This is a difficult hybrid combination to prove. However this male Scaup seems to have some features of Greater Scaup (wide tooth, paler barring on the back, green irridescence on head), some characters of Lesser Scaup (small size, short wing stripe), and some intermediate features (head shape, bill shape). Photos were taken 1/30/2017 at "Ziegler Pond" in Fort Collins, Colorado (first row), and 2/5/2017 at the small pond just to the north. UPDATE 2/6/2017. However, expert opinion is that this bird is within normal variation of Lesser Scaup.