Don't feed them, you'll only encourage this bullying behavior! Though of course if it comes down to being stalked by evil birds or possibly carrying around small bits of bread to distract them with, I'd say go with the third option: carry a large stick. Of course, that might just be the fencer in me talking...

The ducks sound cute, though :D and it must be nice to have wildlife. We have quite a few stray cats on campus, but it's not like I can pet them, or anything.