Greater scaup (Aythya marila) breed across the tundra regions of Europe and North America and then travel by the thousands to our area in winter. They particularly like Pelham Bay in the Bronx and Sheepshead Bay in Brooklyn, and we get occasional visitors to Central Park. They have a rounded head, whereas their cousin lesser scaup have a peak at the back of their heads.
Greater scaup, the Pool, Central Park, December 20, 2021