STEVEN G. MLODINOW
Synopsis of the Problem
The Mexican Duck, Anas platyrhynchos diazi, was recognized as a full species (then A. diazi) until the American Ornithological Society (AOS; then AOU) merged it with the Mallard (AOU 1983), largely based on data from Hubbard (1977). However, recent genetic studies strongly suggest that the Mexican Duck should be returned to full species status (Kulikova et al. 2004, Banks 2010, Lavretsky et al. 2015). Investigators have also found that male Mexican Ducks can exhibit some “Mallard” traits (including green on crown, partial curl to central tail feathers, solid dark tail coverts, more reddish-brown breast). In the past, birds looking like male Mexican Ducks excepting some of these traits were typically considered Mallard x Mexican Duck hybrids. Based on recent evidence, such birds are quite likely Mexican Ducks, not hybrids. Of note, the phenotypic variation of female Mexican Ducks is poorly understood (though work to dene such is currently under way), so we do not currently understand how to reliably distinguish paler female Mexican Ducks from darker female Mallards.
The photos that follow are intended to provide a realistic overview of the challenge of identifying Mexican Ducks in the ABA Area. See Jack Bushong’s article for an analysis of when and where to look for Mexican Ducks—and what to look for. Both Bushong’s and the present analysis are drawn heavily from the authors’ experiences in Colorado, but the lessons apply broadly in the ABA Area.
Note: click the caption in each image to view image with caption full-screen