Greater Scaup - male
Greater Scaup at Lake Merced, San Francisco, from the bridge at the south end. Note the round head, fine vermiculations on the back, and the very white flank. The nail on the bill is medium-sized, which is fine for Greater. Also appears to have slight purple gloss, but that also varies greatly with lighting. Usually we see a beautiful dark green gloss, whereas Lesser Scaup shows purple, especially on the cheek.