Take a look at this bird:

Now look at this one:

And finally, this one:

Which of these birds, if any, are Mallards? Answers will be forthcoming, but for now, I can tell you that they are all members of the mallard complex, a roster of about 20 closely-related Anas-species ducks around the world.

Everyone knows what a male Mallard looks like. The drake of this extremely common, sexually dimorphic species cuts a fine form with his iridescent emerald dome and chestnut breast. A female mallard possesses plumage as dull as her partner’s is bold, a frock of forgettable grays, browns, and blacks.

The mallard is a mighty duck indeed, successful all across its broad range from the Americas through Eurasia down into Australia and New Zealand. Not only are most domesticated duck breeds descended from A. platyrhynchos, but many distinct populations of wild ducks have sprung from the productive loins of this dynamic dabbler. Most of these species are monomorphic and more closely resemble the mallard hen. If you had trouble separating the American Black Duck (A. rubripes), Mallard, and Mottled Duck (A. fulvigula) in the photos above (in that order), you’re hardly alone. The ducks themselves seem to have the same difficulty, as these three species interbreed freely. Such hybridization threatens to undermine A. rubripes and fulvigula as separate species, just as the Mexican Duck (A. diazi) was compromised into mere mallard race status. The Hawaiian Duck (A. wyvilliana) and Laysan Duck (A. laysanensis) also balance on that fine line between species and subspecies.

The genus Anas, dabblers all, includes wigeons, shovelers, teals, and pintails as well as mallards. It’s difficult to say which birds on this list are part of the mallard complex, but many of them, especially the females of the species, show superficial or structural mallard traits.

Here’s a bonus piece of mallard complex trivia: If the extinct Mariana Mallard (A. oustaleti) is ever granted posthumous species status, it will represent one of the most short-lived vertebrate species known to science, with a lifespan measured only in tens of thousands of years from the first rendezvous between Mallard and Pacific Black Duck (A. superciliosa rogersi) to the death of the last individual in 1981.