On a lighthouse preservation sight I volunteer at we use an electrified pair of wires to scare away the birds. They never land a second time!
Here is a system similar to the one we use, and the best part is it does not use replaceable batteries at all:
http://www.harborfreight.com/solar-fencer-47454.html
Drawback is you need to string wires over what you are protecting, simple for us as it is basically a fence rail. Dont touch these, while not deadly it is not pleasant.
by Jake Hertz
by Aaron Carman
by Aaron Carman
by Jeff Child