Spot the difference

I don't know if you get these puzzles any more, but that's what this pair of male teal reminded me of on Blackford Pond. There were in fact six of them, all male, which is five more than I've seen there at any one time. Maybe their usual home had got fully frozen over as they spent their time in the smallish area of the pond which was free of ice, along with most of the other birds. It was another lovely cold, bright day but it looks as if the weather is going to change this evening.