Doesn't look very scary to me...
If I'm home and I hear them up on the mast, I'll whip a spare halyard up there to chase them away. Five minutes later, they're back at it. Bastards.
I'd like to get a trained falcon or something to fly around the marina and keep these guys off my boat, but they're probably too expensive and I don't know where to get one.
As a final assault in my war against the birds, today I picked up one off the goofy-looking scary eyes beachball scarecrow things. I hung it up on the mast and crossed my fingers. Let's hope it works.
I'll just have to remember to take the silly thing down before I hit the yacht club for cocktails.