Poisoning – Poisoning is literally against the law. Systemic poisons are no longer safe as they kill whatever stands on it. Avitrol is a pesticide used for hallucinogenic effects. When not diluted according to the label, it kills in a very unsightly and vicious manner. You and your contractor would also incur the law suit in the event a protected species or pet died from eating scattered feed or dying pigeons (Avitrol label information here). It is against the law to use a pesticide in a manner inconsistent with its labeling, grade 6 felony. – Federal Law Guidelines: (reference here) – See Also: Arizona Revised Statutes 32-2301, R4-29-301 thru R4-29-320 (reference here).
Auditory Distress (loud noises) – Pigeons are intelligent enough to figure these out after about 6-8 weeks. Limited temporary results are realized when used in conjunction with ever-moving scare devices referenced above. You must also consider the obvious problems associated with distressing your neighbors.
Balled-up Wire / Rocks – We have seen very large rounded river rocks on a tiled roofs edge 2 stories up, hmmm. Rolled up chicken wire, colored fencing and even netting must be fastened. Pigeons will literally grab on to these products with their feet and flap their wings to dislodge.
Smells – Bleach, moth balls cayenne pepper. These ideas have some merit if an enormously strong concentration of scent can be maintained long term to the point where the olfactory system is overwhelmed. Similar to humans would be the way onions affect us.
Falconry – This is an enormously expensive temporary solution if permanent preventative measures are not installed. Falconers are hard to come by since they run the risk of losing their prized birds. Falconers maintain control over their birds because the birds are taught to believe they must return for food.
Cats – Cats do not like heights & slippery, hot tiles. If only they would…
Hallucinogenics – There are bait trees which contain drugs which, amongst other things, disorient pigeons. The Urban Wildlife, Fish and Game and avian advocates do not condone any drug or treatment that would kill or disrupt the natural tendencies or physical health of pigeons. Unfortunately, these drugs in some cases have resulted in death.