My guess is, poison one, more will come. I'm not a tree hugger, just don't think it will work.
However, the way we got rid of ours is simple, and they haven't been back for more than 7 years...even after we took these things down:
Put to use all of those free AOL cd's you get in the mail, and the blanks you mess up, or don't need anymore. Or, heck, I guess you could just buy some.
Hold a nail in a pair of plyers or vice grips. Hold the nail over the stove burner until it starts getting red...big nail, big hole. Put the cd on a burner you aren't using. Use the hot nail to burn a hole in the cd. Dangle these from the roof-line over the places the holes are.
That's it. The sun reflects off the holographic surface of the discs and scares the poop out of the birds.
These also work hanging from sticks in your garden.
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them