Thursday, September 11, 2014

Mexican Duck

While Erika and I birded at the Bosque del Apache National Wildlife Refuge last March, I took this photo of a passing duck. I knew this might be a Mexican Duck. A Mallard should show much whiter under tail coverts. Black and Mottled ducks are not found in central New Mexico.

But what is a Mexican Duck? Drilling et al. (2002) warn, “the taxonomy of the Mallard and close relatives is complex with little agreement on how to treat some taxa.” The first problem is that Mexican Ducks and Mallards hybridize extensively in New Mexico, leading the American Ornithologists’ Union and the Handbook of Birds of the World—Alive to consider the two populations to be subspecies, with many individuals showing intermediate field marks. But this dictum does not appear to be consistent, since, despite massive hybridization, Black Ducks and Mallards are considered to be distinct species.

Just to further confuse matters, genetic studies indicate that Mexican Ducks are actually more closely related to Black Ducks than they are to Mallards. Some ornithologists think that Mexican Ducks are a recently diverged species that will become reproductively isolated from Mallards. Not helping this situation is habitat destruction and over-hunting. Mexican Duck numbers are declining in the United States. The more adaptable Mallard is holding its own, and may yet genetically swamp Mexican Ducks (Wikipedia).

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