Regarding spikes to deter pigeons, I want to see a house with these spikes installed. If I put them wherever there are pigeons, my house will look like Guantanamo. But then again, I shoudl suggest to the company to redesign the spikes in the form of spiky flowers ( shhhh, I am going to the patent office ).

I read something about some sonic devices ( warning sounds in bird "language") but I dont know about their range and cost .. etc. or if the birds will finally figure it out and ignore them.

Someone suggested putting dummy predators like rubber snakes near where birds are nesting. Do you think this would work ?