At a distance, the breeding male Lesser Scaup is black and white, but closer views reveal an iridescent purple to green sheen on the head, a finely barred black-and-white back, a bluish bill, and a yellow eye.
Females (last photo) are brown overall with a darker brown head and a white patch next to the bill, but not all females have a white patch.
Non-breeding males look like a cross between a female and a breeding male: a mottled brown-and-gray body and a blackish head.
The Lesser Scaup breeds in the northern part of North America and in winter migrates south through out Central America.
The very similar looking Greater Scaup is rare in this region but, only in winter, is sometimes found in Mexico and Costa Rica.
One distinctive difference between the two is that the Lesser Scaup has a small peak at the back of the head whereas the Greater Scaup has a much more rounded head.

Panajachel, Lake Atitlán, Guatemala, 19 January 2020