Scaup or Tufted Duck?
When I lived in Bedfordshire, an occasional challenge was picking out the Scaup among a flock of Tufted Ducks. At Loch Ryan in Wigtownshire, I had the opposite challenge: picking out the Tufties among the Scaup! This was back in February when several hundred of the latter were wintering at this site and one day a couple of female Tufties appeared. The Scaup are mostly gone now in mid-April.