American Black Duck, Anas rubripes
A northeastern species closely related to the Mallard, sometimes thought to be a form of the same species. As with
the very similar but slightly less dark Mottled Duck of the southeast and Gulf Coast, it is darker than the Mallard,
and its sexes differ only slightly. This bird can be identified as female by the dull olive bill, different from the slightly
more colorful greenish-yellow of the male. A third dark Mallard-like duck group without strong sexual differentiation,
the "Mexican Mallard" of the southwest and Mexico, was formerly considered a separate species, but is now accepted
as a form of the Mallard.