How about a remote control vehicle as a sort of mobile scarecrow? Chase 'em around with a small car from your local hobby store. Or even better, a remote control plane. Even if it doesn’t work too well, I imagine a dogfight with a squadron of seagulls would be pretty entertaining. Maybe get your neighbors in on it and re-enact the battle of Midway.
If you only need them to move a little bit how about making an inviting environment nearby?
That should be fairly easy.
Barring that I think you will need to import a cheeta.
I think getting a Ninja to kill the birds is a bit extreme.
Well, they were there first. What I would recommend, if you’re able to do it, is to make their perching area uncomfortable. Metal spikes/nails sticking up so they can’t land on the railings or posts. Hopefully they would soon find someplace else to hang around where they can perch. I think they do that around here to keep pidgeons from fouling covered walkways, etc.
StG