Approximate breeding distributions of the “northern” wigeons (modified from Peters et al. 2005) with inset photographs of males of both species. Closed circles indicate sampling locations for Mareca penelope, open circles indicate sampling locations for M. americana. Wintering distributions are not shown, although both species are seasonal migrants, and several individuals were sampled from migrating and over-wintering populations (Tables S1–S2). Photos: Eurasian wigeon (M. penelope), Graeme Travers / Pexels; American wigeon (M. americana), Bryan Hanson / Unsplash.