You may have seen the striking male Mandarin duck on a visit to a park, as they are successful in the wild here in the UK, though they are originally from Asia as you might have guessed, with the UK population having grown from escapees. That said, according to Wikipedia and the RSPB (whose numbers don't tally but suggest 1,000 – 7,000 pairs) the UK population may be similar to those in their native homelands, due to exports and loss of habitat.

The BBC doesn't say much about them, but it does have a particularly interesting factoid: they're one of the few ducks that isn't hunted for food, as apparently it tastes really bad!