Unidentified non-flying object!

Yesterday I saw a pair of exotic-looking birds in Bilbao, on the north coast of the Iberian peninsula, and haven't been able to identify them. I couldn't find them in any European bird guides and I don't remember seeing them in any other books or on the internet, although I have to admit to being a novice. They look pretty exotic so I presume they're either way off course or have escaped from a zoo / private collection. Here's the link to a few photos I managed to take:

http://picasaweb.google.es/cluaran/AveDesconocida

If it's any help, they were about 15km inland on the tidal limit of the Nervion river which runs through Bilbao and in an urban setting, next to a reasonably sized public park. I watched them for a good while but didn't see them fly or even extend their wings. They were among a small group of Mallards and Black-faced gulls.

Cheers