Here are the field marks that make this a Lesser Scaup (as opposed to a Greater Scaup, which we also have here):
- The tufty peak above and behind the eye
- The vermiculations on the otherwise white flanks
- The darker pattern on the back
- The appearance of the eye being closer to the crown of the head
- The black on the tip of the bill not extending beyond the "nail" (although it's really hard to see on this photograph)