Would it be possible that your bird was an escapee from a nearby collection, Wild_Foxx ,as it sounds a bit on the exotic side?
However, have a look at this :
http://i31.tinypic.com/34fi7hj.jpg and see if it bears any resemblance.
Emporer penguin head - this would make me say...Guillemot (black body, white underside, but no long legs) Razorbill ( the same, except both are sea birds, not known for canals) Cormorant, Shag?? Have a good look at all the ducks for other possibles. I am really dying to know what this is!