the secondaries, and pale yellow patches on the outer tail feathers reflect American Redstart. Sequences of the mitochondrial ND2 gene, the Z-linked muscle-specific kinase (MUSK) gene, and the myoglobin intron-2 (MYO2) confirmed maternal ancestry from Magnolia Warblers and paternal ancestry in American Redstarts for both hybrids. There is ample opportunity for this species pair to hybridize; they are congeners with broad range overlap, similar habitat preferences, song structure similarities, and plumage similarities in some age categories. Despite these conditions and the unusually high rate of hybridization within the Parulidae, this hybrid combination has never been documented before, and we suggest that this is a rare event that may be expected anywhere in their broad, overlapping ranges.