Sensing
Sensing them is fairly easy through normal observation in the city. There is also the possibilty of hearing the flapping of their wings or their cooing.
Communication
Either just like children do by chasing them or luring them somewhere with food are most likely methods of "controlling" their movement.
Space
The space would probably be the city or rather a small part of it. There migh even be the opportunity to catch them somehow and then work with or train them in some manner.
Signs
Often refered as a rat with wings, wild pigeons are seen as a pest by some people; even though they are rather smart regarding their sense for orientation or their adaptability.
Ethics
Depending on the city, there are often rules for limiting the occurence of pigeons, either by prohibiting to feed them or by even hunting them in some way.
Logistics
There probably is no real need of "getting" pigeons while there is always a chance to just interact with them outside in the city.