i have a foto of a sign above a side walk
that has been fitted with a series of spikes
along the top to prevent pigeons roosting there.

i have also seen owl decoys used.

yes peregrine falcons have been re-introduced
in some areas where there are places high enough
for them to perch and dive from.

falconers use pigeons to train their hawks..
maybe there is a falconer who could bring a
hawk (falcon) over to hunt them down?


http://www.falconryexperience.com/
http://www.northwoodsfalconry.com/