Ducks, surrogate parents or imprinting on other birds?

[Gerry Wallace]

In my local park I photograped a family of smallish brown ducks. However, they are constantly accompanied by a fourth duck almost twice there size. This is a white, goose-like duck which behaves like one of the family and follows behind them everywhere, all the time, even walking in and out of the water with them.
Has anyone ever came accross this beffore? If it is imprinting, I wonder how it could have came about. Could it be an orphan (big orphan) from another family? Ill post a photo to the Gallery if you like.

[aeshna5]

Waterfowl are well known for imprinting, so this is a possibility + occasionally ducks will lay an egg in another's nest.

[Gerry Wallace]

Thanks for that reply It's kinda what I expected but is is good to have it confirmed by someone in the know. My daughter calls it s Kuckoo Duck!