Hi Sterling - this is a huge problem in our urbanisation and I'm afraid Tech's solution, though tempting, is illegal!
We have blocks of apartments back to back with small openings in the gallerias which provide the perfect environment for nesting pigeons. We can't net the area because the blocks are at different heights and we can't put spikes on all the edges or close up the openings because most of the properties have been repossessed and the banks don't maintain them. Even if we wanted to pay for spikes to be installed on their behalf, we can't get access to the back of the buildings as the access is through the properties themselves!
I read about a sonic device with a motion censor which gives out a cry of a pigeon in distress or a bird of prey, so we may explore something like that which doesn't mean we need to access every property. We have a pest control company involved but so far they have just told us what won't work!!
So those are your options - nets, spikes or a sonic system.
Good luck!