'llo Merlinsmagic,
If you can, try to get hold of a bike. I know you can get one together with the trainticket (it takes about 15 minutes by train from Brugge to knokke). You'll need to collect the bike in the destination train station and simply return it there. I've done that a couple of times and it's fairly cheap. There's also a bus going out to the Zwin from the station at Knokke .
A good birding option is: the "Voorhaven" (outer harbor) of Zeebrugge. there's several good spots round there, and it's possible to do several by a combination of foot / bike and coast tram. I'll try to put together a map and some time tables / list of stops.
the Zwinbosjes near to the entrance of the Zwin reserve can be quite interesting for warblers, and you may be able to do some seawatching from the dunes.
Cheers,
filip