Visual Deterrents
Anything that is supposed to irritate or make the birds feel unsafe by appealing to their visual sense is classified as a visual scare. Visual scare devices include objects that are likely to frighten birds away, such as plastic owls and coyotes, Terror-Eyes balloons, and shiny tape. Old CDs also make a good visual deterrent. Tie them from a branch and they will twirl and glint in the sun.
Taste Aversions
Taste aversions are any chemical, spray, or compound that is applied to anything to make it taste or smell bad to birds. Some are targeted to specific species, like GooseChase, while others are used for a specific purpose, like FruitShield. Most are made from a compound called methyl anthranilate, which comes from grapes and is used as a flavoring. Watch out for some that do not use this compound; make sure that the chemical you are applying is safe for humans and birds.
Barriers
Roost inhibitors include spikes, chemical barriers, and netting. These are perhaps the most commonly used methods of bird control and are very effective at keeping birds off of ledges, beams, and other outcroppings. Chemical barriers like BirdProof cause the ledge to feel sticky, which birds hate. This is invisible, but it requires re-application every year or so.
Sound Repellers
Sonic and ultrasonic repellers are sound systems that emit the distress calls of the targeted species, predator calls, other loud noises, or ultrasonic pulses. Sonic repellers are extremely effective if they randomize pitch, frequency, timing, and other factors. Ultrasonic systems emit pulses that bother the birds, but humans cannot hear. They are very similar to sonic systems, only different in the fact that most humans are unaware of their emissions.
